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A numerical investigation was conducted to explore the heat transfer optimization effect of circular tube heat exchanger with L-shaped twisted tape insert and to find the optimal parameter design in this paper. For better thermohydraulic performance, the effects of twist pitch (P), inner diameter (D), tape width (W) and number of tape (N) were studied with Reynolds number ranged from 1875 to 3750. Moreover, response surface method (RSM) was employed to indicate the relationship between the Nusselt number (Nu) and these parameters. With the analysis of flow structure inside the tube, it was conducted that the twisted tape insert was helpful to transform the axial velocity of fluid to radial velocity, forming vortex in the L region. The numerical results showed that the Nu and friction factor (f) of the tube fitted with L-shaped twisted tape insert gained an 199% to 208% increase and 674% to 696% when compared with that of smooth tube respectively. Besides, an optimal parameters set was obtained with P = 65.59 mm, W = 0.95 mm, D = 8.80 mm, in which the Nu and f were increased by 204% and 704% respectively as the results of response surface method. • Effects of L-shaped twisted tapes insert on heat transfer and flow characteristics in were numerically investigated. • The influence of four geometric parameters of twisted tape insert on thermos-hydraulic performance were studied. • The enhanced thermal performance of the L-shaped twisted tapes was obtained by centrifugal force. • The effect of short side of the L-shaped on the thermal performance and flow characteristics were discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive study on the heat transfer in the spiral coiled tubes, employing both numerical simulations and experimental analysis. The investigation includes an exploration of water flow at different mass flow rates, ranging from 0.025 to 0.11 kg / s , to capture a wide range of operating conditions. The numerical simulations were conducted using advanced computational fluid dynamics (CFD) techniques, providing detailed insights into the heat transfer behavior within the spiral tube. Concurrently, experimental tests were performed to validate the numerical results and compare them with existing findings from previous studies. The primary aim of our study is to establish correlations for calculating the Nusselt number and friction coefficient in the spiral coiled tubes. These correlations serve as essential tools for engineers and researchers in predicting heat transfer characteristics and pressure drop, thus facilitating the design and optimization of heat exchangers and heat recovery systems that incorporate spiral coiled tubes. Overall, the results obtained from this investigation enhance our understanding of heat transfer in spiral tubes and contribute to the development of reliable predictive models. The proposed correlations offer practical and efficient means of assessing heat transfer performance, making significant strides towards achieving more energy-efficient and sustainable industrial processes. • Fluid flow and heat transfer in a spiral coiled tube were studied. • Effects of mass flow rate of water on heat transfer in a spiral coiled tube were investigated. • Correlations for calculation of Nusselt number and friction coefficient for water flow in a spiral coiled tube were developed. [ABSTRACT FROM AUTHOR]

The porous microchannel heat sink can be used to meet the increasing demand for electronic device cooling. In this paper, heat transfer is enhanced by optimizing heat flux distribution for porous microchannel heat sinks subject to an exponential heat flux. The Nusselt number, dimensionless wall temperature and thermal resistance are obtained using the semi-analytical method. The Nusselt number is found to be dependent on the product of dimensionless exponent, Reynold number, and Prandtl number. The optimal heat flux distribution is dependent on the length of the channel and it is that under constant wall temperature boundary condition in most cases. The thermal performance is assessed using the thermal resistance ratio between constant wall temperature and constant heat flux boundary conditions. An optimal length exists when the constant wall temperature condition is used to reduce the maximum wall temperature. The effects of Biot number and the ratio between effective thermal conductivities of solid and fluid phases on the minimum value of the thermal resistance ratio and the optimal length are also studied. The result shows that the thermal resistance can be reduced by about 28% by optimizing the heat flux distribution, compared with the commonly used constant heat flux boundary condition. • Heat transfer for porous heat sinks is enhanced by optimizing wall heat flux. • The optimal heat flux distribution is that for CWT conditions in most cases. • An optimal length is found when the constant temperature conditions is used. • The thermal resistance can be reduced by about 28%. [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]

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]

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]

Heat transfer and pressure drop of turbulent fluid flow were studied numerically and experimentally in a quad-channel with twisted tapes placed in a circular tube under uniform heat flux boundary condition. All the tests were conducted with water as the working fluid where the turbulent flow range of Reynolds numbers were maintained at 4250 to 11000. Quad-channel twisted tapes (QCTT) were manufactured by 3D printer with the material PLA, the lengths of 50 mm, 100 mm, 200 mm with the twist ratio of 4.48. The tapes were identified with their tape/pipe length ratios (TPR) of 0.025, 0.05 and 0.1. Validation of the experimental data was performed by the comparison of the experimental results with the data from the well-known empirical correlations. Alteration of the friction factors and Nusselt numbers with the Reynolds numbers are presented in this paper. The results showed that the Nusselt number and the friction factor increased with the increasing of the length of QCTTs. On the other hand, the performance evaluation criteria (PEC) should be declining with the increase of the lengths of the tapes. The evaluated temperature distributions inside the tested tubes with the inserts were plotted in order to investigate the observed data. Based on the obtained experimental data, the empirical correlations for the Nusselt number within the deviation of ±2% and the friction factor within the deviation of ±5% were developed for the practical usage. [ABSTRACT FROM AUTHOR]

In this paper, an experimental research was carried out to study the heat transfer and friction factor characteristics in a tube with a new kind of twisted tape insert. Four twisted tapes with different lengths (2400, 1800, 1200 and 600 mm) were used in the experimental study. The experimental data revealed that Nusselt number caused by these four twisted tapes were 1.45–1.90, 1.23–1.55, 1.18–1.45 and 1.15–1.37 times of that for the plain tube, while the values for friction factor were 3.69–5.75, 2.30–4.48, 2.15–2.75 and 1.21–1.31. The performance evaluation criteria (PEC) for length ratio of 1.0, 0.75, 0.50 and 0.25 is 0.94–1.06, 0.82–0.94, 0.89–1.04 and 0.89–1.06, respectively. What's more, correlations for Nusselt number and friction factor were established in the paper. The predicted values calculated by correlations were in good agreement with experimental data, within 7% for Nusselt number and within 10% for friction factor. [ABSTRACT FROM AUTHOR]

