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BXF Status
The Boiling eXperiment Facility (BXF)
was delivered to the International Space Station (ISS) aboard STS-133
in February, 2011. It was installed in the Microgravity Science
Glovebox (MSG) research facility on Tuesday, March 22, and following
experiment activation, functional and video checkouts, Microheater
Array Boiling Experiment (MABE) and Nucleate Pool Boiling Experiment
(NPBX) heater calibrations were performed. Science test point operations
began on Tuesday, March 29. Two weeks of science test point
operation were conducted until April 11 when the BXF safety circuit
trip due to a pressure reading and the BXF was shut down.
A troubleshooting plan was developed and executed on April 27 and revealed that
the 24VDC bus 1 circuit had a fault. Limited science operations for NPBX
resumed on May 9 using only the 24 VDC bus 2 circuit. Science operations
ceased and the BXF was removed from the MSG Facility on May 13. The BXF
was returned on Space Shuttle Mission ULF-7 landing on July 21.
A Post-Flight Assessment Review (PFAR) Board was convened on July 18 and concluded
in April 2012. It was determined that the 24VDC Bus 1 failure was due
to excessive heating of one of the bulk fluid heaters that initiated an electrical
short to ground.
In spite of the premature cessation of testing, BXF was able to complete 33%
of the MABE test matrix thus meeting 70% of MABE science objectives. BXF
was able to complete 29% of original test matrix and 56% of the recovery test
matrix for NPBX thus meeting 50% of NPBX science objectives.
February 28, 2011- A
nice online story about low-g boiling . . and a video of Prof. Jungho
Kim in the ESA low-g aircraft . . 
Overview
The Boiling Experiment Facility (BXF) will
accommodate two separate investigations, BXF–MABE (Microheater
Array Boiling Experiment)
and BXF–NPBX (Nucleate Pool Boiling Experiment), to examine
fundamental boiling phenomena. BXF is planned for the Microgravity
Science Glovebox (MSG) located in the U.S. Laboratory on the International
Space Station (ISS). The purpose of the BXF is to validate models
being developed for heat transfer coefficients, critical heat flux,
and the pool boiling curves.
Background
Boiling
efficiently removes large amounts of heat by generating vapor from
liquid. It is used to produce steam to turn turbines in electrical
power plants, cool high-powered electronic devices such as supercomputers,
purify chemical mixtures, and even cook dinner. An upper limit, called
the critical heat flux, exists where the heater generates so much
vapor that the liquid can not reach the heated surface. Continued
heating above this limit for prolonged periods can cause the heater
to burn itself out. Determination of the critical heat flux in microgravity
is essential for
designing cooling systems for space.
Pool
boiling generates vapor bubbles by heating a stagnant body of liquid.
It is a complex phase change process here the hydrodynamics,
heat transfer, mass transfer, and interfacial phenomena are tightly
interwoven. By conducting tests in microgravity, it is possible to
assess the effect of buoyancy on the overall boiling process and assess
the relative magnitude of other effects and phenomena such as surface
tension forces, liquid momentum forces, and microlayer evaporation.
Relevance
Boiling
is relevant to space-based hardware and processes such as heat exchangers,
cryogenic fuel storage, and electronic cooling due to the large amounts
of heat that can be removed with small increases in the temperature
of the heat transfer fluid. This reduces the temperature difference
between the heat source and radiator. For space applications, this
reduction in the temperature difference equates to a higher radiator
temperature which can reduce the radiator area and weight.
Pool boiling is an effective means for studying flow boiling. Some
models that are used to predict flow boiling heat transfer coefficients
consist of both pool boiling and liquid-phase forced flow convection
terms. The liquid-phase term is well-quantified in all gravity environments.
Pool boiling is also the limiting case of flow boiling whereby the
flow becomes zero.
Science Objectives
The BXF uses normal-perfluorohexane as the test
fluid and will operate between pressures of 60 to 244 kPa and temperatures
of 35 to 60 °C. Pressure and bulk fluid temperature measurements
will be made, and standard rate video will be acquired.
The objective of MABE is to determine the local boiling heat transfer
mechanisms in microgravity for nucleate and transition boiling and
the critical heat flux by examining the position of the liquid and
vapor adjacent to the heater. MABE uses two 96-element microheater
arrays, 2.7 by 2.7 mm and 7.0 by 7.0 mm in size, to measure localized
heat fluxes while operating at a constant temperature. Most boiling
experiments in the past have operated at constant wall heat flux with
a much larger heater, allowing only time and space-averaged measurements
to be made. Each heater is on the order of the bubble departure size
in normal gravity, but significantly smaller than the bubble departure
size in reduced gravity. A high speed video system will be used to
visualize the boiling process through the bottom of the MABE heater
arrays.
The other experiment, NPBX uses a 85-mm-diameter heater wafer that
has been "seeded" with five individually controlled nucleation
sites to study bubble nucleation, growth, coalescence and departure.
The experiment will selectively activate these nucleation sites in
order to understand bubble growth, detachment, and subsequent motion
of single and large merged bubbles under reduced-gravity conditions.
Hardware Description
The
BXF is currently scheduled to fly on Utilization Flight-5 to the
ISS with facility integration into the MSG and operation during
Increment 26.
The hardware consists of a boiling chamber mounted within a containment
vessel. The boiling chamber has three science heaters (one for NPBX
and two heater arrays for MABE), pressure and temperature measurement
instrumentation, a bellows assembly for pressure control, and pumps
for liquid conditioning. The containment vessel provides the second
and third levels of containment for the test fluid in the event of
a leak from the boiling chamber of the test fluid. Standard rate video
cameras are mounted inside the chamber to provide two orthogonal side-view
images of the vapor bubble during tests with the NPBX heater and a
single side view of the vapor bubble during MABE testing. The high-speed
video camera is mounted on the exterior of the containment vessel
wall and acquires 4 seconds of images through the bottom of the MABE
heater at 500 images per second.
An avionics box contains the data acquisition and control unit, removable
hard drives, indicator panel, and the control unit for the high-speed
video camera. The avionics box interfaces with the MSG mobile launch
computer, the high-speed video camera, and the BXF-embedded controller
boards within the containment vessel.
Contacts at NASA Glenn Research
Center
BXF Project Manager: William
Sheredy
William.A.Sheredy@nasa.gov
216–433–3685
MABE Project Scientist: John McQuillen
John.B.McQuillen@nasa.gov
216–433–2876
NPBX Project Scientist: Dr. David
Chao
David.F.Chao@grc.nasa.gov
216–433–8320
Principal Investigators (PI)
MABE PI: Prof. Jungho Kim,
University of Maryland
kimjh@umd.edu
301–405–5437
NPBX PI: Prof. Vijay Dhir,
UCLA
vdhir@seas.ucla.edu
310–825–8507 |
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