Heat Transfer最新文献

Fins are extended surfaces that are designed to dissipate heat from hot sources to their surroundings. The different profiles of fins are used on the equipment surface to improve heat transfer. Fins are extensively used in refrigeration, solar panels, superheaters, electric equipment, automobile parts, combustion engines, and electrical equipment. On the basis of these applications, we study the thermal performances of magnetized convective–radiative-rectangular fins with magnetized trapezoidal fins with internal heat generation. The shooting technique is used to numerically study the suggested model. It is revealed that magnetized trapezoidal fins transfer more heat than magnetized rectangular fins. It is also revealed that magnetized trapezoidal fins have higher thermal transfer competence than magnetized rectangular fins. When thermal conductivity, radiation–conduction number, and convection–conduction number increase, the fin's efficiency increases. In addition, a Hartmann number indicating the magnetic effect is found to improve heat transfer from the fins. Increasing the magnetism parameter from 0.1 to 0.3 reduced temperature by approximately 4.5%, changing internal heat generation from 0.1 to 0.5 increased temperature distribution by approximately 16%, and changing the Peclet number from 0.1 to 0.3 increased temperature distribution by approximately 15%. The effect of heat transfer coefficient, thermal radiation–conduction and convection–conduction, and dimensionless radiation are also investigated on the performance of the fins.

The onset of thermal convection in an incompressible Oldroydian fluid-saturating porous media is examined to study the combined impact of uniform rotation and temperature-dependent viscosity. A characteristic equation from the basic hydrodynamic equations governing the Brinkman–Oldroyd model is derived using linear stability theory and modified Boussinesq approximation. For various combinations of stress-free and slip-free boundaries, the expressions for the Darcy–Rayleigh numbers for both non-oscillatory as well as oscillatory convection with linear and exponential temperature-dependent viscosity are derived, using the “weighted residual method.” The effects of rotation, variable viscosity parameter, strain retardation and stress relaxation time parameters and other fluid parameters on non-oscillatory and oscillatory convection are investigated numerically and the results are presented graphically. From the analysis, it is found that overstability is the preferred mode of onset of convection. The rotation, the coefficient of specific heat variations (due to temperature variation), and the strain retardation time have a stabilizing influence on the stability of the system, whereas the stress relaxation imparts a destabilizing effect. Additionally, it is noticed that the variable viscosity parameter and Brinkman-Darcy number stabilize the system for each set of boundary conditions.

The paper investigates the effects of the Forchheimer term (form drag) and vertical pressure gradient on the buoyancy-induced instability of power-law saturating fluid in a porous plane medium. Two isobaric permeable layers are assumed to sandwich the horizontal porous plane. In the meantime, Dirichlet and Neumann equations are the thermal boundary conditions considered for the lower and upper layers. A base flow developed analytically via the governing equations is just in function of the Péclet number $��P�$, with no dependence on the characteristic parameter of the power law fluid. A linear stability analysis consists of substituting a base flow with a small perturbation into the governing equations leads to a four-order eigenvalue problem. An analytical solution is performed for the asymptotic cases of an infinite wavelength. The Runge–Kutta solver is applied together with the shooting technique to evaluate numerical solutions for the general case of nonnegligible wave numbers. Among the findings is the contribution of the Forchheimer term in the variation of the threshold Péclet number whose value can switch the wave numbers from zero to nonzero and increase the stability of the system.

The purpose of this paper is to investigate the effects of Soret, thermal radiation, and chemical reaction on an unsteady magnetohydrodynamic free convective flow past an impulsively initiated semi-infinite vertical plate with heat sink under parabolic ramped temperature and parabolic ramped concentration. Using some nondimensional parameters, the flow boundary equations in this case are first converted to dimensionless equations. The closed-form Laplace transform technique is employed here to solve the partial differential equations and get the solutions for fluid velocity, temperature, and concentration. The velocity, temperature, and concentration of the fluid tend to vary with the effect of various flow factors. These changes are graphically represented and analyzed. Differences in skin friction, Nusselt number, and Sherwood number for the different relevant parameters are also recorded. The Soret number hikes the fluid velocity and concentration. The rate of heat transfer, mass transfer, and momentum transfer improves due to the application of parabolic ramped conditions.

The dispersion of solid particles in a viscous fluid leads to a two-phase flow nature. The present study incorporates the time-dependent three-dimensional dusty fluid flow generated by a periodically oscillatory rotating disk. The disk is stretchable along the radial axis with time-based sinusoidal fluctuations. The governing incompressible flow equations for two-phase equilibrium are normalized in the form of similarity systems consisting of the fluid stage and dust phase. The whole normalized system reduces to the familiar Von Kármán similarity system for the flow configuration of rotating disk by removing the dust phase and periodic oscillations of the disk. The two-phase flow model is then numerically solved by a built-in method namely “pdsolve” in Maple built program. The graphical aspects of the obtained physical parameters on velocity and thermal fields of the dust particle stage are investigated to show how the oscillatory disk contributes to the dusty flow features. The wall shears and thermal rates of the fluid and dust particles are also calculated in limiting case of disk rotation. It is observed that in time-based flow, the oscillatory profiles preserve a phase shifting phenomenon. For centrifugal forces, the particle cloud moves away from the surface along a tangential direction. The thermal field is reduced by the dust particle stages.

