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• The thermal-fluid-structure coupling method is proposed in this study. • Thermal deformation of the structure is considered in the proposed model. • The effect of low temperature on the compressor efficiency is analyzed. • The effect of the rotor deformation on the compressor performance is studied. • The effect of operating conditions on the compressor efficiency is investigated. The boil-off gas (BOG) twin-screw compressors are widely used in the transportation of liquefied natural gas. A thermal-fluid-structure (TFS) simulation model of the screw compressor is established based on the conjugated heat transfer and weak fluid-structure coupling method. The thermal deformation of the structure at a steady state is considered in the CFD simulation to improve the calculation accuracy. The accuracy of the calculation results was verified by the experiment on a high-speed oil-free twin-screw air compressor. The thermal performance and the compressor efficiencies at different operating conditions were obtained by simulations. It was found that the volumetric efficiency increased from 67 to 78 % while the isentropic efficiency increased from 64 to 75 % with increasing the suction temperature. The volumetric efficiency reduced from 76 to 71 % with increasing the discharge pressure while the isentropic efficiency reached the maximum value of 70 % when the discharge pressure was equal to the end-of-compression pressure. Besides, when the rotational speed was lower than 6000 rpm, increasing the rotational speed had a significantly positive effect on the compressor efficiencies. The volumetric efficiency increased slowly when the speed raised from 6000 to 10,000 rpm. The isentropic efficiency reached a maximum of 73 % at the speed of 8000 rpm, which decreased to 72 % at 10,000 rpm. [ABSTRACT FROM AUTHOR]

• The underbody flow field of a representative 4-car formation subway is investigated. • Underbody flow regulation is realized through deflector installation. • The maximum temperatures of linear induction motors are reduced. • Influence of deflected flow on underbody flow field and device cooling is analyzed. The low-speed flow, restricted tunnel environment, and degraded motors have resulted in a serious challenge in the underbody equipment of subway trains, where overheating of multiple longitudinally aligned linear induction motors is one of the most urgent challenges to be resolved. In the face of this problem, the flow field distribution of a 4-car formation subway train is investigated. Two deflector installation designs are proposed to regulate the underbody flow using the passive flow control method to enhance the heat dissipation of motors. The influence of deflector installation is analyzed through an experimentally verified conjugated heat transfer numerical method. The results showed that the installation of deflectors can significantly enhance the longitudinal underbody flow. On the one hand, the deflector can effectively enhance the momentum exchange between underbody flow and the surrounding undisturbed flow field. On the other hand, the deflectors can break the large lateral vortices, such that the flow resistance along the longitudinal direction is reduced. Besides, the deflectors can also reduce the size of the wake behind the motor. As a result, the increased incoming flow rate ahead of motors effectively alleviated the overheating issue. The enhancement of heat transfer between different deflector installation designs was compared. It was found that the vertical edge of deflectors should be installed as close to the lateral edge of the subway car as possible. The maximum temperature of motors has been reduced by 9 % according to the installation design proposed in this study. The outcomes of this study can also provide theoretical guidance as well as engineering solutions for the cooling design of bottom heat sources and other similar overheating devices in thousands of railway trains with exposed underbody compartment. The convection enhancement around the heating devices can be realized by the surrounding flow field regulation method proposed in this study. [ABSTRACT FROM AUTHOR]

• A fast numerical method for forced convection transient conjugate heat transfer has been developed. • A new dimensionless number is proposed to determine the moment of suspension of the flow field. • The initial error of the quasi-steady algorithm is optimized by choosing a high fluid development stage. • The computational speed is increased while maintaining a certain level of computational accuracy. In this study, a fast numerical method for solving the forced convection conjugate heat transfer problem was developed. The method first proposes a new dimensionless number (Fs) that represents the degree of influence of convection on the temperature field in the flow field. It delineates the stage of development of the flow field by monitoring the change in Fs to determine the moment when the flow field suspends updating and improve the computational efficiency of the transient temperature field. The accuracy of the algorithm is verified by taking the fluid–solid conjugate heat transfer under forced convection conditions as an example, which can accurately capture the changes of the flow field for a given monitoring step number of 100, and classify the flow field into E3, E4 and E5 development stages according to the judgment criteria. The results show that the higher development stages correspond to smaller levels of root mean square error (RMSE) of monitoring point temperatures within 3600 s of physical simulation time, and stages E3, E4, and E5 can reach the levels of E-2, E-3, and E-4, which are 3.4, 3.3, and 3.1 times faster than the traditional coupled calculations, respectively. The algorithm is still applicable at variable time steps, but it will require a higher number of determinations compared to a fixed step. The initial error of the quasi-steady algorithm can be reduced from the E-1 level to E-4 by choosing a higher stage of development. Finally the algorithm is tested under a variety of conditions by varying the inlet temperature and flow rate and is found to be robust to both device warming and cooling. [ABSTRACT FROM AUTHOR]

