A ground-based experimental facility to perform flow boiling and condensation experiments is built in support of the development of the long duration Flow Boiling and Condensation Experiment (FBCE) destined for operation on board of the International Space Station (ISS) Fluid Integrated Rack (FIR). We performed tests with the condensation test module oriented horizontally and vertically. Using FC-72 as the test fluid and water as the cooling fluid, we evaluated the operational characteristics of the condensation module and generated ground based data encompassing the range of parameters of interest to the condensation experiment to be performed on the ISS. During this testing, we also evaluated the pressure drop profile across different components of the fluid subsystem, heater performance, on-orbit degassing subsystem, and the heat loss from different components. In this presentation, we discuss representative results of performance testing of the FBCE flow loop. These results will be used in the refinement of the flight system design and build-up of the FBCE which is scheduled for flight in 2019.

This study is the second part of a two-part investigation of flow boiling critical heat flux (CHF) in microgravity, which is simulated in parabolic flight experiments. Using FC-72 as working fluid, flow boiling experiments are conducted in a rectangular channel fitted with two opposite heated walls, allowing either one or both heated walls to be activated during a test. While the first part explored flow boiling conditions leading to CHF, this part addresses events just before CHF, during the CHF transient, and immediately following CHF. For both single-sided and double-sided heating, interfacial behavior just before CHF is characterized by dominant wavy vapor layers covering the heated walls, where liquid is able to access the walls only in wetting fronts corresponding to the wave troughs. CHF is associated with successive lift-off of wetting fronts from the walls, consistent with the Interfacial Lift-off Model, which has been validated extensively in past studies using single-sided heating in both μge and 1−ge. It is shown this model predicts μge double-sided flow boiling CHF with excellent accuracy. Additionally, the model points to convergence of CHF values for μge and 1−ge for inlet velocities greater than about 1m/s. Therefore, by maintaining velocities above this threshold allows designers of space systems to achieve inertia-dominated performance as well as to adopt prior data and correlations developed from terrestrial studies.

An experimental facility to perform flow boiling and condensation experiments in long duration microgravity environment is being designed for operation on the International Space Station (ISS). This work describes the design of the subsystems of the FBCE including the Fluid subsystem modules, data acquisition, controls, and diagnostics. Subsystems and components are designed within the constraints of the ISS Fluid Integrated Rack in terms of power availability, cooling capability, mass and volume, and most importantly the safety requirements. In this work we present the results of ground-based performance testing of the FBCE subsystem modules and test module which consist of the two condensation modules and the flow boiling module. During this testing, we evaluated the pressure drop profile across different components of the fluid subsystem, heater performance, on-orbit degassing subsystem, heat loss from different modules and components, and performance of the test modules. These results will be used in the refinement of the flight system design and build-up of the FBCE which is manifested for flight in late 2017-early 2018.

Space agencies worldwide are being confronted with the challenges of more distant manned space missions, which will demand greater energy efficiency and reduced weight and volume. One method being considered to reduce the weight and volume of a long duration mission spacecraft is to replace present single-phase Thermal Control Systems (TCSs) with ones that rely on flow boiling and condensation. This transition will require a thorough understanding of the influence of reduced gravity on flow boiling and condensation, and the development of predictive tools for both. This study is the first part of a two-part study investigating flow boiling of FC-72 in microgravity, which is simulated in a series of parabolic flight maneuvers. Flow boiling experiments are conducted in a rectangular channel fitted with two opposite heating walls. The operating conditions include liquid inlet velocities of 0.1–1.9m/s, liquid mass velocities of 224.2–3347.5kg/m2s, and inlet subcoolings ranging from 2.8 to 8.1°C. The study includes both high-speed video analysis of interfacial features and heat transfer measurements. A dominant wavy vapor layer behavior is encountered for most operating conditions. Boiling is sustained mostly in ‘wetting fronts’ corresponding to contact regions between the wave troughs and the wall, and abated near the wave peaks. During a flight parabola, the heated wall temperatures decrease slightly as the aircraft enters the hypergravity ascent phase, then increase slightly during the microgravity phase, and decrease once again during the hypergravity descent. These temperature variations point to enhancement in flow boiling heat transfer with increasing gravity, and conversely a reduction with microgravity.

Flow boiling and condensation have been identified as two key mechanisms for heat transport that are vital for achieving weight and volume reduction as well as performance enhancement in future space systems. Since inertia driven flows are demanding on power usage, lower flows are desirable. However, in microgravity, lower flows are dominated by forces other than inertia (like the capillary force). It is of paramount interest to investigate limits of low flows beyond which the flow is inertial enough to be gravity independent. One of the objectives of the Flow Boiling and Condensation Flight Experiment sets to investigate these limits for flow boiling and condensation. A two-phase flow loop consisting of a Flow Boiling Module and two Condensation Modules has been developed to experimentally study flow boiling condensation heat transfer in the reduced gravity environment provided by the reduced gravity platform. This effort supports the development of a flow boiling and condensation facility for the International Space Station (ISS). The closed loop test facility is designed to deliver the test fluid, FC-72 to the inlet of any one of the test modules at specified thermodynamic and flow conditions. The zero-g-aircraft tests will provide subcooled and saturated flow boiling critical heat flux and flow condensation heat transfer data over wide range of flow velocities. Additionally, these tests will verify the performance of all gravity sensitive components, such as evaporator, condenser and accumulator associated with the two-phase flow loop. We will present in this paper the breadboard development and testing results which consist of detailed performance evaluation of the heater and condenser combination in reduced and normal gravity. We will also present the design of the reduced gravity aircraft rack and the results of the ground flow boiling heat transfer testing performed with the Flow Boiling Module that is designed to investigate flow boiling heat transfer and Critical Heat Flux (CHF) phenomena.