Accurate evaluation of the wind convection heat transfer coefficient (h_w) for solar-based systems is essential, especially for solar desalination systems. Thermal behavior and productivity of solar stills are highly affected by the external heat loss through the glass cover. This paper describes a new experimental approach to estimate the h_w on the glass cover of the conventional single-slope solar distiller (CSS). Indoor experiments have been conducted under steady-state conditions for a wind speed between 0 and 3 m/s. The h_w has been evaluated through an energy balance performed on the distiller's glass cover. The results showed that increasing the wind speed increases the hw (from 5.64 to 31.57 W/m² K) and enhances the distillation rate (from 5.28 to 7.61 mL/min). A new relationship for the h_w was proposed for the CSS and compared with the experimental data available in the literature. The comparison shows that the obtained results are close to the data from solar systems, with a deviation ranging from 27.4% to 37%. However, a significant deviation was obtained with earlier models derived from flat plates (from 29.5% to 59%).

Solar dryers have been tested with various simple and complex design modifications for better efficiencies. This article attempts to investigate the effect of a very simple design modification on the no-load performance of a natural convection domestic solar dryer (NCDSD). A direct-type domestic solar dryer has been developed with an air cavity surrounding the drying chamber. To compare the effect of air cavity, a domestic solar dryer without air cavity has also been developed and both the dryers were tested simultaneously under the climate of Hisar, India. The values of thermal efficiency were calculated along with convective heat transfer coefficient from absorber plate to the drying air. Both the dryers were also analyzed by developing finite element models in COMSOL multiphysics computer software. The no-load thermal efficiency for the domestic solar dryer without and with air cavity was found to be 22.68% and 34.08%, respectively. The values of coefficient of correlation for modeled and actual drying tray temperatures for dryer without and with air cavity were 0.980466 and 0.9833917, respectively. The proposed finite element model would be helpful in the design and development of NCDSDs.

This paper investigates the heat and mass transfer under magnetohydrodynamic mixed convection flow of a binary gas mixture in a four-sided lid-driven square cavity. The enclosure's left wall is sinusoidally heated and acts as a source term, while the right wall functions as a sink. The cavity's horizontal walls are adiabatic and impermeable to mass transfer. The governing equations under Boussinesq approximation and stream function-vorticity formulation are solved using the alternating-direction-implicit scheme, a finite-difference method. The numerical scheme's consistency and stability are demonstrated using the matrix method. The MATLAB code is written, validated against some existing studies, and used to perform numerical simulations. The numerical solutions are graphically examined by visualizing the streamline, isotherm, and concentration contours for nondimensional parameters, such as Hartmann number $���\left(�\; ��0�\; �\le �\; �H�\; �a�\; �\le �\; �100��\; �\right)��$, heat absorption or generation coefficient $���\left(�\; ��-�\; �2�\; �\le �\; �\varphi �\; �\le �\; �2��\; �\right)��$, Richardson number $���(�\; ��0.01�\; �\le �\; �R�\; �i�\; �\le �\; �100��$

The improvement of the cooling performance of liquid-cooled microchannel heat sinks used for densely packed electronic circuits is sorted via passive techniques like tuning substrate or coolant properties. We propose a design for enhancing heat sink performance by simulataneously modifying the channel geometry and tuning the fluid rheology. By modeling the coolant as a power law fluid, its rheological behavior is varied ranging from shear-thinning to shear-thickening, alongside Newtonian fluid. We introduced tapering to the middle wall that separates the bottom and top channels of a double layered microchannel heat sink (DL-MCHS), causing both channels to converge. This convergence not only increases the flow velocity within the downstream microchannel but also reduces the apparent viscosity of the shear-thinning fluid being subjected to shear, resulting in enhanced thermal and hydraulic performance. We analyze the results from both the first and the second law of thermodynamics context, demonstrating that a tapered DL-MCHS with shear-thinning fluid outperforms a straight partition wall DL-MCHS with Newtonian coolant. However, we also discovered that extreme tapering compromises thermodynamic viability, but by fine-tuning the extent of tapering, we inferred that a DL-MCHS with shear-thinning fluid can become viable with little compromise in the thermal performance.

The rated temperature and its uniformity of lithium-ion (Li-ion) battery (LIB) pack are the main demands for safe and efficient operation. This paper investigates an air cooling system of a pack of five prismatic LIB's generating considerable heat through discharging energy. The cooling system is a three-dimensional channel with flexible baffles of different arrangements installed on the walls of the channel to lower and regulate the temperature of the batteries. Three arrangements of these baffles are studied, transverse; L-shaped and staggered. The study is formulated as turbulent fluid–structure interaction and solved numerically using the finite elements method. The study was conducted for five spaces between batteries, S = 0, 1, 2, 3 and 4 mm and three different inlet air velocities, U_in = 0.5, 1 and 2 m/s. It was found that the flexible baffles guide the coolant towards the batteries smoothly with less pressure drop and this significantly improves the performance of the battery thermal management system due to the reduction of the maximum temperature and temperature variation as well. The staggered arrangement of the baffles shows the most effective configuration, where the maximum temperature difference between batteries is only 1.85°C for S = 1 mm and U_in = 2 m/s.