The multiple meanings of the Stefan-number (and relatives) in refrigeration

The Stefan-number is one out of the multitude of dimensionless numbers which predominantly are used in chemical engineering or heat and mass transfer problems. It relates sensible heat to latent heat and is a key number in solving the problem of heat transfer during solidification or melting.However, numbers similar to this show up also when several thermodynamic problems or relationships in refrigeration engineering are analyzed. Using the Stefan-number it can be distinguished if a refrigerant superheats or condenses during compression, it gives the size of the throttling loss, and it helps to decide if a suction line heat exchanger is beneficial or not. For absorption heat pumping, it allows to quantify the most important loss mechanism, the solution heat exchanger loss. Of course, all this information can be acquired in different ways – and maybe in more precise ways – also, but at least for teaching the basics of refrigeration the Stefan-number is simple to use and very easy to understand.In this paper, the different ways of how to use the Stefan-number in teaching and understanding thermodynamics of refrigerants are presented.