EXPERIMENTAL INVESTIGATION OF ENERGY CHARACTERISTICS OF EVACUATED TUBE HEAT-PIPE SOLAR COLLECTOR SYSTEM

Evacuated tube heat-pipe solar collector system with closed heat pipe has been experimentally investigated. Experiments have been fulfilled using the solar imitator whose energy irradiance on the surface of the solar collector at the constant ambient conditions is 800 W/m(2). Energy characteristics of the solar collector system with different flow-rates of the heat-transfer agent have been investigated using various flow-rate speeds of the heat-transfer agent. It has been stated that the increase of the flow-rate of the heat-transfer agent in the system from 0.01 to 0.12 kg/s would minimize the average collector efficiency from 0.81 to 0.55. When the reduced flow-rate of the heat-transfer agent has been used in the system, the higher temperature of the hot water is reached in the storage tank and at the same time the temperature of the heat-transfer agent in the system is increased. Thus, more energy has been lost in the pipeline and hot water storage tank, but less energy is used for the circulation of the heat-transfer agent energy. Increasing the agent flow-rate speed in the system has reduced the heat losses in the pipeline, but more energy is used for the energy circulation of the heat-transfer agent. Therefore, the medium efficiency of the solar collector system has changed insignificantly (0.47 +/- 0.01).