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Proceedings of the 25th National and 3rd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2019)

ISSN: 2688-7231 (Online)

Numerical Investigations on Flow Regimes in Helical Coil Dry Evaporators

Sanikommu Narasimha Reddy
Department of Mechanical Engineering, IIT Madras, Chennai 600036, India

A. Mani
Department of Mechanical Engineering, IIT Madras, Chennai 600036, India

Shaligram Tiwari
Department of Mechanical Engineering, Indian Institute of Technology Madras Chennai, India, 600036

DOI: 10.1615/IHMTC-2019.840
pages 497-502

Abstract

In any refrigeration system, the evaporator is one of the main components. In dry type (DX) evaporators, part of the heat transfer area is used for superheating of the refrigerant. The helical coil heat exchanger is one of the passive heat transfer enhancement devices. It enhances heat transfer performance due to the action of centripetal force and secondary flows. In the present study, DX evaporator of vertical helical coil type is considered with refrigerant R134a flowing inside the tubes. As the refrigerant liquid is flowing in the evaporator, it undergoes phase change, which leads to the formation of different flow regimes. This phase change phenomenon has been investigated using the Volume of Fluid (VOF) method with the help of commercial software ANSYS Fluent 18.1. This study helps to identify the different flow regimes in DX helical coil evaporator, which will be advantageous for estimating the two-phase heat transfer rates and pressure drops. From the simulation results, it was observed that bubbly, plug, slug, wavy, and annular flow regimes have occurred in phase change phenomenon, and the generated vapour is always pushed towards the inner side of the helical coil. Effects of heat flux and mass flux on pressure drop and vapour quality have discussed. It was found that the vapour quality increases with heat flux and decreases with mass flux. Pressure drop increases with both heat flux and mass flux.

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