Experimental validation of a numerical model of a corrugated pipe-phase change material (PCM) based heat exchanger to harness grey water heat

The harnessing of waste heat from non-industrial greywater (GW) has tremendous potential, both to enhance overall building efficiency and from the exergetic point of view. At the same time, the storage of this harnessed heat into phase change materials (PCMs), would decouple demand and supply unlike commercially available harnessing techniques. A counter-flow heat exchanger embedded in an appropriate PCM, within the sewage lines of conventional buildings would recover this otherwise lost energy. However due to the limited thermal conductivity of PCMs, passive heat transfer enhancement techniques are necessary both internal and external of the heat exchanger pipes. The use of corrugated pipes compared to simple pipes is quite effective to serve this purpose, especially when coupled with this application of harnessing waste heat. These pipes enhance internal turbulence within the pipe, the surface area of contact and guide the flowing fluid along the circumferential length of the pipe to enhance the overall heat transfer coefficient. Additionally, these pipes also have a doubly enhancing effect, in which heat transfer is improved on the external surface.
An experimental model is used to validate a 3D numerical simulation of this corrugated pipe GW-PCM problem. Temperature readings of the three different components of the system are used to validate the simulation developed in the CFD software Star-CCM v12.04. The overall average percentage errors between the two are below 8.5% for the 15-minute duration with results during the steady state time period being in much closer agreement. This numerical simulation would serve as the basis of a future sensitivity analysis to discover the dimensional parameters of a corrugated pipe delivering optimum results within this application.