Project Motivation and Objectives

1. Thermal Transporting of MicrofibersAustin Schwartz1, Xiaopeng Huang2, Xinwei Wang21University of Wisconsin - Stout2Department of Mechanical Engineering, Iowa Sate University Data Analysis Project Motivation and Objectives • Study effect of thermal transport on nonconductive microfibers • Thermal diffusivity testing • Verify technique that is used • Gather different types of fibers • Use technique to calculate thermal diffusivity of each fiber • Methods for calculating thermal diffusivity • Linear fitting at the initial stage of electrical heating • Characteristic point method • Least square fitting method • Least square fitting method is preferred • Linear fitting and characteristic point method only use some experimental data • Least square method calculates normalized temperature increase by using different trial values of thermal diffusivity • The trial value giving the best fit of the experimental data is taken as the sample’s thermal diffusivity • Fig. 2 shows example of experimental data taken and data analysis comparison of all three methods Experimental Method • Transient Electrothermal Technique (TET) • Fiber is suspended between two electrodes with silver paste attached to each end • Thin layer of gold is sputter coated to nonconductive fibers to make them electrically conductive • A step DC current is fed through the sample in a vacuum chamber • Variation of voltage over the fiber is measured using an oscilloscope • Diameter and length of fiber is calculated using an optical microscope • Fig. 1 shows the basic experimental set up (a) (b) Discussion • Platinum Wire • Similar results for experimental and literature data verifies the TET Voltage • Polyester Fiber • Results were off by an order of magnitude of 2 compared to literature value • This suggest more experiments may need to be taken to figure out the problem Time (arbitrary unit) • Experimental uncertainty • Sample preparation could be part of the reason certain values were off • Silk and Linen samples had close values while polyester samples seemed to be varied • Past research has shown that this experiment has an uncertainty better than 10% Fig. 2 – (a) Typical voltage signal over sample wire (Pt wire at 35 mA), (b) Comparison of the three data analysis methods Results Fig. 1 – Schematic of the experimental setup from a side view Conclusions • Thermal diffusivity results for the different materials are separated into different tables Experimental Details • The transient electrothermal technique proved to be capable for thermal characterization of nonconductive fibers • Using the lowest current for each material, the average thermal diffusivity for each material samples are: • Polyester fiber: 2.46 x 10-5 m2/s • Linen fiber: 1.55 x 10-5 m2/s • Silk fiber: 1.81 x 10-5 m2/s • Normalized temperature increase • Used for determining thermal diffusivity in data analysis • Eq. (1) can be used for any type of wire/fiber material with any length • Samples have same normalized temperature increase curve with respect to the Fourier number Fo = αt/L2 1Guo JQ, Wang XW, Wang T., J. Appl. Phys. 101, 063537 (2007). 2Huang X, Wang J, Eres G, Wang X., Carbon. 49.5 (2011): 1680-91. (1) Acknowledgments • This research was supported by the Iowa State University REU Program along with X. Huang and X. Wang. The author would like to thank the program and its members for assistance throughout the entire process. • Effect of gold (Au) coating on nonconductive fibers • Better measurements of thermal diffusivity rely on Au coating that is thin as possible • Large electrical resistance is preferred • Eq. (2) is the simplified equation used to determine the real thermal diffusivity (α) of the fiber (2)