Numerical investigation of flashing of propane (R-290) in a helical capillary tube

Abstract

The present study addresses the expansion of pressurized liquid R-290 through a $1.2\hspace{0.33em}\mathrm{mm}$ diameter capillary tube and its subsequent motion through a metastable condition entailing a change of phase through flashing phenomenon. The expansion of R-290 through a helical capillary tube is numerically simulated using a finite volume-based mixture model. For the simulation of the flashing phenomena, a homogeneous equilibrium approach is used. The Zwart–Gerber–Belamri model is deployed to represent mass transfer during flashing. ANSYS Fluent 2021 R2 software has been used for the numerical simulations. A series of UDF (user defined functions) are developed to read the recorded database of R-290 and perform the cavitation modeling. Bilinear interpolation is performed for determining the fluid properties at the corresponding pressure and temperature. The developed numerical model has been validated against the available numerical and experimental results. For the simulations, tubes with lengths of $1200\hspace{0.33em}\mathrm{mm},\hspace{0.33em}1500\hspace{0.33em}\mathrm{mm},\hspace{0.33em}1800\hspace{0.33em}\mathrm{mm},\hspace{0.33em}2100\hspace{0.33em}\mathrm{mm},$ and $2400\hspace{0.33em}\mathrm{mm}$ have been considered, and the impacts of increasing length on the flow characteristics at the outlet have been determined. In this investigation, the R-290 refrigerant expands from three different condenser pressures of 16, 14, and 12 bar. Evaporator pressure is adjusted from 2 bar to 8 bar to investigate its influence on flow characteristics. The fall in evaporator pressure brings about a flow transition from subsonic to supersonic. The effects of tube length, condenser, and evaporator pressures on mass transfer rate, evaporator entry temperature, mixture quality at the evaporator entrance, and available refrigeration effects have been analyzed.

Keywords:

• ANSYS fluent
• flashing phenomenon
• flow choking
• helical capillary tube
• R-290
• Zwart–Gerber–Belamri model

Acknowledgments

The authors would like to express their heartfelt gratitude to Prof. Gautam Biswas from IIT Kanpur, India for providing the computational facilities and necessary suggestions to improve the quality of the manuscripts.

Disclosure statement

The authors do declare that they do not have any financial transaction or personal agreement with any person or institution that creates any potential conflict of interest with publishing the present research content.

Notes

1 The subscripts refer to the Cartesian components in Einstein tensor notation, and the superscript refers to the information regarding the corresponding phase.