This paper deals with heat transfer in a closed two-phase thermosyphon with a long evaporator and a short condenser, filled with water as operating fluid. The ratio of length to inside diameter of the evaporator is equal to 166. A similar geometry is commonly used in vacuumed tube solar collectors. In the present investigation the input power to the evaporator is provided by means of an electrical resistance wire wrapped around the external wall of the tube, while a water jacket is built at the condenser to reject the heat. An adiabatic section, placed between evaporator and condenser, is used to measure the saturation temperature. The thermosyphon is fully instrumented with thermocouples to measure the wall temperature in the different sections of the tube. The overall performance of the thermosyphon is described by using the wall temperature and overall thermal resistance for different operating conditions: input power at the evaporator, cooling water temperature at the condenser and inclination of the thermosyphon (30°, 60° and 90° tilt angle to the horizontal plane). The experimental study is focused on the evaporator: data of heat transfer coefficient are reported, covering a range of heat flux between 1700 and 8000 W/m² and saturation temperature between 29 °C and 72 °C. The measured vaporization heat transfer coefficients are compared with some correlations for closed two-phase thermosyphons. A new correlation is presented, which accurately predicts the present experimental heat transfer coefficients and other data by independent labs taken in closed two-phase thermosyphons, with different geometries and operating fluids (water and R134a).

Vaporization heat transfer in a closed two-phase thermosyphon

Bortolin S.;Del Col D
2018

Abstract

This paper deals with heat transfer in a closed two-phase thermosyphon with a long evaporator and a short condenser, filled with water as operating fluid. The ratio of length to inside diameter of the evaporator is equal to 166. A similar geometry is commonly used in vacuumed tube solar collectors. In the present investigation the input power to the evaporator is provided by means of an electrical resistance wire wrapped around the external wall of the tube, while a water jacket is built at the condenser to reject the heat. An adiabatic section, placed between evaporator and condenser, is used to measure the saturation temperature. The thermosyphon is fully instrumented with thermocouples to measure the wall temperature in the different sections of the tube. The overall performance of the thermosyphon is described by using the wall temperature and overall thermal resistance for different operating conditions: input power at the evaporator, cooling water temperature at the condenser and inclination of the thermosyphon (30°, 60° and 90° tilt angle to the horizontal plane). The experimental study is focused on the evaporator: data of heat transfer coefficient are reported, covering a range of heat flux between 1700 and 8000 W/m² and saturation temperature between 29 °C and 72 °C. The measured vaporization heat transfer coefficients are compared with some correlations for closed two-phase thermosyphons. A new correlation is presented, which accurately predicts the present experimental heat transfer coefficients and other data by independent labs taken in closed two-phase thermosyphons, with different geometries and operating fluids (water and R134a).
2018
Joint 19th IHPC International Heat Pipe Conference and 13th IHPS International Heat Pipe Symposium
Joint 19th IHPC International Heat Pipe Conference and 13th IHPS International Heat Pipe Symposium
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3279300
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