Visualization and Void Fraction Measurement of Refrigerant Flow in Cross-Flow Type Mini-Channel Evaporator
Purpose
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Toward the realization of a low-carbon society high performance heat exchanger to decrease the temperature difference between fluids is required.
In this study, we focus on diffusion-bonded microchannel heat exchangers as compact heat exchangers with many narrow channels.
In this heat exchanger, the heat flux distribution is not uniform because the channels are orthogonal.
When this heat exchanger is used as an evaporator, the distribution of refrigerant becomes non-uniform due to the non-uniform heat flux distribution, which may affect the heat transfer performance.
Therefore, in this study, boiling heat transfer experiment of HFC-134a is conducted for a single-layer cross-flow type mini-channel evaporator.
The effects of experimental conditions (mass flux, heating medium temperature) on refrigerant flow and heat exchange characteristics are evaluated, and the phase distribution is made uniform by manipulating the rib shape of the refrigerant channel shape.
Research content
The refrigerant boiling flow is visualized by two methods. Neutron radiography using radiation was applied to the same stainless steel evaporator as the actual product, and the time-average void fraction distribution was measured from the visualized image. Neutron radiography experiments are conducted in the research reactor of the Institute for Integrated Radiation and Nuclear Science, Kyoto University. On the other hand, the refrigerant flow channel wall was replaced with transparent polycarbonate resin, and the internal flow was observed with a high-speed camera. The video on the right is taken at a speed of 1/20. The rib is straight and consists of a book channel. Under these conditions, flow fluctuation occurs and it can be seen that the image propagates from the right (heating medium inlet) to the left.
Publications
H. Asano, H. Murakawa, R. Moriyasu, K. Sugimoto, Y. Kubo, K. Fukutani, D. Ito, Y. Saito
Visualization and Measurement of Boiling Flow Behaviors in Parallel Mini-channel
Heat Exchanger by Neutron Radiography, Materials Research Proceedings 15
(2020) pp.274-280. https://doi.org/10.21741/9781644900574-43