Heat Transfer最新文献

During the Stelmor air-cooling process, the temperature distribution has a significant impact on the wire loops' final mechanical properties. The temperature distribution during the air-cooling process is accurately solved by establishing three-dimensional model and numerical simulations. The heat transfer coefficient at the highly dense region is much smaller than that of wire loops at the low dense region, and changes periodically over time, according to a computational fluid dynamics simulation method. It is also found that the heat transfer coefficient on the cross-section of the wire loop is very different, with a difference of 70–100 W/m² K. Finally, the finite difference method is used to calculate the mathematical model of the temperature distribution during the Stelmor air-cooling process. Comparing the results with the measurement data, the simulation results and measurement data match up well.

The researchers explored the free convective flow of a hybrid nanofluid in a vertical microchannel with a rectangular cross-section. Notably, both channel walls were heated alternately, and a transverse magnetic field was applied across the channel. The channel walls had unique properties, one of which was nonslip and the other was exceedingly hydrophobic. The major purpose was to investigate the effects of magnetism and superhydrophobicity on important flow parameters. The differential equations in the investigation were solved, producing accurate results. The study yielded some significant discoveries. First, when heated, the magnetic parameter reduced skin friction on both sides. Second, in both heating conditions, the magnetic field reduced flow rate and velocity. The flow rates in the two reported situations were similar at a crucial temperature jump coefficient. Furthermore, for low-temperature jump coefficients, heating the superhydrophobic side reduced the Nusselt number whereas heating the nonslip side had no magnetic effect. The percentage change in the value of Nusselt number and velocity decreases continuously with increase in nonlinear density variation with temperature (NDT) parameter and magnetic parameter. The percentage increases in the value of skin friction with increase in temperature jump and slip length but decrease in the percentage of skin friction for the effect of magnetic term and NDT parameter. As the NDT parameter increases, the velocity percentage rises to 50.59% when the superhydrophobic surface is heated and to 84.30% when the nonslip surface is heated. The temperature jump is statistically significant for the value of the Nusselt number and skin friction for the no-slip surface condition. These discoveries have practical consequences for the design and management of both tiny and large-scale systems, with possible applications in microfluidics, microelectronics, nanoscience, and nanotechnology.

A hybrid flat solar collector was manufactured from basic materials to combine the effects of both water and air solar heaters. The reason is to increase the amount of heat delivered to water by doubling the heat sources, one from the direct beam of sun and the other from the hot air delivered by the air solar heater. In addition, the flow of water inside the solar heater is made in a thin layer so that much heat can be gained by water per unit time. The outlet hot air of the solar air heater enters air ducts that pass through the solar water heater. With a constant water flowrate of 0.0167 kg/s, three different air velocities (1.7, 2.1, and 2.4 m/s) were applied to determine the optimum air velocity that results in the maximum outlet water temperature and the maximum removal factor FR for the solar water heater. The experiment was run from 10:00 a.m. to 2:00 p.m. every day during June 2023 and the data was recorded every 15 min. The data obtained from the experiment showed that the lowest air speed (1.7 m/s) results in the highest outlet water temperature (63°C) and heat removal factor FR (0.74).

The current work is interested on investigating the impacts of thermal radiation, chemical reaction, and absorption radiation of a hydromagnetic convection-free mass and heat transfer flow in case of an electrically conducting fluid that passes through a vertical plate moving impulsively. The analytical solutions of the governing momentum, energy, and species concentration equations with the initial and boundary conditions are obtained by the Laplace transformation technique. Graphs for fluid characteristics are used to analyze the impact of changing parametric quantities such as M, N, Sc, Kc, Q, Gr, Gm, and t on the temperature, velocity, concentration, and Sherwood number. We derive the engineering curiosity expressions for the Nusselt number and stress, and at the end, we tabulate and discuss the consequences of new parameters. The magnetic field effect and the chemical reaction are seen to diminish the fluid velocity and concentration, respectively, but in contrast, the absorption radiation effect is seen to accelerate both velocity and temperature. It is closely studied that the Nusselt number and skin friction values for hydrogen consistently exceed those for carbon monoxide.

