BT-35 Complete Vaporization in Horizontal Tubes

L. Huang and T. G. Lestina

Prediction of heat transfer for complete vaporization in horizontal tubes requires a comprehensive model of the boiling mechanism and flow regimes. Reliable models accurately predict the transitions from subcooled to flow boiling, from wet-wall to partial dry-wall boiling in the stratified flow regime, and from annular or partial wet-wall to mist flow boiling. When mass velocity is sufficient to keep the tube wall wet, adequate thermal design is assured. For multiple tubepasses, entrained droplets contact the hot wall near U-bends, and the remaining liquid droplets are completely vaporized. Tube inserts such as twisted tape and/or micro-finned tubes enhance heat transfer and maintain wet-wall heat transfer.

Methods in Xist® and EHT predict the thermal performance of tubeside evaporators based on experimental data. Because the underlying data were collected for diverse fluids under various operating conditions, these predictions can vary significantly. Further research is needed to reconcile these differences.