The use of interfacial free energy gradients to control fluid flow naturally leads to simpler and lighter heat transfer systems because of the absence of mechanical pumps. Therefore, “passive” engineering systems based on this principle are ideal candidates for the space program. In this context, “passive” refers to the natural pressure field for fluid flow due to changes in the intermolecular force field under an imposed nonisothermal temperature field. This force field is a function of the shape, temperature, and composition of the system. For example, heat pipes which rely on these forces have been proposed frequently to optimize heat transfer under microgravity conditions. However, the basic thermophysical principles controlling these systems are not well understood and, as a result, they have under performed. In general, the full potential of interfacial forces has not been realized in transport phenomena.

Therefore, the basic experimental and theoretical studies of the constrained vapor bubble (CVB) under microgravity conditions to help remedy this undesirable situation. The proposed use of a transparent glass cell and related optical measurements will increase the understanding of transport systems controlled by interfacial phenomena because the system is viewed directly. Relatively large systems with high heat fluxes and small capillary pressure levels set in the condenser will be emphasized.

In particular, we are concerned with the experimental study of the CVB for a completely wetting system, the liquid will coat all the walls of the chamber.  Since in microgravity the bubble will tend to travel in the middle of the constraining “pipe”.

The first CVB flight unit is presently under construction (March 2007).  Five flight units will be launched with LMM on ULF 1.  With the following samples: