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This communication concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose an efficient numerical scheme to deal with heat transfer problems in pipe flow with a large length/diameter ratio. The generalized finite difference method (GFDM) is combined with a space stepping algorithm (SSA) for the solution. The SSA divides the solution domain into a number of overlapping sections in the length direction of the pipe. Due to the large Peclet number, the heat transport process is dominated by advection, which allows an approximate boundary condition to be applied at the downstream cross section. The problem is then solved section by section. Using the uniform distributed points, the solution matrix for each section does not change, and only the right hand side needs to be refreshed for the changing boundary conditions. This leads to a highly efficient scheme for problems with a large pipe length. To show the accuracy of the numerical scheme, a problem with available analytical solution is studied. Then the method is applied to problems of single pipe with different pipe wall temperature and flow Reynolds number, and concentric annular pipe. Numerical results confirm the stability and efficiency of the GFDM-SSA. The method can be applied to many real world transient heat transfer problems in which the pipe is heated or cooled along its length with arbitrary wall temperature for heat exchange and other purposes. [ABSTRACT FROM AUTHOR]

This research paper focuses on CFD analysis for comparative evaluation of different hybrid nanofluids (NFs): MWCNT-Al 2 O 3 /H 2 O, MWCNT-MgO/H 2 O, Al 2 O 3 -CuO/H 2 O performance as working fluid (WF) inside parabolic trough solar collector (PTSC). The performance of the collector is evaluated using different performance indicators, including Nusselt number (Nu), friction factor (f), and Performance Evaluation Criterion (PEC) for different Reynolds number (Re) (10000-50000). Among the investigated hybrid nanoparticles (NPs), MWCNT-Al 2 O 3 emerges as the most promising choice for significantly enhancing the system's thermal performance with the highest PEC value of 1.9. This outcome signifies the superior efficiency of MWCNT-Al₂O₃/H₂O hybrid NF in enhancing convective heat transfer, thus underlining the paramount significance of adopting them in thermal systems operating within the specified Re range. [ABSTRACT FROM AUTHOR]

When the concentration of porous particles reaches a certain level, the interactions between the particles can't be ignored. Therefore, this paper numerically investigated the interactions between two porous particles using the lattice Boltzmann method. In this paper, two-dimensional steady flow and heat transfer around and through two porous particles with the same diameters (D) was studied numerically. The effects of Reynolds number (Re), Darcy number (Da), center-to-center distance (expressed as dimensionless form L/D), angle between two porous particles (β) and particles with different permeability on the flow and heat transfer characteristics were investigated in detail. The investigated ranges of the parameters were 10 ≤ Re ≤ 40, 10−6 ≤ Da ≤ 10−2, D ≤ L ≤ 4 D and 0° ≤ β ≤ 90°. It is observed that these parameters have significant effects on the flow and temperature fields, drag coefficient and average Nusselt number. The drag coefficient and average Nusselt number of the leading particle (P1) is much larger than those of the trailing particle (P2) in most instances. And the two porous particles show different change tendency to the same changes of these parameters. The effects of Da on P1 are more prominent compared with P2 while the effects of L / D on P2 are more obvious compared with P1. Besides, the drag coefficient of P2 increases with β increasing. In addition, we define drag force ratio and heat transfer enhancement ratio to compare the sensitivity of particles to the changes of Re and/or Da when two particles coexist and when one particle exists alone. The results indicate the heat transfer efficiency of P1 is more sensitive to changes in Da and Re compared with a single porous particle. [Display omitted] • Lattice Boltzmann method is applied to solve the governing equations. • The leading particle has a shading effect on the trailing particle. • The two porous particles suppress each other's heat transfer efficiency. • The heat transfer of leading particle is more sensitive to Reynolds number. [ABSTRACT FROM AUTHOR]

This paper is the second of a two-part series that presents experimental data and analysis on the liquid nitrogen quenching heat transfer process of a stainless-steel tube with an inner surface low-thermal conductivity thin-film coating. This paper focuses on the effects of different flow directions and two tube wall thicknesses. Additionally, this paper also provides an analysis on the chilldown thermal efficiency of the quenching process. Three flow directions with four different inner surface coating modifications, and three tube wall thicknesses were examined. The experimental data covers the Reynolds numbers ranging from 3500 to 140,000. The chilldown efficiency, along with chilldown time and LN 2 (liquid nitrogen) mass consumption were analyzed to assess the overall performance of the LN 2 line chilldown process. For thin tube wall cases, the chilldown efficiencies cover a range between 3% and 41%, and the maximum chilldown efficiency value is found for the tube with 3 L coating at Re = 5278 in the vertical up flow direction. For thick wall tube cases, the efficiencies cover a range between 4% and 52%, and the maximum chilldown efficiency value was found for the tube with 4 L coating at Re = 5308 in the vertical up flow direction. [ABSTRACT FROM AUTHOR]

Pressurizer is widely used in the industrial systems, which can maintain the pressure of the system in a certain range. Especially, as the system pressure rises, the spray droplets interacts with the saturated steam in pressurizer to reduce system pressure. In this paper, a heat and mass transfer model of droplet and steam in pressurizer is established through the lattice Boltzmann method (LBM), and the characteristics of moving droplet in steam space with different Reynolds numbers are analyzed. In this paper, these results show that the flow fields on both sides of the droplet have obvious symmetry at low Reynolds number. As the Reynolds number increasing, the wake region of flow field for moving droplets gradually loses symmetry. When the Reynolds number reaches 103 orders of magnitude, the droplet motion begins to appear horizontal deviation. The growth of droplet condensation radius is inhibited with the increase of Reynolds number. When Reynolds number reaches 2600 and Fo = 0.2, the growth of droplet radius stops and then decreases. Due to the influence of inertia force generated by internal circulation flow and droplet movement, as the Reynolds number increasing, the droplet heat transfer rate decreases at first, but begins increasing when Reynolds number raises to about 2000. The calculation results have reference value for the development of spray droplet model of pressurizer. • A heat and mass transfer model of droplet and steam in pressurizer is established. • The characteristics of moving droplet in steam under different Re are analyzed. • With the increase of Re , the growth of droplet condensation is inhibited. • Heat transfer rate decreases first and then increases with the increase of Re. [ABSTRACT FROM AUTHOR]

Hyperthermia is one of the non-invasive therapy of an Abdominal Aortic Aneurysm (AAA), which is achieved by applying a heat source upon the AAA without surgical operation. This research paper considers laminar flow and heat transfer in a heated abdominal aortic aneurysm using an isothermal boundary condition. Heat is added to explicate the thermal treatment of a diseased artery. The blood is assumed as a non-Newtonian fluid based on the shear-thinning Carreau model. Two unequal aneurysms are assumed in the lower wall to simulate bulges or a disordered artery. Flexible wall segments are assumed in the upper wall and opposing to each aneurysm. The transient momentum and energy equations are solved based on the fluid–structure interaction (FSI) using the Arbitrary-Lagrangian–Eulerian (ALE) method. It is found that the shear stress is much higher for a higher index of the power-law fluid governing the blood viscosity and hence, it is strictly recommended to reduce the viscous nature of the blood in diseased vessels. It is found also that the thermal energy can be greatly transported across the blood at a higher Reynolds number, this means that the hyperthermia therapy becomes effective when blood flows violently through the aortic. [ABSTRACT FROM AUTHOR]

