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This paper numerically compares the flow structures and thermal performance in a swirl chamber with three different inlet chambers. The cross section of inlet chambers are constant, convergent, and divergent along the streamwise direction, respectively. Parametric studies involve Reynolds number and the temperature ratio between cooling air and the wall of swirl chamber. Results indicate that shear layer vortices, corner vortices, and large-scale vortices appear in different sections of swirl chamber. Besides, Görtler vortices appear in convergent inlet chamber. The alternation of the inlet chamber changes more than the value of the Nusselt number. It also changes the flow structures and the distribution of Nusselt number. In comparisons, the swirl chamber with convergent inlet chamber possesses the highest thermal performance coefficient. With the increase of Reynolds number, the intensity of heat transfer is significantly enhanced. Different from former research, the rise of temperature ratio leads to relatively high Nusselt number due to the addition of multiple jet nozzles and the inlet chamber. In addition, empirical correlation among global average Nusselt number, Reynolds number, and temperature ratio is obtained to assist relevant research and design. [ABSTRACT FROM AUTHOR]

This paper presents a novel empirical correlation to estimate the heat transfer in raceway ponds for different pond sizes and depths. The correlation involves the calculation of Nusselt number. Heat transfer in outdoor raceway ponds was modeled with the effects of pond design, hydrodynamics, and environmental conditions. Monthly average water temperature, Nusselt number, and Prandtl number were used to examine the heat transfer phenomena between pond and its surroundings. A novel relation was also employed to estimate the amount of monthly evaporated water from the raceway ponds. Different aspect ratios, pond depths, and paddle wheel rotational speeds were considered to evaluate the effect of pond geometry and turbulent mixing on heat transfer. The use of empirical relation is an effective approach in designing raceway ponds to estimate heat loss in ponds. Algal productivity decreased with increasing amount of evaporated water. Moreover, the environmental conditions, pond design, and turbulent mixing significantly affected the heat transfer rate and the optimum water temperature for algal growth. [ABSTRACT FROM AUTHOR]

Abstract: Paper presents an idea of utilization infinite regular polyhedrons for designing heat exchange devices. The investigated prototype of the heat exchanger was consisted of twenty identical solids. Each of them was composed from eight regular hexagons. CFD simulations, reported in this paper, were used to obtain an influence of the flow domain modification on the intensification of the forced convection heat transfer in the developed device. Computational analyses clearly showed that the experimental testing of the heat exchanger prototype should be realized with include of cuboid turbulence inserts. Heat transfer performance and pressure drop obtained by experimental investigations are presented, too. The average Nusselt number and Fanning friction factor were expressed in terms of the Reynolds number. [Copyright &y& Elsevier]

In this paper, a numerical investigation is performed to study the mixed convective flow and heat transfer characteristics past a square cylinder in cross flow at incidence. Utilizing air (Pr =0.71) as an operating fluid, computations are carried out at a representative Reynolds number (Re) of 100. Angles of incidences are varied as, 0°⩽ α ⩽45°. Effect of superimposed positive and negative cross-flow buoyancy is brought about by varying the Richardson number (Ri) in the range −1.0⩽ Ri ⩽1.0. The detail features of flow topology and heat transport are analyzed critically for different angles of incidences. The thermo fluidic forces acting on the cylinder during mixed convection are captured in terms of the drag (CD ), lift (CL ), and moment (CM ) coefficients. The results show that the lateral width of the cylinder wake reduces with increasing α and the isotherms spread out far wide. In the range 0°< α <45°, CD reduces with increasing Ri. The functional dependence of CM with Ri reveals a linear relationship. Thermal boundary layer thickness reduces with increasing angle of incidences. The global rate of heat transfer from the cylinder increases with increasing α. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the heat transfer performance of the alternating discrete two phase flow in micro-tubes has been numerically investigated. Two immiscible fluids are injected into a micro-tube alternately, generating a plug flow pattern with two completely separated phases. The overall Nusselt number could be increased by sixfold over the single phase fully developed flow when the ratio of primary phase to the tube inner diameter (L 1/D) is kept at about 7. Characteristic of the average Nusselt number is found to be almost independent of the secondary phase. The friction factor is much dependent on the viscosity of the secondary phase. Secondary phase with higher viscosity would induce higher pressure loss and large pressure fluctuation is observed at regions close to the interfaces. The flow field that is far from the interfaces could be approximated as the single phase fully developed flow. Weber number of the primary phase and Capillary number of the secondary phase should be kept below certain critical values in order to maintain the discrete flow patterns. Frictional loss is a more important consideration than the heat capacity when choosing a particular secondary phase. Secondary phase with lower viscosity is preferred due to the overall heat transfer enhancement will become less beneficial if the pressure loss induced by the secondary phase becomes significant. Liquid–gas discrete flow is found to have better heat transfer performance than the liquid–liquid discrete flow. [Copyright &y& Elsevier]

