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Visualization Study of Thermal Counterflow Turbulence in Superfluid 4He

Title: Visualization Study of Thermal Counterflow Turbulence in Superfluid 4He.
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Name(s): Gao, Jian, author
Guo, Wei (Professor of Mechanical Engineering), professor directing dissertation
Li, Hui, 1970-, university representative
Collins, Emmanuel G., committee member
Taira, Kunihiko, committee member
Pamidi, Sastry V., committee member
Florida State University, degree granting institution
FAMU-FSU College of Engineering, degree granting college
Department of Mechanical Engineering, degree granting department
Type of Resource: text
Genre: Text
Doctoral Thesis
Issuance: monographic
Date Issued: 2017
Publisher: Florida State University
Place of Publication: Tallahassee, Florida
Physical Form: computer
online resource
Extent: 1 online resource (100 pages)
Language(s): English
Abstract/Description: Superfluid 4He (He II) has been widely used as a coolant material in many engineering applications. Its unique heat transfer mode is the so-called thermal counterflow. The study of thermal counterflow will contribute to the design of He II based cooling devices and our understanding of quantum turbulence. However, due to the lack of effective visualization and velocimetry techniques, studying the fluid dynamics in superfluid 4He is very challenging. In this dissertation, we discussed the development of a novel flow-visualization technique in He II based on the generation and imaging of thin lines of metastable tracer molecules. These molecular tracers are created via femtosecond-laser field-ionization of helium atoms and can be imaged using a laser-induced fluorescence technique. In steady state thermal counterflow measurement, we demonstrated that such tracer molecules are entrained by the normal fluid component. We revealed for the first time a laminar to turbulent transition in the normal fluid component. We found that the profile of the normal fluid in the laminar flow can exhibit quite different velocity profile compared to the laminar Poiseuille profile of classical fluid in a channel. In the turbulent flow state, the turbulence intensity is found to be much higher than that in classical channel flow. This turbulence intensity appears to depend primarily on temperature. We also found that the form of the second order transverse structure function deviates more strongly from that found in classical turbulence as the steady state heat flux increases, suggesting novel energy spectrum. In decaying counterflow turbulence, we studied the normal fluid flow via flow visualization and measured the quantized vortex line density using 2nd sound attenuation. Comparing the decay behavior of both fluids, we were able to produce a theoretical model to explain the puzzling decay behavior of the vortices. We were also able to determine the effective kinematic viscosity in a wide temperature range. Some preliminary results in the study of decaying grid turbulence were obtained, which allows us to examine the intermittent behavior of superfluid turbulence.
Identifier: FSU_SUMMER2017_Gao_fsu_0071E_13828 (IID)
Submitted Note: A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Degree Awarded: Summer Semester 2017.
Date of Defense: April 28, 2017.
Keywords: Flow visualization, Quantum turbulence, Thermal counterflow
Bibliography Note: Includes bibliographical references.
Advisory Committee: Wei Guo, Professor Directing Dissertation; Hui Li, University Representative; Emmanuel G. Collins, Committee Member; Kunihiko Taira, Committee Member; Sastry V. Pamidi, Committee Member.
Subject(s): Condensed matter
Persistent Link to This Record: http://purl.flvc.org/fsu/fd/FSU_SUMMER2017_Gao_fsu_0071E_13828
Owner Institution: FSU

Choose the citation style.
Gao, J. (2017). Visualization Study of Thermal Counterflow Turbulence in Superfluid 4He. Retrieved from http://purl.flvc.org/fsu/fd/FSU_SUMMER2017_Gao_fsu_0071E_13828