On December 4-5, 2013, the CVB-2 Operations team performed a study of the CVB-2 Experiment Module using the LMM 50x objective camera lead by the Co-Investigator, Professor Peter Wayner, from Rensselaer Polytechnic Institute. The CVB-2 Experiment continues to demonstrate interfacial behavior that is very different than the original CVB Experiment. The current study is to observe CVB-2 at both iso-thermal and heated test points using 50x magnification. The interfaces are clearly more complicated for a binary mixture (see below). The images shown below are stitched together to form a complete observation of the test module. It will take a significant amount of analyses to determine if the semi-circular observations are entirely due to the fluid composition or interfacial effects.
|50x Iso-thermal image taken on December 4, 2013.|
|50x images stitched together, near the dry-out region.|
Surveillance pictures of the vapor bubble and the position of embedded thermocouples in the Constrained Vapor Bubble experiment. The top image is of the 30mm CVB in µg, the middle image is of the 40 mm CVB in 1g and the bottom image is of 40mm CVB in µg. All the images are at heater input of 2W on the left end. Even at this relatively low magnification, the curvature gradient in the corner meniscus is clearly visible. In the 1 g system, the orientation is perpendicular to earth.
October 2013 – The CVB-2 (Constrained Vapor Bubble) experiment is now underway onboard the ISS and will continue through the end of the year. Like the first run of CVB, CVB-2 investigates the science and engineering of heat pipes using its own miniature wickless heat pipe. However, instead of studying a single experiment liquid like CVB, CVB-2 is investigating a binary liquid mixture. CVB-2 proposes that binary mixtures will increase the capillary effect and improve heat pipe efficiency in microgravity.
June 2010 – Two of the four Constrained Vapor Bubble (CVB) science modules were returned from ISS on ULF-4 on May 26, 2010. The 30mm pentane and the dry calibration modules will be used for additional ground testing for the science investigation team. This experiment is expected to produce multiple scientific journal articles.
May 2010 – The STS-132, ULF-4, is scheduled to return two of the completed CVB modules on May 26. The 30mm Pentane and the Dry calibration/control modules have successfully complete science operations and will be used to verify preflight ground testing. To date three journal articles are planned for these results. The 30mm module may be refurbished with a mixed fluid to be a reflight experiment in 2012.
* The Constrained Vapor Bubble (CVB) 40 mm dry module was operated on the International Space Station (ISS) from April 26 to April 30, 2010. In the approximately 112 hours of operation, all the science objectives were fulfilled. The original test matrix was completed and an additional run was performed giving us excellent calibration characteristics.
April 2010 – The Constrained Vapor Bubble (CVB) 30-mm Pentane module was removed from the Light Microscopy Module (LMM) on April 16, 2010 and replaced with the Dry Calibration/Control Module. Operations will continue with the Dry Module on April 26, 2010. Both the 30 mm and dry module will be returned on ULF-4 in August 2010. Below is an image from the video downlink.
|CVB Module Installation|
• Fluids Integrated Rack/Light Microscopy Module/Constrained Vapor Bubble (FIR/LMM/CVB) operations are on-going through day 091. We have completed over 90% of the extended test matrix. We are presently collecting data by holding the heater temperature constant and changing (raising) the cooler temperature. We have also collected video data of lateral oscillations. We are looking forward to starting operations with the dry/calibration module.
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:
• Pentane Cell 1: bubble length of 20 mm ±5% at 20°C
• Pentane Cell 2: bubble length of 30 mm ±5% at 20°C
• Pentane Cell 3: bubble length of 40 mm ±5% at 20°C
• Ethanol Cell 4: bubble length of 25 mm ±5% at 20°C
• Dry cell: evacuated to 5 torr
Contacts at NASA Glenn Research Center
Project Manager: Ronald J. Sicker, NASA GRC
Project Scientist: Dr. David F. Chao, NASA GRC
Principal Investigator: Prof. Peter C. Wayner, Jr., Rensselaer Polytechnic Institute