Guest Blogger: Joel Plawsky

by Michael Mullaney on March 30, 2010

(Professor Joel Plawsky wrote this excellent post for The Approach – enjoy! It follows on this post from last summer detailing the science and launch into space of his CVB project.)

We have never seen anything like this on Earth.”

I’d like to give you an update on our CVB flight experiment. Science operations for CVB (Constrained Vapor Bubble) began at approximately 1930 GMT on day 081, or Monday, March 22. The start was high drama as the vapor bubble for the system was located near the pressure transducer and hence not visible to the microscope. It took nearly 12 hours to nucleate and a grow a bubble in the right spot and the bubble appeared literally a few minutes before we were going to give up and try a different system.

At the moment (March 30) the cell has been running for 8 days and we are collecting a huge volume of data.  Since we are the first experiment running in the new fluids facility, we get to operate the experiment in real time.  The only time we do not have contact with the Space Station is during periodic LOS (loss of signal) times when the station is out of contact with the 3 geosynchronous satellites that it uses for communication to the ground.

I have included a few images and figures to give you and idea of what we are seeing.  Figure 1 below is a composite image of the CVB taken by stitching together about 160 individual video frames.  You can clearly see the fluid in the corner of the cell, the glass wall of the cell and the evaporation and condensation regions inside.

 

Figure 1 - A composite image of the CVB cell taken at a magnification of 10X.  The image shows the evaporation, condensation and intermediate regions of the cell.  The fringes represent a contour map of the liquid film thickness on the walls of the CVB.

 

Figure 2 below is a graph of the temperature profile along the axis of the CVB.  It shows the evaporation (initial steep temperature drop), intermediate (flat portion), and condensation (second temperature drop) regions that are the signature of a heat pipe.  We ran the system suing heat inputs of 0.4 – 2 Watts.  The system appears to be operating most efficiently at the 1.2 W level as the flat region extent is the largest there.

 

Figure 2 - Temperature profiles along the axis of the CVB.  Power inputs of 0.4 - 2 watts were used in this initial measurement.  The broad, flat portion within the temperature profiles are hallmarks of heat pipe operation.  The extent of the flat region is maximum at an input power of about 1.2 W.

 

Figure 3 below shows two features. First it attests to the symmetry conditions we can achieve in a system like this only under microgravity conditions.  Though the image does not show both walls of the cell, the cusp you see defines the symmetry line in the cell.  The shape of the vapor liquid interface is a surprise.  We have never seen anything like this on Earth and are anxious to figure out what could be going on. The large blob of liquid at the top of the picture is a pentane drop, located near the heater in a position where we expected there to be no pentane.

 

Figure 3 - A composite image of the vapor bubble and film thickness near the heater end of the CVB.  The central cusp is along the central axis of the CVB attesting to the high degree of symmetry that is only possible in microgravity.  The cusp is a feature not observed on the ground.