Computational Fluid Dynamics Study and Modelling of Inlet Jet Mixing in Solar Domestic Hot Water Tank Systems

Abstract

<p>Thermal stratification in solar energy storage tanks plays an important role in enhancing the performance of solar domestic hot water (SDHW) system. The mixing that occurs when hot fluid from the solar collector enters the top of the tank is detrimental to the stratification. Mathematical models that are used for system analysis must thus be able to capture the effects of this inlet jet mixing in order to accurately predict system performance. This thesis presents a Computational Fluid Dynamics (CFD) study of the heat transfer and fluid flow in the thermal storage tank (TST) of a solar domestic hot water system employing a vertical inlet jet geometry. The focus of the thesis is on the studying the effects of inlet jet mixing on the thermal stratification in the tarue Predictions of transient temperature profiles were assessed by comparing to experimental data from the literature. CFD was then used to study how the predicted mixing in the TST was affected by parameters such as the inlet velocity and temperature, pipe diameter and the selected turbulence model. From this study of the mixing, a one dimensional empirical model was developed to predict the temperature distribution inside the TST. The model was found to provide improved predictions of the transient axial temperature distribution in comparison to the plug-flow model which is commonly used in the broader system analysis codes.</p>