Page 112 - Mechanical Engineer's Data Handbook

Thermodynamics and heat

transfer

3.1 Heat

3. I. I Heat capacity 3.1.3 Latent heat

Heat capacity is the amount of heat required to raise This is the quantity of heat required to change the state
the temperature of a body or quantity of substance by of 1 kg of substance. For example:
1 K. The symbol is C (units joules per kelvin, J K- I) Solid to liquid: specific heat of melting; h,, (J kg- ')
Heat supplied Q=C(t2-tl) Liquid to gas: specific heat ofevaporation, h,, (J kg- *)
where: t, and t, are the initial and final temperatures.
3. I .4 Mixing of fluids
3. I .2 Specific heat capacity
If m1 kg of fluid 1 at temperature t, is mixed with m, kg
This is the heat to raise 1 kg of substance by 1 K. The of fluid 2 at temperature t,, then
symbol is c (units joules per kilogram per kelvin,
Jkg-' K-'). Final mass m=ml +m, at a temperature
Q=mc(t,-t,)
where: m=mass. t= "lClt1 +m,c,t,
m1c1 +m2c2

3.2 Perfect gases

3.2 Gas laws

For a so-called 'perfect gas': where: m = mass, R =the gas constant
Boyle's law: pv = constant for a constant V
temperature T specific volume u=- (m3kg-')
m
V so that: pv=RT
Charles' law: -=constant for a constant pressure p
T
where: p =pressure, V= volume, T=absolute 3.2.2 Universal gas constant
temperature.
Combining the two laws: If R is multiplied by M the molecular weight of the gas,
then :
e= constant = mR Universal gas constant R,= MR=8.3143
T kJ kg-' K- ' (for all perfect gases)