Page 98 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

3.2 Data: m=1kg; M= 28 kg/kmole p1 = 1.01 bar;

T1 = 20 + 272 = 293 K; p2 = 4.2 bar

From equation
R
R = 0
M

. 8 314
=
28
= 0.297 kJ/kgK

The process is shown on a p-v diagram below. When a process takes place from

right to left on a p-v diagram the work done by the fluid is negative. That is, work
is done on the fluid.

p

4.2

pV=C

1.01

v

From equation 3.4

p
W = mRT 1 ln 1
p 2

. 1 01
= 1 x 0.297x293x ln
2 . 4

= -124 kJ/kg

For an isothermal process for a perfect gas,

Q = W = -124 kJ/kg

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