查看更多>>摘要：In this study, the temperature fields in a thermal barrier coating system (TBC) under various types of thermal loadings, including steady and transient thermal loads, is investigated. TBCs are exposed to a variety of harsh thermal loadings, including thermal shock and periodic thermal loads. Therefore, the need to achieve the temperature distribution in different positions of the TBCs, especially in the protective coating is very crucial. Non-uniform Thermal boundary conditions are considered for both external temperature and heat flux distributions. The coating and substrate are not stationary at the onset of transient thermal load. Using the solution of steady-state problem as initial condition, the transient temperature fields within the coating-substrate system is obtained. The dual-phase lag (DPL) heat conduction is utilized to scrutinize the transient response of the TBC system. Fourier and Laplace integral transforms have been used to solve the temperature field equations. The effect of concentrated thermal shock and steady harmonic thermal load on the temperature fields of coating and substrate is investigated. The results demonstrate that the steady state and transient temperature fields strongly depend on the type of thermal load, the thickness and thermal properties of the coating, and the loading parameters. The results indicate that the effect of concentrated thermal shock is felt after at least 8.33 s at distance 1.2 cm far from the top surface of ceramic coating. The effect of concentrated thermal shock is eminent adjacent to point (x = 0, y = 0) of the free boundary of coating, but after a longitudinal distance of 2 cm drastically reduced. The ceramic coating is able to relieve the amplitude of temperature oscillations up to 128 degrees C at a vertical distance of 3 mm from the free boundary of coating.
查看更多>>摘要：Lithium-ion batteries (LIBs) rely on efficient thermal management systems for their safe and reliable operation. Issues like overheating of LIBs due to excessive heat generation, thermal runaway and thermal propagation are still a challenge for engineers. To address the challenge, numerous cooling methods viz. liquid cooling, air cooling, cooling using phase change materials (PCMs), hybrid cooling (i.e., combining liquid and PCM cooling), etc., have been proposed by different authors in the past. Though all the above methods are best suited for LIBs under normal charging/discharging operations, their suitability for cooling fast charging LIBs remains unexplored. In general, the heat generation and risks due to thermal runaway in LIBs are relatively more during fast charging than normal charging. As regards hybrid cooling employing PCMs, the method is yet to be bench marked, as PCMs themselves suffer from low thermal conductivity issues that may affect their overall thermal performance. The present work is an attempt to address the above-stated aspects. Detailed 3D numerical simulations on three different design configurations (D1-D3) of a prismatic LIB module consisting of four 10 Ah batteries fast charged at 8C rate are reported herein. Two different cooling methods viz. (i) liquid cooling employing a dielectric liquid coolant (STO-50) and (ii) hybrid cooling combining liquid dielectric and a PCM (RT35) are investigated, and their performances compared. The results reveal interesting facts on the ability of liquid cooling (D2) over hybrid cooling (D3) for fast charging LIBs. Parametric studies show that the coolant flow direction (horizontal/vertical) and thermal conductivity of the PCM (k(pcm)) have a profound influence on the cooling obtained compared to PCM's melting temperature (T-m) and latent heat (lambda). It is concluded that PCM based hybrid cooling is not suitable for cooling LIBs under fast charging unless k(pcm) is enhanced to 1 W/mK or above. A minimum coolant flow rate of 2 lpm is needed to limit the battery temperatures to 40 degrees C or below for the module under fast charging conditions. An increase in PCMs latent heat from 160 to 200 kJ/kg has no significant influence on the cooling achieved.
Mauro, Alfonso WilliamMauro, Gerardo MariaPantaleo, Antonio MarcoViscito, Luca...
14页
查看更多>>摘要：This paper presents a semi-empirical model for mass and heat transfer applied to de-watering and cooling of fresh leafy vegetables. This process aims at optimizing vegetables' moisture content and temperature through the interaction with conditioned airflows to ensure proper storage and preservation. It is implemented in different modules - i.e., a first set of hot modules with hot air, a second set of cold modules with cold air - allowing to remove water from the vegetables and to achieve the desired temperature. A dedicated transfer model is developed to follow the evolution of the liquid droplets on the leaves during the process. It is based on water mass and energy balances on product and air sides, where the bed of leaves is treated as a porous medium. The mass and heat transfer coefficients are calibrated by comparison with experimental data. The model is validated with real data from the field, and a parametric analysis is implemented to show its potential application to optimize the process. The calibrated model presents satisfactory reliability - less than +/- 1.0 degrees C as average error for output temperature - according to the uncertainty of the approaches available in literature, thereby ensuring a robust performance assessment. This can support the process application in several fields of the agri-food industry with significant quality and productivity improvements. Finally, the model can be used to develop digital twins to foster the ongoing digitalization of the agri-food sector with a view to sustainability.
