Page 43 - BASIC CONCEPTUAL OF THERMOFLUID

THE IDEAL GAS LAW

PV = nRT

P = Air Pressure in ATM
V = Volume in (m )
3
n = Number of Moles
R = Constant (8.314)
T = Absolute Temp in Kelvin

The characteristic equation is usually written;
PV = mRT

m = mass of gas (kg)
V = volume (m )
3
If gas changes from state 1 to state 2 during a process, then

=
The gas constant, R is different for each gas and is determined from;

=

( kJ/kg.K)

Experiment has shown that the universal gas constant, Ro = 8314.4 J/ mole K

There for the value of =

.
=

= 259.8

EXAMPLE 9

2
3
0.046 m of gas are contained in a sealed cylinder at a pressure of 300 kN/m and a temperature of 45
o C. The gas is compressed until the pressure reaches 1.27 MN/m . If the gas is assumed to be a perfect
2
gas, determine:
a) the mass of gas (kg)
o
b) the final temperature of gas ( C)
Given:R = 0.29 kJ/kg K
SOLUTION : EXAMPLE 9 10

V1 = 0.046 m 3 V = ? m 3
2
P1 = 300 kN/m 2 P 2 =1.27 MN/m =1.27 ´10 kN/m 2
2
3
T1 = 45 + 273 = 318 K
b) sealed cylinder = volume constant
a) = =

=
=

(300)(0.046)
= 318 1.27 10
0.29(318) =
= 0.150 kg 300
= 1346.2 k 39