The application of nanofluids has dramatically increased from the past two decades. Nanofluids have elegantly captivated the attention of researchers nowadays. At present, various papers are being reported dealing with this interesting domain, allied with fascinating applications. However, the nanofluids being captives these days depicts the crucial need to bestow the comprehensive review of nanofluids application in distinct domains. This paper examines the utilization of nanofluids with distinct Plate Heat Exchanger (PHE) geometries. All the reported studies are alienated to two main categories; experimental and numerical. Furthermore, critical information regarding nanoparticle size, base fluids, analytical methods, heat transfer enhancement, flow regime, and pressure drop is presented in a comprehensive table in each section. Also, it was ultimately found that all the studies; analytical, experimental and numerical gave desired and appreciable thermal performance compared to conventional fluids. Author also reported the statistical analysis for the past published papers and the results show the increasing importance of nanofluids application in plate heat exchanger. Most of the studies showed preferred thermal behaviour, heat transfer enhancement, reduction in entropy generation and reduction in exergy destruction compared to the base fluids. An increase in Reynolds number can provide better heat transfer rates. The operating temperature of nanofluids plays a key role in the effectiveness of heat exchanger and heat transfer enhancement. Almost all the studies have demonstrated the preferred nanofluids thermal behaviour in plate heat exchanger, compared to the base fluid but Chevron and Corrugated type geometry of plate heat exchanger gives the appreciable enhancement in Nusselt number. [ABSTRACT FROM AUTHOR]

• Introduced the influence of frequency on the heat transfer performance of AMR. • The frequency correlated characteristic is revealed by synergy principle. • A frequency correlated heat transfer correlation is proposed. • Perforated plate enhances heat transfer performance by more than 20%. This paper investigates the heat transfer characteristics of oscillating flow in active magnetocaloric regenerator (AMR) by numerical simulation. We show that the operating frequency plays an important role to the heat transfer coefficient of the regenerator other than the Reynolds number and the Prandtl number. Moreover, to reveal the mechanism of the frequency correlated heat transfer characteristics, a modified synergy number Fci is proposed based on the field synergy principle. To quantitatively describe the influence of operating frequency, the oscillating Reynolds number is introduced. This paper compares the heat transfer coefficient calculated by three different methods: CFD simulation, correlations with the oscillating Reynolds number and correlations with the conventional Reynolds number. Based on the results of comparison, this paper qualitatively presents a frequency correlated heat transfer correlation for different operating frequency. In addition, a perforated parallel plate matrix regenerator is proposed to improve the heat transfer performance of the AMR. [ABSTRACT FROM AUTHOR]

• Flow and heat transfer characteristics in CW-type PSHE are numerically studied. • The effect of hydraulic diameter is analyzed. • The effect of airflow shuttling on heat transfer enhancement is explained. • The local thermal resistance analysis method is applied. This paper numerically investigates the flow and heat transfer characteristics in the primary surface heat exchanger (PSHE) with cross-wavy (CW) structures. The comprehensive performance affected by hydraulic diameters is evaluated. Moreover, the airflow shuttling behavior at the mixing area of CW-type PSHE is discussed, showing rapid heat transfer enhancement. The advection thermal resistance method and local thermal resistance analysis is proposed, while the impacts of longitudinal pitch and flowrates are considered. Results show that the case with a large hydraulic diameter displays much better comprehensive performance at lower flowrates. When raising the hydraulic diameter from 1.58 mm to 15.8 mm, the heat transfer rate per unit pumping power grows by 36.1 %. However, the priority of large channel is gradually disappeared after increasing the flowrates. Meanwhile, the larger longitudinal pitch of the CW channel may result in pronounced improvement on the heat transfer performance due to the presence of airflow shutting behavior at the mixing area as well as the secondary flow near the channel boundary layers. When no airflow shuttling exists, very high advection thermal resistance region can be observed due to the formation of boundary layers. It can be recognized that the case with airflow shuttling behavior can display similar heat transfer improvement compared to that with increasingly high Reynolds numbers, yet the pressure loss is rarely increased. [ABSTRACT FROM AUTHOR]

The present paper, for the first time, examines the influences of utilizing oil-ZnO nanofluid with different volume fractions φ = 0.5 %, 1 %, and 2 % in alternating flattened tubes (AFTs) with different alternating pitch angles of 30°, 45°, 60°, and 90° on the performance of a dual-tube heat exchanger (DTHE). This work is conducted experimentally and numerically for the Reynolds number (Re) range of 300 < Re < 1900 for oil-ZnO nanofluid and Re = 2000 for water. Based on the experimental results, the optimal case is selected for the numerical simulations of AFTs. The performance evaluation criterion (PEC) is defined for the simultaneous evaluation of pressure drop (Δp) and heat transfer coefficient (HTC). The results demonstrate that the overall heat transfer coefficient (U) and Δp are augmented with the inlet flow rate and the alternating angle between the pitches. Therefore, the maximum heat transfer (HT) and Δp correspond to the AFTs with the angle of 90° (AF4) at Re = 1900. The PEC amount of AF4 shows a 56 % enhancement compared to the circular tube. It is also observed that using copper oxide nanoparticles inside the oil improves the HT rate and Δp in the heat exchanger. Besides, an increment in φ increases U and Δp; however, the values of PEC show that the positive effects of the nanofluid are larger than their negative impacts in such a way that the PEC is improved by 64 % when the nanofluid with φ = 2 % is utilized in AFTs compared to the circular tube. [ABSTRACT FROM AUTHOR]

This research paper presents numerical and experimental investigations to examine the effectiveness of a honeycomb pattern as a form of the geometry of artificial roughness in solar air heaters. Utilizing Computational Fluid Dynamics (CFD) through three-dimensional simulations, the study explores how Thermo-Hydraulic Performance Parameter (THPP) is affected by variations in honeycomb geometry. The research examines various parameters, including the angle of attack (Ø), relative roughness pitch (P/e), and relative roughness height (e/D) within the respective ranges of (90°-120°), (8–12), and (0.03–0.05). The system's performance is evaluated across various flow scenarios, covering Reynolds numbers from (3000) to (21,000). Incorporating the honeycomb design into an absorber is observed to improve the heat transfer rates. The system achieves a maximum Nu of (140.65) at (e/D) of 0.04, (P/e) of 10, (Ø) of 120°, and Re of (21,000). The maximum FF of (0.039) was obtained at (e/D) of 0.05, (P/e) of 9, and (Ø) of 120° at a Reynolds number of (6000). The system exhibited a THPP of (1.7) at a Reynolds number of (6000). This Maximum THPP was associated with specific parameters, including (e/D) of 0.04, (P/e) of 10, and (Ø) of 120°. [Display omitted] • Numerical investigations followed by experimental validations. • Honeycomb-shaped artificial roughness improved the heat transfer rates. • The thermo-hydraulic performance parameter achieved a maximum value of (1.7). [ABSTRACT FROM AUTHOR]

• A model is developed based on OpenFOAM for jet impingement heat transfer. • Many cases are investigated under different boundary conditions. • The boundary layer of jet impingement is analyzed in detail. • The relationship between the secondary Nu and C f is further discussed. Jet impingement has been widely used due to its high heat transfer rate, but numerical simulation of this flow is highly challenging because of complex flow phenomena. In this paper, a turbulence model based on the physics of jet impingement is developed using the shear stress transport (SST) four-equation transition model and the SST with cross-diffusion correction (SSTCD) model. The proposed method is evaluated for plane jet impingement under various nozzle-plate spacings (2.6, 4 and 6) and different Reynolds numbers ranging from 10,200 to 20,000 in terms of heat transfer and flow fields. The results show that the developed model has the ability to capture the second peak of heat transfer and skin friction at low nozzle-plate spacing. Even at high nozzle-plate spacing, this approach also gives accurate trends for the above two features. However, without the cross-diffusion correction, the transition model provides too high energy and low velocity peaks. With the developed model in hand, the effects of pressure gradient on heat transfer and skin friction coefficient are further investigated. It is found that when the adverse pressure gradient becomes strong, the position of the secondary peak of skin friction occurs earlier than that of the secondary peak of heat transfer rate. Conversely, if the adverse pressure gradient disappears, the positions of these features coincide. [ABSTRACT FROM AUTHOR]