查看更多>>摘要：Evaporative cooling systems have attracted increasing attention for energy-efficient air conditioning applica-tions. A hollow fiber membrane-based direct evaporative cooler (HFM-DEC) is proposed in this study. The selected membrane material can selectively allow only water vapor to penetrate, while preventing the passage of bacteria and fungi, thereby avoiding deterioration of indoor air quality. Compared with the conventional evaporative coolers with counter-flow and cross-flow arrangements, the proposed novel configuration performed better cooling ability by installing baffles in the air flow channel to enhance the air disturbance. The parameter sensitivity analysis was conducted on the HFM-DEC with built-in baffles by employing an experimentally vali-dated numerical model. The orthogonal test method was used to study the influence of nine key parameters of the HFM-DEC on its wet-bulb effectiveness, coefficient of performance, and the cooling capacity. According to the optimized scheme, the HFM-DEC with a relatively optimal configuration was proposed. The cooling per-formance of this module was investigated under various inlet air conditions. The results showed that if the inlet air velocity was maintained within the range of 0.5-2 m/s, it was capable of achieving an optimal performance with the wet-bulb effectiveness of 70%-95%, the COP of 17-78, and the cooling capacity of 60-106 W, respectively, under diverse weather conditions. Correlations of Nusselt number and Sherwood number were developed by fitting the simulation results. The influence of Reynolds number on air stream characteristics was obtained based on the analysis of the velocity field, temperature field and concentration field of this module under varying operating conditions.
查看更多>>摘要：In the present work, the influences of variable porosity of CaO/Ca(OH)(2), which is normally regarded as constant, on the thermochemical energy storage characteristics in direct/indirect heated reactor (DHR/IHR), are comprehensively investigated by establishing a transient multi-physics coupled model. It is found that, unlike the traditional constant porosity assumption, the variable porosity shows significantly two-fold competitive impacts. On the one hand, increasing/decreasing porosity increases/decreases the permeability of reaction bed, which leads to the drop/rise in pressure field and further the local reaction equilibrium temperature drop/rise. Thus, the local reaction rate increases/decreases correspondingly. On the other hand, increasing/decreasing porosity also decreases/increases the heat conductivity of the reaction bed, which leads to the drop/rise in transient temperature field. Thus, the transient reaction rate decreases/increases instantaneously. The results indicate that the constant porosity assumption may over/underestimate the performance of DHR/IHR during the charging (dehydration) process by around 9%, while underestimate the performances of both DHR and IHR during discharging (hydration) process by up to around 19%. It is also found that the variable porosity demonstrates greater influence on the discharging (hydration) process in DHR and on the charging (dehydration) process in IHR.
查看更多>>摘要：Research on the reduction of refrigeration systems energy consumption is a topic in which popularity benefits from the contextual growth of the refrigeration market. Solar or waste heat-driven ejector refrigeration systems are very promising in this context. However, the lack of operational flexibility of ejectors penalizes the performance of such systems. Since the mixing chamber has a fixed cross-section, for condensation temperatures above critical, the cooling capacity vanishes and, for temperatures lower than critical, the cooling capacity stagnates. The paper proposes a new variable mixing chamber solution that overcomes these limitations. It is a range extender that allows ejectors to operate at high cooling capacity all over the operation range of the system. This range extender is based on the concept of lateral cylindrical moving slots. The paper compares the new ejector to a reference ejector from the literature. First, the Computational Fluid Mechanics (CFD) model viability is evaluated thanks to the experimental measurements on the reference ejector. Then, the new system's performance is evaluated. The results show that the adaptation of the mixing chamber section to the condensation temperature allows increasing the cooling capacity without supplementary motive energy. That leads to an increase of up to 120% of the cooling capacity at low condensation temperatures and a shifting of 8 degrees C of the critical temperature. Such extension of the operational range was never obtained before. That means that an ejector stalling at 33 degrees C could operate at 41 degrees C using the proposed range extender.
