Thermoelectric cooler may be designed from two different points of view: to obtain maximum temperature drop and to obtain optimum coefficient of performance
. Cooling by cascades of two and three stages for practical use has been devised with p and n types of Bi2Te3 for obtaining deep temperature drop. Experimental results are given in regard to maximum temperature drop and useful cooling at various cascade ratios.
The temperature drop at the cascade ratio (the ratio of the number of elements in upper stage to that in lower stage) of about 1:20 is large; it falls rapidly as the number of elements in lower stage is reduced.
The absorbed heat increases linearly with the decrease in temperature difference at the same rate as in the case of single stage cooling.
The temperature difference depends upon the hot junction temperature. Hence, four or more stage cooling is but vain elaboration.
