Critical situations in laser mirror cooling systems


Аuthors

Leonov E. V.*, Shanin Y. I.**

NII NPO "LUCH", Podolsk, Russia

*e-mail: leonovev@sialuch.ru
**e-mail: ShaninYuI@sialuch.ru

Abstract

The following are the features of boiling in laser mirror cooling systems: 1) one-sided heat supply to the system of narrow channels, 2) large underheating of the coolant to the saturation temperature. The literature reviewed provides extremely sparsely presented results of studies under such conditions. They mainly relate to the possible development of a boiling crisis during cooling of the hot wall of a thermonuclear reactor. We have analyzed critical situations that may occur in laser mirror cooling © Леонов Е.В., Шанин Ю.И., 2025 ТЕПЛОВЫЕ ПРОЦЕССЫ В ТЕХНИКЕ. 2025. Т. 17. № 1 20 THERMAL PROCESSES IN ENGINEERING systems: 1) upon the onset of boiling, steaming of channels and reaching critical heat fluxes that can lead to damage to the mirror, 2) when local peak thermal loads are applied to the mirror, which may result in further damage. We have experimentally examined the effect of a sharp deterioration in heat exchange on the temperature field in a fragment of the cooling system using the electrothermal analogy method for the following cases of «steaming» of a rectangular channel: 1) the upper edge of the cooling channel is covered with steam, 2) a third of the side edge is added to the upper edge, 3) the upper edge and 2/3 of the side edge. It was found that the «steaming» process spontaneously deepens. This results in the complete blocking of the channel with steam (a defect in the cooling system) with subsequent destruction of the mirror. For this case, an analytical study of the temperature field in a mirror with a similar defect was carried out. Critical heat fluxes under one-sided thermal loading of the mirror cooling system, leading to a boiling crisis, were analytically estimated. Depending on the size of the peak load compared to the thickness of the substrate and its material, the temperature fields were analyzed in the case of: 1) considering the substrate as a half-space, 2) the presence of two-dimensional heat leaks in the substrate, 3) the size of the peak is such that a onedimensional temperature distribution was realized across the thickness of the substrate in the area of the peak effect. Relationships were established between the sizes and the magnitude of the peak load, at which the critical heat flux in the mirror cooling system will be achieved.

Keywords:

laser mirror, cooling system, hydraulic resistance, heat transfer, peak heat load, boiling, heat exchange crisis, critical heat flow

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