Monday, January 13, 2014

Thermoelectric cooler Alcohol bath

For the purposes of calibration of temperature sensors at low temperatures or for testing thermo-switches the following layout may be used to make Alcohol cooling bath. The idea beyond using Alcohol is that it has low freezing temperature (-114 C) so it will not freeze in the negative temperature ranges like water which will act like an insulator when it turns into ice. Also, using air as a cooling medium is obviously not reliable because it has low convection heat transfer coefficient, low thermal capacity (and hence low temperature stability), besides the moisture content of air will form frost on the cold sides of the thermoelectric cooler modules resulting in insulation effect.

As you can see in the image above, the insulation cap (on top) not only work as an insulator, but it also prevents the evaporation and loss of Alcohol which has high volatility. 

The cooling capacity may be increased by just increasing the number of thermoelectric coolers (something like the image below). Increasing number of thermoelectric cooler modules for the same path will increase its volume resulting in larger steady state time and may lead to radial non-homogeneity of temperature distribution across the bath.