Abstract: In this paper, laminar copper–water nanofluid flow and heat transfer in a two-dimensional wavy channel is numerically investigated. The Reynolds number and nanoparticle volume fraction considered are in the ranges of 100–800 and 0–5% respectively. Numerical solutions are obtained by solving the governing equation of stream function, vorticity transport and energy in curvilinear coordinates using the finite difference method. The effects of nanoparticle volume fraction, the wavy channel amplitude and wavelength and the Reynolds number on the local skin-friction coefficient, local and average Nusselt number and the heat transfer enhancement are presented and discussed. Results show that the friction coefficient and Nusselt number increase as the amplitude of wavy channel increases. As the nanoparticle volume fraction increases, the Nusselt number is found to be significantly increased, accompanied by only a slight increase in the friction coefficient. In addition, it was found that the enhancement in heat transfer mainly depends on the nanoparticle volume fraction, amplitude of the wavy wall and Reynolds number rather than the wavelength. [Copyright &y& Elsevier]

Abstract: The influence of aspect ratio and shear-dependent viscosity on free convection heat transfer from a horizontal heated elliptic cylinder in power-law fluids has been investigated. In particular, the coupled momentum and energy equations have been solved numerically over the following ranges of conditions: Grashof number, 10⩽ Gr ⩽105; Prandtl number, 0.72⩽ Pr ⩽100; power-law index, 0.3⩽ n ⩽1.5 and aspect ratio, 0.2⩽ E ⩽5. The new extensive results demonstrate the influence of the Grashof number (Gr), Prandtl number (Pr), power-law index (n) and aspect ratio (E) on the macroscopic heat and momentum transfer characteristics like local and average values of Nusselt number (Nu) and drag coefficients (CD ). Further insights are developed by examining the structure of the flow and temperature fields adjacent to the cylinder. Broadly speaking, all else being equal, shear- thinning fluid behaviour promotes heat transfer whereas shear-thickening viscosity has a deleterious effect on it with reference to that in Newtonian fluids. Also, the rate of heat transfer gradually increases as the cylinder shape passes from blunt to slender with respect to the direction of gravity. Finally, the present numerical values of the Nusselt number are correlated using a simple analytical form which facilitates interpolation of the present results for the intermediate values of the governing parameters. The paper is concluded by presenting detailed comparisons with the previous numerical and experimental results available in the literature, especially in Newtonian fluids. [Copyright &y& Elsevier]

Abstract: Heat transfer performance of tube bundles, which are widely used in practical applications, was investigated. Experimental and numerical studies for tube bundles were performed with a tube diameter of 1.5mm and a shell-side Reynolds number of 3,000⩽Re⩽7,000. The average convective heat transfer coefficients of the tube bundles in most previous investigations were based on the difference between the bulk fluid temperature and the average surface temperature of the tubes. However, the tubular heat exchanger design process uses the concepts of overall thermal resistance and the log-mean-temperature-difference (LMTD), which is defined as the temperature difference between two working fluids. This paper examines the variation of the shell-side convective heat transfer coefficients of tube bundles caused by the two different evaluation methods. The comparison showed that the average Nusselt number evaluated based on the LMTD method is 22.6% smaller than that based on the surface temperature method. This shows that it is necessary to consider the discrepancy in the heat transfer coefficient definition for proper design of heat exchangers. The Zukauskas correlation developed for larger diameter tubes and higher Reynolds numbers are still in good agreement with experimental data for the present small diameter tube bundle within a discrepancy of 4.7%. [Copyright &y& Elsevier]

Abstract: The numerical modeling of the conjugate heat transfer and fluid flow of Al2O3/water nanofluid through the microchannel heat sink is presented in the paper. The laminar flow regime was considered along with viscous dissipation effect. The microchannel heat sink with square microchannels and Dh =50μm is considered. The heat flux was fixed to q =35W/m2 with heating and cooling cases. The water based Al2O3 nanofluid was encountered with various volume concentrations of Al2O3 particles and three diameters of the particle dp =13, 28 and 47nm. The analysis is performed on the results obtained for the local heat transfer coefficients based on a fixed pumping power. The results reveal a different local heat transfer behavior compared to the analysis made on a basis of the constant Re. [Copyright &y& Elsevier]

