Specific Heat Capacity

The Specific Heat Capacity is the amount of heat required to change a unit mass of a substance by one degree in temperature

The Specific Heat Capacity 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 = mass (kg, lb)

c = Specific Heat Capacity (kJ/kg ^oC, Btu/lb ^oF)

dt = temperature change (^oC, ^oF)

Expressing Specific Heat Capacity using (1)

c = dQ / m dt         (1b)

Converting between Common Units

• 1 Btu/lb_m^oF = 4186.8 J/kg K = 1 kcal/kg^oC

Specific Heat Capacity Gases

There are two definitions of Specific Heat Capacity for vapors and gases:

c_p = (δh/δT)_p - Specific Heat Capacity at constant pressure (kJ/kg^oC)

c_v = ( δh/ δT)_v - Specific Heat Capacity at constant volume (kJ/kg^oC)

Gas Constant

The gas constant can be expressed as

R = c_p - c_v         (2)

where

R = Gas Constant

Ratio of Specific Heat

The Ratio of Specific Heat Capacities is expressed

k = c_p / c_v         (3)

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