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.
Effect of metallic nanoparticle fillers on the thermal conductivity of diatomaceous earth
Abstract Thermal conductivity of solid nanoparticles (aluminum) in a nanoporous solid matrix (diatomaceous earth) is examined to understand the effect of conductive fillers on the thermal properties of a porous material. We find that thermal conductivity is strongly dependent on load applied to prepare the mixture compacts, while porosity is influenced by the composition of the mixture. The addition of nanoparticles contributes to limited increases in thermal conductivity of the mixture by (1) increasing contact area between the mixture constituents and (2) reduction of porosity that leads to enhanced solid–gas coupling contribution. Thermal conductivity increases exponentially with external gas pressures due to the coupling effect between the solid particles and the entrapped air.
Use of laser scanning confocal microscopy for morphological taxonomy and the potential for digital type specimens (e-types)
The use of laser scanning confocal microscopy (LSCM) for creating taxonomic descriptions of copepods is investigated. A new technique is described, which employs a contour filter to process digital LSCM images, allowing taxonomic information to be quickly and accu- rately distilled into a simple illustration. LSCM allows the imaging of whole specimens, which can be rotated and viewed from any angle—a major benefit over light microscopy. Using this tech- nique, it is suggested that taxonomic descriptions can be rapidly produced in a fraction of the time required to produce similar descriptions using traditional light microscopy and hand drawing techniques. Good staining of specimens is, however, essential to produce accurate descriptions and more research is required in this area. The use of LSCM for morphological taxonomy shows great potential, not only for producing taxonomic descriptions, but also providing a comple - mentary adjunct to traditional type specimens in the form of 3D digital 'e-types' deposited in recognised international databases.