Novel rotary regenerative heat exchanger using cascaded phase change material capsules

Abstract

A novel rotary regenerative heat exchanger with cascaded phase change material (PCM) capsules was proposed and proved to be a better alternative to the traditional one. The rotary regenerative air preheater used in coal-fired power plant was taken as an example to comparatively analyze the performance characteristics of the rotary regenerative heat exchanger with latent heat storage material and the one with sensible heat storage material. The latent rotary regenerative air preheater (LRAPH) can achieve more uniform outlet temperature of air at low rotating speed than the sensible one (SRAPH), which is conductive to the measurement and process control in application. PCM capsule functions as both a latent heat storage material at its phase change temperature and as a sensible heat storage material at other temperature values. At lower rotating speed, more PCM capsules in LRAPH will work at the phase change temperature resulting in small temperature swings of fluid and matrix. The heat exchanger effectiveness is comparatively analyzed for SRAPH and LRAPH with different matrix parameters. The replacement of sensible heat storage materials by the latent ones would lead to an efficiency improvement of RAPH as large as 11% especially at lower rotating speed. The LRAPH is more capable to counter the entrainment leakage and the problems induced by temperature swings than traditional SRAPH. The cascaded distribution of PCM capsules with different phase change temperatures should be reasonably set according to the specific characteristics of temperature distribution in application to make full use of advantages of cascaded PCMs.