Scaling two-phase flows to Mars and Moon gravity conditions K.M. Hurlbert a,* , L.C. Witte b , F.R. Best c , C. Kurwitz c a NASA Johnson Space Center, Houston, TX 77058, USA b Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA c Department of Nuclear Engineering, Texas A&M University, College Station, TX 77843, USA Received 22 June 2002; received in revised form 10 January 2004 Abstract Hydrodynamic measurements are presented for two-phase flows in Mars and Moon gravity conditions. High accuracy pressure drop and flow rate data were obtained using dichlorodifluoromethane (i.e., R-12) as the working fluid flowing in a nominally 11.1 mm inner diameter tube. Measurements were made at Mars gravity, approximately 0.38-g, and Moon gravity, approximately 0.17-g, using NASAÕs KC-135 aircraft. A simplified scaling approach was developed using dimensional analysis and can be used to design an Earth- based test bed to simulate a Mars or Moon gravity prototype. For a specific geometry, a selected working fluid at a fixed temperature and pressure, and a particular flow regime condition, the pressure drop functional scaling equation is a simple, power-law relationship for the Euler number as a function of only the Froude number. The research completed supports the use of Earth-g tests to predict the behavior of two-phase systems for Moon-g and Mars-g applications. Ó 2004 Published by Elsevier Ltd. Keywords: Two-phase flow; Scaling; Partial gravity; Low gravity; Mars; Moon; Annular flow; Stratified flow 1. Introduction The National Aeronautics and Space Administration (NASA), the United States Air Force, other government agencies, and commercial and academic groups continue to pursue the devel- opment of two-phase systems for space applications in numerous areas. The NASA Johnson Space Center (JSC) specifically has an avid interest in two-phase systems for active thermal control and life support. Other areas of potential for these systems might include in-situ resource International Journal of Multiphase Flow 30 (2004) 351–368 www.elsevier.com/locate/ijmulflow * Corresponding author. 0301-9322/$ - see front matter Ó 2004 Published by Elsevier Ltd. doi:10.1016/j.ijmultiphaseflow.2004.01.004