Thermal Conductivity Measuring System (TCoMS)

Author(s)

Lucas Hill

Faculty Mentor(s)

Jeunghwan Choi (Mechanical Engineering Technology), Charles Pringle (Mechanical Engineering Technology)

Abstract

The Mechanical Engineering Technology department at Central Washington University is lacking a method to reliably measure the thermal conductivity of bulk materials, with dimensions of at least a 1 cm radius, within a teaching environment. Thermal Conductivity Measuring System (TCoMS) will be a useful tool to perform these measurements as it is able to obtain measurement readings for materials between 0 C and 50 C within 20 seconds. TCoMS will accomplish this by using the pulse decay method of measuring thermal conductivity, a form of transient heat transfer analysis. This method is performed by generating a pulse of heat at the measurement location and measuring the temperature change with respect to time which can then be used to determine a material’s thermal conductivity. To accomplish these tasks TCoMS runs on an Arduino Due, a programmable circuit board used for controlling, timing, and measuring the temperature and the heat pulses through the thermistor. A voltage divider in the form of a Wheatstone bridge is used to allow for the high accuracy needed in voltage measurements across the thermistor. These voltage measurements are then used to calculate the electrical resistance of the thermistor. To determine the temperature of the thermistor, using the coefficients provided by the thermistor’s manufacturer, the Steinhart-Hart equation is used to determine the thermistor’s temperature. These measurements are accurate to within 5% of a material’s actual thermal conductivity value. This was tested on materials such as water, potatoes, and apples.

Keywords: Thermal Conductivity, Pulse Decay, Thermistor

Presentation

2 thoughts on “Thermal Conductivity Measuring System (TCoMS)”

    1. Some progress was made on improving the accuracy of TCoMS. One major issue resolved regarding the accuracy was an incorrect understanding of the pulse decay equation. The starting temperature T refers to the temperature of the material being tested prior to heating, not the temperature of the material at the end of the heating pulse. This brought the thermal conductivity values up to a more reasonable level, between 0.4 and 1 rather than the under 0.01 W/mk as seen on the poster. Increasing the voltage across the heating circuit to deliver a larger pulse of power also helped to improve the accuracy of this project.

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