In this paper, the fluid-solid coupling analysis is carried out on the vortex cooling. Under rotation conditions, the process of high-temperature gas scouring the blade and the vortex coolant cooling the blade is numerically calculated. At the same time, five rotation numbers of 0, 0.183, 0.339, 0.457 and 0.512 are selected. In addition, this paper proposes a method to improve vortex cooling performance under rotation conditions. The results show that at high rotation numbers, the centrifugal force drives coolant to flow downstream of vortex chamber. The downstream chamber accumulates a large amount of coolant to derive centrifugal buoyancy, which causes the back flow of coolant and makes the upstream heat transfer effect poor. As the rotation number increased from 0 to 0.512, the average Nusselt number on the target wall decreased by 35.49%. For the blade solid region, the effect of thermal load plays a major role on blade stress and displacement characteristics. Insufficient cooling performance in the chamber upstream leads to a higher temperature of the blade root, and a higher thermal stress concentration is generated because the blade root is constrained. In addition, by improving the intake chamber into a convergent structure, the coolant flow into the vortex chamber can be promoted, and the effect of back flow can be reduced, thereby obtaining a better vortex cooling performance. The target wall average Nusselt number of the convergent intake chamber structure is 977.17, which is 23.63% higher than that of the original rectangular intake chamber structure. • Interaction between blade solid and vortex cooling is studied by fluid-solid coupling method. • Vortex cooling flow and heat transfer characteristics, solid region stress and displacement characteristics are researched. • Number of rotations is changed. • Propose a measure to improve the vortex cooling performance under rotation conditions. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents experimental and numerical studies on periodic convection flow and heat transfer in a lid-driven arc-shape cavity with temperature differential. Three cases were considered: Gr=2×105, 5×105 and 1.2×106 at Re=100 (Gr = Grashof number; Re = Reynolds number). The mathematical model was proposed in our previous study. The current study performs an experiment to validate this model, to corroborate the existence of the periodic flow, and to more deeply probe the internal flow and temperature characteristics. The experimental setup primarily comprised an arc-shape cavity, a moving lid, a thermo-system, a smoke generator and an image acquisition system. The periodic convection flow in the cavity was visualized using kerosene smoke. The numerical and experimental results consistently reveal that the periodic flow pattern was observed in the case with Gr=5×105, whereas the steady-state flow pattern took place in the other two cases (Gr=2×105 and Gr=1.2×106). The numerical simulation produced reasonable and satisfactory agreement with the experiment for the periodic flow pattern and period. The difference between the predicted and measured periods is less than 5%. The transport properties, such as average kinetic energy, overall Nusselt number, stream function, phase space trajectory, local kinetic energy, velocity history and temperature distribution, were further analyzed and discussed in this paper. The proposed numerical simulation not only confirms the experimental observation, but also enhances the understanding of periodic convection in an arc-shape cavity subjected to a moving lid and temperature differential. [Copyright &y& Elsevier]

The flow and heat transfer characteristics of mist/steam coolant in U-shaped gas turbine cooling passage are studied in this paper. The mist/steam mass ratio and mist diameter are carefully analyzed with the numerical method. The results show that the heat transfer of the ribbed-wall gradually increases with the increasing of mist/steam mass ratio. Under the condition of water mist diameter = 10 μm, as mist mass ratio increases from 2% to 10%, the averaged Nusselt number of the First Flow Passage increased by 60.13% and the Second Flow Passage increased by 112.5%. The evaporation rate and surviving time of mist can be controlled by controlling the mists diameter. Larger mist diameter is not always good for enhancing the heat transfer of the ribbed walls. When mist/steam = 8%, as for the First Flow Passage and the Second Flow Passage, water mists of 10 μm diameter has higher average Nu number of ribbed wall than mists of 5 μm, 15 μm and 20 μm. The improvement of the heat transfer performance obtained from the evaporation of the water mist is bound to the increasing of the heat transfer non-uniformity of the heated walls. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional numerical analysis for fully developed incompressible fluid flow and heat transfer through triangular microchannels over the slip flow regime is simulated in this paper. In order to study the flow through the channel, the Navier–Stokes equations are solved in conjunction with slip/jump boundary conditions. The influences of Knudsen number (0.001< Kn <0.1), aspect ratio (0.2< A <4.5), and Reynolds number (1< Re <15) on the fluid flow and heat transfer characteristics are extensively investigated in the paper. The numerical results reveal that the rarefaction decreases the Poiseuille number, while its effect on the Nusselt number completely depends on the interaction between velocity slip and temperature jump. It is also found that the aspect ratio has an important role in the analysis, but the variation of Reynolds number is less remarkable. [Copyright &y& Elsevier]

In this paper, a novel butterfly wing type hydrocarbon fuel cooling channel structure is proposed and applied for the first time in the cooling of rotating power generation turbine blades of hypersonic vehicles. The effects of rotating butterfly wing-type channel root height and cross-critical temperature on the friction factor and heat transfer performance of hydrocarbon fuel are investigated in depth. Numerical results show that the thermal performance of the butterfly wing type channel corresponding to the root height of 0.8 D is the highest. Compared to the 1 D channel, the thermal performance of the butterfly wing type channel corresponding to the root height of 0.8 D is increased by a maximum of 1.8 times. Compared to the 1 D channel, the Nusselt number of the wing type channel corresponding to the root height 0.2 D is increased by a maximum of 1.03 times. Compared to the inlet temperature greater than critical temperature, the thermal performance of the wing type channel at inlet temperature less than critical temperature is increased by a maximum of 2.1 times. Compared to the 1 D channel, the wing type channel reduces the first channel backflow and vortex area by almost 50%. • A novel butterfly wing type hydrocarbon fuel cooling channel is proposed and firstly used in hypersonic vehicles. • Thermal performance of the channel with a root height of 0.8 D is increased by maximum 1.8 times. • The butterfly wing type channel can improve the thermal performance of the fuel at high rotation speed. • The wing type channel can reduce the backflow and vortex area by almost 50%. • Fuel "upward convexity" and "downward concavity" cause the wing channel heat transfer level to increase. [ABSTRACT FROM AUTHOR]

