(459a) The CVB Experiment – Constrained Bubble Nucleation In Microgravity

The CVB
Experiment – Constrained Bubble Nucleation in Microgravity

A.   
Chatterjee¹, P.C. Wayner¹, Jr.,
J.L. Plawsky¹

David F. Chao² , Ronald J. Sicker²,

Tibor
Lorik³, Louis Chestney³, John Eustace³,
Raymond Margie³, John Zoldak³

¹Rensselaer
Polytechnic Institute, Troy, NY, USA,

²NASA
Glenn Research Center, Cleveland, OH,

³Zin
Technologies, Cleveland, OH, USA

 E-mail: Plawsky@rpi.edu

The Constrained Vapor Bubble (CVB) is a prototype for
a wickless, grooved heat pipe and is the first fluids experiment flown on the
International Space Station as part of the US space program. The CVB experiment
resides in the Fluids Integrated Rack (FIR) and along with the Light Microscopy
Module (LMM) is designed to probe the details of the fluid mechanics underlying
the operation of a heat pipe in space.

Figure 1. The Constrained Vapor Bubble and Liquid
Pool

The CVB is essentially a wickless
heat pipe. It consists of a fused silica cuvette that is partially filled with
a working fluid - pentane in this case. The pentane forms a pool at one end and
rises up the four corners of the cuvette due to capillary action (see Figure
1). A thin film of liquid adsorbs on the four flat faces of the cuvette; while the remaining volume of the cuvette is filled with
pentane vapor. Thus, the central bubble volume is surrounded by liquid on all
sides - the corners have a liquid meniscus while the flat faces have a thin
adsorbed film. Since the bubble is effectively constrained by the walls of the
cuvette, the experiment is named - Constrained Vapor Bubble.

Four CVB modules were run on the
International Space Station.  This
paper deals with unexpected results from the run of the 20 mm module.  Following launch, the vapor bubble of
the CVB must be coaxed into its central position within the cuvette by subcooling the region behind the liquid pool and turning
the heater on to drive the vapor toward the heater end.  In general this process worked reliably
however initial attempts with the 20 mm, the shortest module, failed and
instead of aggregating the bubble, a series of individual nucleation events
occurred as shown in Figure 2. 
These events occurred as superheats at the heater end of the device
exceeded the 50 ˚C.  Figure 3
shows temperature and pressure traces for one of these events and the purpose
of this paper is to present the results and some analysis of the behavior.

Figure 2 Nucleation and splitting of vapor bubble in the
CVB

Figure 3 Pressure and temperature
traces for two nucleation events.

References

[1] Chatterjee, A., et al., Constrained
Vapor Bubble Experiment for International Space Station: Earth's Gravity
Results. Journal of Thermophysics
and Heat Transfer, 2010. 24(2), 400.