Abstract: A fundamental study of heat transfer characteristics of two-phase slug flow in microchannels is carried out employing the Volume-of-Fluid (VOF) method. Despite of the fact that numerical simulations of two-phase flows in microchannels have been attempted by many investigators, most efforts seem to have failed in correctly capturing the flow physics, especially those pertaining to the slug flow regime characteristics. The presence of a thin liquid film in the order of 10μm around the bubble is a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field and heat transfer characteristics. In the simulations reported in this paper, the film is successfully captured and a very high local convective heat transfer coefficient is observed in the film region. A strong coupling between the conductive heat transfer in the solid wall and the convective heat transfer in the flow field is observed and characterized. Results showed that unsteady heat transfer through the solid wall in the axial direction is comparable to that in the radial direction. Results also showed that a fully developed condition could be achieved fairly quickly compared to single-phase flows. The fully developed condition is defined based on the Peclet number (Pe) and a dimensionless length of the liquid slug. Local and time-averaged Nusselt numbers for slug flows are reported for the first time. It was found that significant improvements in the heat transfer coefficient could be achieved by short slugs where the Nusselt number was found to be 610% higher than in single-phase flows. The study revealed new findings related to slug flow heat transfer in microchannels with constant wall heat flux. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional numerical heat transfer analysis has been performed in order to obtain the temperature distribution and the fin efficiency using the experimentally determined local heat transfer coefficients from the naphthalene sublimation technique and heat and mass transfer analogy. The influences of the fin material, fin thickness, and transversal tube pitch on the fin efficiency are studied for flat tube bank fin heat exchangers. The fin efficiency, obtained by a numerical method using the averaged heat transfer coefficient, is compared with that using the local heat transfer coefficient. The reliability of the generally used formula for fin efficiency is tested also, and then a modified fin efficiency formula with a new equivalent fin height is provided. The results show that the difference between the fin efficiency obtained by the numerical method using the local heat transfer coefficient and the fin efficiency using the averaged heat transfer coefficient is small, but the fin efficiency obtained by the generally used formula is lower than that obtained by the numerical method using the local heat transfer coefficient; the fin efficiency obtained by the modified formula matches very well with the fin efficiency obtained by the numerical method using the local heat transfer coefficient. The modified formula for the fin efficiency calculation is more reliable, and it can be applied directly to the design of a flat tube bank fin heat exchanger and also will be useful in engineering applications. [Copyright &y& Elsevier]

Abstract: This paper examines the steady natural convection in a partially opened enclosure filled with porous media using the Brinkman–Forchheimer model. Whilst the part of the left vertical wall of the cavity is heated, the other walls are adiabatic or thermally insulated Based upon numerical predictions, the effects of pertinent parameters such as Grashof number, Darcy number, porosity, length of the heated wall and the location center of the opened cavity are examined. It is found that as the Grashof number increases, due to strengthening buoyancy driven flows, the local Nusselt number from partially heated vertical wall, at a given position on this wall increases. This, in turn, increases the temperature of the heated wall. The results of this study can be used in the design of an effective cooling system for electronic components to help ensure effective and safe operational conditions. [Copyright &y& Elsevier]

Abstract: Although the conventional internal ribs or turbulators can significantly improve the performances of the convective heat transfer within a channel, the added ribs can also cause two demerits, a larger friction factor and some lower heat transfer areas (LHTA) than that in the corresponding smooth channel, especially behind fully attached (solid-type) ribs and at the corners formed by bottom and side walls. This paper presents a novel design of the ribbed channel, which is here called semiattached rib-design. The ribs are perforated at the rib corners to form two rectangular holes, so a portion of the fluid can pass through the holes. The characteristics of the semiattached rib-design are numerically investigated by the commercial software Fluent 6.3 in a Reynolds number range from 104 to 2.5×104. Five different structures of the rib (width ratios of channel to hole) and two positions (transverse rib and 45° angled ribs) are analyzed. The numerical results show that the semiattached rib-design can significantly improve local heat transfer and fluid flow performances; the semiattached ribs with 45° angle of attack can even achieve a higher efficiency of synthetical heat transfer than that of the fully attached and detached rib-channels, at the same time eliminate the LHTA; although the average Nusselt number over a pitch in the transverse ribbed channel is lower than that of fully attached and detached rib-channels, this semiattached ribs can also fully eliminate the LHTA. [ABSTRACT FROM AUTHOR]

