Hi everyone,

I have a question regarding evaporators (air evaporators). As far as I know, they are all governed by the equation Q = k A Dt, where k depends on a number of factors including geometry, air speed, refrigerant speed, but not absolute temperature, only the difference between refrigerant temperature and and air temperature.

However I have seen some tables supplied by manufacturers where there is a correction factor to be considered when working at different evaporation temperatures, for example, considering that the evaporator performance is given at tev = -7 °C, you need to multiply this performance by 0.93 if the system will work at tev = -20 °C, even when Dt = 8° C in both cases.

I have not been able to find technical references to this subject, it is obvious that mass flow will be less at lower temperatures and so refrigerant speed will decrease also, but I would like to know the real story behind these tables.

Look forward to your comments