The effect of thermal capacitance and phase change on outside plant electronic enclosures

The effect of heat storage on temperatures inside telecommunications outside plant electronic enclosures is examined. A simple thermal analog model is developed to represent the heat flow in an enclosure that contains a thin envelope of phase change material (PCM). Two sets of equations are obtained for the internal and the PCM temperatures, one when the PCM is in a sensible heat storage mode and the one when it is in its latent heat storage mode. Exact solutions are obtained for both modes. For the sensible mode, the solution yields simple expressions for enclosure damping and delay factors. For the latent mode, the internal temperature is shown to be a simple exponential function of time, with maximum value determined by the phase change temperature and internal heat generation. The analytical results are compared with initial data from several small capacitive outside plant enclosures, indicating that the analytical expressions provide a good method for estimating temperatures in these enclosures