• The optimum rod axial location and height are numerically determined. • The temperature uniformity exhibits different responses to the inlet velocity. • Varying rod material contributes to enhancing wall temperature and uniformity. • The non-monotonic dependence of temperature behavior on rod locations is revealed. To enhance the thermal performance and power output of micro-thermophotovoltaic systems, this work conducts a comprehensive numerical analysis of the T-shaped rod-assisted methane/air-fueled combustion. With the validated computational model, the effects of key parameters including the rod axial location (L r), height (H r), and material are systematically evaluated. Varying L r from 3 to 12 mm can lead to a 23.9 K difference in the mean temperature of the outer wall, with the highest value occurring L r at = 9 mm. The non-monotonic wall temperature with rod axial location is mainly caused by the different convection heat transfer intensities arising from the flow field variation. Further analysis of the rod height shows that the mean temperature increases first and then decreases with increasing H r , while the temperature standard deviation presents an opposite trend. Generally, the temperature distribution of the H r = 1.8 mm case is most uniform, especially under a relatively high inlet velocity. This indicates that the rod axial location and height of 9 mm and 1.8 mm respectively can be considered the optimum design parameters. Finally, the rod material is shown to be great important in determining combustor temperature characteristics. When it is changed from quartz to steel, the wall temperature is elevated by 15.2 K, accompanied by the increasing temperature uniformity. Nevertheless, further changing it to a material with a higher thermal conductivity plays a minimal effect. This work sheds light on the feasibility of improving the combustion performance by appropriately designing the rod structure. [ABSTRACT FROM AUTHOR]

Dynamical behavior of solid phase reaction thermally coupled with filtrational gas combustion wave is studied numerically in the frame of one-dimensional model. Examined combustion system is combustible solid cylinder surrounded by inert porous tube through which the gaseous fuel–air mixture is supplied in axial direction. The effects of solid material chemical properties and the gas inlet velocity on the dynamic behavior of coupled combustion waves were investigated. The existence of multiple combustion regimes was found and the regime diagrams in gaseous mixture flow rate/energetic properties of solid material plane were plotted. Numerical results show that in the case of downstream propagating filtrational combustion wave the burning velocity of solid energetic material is essentially increased that create difficulties in organization of stable combustion in the considered system. In contrast, for upstream propagating flames, the combustion waves in gas and solid phases propagate together in strong thermal coupling. The distance between the combustion waves in this case is small and the burning rate of solid material can be controlled by gaseous mixture flow rate. It is numerically shown that the heat flux from the products of gas phase reactions extends the extinction limits of solid phase flame. It is also found, that oscillations of solid phase reaction wave induced by diffusive-thermal pulsating instability can be suppressed by means of thermal interaction with filtrational gas combustion wave. [ABSTRACT FROM AUTHOR]

• We proposed a new algorithm for designing a cooling system for PVT systems. • The algorithm allows us to find design parameters of the required cooling system. • To validate the algorithm, CFD simulation is used for four different scenarios. • Solar panel temperature and efficiency for proposed cooling system are presented. Solar energy is an abundant source of energy for generating electricity. One of the main challenges in using solar energy is that solar photovoltaic (PV) panels are typically used in regions where solar radiation is high; consequently, the temperature of the panels will increase, and the efficiency of the panels will decrease. Adding cooling tubes to the PV panel is a possible approach to cool it down. To design such cooling systems, CFD simulations may be used; however, this approach tends to be time-consuming. In this paper, we report a new algorithm for designing straight cooling tubes. The algorithm can be used to determine important design parameters such as tube center-to-center length, diameter of the tube, and the minimum tube length needed to achieve a desired outlet temperature. The accuracy of the algorithm was tested using real-world data (including various ambient temperatures and solar radiations) and the maximum temperature difference between desired outlet temperature and CFD simulation for the designed cooling system was found to be 1.7oK. [ABSTRACT FROM AUTHOR]

