Gas permeation characteristics through heat-sealed flanges of vacuum insulation panels

Abstract

Application of vacuum insulation panel (VIP) is becoming more practical to reduce the thermal energy loss and to reduce CO2 emission. Outstanding insulation performance and extended service life are the two critical factors in the VIP engineering. Thermal insulation performance of a VIP is degraded with time due to gradual increase of pressure in the VIP. Keeping the effectively low pressure is a key technique to improve the service life. Permeation of gases through heat-sealed flanges in the lateral direction has the greatest effect in it, together with permeation of gases through normal direction to the envelope sheets. This study is made to investigate the permeation characteristics of the envelope seal materials (typically linear low density polyethylene, LLDPE, and low density polyethylene, LOPE). A measurement apparatus using multiple radial permeation passages is designed to measure the gas permeation rate through the polymer films. The measurement shows reliable accuracy compared with other reported results. Inner pressure change in the VIP, which is enveloped with Al-foil-based film, is calculated based on the experimental results of gas permeabilties of seal materials. It is found that the permeation characteristics of heated LLDPE is the same as heated LDPE and unheated LLDPE. H2O, O-2, and N-2 show greatest permeations in this order. Unlike fumed-silica VIPs, glass wool VIPs may exhibit short service life due to this permeation.