Simultaneous measurement of thermal diffusivity and thermal effusivity of liquids by photoacoustic technique

A. Yoshida1, K. Wakamiya1 and T. Yamada1

1Osaka Prefecture University, Japan

Keywords: photoacoustic method, thermal effusivity, thermal diffusivity, liquid, simultaneous measurement
property: thermal effusivity
material: liquid

Recently, efficient machines are often used under severe conditions such as high temperature, high speed, high load and long drive. The lubricants such as grease and oil are used with all machines in the world. Therefore, to design machinery, it is important to understand the thermophysical properties of the lubricants under various conditions, and a handy, prompt measuring method is requested.

In the present paper, the open photoacoustic technique is used to measure the thermophysical properties of high viscosity liquid under the condition of the room temperature and the normal pressure. The photoacoustic technique is one of the non-destructive methods for measurement of thermophysical properties of various materials. In the measurement technique, intermittent light is irradiated and the thermal energy is given to the measuring object. There are implications in the frequency and the detection depth. Thermophysical properties of the measuring object are obtained by reversely analyzing the sound signal as the thermal response.

The method is applied to measure the thermal diffusivity and the thermal effusivity of high viscosity liquid. The sample cell is composed of thin metal plate and backing material, and the sample liquid is enclosed with a thin space of both. The amount of the sample necessary for the measurement is extremely a small. Light is irradiated to the metal plate in the top. The thermal response shows an independent change to the thermal diffusivity and the thermal effusivity of the fluid sample enclosed under the plate according to the numerical simulation of thermal diffusion. The accuracy of the proposed measurement technique was verified by the pure liquid with the already-known thermophysical properties as a sample, and an excellent result was obtained.

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