A TINY HEAT PROBE FOR MEASURING THE THERMAL-CONDUCTIVITIES OF NONRIGID MATERIALS

An improved tiny heat probe for measuring the thermal conductivities o f cion-rigid materials has been developed. There have been a number of modifications suggested to the classical heat probe. In the present h eat probe, a winding copper wire coated with a thin polyester layer, u sed as a heating element and a resistance thermometer, is enclosed in a thin metallic tube which is inserted into the measured medium. A reg ulation voltage is supplied to the wire. The thermal conductivities of the measured materials can be obtained from the resistance increase v alues in the wire over a known time interval. A correction formula for eliminating the effects of varying power in the heater and a time est imation for reducing the effects of the thermal constants and size of the probe are established. Using the heat probe, the thermal conductiv ities of non-rigid materials, such as fruits, powdered graphite, aqueo us NaCl solution, distilled water and biotissues were measured with re lative error less than 3%.