Applications of the thermal wave technique in liquid thermal conductivity measurements and flow field diagnostics Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/pv63g286v

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  • The thermal wave technique has been explored for the use of liquid thermal conductivity measurement and flow property diagnostics in this dissertation. For liquid thermal conductivity measurements, an experimental technique based on the thermal wave approach is developed. A stainless steel strip functions as both a heating element and a sealing cover for a chamber containing a test liquid. A periodic current passing through this metal strip generates a periodic Joule heating source. An infrared detector measures the temperature response at the front surface of the stainless steel strip. The phase and magnitude of the temperature response were measured by a lock-in amplifier at various frequencies. A one-dimensional, two-layered transient heat conduction model is developed to predict the temperature response. The phase information of this temperature response shows high sensitivity to the change of thermal properties of the liquid layer and is employed to match experimental data to find the thermal properties of the test liquid. The measured thermal conductivities of water and ethylene glycol agree quite well with data from the literature and support the validity of this measurement technique. An aqueous fluid consisting of gold nanoparticles was also tested and anomalous thermal conductivity enhancement was observed. Our measurement results also showed a divergence of thermal transport behavior between nanofluids and pure liquids. This suggests a need to carefully examine the role of the measurement technique in the heat transfer experimental studies of nanofluids. For the study of flow property diagnostics, a heat transfer system with a periodic boundary condition in a steady flow field is examined. Due to linearity and homogeneity of the heat transfer system under certain conditions, a thermal wave field generated by a periodic heating flux at the boundary of the flow field may be used to detect important flow field parameters, such as the velocity gradient at the wall, and therefore, the wall shear stress. A wall shear stress sensor design with a heater and two temperature sensors on a silicon dioxide substrate is analyzed. The heater with a periodic heating source generates an oscillating temperature field which interacts with the flow field. The temperature sensors pick up the temperature response that contains information on the velocity gradient at the wall. Based on the above sensor design, a two-dimensional conjugate heat convection model is developed with a periodic heating flux at the solid/fluid interface and a linear velocity profile in the fluid domain. Two designs are studied, one with a silicon heat sink under the silicon dioxide substrate and another without the heat sink. The effects of the two main design parameters, the operating frequency and the distance between the heater and the temperature sensor, are discussed. A reasonable sensitivity of the phase information to the velocity gradient suggests a practical sensor design. A preliminary experimental test on a water channel flow has been conducted to support the concept of applying the thermal wave method to wall shear stress measurements.
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  • description.provenance : Submitted by Zhefu Wang (wangzh@onid.orst.edu) on 2008-08-01T22:05:27Z No. of bitstreams: 1 Dissertation_Wang_930592229.pdf: 1222656 bytes, checksum: ca4e42ae8bcb8c03124c171d131c9783 (MD5)
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  • description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2008-08-11T17:57:59Z (GMT) No. of bitstreams: 1 Dissertation_Wang_930592229.pdf: 1222656 bytes, checksum: ca4e42ae8bcb8c03124c171d131c9783 (MD5)
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