Abstract: This paper conveys a numerical simulation of an active enhancement device for natural convection in the interfin spaces of a fin array. A baseline solution for the non-enhanced situation revealed that the confinement created by the walls of adjacent fins and the base surface gave rise to a drastic reduction of the heat transfer coefficient values compared with those for the standard vertical plate. This outcome demonstrated the necessity for enhancement. The enhancement device investigated here communicated with the interfin space via an opening in the base surface. Enhancement was achieved by alternately introducing and extracting air into and from the space. The frequency of the introduction/extraction cycle was varied over values of 0, 10, 50, and 100Hz. For each of these cases, spatially local, cycle-averaged heat transfer coefficients were determined on the bounding surfaces of the interfin space and on the outboard surface of a fin that faced a large ambient space. Results were also obtained for the cycle- and spatially averaged coefficients. Even at a low oscillation frequency of 10Hz, the interfin heat transfer coefficients were significantly enhanced but not sufficiently to overcome the confinement effect. At 100Hz, the enhancement gave rise to coefficient values that are about 64 times greater than the unenhanced values. [Copyright &y& Elsevier]

Abstract: This paper reports the results of a numerical study of the Nusselt number for the H1 and T boundary conditions in laminar, fully-developed flows of pseudoplastic and dilatant fluids in rectangular ducts. Equations for the apparent viscosity that span the entire shear rate range were utilized and the Nusselt numbers were calculated as a function of a shear rate parameter that determines the flow regime where the duct is operating. Numerical results for the Nusselt number in all flow regimes are included along with correlation equations. Finally, errors associated with applying power law solutions are discussed. [Copyright &y& Elsevier]

Abstract: In the present study, a 3D numerical simulation of a whole heat exchanger with middle-overlapped helical baffles is carried out by using commercial codes of GAMBIT 2.3 and FLEUNT 6.3. At first, the computational model and numerical method of the whole heat exchanger with middle-overlapped helical baffles is presented in detail, and parallel computation mode is adopted for the simulation of a whole heat exchanger with six cycles of the middle-overlapped helical baffles of 40° helical angle on a grid system of 13.5-million cells; second, the validation of the computational model is performed by comparing the total pressure drop and average Nusselt number of the whole heat exchanger with experimental data. Reasonably good agreement is obtained, and the reasons causing to the discrepancy are analyzed. The shell-side fluid pressure and temperature fields of the whole area are then presented. Finally the cycle average Nusselt number of different cycle in the heat exchanger are compared and it is found that within the accuracy allowed in engineering computation, periodic model for one cycle can be used to investigate the heat transfer and pressure drop characteristics for different heat exchanger to save computational source. The companion paper will provide details of simulation results using the periodic model for different helical angles and different structures of helical baffles. [Copyright &y& Elsevier]

Abstract: In this paper, based on the simplified periodic model the performance predictions for heat exchanger with middle-overlapped helical baffles are carried out by 3D simulation for three different helix angles (30°, 40° and 50°), and the commercial codes of GAMBIT 2.3 and FLEUNT 6.3 are adopted in the simulation. It is found that the model average heat transfer coefficient per unit pressure drop of the 40° angle case is the largest, which is in qualitative agreement with the existing literature. The predicted average intersection angle of this case is the smallest, being consistent with the field synergy principle. The performance of periodic model with continuous helical baffle is also compared with that of the noncontinuous middle-overlapped helical baffles. It is found that the heat transfer coefficient per unit pressure drop of the noncontinuous middle-overlapped helical baffles is appreciably larger than that of the continuous helical baffle, indicating that the heat exchanger with noncontinuous middle-overlapped helical baffles has its advantage over the one with continuous helical baffle. [Copyright &y& Elsevier]

Abstract: The secondary flow is frequently used to enhance the convective heat transfer. In this paper, the cross-averaged absolute vorticity flux in the main flow direction is used to specify the intensity of the secondary flow produced by vortex generators that are mounted on a three-row flat tube bank fin surfaces. The relationship between the intensity of the secondary flow and the strength of convective heat transfer is studied using a numerical method. The results reveal that cross-averaged absolute vorticity flux in the main flow direction can reflect the intensity of the secondary flow; a significant relationship between this cross-averaged absolute vorticity flux and span-averaged Nusselt number exists for the case studied. This cross-averaged absolute vorticity flux can account only for the secondary flow effects on convective heat transfer but cannot quantify the effects of developing boundary layer on convective heat transfer. [Copyright &y& Elsevier]

In this paper, non-isothermal flow of a polymeric liquid past a circular cylinder in an infinite domain is investigated numerically. A non-Newtonian fluid, known as a differential-type White–Metzner model, is used in the flow simulation. The computer code developed is based on the elastic-viscous split-stress finite element method incorporating the streamline-upwind Petrov–Galerkin scheme. Numerical solutions for several cases are obtained. Global flow characteristics, such as drag coefficient and heat transfer coefficient, are derived. The effects of fluid elasticity, inertia, and shear-thinning on drag and heat transfer are also investigated. [Copyright &y& Elsevier]