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

Abstract

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%.

An Idea of a Measurement System for Determining Thermal Parameters of Heat Insulation Materials

“…Probes operating as linear heat sources are typically used for measurements of the thermal conductivity of loose materials and viscous fluids [4][5][6][7][8][9][10][11]. A thermal probe is at the same time a heater (a linear heat source) and a thermometer that measures the temperature of a sample at a certain distance from the installed heater or the heater temperature itself.…”

“…Mathematical models of all of them are based on equation (1), the differences lie in how the temperature is measured [5,6,11]. Techniques of temperature measurement in this method were standardized in 1978 by the DIN 51046 Standard-Part 2 and e.g.…”

“…Summing up, we can state that known thermal probe techniques for evaluation of the thermal conductivity use simplified the relationships derived on the basis of the Fourier equation [4][5][6][7][8][9][10][11]. These techniques do not ensure accurate results.…”

Sonda metálica reduzida para a caracterização térmica de polímeros

“…Cheng e Xie [18] apresentaram uma sonda fina para determinar a condutividade térmica de amostras como maçã, músculos, água destilada e etileno glicol. A desvantagem desse trabalho refere-se ao fato da sonda ter um diâmetro externo de 0,6 mm, inviabilizando o processo de furação de qualquer amostra rígida.…”

“…O fato da sonda utilizada ser de pequenas dimensões é a grande vantagem deste trabalho, além de ser a tendência do desenvolvimento desta técnica como apresentado por Cheng e Xie [18] e Zhang et al [19] . A desvantagem de utilizar sondas com maior diâmetro é a necessidade de se utilizar amostras maiores, dificultando o manuseio e aumentando o custo da bancada.…”