查看更多>>摘要：Parabolic trough collector (PTC) is a widely used and efficient Concentrating Solar Power (CSP) technology for generating solar thermal power. Supercritical CO2 (s-CO2) is a heat transfer fluid (HTF) that shows good promising for use in solar PTC for further improvement in its efficiency and operations. A numerical thermal model is developed to understand the performance of s-CO2 as an HTF in a solar PTC. The local temperature and velocity fields were used to calculate the entropy generated within HTF due to finite temperature differences and fluid flow friction. A commercially available LS-3 parabolic trough collector is used for the analysis with a modified receiver. An optical analysis tool based on Monte Carlo Ray tracing is used to calculate non-uniform heat flux distribution around the circumference of the PTC receiver. Entropy generated at various operating pressures, inlet temperatures, and inlet Reynolds number using s-CO2 as HTF is calculated and analyzed. Results showed that entropy generated in the PTC receiver is reduced to a minimum at optimal Reynolds number for each of the operating pressures and inlet temperatures of the HTF. The Bejan number estimates the contribution of entropy generated due to heat transfer irreversibilities to the entropy generated due to heat transfer and fluid flow irreversibilities which is between 0.2 and 0.4 at high flow rates and close to 1 at low flow rates. Exergy efficiency analysis supported the optimized inlet boundary conditions.
查看更多>>摘要：The development of high-performance electronic devices requires high heat transfer components with small thickness and high thermal performance. This paper presented an ultra-thin flat heat pipe (UTFHP), and the total thickness and inner height is respectively 0.68 mm and 0.48 mm. The striped-channel structure was developed to withdraw the deformation of UTFHP and reduce the flow resistance. In order to improve the capillary performance of mesh wick, the oxidation treatment was finished by the thermal oxidation method. The thermal performance of UTFHPs was investigated under natural convection cooling condition. The effects of mesh structure, passage width and filling ratio on the thermal resistance and temperature distribution were analyzed. It is found that the UTFHP with mesh number of N = 200 and passage width P = 1.5 mm showed the best thermal performance under the filling ratio of phi = 57%. The minimum thermal resistance was 0.26 K/W with a maximum temperature of 74.07 degrees C at 8 W heating load, indicating that the proposed UTFHP was able to be a reliable candidate for the thermal management of electronic devices with high heat transfer rates.
查看更多>>摘要：The successful application of oil-immersed transformers inspires the thought about the feasibility of the transformer oil on developing an oil-immersed battery thermal management system. This paper tentatively designs a model-scale transformer oil-immersed battery thermal management system to investigate the feasibility of the cyclic transformer oil fluid on cooling the battery. It is found that at 2C discharge rate, the battery immersed in the stationary transformer oil fluid exhibits a maximum temperature of 37.35 degrees C and a maximum temperature inhomogeneity of 2.64 degrees C, much lower than that exposed to the open air. To further improve the heat dissipation performance of the oil-immersed cooling system, different oil volumetric flow rates ranging from 3 to 50 mL/min are tested to examine the cooling effectiveness. As the oil fluid circulates, the maximum battery temperature can maintain below 35 degrees C. The increasing TO volumetric flow rate can continuously lower the battery temperature, while this effect gradually wanes as the flow rate exceeds 15 mL/min. The theoretical analysis indicates that as the heat transfer mode is dominated by natural convection, the increasing TO flow rate will significantly improve the cooling effectiveness of the system. In other cases, the increasing flow rate improves the cooling performance to a small extent, and concurrently intensifies the consumption of pumping power. The TO fluid with a flow rate of 15 mL/min (Reynolds number = 0.59) is suggested as the optimal choice for the current TO-immersed BTMS. The current oil-immersed battery cooling system validates the concept of direct-contact cooling method through model-scale experiments and theoretical considerations, which provides novel insights into the development of more efficient oil-immersed battery thermal management systems utilizing the dielectric oils.
NSTL
Elsevier