Application of swirling flows in cooling systems of laser mirrors


Аuthors

Shanin Y. I.

NII NPO "LUCH", Podolsk, Russia

e-mail: syi@luch.podolsk.ru

Abstract

The main task of the cooled laser mirror is reflecting the incident radiation and minimizing the radiation wave front distortions caused by mirror heating and bending. The mirror cooling system objective is reduction of the excess temperature level of the mirror structure, and protection of the mirror’s load-carrying structure from heat penetration into it. To achieve this, it is necessary to increase the surface heat-transfer factor in the mirror cooling system due to: a) the heat carrier flow parameters forcing, b) the porous cooling structure grinding, and c) heat exchange intensification application. With technological limitations on the cooling system small-scale porous structure forming various methods are employed for the heat transfer intensification.

The article studies analytically the prospective laser mirrors cooling systems with heat exchange intensification in them by the methods of well-ordered vortex impact on the heat carrier flow structure. Relying on experimental data on the resistance and heat transfer the heat transfer intensification was studied by computation in: 1) slit channels with spiral bands; 2) crossed (coplanar) channels; 3) square channels with spring insertion and spiral band; 4) channels form corrugated tape with dimples applied to it.

Based on the surface heat transfer coefficient computing, the following parameters relevant to the cooled mirrors were defined: the reduced heat transfer coefficient (characterizing the overall heat exchange intensification in the cooling system, including this for account of ribs) and thermal insulation coefficient (the base excess temperature to the mirror’s substrate temperature ratio). These values were employed in comparative analysis of the intensification effectiveness. The intensification energy efficiency was evaluated based on the ratio of the heat transfer growth to the hydraulic resistance growth in cooling systems both with and without intensification.

It was established, that the considered cooling systems significantly reduce the overall level of mirror temperature and contribute to the movements reduction of the mirror optical surface due to bending.

Keywords:

laser mirror, cooling system, swirling flow, hydraulic resistance, heat transfer

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