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The Specific Heat is the amount of heat required to change a unit mass of a substance by one degree in temperature. The heat supplied to a unit mass can be expressed as
dQ = m c dt (1)
where
dQ = heat supplied (kJ, Btu)
m = unit mass (kg, lb)
c = specific heat (kJ/kg oC, kJ/kg oK, Btu/lb oF)
dt = temperature change (K, oC, oF)
Expressing Specific Heat using (1)
c = dQ / m dt (1b)
2 kg of aluminum is heated from 20 oC to 100 oC. Specific heat of aluminum is 0.91 kJ/kg0C and the heat required can be calculated as
dQ = 2 (kg) 0.91 (kJ/kg0C) (100 (oC) - 20 (oC))
= 145.6 (kJ)
One litre of water is heated from 0 oC to boiling 100 oC. Specific heat of water is 4.19 kJ/kg0C and the heat required can be calculated as
dQ = 1 (litre) 1 (kg/litre) 4.19 (kJ/kg0C) (100 (oC) - 0 (oC))
= 419 (kJ)
There are two definitions of Specific Heat for vapors and gases:
cp = (δh/δT)p - Specific Heat at constant pressure (kJ/kgoC)
cv = ( δh/ δT)v - Specific Heat at constant volume (kJ/kgoC)
The gas constant can be expressed as
R = cp - cv (2)
where
R = Gas Constant
The Ratio of Specific Heat is expressed
k = cp / cv (3)
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