Optical evaluation and analysis of an internal low-concentrated evacuated tube heat pipe solar collector for powering solar air-conditioning systems

An optical evaluation and analysis of an internal low-concentrating evacuated tube heat pipe solar collector designed to enhance the collection of solar radiation for medium temperature applications is presented in this paper. The internal low-concentrating evacuated tube heat pipe solar collector was designed with an acceptance angle of 20° given a geometrical concentration ratio of 2.92. The truncation of the upper part of the reflector giving a geometrical concentration ratio of 1.95 was carried and enabled the internal low-concentrating evacuated tube heat pipe collector to be enclosed by a borosilicate glass tube with 100 mm and 93 mm outer and inner diameters, respectively. Ray trace analysis at different transverse angles determines optical efficiencies, related optical losses and flux distribution on the absorber of the internal low-concentrating evacuated tube heat pipe solar collector. A detailed two dimensional ray trace techniques considering only the direct insolation component predicated overall ray’s acceptance of 93.72% and optical efficiency of 79.13% from transverse angles of 0° to 20°.

► Overall ray's acceptance of 93.72% and optical efficiency of 79.13% were predicted from transverse angles of 0° to 20°.
► Angular acceptance reduction of 9.08% and 6.99% were recorded at transverse angles of 7.5° and 0°, 7.5° and 20°, respectively.
► Non-linear variation in optical efficiency showing a decrease occurred within different transverse angles.
► Truncation of internal reflector reduced reflector losses and cost of the reflective material.
► Combine use of concentration and evacuation increased flux concentration and reduces convective heat losses from the absorber.