Abstract
Evacuated-tube solar collector (ETSC) is developed to achieve high heating medium temperature. Heat transfer fluid contained inside a copper heat pipe directly affects the heating medium temperature. A 10 mol% of ethylene-glycol in water is the heat transfer fluid in this system. The purpose of this study is to modify inner structure of the evacuated tube for promoting heat transfer through aluminum fin to the copper heat pipe by inserting stainless-steel scrubbers in the evacuated tube to increase heat conduction surface area. The experiment is set up to measure the temperature of heat transfer fluid at a heat pipe tip which is a heat exchange area between heat transfer fluid and heating medium. The vapor/ liquid equilibrium (VLE) theory is applied to investigate phase change behavior of the heat transfer fluid. Mathematical model validated with 6 experimental results is set up to investigate the performance of ETSC system and evaluate the feasibility of applying the modified ETSC in small-scale industries. The results indicate that the average temperature of heat transfer fluid in a modified tube increased to 160.32 °C which is higher than a standard tube by approximately 22 °C leading to the increase in its efficiency by 34.96%.
Highlights
At present, pollution released from combustion in industries is one of main causes of environmental problems
The heat transfer fluid is responsible for receiving thermal energy from the outside, evaporating to the heat pipe tip, exchanging heat with heating medium flowing through the manifold
The mechanistic model was developed and successfully validated with the experimental results with the overall average deviation in terms of RMSE of 2.16%. This model was used to predict the performance of the modified evacuated-tube solar collector (ETSC) system and evaluate the feasibility of applying the ETSC in a small-scale industry
Summary
Pollution released from combustion in industries is one of main causes of environmental problems. Ma et al [2] studied the thermal performance of evacuated-tube solar collector with U-tube by analyzing a network of thermal resistances. They found that the efficiency of evacuated-tube solar collector with U-tube and exit fluid temperature would increase by 10% and 16%, respectively, if the thermal conductivity increased from 5 to 40 W/m·K. The oil was added to store thermal energy supplied to the heat pipe after the sun set, and the foamed copper was used to enhance heat conduction. They found that the evacuated tube filled with oil and foamed copper could improve heat transfer rate causing the increase in its efficiency by 55.6%. Heyhat et al [4]
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