• In this paper is provided an calculation expression for heat transfer during condensation inside tubes that provides an adequate fit with experimental data available from a total of 22 fluids, including refrigerants, water, and a variety of substances organic. This paper presents a mathematical deduction of a new improved model for heat transfer during condensation inside tubes. This new model has been developed with the aid of the Gaussian Equation for an infinite straight line, considering this relation with the differential equations that govern the heat transfer process. The proposed model was verified by comparison with available experimental data of 22 different fluids, including various refrigerants, water, and organic substances, which condense inside vertical, inclined and horizontal tubes. The proposed model is valid for an reduced pressure values ranging from 0.0008 to 0.91, values of Reynolds number for single-phase between 68 and 84,827 and for Reynolds number for two-phase between 900 and 59,4373, a range of internal diameters ranging from 2 to 50 mm, vapor quality from 0.01 to 0.99, P r values for single-phase from 1 to 18 and mass flux rates in the ranges of 3 to 850 kg/(m2s). The mean deviation found for the analyzed data for horizontal tubes was 11.8%, while for the vertical and inclined tubes data the mean deviation was 13.0%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design. [ABSTRACT FROM AUTHOR]

Abstract Winglet pairs are promising longitudinal vortex generators which can be used to produce streamwise vortices that do not decay until further downstream and consequently increase heat transfer rate with comparatively lower pressure penalty. This paper deals with the effect of delta winglet vortex generator (DWVG) pairs on thermal and flow behaviors in a circular tube for Reynolds numbers (Re) range of 5000–25000. The DWVG pairs involved are the pitch ratio (PR = 9.6), four attack angles (α = 10°, 20°, 30° and 40°), three winglet height (h = 5 mm, 7.5 mm and 10 mm) and three spacing between leading edges (s = 10 mm, 15 mm and 20 mm). The experimental results indicate that the Nusselt number (Nu) increases with Re while friction factor (f) decreases with Re. Nusselt number and friction factors both are increasing with attack angle and winglet height, while the middle spacing yields the highest Nu and f. Maximum Nusselt number increment (Nu / Nu 0) with the DWVG pairs was observed as being 73% larger than that of smooth tube, while the maximum friction factor increment (f / f 0) was 2.5 times larger. Thermal enhancement factor (TEF) decreases with Re. The largest TEF obtained, 1.44, is with the combination of α30°s15 h 7.5 at Re = 5000. Compared with other types of VGs in published experimental research papers, the current DWVG pairs show better thermal performance than many of them. Vortices downstream of the DWVG are visualized with smoke flow for better understanding of the flow behavior. [ABSTRACT FROM AUTHOR]

Highlights • Method of images is successfully adopted to predict the LVG vortex dynamics. • A mixed LVG configuration is suggested to enhance the heat transfer performance. • LVG aspect ratio and channel height are very critical to the LVG effectiveness. Abstract This paper reports a numerical investigation of fluid flow and heat transfer in a rectangular channel with delta-shaped winglet longitudinal vortex generators (LVGs) under different configurations. In addition to the conventional common-flow-down configuration and the common-flow-up configuration, a unique mixed configuration is suggested. The "method of images" is successfully adopted to analyze the dynamics of the longitudinal vortices due to wall interference. The Nusselt number, friction factor and overall performance coefficient for the three configurations are compared at various Reynolds numbers (all less than 2200), LVG row numbers, channel heights, and LVG aspect ratios. It is found that the channel height and LVG aspect ratio are the two most critical factors influencing the effectiveness of the different LVG configurations, which may explain why inconsistent conclusions have been presented by previous studies comparing the performance of the common-flow-down and common-flow-up configurations. When the channel height is relatively small, the unique mixed configuration is found to be the most effective at enhancing fluid mixing (and therefore improving heat transfer) at streamwise cross sections. When the LVG aspect ratio becomes large, the common-flow-down configuration outperforms the common-flow-up configuration. This paper sheds some insight on how to design the optimal LVG configuration for enhancing heat transfer performance. [ABSTRACT FROM AUTHOR]

Highlights • Composite fin with high thermal conductivity coatings deliver large heat transfer enhancement. • At high Re typical of Engine Section Stator vanes, the coating thickness should be around 100 μm. • Composite vanes would be more effective at low Re, as predicted also for composite fins. • Using the internal web structure of vanes can improve heat transfer in long vanes. Abstract This paper main goal is aimed at a paradigm shift in the enhancement of heat transfer rate between finned surfaces and surrounding fluid by presenting a novel approach in composite fins. This approach consists in using high thermally conductive coatings on top of the finned substrate in order to increase the local temperature along the fin washed surface. In the present paper a high thermal conductivity coating has been applied to an aeroengine vane of different shape and dimensions subject to icing conditions at high Reynolds numbers and where the main aim was to keep the vane warm as to avoid icing in aerospace applications. Numerical simulations have been carried out to ascertain the range of thickness of the coatings to be used to maximise the wanted effect. Both short Engine Section Stator (ESS) and longer fan Outlet Guide Vane (OGV) have been modelled, having different final goals. In the case of longer OGV, an additional novel design modification has been suggested to enhance further the heat transfer along the vane length by the use of the internal webs. The experimental validation also carried out at much higher Reynolds numbers than that reported in Buffone et al. (2005), demonstrate that the novel concept of heat transfer enhancement in composite fins is a simple and yet powerful strategy in a wide range of Reynolds numbers. A fin analysis has been performed of both the present ESS vane the fins tested in Buffone et al. (2005) at much lower Reynolds numbers and shows that the improvement obtained with the coated fins tested in Buffone et al. (2005) is much larger than the coated ESS vanes investigated in the present study. This said, the present study demonstrates that the use of high conductive coatings in composite fins can keep the ESS vanes ice free, something that was not possible with uncoated vanes. It is important to note that the actual optimal thickness of the thermally conductive coatings is a function of Biot number, fin shape, dimensions and thermal conductivities of fin substrate and coating; depending on the application, a proper design of the fin substrate and coating should be carried out. [ABSTRACT FROM AUTHOR]

Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The effect of variable baffle configurations on HX performance was investigated. • The influence of water mass flow and heat flux on the HTC was presented. • Experimental correlation for investigated configurations was developed. • Recognized the secondary fluid motion influence on heat transfer was investigated. • Compared the efficiency of the proposed shell-coil design with baffles with typical heat exchanger designs was presented. Abstract The paper presents the possibility of using passive intensification of heat transfer in the form of baffles to increase the energy efficiency of the shell and coil heat exchanger. The experiment was carried out by using a modular coil heat exchanger in the form of an electric heater. Water was used as a working fluid with constant thermal-flow parameters at the inlet of the module. It should be noted that experiments were made for a large range of power i.e. from 200 W to 1200 W and with mass flow rates from 0.01 kg−1 to 0.03 kg−1. For this flow range, Reynolds numbers were obtained in the field 150 < Re < 450. Consequently, all experiments were carried out for laminar flow conditions. This work shows, that due to the presence of mixed convection, natural convection has a significant effect on small values of Reynolds numbers and large values of Richard' number. Also, the baffles location has a significant influence on HX performance. The proposed solution of the shell coil exchanger with a baffle is characterized by better heat transfer efficiency on the shell side, but rather for lower values of Reynolds (Re < 150) numbers and high values of heat fluxes. For all configurations is noticeable the influence of the supplied heat flux value on the rate of heat transfer. The paper presents new experimental Nusselt numbers correlation on the shell side of the heat exchanger with core-baffles. This correlation depends on Grashoff and Dean numbers as well as dimensionless shell diameter (C/D 0), the correlation also includes Prandtl number. Experimental data were compared with selected correlations from literature as well as with own correlation. It was shown that only own semi-empirical correlation has satisfactory compliance with experimental results within 35% error band and with less than 8% of absolute deviation. The considered construction has markedly better heat transfer efficiency on the shell side for small Reynolds numbers (Re <150) comparing to the tube-in-tube exchanger with wire coil turbulator(over 20%). [ABSTRACT FROM AUTHOR]

