Objective In recent years, infrared technology has been widely used in space remote sensing and military reconnaissance. In order to meet the high performance requirements of infrared detectors, on-orbit real-time calibration is needed. The blackbody radiation source system is the key device for calibrating infrared instruments. The blackbody studied in this paper is used in the FY-3 satellite Medium Resolution Spectral Imager (MERSI), its operating temperature range is 260-320 K. The low temperature of 260 K is achieved by connecting the blackbody to the radiation heat dissipation plate through a heat pipe, and the high temperature of 320 K is achieved by heaters attached to area outside the installation area of the heat pipe at back of the blackbody. Due to the large thermal flow difference between the cold source and hot source at back of the blackbody, it is hard to maintain good temperature uniformity of the blackbody. To solve this problem, the idea of applying a whole layer thermal insulation material to the blackbody uniform temperature structure (UTS) was proposed. And the characteristics of good UTSs and the structure of the optimal UTS were obtained.
Methods A simulation environment was established based on the surrounding environment of the black body in the FY-3 MERSI (Fig.2). Based on the simulation environment, a simulation model was built on NX/TMG and verified by experiments (Fig.4). Then, different UTSs using copper plate (Cu), thermal pyrolytic graphite (TPG) and polyimide (PI) were designed and analyzed by the simulation model. Performance of different UTSs were compared by temperature differences and average temperatures of the blackbodies.
Results and Discussions Simulation analysis and comparison of different UTSs were carried out. The results show that the optimal 4-layer UTS is “2TPG-Cu-PI”, compared with the UTSs without PI, the temperature difference can be reduced from 0.232 K to 0.156 K (Fig.5). The optimal 5-layer UTS is “3TPG-Cu-PI”, compared with the 5-layer UTSs without PI, the temperature difference can be reduced from 0.162 K to 0.112 K (Fig.6); while compared with the optimal 4-layer UTS, the temperature difference is decreased by 0.044 K (Fig.5-Fig.6). The optimal 6-layer UTS with 0 or 1 layer of PI is “4TPG-Cu-PI”, compared with the 6-layer UTSs without PI, the temperature difference can be reduced from 0.114 K to 0.086 K (Fig.7(a)); While compared with the optimal 5-layer UTS, the temperature difference is decreased by 0.026 K (Fig.6, Fig.7(a)). The optimal 6-layer UTS with 2 layers of PI is “2TPG-PI-TPG-Cu-PI”, compared with the 6-layer UTSs with 0 or 1 layer of PI, the temperature difference can be reduced from 0.086 K to 0.070 K (Fig.7).
Conclusions In this study, the idea of applying a whole layer thermal insulation material to the blackbody UTS was proposed, and different UTSs were designed and analyzed. It was found that when using 1 layer PI, the temperature differences basically decrease as the PI moves downward; When the PI is at the bottom layer, the temperature difference is the smallest and the average temperatures are higher than the structures without PI. In addition, among the UTSs having the same PI position, the ones with PI right below Cu are the best. When using a 6-layer UTS with 2 layers of PI and the same PI positions, the optimal UTSs have two characteristics. The preferential one is that there are 2 layers of high thermal conductivity materials between the PIs; The other is that there are 2 layers of high thermal conductivity materials near the blackbody side. The optimal UTS is “2TPG-PI-TPG-Cu-PI”, with which the blackbody temperature difference can be reduced to 0.07 K. This result is much better than 0.25 K for similar blackbodies in published literatures. This study improves the temperature uniformity of spaceborne blackbodies significantly. It also expands the thermal control design idea for objects that require high temperature uniformity and provides new possibilities for further improving the temperature uniformity of temperature control targets.
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