In this paper, the impact of nanolayer which shows the relationship between the nanoparticle and pure fluid is investigated on the fluid transport and thermal transfer through a rotating system. The nanolayer shows the relationship between the nanoparticle and base liquid, signifying a higher thermal conductivity than the nanoparticle and lower conductivity than the base fluid. Also, the effect of larger nanoparticle size and volume on fluid thermal distribution is considered. The nanoparticle raises the fluid thermal conductivity with the aim of conserving thermal transfer during fluid transport, consequently saving energy. The mechanics of the fluid is developed using a higher-order coupled system of nonlinear models, solved with the aid of the Homotopy perturbation method. Obtained results from the analysis show the impact of nanolayer expansion on thermal distribution increases boundary layer thickness. Also, the size of the nanoparticle when varied from 10 to 40 nm shows a heat transfer increase of 17.02% at the center of the disk. Particle size increase indicates temperature rise as nanolayer size encompassing the nanoparticle increases. Obtained results when compared against literature give good agreement. The study finds useful applications in coolant and lubricant processing amongst other practical applications.

The cooling and heating sector is responsible for the highest energy consumption in the building sector, comprising approximately 30% of the total. Extensive research has been conducted to address this issue and minimize energy consumption through the implementation of innovative technologies. Among these technologies, the passive earth-air heat exchanger (EAHE) has proven highly effective in reducing energy usage in the cooling and heating sector. This research focused on optimizing U-shaped EAHE systems and examined their functional and thermal-fluidic parameters through numerical analysis. The simulation employed COMSOL Multiphysics software, and the results obtained were in excellent agreement with experimental data. The study investigated a base case, as well as five optimized cases with varying inlet velocities, to evaluate performance. The findings revealed that increasing the working fluid's inlet velocity led to a decrease in the system's thermal efficiency. However, at higher velocities, the economic parameters for energy production showed improvements. Specifically, the system generated a maximum energy output of 9132 W in the fifth case, operating at a velocity of 2 m/s. Additionally, the system achieved an impressive performance coefficient of approximately 5.13 in the same case, with an inlet velocity of 0.46 m/s. Notably, the lowest recorded output temperature of the system was 22°C at the specified inlet velocity.

The onset of convective instability in an internally heated dielectric fluid-saturated porous layer under the influence of a uniform AC electric field for different types of boundary conditions is investigated. The flow in the porous medium is described by the Brinkman model with fluid viscosity different from effective viscosity. The lower adiabatic and the top with finite heat transfer coefficient to the external environment boundaries are considered to be either rigid or stress-free. The presence of a uniform volumetric heat source alters the conduction profile of the temperature field from linear to quadratic in the vertical coordinate. A modal linear stability analysis of the basic motionless state is carried out and the general regime of linear instability is investigated by solving the stability eigenvalue problem numerically using the Galerkin method of weighted residual technique. The neutral stability condition as well as the critical value of the thermal Rayleigh number is computed for rigid–rigid, free–free, and rigid–free boundaries for various values of governing parameters. It is seen that the nature of boundaries affect the stability of the system only quantitatively, though not qualitatively. The rigid–rigid boundaries offer a more stabilizing effect against convection in comparison with rigid–free and free–free boundaries. The study found that the effect of increasing thermal electric Rayleigh number and the Darcy number is to hasten the onset of instability, while the opposite trend is perceived with an increase in the ratio of viscosities and Biot number. The outcomes of this investigation are found to be in good agreement with past studies under the limiting cases.

