2-10 micron water droplets help cool nuclear reactors
Scientists developed technology for nuclear power plants in the Middle East and North Africa
Scientists at the Ural Federal University (UrFU, Russia) have created a technology that dramatically increases the efficiency of cooling systems for nuclear reactors. The technology helps make energy generation more efficient and safer. It is suitable for nuclear power plants in warm and arid countries in the Middle East and North Africa. The authors of the invention are researchers of the Department of Nuclear Power Plants and Renewable Energy Sources at UrFU.
The essence of the development lies in the fact that a water aerosol (droplet size 2–10 microns) is supplied in a stream of cooling air using finely dispersed ultrasonic spraying. When in contact with the heat exchanger, the aerosol absorbs the heat of the heated surface, evaporates, and, together with the air, is released into the atmosphere. The other part of the steam destroys the thermal boundary layer of the air flow in the immediate vicinity of the heat exchanger tubes and reduces the resistance to heat transfer. Evaporation of one kilogram of water leads to the absorption and removal of 2.5 thousand kJ of thermal energy. Such a result is not possible with traditional technologies.
"Under normal conditions, standard systems heat exchangers are designed to remove heat at nuclear power plants", said the head of the Department at UrFU and head of researchers Sergey Shcheklein. "They are used both in normal mode, when operating at rated power, and during a planned shutdown of the reactor, and in emergencies. However, in the climate of African and Middle Eastern countries, such systems are unproductive. We offer a system that ensures high performance and reliability of nuclear power plants in any temperature environment."
Researchers tested the technology on an experimental setup. Air was supplied with different concentrations of air-water "fog" from the aerosol, with different speeds and temperatures. It was found that as the mass and speed of the air-water flow increase, the surface temperature of the heat exchanger decreases, and, therefore, the intensity of heat transfer increases.
"In the experiment, we calculated the parameters of humidity and air-water flow rate, which provide the highest heat transfer efficiency," said Sergey Shcheklein. "For standard heat removal, moisture content of 0.05–0.1% of the total volume of the cooling medium is sufficient, and a relatively low speed of 15–20 m / s is required. That is, the consumption of water and, therefore, the necessary reserves of it at the NPP are insignificant. At the same time, heat removal systems can become more compact and lighter. The surface temperature of the heat exchanger drops by half when the maximum amount of liquid is supplied, and the heat transfer and, accordingly, the intensity of the heat removal increases three times."
"Before us, no one had received such a result, the humidification of air flows led to an increase in performance only by 30-40%," said co-researcher Akram Hamzah Abed. "The secret is in the droplet size: large droplets of 1 mm or more do not evaporate entirely, but droplets a few microns in size evaporate instantly."
Also, researchers developed an option for emergencies. If the power is cut off, the air will circulate in the system due to the temperature difference and the special design of the traction section.
According to Sergei Shcheklein, Egypt, Turkey, Syria, Iraq, Iran and other countries of this region express their readiness to develop nuclear energy in cooperation with specialists from the Russian state corporation Rosatom.
"Taking into account the uniqueness and high efficiency of the created technology, the research team received a patent for the invention of an emergency cooling system for a nuclear power plant reactor," said Deputy Director of the Center for Work with Enterprises at UrFU Alexander Cherepanov. "Nuclear industry specialists show an increased interest in their work. We expect that the technology will find wide application both in Russia and in the partner countries of the Rosatom corporation."
More information:
doi.org/10.2298/TSCI190527055A
Provided by Ural Federal University