In this paper, an experimental and numerical study was conducted to evaluate the impacts of momentum and thermal diffusivity comparing to the thermal conductivity of various types of nanofluids on turbulent forced convection heat transfer. 1%, 2%, and 3% volumetric concentrations of different nanofluids such as Al 2 O 3 -DW, SiO 2 -DW, and Cu-DW were considered in this study and their properties were evaluated numerically at the flow inlet temperature of 30 °C. The experimental works were conducted with distilled water as a working fluid to validate the 2-D numerical model. A two-dimensional domain was constructed using ANSYS-Fluent package, and the standard k–ε turbulence model was employed to solve the continuity, momentum, and energy equations. The flow was maintained in the Reynolds range between 6000 and 12,000, and the data obtained experimentally were validated by results from empirical correlations. The numerical solutions for the average Nusselt number and pressure drop presents a good agreement with the experimental results as the average error was less than 5% for both the cases of heat transfer and pressure loss data. The results showed that Al 2 O 3 -DW nanofluid has the best enhancement in convection heat transfer coefficient compared with the DW and other nanofluids of the same concentration while Cu-DW nanofluids shown the lowest enhancement though it shown the highest value of thermal conductivity. Also, the results showed that the product of kinematic and dynamic viscosities had the greatest effect on pressure drop in the fluid domain. [ABSTRACT FROM AUTHOR]

In this paper, the convective heat transfer and flow characteristics of nanofluids consisting of distilled water and 0.25, 0.5 wt% and 1 wt% Al 2 O 3 nanoparticles were studied experimentally and compared to predicted results using computational fluid dynamics (CFD) that using laminar model was performed to examine the heat transfer characteristics. The Al 2 O 3 nanoparicles with a nominal diameter of 40 nm are dispersed in distilled water to form stable suspensions containing various kind of volume concentrations of nanoparticles. For the even dispersion of the nanoparticles in the base liquid, ultrasound was applied for 3 h. The nanoparticle dispersion on alumina concentration was measured using UV spectroscopy. Thermal conductivities of nanofluid solutions are measured by the transient hot wire method. Heat transfer characteristics were investigated by changing pressure pulsation at each concentration. Finally, calculated heat transfer characteristics results using CFD are compared to experimental results and discussed successfully. Results indicate that the heat transfer coefficient and Nusselt number increase with increasing the Reynolds number and it is also seen that the Prandtl number is getting down when the concentration of nanofluids enlarge and showed the equation by the linear method of the result value. [ABSTRACT FROM AUTHOR]

This paper constructs a three-dimensional model to numerically investigate the heat transfer and fluid flow characteristics of combined microchannel with cone-shaped micro pin fins (MCPF) for inlet Re number ranging from 147 to 637. Firstly, the cases of micro pin fins located in the upstream (case1), middle (case2), downstream (case3) of microchannel and distributed throughout the microchannel (case4) are studied with fixed number of fins. Thereafter, the dimensionless parameters of relative fin diameter, relative space between the fins and relative height of the fin are studied to optimize the design. The variations of apparent friction factor f app,ave and average Nusselt number Nu ave with inlet Re number have been conducted, and the thermal enhancement factor ( η ) has been adopted as evaluation criteria to determine the best comprehensive thermal-hydraulic performance of MCPF. The results show that the microchannel inserted cone-shaped micro pin fins improves the heat transfer accompanied with a higher pressure drop as compared with the smooth rectangular (Rec) microchannel. Microchannel with uniform fins distribution (case4) has the largest η and the bottom wall temperature is the lowest and well-distributed among all cases. When Re < 500, the overall thermal performance of case3 is better than case1 but when Re > 500, it displays a contrary tendency. The geometric configuration optimization of MCPF suggests that there is an optimum pin diameter, fin space and fin height that satisfy the demands of heat transfer and pressure drop. [ABSTRACT FROM AUTHOR]

This paper reports the effect of changing the aspect ratio on the heat transfer and flow quantities over in-line tube banks. Two types of in-line arrangements were employed; square and non-square configurations. The models that were examined are a standard k-ε model, SST k-ω model, v2-f model, EB k-ε model and EB-RSM model. The closer results to the experimental data and LES were obtained by the EB k-ε and v2-f models. For the square pitch ratios, the solution has faced a gradual change from a strong asymmetric to asymmetric and then to a perfect symmetry. The strong asymmetric solution was found by the very narrow aspect ratio of 1.2. However, the behaviour of cases of 1.5 and 1.6 became less strong than that predicted in the case of 1.2. In the larger aspect ratio of 1.75, the flow behaviour is seen to be absolutely symmetric for all variables under consideration except Nusselt number. For the very large pitch ratio of 5, the flow has recorded maximum distributions for all parameters on the windward side of the central tube with a perfect symmetric solution around the angle of 180° while the vortex shedding frequency has recorded minimum value and the Strouhal number; therefore, has given the smallest value. However, for the non-square pitch ratio of constant transverse distance, the solution is still asymmetric for all parameters with merely one stagnation at the angle of 52° at the case of the 1.5 × 1.75 while by increasing the longitudinal distance to 2 and 5, the solution provided a comprehensive symmetry for all variables with two vortices are fully developed mirrored in shape on the leeward side of the central tube. On the contrary, for the non-square pitch ratio of constant longitudinal distance, the flow of the case of 1.75 × 1.5 provided two stagnation locations at around 52° and 308° with a very similar solution to the case square ratio of 1.75 for all variables whereas by increasing the transverse distance to 2 and 5, the solution recorded was not perfectly symmetric resulting in two different vortices and one stagnation position located at the leading edge of the cylinder provided by the case of 5 × 1.5. In terms of vortex shedding effect, the reduction in the Strouhal number at a constant transverse pitch is less steep than those at a constant longitudinal pitch. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose the PV roof solar collector (PV-RSC) to investigate the natural convection heat transfer and estimated the convective heat transfer coefficient in the channel. The experimental set-up was composed of a PV panel on the upper layer and the lower layer is aluminum plate of the channel. The inclination angle and air gap of channel were fixed at 30° and 15 cm, respectively. The channel width is 0.7 m, and length is 1.2 m. The data analysis were confirmed the effect of radiative exchange influent to natural convection within the channel. On the basis of the experimental results, an empirical formula is found; the Nu as a function of Ra s sin30, that is Nu s = 0.3282 ( Ra s sin30) 0.2249 . The correlation obtained to range 3 × 10 8 < Ra s sin30 < 7 × 10 8 . A comparison between PV-RSC and normal PV panel, it was confirmed that the PV-RSC could be generated electric power than that normal PV panel by about 30 W; and also the percentage of power generation increase was rising about 25% throughout the day. [ABSTRACT FROM AUTHOR]

