Session: 11-45-01: Technique development for thermophysical characterization

Paper Number: 114015

114015 - Developing a Low-Cost Instrumented Heat Transfer Apparatus for Measuring Thermal Conductivity Using Steady-State Methods 

Commercially available options for linear heat conduction modules feature computer-controlled water cooling, digital read outs, and proprietary software. By utilizing low-cost, off-the-shelf options, the present work seeks to develop an instrumented apparatus, easily deployable for the determination of thermal conductivity of materials. The system will first be used to explore testing of typically conductive metals, and then testing capabilities with materials of lower thermal conductivities, and porous media. A typical method for assessing the thermal conductivity of a material involves establishing thermal boundary conditions at two ends of a specimen. Upon waiting for the specimen to reach steady state, and assessing the temperature difference between fixed locations, thermal conductivity is calculated in accordance with Fourier’s Law (. Various steady-state methods and standards are based on this principle. Specifically, an approach known as Searle‘s Bar Method uses water vapor (100°C) and ice water (0°C) to create isothermal surfaces on opposite ends of a cylindrical sample of material. Standards that reference this method include ASTM C177 and C518, and ISO standards 8301 and 8302. By measuring the temperature at various positions along the z-axis of a long cylindrical sample Insulated laterally, a temperature gradient can be monitored. Today, various companies sell linear heat conduction modules (LHCM) as educational lab equipment. LHCM's typically use an electrical resistance heater at one end of a specimen and isothermal conditions at the other end. Cylindrical samples (d = 25mm, or about 1 inch) of material are placed between the heating and cooling ends. Under ideal conditions (including perfect insulation), the heater supports a surface with a constant heat transfer rate on one face of a sample, while a cooling loop facilitates an isothermal surface at 0°C. With these boundary conditions maintained, and thermocouples placed every 15mm along the material, upon waiting for steady state, a temperature gradient can be monitored. The present work reports on low-cost components used, development of the system, and modeling and testing of capabilities in assessing a range of materials with various thermal conductivities. Using low-cost microcontrollers, such as Adafruit’s affordable Universal Thermocouple Amplifier MAX31856 Breakout Board, readily accessible thermocouples (K, J, N, R, S, T, E, or B type), fittings, and where useful, 3D printed parts to support the apparatus and instrumentation, the system will be operated to test a range of materials. This includes testing of solid and porous samples of thermally conductive materials, like aluminum and brass, and other less conductive materials. Models and supporting tests will help to establish appropriate operating ranges for the LHCM system, while facilitating comparisons and recommendations for testing porous media and lower conductivity materials.

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