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Abstract This study presents a comprehensive investigation into a 3D simulation of magnetorheological (MR) conical bearings, focusing on considering viscous dissipation using the conjugated heat transfer approach. The behavior of MR fluids is expressed through the utilization of the Bingham-Papanastasiou constitutive equation. Notably, this study considers variations in viscosity and yield stress as functions of both magnetic field intensity and temperature. The study utilizes a multidisciplinary approach, encompassing fluid dynamics, magnetism, and heat transfer, to model and analyze the behavior of MR fluids within conical bearing geometries. The governing equations containing Cauchy momentum, energy, and Maxwell equations are solved using the finite element method. This research delves into the impacts of viscous dissipation on the functional and characteristic attributes of conical bearings. The energy equations in solid and fluid domains and extended considerations to the plug region within viscous dissipation are specifically addressed. Extensive validation is performed through a comparative analysis involving experimental, numerical, and analytical studies to ensure the validity of results. The results reveal the substantial impact of temperature on both the characteristics and functionality of magnetorheological conical bearings.

This study presents a comprehensive investigation into a 3D simulation of magnetorheological (MR) conical bearings, focusing on considering viscous dissipation using the conjugated heat transfer approach. The behavior of MR fluids is expressed through the utilization of the Bingham-Papanastasiou constitutive equation. Notably, this study considers variations in viscosity and yield stress as functions of both magnetic field intensity and temperature. The study utilizes a multidisciplinary approach, encompassing fluid dynamics, magnetism, and heat transfer, to model and analyze the behavior of MR fluids within conical bearing geometries. The governing equations containing Cauchy momentum, energy, and Maxwell equations are solved using the finite element method. This research delves into the impacts of viscous dissipation on the functional and characteristic attributes of conical bearings. The energy equations in solid and fluid domains and extended considerations to the plug region within viscous dissipation are specifically addressed. Extensive validation is performed through a comparative analysis involving experimental, numerical, and analytical studies to ensure the validity of results. The results reveal the substantial impact of temperature on both the characteristics and functionality of magnetorheological conical bearings. [ABSTRACT FROM AUTHOR]

• 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]

This study investigates the unsteady natural convection and entropy generation under the effects of magnetic field and baffles inside a nanofluid filled E-shaped enclosure. The nanofluid flow is driven by time-varying sidewall temperature and is partitioned by baffles. Multiple factors are discussed, including the enclosure aspect ratio (0.2 ≤ AR ≤ 0.7), nanofluid volume fractions (0 ≤ ϕ ≤ 0.1), Hartmann numbers (0 ≤ Ha ≤ 80), frequency of time-varying side wall temperature (0.01 ≤ ω ≤ 0.1), baffle locations (0 ≤ d ≤ 0.4) and length (0 ≤ l ≤ 0.4). An economic analysis is conducted to show the nanofluid cost of enhancing thermal transfer and reducing entropy generation. The modelling results show that increasing aspect ratio and nanofluid volume fraction enhance the thermal transfer behavior, while the magnetic field suppresses the nanofluid natural convection. Total entropy generation monotonically decreases with the increasing nanofluid volume fraction and Hartmann number. Installing baffles into horizontal walls can boost the thermal transfer behavior and decrease the total entropy generation. The economic analysis shows that increasing the nanofluid volume fraction can effectively improve the thermal economy, and this improvement increases with magnetic intensity.

With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches. [ABSTRACT FROM AUTHOR]

An analysis was conducted on the displacement of a heavy fluid by a miscible light fluid in the flow assurance operation of injecting diesel oil to displace heavy oil in an insulated offshore production line. A three‐dimensional computational fluid dynamics model was developed and implemented in OpenFOAM®. It stimulates the production stages, no‐touch time, and oil displacement, considering heat transfer through natural convection and conjugated heat transfer through the solid layers of the pipeline. The specific test case focused on the first 180 m of an existing offshore production line. The simulations revealed two primary mechanisms of mixing: turbulence and secondary flows generated by the pipeline curves. Remarkably, the results demonstrate that by injecting a volume of lighter oil 1.3 times the pipeline volume, approximately 90%–95% of the heavy oil can be effectively removed. [ABSTRACT FROM AUTHOR]

