Near-field heat transfer across a gap between plane-parallel tungsten layers in~vacuo was studied experimentally with the temperature of the cold sample near 5~K and the temperature of the hot sample in the range 10\char21{}40~K as a function of the gap size d. At gaps smaller than one-third of the peak wavelength $\lambda${}m given by Wien's displacement law, the near-field effect was observed. In comparison with blackbody radiation, hundred times higher values of heat flux were achieved at d$\approx${}1\,\,$\mu${}m. Heat flux normalized to the radiative power transferred between black surfaces showed scaling ($\lambda${}m/d)n, where n$\approx${}2.6. This Letter describes the results of experiment and a comparison with present theory over 4 orders of magnitude of heat flux.

The heat transfer efficiency in turbulent Rayleigh-B\'enard convection is investigated experimentally, in a cylindrical cell of height 0.3~m, diameter 0.3~m. We show that for Rayleigh numbers 1012$\lesssim${}Ra$\lesssim${}1015 the Nusselt number closely follows Nu$\propto${}Ra1/3 if the mean temperature of the working fluid\char22{}cryogenic helium gas\char22{}is measured by small sensors directly inside the cell at about half of its height. In contrast, if the mean temperature is determined in a conventional way, as an arithmetic mean of the bottom and top plate temperatures, the Nu(Ra)$\propto${}Ra$\gamma${} displays spurious crossover to higher $\gamma${} that might be misinterpreted as a transition to the ultimate Kraichnan regime.

For bodies spaced in vacuum at distances shorter than the wavelength of the thermal radiation, radiative heat transfer substantially increases due to the contribution of evanescent electromagnetic waves. Experimental data on heat transfer in near-field regime are scarce. We have designed a cryogenic apparatus for the study of heat transfer over microscopic distances between metallic and non-metallic surfaces. Using a mechanical positioning system, a planeparallel gap between the samples, concentric disks, each 35 mm in diameter, is set and varied from 100 to 103 μm. The heat transferred from the hot (10 – 100 K) to the cold sample (∼5 K) sinks into a liquid helium bath through a thermal resistor, serving as a heat flux meter. Transferred heat power within ∼2 nW/cm2 and ∼30 μW/cm2 is derived from the temperature drop along the thermal resistor. For tungsten samples, the distance of the near-field effect onset was inversely proportional to temperature and the heat power increase was observed up to three orders of magnitude greater than the power of far-field radiative heat transfer.

This paper is devoted to the description of a new approach for large-scale electric power systems (EPS) simulation, so-called hybrid simulation approach. The design and research of EPS require solving a large number of non-trivial tasks. Due to the well-known EPS specificity, mathematical modeling is the only way to proceed. According to the hybrid approach, several simulation techniques (analogue, digital, and physical) are used to achieve the best results. An analogue part provides the elimination of methodological integration error, which appears in a case of numerical methods usage. A digital part allows the realization of control and parameter changing algorithms on software level. In a physical part, the connection and switching of modeled elements are provided in a way as in real EPS. In addition, the paper presents hardware features of the simulator-hybrid real-time power system simulator (HRTSim), which is an alternative to the digital simulators currently used. The important part of this paper is the result of comparative analysis of transient processes oscillograms obtained by HRTSim and real disturbance recorders in Tomsk region power system, as well as HRTSim and real-time digital simulator.