查看更多>>摘要：? 2022 Elsevier LtdThe cooling demand for a nominal 300 W power LEDs is around 200 W/cm2 at the chip-scale, and the junction temperature must be maintained below 120 °C for reliable operation. Special thermal management packaging is required to maintain LEDs below this reliability temperature limit. The present study investigates the thermal characteristics of single-nozzle spray cooling over a high-power LED module. The detailed thermal characterization within the LED assembly is explored using both, experimental and numerical approaches. The LED substrate temperature is experimentally obtained for various input power supplies, water flow rate, inlet water temperature, nozzle height, and offset from the LED center. Heat transfer coefficient at two radial locations (R = 0 mm and 12.5 mm) is estimated to evaluate the heat removal capacity of the spray for these operating conditions. Numerical study is performed to visualize temperature and heat flux distribution within the LED module, and to investigate the appearance of thermally critical locations. Junction temperature is the critical parameter for thermal characterization of the LED module, and is numerically investigated for various operating conditions. The junction temperature is maintained below 95 °C at the nominal electrical input power for a Re ≥ 8,000 using the proposed spray cooling design. The present study establishes the efficacy of spray cooling for high-power LED modules, even when the supply power exceeds 112% of the nominal power range.
查看更多>>摘要：? 2022 Elsevier LtdIn this research, experimental study is conducted on a generator connected to a diesel engine to enhance the performance and reduce the emissions using on-board produced H2/O2 gas mixture. The H2/O2 gas mixture is generated and supplied by a HYDI unit, which uses electrolysis of water to produce the required H2/O2 mixture. It is found that through the addition of the H2/O2 mixture via the inlet air there is significant reductions in the exhaust emissions of PM concentrations. The average reductions in PM concentrations are 10.34%, 24.77% and 41.05% across the load range at H2/O2 mixture flow rates of 0.42 LPM, 0.84 LPM and 1.25 LPM, which are equivalent to 0.022%, 0.045% and 0.067% hydrogen energy substitution (HES), respectively. The maximum reduction in exhaust emission of PM concentrations is 56% at 115.4% of the rated load with H2/O2 mixture flow rate of 0.067% HES. It is also found that there are slight reductions in the exhaust emission of CO. The average reductions in CO emissions are 5.50%, 3.40% and 2.32% across the load range at H2/O2 mixture flow rates of 0.022% HES, 0.045% HES and 0.067% HES, respectively. Since the maximum flow rate of H2/O2 gas mixture is only 0.067% HES, there is little or no change of fuel mass flowrate, thermal efficiency and bsfc. The power needed to produce H2/O2 gas mixture is provided by the battery/alternator. It only uses a little amount power of 360 W and there is no issue to start the generator after overnight shutdown. The storage and consumption of water do not possess any issue as it only consumes 0.974 L of water for 24-hours operation.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, a numerical method is used to maximize the performance of an auxiliary entrainment ejector used in multi-evaporator refrigeration system developed for refrigerated trucks in tropical and humid climates. The Computational Fluid Dynamics model based on the previous study is developed to discuss the effects of key design parameters of an auxiliary entrainment ejector. The simulation model is validated against experimental data of an R134a test rig. The numerical models agree fairly well with the experiments. In order to maximize the efficiency of the auxiliary inlet, the diffuser angle is considered critically. The influence of diffuser angle on the optimal position and angle of the auxiliary inlet is then discussed. As well, the effect of secondary flow and auxiliary flow at varying temperatures on the efficiency of auxiliary entrainment ejector is analyzed. The main results are given as follows: (1) optimal auxiliary inlet position as well as angle and entrainment ratio depend on diffuser angle, and optimum parameters combination (length ratio of 1.9, inlet angle of 45°, and diffuser angle of 4°) of the new-type ejector exists; (2) with the secondary flow working temperature of ?10 °C, the entrainment ratio reaches its maximum value of 0.658, and the corresponding entrainment ratio at secondary inlet is 2.60; (3) the auxiliary entrainment ejector can only function if the auxiliary flow working temperature is between ?30 °C to ?22 °C; (4) it is best to connect the secondary inlet to the medium temperature evaporator, with the auxiliary inlet to the low temperature evaporator, when using the secondary and auxiliary inlet connections to separate evaporators with varied operating temperatures.
NSTL
Elsevier