Heat Transfer最新文献

Solar air heaters (SAHs) are widely used for drying vegetables and fruits or for domestic heating. Certain sizing parameters are necessary to obtain the right dimensions for the required air temperature, flow rate, and thus useful thermal energy. The well-known Hottel–Whillier–Bliss equation was used and made dimensionless by applying the collector longitudinal and transversal aspect ratios (r_l and r_t) of a double-glazed flat plate solar air heater (DG-FPSAH). The steady-state equations are solved to determine the average temperatures. Thereafter, one could calculate the overall loss heat coefficient and efficiency factor, obtained analytically. A Matlab code was developed to estimate primarily unknown temperatures, useful energy, and the Nusselt number. An iterative numerical method is used until convergence occurs. The inlet cross-sectional area and air flow velocity are defined as input data. The proposed sizing method depends on the output temperature required by the customer. This temperature can be determined from the plotted curves of the dimensionless ratios. Hence, the SAH-needed dimensions are determined graphically depending on the functional requirements for construction planning, such as technology choice, work breakdown, and budgeting. In the present case study, based on the input parameters, an airflow rate of 1.2 kg/s entering a DG-FPSAH with an output temperature of 41.5°C yields the dimensions of L_in = 3.824 m, W_in = 2.735 m, and H_in = 0.1825, specifying the collector length, width, and air duct height. The gathered energy and thermohydraulic efficiency are: Q_u = 7.91 kW, η_col = 0.752, respectively.

This article explores the utilization of a synthetic jet as an approach to cool microelectronic devices, addressing their thermal management needs. The study includes both experimental measurements and numerical simulations to gain a comprehensive understanding of the heat transfer characteristics and fluid flow patterns generated by the synthetic jet actuator. The average Nusselt number (Nu) of the synthetic jet impinging flow with the dimensionless separation distances of the orifice to the heated surface (H/D) is investigated at different Reynolds numbers. A dynamic mesh scheme is employed in performing the simulations of the fluid domain to showcase the diaphragm's vibration and its deformation over time. The velocity profiles exhibit that the synthetic jet flow prompts the formation of two countervortices during every vibrating cycle of the diaphragm. The experimental results align closely with the predicted outcomes, indicating that the synthetic jet significantly enhances heat transfer by 3.1 times relative to the natural convection in the case of (H/D = 8.4) across different Reynolds numbers while maintaining low power consumption, a compact size, and a noise-free operation.

Heat exchanger research is mainly exploited to develop and optimize new engineering systems with high thermal efficiency. Passive methods based on nanofluids, fins, wavy walls, and the porous medium are the most attractive ways to achieve this goal. This investigation focuses on heat transfer and entropy production in a nanofluid laminar flow inside a plate corrugated channel (PCC). The channel geometry comprises three sections, partially filled with a porous layer located at the intermediate corrugate channel section. The physical modeling is based on the laminar, two-dimensional Darcy–Brinkman–Forchheimer formulation for nanofluid flow and the local thermal equilibrium model for the heat equation, including the viscous dissipation term. Numerical solutions were obtained using ANSYS Fluent software based on the finite volume technique and the appropriate meshed geometries. The numerical results are validated with theoretical, numerical, and experimental studies. The simulations are performed for CuO–water nanofluid and AISI 304 porous medium. The coupled effects of porous layer thickness (δ), Reynolds number (Re), and nanoparticle fraction (φ) on velocity, streamlines, isotherm contours, Nusselt number (Nu), and entropy generation (S) are analyzed and illustrated. The simulation results demonstrate that heat transfer enhancement in clear PCC can be achieved using a porous layer insert. For the porous thickness range of [0.1–0.6], the corresponding range of average Nusselt number increase is [35.7%–176.9%], and the average entropy generation is [105.4%–771.9%]. The effect of the Reynolds number is more important in a porous duct than in a clear one. For δ = 0.4 and φ = 5%, the increase of Re in the range of [200–500] induces an increase in average Nusselt number in the range of [80.9%–108.4%] and average entropy in [222.9%–309.1%] comparatively to clear PCC. The effect of φ is practically the same for porous and clear channels. For φ = 5%, the increase on average Nu is about 9%, and entropy generation is 5%. Accordingly, important improvements in heat transfer in PCC can be achieved through the combined effect of flow Reynolds number and porous layer thickness.

This study analyzes the heat and mass transfer of magnetohydrodynamic flow past an accelerated vertical plate along with exponentially decaying wall temperature and exponential mass diffusion, in which thermal and mass stratification was considered. The governing equations are solved by employing the Laplace transform method, and graphs are produced by implementing MATLAB software. The impacts of both stratifications on various parameters involved in our studies were investigated with the help of graphs. Graphs were used to display the effects of various parameters on velocity, temperature, concentration, skin friction, Nusselt number, and Sherwood number. We consider both the cases, that is, with and without stratification to study the effects of thermal and mass stratification. By evaluating the results of thermal stratification with an unstratified environment, the study comes to an important conclusion. It is seen that the Steady state is reached quickly with the combined effect of both stratifications. It is also discovered that the velocity steadily reduced as the magnetic field parameter increased. This research has many applications in understanding the fluid flow in engineering and technology fields, such as geophysics, astrophysics, and fluid engineering difficulties.

