Heat Transfer最新文献

This study explores the dynamics of unsteady magnetohydrodynamics (MHD) parabolic flow along an infinite vertical plate, emphasizing the effects of thermal and mass stratification in a porous medium subjected to periodic temperature variation and exponential mass diffusion. Utilizing the Laplace transform technique to obtain precise solutions, this study effectively integrates the impacts of both thermal and mass stratification without dependence on approximations. The main goal is to assess how thermal and mass stratification impact MHD flow dynamics, temperature, and concentration profiles under varying conditions. The study provides a thorough comparison of these findings with traditional nonstratified scenarios, presenting a comprehensive analysis of fluid behavior under diverse conditions. The conclusions reveal that thermal and mass stratifications considerably diminish velocity and stabilize temperature distributions, which suggests a damping influence on fluid movement and improved management of diffusion processes. Enhanced Grashof numbers improve heat and mass transfer efficiency, while magnetic and Darcy parameters significantly influence flow resistance and heat transfer characteristics. These conditions also result in higher Nusselt and Sherwood numbers, indicating increased efficiency in heat and mass transfer. In contrast, scenarios without stratification display higher velocities and more unstable temperature and concentration profiles. The findings highlight the critical role of stratification in improving fluid dynamics and increasing the efficiency of heat and mass transfer processes, offering valuable insights for engineering and environmental applications in similar conditions. The main novelty of the research is being the first to use the Laplace transform for exact solutions on combined thermal and mass stratification in MHD flows, enhancing prediction accuracy and process control.

This research paper details an experimental study on airflow dynamics in a solar air heater. The heater's design incorporates unique, discrete V-shaped ribs with staggered elements to enhance thermal performance. The study investigates the influence of various roughness parameters on flow characteristics. These parameters include a relative coarseness pitch (P/e) ratio of 12, a rib inclination angle (α) of 60°, a relative coarseness height (e/D_h) of 0.043, and a staggered element arrangement with a positioning ratio (p′/P) of 0.65. Additionally, the investigation includes scenarios with three gaps (N_g) between elements and a gap-to-rib width (g/e) ratio of 4. The research focuses on how changes to the Reynolds number, ranging from 3000 to 14,000, and alterations to the ratio of staggered element positioning to rib height (r/e), from 2 to 5, impact the flow dynamics. The outcomes indicate a significant boost in heat transfer performance, with the Nusselt number rising to 3.76 compared with a conventional smooth duct. The highest thermal efficiency recorded was 86%, at an r/e ratio of 3.5. These results underscore the potential of using discrete V-ribs with staggered elements in rectangular ducts to improve heat transfer efficiency.

Electric vehicles encounter significant challenges in colder climates due to reduced battery efficiency at low temperatures and increased electricity demand for cabin heating, which impacts vehicle propulsion. This study aims to address these challenges by implementing a thermal management system utilizing Phase Change Materials (PCMs) and validating the performance of a Multilayer Perceptron (MLP) model in predicting PCMs behavior and battery temperature distributions. The study employs an MLP model trained with 160 samples of diverse heat inputs, including pulsating, constant, wiener, discharging, and random temperatures. The model uses these temperatures as inputs and liquid fractions as target values. Performance evaluation is conducted using the MATLAB platform and is benchmarked against existing approaches, such as Long Short-term Memory (LSTM), spatiotemporal convolutional neural network (CNN), and pooled CNN-LSTM. The MLP model's accuracy in predicting PCMs phase transitions is validated by comparing predicted liquid fractions with numerically obtained values. Additionally, this study forecasts temperature distributions within a standard battery pack under various discharge scenarios, considering the performance of commercial lithium-ion batteries. The proposed MLP model demonstrates high efficacy, achieving a correlation of up to 0.999 and root mean squared error below 0.013 compared with numerical results.

