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Thermal analysis and seeing improvement of LAMOST enclosure

Dome seeing, one of the most important problems in LAMOST due to its special optical path, mainly depends on thermal distribution and temperature gradients in the enclosure. It is necessary to compute and then control the thermal distribution inside the enclosure. The paper puts up many thermal analysis models with Icepak software, calculates their thermal distribution under different thermal cases, and analyzes the maximal temperature differences in different cross sections along the optical path. We apply many cooling methods, which include adding openings, forming ventilation, forcing convection and local cooling. We also take the maximal temperature difference as an optimization object to control the thermal distribution and optimize the cooling structure. Computation results demonstrate that improving the thermal distribution can greatly reduce the temperature gradient. Through analysis we have obtained one cooling method that involves a specific ventilating duct forming local cooling and intake cooling air. Simulation shows the maximal temperature difference has been decreased from 3.8°C to 0.8640°C and in every cross section the maximal temperature gradient has reached 0.125°C/m, which is better than the project demand of 0.4°C/m. All results confirm the thermal control system of this project.