Computational fluid dynamic analysis on solar water heater: Role of thermal stratification and mixing on dynamic mode of operation

Abstract

The present work attempts to demonstrate the competence and reliability of the proposed computational solver for real-scale modelling and analysis of a commercially available evacuated tube collector type solar water heater. A 3-D, transient numerical solver with user-defined functions is modelled using CFD program ANSYS-Fluent 15.0®. The objective is to analyse the evacuated tube collector type solar water heater in two states of operation, namely, static (stagnant charging) and dynamic (retrieval) modes. This work emphasizes the determination of the impact of thermal stratification, and fluid mixing in the storage tank on the outlet temperature profile during discharging. Volume flow rates vary from 3-15 Lpm. The reported findings suggest that with an increase of fluid-flow during discharge, the stratified layers disorient and lead to rapid mixing, which eventually results in an earlier drop in the outlet water temperature. Furthermore, at low fluid-flow rates, the stratified layers remain intact with only a gradual decay in the outlet temperature profile. The analysis reveals that based on the user's choice, it is possible to vary discharge flow rate until 7 Lpm without a significant drop in the outlet water temperature. Furthermore, computational results have been successfully validated with experimental findings.