The interaction of longitudinal vortices decreases the intensity of longitudinal vortices and inevitably affects the heat transfer performance of heat exchangers. In this paper, the effects of transverse distance of vortex generators (VGs) on the interaction of longitudinal vortices and the heat transfer performance are quantitatively studied. The increments of longitudinal vortex intensity, Nusselt number and friction factor resulted from the application of VGs are discussed in detail. The results show that the transverse distance of VGs obviously affects the interaction of longitudinal vortices, the heat transfer enhancement and the pressure loss characteristics of the heat exchanger. The interaction of co-rotating longitudinal vortices generated by VGs around the same tube is less affected by the transverse distance of VGs. While the interaction of counter-rotating longitudinal vortices generated by VGs around different tubes is closely related to the transverse distance of VGs. The interaction between counter-rotating longitudinal vortices plays a dominant role in the interaction process of longitudinal vortices. Optimal transverse distance of VGs exists for best heat transfer performance of the heat exchanger. Meanwhile, the transverse distance which leads to the worst heat transfer performance is also reported. For the largest Reynolds number studied in this paper, the maximum differences in the increments of intensity of longitudinal vortices, Nusselt number and friction factor for different transverse distance of VGs are 34.0%, 33.9% and 18.5%, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we experimentally investigated the effect of turbulent intensity on heat transfer in a square rotating channel. The grid generated turbulence is measured by hot-wire, and the heat transfer coefficient is measured by TLCs. In the experiment, the Reynolds number, based on the channel hydraulic diameter ( D = 80 mm ) and the bulk mean velocity ( V m = 1.82 m / s ), is 10,000, and the rotation number ranges from 0 to 0.52. The mean density ratio ( d . r . = ( T w - T b ) / T w ) is about 0.1 in the current work using transparent heater glass (Indium Tin Oxide) to provide uniform heat flux. Two different turbulent intensity of inlet air (0.6% and 5.5%) are taken into consideration to investigate the heat transfer distribution on the leading and trailing side. The results show that turbulent intensity has an effect on heat transfer on both leading and trailing side, especially at rotating conditions. At static conditions, the effect of turbulent intensity on heat transfer is not obvious. However, with the increase of rotation number, in case B with a medium turbulent intensity (Tu) of 5.5%, the Nu/Nu 0 is about 10% higher than that in the case A with low turbulent intensity of 0.6% with the rotation number of 0.52 at X/D = 2 on trailing side. The enhancement of case B decreases along X/D directions. On the leading side, the turbulent intensity has same effect on heat transfer with that on trailing side, but not as prominent as that on the trailing side. In current work, the turbulent intensities at different X/D directions are also presented to explain the phenomenon of heat transfer in the channel. More detail of results will be presented in this paper. [ABSTRACT FROM AUTHOR]

This paper analyses the effect of spirally corrugation in a simple tube on the heat transferred and friction factor using numerical simulations. The simulations have been validated with experimental data available in the literature. The study compares the behaviour of both smooth and spirally corrugated tubes considering turbulent flow at four Reynolds numbers (15- 40 × 10 3 ) and two Prandtl numbers (2.9 and 4.3). The main novelty of this paper is to perform a 3-D simulation because some previous studies using similar geometry were restricted to a 2-D analysis. For the smooth and corrugated tubes, stainless steel tubes with an inner diameter of 18 mm, a length of 6 m and a wall thickness of 1 mm were used. The corrugated tube has a corrugation depth of 0.43 mm and a helical pitch of 15.86 mm. The meshing process was performed using ANSYS Workbench (v.17.0) with an unstructured grid with a refined mesh near the wall to ensure that the laminar viscous sub-layer was captured. Hence, a k-epsilon ( k − ε ) turbulence model with a near-wall treatment was used in the proposed simulations. Two grids were used to perform a grid sensitivity analysis. The results for the corrugated tube indicate that the numerical model predicts an average Nusselt number within a maximum relative error of 17% compared with the experimental data, and the differences in the Fanning factor are lower than 9%. [ABSTRACT FROM AUTHOR]

Many plate fin and tube heat exchangers operate under low loads when the flow rate of air and water is low. The flow regime in tubes can change from laminar through transitional to turbulent. In this paper, much attention was paid to determine a semi-empirical correlation for the Nusselt number on the water-side in the transitional and turbulent range when the Reynolds number Re w is higher than 2300. A new relationship for the friction factor in the transitional flow regime was proposed. The friction factor in the transitional flow range 2300 ⩽ Re w ⩽ 3000 was obtained by linear interpolation of the friction factor for Re w = 2300 , and Re w = 3000 . The influence of the formula for determining the water-side friction factor in the transitional flow regime on the Nusselt number was shown. Based on experimental data, heat transfer correlations were determined for the air and water-side Nusselt numbers for the low velocity of air and water. The semi-empirical correlation for the Nusselt number on the water-side derived by integrating the Reynolds averaged energy conservation equation for turbulent flow agrees well with the empirical correlation for the Nusselt number. The heat flow rate from hot water to cold air was calculated as a function of the water flow rate using a numerical model of the heat exchanger with the correlation for the water-side Nusselt number developed in the paper to compare it with the results of the measurements. The results of the numerical simulation agree very well with the results of the measurements. [ABSTRACT FROM AUTHOR]

• The effect of number of sharp corner of triangular winglet shape obstacles have been investigated on heat and flow behavior. • Type 3 (Triple Triangular winglet) obstacles has showed a maximum enhancement in Nusselt number, reaching upto 3.85 Times. • Experimental analysis shows Type 3 obstacles optimize thermal–hydraulic performance with THPP peaking at 2.293. Solar energy, an inherently pure and abundant source of power, is integral to a myriad of daily activities. Among the various solar thermal systems, Solar Air Heaters (SAHs) are often esteemed for their economic viability and practical utility in heating spaces and drying the products.. However, sometimes the conventional SAHs are criticized for their poor performance and capability in heat transfer, making them not well organized in application. The introduction of a new method of improvement in the efficiency of heat transfer in SAHs using carefully designed obstacles with sharp corners is presented in this paper. The obstacles are conceptualized in a Triangular winglet configuration, type-based on the following: Type 1 (Single Triangular winglet), Type 2 (Dual Triangular winglet), Type 3 (Triple Triangular winglet), and Type 4 (Quadruple Triangular winglet). The setups' empirical configurations were processed for the SAH duct where the experiments were executed with a Reynolds number (Re) up to 2000 to 16,000. The obstacle parameters such as the relative transverse pitch (Pt/b), relative obstacle height (e/H), and the relative longitudinal pitch ratio (Pl/e) were clearly maintained at 4, 0.5, and 4, respectively. From the experiments, the Nusselt number was found to be significantly enhanced, up to 3.85 for the Type 3 obstacle configuration. The Thermohydraulic Performance Parameter (η) also showed a strong value for all obstacle configurations that eventually reaches a peak value of 2.29, hence presenting a comprehensive performance for heat transfer efficiency and hydraulic performance within the SAH system. [ABSTRACT FROM AUTHOR]

In this paper, the gas turbine blades middle double swirl cooling structure under diverse number of nozzles N are constructed to explore the heat transfer and flow behavior. The k-ω turbulence model are applied and the inlet coolant Reynolds number is 12500. The N vary by 4 to 11 and two cases are investigated. For case 1, the cross-sectional area of each nozzle is 6 mm2 for all structures. For case 2, the cross-sectional area of total nozzles stays the constant at 42mm2 when the N is varied. Results show that, in case 1, when the N increases, the area of the high heat exchange zone decreases but the distribution is more uniform. Moreover, the thermal performance factor ξ gets larger, but the average Nusselt number Nu a decreases significantly. In case 2, when the N increases, the ratio of inclination to nozzle length increases for the jet near the outlet, Nu a is almost constant but the heat transfer uniformity is improved. The best ξ is obtained when the N is 8. For case 1, as the N is increased, the Nu a decreases significantly. Therefore, heat transfer and ξ should be considered by case 2 to select the optimum N. • Middle double swirl cooling models with different nozzle numbers are established. • Effects of nozzle number on flow and heat transfer characteristics are explored by two cases. • When the nozzle number is changed, the cross-sectional area of total nozzles in case 1 is changed, but it unchanged in case 2. • The results show that case 2 is more appropriate and the optimum nozzle numbers should be selected by the way of case 2. [ABSTRACT FROM AUTHOR]

