•Unsteady heat transfer from a single spray pulse of various durations was experimentally studied in the evaporative cooling regime (Tw = 70°C).•The change in heat transfer coefficient over time is ...fundamentally different for short (ton<10 ms) and long (ton> 10 ms) duration of pulses.•It has been determined that the greatest value of the thermal efficiency parameter of a single spray is achieved for very short pulses.
The results of an experimental study of heat transfer at the inlet of a pulsed multi-nozzle spray onto a vertical surface in the regime of evaporative cooling (Tw = 70°C) are presented. The main attention is paid to the measurement of unsteady heat transfer for a single spray pulse of various durations (ton = 2–50 ms). The experiments were carried out using pure water and its 50% and 96% mixtures with ethanol as the liquid phase. Initially, with short pulses, the heat transfer coefficient increases with increasing its duration and at ton≈ 10 ms it reaches a plateau with a practically constant value despite the fact that the mass of the liquid injected per pulse increases with ton.The same tendency is observed for time-averaged heat transfer and for all studied coolant compositions. The probable cause of this phenomenon is the increase in the liquid film thickness on the heat exchanger surface, which in turn suppresses evaporation processes. The thermal efficiency coefficient η of the pulsed spray is maximal for the shortest pulses, and it decreases significantly with increasing pulse duration.
The interaction of non-monochromatic radiation with arrays comprising plasmonic and dielectric nanoparticles has been studied using the finite-difference time-domain electrodynamics method. It is ...shown that LiNbO
, TiO
, GaAs, Si, and Ge all-dielectric nanoparticle arrays can provide a complete selective reflection of an incident plane wave within a narrow spectral line of collective lattice resonance with a Q-factor of 10
or larger at various spectral ranges, while plasmonic refractory TiN and chemically stable Au nanoparticle arrays provide high-Q resonances with moderate reflectivity. Arrays with fixed dimensional parameters make it possible to fine-tune the position of a selected resonant spectral line by tilting the array relative to the direction of the incident radiation. These effects provide grounds for engineering novel selective tunable optical high-Q filters in a wide range of wavelengths, from visible to middle-IR.
•We studied the patterns of formation of residual stresses in copper oxide nanoparticles.•We studied the relationship of the residual stresses and the magnetization of nanoparticles.•We detect the ...magnetic behavior of CuO nanoparticles similar to other ferromagnetic nanoparticle systems.
The laws governing the formation of residual stresses in copper oxide nanoparticles in the process of their direct plasma-chemical synthesis in a low-pressure arc discharge plasma are studied. Correlation dependences of the residual stress and the magnetization of nanoparticles on the pressure of the gas mixture of 10% O2 + 90% Ar are presented. The problems associated with the bifurcation of the magnetization curves during cooling in zero (ZFC) and non-zero (FC) magnetic field, non-equilibrium behavior, relaxation of magnetization and magnetic viscosity of the obtained CuO nanoparticles are discussed.
The radiation performance of 18Cr10NiTi-ODS steel with the addition of Y2O3-ZrO2 nano-oxides was compared with that of non-ODS 18Cr10NiTi austenitic steel in terms of radiation-induced hardening and ...cavity swelling. TEM observations were performed to evaluate the effect of grain refinement and nano-sized oxide precipitates on microstructural changes and radiation tolerance in specimens exposed to 1.8 MeV Cr3+ or 1.4 MeV Ar+ irradiations over a wide range of temperatures. Formation of homogenously distributed voids was observed in both alloys upon Cr3+ irradiation but the ODS steel exhibited a considerably broader temperature range of void formation and lower overall swelling. Cavity formation in steels irradiated with Ar+ showed a strong dependence on Ar/dpa ratio. Argon addition was found to enhance the nucleation of cavities, which act as point defects sinks that reduce void swelling. The largest swelling resistance was observed in the ODS steel due to the combined effect of mechanical alloying and Ar gas co-injection. The hardening behavior was investigated in both non-irradiated and Ar+ irradiated samples at room temperature and elevated temperatures by means of nano-indentation. Along with the strengthening effect of radiation-induced dislocations, gas-filled nano-cavities strongly contribute to the hardening of irradiated alloys with a tendency to increase the barrier strength of nano-cavities with decreasing cavity size. The ODS variant was found to be somewhat less susceptible to radiation hardening compared to non-ODS 18Cr10NiTi steel.
