Heat Transfer最新文献

Postharvest management of lotus stems (Nelumbo nucifera) is critically underemphasized in the food industry, leading to significant quality degradation and postharvest losses due to mechanical damage during handling, transportation, and valorization. This study aimed to optimize drying conditions through various pretreatments to enhance the processing and valorization efficiency of lotus stems and to characterize lotus stem flour in terms of its proximate composition, functional properties, and amino acid profile. This is the first study to optimize the drying conditions of lotus stem flour using citric acid and potassium metabisulfite (KMS) pretreatments, ensuring better retention of quality attributes. Lotus stems exhibit substantial variability, with weights ranging from 32.55 to 245.65 g, length from 18.00 to 44.35 cm, and width from 1.30 to 3.80 cm. Lotus stem slices dried at 70°C for 2 h yielded the highest percentage (26.50%), although higher temperatures generally resulted in decreased yields due to moisture loss and structural changes. The color attributes of lotus stem flour are affected by the drying temperature and anti-browning agents. The use of citric acid improved redness and yellowness, whereas potassium metabisulfite affected the color based on the concentration. Lotus stems pretreated with 2% KMS improved the lightness (L) by up to 18% (from 71.85 to 85.25), while the samples treated with 2% citric acid increased redness (a*) by approximately 57% (from 4.20 to 6.60) and yellowness (b*) by 33% (from 14.60 to 19.45), indicating enhanced color retention. Moreover, the lotus stem flour is characterized by moisture (6.30%), protein (7.60 g), carbohydrate (70.90 g), and fat (1.45 g), providing an energy value of 326.77 Kcal. It also contains appreciable amounts of essential minerals, including calcium, potassium, and magnesium, as well as negligible levels of toxic heavy metals. Flour is notable for its essential amino acids, particularly threonine, lysine, and leucine, and includes a range of nonessential and conditionally essential amino acids, contributing to its comprehensive nutritional profile. These findings highlight the potential of lotus stem flour as a functional ingredient for the food industry, particularly in the development of nutritionally enriched and shelf-stable products.

This study explores the experimental and mathematical modeling of energy recovery from hot exhaust gases using a finned tube heat exchanger filled with paraffin. The experimental setup employs air as the heating fluid, water as the cooling fluid, and paraffin with a melting point of 68°C as the phase change material. Key parameters investigated include inlet air temperature, air mass flux during heating, and water mass during cooling. The system's thermal behavior is modeled mathematically by assuming heat accumulation in the paraffin-filled finned tubes. Numerical solutions of the equations are compared with experimental data, and dimensionless parameters are used to evaluate system performance under varying conditions. The model also examines the effects of structural features, such as fin height and the number of fins per unit tube length. The results show that increasing inlet air temperature and reducing air mass flux improve the heating and cooling efficiencies and overall system performance. Enhancing fin height from 0 to 1.5 cm and the number of fins from 0 to 20 within a 10 cm tube length leads to heating efficiency gains of 10.88% and 15%, respectively.

This article presents a precise solution to the problem of a transient MHD-free convective chemically reactive flow of an incompressible, electrically conducting, viscous, optically thick, non-Gray fluid past a temporarily accelerated vertically semi-infinite plate with linear ramped conditions where thermal diffusion, thermal radiation, heat sink, and chemical reaction effects are present. Fluid is subjected to a uniform transverse magnetic field of strength $��\; ��B_0��$. The resulting linear nondimensional governing equations are solved by applying the closed version of the Laplace transform method. To describe the radiation heat flow that appears in the energy equation, the Rosseland model of radiation has been used. Using figures and tables, the impacts of various factors on flow and transport characteristics are studied for both the isothermal and ramped conditions. During the transverse magnetic field's appearance, fluid velocity declines. Viscous force reduces as ramped parameter values increase; hence, we may infer that the fluid's temperature climbs as the viscous force gets higher. There is an improvement in the temperature field with an increase in thermal diffusivity. Increasing mass diffusivity raises the concentration field. As fluid viscosity falls, fluid velocity rises.

