Abstract
Two 22 A‐h nickel‐cadmium cells were continuously cycled at a 1c charge rate and a 2c discharge rate, with cooling provided by an intercell planar (rectangular cross section) heat pipe. For purposes of comparison, thermocouple measurements were also taken with an aluminum conduction fin substituting for the heat pipe. The aluminum fin and heat pipe were cooled, by room temperature forced air. Thermally insulated cells were also cycled at the same rates. Cell case temperatures were measured during cycling, and a maximum of 29°C with a 5°C thermal excursion was noted with the heat pipe under conditions of thermal equilibrium which were observed after 3 complete cycles. For the aluminum fin configuration a maximum of 42°C with a 7°C thermal excursion was obtained near thermal equilibrium after 5 complete cycles. The insulated configuration yielded a battery case temperature of 83°C after 5 cycles, and thermal equilibrium was never reached. Coulombic efficiency values for the heat pipe cooled battery were found to be several percent greater than ∼95% which was recorded for the aluminum fin configuration. The specific heat of the cells was measured to be 0.27 cal/g°C. From this and the measured values of the total heat generated per cycle, the effectiveness of the heat pipe in removing battery heat was calculated to be approximately 26% greater than the aluminum fin at or near equilibrium. It is surmised that the significantly lower operating temperatures produced by the heat pipe should lead to an important lengthening of battery cycle life and an associated reduction of capacity degradation.