Flow Stability in Multitube Forcedconvection Vaporizers

摘要

The report describes work undertaken to resolve the SNAP-50/SPUR liquid-metal boiler two-phase flow stability problems. A review is presented of existing literature pertaining to forced-convection vaporization heat transfer and two-phase flow stability. Dimensionless simulation criteria are defined on the basis of the significant parameters determined from the survey. The test program, in which Freon 113 was used as the test fluid and the values of the dimensionless two-phase flow stability parameters applicable to the SNAP-50/SPUR boiler were simulated, is presented. The design of the transparent closed test loop, which incorporates a five-tube boiler, is described. Conclusions and discussions are presented based on the measured data and the high speed photographs of two-phase flow in both plain tubes and tubes with twisted tape inserts, which indicate that stable flow can be achieved in the SNAP50/SPUR boiler by inserting at the entrance of each boiler tube an orifice which has a pressure drop between 100 and 200 percent of the two-phase pressure drop.