This paper presents the experimental results for R134a flowing through micro-orifices with diameters of 31 and 52 μm, and length-to-diameter ratio of 2.5 and 4.2, respectively. For liquid flow without flashing, the experimental data were in rough agreement with macroscale results. The conventional orifice equation is still applicable. For liquid flow with flashing, the experimental results indicate significant departure of flow characteristics from macroscale orifices. The flow was not choked even when downstream pressure was reduced to more than 400 kPa below saturation pressure corresponding to inlet temperature, whereas in normal size orifices with length-to-diameter ratio larger than 2, the flow is typically choked as downstream pressure is reduced below saturation pressure. Semi-empirical model was developed based on correction of the orifice equation.
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