Trombe wall serves as an effective passive heating element, and its performance is heavily reliant on local climate conditions. This study involved both experimental and numerical analyses of a full-scale test room equipped with a Trombe wall under Iraqi climate conditions. To facilitate this investigation, an experimental test room was constructed in Kirkuk city with dimensions of 4.0 m × 3.0 m × 2.75 m. In addition, a numerical simulation method based on computational fluid dynamics was developed and a computer code was created to investigate the performance of the system. The accuracy of the developed numerical approach was validated against experimental data collected from the test room. This analysis was conducted specifically for the period of February 17–18, which represents the coldest month of winter in the study area. The performance of the system was assessed with respect to various parameters; air gap width variations (2, 4, 6, and 10 cm), massive wall thickness ranging from 15 to 35 cm with 5 cm increments, channel width options (3, 5, 10, 15, and 20 cm), and vent heights ranging from 5 to 20 cm in 5 cm increments. Furthermore, an investigation of the impact of replacing the air in the air gap with inert gases, specifically argon, krypton, and a mixture of these gases with air was conducted, as well. The outcomes indicate that both the channel width and vent height do not have a significant impact on the system's performance. However, the width of the air gap has a modest effect on system performance, and the best performance was observed with a smaller gap width, specifically 2 cm. The most significant impact on room temperature is observed when the storage wall thickness is varied. In the case of wall thickness of 15 cm, there is a notably higher fluctuation in room temperature between the maximum and minimum values, reaching approximately 16°C. For a wall thickness of 35 cm, however, this fluctuation is significantly reduced to about 3°C. The system efficiency as determined after 24 h of operation period improved significantly when the air was replaced by an inert gases or a mixture of gases in the air gap. Compared to air, the increase in efficiency is about 14.8% for argon, 17.7% for krypton, and 20.6% for the mixture of gases.

Thermal performance modeling and performance prediction of a solar still which is single basin single slope (SBSS) for the typical climatic condition of India at Jalandhar (31.3260° N, 75.5762° E) is analyzed in the present work. A numerical investigation of an SBSS solar still is conducted during the month of June 2022 using the ANSYS Fluent 2021 computational fluid dynamics (CFD) package and artificial neural network (ANN) prediction model. A user define function is written and used in fluent to formulate the problem with 9-h solar radiation flux, on solar still glass surface. The simulation outcomes for surface temperature at three different water depths were compared with the existing experimental study. Water temperature and productivity of freshwater were well aligned with experimental results. Three-dimensional domain is used with a two-phase volume of fluid model for the condensation and evaporation processes in a solar still. The performance evaluation parameters, that is, coefficients of convective, evaporative, and radiative heat transfer, different temperature values, distillation output, and system efficiency were calculated numerically. The parametric analysis is expanded, and an ANN model in MATLAB R2020a is utilized to estimate yearly performance and reduce the high computational cost of numerical analysis. The data for solar radiation, design, and operational parameters are fed into the ANN model, and as a result, the water temperature at various depths is computed. The ANN model was trained using numerical results computed for the month of June and tested, showing 99.7% accuracy with CFD results. The annual performance of the solar still was evaluated using ANN models for 9 h of the day and with different boundary conditions. To decrease computational and experimental costs, the recommended technique of combined CFD and ANN models for computing the annual performance of (SBSS) solar still is the most effective option.

In this study, we have investigated magnetohydrodynamic Couette flow across a deformable porous regime with entropy generation having equal suction and injection velocities. The aim of this work is to analyze the novel impact of thermophoresis deposition, activation energy, and magnetic effect by considering viscosity and thermal conductivity as dependent on temperature in a deformable porous regime. The dimensional equations are turned into nonlinear ordinary differential equations (ODEs) through proper similarity variables. To solve these ODEs, we utilized the MATLAB bvp4c approach. Graphs are used to study the behavior of many physical parameters such as skin friction, Bejan number, velocity, displacement, entropy generation, concentration, and temperature. It is found that the viscosity parameter reduces the solid displacement, whereas it enhances the fluid concentration. Due to the impact of suction/injection and drag parameters, fluid velocity becomes reduced. The thermal conductivity parameter raises entropy generation and temperature, but it decays the Bejan number. The volume fraction parameter plays an interesting behavior in skin friction. Moreover, the current work is compared with prior research work while neglecting the newly introduced effects, and the results remain consistent.