Important progress in the development of high-temperature superconductors (HTSC) of the second group made it possible to design the quasi-stationary tokamak with reactor technologies (TRT) with the ...high magnetic field (
B
t0
= 8 T). The high magnetic field will ensure the achievement of plasma fusion regimes in the tokamak with the fusion energy gain
Q
> 1 at the considerably reduced size of the facility (
R
0
= 2.15 m,
a
= 0.57 m), and, consequently, at its reduced cost. TRT will be capable of operating in the quasi-stationary regimes (≥100 s) with hydrogen, helium, and deuterium plasmas (with the densities
n
e
of up to 2 × 10
20
m
–3
) and in the regimes with short (duration Δ
t
< 10 s) deuterium–tritium plasma shots with the fusion energy gain
Q
> 1 limited by the radiation heating of toroidal coils. TRT is being designed as a plasma prototype for both the pure fusion reactor and the fusion neutron source for the hybrid (fusion–fission) reactor. The TRT missions are the development of the key fusion technologies and their integration in one facility. These technologies are as follows: the HTSC electromagnetic system operating at the extremely high magnetic fields; the metal and liquid-metal (lithium) first wall and innovative divertor; the unique advanced systems for the auxiliary plasma heating and non-inductive current drive, including the systems for atomic beam injection with energy of 0.5 MeV and power of several tens of megawatts, the electron cyclotron heating system based on the megawatt-power gyrotrons with a frequency of 230 GHz and a total power of ~10 MW, and the ion cyclotron heating system at frequencies of 60–80 MHz with a power of several megawatts; the tritium fuel cycle; the remote control technologies; the technologies for diagnostics capable of operating under the fusion reactor conditions; the technologies for maintaining quasi-stationary plasma discharges; and the technologies for the tokamak operation in the fusion ignition regime, in which the heating by alpha particles is the dominant heating mechanism at the axis of the plasma column, in the deuterium–tritium experiments limited by the radiation heating of the toroidal coils. The results are presented from the conceptual design of the basic TRT components, as well as the expected characteristics of its operation. It is shown that TRT has a wide window of working parameters suitable for studying the reactor operating regimes. The high magnetic field provides the necessary margins of the pressure, MHD stability, and plasma controllability variation. Implementation of the advanced divertor and first wall concepts, including those using the liquid-metal technologies, will provide the optimum choice of design options in order to reliably control the heat and particle fluxes under the reactor conditions. The advanced systems for the auxiliary heating and current drive will make it possible to implement both the pulsed and stationary regimes of the reactor operation. Calculations of the TRT discharge scenarios show that, for the DT mixture with equal content of components, the long discharges (with duration exceeding 100 s) can be realized with a neutron flux of more than 0.5 MW/m
2
onto the wall, as well as the stationary discharges with a flux of approximately 0.2 MW/m
2
. Thus, TRT can be a real prototype of the fusion neutron source for the hybrid reactor.
The new neutron-deficient isotope
249
No was synthesized for the first time in the fusion-evaporation reaction
204
Pb(
48
Ca,3n)
249
No. After separation, using the kinematic separator SHELS, the new ...isotope was identified with the GABRIELA detection system through genetic correlations with the known daughter and granddaughter nuclei
245
Fm and
241
Cf. The alpha-decay activity of
249
No has an energy of 9129(22) keV and half-life 38.3(2.8) ms. An upper limit of 0.2% was measured for the fission branch of
249
No. Based on the present data and recent information on the decay properties of
253
Rf and aided by Geant4 simulations, the ground state of
249
No is assigned the 5/2
+
622 neutron configuration and a partial decay scheme from
253
Rf to
245
Fm could be established. The production cross-section was found to be
σ
(3n)=0.47(4) nb at a mid-target beam energy of 225.4 MeV, which corresponds to the maximum of the calculated excitation function. Correlations of the
249
No alpha activity with subsequent alpha decays of energy 7728(20) keV and half-life
1
.
2
-
0.4
+
1.0
min provided a firm measurement of the electron-capture or
β
+
branch of
245
Fm to
245
Es. The excitation function for the 1n, 2n and 3n evaporation channels was measured. In the case of the 2n-evaporation channel
250
No, a strong variation of the ground state and isomeric state populations as a function of bombarding energy could be evidenced.
This paper presents the results of observations of atmospheric and ionospheric parameters performed during a meteorological storm that occurred over the Kaliningrad region in December 2010. The ...analysis of the observations shows that the ionospheric inhomogeneities at mid-latitudes arising during the periods of meteorological disturbances are manifested as a decrease in the total electron content and the critical frequency of the F2 layer by 33 and 15%, respectively. It is shown that meteorological disturbances of the mid-latitude atmosphere can be manifested in the ionosphere and in the near-equatorial latitudes as increased TEC values. This indicates the complex nature of physical processes that determine the relationship between dynamics in the lower and upper atmosphere.
The paper presents the results of observations of the sporadic Es layer during the period of meteorological disturbances in Kaliningrad in October 2017 and 2018 under quiet geomagnetic conditions. ...During the meteorological storms (October 29–30, 2017 and October 23–24, 2018), significant changes occurred in the dynamics of the Es-layer critical frequency. Observations of atmospheric and ionospheric disturbances in the Kaliningrad region show that the delay between the ionospheric response and the moment of maximum disturbances in atmospheric parameters is about 3 hours. These phenomena at the heights of the E-region might have been caused by propagation of acoustic-gravity waves generated by convective processes in the lower atmosphere during periods of a meteorological storm. Intensification of turbulent processes in the lower thermosphere leads to an increase in the atmospheric density and, accordingly, to higher recombination rates. This leads to a rapid decrease in the concentration of ions and, consequently, to a decrease in the critical frequency of the sporadic layer below the sensitivity threshold of ionosondes.
PDF
