tailieunhanh - MEMS and Microstructures in Aerospace Applications - Robert Osiander et al (Eds) Part 9

Tham khảo tài liệu 'mems and microstructures in aerospace applications - robert osiander et al (eds) part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 196 MEMS and Microstructures in Aerospace Applications Polymer Supports Su8 Radiator Substrate Gold Membrane Sputtered Nitride Electrically Insulating FIGURE A schematic of SU8 fabricated device. electrostatically attracted to the radiator and makes thermal contact connecting the radiator to the high emissivity surface. The disadvantage of this design is the high switching voltage typically greater than 400 V. A similar design has been developed and fabricated in a MEMS platform by the United States Naval Academy USNA and JHU APL to be flown on the USNA Midstar satellite. For this design the radiator consists of an array of membranes about 400 to 500 mm wide and long suspended a couple of microns above the surface on frames or posts at the corner. Figure shows a schematic of the device which is fabricated using SU8 a photosensitive epoxy with a very low thermal conductivity in the cured state and a gold membrane. An example of a frame-supported device is shown in Figure . The devices have switching voltages between 20 and 40 V very well within spacecraft standard voltages. While the MEMS design performs well the thermal design needs to be improved. The thermal conductance in the off state given by the conductivity in the support posts is very FIGURE An example of a frame-supported device. Courtesy USNA. 2006 by Taylor Francis Group LLC Microsystems in Spacecraft Thermal Control 197 high due to the short length of the supports. In addition coating the gold membrane has not yet achieved the high emissivity required. Microheat Pipes To dissipate thermal energy thermal engineers may use thermal doublers and heat pipes to spread the heat within the structure. With tight footprint restrictions the conductive heat transfer enhancement by thermal doublers may be limited. For high heat flux dissipation heat pipes are proven to be more effective than thermal doublers in achieving a uniform temperature distribution. Heat pipes achieve this through a .

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