boundary work associated with a constant volume system is equal to zero.

# Boundary work associated with a constant volume system is equal to zero.

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Whenever a fluid trapped in a closed system (such as the gas in the piston-cylinder device of Fig. 1) expands or contracts, while being in mechanical equilibrium with its surroundings all along the process, boundary work is transferred between the system and surroundings. Suppose, a closed system undergoes a single process from State-1 (with properties p 1 , v 1 etc.) to State-2 (properties p 2 , v 2 etc.) Step-1: If the volume of the trapped fluid increases, the pressure inside is doing work. Work is coming out. Work is positive. Using this principle, determine the sign of the work.

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Step-2: The magnitude of the work transfer is simply the area under the p-V diagram (or m times area under the p-v diagram). To get the area draw a qualitative plot of p vs. V . A few tips to remember here are: p is the pressure of the fluid inside the control volume. We are interested, here, to find the work done by the system, not by the surroundings. Try to obtain the pressure from a force balance on the piston (see
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Boundary work associated with a constant volume system is equal to zero.

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