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.