Active and passive cooling are the two possible methods for removing heat. An active cooling system is the one that involves the use of energy as opposed to passive cooling that uses no energy. Passive cooling methods are cost effective and more reliable than active cooling due to the absence of moving parts. Microchannel heat sink is one of high-tech devices that have widely considered passive cooling methods especially for electronics cooling. In this paper, the use of passive cooling methods in microchannel heat sink is comprehensively discussed. This paper also present the effects of some important parameters such as the type of channel types, surface roughness, fluid additives, and Reynolds number on the rate of heat transfer in microchannel heat sink. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

• Prediction of dryout is needed for the design of falling film evaporators. • No method available till now. This paper presents one for plain horizontal tubes. • The new correlation has been verified with data for single tubes and bundles. • Data for 7 fluids from 8 sources predicted with mean absolute deviation of 15.8%. Accurate prediction of dryout during falling film evaporation is important to ensure good performance as post-dryout heat transfer coefficients are very low. No prediction method verified with a wide range of data is presently available and there has been a need for one. A new correlation is presented for dryout of saturated fluids on plain horizontal tubes. It has been verified with data for seven fluids from eight sources. The fluids are R-11, R-134a, R-236fa, R-410A, isobutane, and propane. Other parameters in the database are: heat flux from 0.2–95 kW m−2, reduced pressures from 0.00164 to 0.15, and liquid Reynolds numbers from 13 to 970. The new correlation predicts the data from single tubes and arrays of tubes with mean absolute deviation (MAD) of 15.8%. The same data were also compared to other correlations and those had much higher deviations. The new correlation and results of comparison with test data are presented and discussed. [ABSTRACT FROM AUTHOR]

This paper presents the performance investigation of a shell and helical coil type of Solution Heat Exchanger (SHX) in an ammonia–water vapour absorption system. In an absorption system, SHX is one of the major heat recovery components. The main objective of any heat exchanger design is to achieve minimum heat transfer area required for a given heat duty, as it governs the overall fixed cost content of such a system. The required surface area is decided by the overall heat transfer coefficient. Hence, the heat transfer coefficient (HTC) correlation plays a major role in optimizing the heat exchanger. In this paper, shell and helical coil type of SHX is investigated with more emphasis on the dimensionless correlation of shell side co-efficient, which decides the overall HTC and the size of heat exchanger. From the experimental study, shell side heat transfer coefficient of 510–650 W/m 2 K is obtained with the heat exchanger effectiveness of 0.84–0.9 for the tested conditions. A proposed Nusselt number correlation is compared with the experimental results. [ABSTRACT FROM AUTHOR]

• The flow and heat transfer characteristics of single and multiple-synthetic jet impingement cooling is presented. • The equivalent Reynolds and Nusselt numbers were determined for the purpose of describing multiple orifice configuration. • The merging jet process is presented and the merging point is determined. In this paper, the comparison between synthetic jet actuator with single axisymmetric orifice and multiple axisymmetric orifices is presented. The aim of this paper is to compare the flow and heat transfer characteristics of single and multiple synthetic jet impingements cooling. The multiple orifice configurations had a central orifice and a satellite orifices placed in the pitch circle. The synthetic jet actuator had central orifice with 0, 3, 4, 5 and 6 orifices placed in the diameters of the relative pitch circle p / d = 2.5, 3 and 4. A total of 13 various geometric configurations were tested experimentally. In the multiple orifice configurations, the total cross-section area was approximately equal to the cross-section area of the single orifice configuration. The input power delivered to the synthetic jet actuator was maintained constant and equal to 3.00 W. The synthetic jet actuator energetic efficiency, Reynolds number, equivalent Reynolds number, radial and axial distributions of pressure coefficient, and heat transfer characteristic were presented. The synthetic jet issuing from multiple orifice plate merged at some axial distance, creating a single axisymmetric jet. The merging jet axial distances were determined for all investigated configurations. In the present paper, the integral quantities averaged over all orifices cross section area, or over impingement plate much larger than total orifices area, were analyzed for the purpose of objective comparison. From all various investigated parameters obtained from five different and independent experimental methods, the following conclusion may be made: if the total orifice cross section area in the case of single and multiple orifice synthetic jet is similar and real power deliver to the SJA is maintained at the same level the resulting equivalent Reynolds number and equivalent dimensionless stroke length achieved similar values and the impinging jet equivalent Nusselt number also achieved comparable values and distributions. [ABSTRACT FROM AUTHOR]

• This research article investigates the use of pin–fin cooling in gas turbine blades, a crucial technique for managing extreme thermal conditions during operation. • It introduces a novel geometry, the C-shaped-recessed endwall, and explores its impact on pin–fin cooling channels. • The study reveals significant improvements in Heat Transfer Efficiency Index (HTEI) of up to 49.75 % compared to conventional flat endwalls, promising enhanced heat transfer capabilities in gas turbine blades. Pin-fin cooling has long been a crucial technique employed in gas turbine blades to manage the extreme thermal conditions experienced during operation. While numerous studies have investigated the heat transfer characteristics of different pin–fin configurations, the substantial impact of the endwall of the cooling channel on the heat transfer capability of turbine blades has not received adequate attention or thorough investigation. This research paper focuses on studying the influence of a novel geometry, termed C-shaped-recessed endwall, on pin–fin cooling channels in gas turbine blades. The primary objective of this investigation is to analyze the vortex formation and its impact on heat transfer characteristics within the cooling system. The study involved testing five different pin–fin arrays with C-shaped-recessed endwalls inserted between them, spanning a Reynolds number range of 7400 to 36000. The results show that with reference geometrical values, the new geometry increases the Heat Transfer Efficiency Index (HTEI) by 36.53 % compared to the flat endwall at Re = 29000. Higher heat transfer capacities were achieved by manipulating the C-shaped-recessed endwall heights and width of indentations, and the peak HTEI recorded an increase of 49.75 % at Re = 29000 compared to the flat endwall. The findings from this study underscore the potential of the C-shaped-recessed endwall geometry to improve the heat transfer capability of pin-fins by optimizing endwall configurations. [ABSTRACT FROM AUTHOR]

This paper is the first of a two-part series that presents experimental data and analysis on the liquid nitrogen quenching heat transfer process of a stainless-steel tube with an inner surface low-thermal conductivity thin-film coating. The experimental data covers a wide range of flow mass fluxes (43 to 1077 kg/m2s). The experiments were conducted using test tubes with four different coating thicknesses to investigate the effects of various Teflon coating thicknesses. An analysis of the chilldown time and LN 2 mass consumption data are presented to evaluate the effects of the flow mass flux, axial distance from the tube inlet, and coating layer thickness. The chilldown time decreases with increasing flow Re. However, the chilldown mass consumption increases with increasing flow Re. In general, the larger the flow Reynolds number, the lower the percentage reduction in chilldown time is observed. For the percentage reduction in the chilldown time by the coating, the minimum is 27.8% for the tube with 7-layer coating at flow of Re = 100,000 and the maximum is 61.3% for the tube with 14-layer coating at flow of Re = 10,000. The percentage reduction in mass consumption due to coating falls in the range between 35.3% and 54.1%. [ABSTRACT FROM AUTHOR]

