Compressor power calculation issue
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As shown in the figure below, in a reciprocating compressor, why is the work consumed by the compressor over one cycle equal to the area enclosed by the curve? In the inhalation process, textbooks consider it as the gas doing work on the piston; therefore, the total work is equal to the work done on the gas by the external forces during compression and exhaust, minus the work done by the gas on the piston during inhalation. But in reality, shouldn’t the crankshaft pull the piston back and forth through the connecting rod during inhalation? If we take into account the work done by the gas on the piston, would this work be converted into kinetic energy of the piston? Is the power calculated in this way truly the theoretical power required by the compressor? (Ignoring friction and other losses)
I think this is related to the pressure at the inlet and outlet of the compressor; if there is positive pressure at the compressor’s inlet, then the cylinder should be filled with gas after the piston moves backward, and the piston does not provide suction, or rather, the suction is not entirely provided by the piston； If the intake is under negative pressure, then this suction force is provided by the piston. I’m not sure if this way of thinking is correct
Your understanding is a bit confused. The area enclosed by the gas’s curve graph, assuming the gas is the subject of study and by comparing its state before and after compression, represents the difference in energy obtained; this difference is the work done by the compressor on the gas. Don’t worry about whether it’s the gas that pushes the piston or the piston that pushes the gas; the process is too complex to figure out. It is the power required by the gas, not the theoretical power required by the compressor; the compressor’s power takes into account various losses, that is, efficiency is considered.