BT-36 Non-Equilibrium Dry-Wall Mist Flow Heat Transfer in Vertical Tubes

L. Huang
2009; rev 10/2009

Dry-wall mist flow heat transfer is a non-equilibrium process in which liquid droplets and superheated vapor coexist in two-phase flow. The droplets flow with the vapor at slightly different velocities, causing them to vaporize slowly and allowing them to exist even in highly superheated vapor. Predictions of the actual vapor quality and the superheated vapor temperature are crucial for accurately calculating the heat transfer rates in mist flow and determining if inserts are necessary to eliminate the droplets and improve heat transfer.

This report discusses the criteria for dry-wall mist flow and models for predicting heat transfer rates in the mist flow regime. We collected mist flow data using n-pentane and p-xylene as test fluids and compiled literature data over a wide range of operating conditions for different test fluids. Based on the data, we developed a correlation for the critical vapor quality at dryout and a method for determining the actual vapor quality. We also propose new methods for determining heat transfer coefficients in dry-wall mist flow.