查看更多>>摘要：Background/objectives: Solar dryer has reached a remarkable level due to its tremendous contribution towards the saving spoilage of the food, vegetables, spices and ingredients, marine products, and industrial products. The main objective of this review paper is to provide a general idea of recent development of solar dryers integrated with thermal energy storage units and auxiliary units.Methods: Various literature papers are reviewed to highlight the novelty of each dryer with thermal storage and auxiliary units.Observations/findings: The dryer performance, drying capacity, drying time, efficiency, exergy analysis, and material used as thermal storage are presented.Applications: Researchers/farmers may modify their solar dryer and integrate it with thermal energy storage and auxiliary units. This review paper will encourage researchers to develop a suitable dryer for various drying conditions, drying products drying capacity, and drying time.
查看更多>>摘要：A new non-invasive thermal sensor based on transient heat flux and temperature measurements has been developed for accurate and reliable thermal measurement in piping systems. The sensor is clamped onto the outer surface of the pipe and covered by a thin-film heater and heat flux sensor mounted over a thin-film thermocouple. Previously, when the thin-film thermocouple was mounted directly on the copper pipe surface, there was a small temperature shift that affected the accuracy and reliability of the measurements. To eliminate this temperature shift, a new design was developed using a single layer of Kapton tape with an adhesive (dielectric material) between the butt-welded thermocouple foils and the pipe wall. This design gives more accurate, reliable, and practical temperature measurements over a range of fluid flow rates and bulk fluid temperatures. Encouraging temperature measurement results in 150 tests of this new design gave accurate estimates of the internal mean fluid temperature without environmental interference. A new parameter estimation code was developed to estimate the optimal system parameters by using the minimum root mean square error between the calculated and experimental sensor temperature values. The resulting new non-invasive thermal sensor can be used to estimate mean fluid temperature in a variety of applications.
查看更多>>摘要：The heating rates of the microwave in combination with stirring were obtained for a cylindrical container. The experiment was conducted at different operating parameters such as stirring speed, stirrer length, and the penetration depth of microwave. The heating homogeneity is characterized by a ratio between two heating values calculated from microwave penetration and centre temperature. The ratio was evaluated by two dimensionless numbers, the mixing Reynolds number (Re) and our dimensionless microwave number (As) proposed in a previous study. It was found that the heating ratio is linearly correlated to the simple combination of Re and As. The results provide a simple and practical formula for the optimization of microwave heating in industrial processes.
查看更多>>摘要：Thermal network resistances are derived for several geometries of non-isothermal convecting plates, including bars or rectangular plates of constant cross-section, as well as annular and spherical plates. This contribution allows convecting plates, which are ubiquitous in design, to be analyzed in the classical framework of thermal networks. This supplements analytical tools at the disposal of thermal designers and provides an alternative to laborious numerical analysis of complex thermal structures.
查看更多>>摘要：Nowadays, microchannels have been widely utilized in various multidisciplinary fields, and as a consequence, some new and different requirements for microchannels in the process of practical application are required, such as structure, working fluid, and operating conditions, etc. This article reviews the current research achievement of microchannels, as well as the thermodynamic research on microchannels with different structures in the past five years, but mainly focuses on the numerical methods. The purpose of this review article aims to summarize a comprehensive overview of the latest developments of numerical methods in microchannel heat sinks, as well as to provide a useful benchmark for future research. The present article reviews straightforward on the most commonly used numerical methods for solving governing equations and optimizing data, including conventional computational fluid dynamics (CFD) simulation methods, molecular dynamics simulation (MDS), Lattice Boltzmann methods (LBM), direct simulation Monte Carlo (DSMC), and other techniques such as machine learning (ML) approach, artificial neural network (ANN) method, genetic algorithm (GA), Taguchi algorithm (TA), as well as optimisation methods. This review will not only help to understand the physical mechanism of microchannels in different application fields but also help to fill in the gaps in related research and provide research methods for future numerical studies.
查看更多>>摘要：Oscillating heat pipes (OHP) have attracted much attention in thermal management due to its high heat transport capacity and simple structure. OHP also have the potential to transfer heat under rotational conditions, while research on OHP heat transfer performance under a system rotation is still insufficient. The thermal performance of a single closed loop OHP under a centrifugal acceleration due to an axial rotation is here experimentally investigated. This OHP is then treated as a grey system, since the complexity of the internal physical processes is very high and only a limited amount of experimental data is available. The grey system theory, which analyzes an uncertain system with small samples and poor information, is used to provide a novel path of modeling the thermal performance of two-phase systems. The results show that the heat transfer characteristics of an OHP filled with methanol improve with the increase of centrifugal acceleration and heat flux. The data are then modeled by a GM(1,1) grey model to simulate and predict the heat transfer coefficient. The errors range from 3.36% to 16.6%, and the prediction of the performance is satisfying. A case study of applying the prediction model in designing abrasive-milling tool with OHP inside to enhance heat transfer is conducted. It shows that the grey system prediction model provides a reliable guidance for the engineering application of the OHPs.
