Conjugate heat transfer characteristics of enclosure cavity in near space environment
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摘要:
以临近空间浮空器载荷舱为应用背景，对复杂热边界条件下含热源的三维封闭方腔内自然对流、表面辐射和导热的耦合问题进行了数值模拟。综合考虑对流换热、长波辐射、太阳辐射等因素的影响，建立了临近空间热环境模型。通过Fluent软件用户自定义函数（UDF）引入外部非定常的辐射-对流耦合热边界条件，对腔内换热特性的昼夜变化进行研究，并分析了腔壁厚度、发射率和导热系数对其的影响。数值结果表明，腔内平均温度昼夜变化很小，约为12.9 K，但温度场分布随太阳方位变化而变化；腔内对流换热较弱，同一时刻最大温差约为71.3 K；腔壁热阻和发射率增加会削弱自然对流的强度。
Abstract:Aimed at the application of near space aerostats' load cabins, numerical simulation of natural convection, surface thermal radiation and heat conduction in a cubical enclosure cavity with a heat source in complex thermal boundary conditions was carried out. A model of near-space thermal environment was established considering the effects of convective heat transfer, infrared radiation and solar radiation. The diurnal variation of the thermal characteristics in the enclosure cavity was studied by introducing the external unsteady convection-radiation coupling thermal boundary conditions through the Fluent software's user-defined function (UDF). The effects of solid wall thickness, emissivity and thermal conductivity were discussed. The numerical results indicate that the average temperature change in the enclosure cavity is about 12.9 K during one day, and the temperature field distribution changes with the sun's position. The natural convection in the enclosure cavity is weak and the maximum temperature difference is 71.3 K at the same time. Increased thermal resistance and surface emissivity lead to weakening of natural convection in the cavity.
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Key words:
- near space /
- enclosure cavity /
- conjugate heat transfer /
- natural convection /
- numerical simulation
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图 3 不同网格下沿直线X=Y=0.28 m的温度变化曲线
Figure 3. Variation curves of temperature at X=Y=0.28 m for different grids
图 4 腔内温度极值和平均值随时间变化曲线
Figure 4. Variation of extreme and average temperature in cavity with time
图 5 不同时刻腔内温度和垂直速度分布云图
Figure 5. Distribution contours of temperature and vertical velocity in cavity at different time
图 6 0:00和12:00时刻Y=0.28 m截面垂直方向的速度矢量图
Figure 6. Vertical velocity vector of Y=0.28 m section at 0:00 and 12:00
图 7 腔内顶面平均努赛尔数和空气温差变化曲线
Figure 7. Variation curves of average Nusselt numbers and air temperature differences at top surface in cavity
图 8 0:00时刻不同内表面发射率下X=0.28 m截面的温度和速度等值线
Figure 8. Temperature and velocity contours at X=0.28 m section for different values of internal surface emissivity at 0:00
图 9 0:00时刻腔内温度极值和平均温度随内表面发射率的变化
Figure 9. Change of extreme temperature and average temperature in cavity with internal surface emissivity at 0:00
图 10 0:00时刻不同内表面发射率下直线X=Z=0.28 m方向垂直速度变化曲线
Figure 10. Variation curve of vertical velocity at X=Z=0.28 m for different values of internal surface emissivity at 0:00
图 11 0:00时刻不同腔壁导热系数下X=0.28 m截面的温度和速度等值线
Figure 11. Temperature and velocity contours at X=0.28 m section for different values of thermal conductivity at 0:00
图 12 0:00时刻不同腔壁导热系数下直线X=Z=0.28 m方向温度和垂直速度的变化曲线
Figure 12. Profiles of temperature and vertical velocity at X=Z=0.28 m for different values of thermal conductivity at 0:00
图 13 0:00时刻不同腔壁厚度下X=0.28 m截面的温度和速度等值线
Figure 13. Temperature and velocity contours at X=0.28 m section for different values of solid wall thickness at 0:00
图 14 0:00时刻不同腔壁厚度下直线X=Z=0.28 m方向温度和垂直速度的变化曲线
Figure 14. Variation curve of temperature and vertical velocity at X=Z=0.28 m for different values of solid wall thickness at 0:00
图 15 腔内平均温度为262 K时，导热系数和腔壁厚度的关系
Figure 15. Thermal conductivity versus solid wall thickness when average temperature in cavity is 262 K
表 1 0:00时刻腔内顶面辐射和对流换热量
Table 1. Radiation and convective heat transfer at top surface in cavity at 0:00
内表面发射率 辐射换热量/W 对流换热量/W 总换热量/W 0.2 2.99 1.92 4.91 0.4 3.30 1.73 5.03 0.6 3.43 1.65 5.08 0.8 3.47 1.63 5.10 
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