The main component of propulsion system for hypersonic vehicle, such as scramjet, always sustains extremely high thermal loads, and actively regenerative cooling must be considered using its own hydrocarbon fuel as coolant. Due to the limited amount of coolant and the complex physical and chemical problems involved in heat transfer process, the difficulty of cooling channel design increases. In order to explore the ways to improve cooling efficiency, the influences of inlet velocity and flow direction on heat transfer of supercritical cracked-kerosene were investigated via a solid-fluid conjugated simulation method. The results indicate that increasing the coolant velocity can enhance cooling effect with a constant mass flow rate, and the wall temperature at peak heat flux decreased obviously. However, as the wall thickness increases, the enhanced cooling effect is gradually cancelled out. Flow direction has significant influence on heat transfer process. Compared with forward flow, the reverse flow shows considerable uniform wall temperature and low fuel temperature effect. These conclusions can be used as an important reference for cooling channel design under supercritical conditions. [ABSTRACT FROM AUTHOR]

An experimental and numerical investigation is conducted to study the conjugated heat transfer performance on the leading edge of a wedge-shaped concave wall subjected to external cold flow and internal hot jets impingement. A corrugated impinging plate with an extended front-extended port inside the concave cavity is proposed for the purpose of heat transfer enhancement. The effects of corrugation length-to-diameter ratio ( H j / d ) ranging from 5 to 11 and width-to-diameter ratio ( W j / d ) ranging from 2.5 to 6 on the conjugated heat transfer performance are examined under some representative jet Reynolds numbers ( Re j ) in the range of 7900–31,700. The results show that the corrugated impinging plate has a significant impact on improving the conjugated heat transfer performance in the vicinity of concave wall leading edge. The presence of corrugation plays two roles by reducing the jet impinging distance on one hand and aggravating the jet confinement on the other hand. Therefore, it produces more complicated jet impinging flow and convective heat transfer behaviors than the baseline case without corrugation. According to the tested results, the specified area-averaged heating effectiveness is increased approximately 6.3%–18.8% under Re j = 7900 and 2.5%–9.4% Under Re j = 31,700 respectively by increasing the corrugation length when W j / d is fixed as 2.5. The specified area-averaged heating effectiveness is increased approximately 16.1%–22.1% under Re j = 7900 and 7.7%–12.7% under Re j = 31,700 respectively by increasing the corrugation width when H j / d is fixed as 9. In general, the corrugation with larger length and width seems to perform the better heating effectiveness over the entire concave surface. The enhancement of heating effectiveness related to the baseline case behaves more significantly under a smaller jet Reynolds number. [ABSTRACT FROM AUTHOR]

An effect of shielding of an intense solar radiation towards a solar probe with the use of micron-sized SiC particles generated during ablation of a composite thermal protection material is estimated on a basis of numerical solution to a combined radiative and heat transfer problem. The radiative properties of particles are calculated using the Mie theory, and the spectral two-flux model is employed in radiative transfer calculations for non-uniform particle clouds. A computational model for generation and evolution of the cloud is based on a conjugated heat transfer problem taking into account heating and thermal destruction of the matrix of thermal protection material and sublimation of SiC particles in the generated cloud. The effect of light pressure, which is especially important for small particles, is also taken into account. The computational data for mass loss due to the particle cloud sublimation showed the low value about 1 kg/m 2 per hour at the distance between the vehicle and the Sun surface of about four radii of the Sun. This indicates that embedding of silicon carbide or other particles into a thermal protection layer and the resulting generation of a particle cloud can be considered as a promising way to improve the possibilities of space missions due to a significant decrease in the vehicle working distance from the solar photosphere. [ABSTRACT FROM AUTHOR]

Nucleate boiling heat transfer (NBHT) from enhanced structures is an effective way to dissipate high heat flux. In the present study, a 3D multi-relaxation-time (MRT) phase-change lattice Boltzmann method in conjunction with conjugated heat transfer treatment is proposed and then applied to the study of cavities behaviours for nucleation on roughened surfaces for an entire ebullition cycle without introducing any artificial disturbance. The bubble departure diameter, departure frequency and total boiling heat transfer rate are also explored. It is demonstrated that the cavity shapes show significant influence on the features of NBHT. The total heat transfer rate increases with the cavity mouth and cavity base area while decreases with the increase in cavity bottom wall thickness. The cavity with low wetting can enhance the heat transfer and improve the bubble release frequency. [ABSTRACT FROM AUTHOR]

