查看更多>>摘要：Electric vehicle thermal management system (EVTMS) and its corresponding control strategy are essential to ensure the battery performance at low temperatures. Due to the complexity of the low-temperature fast charging process, it is necessary to comprehensively consider the battery heating and charging performance when developing the heating strategy. However, most studies only focus on the charging time. In this context, an EVTMS is investigated in this paper, and the simulation models are established. In addition, the battery heating and charging performance under low-temperature fast charging conditions are analyzed by experiment and simulation. An improved fast charging protocol for reducing the battery-lifetime degradation is proposed. Moreover, an EVTMS multi-stage heating control strategy is developed to realize the cooperative control with the improved charging strategy. Taking dual crucial yet conflicting factors, heating energy consumption and charging time, as the optimization objectives, the proposed EVTMS control strategy is optimized using genetic algorithm. And an optimal heating control strategy is obtained. The results show that compared with the strategy only considering the charging time, the optimal strategy can reduce the heating energy consumption by 11.61% and increase the charging efficiency by 1.2%, only with the increase of the charging time by 2.98 min.
查看更多>>摘要：The concept of coupled storage for dry cooler enhancement, based on the coupling of heat and humidity storages in a single module, has been experimentally studied and characterized in a previous study by the authors. The experimental results have highlighted that such storage can be effective to reduce the drop of performances for air-cooled condenser under high ambient temperatures and that fine understanding and interpretation of what happens inside the storage tank requires a dedicated numerical model. This paper presents in details the modelling of the coupled heat and moisture storages. The model is first validated on data from the literature in purely sensible and sorption operations. When compared to experimental data of coupled heat and moisture storage, the model exhibits very good qualitative agreement and good to correct quantitative agreement, depending on the considered parameters and the tests. The model allows to give physical insight of coupled sensible and moisture storage by giving local information and behaviours that are not available from measurement devices. The model needs further enhancements but is already of upmost importance for characterization and design of such coupled storage.
查看更多>>摘要：Micro/mini-channel heat sinks (MCHS) have been extensively employed for heat dissipation under high heat flux conditions, and their performances are crucial for safe and stable operation. This study presents a multi-objective optimization work to reduce pressure drop Δp and thermal resistance θ for the MCHS with non-uniform fins in a staggered arrangement. Multi-objective genetic algorithm and computational fluid dynamics software were coupled to find the Pareto solutions with optimal fin lengths and longitudinal spacings. Compared with the initial MCHS with four uniform fins, Δp of solution Optimalθ and θ of OptimalΔp were respectively reduced by 13.62% and 10.24%. Meanwhile, Spearman's rank correlation coefficient was obtained to reveal the relationship between fin configurations and performances, which indicated that the front sparse and rear dense fin arrangements are beneficial in achieving high comprehensive performances. To fully utilize the pumping power, the upstream heat transfer performance was sacrificed, however, all the local maximum base temperatures were excellently controlled to ensure thermal resistance. Furthermore, a multi-criteria decision-making approach was applied to select the best compromise solution OptimalTOPSIS. Besides reducing Δp by 8.35% and θ by 6.13%, OptimalTOPSIS also reduced the material cost by 10.80% and improved the uniformity of base temperature by 2.18 K.
查看更多>>摘要：Topology optimization has been increasingly adopted as a non-intuitive methodology for heat sink design in the thermal management of microelectronics. In this work, a bi-objective topology optimization method for heat sink design in micro-electronics is suggested by considering the trade-off between two contradicting objectives, i.e., the heat transfer and hydraulic performances. The method in this work focused on the laminar water flow with Reynolds number less than 100 based on the channel width for a wide temperature range that covers different types of micro-electric devices. A series of Pareto frontiers were acquired for heat sink designs with different topologies, which can be used to decide the optimum design in respect of heat transfer and pressure drop. Particularly, an analytical formula in terms of inlet Reynolds numbers was obtained for the fast generation of the Pareto frontiers under different working conditions which help to determine the weight parameters of two contradicting objectives readily. The new strategy for weight parameter determination significantly reduces the workload of trial-and-error during the weight parameter determination in the traditional bi-objective topology optimization and thus accelerates the design process. Besides, the temperature-dependent physical properties (viscosity and thermal conductivity) in the design model were considered and were found to affect the design results significantly. Finally, the 3D heat sink model was reconstructed from the 2D topology optimization, and the thermal-fluid analyses were conducted. The results indicate that the 3D reconstructed model can well satisfy the design objective specified in the topology optimization, thereby confirming the validity and robustness of our design method.
