Study on Distribution of Flow Rates and Flow Stabilities in Parallel Long Evaporators

Abstract

Distributions of flow rates and flow stabilities in parallel evaporator tube systems have been experimentally investigated. The evaporator is composed of three parallel copper tubes of 4mm inside diameter and 40 m long. Experiments were carried out by using refrigerant R-113 as the fluid in pressure range from atmospheric pressure to supercritical pressure, in order to simulate phenomena in steam generators. It has been shown that distributions of flow rates, their hysterisis and onset of excursion phenomena can be estimated from pressure drop versus flow rate curves for single tubes. Moreover, description is made of behaviors of thermal oscillative instability which are observed at relatively low flow rate. In addition to the experimental results, by a theoretical analysis of a simple model, stability criteria in parallel tube system have been described.