Development and Validation of Design Tools for Advanced, Two-Phase, Space Heat Exchangers

PI: Jungho Kim, University of Maryland

The use of two-phase thermal systems on spacecraft has been greatly hampered by the inability to predict with sufficient confidence their performance at various gravity levels (Earth, Mars, and lunar gravity and low-g). The performance prediction of two-phase systems under these conditions requires a sufficient heat transfer database and reliable models, both of which are not currently available. Although some research in low-gravity adiabatic flows has been performed, very little heat transfer data relevant to advanced space heat exchangers is available and the mechanisms by which heat is removed from the surfaces under varying gravity environments are still unclear. A better understanding of flow boiling and critical heat flux (CHF) in these environments is highly desired for the design of future heat removal equipment in extraterrestrial applications.

Technology Areas (?)
  • TA03 Space Power & energy Storage
  • TA14 Thermal Management Systems
Problem Statement

The primary objective of the experiment is to understand the major mechanisms of heat transfer during flow boiling in a reduced gravity environment. Better understanding of how the heat transfer mechanisms change between earth normal gravity, hypergravity, and low-gravity environments and the quantification of parametric effects such as heat flux, inlet subcooling, inlet mass flux, will enable the design of two-phase heat exchangers to proceed with much more confidence.

Technology Maturation

The experiment would be in preparation for the design and flight of an ISS based experiment (TRL 5). The data provided by the experiment would help identify the actual issues that require further attention before the flight experiment is designed and built.

Future Customers

Results of the work can serve as benchmarks to validate analytical and/or numerical codes, and will impact the ability to reliably engineer the energy rich systems for future space missions.

Flight Experiment Objectives

Unlike previous work where only time- or space-averaged heat transfer data were measured, we will obtain local measurements of the wall heat transfer coefficient with high temporal and spatial resolution. Visualization of the flow will allow the heat transfer to be correlated with the flow regime. An IR camera will be used to visualize fluid flow within a silicon tube and obtain temperature distributions along the inside and outside walls of the tube so local heat transfer coefficients can be determined.

Payload Description

The silicon tubes used to heat the fluid as well as visualize the flow are made of approximately 5 ohm-cm bulk silicon. The tubes are 6 mm ID with 1.0 mm thick walls. A test section that holds the silicon tube and allows IR measurements is shown schematically below. The green tube represents the silicon tube, and the blue tube is a quartz tube used for film thickness measurement.

Technology Maturation Progress

The data obtained thus far indicate the existence of a correlation between gravity level and the Critical Heat Flux (CHF). As expected, reducing the magnitude of the gravity vector experienced by the upward flow decreased the heat flux required for tube dry out and resulted in a rapid increase in tube temperature. Similarly, decreasing the inlet sub cooling of the fluid (PF 5060) also decreased CHF.

Technology Details

  • Selection Date
    AFO1 (May 2011)
  • Program Status
    Testing Complete
  • Current TRL (?)
    Successful FOP Campaigns
  • 2 Parabolic

Development Team

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