A collaborative effort between NASA and Nanotex Corp, where the Hot Disk TPS 2500 S is used for measurement of thermal conductivity, identified as critical tool in the research and development of a new high thermal conductivity carbon nanotube inner-lining for futuristic astronaut suits.
Leading the research on this project, Nanotex Corp. has been developing new applications for nano-materials, with special expertise with carbon nanotubes (CNT). The founder Dr. Felipe Chibante has been actively involved in nanotechnology for over two decades, since his Ph.D work at Rice University under supervising and Nobel Prize Laureate of Chemistry Dr. Richard Smalley at Rice University in Houston, TX.
Space Technology organization at NASA has been researching new innovations in the traditional space suit that has been in use since the Apollo missions in the 60’s. Sewing and cementing various high strength composite materials to conduct an eleven layer suit is the main focus in space textiles of this decade.
Figure 1. Visual representation of the layers within the lining of an astronaut suit.
It has long been an innovative idea within the Aerospace sector to develop an improved space suit that will solve the problem of heat removal of the liquid-cooled ventilation garments (LCVGs) used by astronauts. The current design used today is the same design used during the Apollo program in the 1960’s which incorporates an widespread network of water-cooling tubing that astronauts found to be bulky and uncomfortable, as well as increasing fatigue and lack of range of motion.
With this new innovative idea, the thermal conductivity of the tubing and individual fibers would be greatly improved. A research team was collected from various private companies and universities to seek out this task. They wanted to show that:
- All LCVG components showed thermal conductivity increases with addition of CNT
- Thermal conductivity along fiber length was significantly improved (>250%)
- Final woven fabrics with carbon nanotubes showed increases of 20-30%, but comparison is limited as fibers were of substantially different dimensions
- To obtain highest thermal conductivity possible, it is essential that nanotube alignment is achieved
- Physical properties of the filled systems are notably altered, especially at high loadings and at different fiber processing steps
- Polymer processing was only slightly affected by the presence of small amounts of nanotubes. This suggests that industrial processing will not be hampered or need to be significantly altered to rapidly produce CNT/polymer master batches
- Fiber processing appears to be affected to a greater extent – attention to melt rheology as it effects fiber dimension, draw rate, etc will be required.
Researchers had the task of hand threading the tubing material through a nylon/ spandex mesh layer making sure to incorporate large loops on the ends so not to tangle the tubing. The material was situated along the torso and limbs such that there maintains a form-fitting, close contact with the astronaut. To improve comfort, a nylon liner layer was introduced.
Using nanocomposite engineering alongside high thermal conductivity nanoscale fillers in the tubing components, the production of new LVCG components were made possible. Carbon nanotubes needed to be added using processes such as thermoplastic melt mixing, fiber spinning, and tubing extrusion. Circulating water in the tubing was cooled using an external heat exchanger.
Figure 2. Nanotex Carbon Nanotube Filled Tubing
Carbon fibers were tested for performance, thermal properties, and strength before being produced as yarns and woven into fabric cloths, however, testing individual fibers for thermal conductivity measurements is a major challenge within itself. After discussing an innovative approach to this problem, they devised a composite method to evaluate aligned fibers. “Using a melt process of nylons, the yarns could be wrapped around a flat mold and gently heat pressed to fix their alignment to about 10 degrees below their melting point. The sheets are then cut into flat pads that fit a rectangular mold. The mold is filled with the pads and heat pressed past the melt until a uniform block is achieved.” Then, using the Hot Disk TPS 2500 S Anisotropic Module, which is able to measure axial and radial directions of thermal conductivity measurements were performed.
Experiment Setup for orientated CNT fibers Nylon 6 Blocks
Figure 3. Anisotropic measurements using Hot Disk sensor between two blocks.
Results showed that there was a 75% increase in bulk thermal conductivity in the aligned fibers compared to the transverse direction. They concluded that this is a confirmation of orientation effect and may not be the conductivity of the individual fibers.
Table 1. Thermal Conductivity Results
||Thermal Conductivity (W/mK)
Thermal conductivity testing was also performed using the Hot Disk TPS 2500 S on multiple fabric samples.
Figure 4. Thermal Conductivity Measurements of Various Fabrics
In conclusion, as predicted, researchers were able to measure and confirm that an increase in thermal conductivity is achieved with the use of carbon nanotube fillers. This is the beginning of concurring research that has many application use outside of aerospace technology.