In present paper, solar air heater duct having aspect ratio 12 roughened with broken arc rib has been investigated. The broken arc is formed by creating symmetrical gap in continuous arc with gap width equal to roughness height. It has been planned to investigate the influence of position of gap in arc rib on Nusselt number as well as on friction factor. For this purpose, five broken arc rib roughened plates having relative gap position ranging 0.2–0.8 have been investigated for values of Reynolds number 2000–16000. The remaining roughness parameters like relative roughness height, arc angle, and relative roughness pitch were taken as 0.043, 30 o and 8 respectively. The presence of broken arc ribs enhanced the Nusselt number, friction factor and thermo-hydraulic performance up to 2.37, 2.55 and 1.94 respectively, compared to smooth duct. The results of ducts roughened with broken arc rib and continuous arc rib have been compared under similar flow conditions. The effect of gap in continuous arc rib on the flow pattern has also been observed using ANSYS Academic Research CFD 15.0. [ABSTRACT FROM AUTHOR]

This paper numerically and experimentally investigated the liquid cooling efficiency of heat sinks containing micro pin fins. Aluminum prototypes of heat sink with micro pin fin were fabricated to explore the flow and thermal performance. The main geometry parameters included the diameter of micro pin fin and porosity of fin array. The effects of the geometrical parameters and pressure drop on the heat transfer performance of the heat sink were studied. In the experiments, the heat flux from base of heat sink was set as 300 kW/m 2 . The pressure drop between the inlet and the outlet of heat sink was set < 3000 Pa. Numerical simulations with similar flow and thermal conditions were conducted to estimate the flow patterns, the effective thermal resistance. It was found that the effective thermal resistance would reach an optimum value for various pressure drops. It was also noted that the effective thermal resistance was not sensitive to porosity for sparsely packed pin fins. [ABSTRACT FROM AUTHOR]

In this paper, fluid behavior and the second order statistics of developed turbulent natural convection is numerically predicted by the hybrid lattice Boltzmann method. In order to simulate the high Rayleigh number flow, the high order regularized lattice Boltzmann scheme combined with the finite difference solution of energy equation is used. An in-house code was carefully validated against the reference data computed by different numerical macroscopic and mesoscopic techniques. Simulations were performed for cavity aspect ratio 1 ≤ A r ≤ 4 and Rayleigh number 1010 ≤ Ra ≤ 1011. It was found that two-dimensional (2D) models overpredicted turbulent statistics in comparison with three-dimensional (3D) models. Moreover, less stratified thermal fields are observed under 2D simulations. However, the mean Nusselt numbers are well agreed both for 2D and 3D models. The proposed hybrid model with uniform grid spacing reproduced integral heat transfer characteristics with acceptable accuracy for engineering applications. In particular, the relative error in the mean Nusselt number is within 5% when comparing the results with conventional fully resolved Navier-Stokes formulation. • Hybrid high order regularized lattice Boltzmann model is proposed. • Direct numerical simulation of turbulent thermal convection is performed. • Integral characteristics are in a good agreement with reference data even with uniform grid spacing. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of the flow-induced pitching, heaving or surging of an airfoil in a rectangular channel for heat transfer enhancement. The flow dynamics, airfoil fluttering response, and heat transfer performance are analyzed and discussed at four different Reynolds numbers (Re = 700, 1000, 1300 and 1500), three rotational axis locations (a x / C =0.25, 0.33 and 0.42), two airfoil perturbation modes (passive vs. active), and three combinations of multiple airfoil freedoms (pitch only, pitch and heave, and pitch and surge) with various stiffness coefficients. It is found that after Reynolds number reaches 1000, the pitch only airfoil starts the similar self-fluttering pattern, and the fluttering effect becomes the dominant influencer for increasing the Nusselt number compared to the Reynolds number effect. Placing the rotational axis at a x / C =0.42 achieves the highest thermal enhancement factor η of 1.4, while when a x / C =0.25, the airfoil oscillation diminish effect is vast because of its aerodynamic center. The passive pitching airfoil can achieve more than 6% of the thermal enhancement factor than the active ones. Adding another heave or surge degree of freedom to the pitching airfoil, the heat transfer enhancement of the channel can also be improved. The present work can facilitate future optimizations of airfoil-based flow-structure interaction system for heat exchanger channels. [ABSTRACT FROM AUTHOR]

This paper studies the effect of jet plate V-shaped protrusions (VP) on impingement cooling at the crossflow-to-jet mass flow ratio (CMFR) ranging from 0 to 0.5. The effects of location (L), height (H), open angle (θ) of VP and crossflow-to-jet temperature ratio (TR) are discussed. From results, compared with Baseline case (impingement cooling without VP), all VP cases can enhance heat transfer (Nu ave), although friction loss coefficient (f) also increase, thermal performance factor (TPF) are improved. When L varies from 1.5 D to 3.0 D , VP case with L of 1.5 D has the highest Nu ave and f , and at CMFR of 0.5, it owns the highest TPF of 1.081. When H increases from 0.1 D to 0.4 D , Nu ave , f and TPF gradually increase. However, when H varies from 0.4 D to 0.5 D , only Nu ave and f also increase, TPF increases only at CMFR ranging from 0.4 to 0.5. Besides, with the increase of θ , Nu ave , f and TPF increase, and VP case with the θ of 110° always obtains the highest TPF. At CMFR of 0.5, TPF is up to 1.098. Finally, for impingement cooling with/without VP, as TR increases, the heat transfer always decreases. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the method used in a recently published paper to measure the latent heat of the martensite transformation during quenching of a steel is analysed. The arrangement of the experiment made it possible to obtain reasonable values for the latent heat of transformation, but cannot be expected to produce reasonable values for the heat transfer coefficient. Improved methods are discussed, including the novel probe design of the present authors. [Copyright &y& Elsevier]

