Technique for Determination of Thermal Properties of Iron Ore Materials

Abstract

Methods for determination of thermal properties of various materials, including iron ore, are adequately covered in the relevant literature. They rely, as a rule, on certain solutions to the problem of heat conductivity without consideration of internal heat sources that occur in the body of sample under study if the heating (cooling) process is accompanied by various thermochemical and phase transformations, which is typical of iron ore materials. Therefore, such methods allow determination of only effective or apparent values of thermal properties, which adequately reflect properties of the material only in specific heat treatment conditions. The point is that in the presence of internal heat sources, parameters to find substantially depend on the heating rate and sample shape and size. This paper considers a new technique, which allows finding (at known calculated values of heat capacity and material density) how five thermal parameters (temperature and heat conductivity coefficients, power of internal heat sources, as well as effective values of heat and temperature conductivity) depend on the heating (cooling) temperature. Improvement of methods of processing iron ore materials at elevated temperatures in various heat aggregates requires knowledge of thermal properties of the materials and variation of these parameters during heat treatment in a wide temperature range. This is due to the fact that heating of such materials is usually accompanied by development of complex physical and chemical processes such as oxidation and reduction of iron oxides, decomposition of carbonates, porosity and strength change, formation of new chemical compounds, and others, many accompanied by release or absorption of heat [1–12]. The degree of completion of these processes depends on the temperature conditions and composition of the material and coolant. Consideration of the effect of these conditions on the temperature distribution in the treated layer of material and consequently on the duration of the heat treatment it is possible only having reliable data on the thermal constants [13]. Methods of determination of thermal properties of iron ore materials are widely discussed in the literature [14–20]. However, all they address the heat conductivity problem without consideration of internal heat sources, and thus can determine only the effective values of thermal parameters, valid for specific conditions of heating. The effect of internal heat sources on thermal properties to find can be taken into account only by using respective solutions to the heat conductivity problem. The below method to determine the complex of thermal properties of iron ore materials relies on the solution to the heat conductivity problem with internal heat sources under symmetric heating conditions of the first kind, which is valid for objects of simplest shape (infinite plate, infinite cylinder, ball).