Thermal Characterization Of Biomass Materials As Coldstore Thermal Insulator

In several countries, principally developing countries, many people live onagriculture and fishing, and a share of the products are transported from villages to bigcities to be sold. But, because of the climatic conditions, important quantities of theproducts become rotten during the transportation through lack of good storage. Somebuildings, such as coldstores, must be maintained at a specific inside temperature. Coldstorage buildings are designed so that the inside conditions (temperature and humidity)do not drop below the tolerance of the goods. Getting the desired indoor temperature isrealized by setting a refrigeration system and also, by insulating the coldstore walls. Mostimportant insulating characteristics are: low thermal conductivity, good mechanicalproperties, high resistance to water absorption, chemical resistance, durability, opticaldensity and low cost.The project of this thesis is to build thermal insulators based on natural low costmaterials, such as groundnut coquets and coconut fibber very abundant in tropicalcountries as refuse. The product we plan to do will be used as insulating in coolingchamber for food storage and housing. Therefore, the cooling loads supplied by a foodstorage refrigeration system were analyzed by a model that included air infiltration andworkers entering and leaving. The calculations were based on the temperature andhumidity conditions in Beijing in July and for different room temperatures (-5oC, -20oCand +10oC). Experimental investigations are done to characterize the thermal propertiesof natural and low cost materials (coconut fibbers and groundnut coquets) as thermalinsulator. A one dimensional steady state model is used to calculate thermal conductivitycoefficient function of temperature. Investigations are carried out to analyze waterabsorption process when the materials are used with very low temperatures and high airhumidity.The theoretical and experimental investigations lead to the conclusions that the moreefficient optimization of a coldstore cooling loads would be from the well thermalinsulation of its envelopes. Also, the size of coldstore must be carefully selected so as tonot have an excessively large room. The two experimental methods used for measuringthermal conductivity gave almost same value with an average of 0.08 W/(mK). Thethermal conductivity for all the materials increased with temperature. The thermalconductivity varied in the same manner both for coconut fiber and aluminum silicatefiber with less effect of temperature at temperatures less than 40oC. For the groundnutcoquets the temperature dependence was important even at low temperatures due to itslow porosity compared to coconut fibers. Both the coconut fibers and the groundnutcoquet at low temperatures and high humidity may absorb water. The thermalconductivity of moist insulations depends considerably on the amount of the liquid itcontains. Thus, since water is a good thermal conductor, the thermal conductivity of thesoaked insulation would increase and the insulating value of the material would bedestroyed. For the experimental investigation of water absorption, two motions of speciesclearly occurred: the flow of water vapor from the bottom to the top layer of the testsample and the flow of condensate water by gravity and capillary action from the top tothe bottom layer.Finally, inorganic materials such as mineral wool or cellular glass should be the bestinsulation materials because of their harmless behavior to the environment and theunlimited quantity present in nature as well as some natural materials such as coconutfiber and groundnut coquets. The measured thermal conductivities show that the coconutfibers and groundnut coquets may be used as thermal insulator for the tested temperaturerange. However, moisture absorption may occur when the materials are used at very lowtemperatures and high humidity. A thin plastic vapor barrier should be placed over theinsulation to prevent moisture from entering the insulation. Also, they must be protectedfrom fire and insects and, their thermal conductivity properties may be improved byreinforcing them with some common insulation materials.