Abstract
The maximum temperature differences (MTDs) of three types of two-stage thermoelectric (TE) coolers are analysed, which are the ones with thermocouples at two stages electrically connected in series and parallel and electrically separated, respectively. The analyses are all performed with respect to an important ratio
r in two-stage TE coolers, viz the ratio of thermocouple number between stages. The MTDs of the first and the last configurations can be both far higher than that of a one-stage TE cooler, which may promote the cryogenic applications of TE coolers. When
r approaches to infinity, close-form formulae of their limiting MTDs are found. In the mean time, the polar characteristic of two-stage TE coolers is discussed, when the supplied electric current(s) is alternated.