a pair of undergraduate physics students at the university of chicago (uchicago) demonstrated how to levitate a variety of objects, including glass bubbles, polyethylene spheres, and ice particles, using the movement of heat from a warm plate towards a chilled cylinder, according to a report on the school’s website.
uchicago researchers achieved levitation of macroscopic objects between warm and cold plates
in a vacuum chamber. (jean lachat/uchicago)
third-year student frankie fung and fourth-year student mykhaylo usatyuk used a copper plate kept at room temperature as the bottom plate in the experiment and the top plate was a stainless steel cylinder filled with liquid nitrogen and kept at -300°f.
the flow of heat from the bottom plate to the top was not only able to lift the objects but also kept them levitated for more than an hour, rather than just a few minutes as previous attempts using magnetic or optical levitation. in addition, this process proved successful vertically and radially.
the article explained, “the key to obtaining high levitation stability is the geometrical design of the two plates. a proper ratio of their sizes and vertical spacing allows the heat to flow around and efficiently capture the levitated objects when they drift away from the center.
it continued, “another sensitivity factor is that the thermal gradient needs to be pointing upward—even a misalignment of one degree will greatly reduce the levitation stability.”
according to fung, the temperature gradient between the plates created a “force” that balanced out gravity and allowed the students to suspend the objects indefinitely.
this breakthrough could lead to advancements in the study of particle dynamics. it could have applications in aerospace, research, and other industries that incorporate thermophoresis (the movement of particles by means of a temperature gradient), which includes nuclear reactor safety and manufacturing optical fibers.
the work was recently published in applied physics letters. the abstract stated:
“we demonstrate levitation and three-dimensionally stable trapping of a wide variety of particles in a vacuum through thermophoretic force in the presence of a strong temperature gradient. typical sizes of the trapped particles are between 10 μm and 1 mm at a pressure between 1 and 10 torr.
“the trapping stability is provided radially by the increasing temperature field and vertically by the transition from the free molecule to hydrodynamic behavior of thermophoresis as the particles ascend. to determine the levitation force and test various theoretical models, we examine the levitation heights of spherical polyethylene spheres under various conditions.
“a good agreement with two theoretical models is concluded. our system offers a platform to discover various thermophoretic phenomena and to simulate dynamics of interacting many-body systems in a microgravity environment.”