Numerical investigations are performed to study the conjugated convective heat transfer on the leading edge of a conical wall subjected to external cold flow and internal hot jet impingement by a single chevron nozzle. The effects of the chevron length ( l / d = 0.1, 0.2, 0.3) and chevron penetration depth ( p / d = 0.1, 0.15, 0.2) on the hot-jet impingement heat transfer performance are analyzed for a 6-chevrons nozzle. In the current study, non-dimensional jet-to-leading edge distance ( H / d ) is varied from 2 to 4 and the jet Reynolds number ( Re j ) is varied from 7800 to 39,400. In relative to the conventional nozzle, the presence of chevrons increases the jet core velocity and produces more intensive jet fluctuation, thereby improves the heat transfer in the vicinity of the conical surface leading edge, particularly under a small jet Reynolds number or a smaller jet-to-leading edge distance. In general, the local circumferentially-averaged heating effectiveness is improved with the increase of chevron penetration depth ratio for a fixed chevron length ratio or decrease of chevron length ratio for a fixed chevron penetration depth ratio. Due to a large curvature of conical surface, the circumferentially-averaged heating effectiveness under H / d = 4 is greater than that under H / d = 2 at the same chordwise location once s / d is beyond 6. [ABSTRACT FROM AUTHOR]

Although numerous technologies – such as double skin façade (DSF), double glazing window (DGW), etc. – have been applied in the glass envelope, the heat transfer of the glass envelope is still considerable. Cooling pipes embedded in the venetian blinds of a double-skin envelope are presented in this study as a system for reducing the heat transfer of the glass envelope in summer. Solar radiation is taken away directly by pipes through which cooling water is circulated, and the water can be produced from natural cooling. CFD software is employed in this paper to simulate the conjugated heat transfer in the double-skin envelope and the numerical model has been validated. The effect of embedded pipes is numerically investigated based on DGW. Different DGW structure and glass assemblies are taken into consideration. The results show that the cooling pipes can significantly reduce the temperature of the venetian blinds and air cavity, which will in turn lower heat transfer and improve thermal comfort. With pipe embedded, cooling water averagely takes away about 60% of the solar radiation directly and the average solar energy transmittance is only 13%. In addition, cheap glass can be employed to the pipe-embedded DGW with only small negative influence. [ABSTRACT FROM AUTHOR]

Advanced coolants such as nanofluids or PCM slurries are realized and reported as effective substitutions for conventional coolants in order to enhance the cooling performance of microchannel heatsinks. However, there are a number of disadvantages associated with using these advanced coolants that are always considered as their inevitable downsides including the increase of the needed pumping power of the system for both of the mentioned coolants and decrease of the fluid average thermal conductivity for PCM slurries. In this paper, a 3D conjugated heat transfer model of a double layer microchannel heatsink (MCHS) to investigate its thermal performance is presented and the effectiveness of simultaneous employing of both of these types of advanced coolants in a heatsink is assessed. Finite volume method (FVM) is used to solve the flow and heat governing equations simultaneously and the obtained results are validated with the experimental data. The assessed parameters in this study are: coolant type, coolant configurations, particle concentration, bottom surface temperature, and inlet fluid velocity. In order to investigate the flow and cooling efficiency of the heatsink, two dimensionless parameter, Nusselt and Euler numbers, are computed and compared between the considered configurations. The goal is to balance and optimize the desirable cooling enhancement that is obtained by using advanced coolants and is represented by associated Nusselt number from one side, and undesirable increase of the needed pumping power which is implied by relevant Euler number, from the other side. Results showed that using the proposed configurations, the cooling performance of the systems are enhanced and the disadvantages associated with advanced coolant are relieved, substantially. [ABSTRACT FROM AUTHOR]

The performance of an enhanced microchannel heat sink with sectional oblique fins and with a coolant that contains Nano-Encapsulated Phase Change Material (NEPCM) particles is investigated using a 3D conjugated heat transfer model. Three volume fractions from ξ = 0 (pure water) to 0.3 are studied to investigate the effects of presence of NEPCM particles. Then the effects of introducing tip-clearance to the heat sink on thermal and hydrodynamic performance is examined at low Reynolds numbers (less than 215). Four values of tip-clearance to channel width ratio ( t / W c ) are investigated ranging from a no gap ( t / W c = 0) to t / W c = 0.74. On the bottom wall of the heat sink a range of uniform and fixed temperatures of 299.15 K to 340.15 K are applied. The cooling and hydrodynamic performance of the heat sink is studied using Nusselt and Euler numbers, respectively. It was observed that using of NEPCM slurry in contrast with pure water, enhanced the cooling performance of the heat sink but increased the Euler number. Furthermore, it was seen that the introduction of tip-clearance to the heat sink, if the clearance ratio is chosen properly, has the potential to enhance the cooling performance and reducing the Euler number simultaneously. [ABSTRACT FROM AUTHOR]

