This study is mainly focused on applying the Particle Image Velocimetry (PIV)
technique to the unique fluid system of He II. Challenges associated with the
application are identified and discussed in the context of the exceptional physical
properties and experimental environment of He II. The particle dynamics in He II is
studied, and two important parameters, slip velocity and relaxation time, are derived.
Based on this information, the tracking characteristics of a variety of candidate tracer
particles, including commercially available solid particles and particles generated by
freezing liquids and gases, are discussed, as well as their potential applications to
liquid helium. It is indicated that polymer particles with a mean diameter of 1.7 μm and
specific gravity of 1.1 are the most suitable for tracking the thermal counterflow in
our experiments. To introduce these very fine particles into liquid helium, a simple
seeding method based on the two-phase fluidized bed technology was developed. The
seeding results show an adequate concentration and also a quite uniform spatial
distribution of seeded particles. Using the PIV technique, velocity fields of He II
thermal counterflow in steady state have been measured in a range of bath temperatures
from 1.61 K to 2.0 K and applied heat fluxes from about 1.1 kW/m2 up to 13.7 kW/m2. A
significant discrepancy between the measured particle velocity vp,a and theoretical
normal fluid velocity vn,t is present at all the temperatures, and the ratio of
vp,a/vn,t is most likely a temperature-independent constant around 0.5. Careful analysis
suggests that this velocity discrepancy may be caused by an additional force from the
superfluid component. A semi-empirical correlation for this force is developed. By
adding the force to the particle dynamics equation, the analytical results are shown to
be consistent with the experimental results. Also, the propagation of second sound shock
and heat diffusion has been studied by measuring the instantaneous velocity fields of
induced transient thermal counterflow. The arrival of shock front, effect of expansion
fan, passage of shock tail, and the onset of heat diffusion are clearly observed from
the particle velocity profiles versus time. The generated particle velocity profiles are
compared and discussed in respect of the critical energy flux for the onset of quantum
turbulence, and the additional force from the superfluid component is further addressed
regarding its application to the transient state. / A Dissertation submitted to the Department of Mechanical Engineering in partial
fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2004. / Date of Defense: March 24, 2004. / Helium II, PIV, Thermal Counterflow / Includes bibliographical references. / Steven W. Van Sciver, Professor Directing Dissertation; Stephen J. Gibbs, Outside Committee Member; Chiang Shih, Committee Member; David Cartes, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_168696 |
| Contributors | Zhang, Tao (authoraut), Sciver, Steven W. Van (professor directing dissertation), Gibbs, Stephen J. (outside committee member), Shih, Chiang (committee member), Cartes, David (committee member), Department of Mechanical Engineering (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
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