Cellulose Triacetate Honeycomb Compounds for Improved Flat-Plate Collectors: Performance and Reliability
Abstract
Honeycomb structures are a well known device to reduce convective and radiative heat losses in solar thermal flat-plate collectors, thus improving their efficiency at high temperature and/or low irradiance (Hollands, 1965). Despite several investigations of the last decades no suitable material has been found so far which can provide for the requested high performance and durability at reasonable costs. A commercially available modified cellulose triacetate film, already in use assembled in honeycomb compounds as transparent insulation, exhibits promising properties. The present work experimentally investigates the suitability of these compounds for solar thermal applications, focusing on their performance and long-term reliability. Beside this commercial product, other kinds of acetate films were tested. Special attention is given to the ageing effects caused by UV radiation and high temperature as well as on outgassing, which are collector specific occurrences, not considered by the technical specifications of the materials and not yet reported in the literature.