Enhancement of “heat transfer” using “nanofluid” has diverse potential applications in heat exchangers, thermal management of electric devices, cooling of tractors, solar thermal systems, manufacturing of paper, and many others. Hence, the aim of the current investigation is to explore the impacts of “mixed convection” on “nanofluid flow” over a permeable rotating disk, which is stretched radially in a porous medium. Variable wall “temperature” and “convective boundary conditions” are also considered here. This makes the present investigation different from others. The suitable “similarity transformations” are imposed to alter the governing partial differential equations into a set of coupled ordinary differential equations (ODEs). Then, these ODEs are solved numerically by the “4th order Runge-Kutta method” using the “shooting technique” with the help of the bvp4c package in MATLAB software. The effects of fluid controlling “parameters” on “flow and thermal fields” as well as “skin friction coefficient” and “Nusselt number” are presented graphically and explained physically. Due to enhanced rotation of the disk, the radial and azimuthal velocity of the fluid increase and the temperature of the fluid decreases. Most importantly, it is observed that when the disk rotates faster than the stretching rate, the temperature of the nanofluid decreases rapidly, which has wider applications for cooling purposes. It is also noted that when the suction parameter increases its value from −1 to 1, for Ag–water nanofluid, the “skin friction coefficient” decreases by 73.56%, and the Nusselt number also decreases by 24.11%, and for Fe₃O₄–water nanofluids, the “skin friction coefficient” decreases by 71.25% and the Nusselt number decreases by 24.47%.

Many nations have committed to becoming carbon neutral by 2050 as a means of addressing the global warming challenge. To achieve carbon neutrality, transportation is one of the most essential and important tasks. Energy-efficient pure electric vehicles (EVs) and hybrid electric vehicles (HEVs) with green energy power are being developed in response to the worldwide energy and environmental crises, as the potential replacements for the current generation of combustion-engine automobiles. EVs require batteries more than ever before. In this perspective, lithium-ion batteries (LIBs) stand out as remarkable energy storage technologies and have been widely used due to their numerous impressive benefits. Owing to LIBs sensitivity to temperature, EVs typically use the battery thermal management system (BTMS). The working temperature span of a lithium-ion battery in an electric car is 15°C–35°C, which is achieved by the use of a BTMS. The production of internal heat during charging and discharging also affects how well lithium-ion batteries work. A battery heat control system is therefore required. The temperature of the LIB pack might be efficiently controlled by liquid-cooled systems in discharge and charge scenarios. Based on Al₂O₃ nanofluid (NF), the current experimental study suggests a novel active cooling technology for regulating the heat produced by the 18650-format lithium-ion batteries. A thorough analysis is conducted on the impact of charge/discharge C-rates, Al₂O₃ nanoparticle (NP) volume fractions, inflow coolant velocity, and intake liquid temperature on the thermal efficiency of the LIB pack. By incorporating aluminum oxide NPs into the water at varying volume fractions of 0.3%, 0.5%, and 1%, the LIB pack's maximum temperature was significantly reduced by 7.9%, 18.09%, and 19.56%, respectively. With increase in mass flow rate of coolant from 0.0290 to 0.5810 kg/s, the maximum temperature has been substantially reduced by 3.7%–8.6%. Results show that using higher fluid inflow temperature significantly increased both the highest experienced temperature and temperature diversity throughout the discharge operation by about, 6°C and 5°C, respectively. The outcomes of the study indicate that NFs exhibit superior cooling performance compared to conventional coolants such as water and ethylene glycol.

Direct heat transfer problems can be solved analytically or numerically to predict the temperature profile when the thermal properties, boundary conditions, and other relevant parameters are known. Though it is common practice to measure temperature experimentally, heat transfer parameters and boundary conditions are more challenging to measure and can instead be inferred through the use of inverse heat transfer (IHT) techniques, which can be solved through optimization. In this study, the IHT method with the conjugate gradient method is used to determine the energy consumption of bread during the cooking process in a developed baking oven with and without a reflector. A complex variable differentiation method is integrated to calculate the accurate sensitivity coefficient matrix. The results demonstrated that the estimated heat flux is very close to the exact heat flux and relative error is less than measurement errors.

This paper scrutinizes the combined effect of radiation, Soret, Joule heating, and chemical reaction on an unsteady magnetohydrodynamic visco-elastic (Kuvshiniski type) fluid flow over an infinite vertical moving plate. The viscous dissipation, heat source, thermal and solutal buoyancy forces are taken into account. The plate is assumed to be embedded in a porous media and a transverse magnetic field is applied to the stream. The nondimensional governing equations are solved analytically using perturbation techniques. The influences of various dimensionless parameters on fluid velocity, temperature and concentration profiles, as well as the skin-friction, Nusselt number and Sherwood number are analyzed and discussed graphically. Also, the present results are compared with previous studies and is found to be in excellent agreement. It has been shown that rising Soret numbers cause velocity, temperature and concentration to rise. Further, a hike in visco-elastic parameter leads to decrease in motion, temperature and concentration profile.

