Read the problem statements and answer the discussion problems, based on the ide
ID: 3162019 • Letter: R
Question
Read the problem statements and answer the discussion problems, based on the ideal gas law knowledge and compare the results graph of the expansion method:Method 1 (rapid): Method 2 (slow):
Discussion questions: 1. Explain the heat transfer between the tanks and the surrounding for both expansion cases. Is it ''+'', ''-'', or unknown? (No calculation needed)
2. Sources of errors for each of the cases and the sources of discrepancies between 2 cases 2- Two tanks are connected through two pipes, in parallel, one with a solenoid valve and the other with a needle valve in between. The tanks initially contain air at ambient pressure and temperature. The left tank is connected to a high pressure air line and is filled until the pressure and temperature reaches Ph and T1, respectively. The right tank is vacuumed to P2 and 72, using a vacuum pump. At the first try of expanding the left tank to the right one, the solenoid valve is opened abruptly and the air flows from the left tank to the right one in a fast way. In the second try, with a similar initial condition, the opening of needle valve is small and the air flows gradually from left to right. The final properties are read for both cases, after two tanks reach equilibrium. Objectives: a) To understand different processes happening in both cases b) To calculate the volume ratio of two tanks.
Explanation / Answer
1. In the first case as the expansion is adiabatic (fast) the air enters into the second tank abruptly thereby increasing its pressure from vaccuum level to half the pressure (pressure distribution assuming that the tanks have idential shapes) of the first tank with oscillatory condition. The tmperature of the first tank falls in the begining and gradually gains the ambient temperature condition. In this process heat tis taken from surroundings by the first tank. It is +
2. In the second case, the expansion is slow but through controlled expansion. Hence the effect is similar to joule Thomson expansion (throttle expansion). The pressure in the second tank slowly increases and reaches half the initial high pressure of first tank, once again assuming that the tanks have identical shapes. But at the nozzle, the temperature falls gradually, can be to sub zero temperatures, depending on the pressure level to which it is rised to. In this case more amount of heat transfer takes place from the surroundings to the first tank and attains thermal equilibrium after a long time, once again depending on the temperature fall and ambient temperature. Sources of error: In the first case the pressure settlement in both the tanks cannot easily be predicted since the high pressure air enters vaccuum chamber. In the second case errors are limited. Source of descrepancy is greater in the first case than the secon one.
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