DETERMINATION OF THERMAL CONDUCTIVITY OF HIGH PERFORMANCE CONCRETE AT ELEVATED TEMPERATURE USING HOT WIRE METHOD

Abstract

The concept of thermal conductivity encompasses a great many fascinating areas like Internal Combustion engines, refrigeration and air-conditioning units, design of cooling systems for electric motors, transformers etc.; insulation in wires, pipes etc.; building materials and in almost every application in the field of engineering and science. In recent times this concept has also entered critical applications like containers in nuclear power plants, nano fluids, fire propagation in buildings etc. So accurate measurement of this thermo-physical property is of utmost importance and various methods have been proposed to measure these thermo-physical properties accurately for all kinds of solids and fluids. The Transient Hot Wire (THW) technique is one such technique that has. for long been used and modified and now has become a standard technique everywhere for the measurement of thermal conductivity for almost all kinds of materials. Its apparatus consists of an infinite line heat source usually a Platinum wire having constant heating power per unit length, embedded in the sample made of material whose properties has to measured. A step voltage is applied to the wire to produce heat so that the wire acts as a line source. Proper measurements of temperature are performed at various locations in the sample and at various times which are then applied to correlations given in the vast literature available where the values of these thermo-physical properties can be obtained for comparison. This method has been under consideration of researchers from centuries and is still being modified to improve its performance to operate at high temperatures. An experimental study is carried out the measure the thermal . conductivity of high performance concrete at elevated temperature of the order of 700°C using the hot wire method. An apparatus on the same principle has been designed and fabricated and various mixes of high performance concrete has been tested for thermal conductivity and analyzed. Furthermore, the effect of radiation heat transfer at elevated temperatures has been analyzed. The trends of variation of thermal conductivityy of various mixes of high performance concretes with respect to temperature are observed with and without considering the effect of radiation and error analysis has been done.