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Boiling eXperiment Facility - Nucleate Pool Boiling eXperiment (BXF-NPBX)
06.05.09

Overview | Description | Applications | Operations | Results | Publications | Images

Experiment/Payload Overview

Brief Summary

BXF-NPBX will provide an understanding of heat transfer and vapor removal processes that take place during nucleate boiling from a well characterized surface in microgravity. Such an understanding is needed for optimum design and safe operation of heat exchange equipment employing phase change for transfer of heat in microgravity.

Principal Investigator

  • Vijay Dhir, Ph.D., University of California - Los Angeles, Los Angeles, CA

    • Co-Investigator(s)/Collaborator(s)

  • Gopinath R. Warrier, Ph.D., University of California - Los Angeles, Los Angeles, CA
  • David F. Chao, Glenn Research Center, Cleveland, OH

    • Payload Developer

    Glenn Research Center, Cleveland, OH

    Sponsoring Agency

    National Aeronautics and Space Administration (NASA)

    Expeditions Assigned

    Information Pending

    Previous ISS Missions

    BXF-NPBX is a unique investigation, nothing like this has flown in space before.

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    Experiment/Payload Description

    Research Summary

    • BXF-NPBX is one of a two investigations to be operated in the Boiling eXperiment Facility (BXF). The other investigation scheduled for operation in BXF is the Boiling eXperiment Facility- Microheater Array Boiling Experiment (BXF-MABE).


    • To understand bubble growth, detachment and subsequent motion of single and large merged bubbles, boiling experiments will be conducted in microgravity on ISS. In these experiments, designed surfaces will be used, visual observations and heat transfer data will be taken.

    Description

    BXF is accommodating two investigations, BXF-MABE and BXF-NPBX. The purpose of BXF-NPBX is to experimentally validate varying-gravity models being developed for the bubble dynamics and associated heat transfer (heat transfer coefficients and pool boiling curves). Applications of boiling heat transfer in space can be found in the following areas:

    • thermal management

    • fluid handling and control

    • power systems

    • on-orbit storage and supply systems for cryogenic propellants and life support fluids

    • for cooling of electronic packages for power systems associated with various instrumentation and control systems

    Recent interest in exploration of Mars and other planets, and the concepts of in situ resource utilization on Mars highlights the need to understand the effect of gravity on boiling heat transfer at varying gravity levels.

    BXF-NPBX will determine the effect of gravity on bubble nucleation, growth, merger and departure from prescribed cavities during subcooled pool nucleate boiling in microgravity. Based on the experimental data and the numerical simulations, the relative contributions of various heat transfer mechanisms to the overall heat flux will also be determined. The scaling of the bubble length and time scales with gravity will be clearly discerned. Experiments will be conducted using a polished silicon wafer (85 mm diameter) with prescribed nucleation sites. Five nucleation sites are etched onto the wafer using standard microfabrication techniques. The backside of the silicon wafers are instrumented with strain gage heaters and thermocouples, such that each of the cavities can be controlled independently. Since a building block type approach is adopted here, the number of cavities that will be nucleated will be systematically varied from one to five. The experiments will be conducted for various wall temperatures, liquid temperatures, and number of active cavities. Visual data of the bubble dynamics will be recorded using a camera. The system pressure, gravity levels, and the temperatures of the heater and the liquid will be measured. This data along with the visual data will be used to validate the numerical simulations. Based on the results of the numerical simulations performed for various parameters, the scaling of the bubble growth and departure process and the associated heat transfer mechanisms will be determined. These models will provide a design tool for the development of phase-changes processes in microgravity environments.

    Working fluids for thermal management systems, especially for manned spacecraft need to have low freezing temperatures and low toxicity. Current manned systems rely on a dual loop system whereby low pressure water is used as the internal or crew compartment working fluid and high pressure ammonia or refrigerant is used as the external working fluid. A thin plate separates the two working fluids in the heat exchanger. In the event of a leak across that plate, the results would be catastrophic. Identification of a new working fluid is critical for removal of this risk.