AbstractIn this study, straight and z-shaped channel PCHEs are employed as hydrogen-helium heat exchangers in Synergistic Air-breathing Rocket Engine (SABER). Conjugated heat transfer mechanisms and characteristics of supercritical hydrogen-helium are studied numerically. The results of the straight channel indicate that when the mass flow rate of the cold (H2)/hot (He) side is 38/280 kg/(m2·s), a greater comprehensive performance of flow and heat transfer can be obtained. The influence of gravity on the hot side is significantly less than that on the cold side. The increase in plate thickness enhances heat transfer, while the effect of rib thickness is the opposite. As the bend angle decreases, the heat transfer coefficient of the z-shaped channel becomes higher. The heat transfer characteristics of the cold side vary more significantly with the bend angle than that of the hot side. [ABSTRACT FROM AUTHOR]

The results of experimental and computational studies of the processes of hydrodynamics and heat transfer of a swirling flow, heated by the counter coolant flow in the heat exchange channel under standard technological parameters of a nuclear power plant are presented in this paper. The temperature field of the heat exchange channel as a whole and the coefficient of hydraulic resistance of channels with twisted tapes of a constant swirl pitch were obtained in experiments. The numerical study was carried out using the domestic software package LOGOS and the Ansys CFX complex. The simulations were performed using the k-ω SST turbulence model, corrected for streamline curvature and rotation. Two versions of the calculation grid were developed. A comparative analysis of the calculated and experimental values of the hydraulic friction coefficient, the swirling flow temperature, and the heat transfer coefficients from the wall to the swirling flow was carried out. The analysis allowed identification of the strengths and weaknesses of the calculation methodology implemented in the domestic package. Deviations of the obtained values were compared. There is a good agreement between the calculated and experimental data, as well as with the data based on generalized dependences. One of the most important conclusions of the study is the need to modernize the process of solving the coupled heat transfer problem in the LOGOS package to expand the range of problems to be solved. [ABSTRACT FROM AUTHOR]

In addition to taste and melting behavior, the gloss is an important quality criterion of chocolate products. Differences considering the gloss on products can be attributed to different causes in the production process. The chocolate that has been pre‐crystallized by shearing and supercooling is further cooled, crystallized and transported as a solid chocolate out of the cooling process. The cooling of the chocolate is largely unexplored in a paternoster refrigerator and therefore the resulting streaming profile and temperature profile are numerically studied in this work. [ABSTRACT FROM AUTHOR]

With ever increasing integration density of electronic components, the demand for cooling solutions capable of removing the heat generated by such systems grows along with it. It has been shown that a viable answer to this demand is the use of direct liquid jet impingement. While this method can generally be scaled to the cooling of large areas, this is restricted by the necessity of coolant flow rate scaling. In this study, the benefits and restrictions of using increased nozzle pitch to remedy the increasing demand for overall flow rate are investigated. To this end, a model is validated against experimental findings and then used for computational fluid dynamics simulations, exploring effects of the pitch change for micro-scale nozzle diameters and nozzle-to-target spacings. It is found that while this method is efficient in adjusting the tradeoff between total coolant flow rate and pressure drop up to a certain pint, the occurrence of a hydraulic jump in the cavity causes a deterioration of its effect for large nozzle pitches.

With the ammonothermal method, one of the most promising technologies for scalable, cost-effective production of bulk single crystals of the wide bandgap semiconductor GaN is investigated. Specifically, etch-back and growth conditions, as well as the transition from the former to the latter, are studied using a 2D axis symmetrical numerical model. In addition, experimental crystal growth results are analyzed in terms of etch-back and crystal growth rates as a function of vertical seed position. The numerical results of internal process conditions are discussed. Variations along the vertical axis of the autoclave are analyzed using both numerical and experimental data. During the transition from quasi-stable conditions of the dissolution stage (etch-back process) to quasi-stable conditions of the growth stage, significant temperature differences of 20 K to 70 K (depending on vertical position) occur temporarily between the crystals and the surrounding fluid. These lead to maximum rates of seed temperature change of 2.5 K/min to 1.2 K/min depending on vertical position. Based on temperature differences between seeds, fluid, and autoclave wall upon the end of the set temperature inversion process, deposition of GaN is expected to be favored on the bottom seed. The temporarily observed differences between the mean temperature of each crystal and its fluid surrounding diminish about 2 h after reaching constant set temperatures imposed at the outer autoclave wall, whereas approximately quasi-stable conditions are reached about 3 h after reaching constant set temperatures. Short-term fluctuations in temperature are mostly due to fluctuations in velocity magnitude, usually with only minor variations in the flow direction. [ABSTRACT FROM AUTHOR]