In this paper, turbulent flow of aviation kerosene at supercritical pressure through cooling channels respectively with streamwise sinusoidal corrugation, spanwise sinusoidal corrugation and streamwise and spanwise coupled sinusoidal corrugations are numerically studied. The Reynolds-averaged Navier-Stokes method with RNG k − ε turbulence model is used to perform numerical simulation. The independence of grids is first examined, and the numerical results are compared with experimental data for validation. The present results show that the streamwise corrugation significantly improves convective heat transfer performance of cooling channels, the increase ratio of Nusselt number and Thermal Performance Factor reaches 20.44% and 6.7%. With the streamwise and spanwise corrugations coupling, the increase ratio of Nusselt number and Thermal Performance Factor are both larger than those in cooling channels with only streamwise corrugation. Furthermore, the results of flow and heat transfer of aviation kerosene at supercritical conditions with corrugations effect show that corrugations can eliminate heat transfer deterioration occurring at supercritical conditions. The present study is aimed to provide useful references for cooling optimization with wall microstructures for engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, the performance of ethylene glycol and water based TiO 2 nanofluids as an automobile radiator coolant is determined experimentally. Forced convective heat transfer coefficient of TiO 2 nanofluids has been measured and compared with the data of base fluid in an automobile radiator. Nanofluids were prepared taking 40% ethylene glycol and 60% water with volume concentrations of 0.1%, 0.3% and 0.5% of TiO 2 nano powder. All the experiments were conducted in the range of Reynolds numbers from 4000 to 15,000. In all the experiments the nanofluids made to flow through the radiator tubes with elliptical cross section and airflows with constant speed in the crosswise direction in between the tubes of a tube bundle. Results demonstrate that increasing the fluid circulation rate can improve the heat transfer performance while the fluid inlet temperature to the radiator has little or no effect. Nanofluids investigated in the present work with low concentrations enhanced the heat transfer rate up to 37% in comparison with base fluid. The results of the investigation are presented graphically in terms of non-dimensional heat transfer coefficient as a function of volume concentration, temperature and flow rate. [ABSTRACT FROM AUTHOR]

Heat transfer characteristics of Fe 2 O 3 /water and Fe 2 O 3 /EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe 2 O 3 nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe 2 O 3 nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the forced convection and entropy generation of Fe 3 O 4 water nanofluid inside a cylindrical tube with porous hemisphere media. The flow regime is turbulent under a uniform magnetic field and constant heat flux, and to solve the equations, the finite volume method is applied. The combination of nanofluid, magnetic field and porous hemisphere media on the flow and heat transfer in a tube is the main novelty. The effects of different parameters such as Reynolds number (10,000 to 25,000), porosity (ε = 20%, 40%, and 80%.), the solid volume fraction of nanofluid (0.5 vol%, 1 vol%, and 2.5 vol%), friction factor and entropy generation of Ferro-nanofluid in the tube are investigated. The Nusselt number, entropy generation, and friction factor have been discussed and analyzed detailly. It is found that as the Reynolds number enhances, the effect of inertial forces becomes more dominant. Furthermore, by increasing the porosity to 0.8, the Nusselt number decreases to a minimum value. Heat transfer enhancement by increasing Hartmann's number is less effective than adding nanoparticles. A more significant Hartmann number and larger nanoparticle volume fraction lead to more extensive performance evaluation criteria. It is also found that adding a magnetic field increases the friction factor. Adding nanoparticles to the pure water decreases entropy generation by heat transfer per unit volume. [ABSTRACT FROM AUTHOR]

In this paper, a regularized diffuse domain-lattice Boltzmann model for heat transfer with the Dirichlet boundary condition in complex geometries is proposed. In this model the complex computational domain is embedded into a larger and regular domain. The level set function is used to capture the complex interface. A diffuse domain formulation for the temperature field is established on the larger domain. To remove the ill-conditioned property of the original diffuse domain equation, we develop a new regularization technique to tackle this issue. We also give a multiple-relaxation-time lattice Boltzmann model to solve the regularized diffuse domain equation. The convergence rate of present model is investigated by the steady state and time-decay heat conduction problems. Then the natural convection problems in a square enclosure with a heated circular cylinder and in a horizontal concentric annulus are simulated. Both the uniform and non-uniform wall temperature cases are considered. Moreover, an alternative method to calculate the average Nusselt number on the complex boundary is employed. The numerical results show a good agreement with the previous solutions in previous literatures. The effect of non-uniform wall temperature on the heat transfer rate is also investigated. At last, the forced convection across the staggered tube banks is also simulated to verify the potential capability of the present model in solving practical heat transfer problem with the complex geometries. • We give a simple method to regularize the original diffuse domain equation to remove the ill-conditioned property. • We present a lattice Boltzmann model to solve the regularized diffuse domain equation. • An alternative method to calculate the average Nusselt number on the complex boundary is employed. • Both the uniform and non-uniform wall temperature cases are considered. [ABSTRACT FROM AUTHOR]

All studies regarding the double passages channel use a rigid baffle to separate the two passages. In the current paper, we use a flexible separator and inspected its role in enhancing the performance of the heat transfer. The cold fluid is forced upward in the channel which is heated isothermally by different temperatures on its walls. A flexible sheet is fixed from its two ends and equally separate the channel to two passages. The problem is investigated numerically using the finite element method coupled with the arbitrary Lagrangian-Eulerian approach. The problem is casted in dimensionless form and several pertained parameters have been inspected, like Reynolds number in each passage, elasticity of the separating sheet and the temperature ratio of the channel walls. Results are promising where it is found that the enhancement of heat transfer is possible passively in either passage with the aid of using a flexible separator rather than rigid separator. A 6% enhancement in the Nusselt number of the left passage, which comprises the higher temperature, is obtained by making the separator flexible. The flexible sheet is found to increase the pressure drop to 200% in some cases which leading to decline the thermal performance criterion to lower than unity. However, the thermal performance criterion TEC was feasible in the right passage which subjects to lower temperature. • A monolithic finite element approach using high-order schemes in space and time is utilized. • Heat transfer enhancement is possible passively in a passage with the aid flexible separator rather than rigid separator. • A 6% enhancement in the Nusselt number of the left passage is obtained by making the separator flexible. • The flexible sheet increases the pressure drop to 200% in some cases leading to decline the thermal performance criterion. • Thermal performance criterion TEC was feasible in the right passage which subjects to lower temperature. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional analysis is used to study the heat transfer and entropy generation inside a helically coiled tube-in-tube heat exchanger in laminar flow regime using two different types of nanofluids. Overall heat transfer coefficient, effectiveness, Nusselt number, and entropy generation of helically coiled tube-in-tube heat exchanger were investigated considering the nanoparticle volume concentrations between 0 and 2.0 vol.%. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The present contribution is a companion paper of Huminic and Huminic [1]. The numerical results reveal that the use of nanofluids in a helically coiled tube-in-tube heat exchanger improves the heat transfer performances. Thus, the maximum effectiveness was 91% for 2% CuO nanoparticles and 80% for 2% TiO 2 nanoparticles. Also, the increase of nanoparticles volume concentration leads to the Nusselt number increase and the reduction of the entropy generation due heat transfer effects, the viscous effects to entropy generation being negligible. [ABSTRACT FROM AUTHOR]

