Experimental study on the thermal performance of a grey water heat harnessing exchanger using Phase Change Materials

To integrate heat extraction and storage into a single unit along with decoupling of demand and supply,\Phase Change Materials (PCMs) can be used to harness heat from grey water (GW). A simple heat\exchanger linking both the GW and incoming mains cold water (CW) in a counter flow arrangement with\a PCM is experimentally tested. To enhance the thermal conductivity of the PCM, metallic copper fins are\placed throughout the cross-section of the pipes.
The charging with a GW temperature of 325 K and the discharging with a CW temperature of 285 K, of\the PCM is investigated. The influence of the mass flow rates of both the fluids is investigated by varying\it between discrete values of 0.1 kg/s and 0.05 kg/s. Similarly the operation strategy of the heat exchanger
is varied between the solo operation of the GW and CW compared with the simultaneous flows of both.
Finally two different PCMs; with a melting temperature of 298 K (RT-25) and 315 K (RT-42) are also\tested.
The mass flow rate is proportional to performance with 0.1 kg/s showing the best results but being less\influential for RT-25 as compared to RT-42. In RT-25 most heat is transferred as latent heat with a higher\phase change rate whilst RT-42 transfers sensible heat. The solo operation strategy of non-simultaneous
GW and CW flow is more effective as this exchanger is meant to decouple demand and supply. The ability\of RT-25 to retain heat over the long term is also greater compared to RT-42. Ullage issues and corrosion\concerns of the metallic container and pipes are also dominant over the long-term usage of these PCMs.