A numerical investigation of the thermal transport processes in the near-wall region of a reactor packed with metal open-cell foams is presented in view of the development of externally-cooled tubular reactors packed with catalytically active foams. Two different aluminium open-cell foams were scanned by X-ray micro-computed tomography in order to generate the 3D models used in this study. The conjugated solid–fluid heat transfer problem is solved by finite volume analysis (FVA) for different flow rates and fluid properties (Peclet number range from 1 to 10 5 ). Predictive correlations for the wall heat transfer coefficient are derived according to different thermal coupling scenarios between the open-cell foam bed and the reactor wall. Such kind of systematic study and the proposed correlations that account for the gap size represent a novelty in the field of published literature on open-cell foams. [ABSTRACT FROM AUTHOR]

This article presents numerical simulations of conjugated heat transfer in a fouled channel with a moving depositing front. The depositing front separating the fluid and the deposit layer is captured using the level-set method. Fluid flow is modeled by the incompressible Navier–Stokes equations. Numerical solution is performed on a fixed mesh using the finite volume method. The effects of Reynolds number and thermal conductivity ratio between the deposit layer and the fluid on local Nusselt number as well as length-averaged Nusselt number are investigated. It is found that heat transfer performance, represented by the local and length-averaged Nusselt number reduces significantly in a fouled channel compared with that in a clean channel. Heat transfer performance decreases with the growth of the deposit layer. Increases in Reynolds, Prandtl numbers both enhance heat transfer. Besides, heat transfer is enhanced when the thermal conductivity ratio between the deposit layer and the fluid is lower than 20 but it decreases when the thermal conductivity ratio is larger than 20. [ABSTRACT FROM AUTHOR]

Highlights: [•] We represent a new correlation for density of nanofluid as a function of temperature. [•] Increasing the nanoparticle volume fraction rises the Nu dramatically. [•] Increasing the Ha leads to a slight increase in the average Nusselt number. [•] As the ϕ increases the effect of magnetic field on the heat transfer decreases. [Copyright &y& Elsevier]

Abstract: Condensation and evaporation processes from wetted surfaces are of utmost importance in many technological or industrial applications. In many devices such as home-appliances and air conditioning systems just to name a few, condensation and evaporation processes greatly impact their performance and energy efficiency; The physics of these processes is quite complex, involving conjugate heat transfer among solid–liquid film-gaseous phase together with the change of phase associated with evaporation and/or condensation. In spite of their own importance in technological applications, most physical aspects of this class of multiphase flows still need to be addressed. So far, many studies have been performed focusing on individual issues of full process, and, to the authors knowledge, their mutual influences was not addressed as yet. The aim of the present study is to supplement this field with a reliable numerical model for evaporation and condensation of thin liquid films in buoyant, conjugated heat transfer systems with vapor transport. The model is presented, validated on a simple case and successively applied to a literature relevant case. Validation is carried out considering a simple, insulated, 2-D geometry consisting of a fluid box connected to a solid. This allows to validate the model in a tightly controlled environment. Successively we reproduce the work of N. Laaroussi, G. Lauriat, G. Desrayaud, Effects of variable density for film evaporation on laminar mixed convection in vertical channel, Int. J. Heat Mass Transfer 52, 2009, 151–164, and we highlight the importance of considering the thermal characteristics of the solid part for the accurate reproduction of the complex physics associated to evaporation/condensation processes. [Copyright &y& Elsevier]

Abstract: The present work advances an analytical approach for conjugated conduction-convection heat transfer problems, by proposing a single domain formulation for modeling both the fluid stream and the channel wall regions. Making use of coefficients represented as space variable functions with abrupt transitions occurring at the fluid-wall interface, the mathematical model is fed with the information concerning the transition of the two domains, unifying the model into a single domain formulation with space variable coefficients. The Generalized Integral Transform Technique (GITT) is then employed in the hybrid numerical-analytical solution of the resulting convection-diffusion problem with variable coefficients, and critically compared for two alternative solution paths. A test problem is chosen that offers an exact solution for validation purposes, based on the extended Graetz problem including transversal conduction across the channel walls. The excellent agreement between approximate and exact solutions demonstrates the feasibility of the approach in handling more involved conjugated problems. [Copyright &y& Elsevier]