Due to the uneven temperature field and temperature gradient introduced by an efficient cooling structure, the analysis of the stress field is necessary. In this study, the cooling characteristics and stress characteristics such as the thermal stress and thermomechanical stress of an impingement/effusion cooling system were investigated by employing a fluid–thermal-structure coupling simulation method. The effects of film hole injection angle (30°–90°) and blowing ratio (0.5–2.0) were studied. The results showed that the film hole shape and the non-uniform temperature field introduced by the cooling structure had a great influence on the stress field distribution. With the increase in the blowing ratio, not only the overall cooling effectiveness of the cooling system increased, but the maximum thermal stress and thermomechanical stress near film holes also increased. The cases with a smaller inclination angle could provide a better cooling performance, but caused a more serious stress concentration of the film hole. However, the thermal stress difference at the leading and trailing edges of the film hole increased with a decreasing inclination angle. The cases with a = 30° and 45° showed serious thermal stress concentration near the hole's acute region. [ABSTRACT FROM AUTHOR]

In addition to taste and melting behavior, the gloss is an important quality criterion of chocolate products. Differences considering the gloss on products can be attributed to different causes in the production process. The chocolate which has been precrystallized by shearing and supercooling is further cooled, crystallized, and transported as a solid chocolate out of the cooling process. The cooling of the chocolate is largely unexplored in a paternoster refrigerator. Therefore, the resulting flow profile and temperature profile are numerically studied in this work. [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 aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a "common flow up" orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied. [ABSTRACT FROM AUTHOR]

Due to the uneven temperature field and temperature gradient introduced by an efficient cooling structure, the analysis of the stress field is necessary. In this study, the cooling characteristics and stress characteristics such as the thermal stress and thermomechanical stress of an impingement/effusion cooling system were investigated by employing a fluid–thermal-structure coupling simulation method. The effects of film hole injection angle (30°–90°) and blowing ratio (0.5–2.0) were studied. The results showed that the film hole shape and the non-uniform temperature field introduced by the cooling structure had a great influence on the stress field distribution. With the increase in the blowing ratio, not only the overall cooling effectiveness of the cooling system increased, but the maximum thermal stress and thermomechanical stress near film holes also increased. The cases with a smaller inclination angle could provide a better cooling performance, but caused a more serious stress concentration of the film hole. However, the thermal stress difference at the leading and trailing edges of the film hole increased with a decreasing inclination angle. The cases with a = 30° and 45° showed serious thermal stress concentration near the hole’s acute region.

In nuclear reactors, the research of conjugated heat transfer between the fuel and coolant in the fuel assembly is fundamental for improving the safety, reliability and economy. The numerical approach based on Computational Fluid Dynamics (CFD) can be used to realize the rapid analysis of the conjugated heat transfer. Besides, the numerical simulation can provide detailed physical fields that are useful for the designing and optimizing of the fuel assembly. The plate-type fuels are generally used to enhance heat transfer in research reactors with high power density. In this study, a standard plate-type fuel assembly in the research reactor was taken into consideration. The solid-fluid conjugated heat transfer of the fuel assembly and coolant was numerically investigated. In the fluid region, the subcooled flow boiling simulation model was established by implementing the Rensselaer Polytechnic Institute model into the Euler multi-phase flow method. The results show that the conjugated heat transfer of the fuel assembly and coolant can be simulated using the model established in this work. The influence of fluid velocity, power density and the width of the flow channel on the temperature distribution and the conjugated heat transfer was investigated and discussed.

• 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]

Thermal barrier coatings (TBCs) as a kind of temperature-resistance materials have been widely applied in super high temperature components in aircraft engines. However, TBCs are subjected to harsh service environment such as high temperature oxidation and erosion, which lead to the coating failure. It is important to investigate the effect of fire temperature, angle and velocity of particle on erosion to understand the failure mechanism. In this paper, the temperature and velocity distributions of erosion particles in high temperature gas burner rig are investigated by using the fluid–solid coupling method with the discrete random walk model. The results show that a non-uniform distribution of temperature appears in different positions of the central axis, and the temperature of particle is affected obviously by the gas stream and particle size. The trajectory of particles and velocity diagrams under different particle size are determined by coupling the continuous phase with the erosion particles.

