Measurement of velocity and vapor thickness during film boiling in cryogenic fluids using laser doppler anemometry supplemented with optical visualization

摘要

An experimental study has been carried out to measure the velocity profiles and vapor thickness during film boiling on vertical surfaces immersed in cryogenic fluids. The experiments were done inside a vacuum jacketed test tank. The test specimen which is a heater element made up of polished stainless steel is suspended from the top of the test tank by two aluminum rods. The specimen is heated by electric current supplied by a constant current transformer. The velocity of the vapor and the liquid near the heated surface was measured using a Laser Doppler Anemometer (LDA). These measurements were than used to construct the vapor velocity profiles along the heated surface. The development and retention of the vapor around the specimen was also studied by optical means using a high resolution CCD camera. The optical pictures from the camera were used to verify the location of the vapor-liquid interface. The LDA data is used to determine the velocity of this interface. The pressure and temperature of the liquid and the temperature of the test surface was monitored during all the experiments using a digital data acquisition system. The velocity profiles generated from the LDA measurements show the expected trends. A thin liquid boundary layer adjacent to the vapor boundary was observed for most of the experiments. The velocities inside this layer was also measured by LDA techniques.