I came up with my own design problem, after completing a refrigeration design problem on the completion of my thermo I class. My design problem is this: I want to accelerate air to 56m/s via a compressor and then a nozzle. I'm trying to do a cost analysis of how much power I would save if the inlet of the nozzle is 0m/s versus 30m/s. Here's the problem, I can't really get enough information to actually do the problem. For example, I'm using a compressor to bring the air up to pressure and then a a nozzle to actually accelerate the air. The object I'm designing would be used in the real world so say the inlet of the compressor is around 21 degrees centigrade so 294K. The compressor brings in air from the atmosphere so say the pressure is 101.3kpa. I can get enough information about state one, the inlet to the compressor but not enough information about state 2 (outlet compressor/inlet nozzle). What sort of real world assumptions can I make here to solve this problem, also I did some google searching to try and find some real world examples of nozzles and compressors isentropic efficiencies and couldn't find them, what are realistic isentropic efficiencies for them?(adsbygoogle = window.adsbygoogle || []).push({});

I'm using air, ideal gas conditions.

State 1 is fixed with T1=294K, P1=101.3Kpa. State 2: I only know that V2=0, state 3: V3=56m/s

Once I get some % figures for real world isentropic efficiencies I know that I can use the definition of isentropic efficiency for the compressor and nozzle, and if I can fix state 2 then I can calculate the ideal state 2, and from that I should be able to get the actual enthalpy at state 2, and then I can use that to interpolate for T. However, from there I'm not quite sure what to do to calculate what the pressure would have to be at state 2, since, if I were to use the ideal gas equation for instance, I would need to know one more piece of information, the specific volume, or volume and mass. So I need to somehow fix state 2, and state 3, what are some realistic assumptions, I know I've got the first law for an open system SSSF at my disposal as well as the 2nd law, but I need to be able to make some general assumptions to get the ball rolling.

Also, I was just wondering how realistic of an assumption it would be to assume the compressor/nozzle to be adiabatic. Keep in mind I've only completed thermodynamics I. It is possible that I may need to complete some more courses to be able to do this. Thanks for all the help,

Kevin

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# Accelerate Air

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