Ice is still an important item in the refrigeration industry. As stated before, ice changes to water at 32 F. at atmospheric pressure. Changing ice to water at 32 F., the heat absorption is 144 British thermal units per pound. The heat absorption ability of ice, when changing from a temperature below 32 F. to 32 F., is .504 British thermal units per pound per degree change in temperature. The specific heat of ice = .504 Btu per pound. The latent heat of fusion (melting) of ice = 144 Btu per pound. The specific heat of water = 1 Btu per pound. Example: How many Btu will 25 pounds of ice at 5 F. absorb in changing to water at 40 F.? From ice at 5 F. to ice at 32 F.
Wt. of ice x sp. ht. of ice x temp. change
25 x .504 x (32 -5) or
25 x .504 x 27 = 340.2 Btu
From ice to water at 32 F.
Wt. of ice x latent heat of fusion of ice
25 x 144 = 3600. Btu
From water at 32 F. to water at 40 F.
Wt. of water x sp. ht. of water x temp. change
25 x 1 x (40-32) or
25 x 1 x 8 = 200. Btu
340.2
3600.0
200.0
Total 4140.2 Btu
Tags:
Basics of Refrigeration