Absolute measurement of thermal conductivity and thermal diffusivity of poly (acrylic acid) by transient hot wire technique

Absolute measurements of thermal conductivity and thermal diffusivity are of considerable significance to the industrial and research work. The transient hot wire method is now considered the most accurate technique to measure the thermal conductivity of fluids. In this work, a new transient hot wire instrument is presented to measure the thermal conductivity and the thermal diffusivity of electrically conducting and polar liquids. The instrument employs tantalum wire 25.4 mum in diameter with a tantalum pentoxide coating as sensing element. The oxide layer is used to insulate the wire from the electrically conducting fluid in which the wire is vertically submerged. This instrument has been used for PAA (poly acrylic acid) and PAA-Na (0.5% Na-salt of poly acrylic acid) which are widely used in water treatment, pulp and paper processing and reverse osmosis system. The thermal conductivity and the thermal diffusivity of poly (acrylic acid) solution (50 wt. %) and poly (acrylic acid) with 0.5% Na solution have been measured over the temperature range of 20-100°C at 1 atm pressure. The measurement of thermal conductivity is estimated to be accurate within 4%. The thermal diffusivity of data is large and estimated to be about 20%. As there are no previous measurements available in these fluids, the thermophysical properties data for distilled water obtained with this instrument were used to estimate the accuracy of measurements. The possible reasons for the accuracy are discussed. Correlations of the experimental data are also proposed.;Key Words: hot wire; thermal conductivity; thermal diffusivity; PAA; PAA-Na; tantalum; coating.