The aim of this work is to numerically analyse fluid flow and heat transfer characteristics in a crossflow air-to-water fin-and-tube heat exchanger (FTHEX) by implementing two configurations of delta-winglet type vortex generators at the air side: delta-winglet upstream (DWU) and delta-winglet downstream (DWD). The vortex generators are mounted on a fin surface and deployed in a “common flow up” orientation. The effects of attack angles of 15°, 30° and 45° on air-side heat transfer and pressure drop were examined. Since the implementation of the full-size model would involve large numerical resources, the computational domain is simplified by considering a small segment in the direction of water flow. The fully developed temperature and velocity boundary conditions were set at the water inlets. To validate the defined mathematical model and numerical procedure, measurements have been performed on a plain FTHEX. The air side Reynolds number, based on hydraulic diameter, was in the range of 176 ≤ ReDh ≤ 400 and water side Reynolds number, based on inner tube diameter, was constant Redi = 17,065. The results have shown that the highest increase in the Colburn factor j (by 11–27%) and reduction in the air-side thermal resistance fraction (from 78.2–76.9% for ReDh = 176 to 76–72.4% for ReDh = 400) is achieved by using the DWD configuration with attack angle 45°. In addition, the overall heat transfer coefficient is improved by up to 15.7%. The DWD configuration with the attack angle 30° provides the greatest improvement in the heat transfer to pressure loss ratio, 5.2–15.4% over the range of ReDhstudied.

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]

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The vacuum tube transportation (VTT) system has been a promising direction of future transportation. Within this system, a high-speed maglev travels in a low-vacuum environment to reduce aerodynamic drag. However, the heat dissipation of on-board heating devices will be compromised under low-vacuum conditions, and the device performance may thus be lowered. This study investigates the low-vacuum conjugate heat transfer characteristic of a levitation electromagnet module of a maglev using an experimentally verified numerical method. During the heating process, the surface temperature distribution of the levitation electromagnet, and the temperature and velocity characteristics of the flow field are examined. It is found that, as the vacuum level increases from 1.0 atm to 0.1 atm, the total heat dissipating from the levitation electromagnet module is decreased by 49% at 60 min, the contribution of convection heat flux over the total heat flux is decreased from 49% to 17%, and the convection heat transfer coefficient of the levitation electromagnet is decreased by 89%. This study can provide an efficient numerical model for low-vacuum heat transfer study on a VTT system as well as help the evaluation and optimization of low-vacuum maglev thermal management systems. [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]

In this paper, conjugate heat transfer from a circular cylinder with a heat source to a non‐Newtonian power‐law fluid is studied. Numerical calculations are carried out in an unconfined computational domain for Reynolds numbers (5≤Re≤40), power‐law indices (0.6≤n≤1.4), and Prandtl numbers (1≤Pr≤50) with different heat source values. The pressure coefficient, value, and position of maximum temperature inside the cylinder and the local and average Nusselt number are calculated. Also, the effects of Re, Pr, n, and heat source value on the thermal characteristics in the solid cylinder and the fluid around it are studied and discussed. [ABSTRACT FROM AUTHOR]

The present study reports numerical simulations of water-based Al2O3 nanofluid flowing in a 2D channel with a heated wall-mounted obstacle. The conjugated heat transfer problem including forced convection within the fluid and conduction inside the obstacle is numerically solved using the mixture model with temperature-dependent properties. The model has been first carefully validated against published data. Then, the fluid flow and heat transfer have been investigated for six nanoparticle volume fractions φ up to 1.8% and bulk Reynolds numbers within the range 100≤Re≤1600. The results show that only the Reynolds number has an influence on the hydrodynamic field, especially on the reattachment length behind the obstacle. The heat transfer rate increases with increasing nanoparticle concentrations and/or Reynolds number. The second law analysis is employed to study the heat transfer and fluid friction irreversibilities. The average entropy generation increases linearly with the Reynolds number. Increasing the nanoparticle volume fraction reduces the thermal entropy generation while the frictional one increases. Finally, the benefit of using this nanofluid is discussed regarding five merit criteria. [ABSTRACT FROM AUTHOR]

Numerical simulations are a valuable tool for the design and optimization of crystal growth processes because experimental investigations are expensive and access to internal parameters is limited. These technical limitations are particularly large for ammonothermal growth of bulk GaN, an important semiconductor material. This review presents an overview of the literature on simulations targeting ammonothermal growth of GaN. Approaches for validation are also reviewed, and an overview of available methods and data is given. Fluid flow is likely in the transitional range between laminar and turbulent; however, the time-averaged flow patterns likely tend to be stable. Thermal boundary conditions both in experimental and numerical research deserve more detailed evaluation, especially when designing numerical or physical models of the ammonothermal growth system. A key source of uncertainty for calculations is fluid properties under the specific conditions. This originates from their importance not only in numerical simulations but also in designing similar physical model systems and in guiding the selection of the flow model. Due to the various sources of uncertainty, a closer integration of numerical modeling, physical modeling, and the use of measurements under ammonothermal process conditions appear to be necessary for developing numerical models of defined accuracy.

