Nitrogen latent heat

Helium vapour pressure and latent heat of evaporation The latent heat of evaporation L and the vapour pressure />vap are fundamental parameters when using these two cryoliquids in the refrigeration process. Figure 2.5 shows L of 3He and 4He as a function of temperature. Note that L ( 20.9 J/g for 4He) is very small in comparison, for example, with that of hydrogen (445 J/g) or of nitrogen (200 J/g). Note also the minimum at 2.2 K in the graph for 4He, in correspondence with the superfluid transition. 

The heat of evaporation of liquid air was measured by T. Estreicher,13 and U. Behn. According to J. S. Shearer, the heat of vaporization depends on the proportion of oxygen and G. Witt represented the latent heat of vaporization of liquid air by A=49-59+0-0143p cals., where p represents the percentage of oxygen in the mixture the latent heat of vaporization of nitrogen is 49-59 cals., and of oxygen, 51-92. 

Nitrogen boils at -196°C and allowing for its latent heat and sensible heat to -50 °C it yields 7.9kcal/kg. The latent heat of solvents lies in the range 75-150 kcal/kg. 

Similarly, the coldness arising from the latent heat of evaporation of the liquid nitrogen and from the sensible heat to raise the gas to near ambient temperature can be replaced by refrigeration operating at the required temperature. 

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