Abstract: The study of the mechanics of evaporating thin-films is important for improving the performance of phase-change heat transfer equipment. Various factors, including the changing profile of the thin-film with superheating and the use of small-scale and one-dimensional higher-order nonlinear governing differential equations, create difficulties for the study of the conjugated heat transfer of the thin-film and its surrounding regions. In previous studies, models of the conjugated heat transfer are simplified. The shape of the evaporating thin-film is treated as fixed, or the constant substrate temperature (CST) thin-film model is used. In this paper, a full conjugated heat transfer model, including the evaporating thin-film, the near-solid substrate and the intrinsic liquid, is proposed to study the heat transfer characteristics in the contact line region in a micro channel or a micro groove. The results show that a temperature valley value exists on the surface of the solid substrate corresponding to the peak value of the heat flow rate in the thin-film. The apparent contact angle is smaller than that of the CST model. The CST model overestimates the peak and the total heat flow rate, especially when the thermal conductivity ks of the substrate is low. For convenience in engineering applications, two simplified conjugated models are developed and evaluated by the full model. For low ks substrates, the simplified models can be used directly. Changing the thickness of the substrates affects the relative errors only slightly. [Copyright &y& Elsevier]

Abstract: The exact analytical solution of the unsteady impulsive Thermo-Fluid Dynamic field arising in a two-dimensional channel with thick solid walls is presented when the thermal field in the fluid is coupled with the thermal field in the solid (conjugated heat transfer). The cases studied in this paper depend on the boundary conditions imposed on the unwetted sides of the channel walls: assigned temperature and adiabatic condition. Moreover the case of a given heat loss at the unwetted wall is also considered in an appendix. The temperature and heat flux at the solid–fluid interface are analyzed as function of time and of the nondimensional parameters governing the problem. [Copyright &y& Elsevier]

Abstract: Prediction of heat transfer coefficients and stresses on blade surfaces keys a role in thermal design of a gas turbine blade. The present study investigates heat transfer and stress in a gas turbine blade with 10 circular internal cooling passages. 3D-numerical conjugated simulations using a FVM and FEM commercial codes, CFX and ANSYS are performed to calculate distributions of the heat transfer coefficients and the stresses, respectively. The heat transfer coefficient is the highest on the stagnation point of leading edge due to impingement of incoming gas flow. It is the lowest at the trailing edge on both pressure and suction sides due to development of thermal boundary layer. However, the maximum material temperature and the maximum thermal stress occur at the trailing edge near the mid-span. Therefore, the failure of turbine blade should be predicted by total stress resulted from the combination of thermal load and cooling. [Copyright &y& Elsevier]

Abstract: Transient conjugated heat transfer in thick walled pipes for thermally developing laminar flow is investigated involving two-dimensional wall and axial fluid conduction. The problem is solved numerically by a finite-difference method for hydrodynamically developed flow in a two-regional pipe, initially isothermal in which the upstream region is insulated and the downstream region is subjected to a suddenly applied uniform heat flux. A parametric study is done to analyze the effects of four defining parameters namely, wall thickness ratio, wall-to-fluid thermal conductivity ratio, wall-to-fluid thermal diffusivity ratio and the Peclet number. The results are given by non-dimensional interfacial heat flux values, and it is observed that, heat transfer characteristics are strongly dependent on the parameter values. [ABSTRACT FROM AUTHOR]

