Mist/steam cooling in a heated horizontal tube - Part 2: Results and modeling

Experimental studies on mist/steam cooling in a heated horizontal tube have been performed. Wall temperature distributions have been measured under va rious main steam flow rates, droplet mass ratios, and wall heat fluxes. Gen erally, the heat transfer performance of steam can be significantly improve d by adding mist into the main flow. An average enhancement of 100 percent with the highest local heat transfer enhancement of 200 percent is achieved with 5 percent mist. When the test section is mildly heated, an interestin g wall temperature distribution is observed: The wall temperature increases first, then decreases, and finally increases again. A three-stage heat tra nsfer model with transition boiling, unstable liquid fragment evaporation, and dry-wall mist cooling has been proposed and has shown some success in p redicting the wall temperature of the mist/steam flow. The PDPA measurement s have facilitated better understanding and interpreting of the droplet dyn amics and heat transfer mechanisms. Furthermore, this study has shed light on how to generate appropriate droplet sizes to achieve effective droplet t ransportation, and has shown that it is promising to extend present results to a higher temperature and higher pressure environment. [S0889-504X(00)02 502-2].