Plastic helical coil heat exchanger as an alternative for a domestic water storage tank

Abstract

A reduction in weight and cost of a domestic hot water storage vessels is an interesting case for the industry, that can be reached by an alternative material of the helical coil heat exchanger inside them. The goal of the present study was to design a fully polymer solar boiler demonstrator and to explore its thermal performance in the low pressure and low temperature conditions. The metal coil of the conventional solar boiler for domestic usage was replaced by a plastic tube and the heat transfer behavior of helically coiled smooth plastic tube heat exchanger was investigated experimentally. The heat exchanger is placed in the middle of the tank in two parallel coils that fill almost whole height of the vessel in order to achieve maximal surface area. The water inside the tank was heated by circulating in closed loop with heater to achieve constant initial temperature across the whole volume of the vessel. When reached, the heating was stopped and a cold water of the tap temperature started to flow inside the polymeric tube. All the required parameters like inlet and outlet temperatures of tube-side and stratified temperatures in fifteen different points, flow rate of fluids and pressure drop were measured using appropriate instruments. The test runs were performed for different initial temperatures inside the tank ranging from 30-60°C from which the overall heat transfer coefficient and thermal resistances were calculated. The validity of obtained results was compared with the numerical simulation and the experimental results on the initial metallic tube.