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    Applications

    Space Applications

    Boiling is an effective means of cooling because most of the heat transfer is from the latent heat of vaporization as opposed to heating and pumping a single-phase fluid. Pool boiling is necessary for predicting flow boiling and spray cooling heat transfer coefficients because these coefficients rely on a heat transfer term for pool boiling and a single phase convective term. The single phase convective term is always gravity independent; however, the pool boiling term is not and its magnitude easily affects the overall heat transfer coefficient. In addition, pool boiling is a limiting case of flow boiling whereby the flow term is zero. From a practical standpoint, this can occur when there is a pump malfunction shutting down flow past a heat source. While the change in the flow inertia is almost instantaneous, the thermal inertia requires a much longer time to dissipate. Finally, in the worst case scenario of a Loss of Coolant Accident, models for pool boiling can determine the amount of fluid expelled from the coolant loop after the system pressure has dropped to ambient.

    Earth Applications

    The proposed research will provide fundamental understanding of bubble dynamics and heat transfer during nucleate boiling in extreme conditions. Such an understanding is needed for optimum design and safe operation of heat exchange equipment employing phase change for transfer of heat in the environments of the deep ocean, extreme cold and high altitudes.

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    Operations

    Operational Requirements

    BXF-NPBX utilizes a single heater array, consisting of 5 independently controlled nucleate sites (heaters). The BXF-NPBX heater is activated during the test to a point at which a bubble will start to nucleate on it. This bubble will then grow to a point at which it will detach from the heater. Depending on the test, one to five bubbles will be created. During this process, various data will be acquired and stored. BXF-NPBX has been designed to develop a mechanistic model of nucleate boiling heat transfer in reduced gravity for pool boiling using a predefined boiling surface.

    BXF-NPBX will require crew time to set up the hardware to perform eight test sessions. The data from the test sessions will be captured on videotapes and hard drives that will be changed out by the crew. If Ku band is available video data will be downlinked from ISS to the Glenn Research Center TeleScience Center in Cleveland, OH. The hard drive and videotapes will be stowed for later return to Earth for analysis by the investigator.

    Operational Protocols

    This investigation will require the crew to setup the BXF hardware in the Microgravity Science Glovebox. The crew will install the BXF-NPBX samples and activate the BXF, at this point the BXF is automated to perform the test sessions for BXF-NPBX. BXF-NPBX will run for five hours and perform a total of eight test sessions. The crew will have to perform a hard drive and a videotape change out half way through the BXF-NPBX session. After the session is completed the crew will deactivate the BXF hardware. The hard drive, videotape and NPBX samples will be labeled and stowed for return to Earth.

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    Results/More Information

    Information Pending

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    Related Web Sites
  • UCLA Boiling Heat Transfer Laboratory

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    Publications

    Results Publications

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      Related Publications
      • Warrier GR, Dhir VK. Visualization of Flow Boiling in Narrow Rectangular Channels. Journal of Heat Transfer and Mass Transfer. ;126:495. 2004
      • Jiang S, Dhir VK. Spray cooling in a closed system with different fractions of non-condensibles in the environment. International Journal of Heat and Mass Transfer. ;47:5391-5406. 2004
      • Abarajith HS, Dhir VK, Warrier G, Son G. Numerical simulation and experimental validation of the dynamics of multiple bubble merger during pool boiling under microgravity conditions. Annals of the New York Academy of Sciences. ;1027:235-258. 2004

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      Images

      imageIn Earth's gravity (image on the left) the action of buoyancy allows the bubbles to overcome surface tension forces. The bubbles rise upward away from the heater surface. In microgravity (image on the right) the buoyancy force is very weak. Consequently, the bubbles often remain attached to the heater because of surface tension and become large as more vapor is produced due to the continuous input of energy from the heater. Courtesy of University of California.
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      imageThe figure above shows a comparison of the experimental and numerical bubble shapes during bubble growth, merger and departure for low gravity conditions. The numerical simulations match very well with the experimental data. Water was the test fluid used.
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      Information Provided and Updated by the ISS Program Scientist's Office
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