There are two questions on air separation; please take a look
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1. Assume that nitrogen expands from 40 atmospheres (absolute pressure) to 5 atmospheres (absolute pressure), with an expansion ratio of 8; as a result, the temperature of nitrogen drops from -100°C to -124°C. At the same expansion ratio, what should be the exit nitrogen temperature when the nitrogen inlet temperature is +20°C? A: -4℃ B: -10℃ C: +13℃ 2. Assuming nitrogen expands from 40 atmospheres (absolute pressure) to 5 atmospheres (absolute pressure), with an expansion ratio of 8, the temperature of nitrogen drops from -90℃ to -176℃. At the same expansion ratio, what should be the exit nitrogen temperature when the nitrogen inlet temperature is +20°C? A:-113℃ B:-66℃ C:-52℃
The answer on the test is 1, A； 2. A, this is also something I don’t understand.
The answers are B for the first question and C for the second question.
The simulated answers just now were C and A respectively, but why? I really haven’t researched what his formula is It must be possible to see from the formula
Shouldn’t we use the law of conservation of energy to calculate it?
I think B/A should be chosen; the higher the inlet temperature, the greater the cooling capacity should be, and the lower the temperature should be.
The first one is roughly an isenthalpic process, with the work done on the system being negligible. The second one is roughly an isentropic process, with significant work done on the surroundings, and cannot be ignored