Abstract: The two equation numerical model has been applied for parallel flow double-pipe heat exchanger filled with open cell metal foams. The model fully considered solid–fluid conjugated heat transfer process coupling heat conduction and convection in open cell metal foam solid matrix, interface wall and fluid in both inner and annular space in heat exchanger. The non-Darcy effect and the wall thickness are also taken into account. The interface wall heat flux distribution along the axial direction is predicted. The numerical model is firstly verified and then the influences of solid heat conductivity, metal foam porosity, pore density, relative heat conductivity and inner tube radius of the heat exchanger on dimensionless temperature distribution and heat transfer performance of heat exchanger are numerically studied. It is revealed that the proposed numerical model can effectively display the real physical heat transfer process in the double pipe heat exchanger. It is expected to provide useful information for the design of metal foam filled heat exchanger. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical study on conjugated heat transfer (natural convection, radiation and conduction) in a square cavity with turbulent flow is presented. The cavity is a representation of a room, where the left wall is isothermal, the right wall is semitransparent (glass), the lower wall is considered as insulated and on the upper opaque wall heat conduction is present. Both conductive walls (opaque and semitransparent) interact with the ambient. The semitransparent wall is subject to a constant heat flux (G2  = 736 W/m2) whereas on the opaque wall a constant heat flux (G1  = 875 W/m2) falls perpendicularly. The sizes of the cavity under study were 5.0, 4.0, 3.0 and 2.0 m. The upper opaque wall was considered as a mixture of concrete and a composite material (concrete–expanded polystyrene) with different thicknesses and diverse types of water-repellent coatings on top of it. From the results, it was found that the white coating on top of the opaque wall significantly reduces the amount of energy towards the inside of the cavity. It was also determined that the opaque wall with a 20 cm thickness shows the best thermal performance and it is the most adequate to reduce thermal gains inside the cavity. Correlations for the total heat transfer as a function of the cavity size, the type of coating and material of the opaque upper wall are proposed. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study of conjugated heat transfer in a ventilated cavity was carried out in order to analyze temperature distribution effectiveness inside it, and to determine a good ventilation configuration. The space was represented by a ventilated cavity under turbulent flow regime. All the walls were considered adiabatic, except the vertical wall on right, which was defined as a conductive opaque wall with a gap in its lower side for the incoming air. The conductive wall is submitted to a constant heat flux of 736 W/m2 and it is considered to interact with the outside ambient. Four cases for the air exhaust location were considered for the analysis; the incoming air velocity was varying depending on the Reynolds number between . The conductive wall was analyzed for two different materials (construction brick and adobe block) and three different widths each (0.1, 0.2 and 0.3 m). The mass, momentum and energy equations, coupled with the turbulence model were discretized in finite volumes. From the results can be concluded that the 0.3 m width adobe block is the appropriate to minimize thermal load gains to the inside of the room and it helps to reduce the efforts made on ventilation to remove heat. Regarding the air exhaust location, it was concluded that the right side of the upper horizontal wall was the best position for the air exhaust for a Reynolds number between and based on the effectiveness of temperature distribution and velocity according to ASHRAE Standard 55, Thermal environment conditions for human occupancy, 2004 [1]. [Copyright &y& Elsevier]

• Turbulent mixed convection conjugated with a conducing solid was studied via CFD. • Exergy destruction is analyzed by heat transfer and viscous dissipation sources. • Surface thermal radiation notably reduces the maximum temperature in the cavity. • The surface's emissivity affects notably the heat transfer and exergy destruction. • Thermal diffusivity ratio has no effect on heat transfer and exergy destruction. The study of natural and forced turbulent convection of heat has been essential to improving the design parameters of several engineering applications. However, few works have described the simultaneous effect of turbulence and thermal radiation phenomena on heat transfer and exergy destruction in cavities with inner solid bodies. This work investigates the turbulent mixed heat convection of air and the surface thermal radiation in a cavity with a heat-conducting square solid at its center through computational modeling. A turbulent k -ε model with damping functions and temperature-variable thermal properties are used for the air, while the local exergy destruction is computed by a direct method for turbulent flows. The effects of turbulence and surface thermal radiation are analyzed through the variation of the Grashof (108 ≤ Gr ≤ 1010) and Richardson (0.1 ≤ Ri ≤ 10) numbers, the emissivity of the surfaces (0 ≤ ∈ ≤ 0.9) and the thermal diffusivity ratio between solid and fluid (1 ≤ R ≤ 103). The main results indicate that the increment of Ri notably changes the magnitude and distribution of velocities and temperatures, increasing from 30% to 300% the maximum dimensionless velocity. The maximum temperatures in the cavity are reduced by 30% when thermal radiation is considered, resulting in weaker buoyancy-driven flows. The increment of the emissivity increases up to 5 times the value of the dimensionless heat transfer at the inner-solid surfaces, Nusselt number N u ¯ , and decreases from 45% to 75% the total exergy destroyed (Xd T) in the cavity. On the contrary, the increment of R only produces variations lower than 8% of the N u ¯ and the Xd T for all the cases investigated. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper an exact analytical self-similar solution of the thermo-fluid dynamic field arising in an impulsively accelerated flow over a flat plate is proposed. The plate is considered of infinite thickness and the thermal field is computed both in the fluid and in the solid with the temperature and the heat flux unknown at the solid–fluid interface (conjugated heat transfer). The values of the initial temperatures in the solid and in the fluid are different constants. The solution, obtained in the incompressible case, is extended to compressible flows by the Stewartson–Dorodnitsin transformation. The influence of the non-dimensional parameters governing the phenomenon is discussed with particular emphasis to the simple expressions of the interface temperature and heat flux. [Copyright &y& Elsevier]

