Which of the following statements is true?
A. Pump and compressor are two different names for the same thing.
B. If a system is at steady state, you must start with the time-independent form of the generalized energy balance. The time dependent form
of the equation will not work.
C. If the system is a heat exchanger, Q ? will always be negative by our sign convention.
D. If the system is a turbine, W ?_s will always be negative by our sign convention.
E. None of the above statements are true.
A. Incorrect. A pump is used to compress a liquid to higher pressure. A compressor is used to compress a gas or vapor. While there is clearly similarity in function (and energy balance) they are two different processes.
B. Incorrect. Either will describe the system. Steady state means the accumulation term of the energy balance is 0, but material and energy flows in and out of the system can be expressed as either rates or total quantities.
C. Incorrect. A heat exchanger may be used to heat or cool a fluid. Additionally, Figure 3-21 shows that there are at least three different ways of interpreting “the system is a heat exchanger”.
D. Correct. If work exits the system, the sign is negative. A turbine by definition extracts shaftwork from a fluid.
E. Incorrect. One of these statements is correct.
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