查看更多>>摘要：A computational fluid dynamics (CFD) model based on the compressible, nonlinear Navier-Stokes equations is developed to simulate the nonlinear phenomena in a gas-liquid standing-wave thermoacoustic engine, which employs gas as the working fluid and liquid as the phase-matching element. The CFD model is well validated when comparing the simulated onset and steady-state performances with those measured from a real experimental system. Based on the CFD model, the nonlinear phenomena of the engine are analyzed from three aspects. Firstly, the nonlinear dynamic phenomena of self-excited thermoacoustic oscillation from onset to saturation are investigated, focusing on onset temperature difference and steady-state pressure amplitude. Then, the nonlinear acoustic phenomena of the engine operating at steady state are analyzed. The steady-state fluctuating pressure is decomposed into a superimposition of the acoustic modes with different frequencies, which reveals the existence of high-order harmonics. Finally, the nonlinear hydrodynamic phenomena including multi-dimensional flow effect and mass streaming are observed by examining the steady-state flow fields in the engine. The proposed CFD model provides an effective approach to comprehending the mechanism of nonlinear phenomena in gas-liquid coupling thermoacoustic engines.
查看更多>>摘要：Under specific conditions of low mass flux and high heat flux, heat transfer deterioration (HTD) occurs in tubes, which is detrimental to the supercritical CO2 heat exchanger. To suppress the HTD and promote the overall heat transfer capability of supercritical CO2 in a vertical heated tube, the effect of the body-centered cubic (BCC) lattice structure on the fluid flow and heat transfer characteristics were studied. The BCC lattice structure was applied to a supercritical heat transfer experiment by exploiting selective laser melting (SLM) metal additive manufacturing. The results of the experimental and numerical studies indicate that the BCC lattice structure can effectively suppress the HTD by generating a composite vortex composed of a horseshoe vortex at the leading edge of the lattice ligaments, the streamwise vortex at the trailing edge of the ligaments, and the counter-rotating longitudinal vortex at the center of the ligaments. The vortex system strengthens the local turbulence intensity and enhances flow mixing, thus weakening the buoyancy effect and suppressing the HTD. Compared with the smooth tube, the average heat transfer coefficient of the tube with BCC lattice structure increased by up to 100%, whereas the pressure drop increased by 13.5%.
查看更多>>摘要：This work studies the 3E aspect (energy, exergy, and economic) of a poly-generation setup via a novel and innovative configuration based on two renewable energy sources through converting the thermal energy to useful energies and energy-based products. This system embraces geothermal energy via a flash-binary cycle and solar power employing a parabolic trough solar collector-based solar field. The other subsystems are a carbon dioxide-based transcritical organic Rankine cycle integrated with a modified transcritical refrigeration cycle to generate electricity and cooling, a humidification-dehumidification desalination unit to provide freshwater, and a proton exchange membrane electrolyzer to produce hydrogen. In this way, the newly designed system has been evaluated respecting the weather data of Beijing city in China throughout the year. Subsequently, the first and second laws of thermodynamics together with thermo-economic analysis and net present value assessment have been implemented. The sensitivity of principal variables regarding crucial design parameters has been examined via a parametric study. Also, the genetic algorithm was the optimization tool to optimize the calculations in different modes. The results indicated that the exergy-cost case of optimization correspondingly led to exergy efficiency and levelized cost of products of 19.2% and 13.9 $/GJ with a payback period of 3.96 years.
