Mist/steam cooling in a heated horizontal tube

Experimental studies on mist/steam cooling in a heated horizontal tube have been performed. The objective of this study is to investigate the heat transfer enhancement and its physical mechanisms of mist/steam mixture. The mist/steam mixture is obtained by blending fine water droplets (5 ∼ 10 μm) generated by commercial atomizers with the saturated steam at 1.5 bars. The test section consists of a thin-walled (∼0.9 mm), circular stainless steel tube which is heated directly by a DC power supply.; A distinct feature of this study is the measurement of droplet size and distribution within the test section. The droplet sizes are measured by a Phase Doppler Particle Analyzer (PDPA) system. Based on the PDPA measurements, the effects of heat flux and the main steam flow rate on droplet size and distribution are discussed. Effects of the mixing chamber design and the transportation length on droplet size and distribution are also investigated.; Wall temperature distributions have been measured under various main steam flow rates, droplet mass ratios, and wall heat fluxes. Generally, the heat transfer performance of steam can be significantly improved by adding mist into the main flow. An average enhancement of 100% with the highest beat transfer enhancement of 200% is achieved with approximately 5% mist. Based on the PDPA results and the improved understanding of water droplet dynamics, a three-stage heat transfer model, which incorporates different heat transfer mechanisms for the internal mist/steam flow, has been proposed and has shown success in predicting the wall temperature of the mist/steam flow. Numerical simulations of the mist/steam flow are also performed by using simple interphase models and the Inter-Phase Slip Algorithm (IPSA) and the SHADOW technique. The numerical results are compared with the experiment.