Heat Transfer最新文献

Amputees who use prosthetic limbs suffer from the problem of high contact temperature between the socket of the prosthetic limb and the amputated part and lack of evaporation of sweat. These conditions lead to discomfort and failure to perform functions properly. In addition, these conditions help generate ulcers and accumulate harmful bacteria in this area. This paper presents a heatsink design to extract heat from the contact area. A cylindrical heat sink is designed for phase-changing materials with three branched tubes in two stages. The current heat sink is used to cool the contact area between the amputated part and the socket in the lower prostheses. Three distributions of pipe branches are proposed. The distribution and pipe lengths were obtained using a constructal design method. In the constructal design, the lengths of the branched tubes were the degrees of freedom, the objective function was the minimization of the inlet temperature to the heat sink, and the constraint was the volume of the cylindrical heat sink. The metabolic heat transfer during exercise was estimated and its value was used to calculate the size of the cylindrical heatsink and the selection of the phase change material by testing three of them: water, tridecane, and dodecane. It was found that water gives the highest latent heat of melting and the lowest volume in addition to its availability. On the other hand, two cooling fluids were tested: water and air. It was found that water as a cooling fluid gave the lowest flow and the largest heat capacity. Constructal theory was used to design a cylindrical heat sink using branched tubes for the coolant in two steps: the first with three branches, and the second with nine branches. The degree of freedom for constructal theory was the length of the branches through the choice of their end locations. It was found that the branches of the highest length led to a reduction in temperature from 40°C to 15.48°C compared with the single tube, which reduced the temperature to 23.87°C. All tests recorded a pressure drop within the acceptable range of 3.1–5.43 Pa for the branches examined. The research demonstrated that using constructal theory achieved the best thermal dissipation within a restricted volume.

In agricultural greenhouses, effective heating systems are essential for maintaining proper temperature control and air circulation during the winter. This study delves into the analysis of heat exchange through natural convection within heated greenhouses, with a particular emphasis on the impact of bottom heating. Two distinct types: mono-chapel and bi-chapel, each featuring triangular or spherical roofs are examined. To capture the variable roof shapes, we employ a change-of-variable method, and the numerical solutions are obtained using the finite volume method. The results show that heat transfer is enhanced by increasing the Rayleigh number. This improvement differs according to the shape of the roof. Heat transfer decreases by about 5% for the spherical mono-chapel case compared to the triangular case for Ra = 10³. For Ra = 10⁵, the monospherical case favors heat transfer, with an increase of 0.35% compared to the triangular case. In the case of bi-chapel roof, heat transfer is greater with a triangular roof for Ra = 10³, showing an increase of 6.4% compared to the spherical case. This study not only sheds light on the fundamental aspects of heat transfer in greenhouses but also provides valuable insights for optimizing greenhouse design based on specific roof configurations and heating conditions.

Microcombustors are microscale combustion devices that can be used to power microelectromechanical systems. Many combustor configurations are reported in the literature and, among them, combustion in a microscale recirculating heat exchanger is a feasible option. In this work, a simple, double-channel, recirculating heat exchanger is considered. The novelty of the present work lies in the heat transfer analysis approach to design a microcombustor. A combustor is designed using thermal resistance networks for a premixed fuel containing a methane–air mixture in stoichiometric ratio. The length of the combustor is designed based on the position of the combustion flame. Computational fluid dynamics is utilized to validate the theoretical results. The analysis is carried out for adiabatic and nonadiabatic conditions. The combustor lengths for adiabatic and nonadiabatic (ceramic) combustors vary from 39 to 242 mm and 49 to 276 mm, respectively, for variations in the mass flow rate of the premixed gases from 6 to 10 mg/s. A minimum limiting flow rate of 6 mg/s was identified. The average error in the maximum combustion gas temperatures between the theoretical and CFD results obtained in this work is 4.2%. The theoretical approach presented can be suitably applied to more complex geometries involving multichannels and variations in geometrical properties.

This current work aims to decrease temperature nonuniformity in a microprocessor. The proposed composite pin-fin heat sink design is analyzed computationally, and its functioning is compared with the conventional heat sink design. According to the heat rate, the composite heat sink is divided into two sections: the hotspot and the background section. Aluminum, copper, and graphene are chosen for the background and hotspot sections. Both noncomposite and composite heat sinks are designed with similar geometrical dimensions. DI water is used as the working fluid. They are studied for heterogeneous hotspot heat flux varying from 200 to 600 kW/m² by keeping constant background heat flux as 100 kW/m² with the inlet mass flow rate of 0.05 kg/s. Further simulations are performed for various Reynolds numbers (Re = 150, 225, 300) with a constant background and hotspot heat flux of 100 and 600 kW/m², respectively, for different inlet temperatures of 15°C, 20°C, and 25°C. The simulations are also carried out for other working fluids, such as TiO₂ and Fe₂O₃ based nanofluids with the constant volume concentration of 0.65% and 3%, respectively in the DI water, at the constant background and hotspot heat flux of 100 and 600 kW/m², respectively. The results are shown for all the above studies planned. The results suggest that composite heat sinks with graphene as a composite material and Fe₂O₃ based nanofluid yields higher heat dissipation.