Rising temperature of gas turbine inlet brings great challenge for blade temperature tolerance, thus high effective cooling structure for turbine blade is vital. In this paper, aerothermodynamic features including heat transfer and pressure drop of a Coriolis-applied rotating smooth U channel are studied in detail. Both experiment and numerical methods are utilized in the study. A rotating cooling structure experiment rig system has been established and validated. The experiments were conducted in the rotating cooling structure experiment rig. Besides, RANS was chosen in the simulation. In the experiment and numerical studies, Reynolds number is constant at 16000 and Rotation number ranges from 0 to 0.024. The results indicate that Coriolis force plays a dominant and positive role on heat transfer ability on trailing wall, and that bend outlet impingement effect is the primary factor compared to Coriolis force for the Nusselt number of smooth leading surface. Besides, Coriolis force at bend region probably suppresses the formation of K–H vortices, thus boosts the flow stability, reduce pressure loss of channel and weakens second heat transfer peak of impingement at the bend outlet. What's more, the total performance of the Coriolis-applied smooth U channel at Ro of 0.006 and 0.024 are 2.18 % and 8.51 % higher than the channel at Ro of 0, which means that rotation is good for the Coriolis-applied smooth U channel and that the channel has superior performance and is encouraging in future rotating blade cooling application. • A Coriolis-applied smooth U channel is proposed and investigated. • Detail heat transfer experiments on the channel were implemented. • Simulations were conducted to unveil the heat transfer and pressure drop mechanisms. • Rotation enhances overall heat transfer of the Coriolis-applied smooth U channel. • Rotation brings pressure loss of the Coriolis-applied smooth U channel decreased. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of heat transfer enhancement and pressure drop in a Coiled Flow Reverser (CFR) with a twisted tape insert. Both laminar (10 < Re < 2000) and turbulent (12,000 < Re < 18,000) regimes have been studied using both experimental and numerical methods. The effects of twist ratio of twisted tape, inlet Reynolds number, and perforating the twisted tapes have been investigated. The study found that the best performance in the laminar regime is achieved with a twisted tape with a twist ratio of 15.73 and no holes on it at a Reynolds number of 2000. In the turbulent regime, the same twisted tape performs the best at a Reynolds number of 17,000. The highest Thermal Performance Ratio (TPR) in laminar regime is 1.55 and in turbulent regime is 0.99. In comparison to the straight pipe, all types of CFRs show better performance in heat transfer enhancement. Also, as the Reynolds number increases, the friction coefficient decreases in all configurations. The study reveals that the twisted tape insert enhances heat transfer performance while increasing pressure drop. This study provides valuable insights into the design and optimization of heat exchangers with CFR. The findings can be used to improve the efficiency and performance of various industrial processes, such as refrigeration systems, air conditioning, and power plants. • Fluid flow and heat transfer in a coiled flow reverser (CFR) were studied. • Effects of tube insert on the heat transfer enhancement of CFR were investigated. • Effects of perforation of tube insert on heat transfer enhancement of CFR were examined. • The effects of tube insert at laminar flow are more than turbulent flow. • Perforation has no significant effects on the thermal performance ratio. [ABSTRACT FROM AUTHOR]

This paper explores the impact of hybridisation and geometric variations in micro heat exchangers featuring cylindrical fins. The primary aim of the study is to maximise the thermal conductance. Solid, half-hollow and hollow circular fins are modeled and mounted on a heat sink with a rectangular flow channel. A high-density heat flux of magnitude 500 W / cm 2 is dissipated on the bottom surface by a microelectronic device. Single-phase water of Reynolds number range of between 400 and 500 is supplied through the inlet of the heat sink to remove the heat at the bottom and in the inner walls of the hollows, while cool air stream of Reynolds number range 10 ≤ Re a ≤ 14 is allowed to convectively flow over the vertical micro cylindrical fins to take away extra heat deposited on the fins. The computation domain is descretised and computational fluid dynamic code applied to solve mathematical equations. The numerical results show that the thermal conductance in the half-hollow fins is 16.4% greater than in the solid fins, and 0.14% higher than the hollow fins in parallel flow, while in counter flow the half-hollow fins increase above the solid fins by 5% and by 0.5% higher than hollow fins. The integrated micro heat sink with half-hollow is superior in both parallel and counter flow. Experimental data is used to validate the numerical prediction. [Display omitted] • A groundbreaking method for cooling micro heat exchangers. • Dual cooling technique in integrated heat sink. • The application of cylindrical fins in an integrated heat sink. • A novel approach to enhance heat transfer efficiency in heat sinks. • A cutting-edge innovation in heat sinks with a hybrid configuration. [ABSTRACT FROM AUTHOR]

With the development of science and technology, the heat dissipation problem of high-density electronic products has gradually emerged in engineering practice. In this paper, the enhanced heat dissipation process of fluid induced oscillation through flexible membrane is proposed, which belongs to the multi-field synergistic bidirectional coupling effect of thermal-fluid-solid coupling. Through the comparative numerical analysis of the flow induced oscillation of the flexible membrane and the fixed rigid fin in the flow channel, the mechanism of the fluid induced oscillation of the flexible polyethylene membrane is revealed. Based on the two-way fluid-solid coupling method, a numerical model for the heat transfer process of polyethylene membrane with thickness of 0.02 mm in the fluid channel was established. The temperature field, Nu (Nusselt number) and PEC (Performance comparison index) number of the rigid fin and polyethylene membrane installed in the channel under different Reynolds numbers were calculated respectively. The ratio of the length of the membrane to the height of the channel was adjusted for multiple groups of calculations to verify the positive effect of the polyethylene membrane installed in the channel on the heat exchange effect. The results show that in the fully developed area of heat transfer, the channel with polyethylene membrane is better than that with rigid fins in terms of turbulence and vortex shedding; at Re = 4400, the comprehensive enhanced heat transfer factor of heat exchange is the largest, up to 1.27; as the ratio of the height of the new flexible membrane to the height of the channel is 1, the heat transfer enhancement effect is best. In the next step, the correlation theory between oscillation characterization parameters and heat transfer enhancement effect under pulsating fluid excitation will be investigated. [ABSTRACT FROM AUTHOR]

In order to enhance the heat transfer performance of the battery thermal management system, to obtain a more uniform temperature distribution and to achieve the lightweight design requirements, a new liquid cooling plate design approach with primary and secondary combined fins synergistic phase change materials and nanofluid is proposed in this paper. Based on the traditional square fins, 10 new improved fin design options are proposed in this paper. Firstly, the thermal and flow characteristics of the 10 new improved fins are compared and analyzed, and the optimization is carried out. Next, the optimal model is obtained by considering the primary fin size and introducing the secondary fins of the partitioned combination for optimization. Compared to the traditional square fins, the average temperature is reduced by 0.288 °C and the pressure drop is reduced by 1.287 Pa (17.42%). Then, based on the optimal model, the thermal performance of the combined filling method and thickness of PCM is discussed and analyzed for different Reynolds number conditions. The results indicated that the smaller the Reynolds number, the more significant the heat dissipation effect of the filled PCM. The optimal model with PCM filling reduces the mass by 41.4 g (68.86%) compared to the model without PCM, with significant lightweighting effect. Finally, to further improve the thermal performance of the system, different types of nanoparticles with different volume fractions are introduced into the system. Compared to pure water liquid cooling, the Nusselt number can be increased by 9% to 78%, and the heat dissipation effect is significantly improved. • Based on the traditional directional fins, 10 new and improved fins are proposed. • Thermal performance of the system was improved after introduction the secondary fins. • A new liquid cooling plate with PCM synergistic combination fins was proposed. • The mass of the optimal model after filling the PCM was reduced by 41.4 g (68.86%). • Nusselt number of system can be improved by 9% to 78% after introduction nanofluid. [ABSTRACT FROM AUTHOR]

In this article, turbulent flow characteristic of nanofluids is thoroughly reviewed. Turbulent flows have unique characteristics and are preferred in many industrial applications. Therefore, this paper reviews different techniques used to enhance heat transfer using nanofluids within turbulent regime. This paper also presents the effects of some important parameters such as nanoparticle type, nanoparticles concentration, and Reynolds number on heat transfer rate. Studies on numerical techniques are also discussed. Finally, the conclusions and important summaries are presented according to the data collected. [ABSTRACT FROM AUTHOR]

