title: Anomalous heat transport and condensation in convection of cryogenic helium.
abstract: When a hot body A is thermally connected to a cold body B, the textbook knowledge is that heat flows from A to B. Here, we describe the opposite case in which heat flows from a colder but constantly heated body B to a hotter but constantly cooled body A through a two-phase liquid-vapor system. Specifically, we provide experimental evidence that heat flows through liquid and vapor phases of cryogenic helium from the constantly heated, but cooler, bottom plate of a Rayleigh-Bénard convection cell to its hotter, but constantly cooled, top plate. The bottom plate is heated uniformly, and the top plate is cooled by heat exchange with liquid helium maintained at 4.2 K. Additionally, for certain experimental conditions, a rain of helium droplets is detected by small sensors placed in the cell at about one-half of its height.
authors.affiliation: Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, 61242 Brno, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Urban
authors.forename: David
authors.initials: D
authors.lastname: Schmoranzer
authors.forename: Pavel
authors.initials: P
authors.lastname: Hanzelka
authors.forename: Katepalli R
authors.initials: KR
authors.lastname: Sreenivasan
authors.forename: Ladislav
authors.initials: L
authors.lastname: Skrbek
keywords: condensation; rain formation; temperature inversion; two-phase convection