John Choi (Mechanical Engineering Technology), Charles Pringle (Mechanical Engineering Technology)
Currently, there are several ways in which thermal conductivity can be calculated or assessed on a given material. However, with each method of testing comes potential limitations such as size, material state, complexity, and time. The goal of this study was to develop a pulse heated thermistor that would reduce all four limitations, thus provide precise and timely results regardless of the material state and size. A thermistor is resistor which changes resistance in accordance to temperature. To achieve the design, heat transfer and electrical methods were applied. As with all resistors, heat is dissipated across the element and released into the surrounding environment. With this idea, the thermistor can be introduced with a large voltage, causing its resistive element to overheat and thus reduce its resistance. To manufacture such a device insulative material was added to prevent heat dissipation in the wrong direction. To achieve precise results, test specimens were required to be prepared to reduce the effects of ambient convective heat transfer. Measurement times after pulse were shown to have best results after seven seconds due to the thermistor achieving a steady decay of temperature back to equilibrium. Water was observed to have a thermal conductivity value of 0.613 W/m-K, within 5% of its accepted value. The results were obtained within five minutes, exceeding the fifteen-minute requirement. With the results obtained, it is conclusive that the device is functional and precise.
Keywords: Thermistor, Conductivity, Pulse-Decay