Usually, suction/blowing is used to control the channel's fluid flow, which is why this worth-noting effect is considered. The fluid velocity is considered along the x-axis due to the oscillations of the right plate. The thermal effect on the flow due to the heated right plate is also considered. The fluid and dust particles have complex velocities due to the rotation, which are the sum of primary and secondary velocities. To convert the aforementioned physical phenomenon into mathematical form, partial differential equations are used for modeling the subject flow regime. Appropriate nondimensional variables are employed to nondimensionalize the system of governing equations. With the assistance of assumed periodic solutions, the system of partial differential equations is reduced to a system of ordinary differential equations which is then solved by the perturb solution utilizing Poincare–Lighthill perturbation techniques. The engineering interest quantities, the Nusselt number, and skin friction are also determined. The impact of various parameters on skin friction, viscoelastic fluid, and dust particle velocity profiles is also investigated. It is worth mentioning that suction controls the boundary layer to grow unexpectedly, even in the resonance case. The obtained solution is also valid in the case of injection. The radiation parameter, Grashof number, and second-grade parameter cause a decrease in skin friction as their values increase. On the other hand, the suction, rotation, magnetic, dusty fluid, and Reynolds numbers cause a rise in skin friction.

Solving the inverse problems of heat conduction often requires performing a very large number of Green's function evaluations. This paper addresses the calculation of Green's functions in anisotropic curved media, such as composite lamina, where the principal axes of thermal conductivity follow the curved surface. We start with established exact series solutions for cylindrical convex and concave shapes. These solutions are extended to accommodate geometries of real-world composite materials that do not form a closed surface like a cylinder. Unfortunately, the exact solutions have the form of an infinite series of sums or integrals and are computationally infeasible for the inverse problems of interest, especially for large radii of curvature. This motivates a perturbation solution that is accurate and computationally efficient at large radii of curvature. In addition, it motivates a phenomenological approximation that is extremely computationally efficient over a broad range of curvatures, but with some sacrifice in accuracy. These solutions are compared with exact solutions, with each other, and with numerical finite difference calculation. We identify regions in parameter space where the different approaches are preferable and where they lead to the same numerical result.

This study investigates the heat and mass transfer dynamics in exothermic, chemically reactive fluids over variable-thickness surfaces using advanced numerical methods and artificial neural networks (ANN). The importance of understanding these processes lies in their significant industrial applications, such as in chemical reactors and heat exchangers. We transformed nonlinear partial differential equations into ordinary differential equations and used the bvp4c numerical method to generate a comprehensive data set. The ANN model, trained with the Levenberg–Marquardt algorithm, was evaluated for its accuracy in simulating complex fluid dynamics and thermosolutal transport phenomena. Our results revealed that increasing the second-grade fluid parameter $��\; ��{\alpha }_1��$ enhanced skin friction by 20.38%, heat transfer rate by 1.16%, and mass transfer rate by 4.06%. The ANN model demonstrated high predictive precision with a validation mean squared error of $��\; ��1.145�\; �\times �\; �{10}^{�-�\; �9�}��$. These findings highlight the effectiveness of the ANN methodology in providing precise simulations of fluid dynamics, which is crucial for optimizing industrial processes.

The thermosyphon heat exchanger contributes significantly to the improvement of energy conservation technology and has been used in multiple applications, raising the possibility of further studies to contribute to increasing the efficiency of heat pipes. This experimental study examines the different filling ratios of pure Acetone liquid inside a WHPHE integrated with the double-effect of evaporative cooling to improve the energy-saving technology. This work studies changing the filling ratio of pure acetone working fluid to investigate the effect of the filling ratio on heat exchanger performance in waste energy recovery technology. The heat exchanger was used with four rows and five tubes per row arranged in a staggered manner. The filling ratio of acetone inside the heat pipe was changed from 50% to 100%. The effect of the mass flow rate of air flowing in direct evaporative cooling on energy conservation technology was studied while the mass flow rate of air through indirect cooling remains constant in addition to the effect of ambient temperature. The results showed that the best filling percentage was between 80% at different temperatures, and the highest energy recovery percentage was when it was at the filling percentage of 80% in the presence of evaporative cooling.

This study introduces a new analytical framework that employs the image-well method to simulate the spatial and temporal temperature distribution in vertical borehole thermal energy storage (BTES) systems. The model accommodates complex boundary shapes and conditions, including insulation, convection, and constant temperature, without requiring iterative solutions at each time step. The model's accuracy and utility are demonstrated through an application to a borehole heat exchanger cluster arranged in an octagonal shape with insulating boundaries, based on a BTES site in Drake Landing (Canada). Model predictions are validated against a finite element model, showing a root-mean-square error of 0.012°C. A global sensitivity analysis highlights the influence of thermal parameters on system performance, identifying the heat flux of the borehole heat exchanger as the most sensitive parameter. Overall, this approach combines the advantages of analytical and numerical techniques to provide a clear and efficient tool for evaluating BTES systems, offering significant potential for advancing sustainable energy solutions.

We consider heat transfer with convection and radiation effect on a longitudinal wet and porous fin. The trapezoidal fin moving at a constant speed is subject to stretching and shrinking, and their influence on the fin's heat transfer rate and thermal distribution is investigated. The governing equation of the model mentioned above is nondimensionalized, and the resultant second-order nonlinear boundary value problem is solved numerically using the Chebyshev collocation method and validated using the shooting technique. All the simulations are carried out using MATLAB software. The impact of the critical dimensionless parameters on the fin tip temperature, the thermal profile, and the base heat transfer rate are analyzed graphically. Fin efficiency is also computed, and the influence of the pertinent parameters on it is inferred. For a moving fin, the shrinking mechanism favors a faster base heat transfer, an uptick of about 9%, and the stretching fin enhances thermal distribution and efficiency by around 3% and 14%, respectively. The rise is further accelerated with the enhancement of the Peclet number. The fin tapering from that of a rectangular profile ($��\; ��C�\; �=�\; �0��$) helps achieve a faster heat transfer rate along the fin length, a gain of nearly 22%, when the fin taper ratio $��\; ��C��$ varies from 0 to 0.8.