Numerical investigation of the performance improvement of instantaneous gas water heater by introducing new geometries for the heat exchanger

Abstract

Tankless gas water heaters are known for their efficient energy consumption, as they only heat water on demand, resulting in reduced energy usage compared to traditional storage tank water heaters. A typical water heater uses a U-shaped heat exchanger. To enhance the performance of instantaneous gas water heaters, as well as reduce energy consumption and save energy in residential buildings, a numerical study on heat transfer in the heat exchanger of these water heaters is presented in this paper. The main purpose of this study is to achieve a better performance for gas water heaters by examining the geometry change of the heat exchanger using Computational Fluid Dynamics (CFD). Four different geometries, namely U-shaped, W-shaped, spiral, and sinusoidal tubes, were investigated. The results demonstrate that spiral geometries increase the Nusselt number significantly by creating secondary flows with a much lower pressure drop. SP-L-1.5L, SP-1.5X2, and SP-0.75X3 geometries exhibited the best thermal performance under all conditions, with maximum thermal performance factor of 13 %, 11 %, and 8 %, respectively.