Augmentation of thermal efficiency of the glass evacuated solar tube collector with coaxial heat pipe with different refrigerants and filling ratio

• Published in: Energy conversion and management Vol. 138; pp. 286 - 298
• Main Authors: Kabeel, A.E., Khairat Dawood, Mohamed M., Shehata, Ali I.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 15-04-2017; Elsevier Science Ltd
• Subjects: Annuli; Evacuation; Flow rates; Glass evacuated solar collector; Heat; Heat pipe; Heat pipes; Mass flow rate; Pipes; Refrigerants; Refrigeration; Solar collectors; Solar energy; Thermal efficiency; Thermodynamic efficiency; Tilt angle; Tubes; Working fluids; Glass evacuated solar collector; Tilt angle; Thermal efficiency; Heat pipe
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2017.01.048

•An inclusive experimental model of modified coaxial heat pipe inserted inside evacuated glass was designed and analyzed.•The optimum filling ratio was investigated at the four mass flow rates.•The maximum thermal efficiency was achieved at filling ratio 30% for mass flow rate m⁰=0.0051 and 0.0062kg/s.
Modified coaxial heat pipes have been designed and manufactured to improve the thermal performance of the glass evacuated solar collectors. Heat pipes were made up of two concentric copper tubes so that the annulus volume space between the concentric tubes was charged with refrigerant. In addition, the air as the working fluid at four different mass flow rates 0.0051, 0.0062, 0.007 and 0.009kg/s flows through the inner tube of the heat pipe to the flow through the annulus between the heat pipe and glass evacuated solar tubes. The effect ofthe tilt angleofthe evacuated tube on thermal performance of the evacuated solar tube collector was examined to obtain the optimum tilt angle during the experiments period. The influence of filling ratio for the two types of refrigerant R22 and R 134a on the thermal efficiency of the coaxial heat pipe solar collector at filing ratio range from 30% to 60% was conducted experimentally. Results show that the maximum increased in the thermal efficiency reached 67% corresponding to without heat pipes at mass flow rate 0.009kg/s. The experiment results showed similarity between the two refrigerants.