Transient Response of a Thermocouple Circuit Under Steady Currents

Abstract

Heat transfer calculations for a thermocouple circuit functioning as a Peltier cooler have been carried out. The calculations depend upon the exact solution of a one-dimensional time-dependent heat equation. It is shown that for an unloaded couple the temperature at the cold junction will be less than or equal to the reference junction temperature only for currents in the range from zero to twice the optimum current (i.e., the current that produces the minimum cold junction temperature). The temperature at the cold junction has been investigated as a function of time, and shown to approach the steady-state values appropriate to any particular multiple of the optimum current at that point with increasing time. It has been shown that one cannot produce a transient thermal spike at the cold junction which is greater in magnitude than the steady-state temperature for the optimum current by initially applying currents greater than the optimum. The possibility of achieving such thermal spikes by superposing a current pulse upon the steady-state current is discussed. The possibility of using the transient response of thermocouple junctions for the measurement of thermal conductivity is examined.