Measuring the heat transfer rates in a hypersonic shock tunnel is a costly and time consuming affair. Now, scientists at the Indian Institute of Science, Bangalore, have introduced a novel method that cuts the costs and improves the response times of these measurements.
Hypersonics is the study of objects moving at speed greater than Mach 5, that is 5 times the speed of sound. In today’s world of space exploration and commercialized space travel, hypersonics has become an important field of study. The measurement of heat transfer rates during hypersonic travel is especially an important area of study since objects entering a planet’s atmosphere are usually heated to high temperatures. This is usually achieved using thin films of metals like Platinum or Nickel, which increases the cost of these measurements. The thin films also need to be able to make quick measurements since hypersonic speeds are achieved for a very short duration during experiments. To be able to continue research in this field, it was impervious to develop new methods of measurement that would greatly reduce the cost and improve efficiency.
Now, Prof. KPJ Reddy and S Srinath at the Laboratory for Hypersonic and Shock Wave Research at IISc have proposed a novel method to replace the use of Platinum in these measurements. The proposed new technology not only improves the efficiency of the experiments but also greatly decreases the cost of such measurements.
“There are a few problems with using Platinum or Nickel films for measuring the heat transfer rates in Hypersonic shock tunnels. Firstly, each thin film cost around 700 Euros. And considering the fact that a Ph.D. student uses around 30 such thin films during the course of each experiment, the cost of conducting an experiment becomes very high. Secondly, during the experiments, we get only a small window of opportunity, of around 1 millisecond, to make the measurements and the films lack the response times for such quick measurements. And finally, since these thin films have to be deposited on the substrate using either the sputtering method, that causes a lot of wastage, or other methods, all of which increases the cost and is time consuming. These are some of the reasons due to which we started looking for alternatives for the Platinum thin films” explains Prof. Reddy.
After testing several materials, the team finally found that Carbon nanotubes performed exceptionally well as a heat transfer measuring agent. And on further studies, they finalized on using Large Carbon Clusters (LCC) thin films as the measuring agent. “The Carbon clusters cost only around Rs. 10 per film, which significantly reduces the cost of running the experiments. Apart from this, since the carbon clusters are directly grown on the substrate, it also reduces wastage. And finally, the response times of these cluster are in the order of microseconds which increases the time available for making the measurements” says Prof. Reddy.
The team has used the LCC thin films on space-capsule recovery model, which replicates the capsules re-entering the earth’s atmosphere, and on a 120° apex angle blunt cone model, which replicates a capsule entering Martian atmosphere. In both cases, the new LCC thin film technology outperformed the old Platinum thin films. University of Queensland, Australia have already used the LCC thin films to make further tests and have placed orders for more, having been satisfied with its performance. The research paper has also been awarded the “Most Outstanding Paper of 2015” by the prestigious journal, Measurement Science and Technology.
In the age of ever increasing travel speeds, studying the field of Hypersonics is an imperative. To progress our understanding in the field, there is an urgent need for huge amounts of experimental data. And this data and the technology to gather the data must be available ubiquitously for progress in the field “I did not want to patent this technology because that would mean there would be no progress in the field of Hypersoinics and this research would have stayed behind closed doors and wouldn’t go anywhere”, expresses Prof. Reddy.
About the Authors:
Srinath S is a research student at Laboratory for Hypersonic and Shock Wave Research at IISc.
Prof. KPJ Reddy is a Professor and heads the Laboratory for Hypersonic and Shock Wave Research at IISc.
About the Paper:
The paper titled ‘Large Carbon Cluster thin film gauges for measuring aerodynamic heat transfer rates in hypersonic shock tunnels was published in the journal Measurement Science and Technology. A link to the paper is provided below: