Work exchange signs during compressor processes Consider an ideal reciprocating air compressor. During the suction stroke the cylinder pressure is slightly below ambient, during compression it is high, and during delivery it exceeds receiver pressure. Identify whether work is done on or by the piston in each part and assess the correctness of the composite statement given.

Introduction / Context:
Work exchange in compressors depends on the pressure-volume path over a cycle. Understanding whether the piston does work on the gas or the gas does work on the piston in the suction, compression, and delivery phases clarifies the indicator diagram and net work input.

Given Data / Assumptions:

• Slight pressure drop during suction below ambient.
• Finite delivery pressure above cylinder pressure at valve opening.
• Conventional sign: positive work is work done by the piston on the gas.

Concept / Approach:
In suction, the gas pressure in the cylinder is slightly below ambient; the ambient performs work on the gas/piston combination as the volume increases, so the net work from the piston to the gas is negative (i.e., work is done on the piston). During compression, the piston reduces volume against rising pressure, doing positive work on the gas. During delivery, the piston overcomes discharge pressure to push air into the receiver, again doing positive work on the gas.

Step-by-Step Solution:
Suction: p_cyl < p_amb → gas (via ambient) does work on piston → “work is done on the piston”.Compression: piston compresses gas → work done by piston on gas.Delivery: piston forces gas into receiver at higher pressure → work done by piston on gas.Composite statement matches these signs → Agree.

Verification / Alternative check:
Indicator diagrams show a small negative area during suction and a larger positive area during compression plus delivery, resulting in positive net work input to the compressor.

Why Other Options Are Wrong:

• Disagree: contradicts the accepted sign convention and observed indicator area.
• Zero suction drop or “no work in delivery” assumptions are nonphysical.
• Restriction to multistage operation is unnecessary; the logic holds for single-stage too.

Common Pitfalls:
Mixing thermodynamic sign conventions (work of gas vs. work on gas) and overlooking the small but real suction work magnitude.

Final Answer:
Agree