c v = specific heat capacity at a constant volume process (kJ/kgK)
c p = specific heat capacity at a constant pressure process (kJ/kgK)
T = absolute temperature (K)
R = individual gas constant (kJ/kgK)
ρ = density of gas (kg/m 3 )
p = absolute pressure (Pa, N/m 2 )
Air - 10 kg - is heated at constant volume from temperature 20 o C and 101325 N/m 2 to a final pressure of 405300 N/m 2 .
The final temperature in the heated air can be calculated with the ideal gas equation :
p v = R T (3)
v = volume (m 3 )
The ideal gas equation (3) can be transformed to express the volume before heating:
v 1 = R T 1 / p 1 (4)
Since v 1 = v 2 the ideal gas equation (3) after heating can be expressed as:
p 2 v 1 = R T 2 (5)
or transformed to express the final temperature:
T 2 = p 2 v 1 / R (6)
Combining (5) and (6):
T 2 = p 2 (R T 1 / p 1 ) / R
= p 2 T 1 / p 1 (7)
= (405300 N/m 2 ) (273 K + 20 K) / (101325 N/m 2 )
= 1172 K - the final gas temperature
The change in entropy can be expressed by (2)
ds = c p ln(T 2 / T 1 ) - R ln(p 2 / p 1 )
ds = (1.05 kJ/kgK) ln((1172 K) / (293 K)) - (0.33 kJ/kgK) ln((405300 N/m 2 ) / (101325 N/m 2 ))
= 1 (kJ/kgK)
Total change in entropy:
dS = (1 kJ/kgK) (10 kg)
= 10 (kJ/K)
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
Entropy and disorder.
Basic steam thermodynamics - entropy diagram.
The entropy of steam superheated to temperatures above saturation points.
The Wet Bulb Globe Temperature can be used to measure the general Heat-Stress index.
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