Page 111 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

Consider the fluid in the piston cylinder as shown in Figure 3.2.3-5. If the load on the

piston is kept constant the pressure will also remain constant.

The general property relation between the initial and final states of a perfect gas is
applied as:

p V p V
1 1 = 2 2
T 1 T 2

If the pressure remain constant during the process, p2 = p1 and then the above relation

becomes

V V
1 = 2
T 1 T 2

or

T V
2 = 2 (3.20)
T 1 V 1

From this equation it can be seen that an increase in volume results from an increase in

temperature. In other words, in constant pressure process, the temperature is

proportional to the volume.

Work transfer:

Referring to the process representation on the p-V diagram it is noted that the volume
increases during the process. In other words, the fluid expands. This expansion work is

given by

2
W =  pdV
1

2
= p  dV (since p is constant)
1

= p (V2 – V1) (larger volume – smaller volume) (3.21)

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