Flow Boiling and Condensation Experiment (FBCE)

The Flow Boiling and Condensation Experiment (FBCE) is a flight experiment that aims to understand flow boiling and flow condensation in microgravity and is planned to run onboard of the International Space Station (ISS). The FBCE will serve as a primary platform for obtaining two-phase flow boiling and condensation heat transfer data in microgravity. By comparing the microgravity data against data obtained in Earth’s gravity, it will be possible to ascertain the influence of body forces on two-phase transport phenomena in pursuit of mechanistic models as well as correlations, and to help determine the minimum flow criteria to ensure gravity independent flow boiling and condensation. Key areas of impact include the Rankine cycle-based power systems and two-phase thermal control systems. Rankine cycle power systems are considered one of the most viable options for space application due to their high power output per unit mass and volume. Similarly, two-phase thermal control systems can yield significant advancement in thermal performance for spaceflight applications compared to current single-phase thermal control loops.

The four primary objectives for FBCE are:

1. Develop experimentally validated, mechanistic model for microgravity flow boiling critical heat flux (CHF) and dimensionless criteria to predict minimum flow velocity required to ensure gravity independent CHF.
2. Develop experimentally validated, mechanistic model for microgravity annular condensation and dimensionless criteria to predict minimum flow velocity required to ensure gravity independent annular condensation. Also, develop correlations for other condensation regimes in microgravity.
3. Obtain flow boiling data (heat flux, void fraction, the wall temperature difference) in long duration microgravity environments for a well-characterized heating surface as functions of liquid inlet mass velocity and subcooling.
4. Obtain flow condensation data (heat flux, void fraction, the wall temperature difference) in long duration microgravity environments for a well-characterized condensing surface as functions of inlet quality and flow rate of condensing vapor.

Specific tasks associated with this effort will be as follows:

1. Develop a two-phase flow loop to condition dielectric coolant Normal Perfluorohexane (nPFH, C6F14) to preset values of flow rate, pressure, and temperature to the three primary loop test components, the Flow Boiling Module (FBM) and two Condensation Modules (CM-HT and CM-FV).

2. Develop a Flow Boiling Module (FBM) to enable the study of spatial development of both subcooled and saturated flow boiling, and critical heat flux (CHF). The test module will feature two opposite heated walls with transparent sidewalls to facilitate detailed photographic study of interfacial behavior. The heated walls may be operated under uniform heat flux or uniform temperature conditions.

3. Develop two separate Condensation Modules to enable the study of spatial development of condensation flow and heat transfer regimes. The first Condensation Module (CM-HT) will feature a tube-in-tube construction, with nPFH vapor flowing through the central metal tube to extract heat from water flowing in the opposite direction through an annulus between the inner and outer tubes. CM-HT will provide most of the pressure drop and heat transfer measurements. In the second Condensation Module (CM-FV), the nPFH vapor will be supplied through a square transparent channel along the center of which a circular metal tube will carry water in counterflow to condense the vapor along the inner tube’s outer wall. The transparent outer square channel will enable detailed photographic study of interfacial behavior of the condensing nPFH flow.

Knowledge gained from the Flow Boiling and Condensation Experiment (FBCE) will help advance the understanding and design of boilers in high power thermodynamic cycles like nuclear-based Rankine cycles especially when it comes to the Critical Heat Flux (CHF) in liquid metal boilers. FBCE will also advance understanding achieving gravity independence in critical heat flux predictions. FBCE will be crucial for the design of two-phase thermal control systems which involve heat generation, transport, and rejection, and for the gravity-insensitive vapor compression heat pump design for future long duration mission. FBCE will have tremendous contribution in the cryogenic technology for the knowledge it will generate in flow boiling and condensation.

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