Effective emissivity of the endface of a packet of screen-vacuum thermal insulation

An analytical expression for the effective emissivity of the endface of a screen-vacuum thermal insulation (SVTI) packet is derived with the help of the quasi-diffusion approximation under the assumption that the reflection at the screens is diffusely specular. The packet is regarded as a collection of separate flat channels and the assumption is made that the temperature remains constant along each channel. To simplify the problem and without losing generality the medium outside the SVTI packet is modeled by an absolute black body whose temperature equals zero. Effective emissivity of the endface of the gap between the strips versus the relative length of the gap is determined for both purely specular reflection and diffuse reflection of the walls.