The specific heat of a substance is the amount of heat required, or released, to change the temperature of one pound of the substance to one degree Fahrenheit.
The sensible heat required to cause a temperature change in a substance varies with the kind of substance and the amount of the substance. The specific heat of water is 1.0. Different substances require different amounts of heat per unit quantity to effect these changes in temperature.
The specific heat of several common substances is shown in Fig 1-15.
To determine the amount of heat necessary to cause a desired change of temperature in a substance multiply the weight of the substance by the specific heat and by the temperature change, provided there is no change of state.
In order to calculate the amount of heat added or removed from substances, the following formula should be used.
Amount of heat added or removed in Btu = Wt. of substance x sp. ht. x temperature change in degrees F., or Btu = Wt. x sp. ht. x F. change.
Example: How many Btu must be removed to cool 40 lbs. of 20% salt brine (see Fig. 1-15) from 60 F. to 20 F.?
Solution:
Btu = Wt. x sp. ht. x F. change
Btu = 40 x .85 x 40
Btu = 1380
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Basics of Refrigeration