Numerical Investigation of Transient Heat Transfer Process in Organic Phase Change Material (OPCM) - Airheat Exchanger

Abstract

This paper presents the analysis of the numerical investigation of the Transient cooling heat transfer process of air flow within a circular duct, embedded in a rectangular container of PureTemp20- a bio-based Organic Phase Change Material (OPCM) with applications in Heating Ventilation and Air Conditioning. The heat transfer process was studied by constructing an axisymmetric 2-D geometrical model of the domain in GAMBIT 2.4.6, while the numerical simulation of the melting process was done using ANSYS FLUENT 6.3 enthalpy-porosity approach. The simulation shows heat transfer pattern from ambient Air to OPCM as well as thermal and hydro dynamic boundary development within the duct. Also, the cross-sectional velocity profile and static temperature within the duct were simulated. During the first stage of the OPCM melting process heat conduction was the main heat transfer mechanism, but as melting progresses heat transfer takes the form of natural convection. This slows down heat transfer rate from Air to OPCM. This indicates that the heat transfer from Air to OPCM starts at the OPCM’s solidus temperature with conduction controlled heat transfer process (CDC-HTP), and as the OPCM starts to melt Free Convection controlled heat transfer process (FCC-HTP) set in, while the effect of CDC-HTP is minimal. Simulations of Instantaneous air flow velocity u(r) distributions and Instantaneous Static Temperature T(r) profiles agreed with published research works within the hydro-dynamically and thermally developing region. Thermal boundary layer is thicker than the Velocity boundary layer in the Air Duct. Thus, Prandtl number (Pr) of Air is less than 1. This confirms Prandtl number Pr=0.7 < 1 in published research works.