In this paper, natural convection heat transfer and fluid flow within a single slope solar still (SSSS) are investigated numerically. To enhance the productivity and performance of this system, the differences of bladed and non-bladed solar stills in terms of vortices resulted from natural convection heat transfer are presented. It is assumed that the flow within the still is two-dimensional, steady and laminar. The numerical method is based on SIMPLEC algorithm and is used for discretization and solving continuity, momentum, energy and concentration conservation equations. The blades are installed on the non-insulated walls of solar stills in two different ways; downward and upward. Results are posed for different blade locations, Rayleigh and Nusselt numbers. Moreover, results depict that exploiting a blade can augment system's performance substantially in comparison with more than one. Comparison of the present numerical approach and well-known published empirical correlations proves the acceptable accuracy of this study. [ABSTRACT FROM AUTHOR]

In this paper, the effect of an unheated starting length, L 0 varying between 0 and 30 cm, on the burning and heat transfer characteristics over a horizontal Poly (methyl methacrylate) flat plate is experimentally investigated under wind velocities ranging from 0.5–2.0 m/s. The flame images, flame standoff distance, and Nusselt number are measured or calculated. In comparison to the wind velocity, the effect of an unheated starting length is of first-order importance in influencing the flow, heat transfer, and combustion over a solid fuel surface. The unheated segment introduces unique streamwise streaky flames. A critical condition is found to exist at L 0 = 10 cm, where the spanwise wave and lattice structures are observed in the flame, causing the standoff distance and Nusselt number to increase markedly beyond the theoretical prediction. When the unheated segment exceeds a certain length, the increased unheated length effect becomes negligible. Furthermore, the unheated segment shortens the laminar forced convection region and broadens the turbulent buoyant convection region. The study provides very crucial information regarding the effects of an unheated segment on the transitioning mechanism of a wind-driven flame which might be useful and important for fire research. [ABSTRACT FROM AUTHOR]

Recent works have examined the thermal and dynamical aspects of natural convection occurring in tilted hemispherical cavities whose disk constitutes the hot active wall. The influence of some important aspects on the natural flows have been considered such as the Rayleigh Number, the disk inclination angle with respect to the horizontal plane and the thermal boundary condition on the disk (Dirichlet, Neumann). Combinations of these parameters have been treated in steady state as well as is transient regime. Correlations of Nusselt–Rayleigh type (steady state) and Nusselt–Rayleigh–Fourier type (transient regime) that allow quantifying the heat transfer are proposed in these surveys. The objective of this paper is to synthesize and summarize these works in order to facilitate their implementation in engineering applications. [ABSTRACT FROM AUTHOR]

It is significant to develop an expression for the rarefaction correction to the continuum solution for heat transfer. An extended Reynolds analogy for slip and transition flow heat transfer in microchannels and nanochannels is proposed. A relationship between the rate of the dimensionless mean wall shear stress reduction and the rate of the dimensionless mean wall heat flux reduction may exist. The extended Reynolds analogy can be utilized to obtain an initial engineering approximation of the Nusselt number. As slip flow heat transfer is inherently complex, the proposed simple model may provide an insight into the mechanism of slip flow heat transfer. This paper cultivates the facility to perform the kind of engineering analysis which, although not exact, still provides useful information concerning real engineering needs. [ABSTRACT FROM AUTHOR]

In this paper, laminar natural convection heat transfer was numerically investigated in cubical air-filled enclosures with partitions attached to the walls with different positions. Steady-state governing equations were solved using the Boussinesq approximation by the finite volume method. Two cases were considered that the partitions were placed perpendicular (Case 1) and parallel (Case 2) to the active walls, respectively. The opposing lateral walls of the enclosure are heated and cooled while the other walls are adiabatic. The effect of the two inclined partitions attached to the bottom and top adiabatic walls at the different positions on the heat transfer rate was examined. The dimensionless partition heights and positions were h/H = 0.1, 0.2 and 0.3, and c/H = 0.25, 0.5 and 0.75, respectively. The inclination of the partitions was θ =3°, 4°, and 5°. The air (Pr = 0.7) streamlines and the temperature fields were obtained for the Rayleigh numbers 103 ≤ Ra ≤ 106 for both cases studied. The mean dimensionless heat transfer ratio (Nusselt number) over the cold wall for both cases was also obtained. The effects of the dimensionless parameters considered on the heat transfer for both cases were concluded. It was seen that the parameters considered are important for Case 2 whereas they did not play a major role for Case 1. • The effect of dual partitions on the laminar natural convection in a cubical enclosure was investigated. • The parameters are the dimensionless heights, positions and inclinations of the partitions. • Novel correlations are derived for the cubical enclosure with dual partitions. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows how to predict the heat transfer and pressure drop for in-line flat tube configuration in a crossflow, using an adaptive neuro-fuzzy inference system (ANFIS). A numerical study of a 2D steady state and incompressible laminar flow for in-line flat tube configuration in a crossflow is also considered in this study. A finite volume technique and body-fitted coordinate system is used to solve the Navier–Stokes and energy equations. The Reynolds number varies from 10 to 320. Heat transfer and pressure drop results are presented for a tube configuration at transverse pitch and longitudinal pitch. The variation in velocity profile, isotherm contours and streamlines were compared for various configurations. The predicted results for average Nusselt number and dimensionless pressure show a good agreement with available previous work. The accuracy between numerical values and ANFIS model results were obtained with a mean relative error for average Nusselt number, pressure drop less than 1.9% and 2.97% respectively. Therefore, the ANFIS model is capable of predicting the performance of thermal systems in engineering applications, including the model of the tube bundle for heat transfer analysis and pressure drop. [Copyright &y& Elsevier]

