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

Hardware Description

The BXF is currently scheduled to fly on Utilization Flight-10A to the ISS with facility integration into the MSG and operation during Increment 16.

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