A fine needle probe for determining the thermal conductivity of penetrable materials

A fine needle probe for determining the thermal conductivity of penetrable materials such as fluids, fruit and animal flesh has been developed. The present probe is constructed by inserting twenty strands of copper wire with electrical insulation coating into a fine stainless steel needle. The copper wire serves both as a heating unit and as an electrical resistance thermometer. The effects on the thermal conductivity measurement caused by the thin needle wall have been analysed. It is found that the effects can be negligibly small if the instruments and the measurement procedure are adequately designed. The usability of the as-constructed apparatus for penetrable materials has been tested to measure the thermal conductivities of liquid, fruit and animal flesh. The accuracy of the present measurement was estimated to be within ±3%.