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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

A DEVICE FOR MEASURING THERMAL CONDUCTIVITY WITH A DROP OF LIQUID

Takanobu Fukunaga
Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan

Y. Okuno
Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan

K. Kitamura
Graduate School of Engineering, Kyushu University, Fukuoka 819-0395, Japan

H. D. Wang
Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan

Kosaku Kurata
Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan

Hiroshi Takamatsu
Department of Mechanical Engineering, Kyushu University, Fukuoka 819-0395, Japan

DOI: 10.1615/IHTC16.tpm.024286
pages 8955-8960


KEY WORDS: Measurement and instrumentation, Thermophysical properties, MEMS, Sensor, Thermal conductivity

Abstract

Measurement of thermal conductivity of liquid was demonstrated with a sample considerably smaller than previously reported methods. The sensor that was named micro-beam sensor is a free-standing platinum strip suspended across a trench on a silicon substrate and heated in a sample liquid by DC. The temperature of the sensor is measured from the electrical resistance of the sensor. The measurement is based on the principle that the temperature rise of the sensor depends on the thermal conductivity of the liquid. The advantage of this method includes: 1) the system has a steady state because the substrate at both ends of the sensor remains at a constant temperature irrespective of heating, 2) the steady state is reached within several hundred microseconds because the sensor is only ~10 μm long, 3) the temperature of the sensor does not change after the initial rise due to heating because the effect of free convection is negligibly small, and 4) the sensor is useful for measuring small samples. Comparing the measured temperature rise with the result obtained by numerical analysis of steady-state heat conduction, we can determine the thermal conductivity of the sample liquid. To demonstrate the advantage of this method, we developed a device that consists of a micro-beam MEMS sensor placed in a micro chamber fabricated in a PDMS block. The fabricated platinum sensor was ~10 μm long, ~0.7 μm wide and 40 nm in thickness. The electrical and thermal properties were first determined as a function of temperature by a calibration experiment in a vacuum chamber together with two-dimensional electrical/thermal analyses. Then the thermal conductivities of four kinds of liquid, i.e. FC-72, toluene, ethanol and methanol, were measured at atmospheric pressure and temperature by injecting a sample of ~30 μL into the chamber with a micropipette. The measured thermal conductivity agreed with literature values within 4 % error.

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