Determining the Thermal Conductivity of Liquids Using the Transient Hot Disk Method.

 

Part II: Establishing an Accurate and Repeatable Solution

The transient hot disk thermal characterization method is increasingly being used to measure the thermophysical properties of a wide variety of materials. Its advantages include its robust design and its rapid characterization time, which allows it to simultaneously measure the thermal conductivity and diffusivity in challenging applications including nanofluids, fluids with high Prandtl numbers, and adhesives without damage to the system during, or after, operation. However, as with other transient thermal characterization techniques, extreme care must be taken to ensure an accurate solution for liquid phase thermal properties. For accurate use of this technique, steps must be taken to confirm that the fluid will not experience buoyancy related flow during the measurement time.

Using experimental techniques in tandem with an accurate determination of the maximum measurement time allowable before the onset of natural convection, this work establishes an accurate and repeatable method to implement the transient hot disk measurement technique for liquid phase thermal conductivity and thermal diffusivity over a wide range of Prandtl numbers (Pr = 0.7 to 11,000) to within 5% accuracy. The method is validated for common heat transfer fluids with well-known thermal properties over a wide range of temperatures.