An-Najah National University

Chemical Engineering


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  • Saturday, December 1, 2007
  • Cooling of High Heat Flux Electronic Devices by Two Phase Thermosyphon System
  • Published at:Master Thesis - An-Najah National University
  • Two phase closed thermosyphon system for cooling high heat flux electronic devices is built in the laboratory and tested under different operating conditions.

    This Study presents an experimental investigation on the heat transfer coefficient, temperature difference between the evaporator and the refrigerant inside evaporator channels, overall heat transfer coefficient, and overall thermal resistance in two-phase thermosyphon system. Investigations are carried out at different conditions: different system pressures, two different types of refrigerants R134a and R22, two different evaporator designs, natural and forced convection heat transfer mode in the condenser. The heat flux and the amount of refrigerant are the manipulated parameters in the system.

    It is found that the heat transfer coefficient increases almost linearly with the applied heat to the evaporator, and reduced pressure. It is also highly dependant on the type of refrigerant, because the performance of the refrigerant R134a likely to be better than that of R22. The heat transfer coefficient is also higher at natural convection condensation than forced convection condensation at the same heat load, while the overall heat transfer coefficient in the system for forced convection is higher than for natural convection condensation. The heat transfer coefficient is highly dependant on the design of evaporator, especially on the diameters channels.

    The natural convection heat transfer coefficient is found to be 27 kW/m².˚C and  3.7 kW/m².˚C using R134a and R22, respectively at heat load of 115W. The forced convection heat transfer coefficient is found to be 2.4 kW/m².˚C and 1.6 kW/m².˚C, using R134a and R22, respectively at heat load of 450W. The forced convection overall heat transfer coefficient using R134a is found to be 9.4 kW/m².˚C at 415W while it is 1.08 kW/m².˚C at natural convection at 155W.

    The temperature difference [Tevaporator–Tsaturation] depends on both the applied heat flux to the evaporator, systems pressure and type of the refrigerant.

    The natural convection temperature difference does not exceed 1˚C and exceeded 8˚C for R134a and R22, respectively at heat load of 100W.

    The obtained evaporator temperature for R134a is 94˚C at 155W and 44˚C at 414W using natural and forced convection, respectively. While, the obtained evaporator temperature for R22 is about 80˚C at 115W and 40˚C at 450W for natural and forced convection, respectively.

    The overall thermal resistance decreases almost linearly with increasing the heat load regardless of the used refrigerant. Moreover, for forced convection, the thermal resistance is much lower than the other heat transfer processes.

    The overall natural convection thermal resistance is 0.47˚C/W at 155.6W and 0.53˚C/W at 115W while overall forced convection thermal resistance is 0.056˚C/W at 414W and 0.044˚C/W at 417W for R134a and R22 refrigerants, respectively.


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Abdelrahim Abusafa
Chemical Engineering - Unit Operations
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