An optimizer using the PSO algorithm to determine thermal parameters of PCM: A case study of grey water heat harnessing

The melting and freezing of Phase Change Materials (PCMs) is categorized as a moving boundary problem. For this reason the mathematical solution to study the behaviour of practical applications is only possible via complex numerical approximations. However for a preliminary design the main concern is to select the optimum thermal characteristics of the PCM storage unit, for both melting and freezing. This is to be done before the detailed design by integrating an optimization algorithm with a numerical simulation. The application of using PCMs to harness the waste heat from non-industrial grey water is investigated as a case of study. For this purpose, the 2-phase analytical solution to the Stefan problem is coupled with the particle swarm optimizer (PSO) to find the best combination of thermal characteristics within the prescribed boundary conditions of this case study. Results show that the optimum phase change temperature lies between 20 and 22 °C, depending on various sets of input parameters. At the same time the ratio of latent to sensible heat transferred by the PCM highly influences this optimum temperature for the combination of both melting and freezing. Similarly results show melting being faster and more intensive in term of latent heat charging compared to a higher sensible heat discharging while freezing.