Pool Boiling Heat Transfer In Microgravity
- Paper number
IAC-07-A2.3.04
- Author
Prof. Jian-Fu Zhao, Institute of Mechanics, Chinese Academy of Sciences, China
- Coauthor
- Coauthor
Ms. Na Yan, Institute of Mechanics, Chinese Academy of Sciences, China
- Coauthor
Dr. Wen Rui Hu, Institute of Mechanics, Chinese Academy of Sciences, China
- Year
2007
- Abstract
A space experiment has been conducted aboard the Chinese recovery satellite SJ-8 in September, 2006. Three modes of heat transfer, namely single-phase natural convection, nucleate boiling, and transition boiling, are observed both in normal gravity and in microgravity, while the nucleate pool boiling are the major subject for discussion in the present paper.
The boiling chamber is filled with about 1700 ml of degassed FC72, and fixed inside an air-proof container in which the pressure is initially about 100 kPa. A bellows connected with the chamber will allow the pressure in the chamber to be approximately constant. After the first stage of the space experiment had been performed, a valve was open and then the pressure inside the container was reduced to the same of that in the module of the satellite, namely 40 60 kPa. Thus, in the second stage of the space experiment, the pressure in the boiling chamber is different from those in the first stage. The absolute pressure within the boiling chamber is measured using a pressure transducer with a range of 0 0.2MPa and an accuracy of 0.25%FS (full scale). An auxiliary heater is used for adjusting the temperature of the bulk liquid from the ambient temperature to about half of the saturation temperature under the corresponding pressure. Two thermocouples with a range of 0 100 oC are used to measure the bulk temperature of the fluid in the boiling chamber, which are calibrated to within 0.5 oC. The outputs signals are sampled at rate of 1 Hz.
A plane plate with a heating area of 15*15 mm 2 was used as the heater. A pseudo-steady heating method is adopted, in which the heating voltage is controlled as a exponential function with time, namely U=U 0exp(t/τ). The parameter τ=80 s and then the heating process will be pseudo-steady. The electric current through the heater is measured by a Hall transducer. Its output and the voltages across the heater are sampled at a rate of 100 Hz.
A CCD video camera is used to obtain images of the motion of vapor bubble or film around the heater, which is digitized and recorded at a speed of 25 fps in MPEG. Four LEDs (light-emitting diode) are used to light the boiling chamber through two optical windows.
There are 8 runs obtained in the space experiment. Three modes of heat transfer, namely single-phase natural convection, nucleate boiling, and transition boiling, are observed, while the nucleate pool boiling are the major subject for discussion in the present paper. The results of the control experiments performed on the ground before the flight are also discussed in the present paper.
- Abstract document
- Manuscript document
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