Session: K7-01: THERMOPHYSICAL PROPERTIES I

Paper Number: 131904

131904 - Improvement of a Low-Cost Apparatus for Measuring Thermal Conductivities of Solids at Steady-State 

Abstract: 

This study aims to demonstrate the capability to use steady state methods with an instrumented heat transfer apparatus to assess thermal conductivities of samples ranging in anticipated thermal conductivity values from as high as 398 Wm-1K-1 down to 0.3 Wm-1K-1. Samples include copper, aluminum, brass, alumina ceramic, stainless steel, thermally conductive silicone, and ELEGOO resin (3D printed). The system used in this work was developed as part of a previously published study detailing development of a low cost linear heat conduction module (LHCM). A LHCM is an experimental apparatus that approximates one dimensional heat transfer through a stack of cylinders of material. At the center of the LHCM, a sample material is placed between two cylinders of brass of a known thermal conductivity. By maintaining an isothermal boundary layer on the bottom side of the LHCM, applying constant energy through an electrical resistance heater on the top side, and waiting for steady-state, the thermal conductivity of the sample material can be calculated from a recorded temperature difference.

A key interest in these systems is in assessing thermophysical properties of low conductivity materials. The work here aims to (1) experimentally demonstrate the capabilities to assess thermophysical properties of materials of a range of conductivities; (2) experimentally explore the limitations of assessing materials of lower thermal conductivities; and (3) propose alterations to the approaches used, that would allow for assessment of low-k materials within a limited range of uncertainty (under 10%). Alterations considered include consideration of the impact of geometry and dimensions of the apparatus, potential use of guarded hot plate approach, and vacuum insulation. Models will also be presented to describe the anticipated results. Assessing low conductivity materials presents challenges. Low accuracy with low conductivity materials can be attributed to heat lost from the electrical resistance heater to the surrounding environment. This is because the thermal conductivity of the sample is low enough to rival that of the insulation of the LHCM itself. As a result, the system is unable to maintain a large enough temperature difference to accurately determine the sample material’s thermal conductivity. While assessing lower conductivities is a driver of the work performed here, much higher conductivity materials such as copper are also tested. Currently, the LHCM also demonstrates low accuracy (above 10%) with high conductive materials like copper (398W/mK), attributed to the need to measure small temperature differences over small distances, and deviations from equilibrium due to changes in the cooling loop temperatures.

In the previous study, authors demonstrated the low-cost LHCM made with machined sample materials and off-the-shelf components for a data acquisition system could achieve a 4% accuracy of measuring the thermal conductivity of Brass 360. Additional testing with the same apparatus is conducted here, demonstrating the thermal conductivity of metals, such as aluminum, could also be measured accurately within an uncertainty of 5.6%. It is anticipated that the accuracy of measuring the thermal conductivity of materials on the order of magnitude of 10W/mK within 10% accuracy.

Presenting Author: Brandon Bunt The Cooper Union

Presenting Author Biography: Brandon Bunt is a graduate student at The Cooper Union

Authors:

Brandon Bunt The Cooper Union
Kamau Wright Cooper Union
Benjamin Davis The Cooper Union