Conference Year

2016

Keywords

visualization measurement, ejector, refrigeration cycle, phase transition, flow pattern

Abstract

As an important component in transcritical CO2 refrigeration cycle, complex flow in ejector have not been clearly elucidated. In this paper, CO2 flow in two-phase rectangle ejector was investigated experimentally by visualization measurement. The phase transition and the relaxation phenomena in the ejector were observed. By analyze the picture and the data collected from this experiment, we study the relationship between efficiency of ejector and the phase transition position in the ejector. Firstly, the microstructure of the flow pattern in the ejector was captured by a high speed digital video camera with a microscope to analyze the mixing process in mixing chamber. It was found that there were two stages with different characteristics in mixing process ,which were named fluid mixing section and fluid equilibrium section. When fluid get through mixing channel, the ejector realize the majority functions of entrainment in the first stage, and the ejector also homogenize the velocity of primary fluid and secondary flow by the way of flow core expand to almost all the channel in the second stage. Secondly, based on the comparison of pictures collected from different ejectors under different operating conditions, we found that phase transition position and the form of phase transition was mainly depended on the entrance condition of motive nozzle. For an ejector that keeps the suction nozzle under the same operation condition, when the phase transition point trend to exit of motive nozzle, in mixing channel ,motive flow will occupy more space meanwhile the relaxation phenomena occurred in longer region. It was worth mentioning that the phase transition point will change with different operation condition. But there exist only one best position where the ejector contributes to best efficiency. So, it is of great significance to treat phase transition point as an important sign which was easy to be recognized. Visualization research of ejector will be an important reference for theoretical study of flow pattern in the ejector. It also can provide some date to validate the results from the numerical calculation. The visualization study of ejector will also be the basis of further learn of shock waves and delayed phase transition in the ejector.

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