结构参数对弹射器气动性能影响分析

针对高压空气弹射系统高压工质功率密度高、扩张性大、冲击力强等特点,引入真实气体效应,分析了结构参数对气动弹射性能的影响。理论推导了真实气体条件下的比热力学能、比焓等热物理性质参数,建立了基于真实气体条件下的气动弹射封闭方程组,并进行了数值求解;通过各种结构参数与弹射器性能关系的对比研究,获得了弹射器参数对弹射性能影响的变化规律及参数选择规律。数值分析表明:流量开口截面直径越大,高压室体积越大,低压室体积越小,则系统的弹射性能越好,弹射性能的动态分析也为系统的全局模糊设计提供了参考依据。     

A new combined cooling, heating and power system driven by solar energy

A new combined cooling, heating and power (CCHP) system is proposed. This system is driven by solar energy, which is different from the current CCHP systems with gas turbine or engine as prime movers. This system combines a Rankine cycle and an ejector refrigeration cycle, which could produce cooling output, heating output and power output simultaneously. The effects of hour angle and the slope angle of the aperture plane for the solar collectors on the system performance are examined. Parametric optimization is conducted by means of genetic algorithm (GA) to find the maximum exergy efficiency. It is shown that the optimal slope angle of the aperture plane for the solar collectors is 60° at 10 a.m. on June 12, and the CCHP system can reach its optimal performance with the slope angle of 45° for the aperture plane at midday. It is also shown that the system can reach the maximum exergy efficiency of 60.33% under the conditions of the optimal slope angle and hour angle.     

New theoretical model for convergent nozzle ejector in the proton exchange membrane fuel cell system

A new theoretical model for the convergent nozzle ejector in the anode recirculation line of the polymer electrolyte membrane (PEM) fuel cell system is established in this paper. A velocity function for analyzing the flow characteristics of the PEM ejector is proposed by employing a two-dimensional (2D) concave exponential curve. This treatment of velocity is an improvement compared to the conventional 1D “constant area mixing” or “constant pressure mixing” ejector theories. The computational fluid dynamics (CFD) technique together with the data regression and parameter identification methods are applied in the determination of the velocity function's exponent. Based on the model, the anode recirculation performances of a hybrid PEM system are studied under various stack currents. Results show that the model is capable of evaluating the performance of ejector in both the critical mode and subcritical mode.     

带外经济器的喷射节流制冷装置的研究

由于在传统制冷空调循环中的节流阀造成了大量能量损失,故现在以喷射器代替节流阀,并配合使用外经济器来达到节能效果。通过与不同制冷循环在不同工况下的对比与研究,最终确定带外经济器的喷射节流制冷循环所适合的制冷工况。     

Design and investigation of multi-nozzle ejector for PEMFC hydrogen recirculation

In this study, a multi-nozzle ejector is proposed for hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) systems. Numerical simulations are performed on the basis of an experimentally verified three-dimensional numerical model to investigate the performance and inner-flow distribution of the proposed multi-nozzle ejector. We show that the fuel cell system with the multi-nozzle ejector can achieve a wide output-power range without a significant change in the primary pressure by simply switching the operating mode of the nozzles; moreover, the recirculation ratios are acceptable. The output-power can cover the range of 20–25 kW and 35–100 kW theoretically; in addition, a relatively stable anodic inlet pressure can be achieved. The collaboration of nozzles can effectively restrain the vortex, and the operating mode with two nozzles can achieve the best recirculation capacity. The proposed method extends the operating range of the ejector and the results of this study may contribute to the further multi-nozzle ejector design.     

Numerical studies on ejector structure optimization and performance prediction based on a novel pressure drop model for proton exchange membrane fuel cell anode

The performance of hydrogen ejectors can be affected by the working conditions of the fuel cell system especially associating with the working pressure and pressure drop of the anode. However, the pressure drop characteristics model of the anode is correlated to the fuel cell parameters. In this work, a porous jump boundary is used as a pressure drop characteristics model of the anode which is weakly relevant to the parameters of fuel cells by employing the pressure drop characteristic curve of fuel cells. Based on the model, the influence of the condition parameters on the property of the ejector can be predicted. According to our results, the entrainment performance of the ejector can be influenced by anode inlet temperature, relative humidity, and differential pressure. Also, it is helpful for the design and prediction of the ejector in different fuel cell systems depend on the pressure drop.     

推卸铲运机在采矿新方法中的应用

推卸铲运机是一种新式铲运机。在丰山铜矿分段碎石胶结充填采矿法中,我国首次成功应用了自行研制的推卸铲运机,取得了很好的生产效果。本文就推卸铲运机解决的主要技术难题以及结构特点、工作原理等作了论述。     

发动机短舱冷却的计算研究

采用一维的方法对发动机短舱冷却进行了研究,介绍了两种不同的冷却形式,并且给出了这两种冷却形式中短舱冷却空气流量和换热的计算公式,对某型发动机短舱在四种不同状态下的流动及换热进行了计算,并对计算结果进行了分析。     

Thermodynamic investigation and optimization of novel ejector-expansion CO2/NH3 cascade refrigeration cycles (novel CO2/NH3 cycle)

The present study thermodynamically evaluated the ejector utilization's impact on the performance of the cascade cycle that uses CO₂ and NH₃ as refrigerants. The theoretical analysis on the functional features based on the first and second laws of the thermodynamics illustrates the facts that the maximum cop and the maximum second law efficiency are on average7 and 5 percent higher than the conventional cycle. However, the exergy destruction rates roughly 8 percent lower as compared to the conventional cycle. Therefore, the novel ejector-expansion cascade cycle is a promising refrigeration cycle from the thermodynamically and practical points of view. A linear regression through the terms of T_eva, T_cond, ΔT yields to three useful correlations for maximum COP, maximum second law efficiency, and in accordance with their optimal temperature.     

大外侧凹注塑件的脱模实践与认识

大外侧凹注塑件通常采用瓣合阴模成型外形,斜导柱分型,顶杆顶出制品。在这种情况下,必须确保顶杆复位的安全性。本文介绍了顶杆安全半径的计算和采用压缩弹簧使顶出杆复位的方法。