Abstract: This work compares heat transfer characteristics across a square cavity partially filled with a fixed amount of conducting solid material. The solid phase is shaped into two different geometries, namely square and cylindrical rods, which are horizontally displaced inside the cavity. Comparisons are obtained by numerically solving a conjugate heat transfer problem that considers both the solid and the fluid space. Governing equations are solved using the finite volume method and the algebraic equation set is relaxed with the SIP procedure. The average Nusselt number at the hot wall, obtained from the cavity with square obstacles and for several Darcy numbers, are compared with those calculated with circular obstacles. When comparing the two geometries considering the same modified Rayleigh number Ra m, this study shows that the average Nusselt number for cylindrical rods are slightly lower than those for square rods. [Copyright &y& Elsevier]

Abstract: The paper presents both three and two-dimensional numerical analysis of convective heat transfer in microchannels. The three-dimensional geometry of the microchannel heat sink followed the details of the experimental facility used during a previous research step. The heat sink consisted of a very high aspect ratio rectangular microchannel. Two channel spacings, namely 1mm and 0.3mm (0.1mm), were used for three-dimensional (two-dimensional) numerical model, respectively. Water was employed as the cooling liquid. The Reynolds number ranged from 200 to 3000. In the paper, thermal entrance effects and conduction/convection coupling effects are considered both for the test case of uniform channel inlet conditions and the complete geometry of the experiment. Finally, the comparison between measured and computed heat flux and temperature fields is presented. Contrary to the experimental work, the numerical analysis did not reveal any significant scale effect on heat transfer in microchannel heat sink down to the smallest size considered (0.1mm). [Copyright &y& Elsevier]

Abstract: The steady-state analysis of conjugated heat transfer process for the hydrodynamically developed forced convection flow on a heated flat plate embedded in a porous medium is studied. The governing equations for the fluid-saturated porous medium are solved analytically using the integral boundary layer approximation. This integral solution is coupled to the energy equation for the flat plate, where the longitudinal heat conduction effects are taken into account. The resulting equations are then reduced to an integro-differential equation which is solved by regular perturbation techniques and numerical methods. The analytical and numerical predictions for the temperature profile of the plate and appropriate local and average Nusselt numbers are plotted for finite values of the conduction parameter, α, which represents the presence of the longitudinal heat conduction effects. [Copyright &y& Elsevier]

The transient analysis of a conjugated heat transfer process in the thermal entrance region of a circular tube with a fully developed laminar power-law fluid flow, is studied. This conjugated heat transfer process is characterized by the simultaneous thermal interaction between the wall tube and the adjacent thermal boundary layer of the power-law fluid. We apply the quasi-steady approximation for the power-law fluid, identifying the suitable time scales of the process. Thus, the energy equation in the fluid is solved analytically using the well-known integral boundary layer technique. This solution is coupled to the transient energy equation for the solid where the axial heat conduction effects are taken into account. The governing equation is reduced to a integro-differential equation which is solved by muliple-scale analysis and a conventional numerical technique. The results for the temperature of the wall tube and the corresponding average temperature are plotted for differents parameters such as conduction parameter, α, the aspect ratios of the tube, ϵ and ϵ0 and the index of power-law fluid, n. [Copyright &y& Elsevier]

• Single- and two-phase heat transfer of slender rectangular 180° return bends. • Local heat transfer ratios between the concave and convex surface. • Conjugated heat transfer is considered via a Biot number approach. The convective heat transfer characteristics of single-phase water flows and two-phase air-water flows through a slender 180° return bend with a rectangular cross-section are investigated. A moderately curved section is considered with a curvature ratio around 58, a hydraulic diameter of 3.9 mm and an aspect ratio of 1.067. The focus of this work is to investigate if there is a recognizable difference in heat transfer, respectively Nusselt numbers, between the outer (convex) and inner (concave) curved surface of the duct. An approach that considers the conjugated heat transfer is applied to adequately investigate this difference. Additionally the impact of the secondary gas-phase on the heat transfer characteristics is discussed. [ABSTRACT FROM AUTHOR]