查看更多>>摘要：R152a has similar thermodynamic properties to R134a and can be used as one of the alternative refrigerants to R134a. However, flammability restricts the use of R152a in conventional domestic refrigerators. The oil-free VCR system allows the elimination of lubricating oil and therefore reduces the refrigerant charge, thus allowing a reasonable level of safety to be achieved with R152a. This study tests the performance of R152a and R134a in an oil-free domestic refrigerator under various operating conditions. The oil-free VCR system is made up of two oil free linear compressors with strokes of 0-14 mm, a water-cooled coaxial condenser, an expansion valve and an evaporator with an electric heater. The results show that R152a has an average energy efficiency ratio (EER) that is about 26% higher than R134a. Furthermore, the total exergy destruction of R134a is 9% higher than R152a on average due to a higher vapour density. The lower total exergy destruction allows the VCR system using R152a to achieves an exergy efficiency 7% higher than R134a on average. This paper also reports the experimental results of power input, volumetric efficiency, mass flow rate, normalised coefficient of performance (COP) and isentropic efficiency. It can be concluded that R152a can replace R134a in the oil-free domestic refrigerator.& nbsp;
查看更多>>摘要：We have numerically investigated the melting and solidification process of a low melting temperature metallic phase change material, gallium, in a semi-circular enclosure with a hot circumferential wall under the influence of thermocapillarity and externally applied uniform magnetic field for different gravity conditions. The governing equations coupled with the enthalpy porosity method are solved to predict the effects of applied magnetic field direction (0 <= 0 <= 90 degrees), and strength (0 <= Ha <= 125), Rayleigh number (Ra = 4.656 x 10(2), 4.656 x 10(4), 1 x 10(5), 1 x 10(6)), Marangoni number (Ma = -1.44 x 10(3), 5 x 10(3) and 1 x 10(4)) and gravity conditions (0.05g, 0.25g, 0.5g and 1g) on the velocity, temperature and liquid fraction profiles. The predictions of the developed numerical models are compared with the experimental and numerical data reported in the literature and found to be in good agreement. The results reveal that the surface tension gradient driven convection significantly enhances the melting process under the microgravity condition without the magnetic field. Fluctuating behaviour of transient average Nusselt number under normal gravity conditions observed during melting of gallium in the presence of thermocapillary and natural convection is reduced by applying the magnetic field. The complete gallium melting time is increased by 5.48% for the change in Hartmann number from 0 to 25 applied at theta = 45 degrees. The direction of the applied magnetic field marginally increases the complete melting time for theta = 75 degrees and insignificantly affects the complete solidification time. The increase in Rayleigh and Marangoni numbers considerably alters fluid flow patterns and the temperature field.
查看更多>>摘要：A three-dimensional model is established to investigate the flow and heat transfer characteristics influenced by the winding angle in the shell side of a spiral wound heat exchanger. Numerical simulations are conducted with the winding angle varying from 0 to 20 and the Reynolds number varying from 430 to 1935. The flow states of different conditions are observed, and the film thickness is measured in the axial and circumferential directions. Moreover, the heat transfer characteristics of the liquid falling film flow are investigated at constant wall temperature. The results indicate that the winding angle has a distinct effect on the flow and heat transfer characteristics. Under the same Reynolds number, the local film thickness distribution varies with the winding angle, and the average film thickness in the axial direction decreases with the increase of winding angle. The local heat transfer coefficient distribution is consistent with that of film thickness, and the average heat transfer coefficient increases with the Reynolds number but decreases with the winding angle. Based on the results, a comprehensive heat transfer correlation involving winding angles is developed, the deviations of the data are within +/- 3%.
查看更多>>摘要：This paper presents a novel combination of Phase Change Material (PCM) and fins as Thermal Conductivity Enhancer (TCE) for effective thermal management of battery module. A numerical study of the battery module thermal management system using PCM and internal fins for maintaining the battery temperature below the safe limit of 60 degrees C for more than one cycle is carried out. Both joule and entropic heat generation is considered for more generality in line with the actual case. An implicit finite volume based numerical methodology is used to solve the governing energy transport equation. Phase change in PCM is modelled using the implicit source based enthalpy method. A two-dimensional model is developed to study the thermal performance of battery module with 4S4P cell structure (16 cells) with PCM filled in between the cells. To improve the heat dissipation more effectively from PCM, metal fins as TCE are inserted in the space filled with PCM. Five fin structures with fin arrangement parallel to the boundary and tilted at an angle of 45 degrees to the boundary are developed and studied to find the best configuration for effective transport of heat from the system to the boundaries and subsequent convection away to the ambient. Results shows more uniformity in temperature distribution within the battery module for better thermal performance for longer period of operation. Using fins embedded in PCM, the battery module temperature is maintained below 60 degrees C even after two and half discharge-charge cycle of 2C and 3C discharge rates where FS-3 structure is proved to be most efficient.
NSTL
Elsevier