SBIR-STTR Award

Low speed, two Phase (vapor-liquid) flow regimes are important to several significant heat transfer problems in spacecraft. Low speed flow rates also create the most gravity-affected flow regimes. High speed flow rat s create flow regimes that are affected little by gravity. Few studies exist which give an overview of flow regimes in zero gravity. In particular, few studies have attempted to use recent successful and largely analytical flow regime models (which include gravity) as a starting point for flow regime modeling in zero gravity. Aeta propose to conduct two phase flow regime lab tests on earth which eliminates effect of gravity by using flow of water and oil of equal density. In addition, we will use two recent, nearly analytical flow regime prediction model to indicate probable flow regimes in very reduced (and also zero) gravity. One of these models has already been computerized by AETA and used to obtain preliminary low gravity results. To create a first-order analytical model to predict flow regimes in zero gravity, using lab and semi-analytical computer studies. To suggest areas for very focused two phase flow experimental work in true gravity conditions; to suggest areas for more focused analytical effort.

The ppg/water experiments carried on in phase I present a possible model of two phase behavior in zero gravity. A number of unexpected phenomena were found to occur in zero g liquid-vapor flows. These observations and their significance to good design of spacecraft heat transfer loops form the basis for this phase 2 effort. We intend to: 1) perform experiments with a wide variety of immiscible fluids of equal density in order to understand the effect of surface tension, viscosity, and entrance conditions at zero g. 2) use targeted experiments to explore details of entrainment/de-entrainment using a freon loop or ferrofluid. 3) perform analysis using dimensionless groups and straight-forward differential equation flow models initiated in phase 1; develop two phase flow simulation code. The ultimate goal of the phase 2 work is an accurate analytical engineering design tool to predict flow regime behavior in zero gravity, spacecraft heat transfer loops.