This study provides an analytical investigation on steady magnetohydrodynamic (MHD)-free convection Couette flow of heat-generating fluid through a vertical channel. The coupled nonlinear differential equations describing the system were solved analytically using Homotopy Perturbation Method. The research examines the influence of various flow parameters, including the Eckert number, magnetic field strength, heat generation/absorption, Prandtl number, and Grashof number. Comprehensive analyses and physical interpretations are presented. The findings showed that fluid velocity and temperature decrease with an increase in magnetic field strength, while higher Eckert numbers led to an increase in both velocity and temperature. Furthermore, the rate of heat transfer decreases at the moving plate but increases at the stationary plate with rising viscous dissipation, magnetic field strength, and Grashof number.

The heat pipe is one of the prime candidates in electronic thermal management due to its higher thermal performance and passive nature. The present study aims to develop a 3D mathematical model to simulate the thermal behavior of the heat pipe of length 380 mm under different operating conditions. Steady-state numerical simulations are performed to predict the effect of heat inputs (in the range of 10–50 W), the coolant flow rates (40 LPH, 25 LPH, and 10 LPH), and the coolant inlet temperatures (298.15, 293.15, and 288.15 K) on the heat pipe's thermal characteristics. The analysis reveals that by increasing the heat input from 10 to 50 W, the heat pipe's thermal resistance is reduced by 49.23%, with the same amount of augmentation in its evaporator heat transfer coefficient. The cooling water flow rate also significantly impacted the heat pipe's thermal resistance and heat transfer coefficient. The evaporator heat transfer coefficient decreased by 2.01% at 25 LPH compared to 10 LPH and increased by 1.68% at 40 LPH compared to 25 LPH. Additionally, with the increase in the cooling water inlet temperature from 288.15 K to 293.15 K, the heat pipe's evaporator heat transfer coefficient increased by 7.55%, and thermal resistance was reduced by 6.02%. This confirms the vivid influence of the input thermal energy and cooling water inlet temperature on the heat pipe's thermal characteristics, while the cooling water Reynolds number (flow rate) had a minimal influence on its operating conditions. Hence, this comprehensive analysis of using the heat pipe offers valuable insight for improving heat dissipation and thermal management in electronic devices.

High operating temperatures significantly reduce the efficiency and lifespan of photovoltaic (PV) panels, necessitating innovative cooling solutions. This study investigates a novel passive cooling technique for photovoltaic/thermal (PV/T) systems, integrating moving air through a gap between the PV panel and a stagnant water heat sink. The goal is to enhance thermal management and energy output while minimizing reliance on active cooling mechanisms. Two configurations are compared: a standard PV panel (reference) and an optimized PV/T system with the proposed air-gap cooling design. Key findings demonstrate the effectiveness of the optimized system, achieving a maximum air temperature difference of 22.84 K between inlet and outlet, an average thermal power output of 135.68 W, and a 4.15% increase in electrical power output. The thermal efficiency reached 30.05%, marking an 84.90% improvement over the reference setup. These results highlight the system's ability to maintain lower operational temperatures, thereby boosting both electrical and thermal performance. The innovative aspect of this study lies in its unique passive cooling approach, which combines air movement and stagnant water without requiring external energy input. This addresses a critical gap in PV/T literature by offering a cost-effective, low-maintenance solution for hot climates. The study provides valuable insights for optimizing solar energy systems, contributing to sustainable and efficient renewable energy technologies.

This study explores the flow dynamics and heat transference of fluid along a stretchable horizontal cylinder with a variable radius depending on time in the existence of chemical reactions and thermal radiation. The mathematical model comprises a set of partial differential equations with boundary conditions that describe the changing flow, thermal radiation, mass movement, suction or injection, and chemical reactions. Similarity transformation reduces such a system to a set of ordinary differential equations. The resulting system is solved using numerical methods to find how velocity, temperature, and concentration change based on the similarity variable, showing the effects of important factors like the unsteadiness parameter, the Schmidt number, suction/injection, thermal radiation, and the chemical reaction rate. This study validates its numerical technique by comparing certain findings to those published in the literature for constraints. The findings show that the increase of the unsteadiness parameter enhances the flow acceleration. Increasing the unsteadiness parameter also increases the fluid temperature and concentration. Chemical reaction parameters tend to modify the concentration distribution by enhancing the species diffusion. Additionally, higher values of thermal radiation and suction parameters decrease fluid temperature. These findings help control the thermal and mass transport processes in chemical reactors, heat exchanger systems, polymer extrusions, and many other engineering applications.