Abstract: In this paper, heat transfer of a multi-lobe particle (tri-lobe, tetra-lobe and penta-lobe) affected by wall in cross and axial-flow was investigated numerically and experimentally. In numerical analysis, finite element method (FEM) was used for solving partial equations using FEMLAB version 2.3. The experimental work was performed for checking the accuracy of numerical results and computing the mass transfer coefficient. The heat and mass transfer analogy was applied for gaining the Nusselt number for each particle in axial and cross flow. The results showed that the cross flow heat transfer rate is more than axial flow. In addition, the size of particle for tri-lobe and tetra-lobe particles in axial flow and the effect of rotation-angle of tri-lobe particle on heat transfer in cross flow were investigated. The results showed that increasing the rotation angle can cause the Nusselt number to decrease. The influence of cylinder to particle diameter ratio (N) on heat transfer of particles in cross flow and axial flow was studied; the results depicted that when N is greater than 5 wall effects can be ignored. Moreover, Mirhashemi et al. correlation has been modified according to gaining CFD results for horizontal multi-lobe particles. [Copyright &y& Elsevier]

Abstract: Heat transfer, friction factor and thermal performance characteristics in a tube equipped with twisted-rings (TRs) are experimentally investigated. The experiments were conducted using TRs with three different width ratios (W/D=0.05, 0.1 and 0.15) and three pitch ratios of (p/D=1, 1.5 and 2) for Reynolds numbers ranging from 6000 to 20,000 using air as a test fluid. The typical circular rings (CRs) were also tested for an assessment. The experimental results reveal that most TRs yield lower Nusselt numbers and friction factor than CRs, except at the largest width ratio (W/D=0.15) and the smallest pitch ratio (p/D=1.0). In addition, Nusselt number and friction factor increase as width ratio increases and pitch ratio decreases. However, a maximum thermal performance factor is associated by TRs with the smallest width ratio and pitch ratio. The empirical correlations of the heat transfer (Nu) and friction factor (f) are also included in this paper. [Copyright &y& Elsevier]

Abstract: This paper presents a parametric study on mixed convection heat transfer in an inclined arc-shape cavity subjected to a moving lid. The governing equations for the inclined arc-shape cavity were derived with the incorporation of inertia and buoyant force terms and solved by using the finite-volume method and numerical grid generation scheme. The parametric study considered three physical parameters including inclination angle, Reynolds number and Grashof number, and explored the effect of these parameters on the flow field and heat transfer characteristics. Computations were conducted for the Reynolds number ranging from 100 to 1500, Grashof number from 105 to 107 and inclination angle from 150 to 600. The numerical results show that the flow pattern becomes inertia-dominant and the strength of the primary vortex generally increases as the Reynlods number increases. As the Grashof number increases, the strength of the inertial-induced vortex decreases and the strength of the buoyancy-induced vortex increases. The strength of the vortexes decreases with the increasing inclination angle and the buoyancy-induced flow becomes more dominant. The average Nusselt number increases as the Grashof number increases for all the inclination angles studied here. The local friction increases with the increasing inclination angle, and becomes significant as the Grashof number increases. [Copyright &y& Elsevier]

Abstract: In the present paper a numerical study has been performed of the flow behavior and natural convection heat transfer characteristics of liquid fluids contained in an inclined arc-shaped enclosure. The governing equations are discretized using the finite-volume method and curvilinear coordinates. The Prandtl number (Pr) of the liquid fluids is assigned to be 4.0 and the Grashof number (Gr) is ranged within the regime 1×105 ≦≦4×106. On the other hand, the inclination angle (θ) of the enclosure is varied within 0°≦θ≦360°. Of major concern are the effects of the inclination and the buoyancy force on the flow and the thermal fields, and based on the numerical data of the thermal field the local and overall Nusselt numbers are calculated. Results show that the arc-shaped enclosure for Pr=4.0 at Gr=4×106 and θ=90° exhibits the best heat transfer performance. The poor heat transfer performance for Pr=4.0 fixed at Gr=1×105 and θ=180° exhibits the arc-shaped enclosure, respectively. As the value of Grashof number is elevated from 105 to 4×106, at θ=90°, the magnitude of Nu is elevated from 13.946 to 25.3 (81.4% increase); however, at θ=180°, the magnitude is elevated from 11.655 to 13.475 (15.6% increase) only. [Copyright &y& Elsevier]

Abstract: This paper analyzes the detailed heat transfer and fluid flow within two entrapped porous trapezoidal cavities involving cold inclined walls and hot horizontal walls. Flow patterns and temperature distribution were obtained by solving numerically the governing equations, using Darcy''s law. Results are presented for different values of the governing parameters, such as Darcy-modified Rayleigh number, aspect ratio of two entrapped trapezoidal cavities and thermal conductivity ratio between the middle horizontal wall and fluid medium. Heat transfer rates are estimated in terms of local and mean Nusselt numbers. Local Nusselt numbers with spatial distribution exhibit monotonic trend irrespective of all Rayleigh numbers for the upper trapezoidal whereas wavy distribution of local Nusselt number occur for the lower trapezoidal. [Copyright &y& Elsevier]

Abstract: In this paper, heat transfer of single cylindrical particle affected by wall has been investigated numerically and experimentally for Reynolds number range 2000 to 6000. The heat transfer in two different orientations, axial and cross flow over the particle has been considered in simulation with MultiPhysics Software FEMLAB version 2.3. The heat and mass transfer analogy technique has been applied for validation of the simulation results. The coated particle with naphthalene was sublimated to obtain the corresponding Sherwood numbers. The results show that the CFD model can predict the particle-to-fluid heat transfer for two situations due to trivial error (an average error of 6%) compared to experimental values. Influence of wall on heat transfer of particle in seven different bed-to-cylinder diameter ratio (N=1.66, 2.65, 2.75, 5, 6.66, 12, and 18) have been discussed in different velocities. According to obtaining results, with increasing the bed-to-cylinder diameter ratio over the 12 wall have no significant consequence on Nusselt number. Due to this fact, a CFD based correlation has been proposed to consider the wall effects on particle-to-fluid Nusselt number with an average error of 2.19%. [Copyright &y& Elsevier]

