Vacuum insulation panel core materials and modelling the thermal conductivity of granular materials
Two potential alternative core materials, diatomaceous earth (DE) and glass bubbles (GB), were considered for cost effective and long life-time vacuum insulation panels (VIP). The pore size distribution of the DE was determined quantitatively by mercury porosimetry and nitrogen sorption. The majority of pores in DE centered around 1 μm. The average pore size of GB was estimated to be 50 μm via scanning electron microscopy. Subsequently, the relationship between pore size and gaseous thermal conductivity was established using the Kaganer relation. Composites of DE and fumed silica (FS) showed remarkable insulating performance whereby thermal conductivity only rose by 11 mW/m.K as pressure increased to 10,000 Pa. A similar analysis on composites of GB and fumed silica showed an increment of 16 mW/m.K. It was estimated that the duration for a typical VIP to reach 10,000 Pa is approximately 50 100 years depending on the type of barrier used. [30] Hence, both composites are capable of providing long vacuum insulating service life. Furthermore, DE/FS composites would greatly reduce the cost of VIPs because of the inexpensive nature of DE. Both composites show superior life-time when compared to glass fibers, which are already commercially used in VIPs.
High-Performance Vacuum Insulation Panel: Development of Alternative Core Materials
Energy efficiency of the built environment greatly depends on the performance of the insulating materials used in the building envelope construction. Vacuum insulation panels (VIPs) offer excellent thermal resistance properties that can enhance the energy efficiency of the insulating systems and provide savings in energy consumption. However, VIP systems are virtually unknown and rarely used for building construction in North America. There is a need to investigate the use of VIPs in various components of building envelopes and their long-term performance. The National Research Council, Canada, Institute for Research in Construction is investigating a number of fundamental aspects related to the performance and construction of VIPs, which this paper discusses. More specifically, it reviews the underlying basics behind the functioning of VIPs and presents results from the investigation into the development of alternative core materials for VIP construction.
Effect of Calcium Glycerophosphate on Demineralization in an in vitro Biofilm Model
The aim was to investigate the anti-caries properties of calcium glycerophosphate (CaGP) using an in vitro bacterial flow cell model. Four flow cells, inoculated from a chemostat containing a seven-organism bacterial consortium, were pulsed with sucrose twice daily, to provide an acidic challenge and pH-cycling conditions. Blocks of enamel and dentine were mounted in each flow cell. In a study on the effect of CaGP concentration, CaGP was pulsed into three of the flow cells, at the same time as the sucrose, to give concentrations of 0.10, 0.25 and 0.50%. Water was pulsed into the fourth flow cell with the sucrose. Microradiography revealed a significant dose response of decreasing demineralization as CaGP concentration increased. Reductions at 0.25 and 0.5% were significant when compared to the control. A second study investigated the effect of timing of CaGP pulsing, relative to sucrose, on enamel and dentine demineralization. CaGP (flow cell concentration 0.2%), was pulsed 1 h before, during or 1 h after the sucrose pulse; a water control was employed. In enamel, pulsing CaGP before the sucrose reduced demineralization significantly compared to concurrent pulsing, which in turn gave a significant reduction compared to pulsing after sucrose, which did not reduce demineralization significantly compared to the water control. In dentine, CaGP reduced demineralization significantly only when pulsed before the sucrose. The findings suggest that in vivo, the anti-caries potential of CaGP may be greater if it is applied before a cariogenic challenge.