Improvement of the performance of metal hydride pump by using phase change heat exchanger

Abstract

Some metals and alloys called metal hydrides (MHs) may react reversibly with a large amount of hydrogen under certain conditions. Such materials may be used not only as hydrogen storage carriers but also as energy conversion materials. Thermally driven metal hydride pump (MHP) system is a promising candidate to utilize low-grade heat because it has no mechanical moving parts and uses an environmentally friendly working fluid.The present work discusses a new concept of a MHP equipped with a phase change heat exchanger. This system was developed to store the heat of reaction during absorption and to release it during desorption process by using a Phase Change Material (PCM). The governing equations describing the dynamic behavior of the pump were established and discretized and a computer code is developed to solve the obtained algebraic equations. Using this code, a comparison between a MHP with and without PCM is made. The impact of operating parameters (heat transfer coefficient, gear ratio, pumping head, desorption pressure, PCM mass, PCM thermal conductivity, solidification enthalpy) on the performance of the pump was done, and it was noticed that the integration of a PCM reduces the pumping time by about 88% and provides an efficiency nearly 8 times higher than the case without PCM.