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]

The vacuum tube transportation (VTT) system has been a promising direction of future transportation. Within this system, a high-speed maglev travels in a low-vacuum environment to reduce aerodynamic drag. However, the heat dissipation of on-board heating devices will be compromised under low-vacuum conditions, and the device performance may thus be lowered. This study investigates the low-vacuum conjugate heat transfer characteristic of a levitation electromagnet module of a maglev using an experimentally verified numerical method. During the heating process, the surface temperature distribution of the levitation electromagnet, and the temperature and velocity characteristics of the flow field are examined. It is found that, as the vacuum level increases from 1.0 atm to 0.1 atm, the total heat dissipating from the levitation electromagnet module is decreased by 49% at 60 min, the contribution of convection heat flux over the total heat flux is decreased from 49% to 17%, and the convection heat transfer coefficient of the levitation electromagnet is decreased by 89%. This study can provide an efficient numerical model for low-vacuum heat transfer study on a VTT system as well as help the evaluation and optimization of low-vacuum maglev thermal management systems.

In this paper, an unsteady forced convection of two-dimensional flow of Ethylene Glycol/CNT and Ethylene Glycol/CNT-Ag in horizontal cylinder is studied. The wall is submitted to a uniform or periodic heat flux. The transient distribution of the temperature is obtained by solving, at each axial position and time, a tridiagonal system by TDMA algorithm. The convective heat transfer coefficient and bulk temperature of nanofluid are investigated versus space-time and versus different nanoparticles volume fraction. The thermal phase shift is brought out for Ethylene Glycol base fluid and EG-CNT nanofluid. The obtained results show an improving of heat transfer rate when the volume fraction increases from 0 % to 10 % of CNT. Ethylene Glycol/CNT-AG seems to be more advantageous for the enhancement of convective heat transfer than EG/CNT. The results found can be exploited for various applications especially for the enhancement performances of heat transfer rate for the absorber tube of solar collector. [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]

Combined convection heat transfer and thermal conduction for film cooling of a flat plate with 45° ribs on one wall was investigated experimentally and numerically. The flat plate surface temperature was measured using thermochromic liquid crystals. The results show that the film cooling is the main mechanism for the local cooling with a very low thermal conductivity while the convection heat transfer of the coolant in the coolant channel is the dominant heat transfer mechanism for the high thermal conductivity plate, with both film cooling and convection heat transfer by the coolant being important with medium thermal conductivity walls. [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]

In this paper, a 3D-conjugated heat transfer model for nano-encapsulated phase change materials (NEPCMs) cooled micro pin fin heat sink (MPFHS) is presented. The governing equations of flow and heat transfer are solved using a finite volume method based on collocated grid and the results are validated with the available data reported in the literature. The effect of nanoparticles volume fraction (C = 0.1, 0.2, and 0.3), inlet velocity (Vin = 0.015, 0.030, and 0.045 m/s), and bottom wall temperature (Twall= 299.15, 303.15, 315.15, and 350.15 K) is studied on Nusselt and Eider numbers as well as temperature contours in the system. The results indicate that significant heat transfer enhancement is achieved when using the NEPCM slurry as an advanced coolant. The maximum Nusselt number when NEPCM slurry (C = 0.3) with Vin = 0.015, 0.030, and 0.045 (m/s) is employed is 2.27, 1.81, and 1.56 times higher than the ones with base fluid, respectively. However, with increasing bottom wall temperature, the Nusselt number first increases then decreases. The former is due to higher heat transfer capability of coolant at temperatures over the melting range of phase change material (PCM) particles due to partial melting of nanoparticles in this range. However, the latter phenomenon is due to the lower capability of the NEPCM particles and consequently coolant in absorbing heat at coolant temperatures is higher than the temperature correspond to fully melted NEPCM. It was observed that the NEPCM slurry has a drastic effect on the Euler number, and with increasing volume fraction and decreasing inlet velocity, the Euler number increases accordingly. [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]