First detection of two superoutbursts during rebrightening phase of a WZ Sge-type Dwarf Nova : TCP J21040470+4631129

We report on photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9 mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed Balmer, He I, and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk needs to have expanded beyond the 3 : 1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the accretion disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-type dwarf novae.peer-reviewe

First Detection of Two Superoutbursts during Rebrightening Phase of a WZ Sge-type Dwarf Nova: TCP J21040470+4631129

We report photometric and spectroscopic observations and analysis of the 2019 superoutburst of TCP J21040470+4631129. This object showed a 9-mag superoutburst with early superhumps and ordinary superhumps, which are the features of WZ Sge-type dwarf novae. Five rebrightenings were observed after the main superoutburst. The spectra during the post-superoutburst stage showed the Balmer, He I and possible sodium doublet features. The mass ratio is derived as 0.0880(9) from the period of the superhump. During the third and fifth rebrightenings, growing superhumps and superoutbursts were observed, which have never been detected during a rebrightening phase among WZ Sge-type dwarf novae with multiple rebrightenings. To induce a superoutburst during the brightening phase, the accretion disk was needed to expand beyond the 3:1 resonance radius of the system again after the main superoutburst. These peculiar phenomena can be explained by the enhanced viscosity and large radius of the disk suggested by the higher luminosity and the presence of late-stage superhumps during the post-superoutburst stage, plus by more mass supply from the cool mass reservoir and/or from the secondary because of the enhanced mass transfer than those of other WZ Sge-type dwarf novae.Comment: 13 pages, 10 figures, accepted for publication in PAS

Heat Transfer during Nitrogen Boiling on Surfaces Modified by Microarc Oxidation

Despite the many different methods for creating modified heat transfer surfaces to increase critical heat fluxes and heat transfer coefficients at pool boiling of various liquids at given reduced pressures, active research is currently underway to find optimal surface morphology and geometric parameters of structures for practical application. In this work, we used the method of microarc oxidation (MAO) to obtain coatings with different microstructures on the surface of duralumin heaters. In the present work, we studied the effect of MAO coatings on heat transfer, critical heat flux, and evaporation dynamics during liquid nitrogen boiling under conditions of steady-state heat release at pressures of 0.1, 0.05, and 0.017 MPa. It was shown that the modification of heaters led to a 50–60% increase in heat transfer coefficients as compared to the smooth one under the atmospheric pressure. Based on the data of high-speed video filming of boiling, it was shown that the main mechanism of intensification is the increase in quantity of active nucleation sites. A significant decrease in pressure led to the absence of a significant difference in both heat transfer intensity and evaporation dynamics for the smooth and modified heaters

Numerical simulation of heat transfer in falling wavy liquid films on unsteady heat release

The mathematical model which allows the calculation of the wave surface profile as well as velocity and temperature fields has been presented. The numerical simulation of heat transfer in falling wavy films of liquid nitrogen has been performed. The dependencies of boiling expectation time and total local evaporation time on heat flux density for different inlet Reynolds numbers have been calculated. The regime map which describes the different mechanisms of film decay was obtained by summing up the simulation results. The results of numerical simulation are in satisfactory agreement with the experimental data