Gauge for nondestructive measurement of the internal pressure in powder-filled evacuated panel superinsulation

Abstract

A gauge that measures the internal pressure (P) in powder-filled evacuated panels (PEPs) is described. PEPs are superinsulators consisting of high thermal resistivity powders encapsulated in hermetically sealed flexible barriers enclosing a vacuum. To measure P, the gauge supplies a vacuum to the outer surface of the barrier. When the P in the PEP exceeds that supplied by the gauge, the barrier deflects. This deflection is sensed by a bifurcated-fiber-optic light system that converts the motion of the barrier into a voltage proportional to the displacement of the barrier. A pressure transducer mounted in the gauge provides a dc voltage proportional to P at the interface of the barrier and PEP. An X-Y recorder displays the relationship between these two signals. Experiments show that the gauge yields P measurements with uncertainties of +0.27 kPa and reproducibilities of ±0.16 kPa for PEPs with 0.13-mm-thick flexible polymer barriers. To achieve more accurate measurements, the gauge should first be calibrated on a PEP of known internal P then used to measure P on similar PEPs with unknown P’s. Besides PEPs, experiments suggest that the gauge can nondestructively and rapidly measure the pressure in a hermetically sealed container having a flexible enclosure, such as vacuum-packaged food. Patent applications for this gauge are on file with the United States Patent Office.