Abstract: The effects of pressure work and radiation on natural convection flow around a sphere in presence of heat generation have been investigated in this paper. The governing equations are transformed into dimensionless non-similar equations by using set of suitable transformations and solved numerically by the finite difference method along with Newton''s linearization approximation. Attention has been focused on the evaluation of shear stress in terms of local skin friction and rate of heat transfer in terms of local Nusselt number, velocity as well as temperature profiles. Numerical results have been shown graphically and also in tabular form for some selected values of parameter set consisting of heat generation parameter Q, radiation parameter Rd, pressure work parameter Ge and the Prandtl number Pr. [Copyright &y& Elsevier]

Abstract: This paper is related to heat transfer performance of Al2O3/H2O and TiO2/H2O nonofluids through an annular channel with constant wall temperature boundary condition under turbulent flow regime. The constant temperature is applied on the outer wall of the channel. Experimental investigation was done for a wide range of Al2O3 and TiO2 nanoparticle concentrations and Reynolds number. Based on the experimental results, for specific Peclet number, Nusselt number of nanofluids is higher than that of the base fluid. The enhancement increases with increase of nanparticle concentration for both employed nanofluids. Based on the results of this investigation there is no significant difference on the heat transfer enhancement associated with two employed nanofluids. [Copyright &y& Elsevier]

Abstract: In this paper, we examine the convective flow and heat transfer of an incompressible viscous nanofluid past a semi-infinite vertical stretching sheet in the presence of a magnetic field. The governing partial differential equations with the auxiliary conditions are reduced to ordinary differential equations with the appropriate corresponding conditions via scaling transformations. The analytical solutions of the resulting ODEs are obtained, and from which the analytical solutions of the original problem are presented. The influence of pertinent parameters such as the magnetic parameter, the solid volume fraction of nanoparticles and the type of nanofluid on the flow, heat transfer, Nusselt number and skin friction coefficient is discussed. Comparison with published results is presented. [Copyright &y& Elsevier]

Abstract: In this study, forced convection flows of nanofluids consisting of water with TiO2 and Al2O3 nanoparticles in a horizontal tube with constant wall temperature are investigated numerically. The horizontal test section is modeled and solved using a CFD program. Palm et al.''s correlations are used to determine the nanofluid properties. A single-phase model having two-dimensional equations is employed with either constant or temperature dependent properties to study the hydrodynamics and thermal behaviors of the nanofluid flow. The numerical investigation is performed for a constant particle size of Al2O3 as a case study after the validation of its model by means of the experimental data of Duangthongsuk and Wongwises with TiO2 nanoparticles. The velocity and temperature vectors are presented in the entrance and fully developed region. The variations of the fluid temperature, local heat transfer coefficient and pressure drop along tube length are shown in the paper. Effects of nanoparticles concentration and Reynolds number on the wall shear stress, Nusselt number, heat transfer coefficient and pressure drop are presented. Numerical results show the heat transfer enhancement due to presence of the nanoparticles in the fluid in accordance with the results of the experimental study used for the validation process of the numerical model. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to investigate the conjugated heat transfer in a thick walled cavity filled with copper–water nanofluid. The analysis uses a two-dimensional rectangular enclosure under conjugated convective–conductive heat transfer conditions and considers a range of Rayleigh numbers. The enclosure was subjected to a constant and uniform heat flux at the left thick wall generating a natural convection flow. The thicknesses of the other boundaries are assumed to be zero. The right wall is kept at a low constant temperature while the horizontal walls are assumed to be adiabatic. A moveable divider is located at the bottom wall of the cavity. The governing equations are derived based on the conceptual model in the Cartesian coordinate system. The study has been carried out for the Rayleigh number in the range of 105 ≤Ra≤108, and for the solid volume fraction at 0≤ϕ≤0.05. Results are presented in the form of streamlines, isotherms, average Nusselt number and input heat absorption by the nanofluid. The effects of solid volume fraction of nanofluids, the location of the divider and also the value of the ambient convective heat transfer coefficient on the hydrodynamic and thermal characteristics of flow have been analyzed. An increase in the average Nusselt number was found with the solid concentration for the whole range of Rayleigh number. In addition, results show that the position of the divider and the ambient convective heat transfer coefficient have a considerable effect on the heat transfer enhancement. [Copyright &y& Elsevier]

Abstract: In this paper heat transfer and flow field in a wavy channel with nano-fluid is numerically studied. The temperature of input fluid (Tc) is taken less than that of the wavy horizontal walls (Tw). The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Copper–water nano-fluid is considered for simulation. A wide spectrum of numerical simulations has been done over a range of Reynolds number, ReH, 5≤ReH ≤1500, nano-fluid volume fraction, ϕ, 0≤ ϕ ≤20% and the wave amplitude, α, 0≤α≤0.3. The effects of these parameters are investigated on the local and average Nusselt numbers and the skin friction coefficient. Simulations show excellent agreement with the literature. From this study, it is concluded that heat transfer in channels can enhance by addition of nano-particles, and usage of wavy horizontal walls. These can enhance the heat transfer by 50%. The present work can provide helpful guidelines to the manufacturers of the compact heat exchangers. [ABSTRACT FROM AUTHOR]

Abstract: This paper studies the double diffusive natural convection near an inclined wavy surface in a fluid saturated porous medium with constant wall temperature and concentration. A coordinate transformation is employed to transform the complex wavy surface to a smooth surface, and the obtained boundary layer equations are solved by the cubic spline collocation method. Effects of angle of inclination, Lewis number, buoyancy ratio, and wavy geometry on the heat and mass transfer characteristics are studied. Results show that a decrease in the angle of inclination leads to a greater fluctuation of the local Nusselt and Sherwood numbers. Moreover, increasing the angle of inclination tends to increase the total heat and mass transfer rates. [ABSTRACT FROM AUTHOR]