The limitation of heat losses from horizontal surfaces by a layer of open hexagonal cells

Abstract

A study of the limitation of heat transfer from a flat horizontal surface insulated by a layer of cellular material was carried out. A model for heat transfer from a flat horizontal isothermal surface through the insulating layer open at the top is presented, in which conduction and natural convection heat transfer mechanisms are considered. The solution of the model was verified experimentally. The experiment was performed using a round plate of diameter D = 0.07 m covered by panels of cellular material of height expressed as H/ D = 0.1, 0.143, 0.371, 0.6, 0.857 and 1.186 for two sizes of cell given by d/ D = 0.143 and 0.214. To eliminate the radiation component in the global heat transfer and to provide a low range of heat flux, glycerine was used as a test fluid. Good agreement between theoretical and experimental results was found. The results obtained indicate that with the use of such a material it is possible to reduce the majority of heat loss from a flat horizontal surface. For example the panel with H/ D = 0.6 and d/ D = 0.143 limits the heat transfer 2.11, 1.97 and 1.87 times for Ra = 10 4, 10 5 or 10 6 respectively, in comparison with the plate without cellular material. This method of modification of heat losses could be used in solar collectors, civil engineering, chemical technology and in industry.