Today radar stations are in great demand in our country. Radars can be used to conduct geological exploration, obtain images of the earth’s surface, assess the scale of a natural disaster, and perform many other important tasks. Ideally, they should be able to see as far as possible and as detailed as possible.
For a radar to see as far as possible, its signal must be very powerful. However when the radiation signal is amplified, the semiconductor chips of the transceiver modules heat up. This leads to a deterioration in their performance, reduced reliability and service life.
To reduce the temperature of the chips, air or liquid cooling systems are used. Air systems are simpler but not very efficient, while liquid systems are much more expensive but can leak.
So here comes the dilemma: the power of transceiver modules needs to be significantly increased, but it is impossible to do so in existing designs. So how to cool the modules?
Researchers at National Technical University of Ukraine ‘Igor Sikorsky Kyiv Polytechnic Institute’ have solved this problem. With grant funding from the National Research Foundation of Ukraine, the researchers are implementing the project ‘Development of thermophysical, structural and technological foundations for improving the cooling efficiency of radar transceiver modules’.
“We decided to create a new efficient air cooling system that does not require additional electricity consumption to increase efficiency. It is important that this system can be easily installed into stations that are already in operation, and that it is relatively inexpensive to manufacture,” said Yurii Nikolaenko, project PI and leading researcher at the University. “And we succeeded! We came up with a cooling system that, figuratively speaking, is powered by the forces of nature.”
How does the new system work?
The researcher explained that the secret lies in the use of a new design of a flat gravitational heat pipe. This tube can be easily mounted in the base of the radiator, under the chips.
The design of a classical heat pipe was invented in the last century. Its inner surface is covered with a capillary-porous structure, and the pores are saturated with liquid. “A heat pipe is a hermetically closed evaporation and condensation system. If it is heated at one end, the liquid evaporates, absorbs the heat which is quickly transferred over the entire surface and length of the pipe. Then the condensed liquid from the cooler part returns to the heating zone through the capillaries,” the PI explained.
The capillary-porous structure abroad is usually made of fine-pored sintered metal powder. It is important that the capillary-porous structure allows to increase the number of centers of steam bubble formation and intensify the boiling process.
“Back in the 70s of the last century, Kyiv Polytechnic Institute, under the leadership of Professor Mykhailo Semena, created its own capillary-porous structure from sintered metal fibers,” the researcher continued. “Copper fibers with a diameter of 50 microns and a length of three millimeters were sintered into a thin layer. This layer was then sintered to the inner surface of a copper tube.”
The invention was remarkable, but complicated in manufacturing. To sinter a capillary structure from copper fibers or powders, you need a special furnace with a temperature of about a thousand degrees and a reducing or protective environment inside (hydrogen, vacuum, or nitrogen)…
The idea to create a simple and efficient heat pipe came to the researcher’s mind when he was studying new foreign publications on the construction of radar and cooling systems. “I noticed the tilted canvases of the antenna arrays and I thought, what if we abandoned the sintered capillary-porous structure on the inner surface of the pipe? What if the condensate that forms in the cooler part flows down by gravity? In order to make it easy for boiling bubbles to form in the heating zone, we can create a threaded capillary structure,” the researcher recalls.
The researchers managed to create a new flat heat pipe with a threaded structure before the full-scale invasion began.
“It is very easy to make such a structure, 5 minutes and it is ready. To make a heat pipe with a threaded structure, we take a copper tube with a diameter of 12 millimeters, cut a thread with a fine pitch, from 0.2 mm to 0.5 mm, inside one end,” explains Yurii Nikolaenko. “We seal the ends, vacuum, fill the tube with coolant, seal the filler tube and flatten it. Then we mount the flat heat pipes in the base of the radar module’s radiator. The station’s antenna is tilted in the working position, so the cooler part of the heat pipe is above the heating zone. Condensation drains off by itself!
Thanks to this idea, the new heat pipes are several times cheaper than the classic ones, and the power of the chips increases.
The new cooling system has already been patented. The researchers received a patent for the invention in Ukraine, which means that the development has a global novelty, and two patents for utility models.
Estimates of the invention’s effectiveness have shown that if a thousand modules are installed in the radar, the savings per station in Ukraine will amount to UAH 663 thousand (in pre-war prices). In Germany, it will be possible to save 171 thousand euros, in the United States – 122 thousand dollars. The savings will be achieved due to the fact that it will not take many hours to sinter capillary-porous structures in high-temperature furnaces, buy expensive materials, etc. To produce the threaded structure, only the electricity needed for a lathe is consumed. Thousands of modules can save 28,400 kWh of electricity.
In 2023, the team aims to study the thermal characteristics of the new cooling system. They also plan to test even simpler pulsating heat pipes. Upon completion of the work, the researchers plan to share the research results with interested companies to introduce the invention into production.
During the project implementation, three articles were published in reputable foreign journals of the first and second quartiles (Q1 and Q2), and two more are under review. In 2022, the researchers presented their development at the International Scientific and Technical Conference on Electronics ‘ELNANO-2022’.
The team consists of two leading and five early-career reserachers. All of them work in Kyiv despite the war.
“During their work in the project, early-career researchers received brilliant results that they needed for their research professional growth. And most importantly, they realized that they can do an important job and receive a worthy reward for it, for which we are sincerely grateful to the National Research Foundation of Ukraine.”
Interviewed by Svitlana GALATA