In this paper an attempt has been made with experimental as well as theoretical analysis to find the variation in heat transfer coefficient with Reynolds number and numerical simulation attempt has also been done with different turbulence models in forced convection turbulent flows. Experimental analysis was carried out by using forced convection experimental setup at constant power supply to the heater and by varying the different flow rates of air with the help of a blower. The tube heat exchanger is fully insulated. In turbulent flows, the heat transfer coefficient is greatly affected by the turbulence, hence in this paper numerical analysis was carried out with different turbulence models and analysis has been done with both experimental and theoretical values to find the best turbulence model. [ABSTRACT FROM AUTHOR]

In current attempt, swirl generator and four-lobed pipe were installed in a solar collector to achieve higher performance not only in view of cooling rate but also available energy. In outputs, components of irreversibility were illustrated for different values of revolution (N), pumping power (Re (Reynolds number)) and width of tapes (D∗(diameter ratio)). Four functions were scrutinized namely; Xd (exergy loss); S gen,th (thermal irreversibility); S gen,f (frictional irreversibility); Φ s (Augmented irreversibility). Experimental articles were utilized to not only verify the nanofluid modeling but also the correctness of selecting k-ϵ turbulent model. S gen,th declines with rise of active parameters because of reduction in temperature gradient and highest impact belongs to Re. Although increasing revolution provides stronger secondary flow as well as trend of Re, the influence of N on S gen,th is lower than that of Re. At lowest values of other factors, Be (Bejan number) declines about 0.016%, 0.004% and 8.2% with enhance of diameter ratio, N and Re. Revolution of tape has lowest impact on Be in comparison to other factors. Be decreases about 1.67% with rise of N at Re = 20000, D∗ = 0.045. The component of ∇T reduces as greater secondary vortex appears. So, augment of inlet velocity, width and revolution of tape makes exergy loss to decline. • Swirl generator and four-lobed pipe were utilized considering nanofluid. • Experimental articles were utilized to prove correctness of K-ϵ model. • Be decreases about 1.67% with augment of N when Re = 20000, D∗ = 0.045. • When D∗ = 0.02, Re = 4000, Xd for N = 4 is 1.02 time greater than that of N = 7. • Thinner boundary layer can be produced with augment of all three parameters. [ABSTRACT FROM AUTHOR]

The determination of the effectiveness of large heat wheels using standard measured data and test conditions can be very expensive and time consuming. The main contribution of this paper is that it tests heat wheel components rather than the wheel itself. In addition, this paper deals directly with the question of what accuracy can be achieved for the determination of sensible energy effectiveness by using a transient step change method for the exchanger matrix materials in a test cell. In this study, the sensible effectiveness of heat wheels is predicted by performing a number of cyclic and single step change transient experiments on a parallel-plate heat exchanger. A new experimental facility is developed to cause a step change for the inlet air temperature of the exchanger. In the cyclic tests, the heat exchanger is exposed to a periodic inlet temperature steps; afterward, the sensible effectiveness of parallel-flow and counter-flow heat wheel, comprised of the same material as parallel-plate exchanger, is determined using the obtained temperature profiles. It is find that this method can be used to determine the sensible effectiveness of parallel-flow heat wheel. However, the high uncertainty found in the sensible effectiveness of counter-flow heat wheel, ±32%, makes the results unreliable. In the single step-change test, a time constant is assigned to the exchanger response when it is subjected to a step change in inlet temperature. The time constant is obtained by fitting the experimental data to a first order exponential time response curve. An analytical solution posits that the effectiveness of the heat wheel depends only on the product of the time constant and the wheel angular speed, or angle ratio. Comparing values of the sensible effectiveness calculated through available empirical correlations and the ones obtained by single step change experiment showed less than 3% difference in results when the heat capacity rate ratio is greater than 5. It is concluded that due to simplicity, accuracy, and low cost of the single step change experiments, it is the preferred method to determine the effectiveness of heat wheels operating at a specified rotary speeds, provided the flow channel geometries and Reynolds numbers for both the wheel and the small-scale test cell. [ABSTRACT FROM AUTHOR]

In this paper, the MRT (Multiple Relaxation Time)-D2Q9 model and the MRT-D2Q5 are employed to simulate the flow and heat transfer of laminar confined impinging jet flow. For impinging jet flows, the paper considers the effect of Reynolds numbers and jet-impingement surface distance ratio ( H / W ) on the flow and temperature fields. As for the investigation of heat transfer behaviors on stagnation Nusselt number, it is evident that the effect of H / W is not significant. The Nu number increases dramatically with increasing Reynolds number. And what’s more, this study presents flow and heat transfer predictions of slot jets impinging on cylinder and obtains distribution of Nusselt numbers around the cylinder for different Reynolds number. [ABSTRACT FROM AUTHOR]

A model accounting for wall roughness effects in k - ɛ low-Reynolds turbulence models is described in the present paper. In particular, the introduction in the transport equations of k and ɛ of additional source terms related to roughness, based on simple assumptions and dimensional relationships, is proposed. An objective of the present paper, in addition to obtaining more realistic predictions of wall friction, is the application of the proposed model to the study of heat transfer to supercritical fluids. A first validation of the model is reported. The model shows the capability of predicting, at least qualitatively, some of the most important trends observed when dealing with rough pipes in very different flow conditions. Qualitative comparisons with some DNS data available in literature are also performed. Further analyses provided promising results concerning the ability of the model in reproducing the trend of friction factor when varying the flow conditions, though improvements are necessary for achieving better quantitative accuracy. First applications of the model in simulating heat transfer to supercritical fluids are also described, showing the capability of the model to affect the predictions of these heat transfer phenomena, in particular in the vicinity of the pseudo-critical conditions. A more extended application of the model to relevant deteriorated heat transfer conditions will clarify the usefulness of this modelling methodology in improving predictions of these difficult phenomena. Whatever the possible success in this particular application that motivated its development, this approach suggests a general methodology for accounting for wall roughness effects in low-Reynolds number turbulence models. [ABSTRACT FROM AUTHOR]

The Partially-Averaged Navier–Stokes (PANS) method is intended to provide the optimum fidelity on any given numerical grid while varying seamlessly between the Reynolds-Averaged Navier–Stokes (RANS) model and direct numerical simulation (DNS). This method belongs to so called bridging or seamless methods. The PANS method has been more often used in the research community but also in the industry in last years. This is probably due to its simplicity, robustness and recent theoretical extensions as well as due to the detailed validations on the number of complex cases presented in many publications. As for any relatively new modeling approach, the list of validation cases should be further extended. Therefore, an additional test case is included in this paper. The PANS method is validated here for the fluid flow and heat transfer in a matrix of surface-mounted cubes. The ζ-f variant of PANS was used and compared with its RANS counterpart. The calculation procedure, which now includes the energy equation as well, is explained. A brief description of on-going developments and possible next improvements is also given in this paper. [ABSTRACT FROM AUTHOR]

In this study heat transfer and fluid flow analysis in a straight channel utilizing nano-fluid is numerically studied, while flow field is under magnetic field. Usage of nano-particles in base fluid and also applying magnetic field transverse to fluid velocity are two ways recommended in this paper to enhance heat exchange in straight duct. The fluid temperature at the channel inlet ( T in ) is taken less than that of the walls ( T w ). With assuming thermal equilibrium state of both the fluid phase and nano-particles and ignoring the slip velocity between the phases, single phase approach is used for modeling of nano-fluid. The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Numerical studies are performed over a range of Reynolds number, nano-fluid volume fraction and Hartmann number. The influence of these parameters is investigated on the local and average Nusselt numbers. Computations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance up to 75% due to the presence of nano-particles and magnetic field in channels. In industrial applications for cooling or heating purposes, the recommended ways in this paper, can provide helpful guidelines to the manufacturers to enhance efficiencies without heat exchanger area increase. [ABSTRACT FROM AUTHOR]

• Al 2 O 3 /water nanofluids laminar flow inside a tube was numerically investigated. • A comparative analysis between eight various models was carried out. • Simulations were compared with two different experiments and Shah Equation. • Xuan-Roetzel and Talieh-Abbas dispersion model are suggested for applications where the calibration data are available. • Discrete phase model is firstly suggested if no prior experiments are conducted for nanofluids. This paper numerically studies Al 2 O 3 /water nanofluids that convectively flow inside the laminar regime of a tube with a constant wall heat flux with various models. Eight different models are utilized to predict the heat transfer behavior of the nanofluids, and the predictions are compared with the available experimental data from literature and the values of the conventional correlation. Comparisons show that all eight models are suitable for the prediction of Al 2 O 3 nanofluids with relatively small particle concentrations (0.25 wt% and 0.5 wt%, mass fractions) of Al 2 O 3 /water, within the maximum deviation between the predictions of all models and corresponding experimental data less than 20%. While comparison results with experiments of relatively large particle concentrations (0.6%, 1.0% and 1.6%, volume fractions) show that Mixture model overestimates the heat transfer performance. Discrete phase model increases the prediction accuracy about 10% for two-phase models and agrees well with the classical Shah Equation within the maximum error of 5.5%. The error of Nusselt number between the predictions of discrete phase model and experimental data falls off with the increase of Reynolds numbers and axial direction position. The discrete phase model, Xuan-Roetzel dispersion model, and Talieh-Abbas dispersion model are precise approaches to predict the laminar convectional heat transfer behavior of Al 2 O 3 /water nanofluids in the scope of 0–1.6% nanoparticles. The Xuan-Roetzel dispersion model and Talieh-Abbas dispersion model are suggested for applications where the calibration data are available. [ABSTRACT FROM AUTHOR]

• Unsteady wake dynamics past a blunt headed cylinder at incidence is studied. • Determined critical Reynolds number (Re) based on primary stability analysis. • Identification of various flow regimes during vortex shedding. • Evaluation of forced convective heat transfer for various Re and angles of incidence. • Entropy generation optimization at different Re and angles of incidence. In the present paper, a numerical investigation has been carried out to study the forced convective flow and heat transfer characteristics past a blunt-headed cylinder in crossflow. Employing air as an operating fluid, calculations are carried out for a range of Reynolds number (Re) from 40 to 160. The angle of incidence is varied in the range of 0∘ ≤ α ≤ 180 ∘. The thermofluid features of flow and heat transport are analysed in detail for different angles of incidence. To analyse the aerodynamic characteristics, several parameters such as drag and lift coefficients, moment coefficient, Strouhal number, recirculation length, and local time-averaged vorticity flux have been calculated. Furthermore, a stability analysis has been undertaken by using the Stuart Landau equation to enumerate the critical Reynolds number at each angle of incidence. Heat transfer characteristics are studied by computing local and time-averaged values of Nusselt numbers. When compared to a rectangular cylinder, a blunt-headed cylinder exhibits an enhanced heat transfer rate. In the end, an entropy generation analysis has been carried out to study the effects of Re and angle of incidence on the efficiency of thermofluid transport characteristics. [ABSTRACT FROM AUTHOR]

• The heat transfer process of NH 4 Cl fouling was studied experimentally. • The local heat transfer characteristics around tube wall was analyzed. • The effects of flow rates and temperature on heat transfer process were investigated. • The fouling resistance and average fouling thickness on the HET wall were obtained. The crystallization fouling of ammonium chloride (NH 4 Cl) often occurs on heat exchange tube bundles in petroleum refining equipment, which seriously reduces the heat transfer and operational efficiency of the equipment. In this paper, the heat transfer characteristics of heat exchange tube (HET) with NH 4 Cl crystallization fouling was studied experimentally. The effects of velocity, temperature and mass flow rate of hot and cold fluids on the overall and local heat transfer characteristics were analyzed. The results indicate that the local heat transfer coefficient around the tube wall decreases first and then increases with the increase of the circumferential angle (θ) under clean condition. At the position of 0°-45°, the local heat transfer coefficient is the largest. At 90°-135°, the local heat transfer coefficient is the smallest. Under fouling condition, the local heat transfer coefficient increases with the increase of circumferential angle. In the region of 0°-45°, the local heat transfer coefficient is the smallest. The region with the largest local heat transfer coefficient is 135°-180° The heat transfer coefficient (h), fouling resistance (R f) and average fouling thickness increase with the increase of Reynolds number (Re), temperature of hot fluid (T h) and mass flow rate of cold fluid (q m,c), but decrease with the increase of temperature of cold fluid (T c). [Display omitted] [ABSTRACT FROM AUTHOR]

• The pressure drop through polyurethane foams was studied. • A correlation for friction factor based on fiber diameter and permeability in polyurethane foams was obtained. • A correlation for Nusselt number based on fiber diameter in polyurethane foams was obtained. • Comparison of heat transfer and friction factor in polyurethane foams with metal foams was made. Foam-like materials have a large specific surface area and complex structure that promotes flow turbulence, which makes them useful for heat transfer. In the literature, heat transfer in metal foams (MF) with high thermal conductivity is mainly considered. In the present paper, an experimental study of the hydraulic and heat transfer characteristics of a rectangular channel filled with polyurethane foam (PUF) inserts with a thermal conductivity of 0.2 W⋅m−1⋅K−1 in the air flow was carried out. The open-cell PUF samples had 20 and 80 pores per inch (PPI), 0.97 and 0.98 porosity, 269 µm and 60 µm fiber diameter, respectively. The Reynolds number, based on the fiber diameter ranged from 0.04 to 50. From the results of hydraulic tests, friction coefficients were determined based on the fiber diameter and permeability. The Forchheimer coefficient was 0.198 and 0.318 for 20 and 80 PPI samples, respectively. The permeability was 1.889 10−7 ⋅m2 and 7.535 10−9 ⋅m2 for 20 and 80 PPI samples, respectively. The Nusselt number for both tested PUF samples was correlated with the Reynolds number based on the fiber diameter in a power law with the Reynolds number exponent and constant equal to 0.61 and 0.037 respectively. The intensity of heat transfer in the PUF samples was 7–12 times lower than that in MF. However, a significant heat transfer enhancement is still possible compared to the empty channel up to 7 times. The heat transfer performance of PUF was higher compared to the empty channel, but the thermal performance factor was lower than one. Nevertheless, in practical situations where the mass or cost of the heat exchanger is preferable, PUF can be considered as a heat transfer intensifier. [Display omitted] [ABSTRACT FROM AUTHOR]

• Reduced gravity cryogenic line chilldown data presented. • Investigation is carried out on effect of low thermally conductive coatings and pulse flow. • Comparisons are made between 1-g and reduced gravity for similar conditions. • No appreciable degradation in chilldown efficiency at moderate-to-high Reynolds numbers in reduced gravity relative to terrestrial gravity. Future cryogenic propulsion systems will require efficient methods to chill down transfer lines and propellant tanks prior to transfer of propellant while in space. When chilling down the transfer line, there is an inherent tradeoff between propellant mass consumed and chilldown time to steady state, depending on mission constraints and desires. This paper examines an efficiency parameter based on a simplified energy balance that can be used to compare the performance of different chilldown methods and to determine the optimal chilldown method. The parameter, along with chilldown time and mass, is then applied to recent liquid nitrogen line chilldown experiments conducted in both terrestrial and microgravity to compare efficiencies between numerous continuous and pulse chilldown tests on bare as well as coated tubes across a range of thermodynamic conditions. Despite a well-known reduction in heat transfer in microgravity due to the absence of buoyancy-assisted cooling, results indicate no appreciable degradation in chilldown efficiency at moderate-to-high Reynolds numbers in microgravity relative to terrestrial gravity. [ABSTRACT FROM AUTHOR]