This article enables the changing specific heat coefficient to solve two nonlinear heat transfer problems. With mechanical engineering at the cutting edge, efficient heat transmission is essential to the effectiveness, safety, and performance of many engineering systems. The transfer of heat occurs through multiple pathways, including conduction, convection, and radiation, each playing a vital role in shaping the thermal landscape of modern technologies. We propose a fractional-order approach to reduce the complexity of the study. Here, using the Caputo fractional derivative (CFD), we examine and evaluate the solutions of the considered problems using the Predictor-Corrector method (PCM). To verify the reliability of the considered approach, the present findings are compared with those of the variational iteration method (VIM), homotopy perturbation method (HPM), hermite wavelet method (HWM), differential transformation method (DTM) and the accurate solutions. The PCM is typically more advantageous for actual numerical calculations, particularly when flexibility, stability, and accessibility of implementation are needed. The outcomes suggest that the PCM can forecast the solution of such problems with more appropriate results.

Drying is one of the most popular methods used in the food industry to reduce postharvest losses, extend shelf life, add value, and reduce handling. However, conventional drying methods such as hot-air (HA) dryers are time-consuming, energy-intensive, and can affect the food quality. To address these challenges, infrared (IR) drying has been added as a booster heat source, ensuring faster drying, energy saving, and quality improvement, since each method has its limitations. Therefore, combining HA and IR drying has been shown to be a more efficient technique, ensuring better drying performance. The aim of this study is to design and test the performance of using the HA and IR hybrid dryer for drying zucchini, by evaluating the zucchini quality attributes, such as moisture content (MC), water activity, rehydration ratio (RR), and shrinkage in diameter. In this study, different samples of zucchini slices were dried in a hybrid dryer under three different combinations of heat air and air speed, selected based on preliminary trials, including IR2-S1-H2, IR2-S2-H2, and IR2-S2-H1, where IR2 refers to the use of two IR tubes, S refers to the air speed and H indicates the heater level. The physicochemical properties of dried zucchini samples were analyzed and compared, including MC, moisture ratio, drying rate, water activity, rehydration, and diameter shrinkage. The results showed that IR2-S2-H2 was the fastest among the three drying combinations, reaching 10% MC within 40 min, while IR2-S1-H2 and IR2-S2-H1 required 60 and 80 min, respectively. The Midilli–Kucuk model offered the best-fit model for the MC data of IR2-S1-H2 and IR2-S1-H1 (R² = 0.9999 and 0.9999, RMSE = 1.6340 × 10⁻⁶ and 0.0011, respectively), while the logarithmic model provided the best-fit model for IR2-S2-H2 (R² = 0.9999, RMSE = 1.5421 × 10⁻⁷). All dryer combinations resulted in an RR of 4.67–5.80, and the water activity of dried zucchini samples was within the recommended food safety threshold (water activity = 0.207–0.411 < 0.6). In addition, the lowest diameter shrinkage (28.21%) was observed with the IR2-S2-H1 condition. This study recommends further research to optimize drying parameters and improve food quality as well as to evaluate the application of this dryer to other fruits and vegetables.

Brazed plate heat exchangers are renowned for their compact design and exceptional heat transfer capabilities. However, their intricate geometry sets them apart from other type of heat exchangers. Traditionally, studies have been somewhat limited in exploring diverse geometrical parameters due to the considerable manufacturing costs associated with each variation. Moreover, the complexity of the geometry poses challenges for simulation and numerical analyses, often resulting in inefficient models due to the generation of a large number of elements. To address these challenges, simulation models have been devised leveraging the concept of periodicity and simulated using periodic boundary conditions within ANSYS Fluent. This novel approach enables the variation and simulation of all geometric features with significantly fewer elements. Parameters such as pitch, amplitude, and chevron angle have been subjected to variation and simulated under similar conditions which was not done in any previous studies. The findings underscore the pronounced influence of the chevron angle, whereas the impact of amplitude and pitch becomes significant primarily at higher Reynolds numbers, affecting heat transfer and pressure drop. Furthermore, the discussion extends to an experimental setup proposed to evaluate the heat performance of heat exchanger across varying heat loads and flow rates.