Heat Transfer最新文献

This study optimizes the main parameters of the cold-side heat exchanger (CHE) longitudinal fin, including fin quantity (N_f), fin thickness (T_f), and fin height (H_f), to enhance the performance of motorcycle exhaust thermoelectric generator units (TGUs) utilizing the computational fluid dynamics approach. The investigation shows that these parameters significantly affect the dissipation area of the CHE heat and the outside air velocity distribution in fin gaps, resulting in the fluctuation of TGU output power. The output power increases with respect to H_f; nevertheless, it first increases as N_f and T_f increase but decreases dramatically when N_f or T_f becomes too large. Besides, H_f significantly affects output power, and its impact is almost independent of T_f and N_f, and vice versa; meanwhile, T_f and N_f have a strong relation. This study proposes two H_f of 40 and 60 mm along with the optimal T_f of 1 mm and N_f of 29, providing significantly high output power, low weight, and compact size for TGU. This work contributes insight into the effect of CHE parameters on the TGU performance, and it is a crucial case study for selecting suitable heat sink parameters for TGU, considering practical requirements and conditions.

The onset of convection in a horizontal porous layer with chemical reaction and local thermal nonequilibrium is investigated. The nondimensional governing equations have been solved using the normal mode technique, which results in an eigenvalue problem. The analytical expressions for both stationary and oscillatory Rayleigh numbers are obtained. The effect of different parameters has been investigated and presented. The amplitude equation is derived using weakly nonlinear theory. Nusselt number is calculated using an amplitude equation to investigate heat transport. When modeling a fluid-saturated porous medium, previous research on double-diffusive convection has uniformly operated under the assumption of local thermal equilibrium (LTE) between the fluid and solid phases at all points within the medium. This standard practice assumes a minimal temperature gradient between the phases at any given location. However, in practical scenarios involving high-speed flows or significant temperature differentials between the fluid and solid phases, the LTE assumption proves insufficient.

Water shows a strong tendency to absorb the energy of wavelengths of 3 and 6 µm, which are in the infrared (IR) range. Therefore, IR dryers are used to dry food and fruits that have a high-water content. Thus, modeling and optimizing energy and exergy parameters of terebinth drying in an IR–rotary drum (RD) dryer were evaluated using the response surface methodology. Independent factors included IR power and rotary rotation speed, and response factors were specific energy consumption (SEC), energy efficiency (EFF), exergy efficiency (EXEFF), specific exergy loss (EXLOSS), and exergy improvement potential (EIP). According to the obtained results, the range of EFF and EXEFF was between 28.93%–9.11% and 0.88%–6.62%, respectively. As IR power and RD speed increased, SEC (123.75–39.21 MJ/kg), EXLOSS (3.97–2.97 MJ/kg), and EIP (3.62–1.009 MJ/kg) decreased, while EFF and EXEFF increased. The results obtained in this study showed that the optimal IR drying power is 616.39 W, and the optimal rotary rotation speed is 13.46 rpm.

In many heat transfer applications, the design of the flow field should warrant high heat transfer rates and, meanwhile, reduce the thermal stresses so that hot spots along the heat transfer surface be avoided. A combination of multiple jets impinging on a channel bed together with the surface covered by a porous layer is proposed to satisfy both objectives in the current study. A three-dimensional numerical simulation using a finite volume method with the second-order discretization has been applied to visualize the multiple-impinging jet flow behavior. The impacts of the porous medium parameters, including the thickness, permeability, and porosity, on the magnitude and distribution of the heat transfer along the channel bed have been evaluated. It is shown that the overall heat transfer performance of the proposed flow is significantly improved in comparison with the conventional case of the fluid flowing parallel to the channel bed. The presence of the porous layer leads to a more even spread of the fluid on the target surface, which reduces the thermal stresses and prevents the large differences between the highest and lowest values of heat transfer coefficients. They also found that both the porosity and particularly the permeability of the porous layer enhance the effect of the crossflow along the flow associated with the multiple-impinging jet setup. For a certain thickness of the porous layer, it is possible to reduce the amplitude of the Nusselt number oscillations effectively, while keeping the overall Nusselt number desirably high.

