Liquids - Latent Heat of Evaporation
The input energy required to change the state from liquid to vapor at constant temperature is called the latent heat of vaporization. When a liquid vaporize at the normal boiling point the temperature of the liquid will not rise beyond the temperature of the boiling point.
The latent heat of vaporization is the amount of
"heat required to convert a unit mass of a liquid into vapor without a change in temperature".
| Product | Latent Heat of Evaporation*) - he - | |
|---|---|---|
| (kJ/kg) | (Btu/lb) | |
| Acetic acid | 402 | 173 |
| Acetone | 518 | 223 |
| Alcohol | 896 | 385 |
| Alcohol, ethyl (ethanol) | 846 | 364 |
| Alcohol, methyl (methanol alcohol, wood alcohol, wood naphtha or wood spirits) | 1100 | 473 |
| Alcohol, propyl | 779 | 335 |
| Ammonia | 1369 | 589 |
| Aniline | 450 | 193 |
| Benzene | 390 | 168 |
| Bromine | 193 | 83 |
| Carbon bisulphide | 160 | |
| Carbon dioxide | 574 | 247 |
| Carbon disulphide | 351 | 151 |
| Carbon tetrachloride | 194 | 83 |
| Chlorine | 293 | |
| Chloroform | 247 | 106 |
| Decane | 263 | 113 |
| Dodecane | 256 | 110 |
| Ether | 377 | 162 |
| Ethylene glycol | 800 | 344 |
| Trichlorofluoromethane refrigerant R-11 | 180 | 77 |
| Dichlorodifluoromethane refrigerant R-12 | 165 | 71 |
| Chlorodifluoromethane refrigerant R-22 | 232 | 100 |
| Glycerine | 974 | 419 |
| Helium | 21 | 9 |
| Heptane | 318 | 137 |
| Hexane | 365 | 157 |
| Hydrogen | 461 | 198 |
| Iodine | 164 | 71 |
| Kerosene | 251 | 108 |
| Mercury | 295 | 127 |
| Methyl chloride | 406 | |
| Nitrogen | 199 | 86 |
| Octane | 298 | 128 |
| Oxygen | 214 | 92 |
| Propane | 428 | 184 |
| Propylene | 342 | 147 |
| Propylene glycol | 914 | 393 |
| Sulphur | 1510 | 650 |
| Sulfur dioxide | 164 | |
| Toluene | 351 | 151 |
| Turpentine | 293 | 126 |
| Water | 2256 | 970.4 |
- 1 kJ/kg = 0.43 Btu/lbm = 0.24 kcal/kg
*) The latent heats of evaporation are based on fluid boiling point temperatures at atmospheric pressure.
Evaporation Heat
The heat required to evaporate a fluid can be calculated as:
q = he m (1)
where
q = evaporation heat (kJ, Btu)
he = evaporation heat (kJ/kg, Btu/lb)
m = mass of liquid (kg, lb)
Example - Calculate heat required to evaporate 10 kg of water
The latent heat of evaporation for water is 2256 kJ/kg at atmospheric pressure and 100oC. The heat required to evaporate 10 kg can be calculated as
q = (2256 kJ/kg) (10 kg)
= 22560 kJ
Related Topics
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Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.
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