Heat Exchange Characteristics of Different Piping Systems When Using Thermal Energy from Running Water in Shallow Water Hydraulic Conditions

Abstract

The authors have been studying heat utilization by heat pumps for running water in irrigation canals, and in a previous report, they have shown that the higher the water temperature in the canal, the higher the heat exchange rate of the heat exchanger, the amount of heat exchanged by the heat pump, and the energy consumption efficiency (SCOP) of the heat pump system. The objective of this study is to construct a heat pump system that can handle the hydraulic conditions that may occur in irrigation canals. In this study, focusing on flow velocity and water depth, a full-scale model experiment was conducted using flowing water in a shallow canal with a water depth between 0.23 m and 0.50 m as a heat source, and the heat exchange characteristics of the heat exchanger and SCOP were evaluated. The experimental results showed that the heat transfer coefficient increased by approximately 5% for each 0.20 m･s^-1 increase in flow velocity under relatively high velocity conditions of 0.50-0.90 m･s^-1, that the heat transfer coefficient, quantity of heat and SCOP decreased when the heat exchanger was exposed to air, and that the quantity of heat were higher for parallel pipes.