Abstract
Two-Phase Flow Instability Experiment in a NaturalCirculation LoopAbstractBecause of their high heat transfer capability,simplicity, and inherently safe nature, two phase naturalcirculation loops have manyindustrial applications, suchas waste heat recovery, chemical processes usingthermosiphon reboilers, and the next generation boiling waterreactor. The thermal-hydraulic instability of a two-phasenatural circulation loop, which is a complexmultivariable system with high non-linearity, wasinvestigated experimentally based on the Taguchi method.Excellent results were obtained and a broad picture of thetrends producedby the various parameters that affectinstability is presented. This study concluded that, withinthe experimental range, the inlet temperature,heatingpower and the presence of the unheated bypass channelare the three most dominant factors affecting the loopinstability. The Taguchi method is found to be veryefficient and there is a great deal of savingin the experimentalwork. The 20 runs of experiment based on the Taguchi methodsuggests that the stability of the present two-phasenatural circulation loop would be improved under the followingconditions: decreased inlet temperature, decreased thermalload, disconnected unheated bypass channel, installing thecompressible volume with a higher water level in thedownstream two-phase flow region, disconnected upstreamcompressiblevolume, increased single-phase flow restrictions,and decreased two-phase flow restrictions. Although thesame trends bear the standard method of stabilizing a boilingchannel, the restriction factors in the presentexperimentalinvestigation are found to be ineffective in dampening thethermal-hydraulic instability.( Keywords: two-phase flow, natural circulation loop,instability, Taguchi method )