Experimental Results for Thermal Conductivity of Paraffin Waxes

Transcription

1 Department of Mechanical Engineering 5711 Boardman Hall Orono, ME Tel: Fax: Experimental Results for Thermal Conductivity of Paraffin Waxes Crosby Laboratory University of Maine Orono, ME December 13th, 2011 By: Warren J Taylor Rory Dunn Parker Hovey Page 1

2 Department of Mechanical Engineering 5711 Boardman Hall Orono, ME Tel: Fax: Problem/Purpose Statement: Paraffin wax is incorporated into our group s design project as an energy storage device. The energy is stored primarily as heat by raising the temperature and by changing the phase of the material. The rate at which the wax can store energy is critical to the overall design of our project. The thermal conductivity of the paraffin wax is just one constant that we must know to make accurate design decisions. The purpose of this paper is to describe the experimental method used for testing the thermal conductivity in a solid paraffin wax material. The experimental results will also be presented. Figure 1: Sketch of the experimental setup. Page 2

3 5711 Boardman Hall Orono, ME Tel: Fax: Department of Mechanical Engineering Description of Experiment Test Rig and Method: Figure 2: Picture of the test setup Equipment List: Paraffin Wax Manufacturer: Material: Melting Point F: The International Group, INC. 1230A 130 Variac (2x) Manufacturer: Model: Powerstat Variable Autotransducer Heating Source Primary: Secondary: Westinghouse Dual Hot Plate Benchmark Magnetic Hotplate Stirrer Guarded Hot Box Insulation: 2 Polystyrene Thermocouple Page 3

4 Department of Mechanical Engineering 5711 Boardman Hall Orono, ME Tel: Fax: Manufacturer: Type: Omega Engineering K Digital Thermometer (2x) Manufacturer: Model: Omega Engineering HH509 Miscellaneous Digital Multimeter: Digital Multimeter: Power Strip Banana Cables Micronta, Auto Range Hewlett Packard, 34401A Test Method: Our test method is taken primarily from ASTM C : Standard Test for Steady State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded Hot Plate Apparatus. The standard test was altered to fit our experimental conditions. This standard has been attached to this report as Appendix B. Results/Summary: Thermal conduction is the rate at which heat energy flows through a material. Our test is designed to limit the direction of heat energy flow to one dimension. Fourier s law of conduction for one dimensional conduction is: The majority of the test is based around limiting the heat transfer to one dimensional flow. The purpose of the guarded hot box is to create adiabatic boundaries around the primary heater. The guarded hotbox apparatus is described in detail in Appendix B. The adiabatic boundaries force all the energy inputted to the hot plate through the paraffin wax. Although all the energy is leaving through the wax material, it must be ensured that the energy is passing through the wax at a uniform rate. This is done by first selecting a uniform base plate with a constant temperature distribution throughout. Once a uniform base plate temperature is achieved, the energy should flow through the wax material at a uniform rate, creating a uniform temperature distribution on the top surface of the wax. The total input energy is measured from monitoring the input voltage and current to the primary hot plate. The input power is computed using the standard equation for power. Page 4

5 Department of Mechanical Engineering 5711 Boardman Hall Orono, ME Tel: Fax: The input power has been computed, it is divided by the test specimen area to achieve heat flux. The change in temperature between the two specimen surfaces is done through multiple thermocouples attached to the paraffin wax specimen. The test temperatures are limited to below the melting temperature of the wax. This assures that no transient phase change processes are occurring during the test. Once the test is set up, the primary and guard heaters are turned on until the hot plate surface is at a uniform temperature of 100 degrees F. Once the primary surface is at 100 degrees, the secondary guard heater must be adjusted to achieve an adiabatic boundary for the primary heater. This is done by setting the guard insulation temperature to 100 degrees F. It may take many hours to achieve steady state throughout the entire apparatus. After steady state is achieved, the temperature on the top and bottom of the test specimen is recorded. The thermal conductivity of the material is then computed by rearranging Fourier s law of conduction for one dimensional flow. The heat flux, specimen thickness, and temperature change have all known. The results from our test are as follows: Ts ( C) T2( C) Primary Heater Trial Guard Temp 1 2 Avg 1 2 Avg Amb. Temp With these experimental test results, the thermal conductivity of the wax is: Current (Amps) Voltage (Volts) Power (Watts) Average These results are concurrent with thermal conductivities that we have encountered from other paraffin waxes. Page 5

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