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CRich
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Uncle Sam claims that he invented a black-box device which operates at steady state, and has two inlet streams and one outlet stream as shown in the figure below. Inlet 1 allows air to enter at a pressure of 200 kPa, temperature of -50 oC, and mass flow rate of 30 kg/min. Inlet 2 allows air in at 100 kPa, temperature of 150 oC, and mass flow rate of 20 kg/min. The outlet is at a pressure of 190 kPa. He further claims that this device is insulated and requires no work input. After a thermodynamic analysis, one can show that a work input to the device is actually needed. In your analysis treat the air as an ideal gas with constant specific heats. Also R=0.287 kJ/kgK and cp=1 kJ/kgK. Determine the minimum amount of work that must be done on the system to make the device possible. Assume that the outlet pressure remains unchanged
So this is what I was thinking:
1) change deg. C to deg K
2)interpolate for h
3)Wcv=Qcv+[mi1(hi1+Vi1^2/2)+mi2(hi2+Vi2^2/2)]-me(he+Ve^2/2)
However: I think I should find the entropy change 1st but, I'm unsure how to
So this is what I was thinking:
1) change deg. C to deg K
2)interpolate for h
3)Wcv=Qcv+[mi1(hi1+Vi1^2/2)+mi2(hi2+Vi2^2/2)]-me(he+Ve^2/2)
However: I think I should find the entropy change 1st but, I'm unsure how to