Page 93 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

mR (T −T
W = 1 ) 2 (3.11)
 − 1

But, mRT2 = p2V2 and mRT1 = p1V1

Then the expression for the expansion becomes

p V − p V
W = 1 1 2 2 (3.12)
 − 1

Referring to the process represented on the p-V diagram it is noted that during this

process the volume increases and the pressure decreases. For a perfect gas, equation 4.6

tells that a decrease in pressure will result in a temperature drop.

Example 3.1

In an industrial process, 0.4 kg of oxygen is compressed isothermally from 1.01 bar

o
and 22 C to 5.5 bar. Determine the work done and the heat transfer during the

process. Assume that oxygen is a perfect gas and take the molecular weight of oxygen

to be M = 32 kg/kmole.

Solution to Example 3.1
o
Data: m = 0.4 kg; p1= 1.01 bar; t1= 22 C
p2 = 5.5 bar; W = ? Q = ?

From the equation
R
R = 0
M

8314
=
32
= 260 J/kgK

= 0.260 kJ/kgK

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