Influence of manufacturing technology of laser mirror cooling systems and operating conditions on their efficiency

Аuthors

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

NII NPO "LUCH", Podolsk, Russia

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

Abstract

The article discusses the peculiarities of influence on heat exchange in cooling systems of laser mirrors of technological and operational factors. The operation of the cooling systems in a wide temperature range is associated with a change in the thermophysical properties of the coolant in the temperature range from minus 50 °C to +50 °C. The strongest temperature dependence is manifested for the kinetic and dynamic viscosity of the coolant. To solve the problem, cooling systems are needed in which the coefficients of hydraulic resistance and effective heat transfer would be automodel or weakly dependent on the Reynolds number. These requirements are met by two types of heat exchange devices: collector-type systems and cooling systems with the presence of rip currents. As a possible solution, a checkerboard waffle system having suitable characteristics is proposed. The technology of manufacturing mirror cooling systems is briefly considered: formation of channels, connection of the cooling system with the substrate and the mirror base (soldering or diffusion welding). Technological factors have the strongest impact on the thermal and hydraulic characteristics of the cooling system: 1) the roughness inherent in the methods of forming the structure and its connection, and 2) the thermal resistance at the points of connection of the cooling system with the substrate and the mirror base. Roughness of heat exchange surfaces increases resistance and heat transfer. It has been revealed that in relation to cooling systems of mirrors operating on water, energy efficiency (ratio of Nusselt number to hydraulic resistance coefficient) practically does not depend on technological roughness, since the increase in heat transfer is counteracted by the increase in hydraulic resistance. The thermal resistances of soldered and welded joints used in the manufacture of laser mirrors have been experimentally determined. The influence of thermal resistance in the places of connection of the cooling system with the substrate and the mirror base on its characteristics was studied analytically. An experimental study of the influence of local inhomogeneities (non-soldering joints at the junction of the mirror substrate with the fins of the cooling system) on the temperature state of cooled laser mirrors was conducted using the electrothermal analogy method.

Keywords:

laser mirror, cooling system, hydraulic resistance, heat transfer, roughness, non-soldering, contact resistance.

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