Effect of twisted tape inserts on thermal performance of heat pipe evacuated-tube solar thermal collector

Abstract

The effect of twisted tape (TT) inserts on the thermal performance of a heat pipe evacuated-tube solar thermal collector (HP-ESTC) with an eccentric inlet and outlet developed by the present research team is experimentally investigated. An experimental apparatus was constructed to simulate the flow and heat transfer phenomena inside the manifold header of an HP-ESTC and tested in the laboratory. Based on a comparison analysis between the HP-ESTC with TT inserts and an existing HP-ESTC, it was found that adding TTs enhanced the heat transfer performance by eliminating the stagnation flow region, reducing the degree of flow skewness, and generating rotating flow. Because adding the TT inserts increased the flow resistance, resulting in a greater pressure drop based on the pressure drop experiments, an overall performance analysis considering both heat transfer and pressure drop characteristics was conducted. It was confirmed that applying TT inserts could improve the overall performance by up to approximately 7.7%. To assess the applicability of TT inserts for commercial HP-ESTCs, an HP-ESTC containing TT inserts was manufactured and tested outdoors based on test standards (KS B 8295).