The technology of solar still shows up as an effective and affordable solution to convert available brackish water into potable water. The present study aims to address the challenge of providing freshwater by desalinating brackish water using solar energy. An attempt has been made in this work to make a desalination system for the efficient utilization of solar energy by using a parabolic reflector and energy-storage material. Modification in the desalination system and storage of energy facilitates the continuation of the process in sunshine and off-sunshine hours which increases yield output. To investigate the objectives, helical-shaped focal tubes and nano-enhanced phase change material (PCM) are prepared. The desalination system is coupled with nano-enhanced PCM by placing it in the annular space of a helical-shaped focal tube. The heat transfer coefficient ranged from 11.46 to 28.77 W/(m² K). PCM 3 (i.e., base PCMs with 1.5% nanoadditives) achieved a maximum productivity of 3533.3 mL/m²/day, marking a 97.89% improvement over the system without PCM. The preheated water outlet temperature reached 67.4°C, and the basin water temperature was 75.35°C. The highest concentrator efficiency recorded was 49.82% at a mass flow rate of 0.0053 kg/s. Thermodynamic analysis showed a 67.19% enhancement in overall thermal efficiency with PCM 3 compared with the non-PCM scenario. Additionally, the system attained a maximum average exergy efficiency of 12.29% and the shortest payback period of 115 days. The study concludes that the base PCM sample with a 1.5% mass concentration of nanoparticles was optimal.

Free convection is commonly applied in various engineering fields such as solar energy, electronic devices, nuclear energy, and heat exchangers. A computational simulation was used to analyze the natural heat transfer through convection in a wavy cavity with squared shape that was filled with tap water and saturated metal foam to assess the influence of hump configuration (square, triangle, circular, down semicircular, and up semicircular) and magnetic fields (magnetohydrodynamics) on heat transfer rate. The bottom wavy wall of the enclosure exhibits a high temperature (T_h), whereas the top and side walls maintain a low temperature (T_c). The present paper will examine how the bottom wall hump number (N), aspect ratio (L), geometry inclination angle (θ), Hartman number (Ha), magnetic field intensity inclination angle (ɤ) affects the heat transfer rate at various Rayleigh numbers. When the circular hump design is used with specific parameters, including ɛ = 0.85, L = 1.25, N = 4, T_c = 0°C, θ = 0°, Ha = 600 and ɤ = 45°, for different Ra values, it leads to increased heat transfer and notable improvements in heat transfer enhancement (ɸ) and energy enhancement (e). The enhancements were measured at 2.5 times for heat transfer enhancement and 8.9 times for energy enhancement. Moreover, the ideal case of the current study had Ha = 600, L = 1.25, Ra = 30 × 10³, and θ = 0° compared to the baseline case. Simulations were accomplished using CFD. The results demonstrate that the primary goal of the research was achieved by optimizing the design, leading to a significant improvement in hydrothermal performance for both ɸ = 2.5 and e = 8.9.

In recent years, the research in the field of medicinal plants as therapeutic supplements has increased significantly. Lavender extract is widely used among medicinal plant products due to its unique therapeutic properties. Since drying processes require high energy, this study was conducted to study the performance of the spray dryer in the production of lavender extract powder at three levels of air temperature 150°C, 180°C, and 210°C, three levels of compressed air flow rate 6, 8, and 10 L/min and ratios of maltodextrin-drying aid to the mass of dry matter of the extract 0%, 25%, and 50% by response surface method. For this purpose, the energy efficiency and exergy of the powder production process were examined. According to the obtained results, increasing the inlet air temperature and the inlet air flow rate increased the energy efficiency and exergy and decreased the energy efficiency and exergy, respectively. The energy efficiency of the drying process varied in the range of 6.55%–15.87%, and the exergy efficiency ($��\; ��{\eta }_{�e�\; �x�}��$) of the drying process in the range of 2.87%–5.84%. Also, the $��\; ��{\eta }_{�e�\; �x�}��$ of the spray dryer was calculated in the range of 20.05%–38.78%. Based on the energy efficiency and exergy, the optimal production of lavender plant extract powder was obtained at the air temperature of 210°C, the compressed air flow rate of 6 L/min, and the amount of drying aid of 11.9 g/L.