Transient thermal characteristics of infrared window coupled radiative transfer subjected to high heat flux

<abstract> <p>In infrared detection system on aircrafts, the infrared window, as an essential part, always faces heating condition generated by aerodynamic effects. The accurate thermal analysis can ensure the safety and reliability of internal detection system. In this work, the transient thermal characteristics of infrared window-based encapsulation structure are investigated under a high heat flux loading. The physical model of coupled radiative-conductive heat transfer in the window is established while the spectral selectivity of the window to thermal radiation is considered. The transient temperature response is used to evaluate the thermal characteristics. The effect of the radiative heat transfer is firstly analyzed and compared with the pure heat conduction model. There is a temperature deviation (74.1 K) when the radiative heat transfer is ignored. Subsequently, the transient temperature response is simulated under three different kinds of heat flux respectively. It is found that the effect of external heat flux loading is significant. The highest temperature difference reaches 32.9% (299 K) when the heat flux is reduced by 0.5 times and achieves 86.3% (794 K) when the heat flux is increased by 2.5 times. Moreover, the geometric dimensions of window (shape of a truncated cone) generate an effect on its heat transfer characteristics. The temperature decreases significantly (37.8%) when the thickness rises from 10 mm to 20 mm (<italic>r</italic> = 25 mm) while the temperature decreases relatively small (8.1%) when the radius increases from 15 mm to 45 mm (<italic>d</italic> = 15 mm). The results reveal that the radiative heat transfer in the window should be carefully considered, especially under the high heat flux loading. Additionally, reducing heat flux or thickening window can improve insulation effectiveness so as to ensure the stable working of the internal equipment.</p> </abstract>