Development of a Flow Boiling Heat Transfer Correlation for a Helically Coiled Tube

Abstract

Helically coiled tubes have been widely used in heat exchangers across various industries. Particularly in the nuclear sector, many small modular reactor (SMR) designs adopt helical coil heat steam generators. Heat transfer in a helically-coiled tube has a unique feature due to the centrifugal force generated by the fluid motion. This in known to enhance the boiling heat transfer inside the tube. However, accurately predicting the heat transfer performance of helically coiled tubes remains a significant challenge. This is primarily attributed to the complex boiling mechanisms influenced by centrifugal forces. Existing research on boiling heat transfer correlations has largely been based on experimental data from vertically oriented straight tubes. In this study, we investigated the effect of centrifugal force on boiling heat transfer in a helically coiled tube; at first we devised a new dimensionless number defined by centrifugal force over gravity and, then, demonstrated its effect on boiling heat transfer. Using the findings, we incorporated the dimensionless centrifugal force number into a new boiling heat transfer correlation, of which the basic structure was adopted from the Kandlikar correlation for saturated flow boiling. We showed the enhanced accuracy of the new correlation compared to existing ones and its applicability to boiling heat transfer within a straight tube as well.