Solar energy could be used to generate both electricity and heat with the aid of photovoltaic thermal (PV/T) systems. Although the systems have a variety of advantages, they nevertheless hold a significant constraint. The system suffers a susceptible constraint wherein the photovoltaic (PV) module experiences an increase in temperature due to exposure to solar irradiation. The integration of a cooling system is necessary to enhance its operational efficiency. A novel approach, known as the reversed circular flow jet impingement (RCFJI), was proposed as a means to improve the performance of a PV/T collector. The current work seeks to assess the thermohydraulic and electrohydraulic performance of the RCFJI PV/T collector. The experiment was conducted under an irradiance level of 500–900 W/m². From the result obtained, the thermohydraulic efficiency reached its maximum value of 59.20% under 900 W/m² at 0.14 kg/s. Conversely, the electrohydraulic efficiency attained the highest reading of 10.91% under 500 W/m² at 0.13 kg/s. It was concluded that a higher flow rate reduces the friction coefficient while increasing the pressure drop. The thermohydraulic and electrohydraulic analyses emphasize the importance of assessing the friction coefficient and pressure drop to attain optimal performance. This study addresses the lack of research by presenting a new cooling approach that utilizes jet impingement. In addition, this study provides an understanding of the thermohydraulic and electrohydraulic performance of a RCFJI PV/T collector.

The current research work involves the design and performance assessment of a solar still, which is a conventional single-slope basin-type solar still (CSSBTSS) and a modified single-slope basin-type solar still (MSSBTSS) under the meteorological conditions of Solan city, Himachal Pradesh, India (30.90° N, 77.09° E). The individual and the combined effect of different sample quantities of sensible Himalayan Rambaan fibers (HRFs) and mass of latent paraffin wax (PW) A48 on the performance of MSSBTSS is evaluated and compared with CSSBTSS. The use of HRF material enhanced the evaporation rate significantly and improved the daytime distillates. Besides, different masses of latent PW filled inside the aluminum tubes improved the nocturnal distillates. For the analysis, three cases have been considered which are, namely: Case 1, solar still with sensible HRFs (MSSBTSS-HRF); Case 2, solar still with latent PW A48 (MSSBTSS-PW); and Case 3, solar still with sensible and latent material (MSSBTSS-HRF-PW). The results showed that the maximum thermal efficiency for Cases 1 and 2 was improved by 30.02% and 42.41% with five sample quantities of HRF material and 5000 g of PW. For Case 3, the maximum energy efficiency was 90.71% with a gain of 45.16% over CSSBTSS. The economic analysis concluded that the cost per liter of distillate yield produced using MSSBTSS-HRF-PW and CSSBTSS is ₹1.5 and ₹1.6, respectively. These outcomes showed the great potential of MSSBTSS-HRF-PW approach towards enhancing the overall performance and cost-effectiveness of solar still.

This study conducts a computational analysis to explore how magnetic fields, radiation, heat, and mass transfer collectively influence a horizontal stretching sheet within a porous medium. The research focuses on elucidating the dynamics of thin film flow through the formulation of time-dependent equations and subsequent transformation of fluid flow equations into ordinary differential equations via similarity transformation. The numerical solution is attained employing the Runge–Kutta fourth-order method coupled with a shooting technique. MATLAB software is utilized to generate graphs and numerical values, offering a detailed representation of engineering-relevant physical quantities in tabular form. The investigation revealed notable trends associated with varying parameters. Increasing unsteadiness parameters lead to a reduction in velocity, temperature, and concentration fields, while the temperature distribution demonstrates a positive correlation with radiation parameters. Moreover, elevated Prandtl numbers and unsteadiness parameters correspond to augmented heat and mass flux, respectively. Of particular significance is the observed heightened heat transfer rate during the transition from a Prandtl number of 1 (representing air) to 2 (representing oil), alongside an increased mass transfer rate with the escalation in Schmidt number from 0.62 (representing hydrogen) to 0.78 (representing ammonia). A comparative analysis of the numerical findings with existing literature demonstrates excellent agreement, affirming the validity and relevance of the present study. These insights offer valuable implications for understanding and optimizing heat and mass transfer processes in porous media, with potential applications in various engineering and scientific domains.

This study investigates the fluid flow, heat, and mass transfer phenomena within a vertical channel containing two immiscible fluids, with a particular focus on slip effects. These effects include no slip, velocity slip, thermal slip, and multiple slips, each analyzed with appropriate boundary conditions. The study thoroughly examines key characteristics, such as variations in thermal conductivity and viscosity. Using a sixth-order Runge–Kutta numerical method implemented using Mathematica, the study achieves precise solutions for complex scenarios. The detailed results show how the various slip mechanisms and relevant parameters interact with each other in complex ways. These findings are useful for both theoretical understanding and application in real-life engineering situations. This study also gives important information about how fluid flow, heat transfer, and mass transfer change under different slip effects. It looks at these effects and shows how they change visually. It also carefully calculates and analyzes engineering parameters like the Nusselt number, shear stress, and Sherwood number using bar charts, showing how they affect and behave. The study resulted in velocity slip having a minimal impact on temperature, whereas thermal slip resulted in higher temperatures. Both velocity and thermal slip conditions simultaneously result in the lowest temperatures.