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A film thickness probe based on capacitance measurements has been developed which is used to measure the liquid film thickness on both the upper and lower surface of a horizontal tube containing a two-phase mixture. Using appropriate nondimensionalization of the capacitance versus film thickness relationship, a new method has been developed in which the sensor may be used in temperature-dependent flow fields. The liquid film thickness probe was calibrated at room temperature and tested in a refrigerant R 113 flow boiling facility over a 60 "C temperature span. Measurements made over a film thickness range of 25 mm using the capacitance probe are in close agreement with optical measurements made with a charge coupled device camera. In addition, spectral analysis of the probe signal allows for a trace of the low-frequency characteristics of the liquid film.

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