Use EzeJector software as your ONE STOP SERVICE for ejector design. Get quick and accurate results to close in on your best alternative! Or do you need an ejector design done for you? We can size and specify ejectors for a wide range of applications. Or do a rating for an existing ejector. Go to our Case Design Page. Your challenge as a process engineer is working out whether an application will work and what the flow rates and conditions are to make it work.
How the ejector energy balance works:The motive gas accelerates to sonic velocity in the nozzle throat (choked flow) with pressure decreasing by approximately 45% (depending of gas properties). The gas continues to accelerate to Mach >1 in the outlet section of the nozzle, with the pressure reducing to that required to draw in the entrained gas. The ejector nozzle is also known as a De Laval nozzle. Pressure reduction of the motive gas has thus been converted isentropically into usable kinetic energy. Some energy is lost because of isentropic efficiency <100%. The entrained gas is drawn into the mixing section and also accelerates to sonic velocity (there are cases where it does not reach sonic velocity but these are not described here). Once again there is some energy loss due to isentropic efficiency <100%. The motive gas and entrained gas have different velocities. Momentum is preserved as they mix, but kinetic energy is lost. In general, the greater the ratio of motive gas pressure to entrained gas pressure, the greater the loss of kinetic energy. The mixed gas is still supersonic as it leaves the mixing section. A shock wave then occurs as it enters the diffuser . Flow becomes subsonic and a step change increase in pressure occurs. The gas decelerates in the diffuser with kinetic energy being recovered as increased pressure. As above, some energy is lost due to isentropic efficiency <100%. Friction against the internal metal surfaces of the ejector causes additional energy losses. 在压力降低约45％时（取决于气体特性），动力气体在喷嘴喉部（（流）中加速至声速。气体在喷嘴的出口部分继续加速到Mach> 1，压力降低到吸入夹带气体所需的压力。喷射器喷嘴也称为拉瓦尔喷嘴。因此，原动机的减压已等熵地转换为可用的动能。由于等熵效率<100％，会损失一些能量。夹带的气体被吸入混合区并加速至声速（在某些情况下未达到声速，但此处不作描述）。再次由于等熵效率<100％而导致能量损失。动力气体和夹带气体具有不同的速度。当它们混合时，动量得以保留，但动能却丢失了。通常，运动气压与夹带气压之比越大，动能损失越大。混合气体离开混合区时仍是超音速的。进入扩散器时会产生冲击波。流量变为亚音速，并且压力发生阶跃变化。气体在扩散器中减速，动能随着压力的增加而回收。如上所述，由于等熵效率<100％，会损失一些能量。喷射器内部金属表面的摩擦会导致额外的能量损失。链接到与能量平衡有关的方程式。购买喷射器的最后一站是在供应商那里，但是对能量平衡进行建模和校准使我们在这条路上走了很长的路要走。最终设计很复杂，但是初始过程设计不必如此神秘。对能量平衡和几何形状的了解可以直观地了解控制方法和约束。
数据输入到高亮字段中，程序运行。在低于（蒸汽喷射器）动力压力的情况下，夹带气体压力和夹带率保持恒定。
然后可以改变夹带率，以产生类似于下面的喷射器曲线。 （PR是动力气体与夹带气体压力之比）。请注意，这些曲线是针对特定的温度和气体特性的，如果其中任何变化，则将显着变化。
上面曲线上的每个点代表针对特定条件确定尺寸的喷射器的性能。选择的特定喷射器将具有正确的几何形状，以在一个特定的设计点获得最佳性能。随着工作点偏离设计点，性能将越来越偏离上述理想曲线。动力气体的压力和流量保持相对恒定-控制系统保持夹带的气体压力和流量与排气压力之间的平衡。这对于真空喷射器尤其重要。
[ 此帖被pony8000在2024-04-29 10:48重新编辑 ]
微博帐号登录