(a) Temperature distribution of the metal chamber. (b) Temperature distribution of the vacuum entity. (c) The relationship between the radiation coefficient and temperature gradients with the convective heat transfer coefficient being 13 W/(m²·K). (d) The relationship between the convective heat transfer coefficient and temperature gradients with the absorption coefficient being 0.8. HF means the convective heat transfer coefficient and it is in units of W/(m²·K).