TWO PHASE FLOW PATTERNS AND HEAT TRANSFER OF FLOW BOILING IN A 3-DIMENSIONAL MICRO-FINNED HELIX TUBE

摘要

Flow and heat transfer Experiments have been conducted in a 3-dimensional micro-finned and smooth helix tubes. The flow patterns observed in the test tubes can be divided into bubbly flow, plug flow, stratified-wavy flow, intermittent flow and annular flow. Experimental data are plotted in the flow map following Taitel-Dukler method. For the micro-finned helix tube, the boundary between stratified-wavy flow and annular flow are similar to that of corresponding smooth helix tube. And the transition from intermittent flow to annular flow of micro-finned helix tube is obviously different from that of smooth tube. Martinelli parameter, X_(tt), can be used to indicate the later transition. Compared with smooth tube, the X_(tt) of micro-finned tube is increased from 0.4 to 0.7. Local Heat transfer coefficients are measured for a range of heat flux (2.0-21.8 kW/m~2), mass velocity (65-315kg/m~2s), and equilibrium quality (0.05-0.95). The influences of these parameters on heat transfer performance are presented and discussed. The 3-dimensional micro-finned helix tube can perfectly enhance flow boiling heat transfer process. The data of micro-fin tube are compared with the performance of smooth helix tube, and the heat transfer enhancement factor is from 1.5 to 2.1.