Saturday, 15 July 2006

Experimental Measurements of Heat Storage Coefficient of Different Types of Soil.

Anil Kumar Shrotriya, Seth Motilal (Post Graduate) College, Opposite Ranisati Temple, Jhunjhunu, India and Sunil Kumar Jain, Engineering College, Rawat Bhata Road, Kota, India.

The thermal properties of soil are of considerable importance to scientists and engineers in several disciplines. Geologists have long been concerned with heat flow from the interior of the earth and with the thermal effects of natural geological processes. Heat transfer engineers have used crushed or expanded minerals as insulations for both high and low temperature service and have required knowledge of the thermal properties of these materials. Knowledge of the thermal properties of soils is important in many other fields also. Calculations of heat dissipation from underground nuclear expansions and of the rate of heat loss from the earth due to the geothermal gradient depend directly upon the thermal coefficients values of the material involved. Determinations of the current carrying capacity of buried cables and of the heat losses from underground stem and hot water pipes require values for the thermal parameters of soils. The design of packed columns, thermal insulating refractory materials depends upon the heat transfer characteristics of soils. The properties of interest are the thermal conductivity λ, the thermal diffusivity α and specific heat c. Since these three quantities are inter-related, ( α = λ /ρc, where ρ is density). Knowledge of any two determines the third. Besides the three thermo physical coefficients needed to describe the thermal status of a substance, the heat storage coefficient (HSC)β is an additional useful parameter to describe its thermal behaviour. Although its value is related to the three constants β=√ λρc in many cases it behaves as an independent characteristic of the sample. The various factors which generally affect the HSC of materials are: chemical composition physical texture temperature pressure heat flow In addition to providing reliable HSC data, it is desirable to find a correlation, empirical or otherwise between the HSC and other easily measured parameters such as porosity, formation factor, etc. In this paper, the HSC of different type of soil materials like dry dune sand, marble stone powder, surkhi sand, dry cement, loamy soil, lime stone powder and ash have been studied experimentally with the variation of particle size, temperature, pressure and moisture content. The plane heat source method was used for the measurement of HSC of the materials. The design and fabrication of experimental set up for the measurement of HSC of the materials has also been discussed. The main considerations that motivated to undertake this study are the following: These materials are naturally abundant and are commonly used in building construction. The knowledge of thermo-physical properties of sand and ash has importance in agriculture. The HSC parameter has not been much investigated so far. If the HSC of these materials at low interstitial air pressure is comparable to the HSC of silica and glass wool, these cheaper materials may possibly replace the costly and hazardous insulation in huge installation. Field solar ponds are surrounded with soil and concrete. The heat storage efficiency of power generation of these ponds depends upon the heat losses from the pond through these materials. It is also important from energy storage point of view, to know the HSC of these materials, as well as moisture content and temperature.

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