查看更多>>摘要：The Tesla turbine with insulated rotors has been investigated numerically and analytically for the application in Rankine cycle power plants for waste heat recovery. Simulations are performed for the multiphase, compressible, turbulent flow of wet steam to study the thermofluid dynamics and performance characteristics for a wide range of dimensional and dimensionless parameters. The expansion of steam inside the rotor is verified by density and Mach number contours. The increase in radius and inlet angle seems to increase the power obtained, with the maximum total recoverable power reaching as high as 2MW using 750mm rotors for inlet angle 3°, keeping in view the efficiency. The efficiency curves are compared with that of the laminar, incompressible flow of air, which seems to follow a similar qualitative nature but with a significant decrease in the effect of inlet angle. Fuel cost estimation of a 2000MW power plant employing the Tesla turbines that use 20% bled steam is performed and encouraging preliminary reduction in cost is observed. The previously derived scaling laws have been modified and extended to include thermal similarity characteristics using a new dimensionless parameter (Ts). Exergy analysis is performed on the rotors, which show that the second law efficiency seems to follow a decreasing trend with increasing inlet angle similar to the rotor efficiency. Sharp drops in rotor and second law efficiencies are observed when the dynamic similarity number Ds drops or rotor radius increases beyond certain values. The exergy destruction seems to increase exponentially with increasing radius. Impact on the performance by the variation of the dryness fraction of wet-steam has been reported for steam qualities 0.8-0.95. Although the obtainable power decreases with the dryness fraction, the rotor and second law efficiency seem to increase, cementing the previous claims of the ability of Tesla turbines to perform efficiently at poor steam qualities.
查看更多>>摘要：Two phase immersion liquid cooling cabinet can meet the cooling needs of high-density data center. However, the cabinet has the problem of poor heat dissipation effect caused by evaporation pressure fluctuation. The two-phase liquid-immersion cabinet with external condenser can discharge the generated vapor in time to maintain its pressure stability. But its cabinet-scale thermal management performance has not been investigated in detail yet. In this paper, the cabinet simulation model is established to evaluate the effects of inlet velocity, coolant type and cabinet internal structure on chip cooling effect from two aspects of thermal safety and temperature uniformity. The results show that the inlet velocity and the coolant type have great influence on the chip safety. When the inlet subcooling degree is constant, the drop range of chip temperature decreases gradually with the increase of coolant flow rate. The decline range is almost unchanged when the inlet velocity is greater than 0.6 m/s. At the same inlet subcooling degree and velocity, compared with Novec 649, the chip temperature decreased significantly after using Novec 7000 with lower boiling point. And the latent heat of vaporization also affected the temperature drop range, the average chip temperature decreased by 17.32 °C at most. The horizontal baffle between the upper and lower chips can significantly improve the overall temperature uniformity of the cabinet. Under the design conditions, the temperature uniformity coefficient of chip can be decreased by 55.64%, which is conducive to its safe and stable operation.
查看更多>>摘要：The exit shape of a fan-shaped hole plays an important role to improve the film cooling effectiveness. In this study, a fan-shaped cooling hole on a flat plate was optimized through Reynolds Averaged Navier-Stokes (RANS) analysis for a specific cooling application of unusually large lateral span. A novel hole was configured with four linear dimensions including the leading and trailing edge lateral widths, the exit longitude, and the round metering length. Two rounds of Latin Hypercube Samples were used to narrow the design space for an accurate surrogate model. The first samples were used to evaluate individual variable sensitivity. The second samplings of predominant variables were then combined with the first sampling to build a Kriging surrogate model to predict the film cooling effectiveness of new candidates. A multi-island algorithm was adopted to obtain the optimization solution. The enhanced cooling effectiveness of the final optimal design got verified in an experiment. Results show the improved prediction accuracy of Kriging model and the fast convergence rate of the optimization solution. For a cooling case with a relatively large lateral span, an optimal fan-shaped hole intends to increase the lateral expansion width and to reduce longitude opening width. The spatial averaged cooling effectiveness of the optimized hole achieved a 70% increment over the baseline one.
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Elsevier