The squeezing flow bears a major importance in everyday phenomena and has vast industrial and biomedical applications. The current study looks at the nanofluid flow among two infinite “parallel plates” that are squeezed. The velocity slip and first-order compound response have been considered in this problem for a clear understanding of their consequences in the flow of nanofluid and heat transport mechanism. This fluid replica thinks about “Brownian motion” and the influences of “thermophoresis” of nanofluid. The novelty of this work lies in exploring the combined effects of first-order chemical reaction and the velocity slip on unsteady squeezing flow of nanofluid between two parallel plates as one has not yet reported such effects. The prevailing equations are altered into simplified forms by deploying suitable similarity transformations. Then “numerical solutions” of these equations are obtained by applying the fourth-order “Runge–Kutta method” with the help of the shooting technique. The accuracy is verified by using two different methods and also comparing our data with the available existing literature. The main goal is to study heat and mass transfer through unsteady squeezing plates by the influence of velocity slip and chemical reaction. The consequences of diverse pertinent parameters on fluid flow, thermal, and concentration fields have been explored in this study. With the rise in “velocity slip parameter” from 0 to 1, 81.37% decrease in skin friction coefficient, 15.81% increase in Nusselt number, and 29.13% increase in Sherwood number are observed. Rising values of the chemical reaction parameter from 0.3 to 0.5, the mass transfer coefficient increases by 66.94%.

Thermal enhancement remains a critical requirement in different engineering applications. Many factors can affect the efficiency of the techniques used for this aim. The purpose of this study is to investigate the impact of particle-fluid suspensions with heat transfer through porous annular-sector duct on enhancement techniques and address the potential application of deep learning to suspension problems. The analysis is focused on the fully developed region of the forced convection flow. Thermal and rheological properties of particle-fluid suspensions were studied using physics-informed neural networks exploiting transfer learning capabilities for making parameter analysis. Another finite element solution was introduced as a measure of accuracy and to support our findings. Results were prepared in a comparative manner for both solvers including contour plots, tabular, and two dimensional figures. The average Nusselt number and friction factors were calculated for different cases to investigate the value of the thermal performance factor. Our results indicate the downside of suspensions on thermal enhancement and their negative impact on other techniques.

In this article, an experiment has been carried out with heat pipe vacuum or evacuated tube collector to produce water from atmospheric air. In this experiment, the regeneration and adsorption method has been adopted, that is, water has been produced through the adsorption and regeneration of desiccants. The desiccant is heated through a hot surface to facilitate its regeneration. Limited experiments have been conducted to obtain water through the regeneration of desiccant using a hot surface. For the condensation of water vapor, a novel box has been designed, named the “novel-designed acrylic box.” The water is collected in a measuring flask or beaker to determine its quantity. Silica gel desiccant has been used for the adsorption and regeneration of water vapors. In this experiment, the adsorption process for silica gel was carried out in two different ways. In the first method, 1 kg of silica gel was scattered on the copper tray, that is, inside the system, while in the second method, 1 kg of silica gel was scattered on the paper, that is, outside of the system. In the first case silica gel adsorbed 137 g water vapor, and in the second case, it adsorbed 232 g water vapor. In the first case of adsorption, 70 mL water was produced while in the second case of adsorption, 175 mL water was produced from ambient air. The system's maximum efficiency was found to be 4.9%. Effects of various parameters, such as solar intensity, ambient temperature, wind speed, and so forth, have been studied.

In the presence of viscous dissipation and radiation effects, a numerical analysis is performed for an unsteady-free convective, radiative, chemically reactive, radiation absorption, viscous, incompressible, and electrically conducting fluid passing through an exponentially accelerating vertical porous plate. Numerical methods are used to solve the collection of nondimensional governing equations and their boundary conditions. Graphs are used to study the effects of different physical characteristics on flow quantities. Tables are used to study the differences in skin friction, the Sherwood number, and the Nusselt number for the physical interest. The analysis and explanation of the fluctuation in radiation and flow parameters on velocity and temperature gradient profiles through graphs using the Galerkin technique is the novelty of this work. For the magnetic, Prandtl, heat sink, radiation, Schmidt, and chemical reaction parameters, skin friction is significantly higher; however, for the Grashof, modified Grashof, permeability, radiation absorption, Dufour, and Soret numbers, skin friction has the opposite tendency.

The study aims to find the optimal fin length distribution for improved heat transfer during melting and solidification in a tubular phase change material (PCM) heat exchanger (HE) designed for heat storage. Three types of horizontal PCM tabular HEs, all with five longitudinal fins, were studied numerically. While maintaining a constant heat-transfer area, each model depicts a unique fin length distribution design. The first model, which serves as the reference design, has a uniform fin length distribution and each fin is 30 mm long. The second model has shorter upper and side fins and longer lower fins. The third model has long lower fins but shorter than that of the second model, with short side fins and no change in upper fin length with reference design. The findings indicate that the second model exhibits the best heat-transfer performance for the melting process, while the first model is most effective for solidification. Interestingly, the third design emerges as the optimum choice for both melting and solidification processes, where for 1 h of melting operation, results obtained 87%, 92%, and 90% for three models, respectively, from the first uniform model to the third model. While for 2 h of solidification the result obtained 11%, 17%, and 13% liquid fraction for the three models, respectively.

The aim of the study is to measure the Dufour number effects on the flow patterns and heat transfer in an exponentially accelerated infinite vertical plate embedded in a porous medium in the presence of heat source and chemical reaction. Time-dependent variations in temperature, velocity, and other factors should be taken into consideration due to the flow's unsteadiness. The fluid considered is a gray, absorbing/emitting radiation but nonscattering medium. Using the finite element method, a set of nondimensionless equations is solved analytically. Results are discussed graphically for concentration, temperature, and velocity profiles. Skin friction, Sherwood number, and Nusselt number are also explained for flow parameters through graphs.