Asymmetry of the wall shear stress in a stimulated ascendant flow of a liquid with monodisperse bubbles

Results of an experimental investigation of the two-phase wall shear stress averaged over the tube perimeter and the pulsation of wall shear stress in a stimulated ascendant flow with monodisperse bubbles with an average diameter of 1.2 and 2.2 mm are presented. Regimes with various hydrodynamic parameters such as high shear stress on the wall, low and negative wall shear stress, a high level of shear stress pulsation on the wall, and possible decrease in this level of pulsation are found. An increase in the void gas fraction results in a monotonic increase of perturbation of the single-phase flow. The dependences of the ratio of two-phase and single-phase wall shear stresses for two average bubble diameters seem to be qualitatively similar. The analysis of data revealed a complex dependence of the shear stress pulsation on the bubble diameter. The averaged flow characteristics quantitatively change upon the decrease in the bubble diameter. A further decrease in the average bubble diameter at the same void gas fraction will probably increase the heat-and mass-transfer characteristics of the flow. This is an issue for the futures study.     

Experimental study of the Taylor bubbles shear stress in an upward flow in a vertical tube

The modification of electrodiffusional method of the wall shear stress measurements is applied for registration of the Taylor bubble shear stress in an upward liquid flow. Time realization of shear is considered as a structure frozen into the flow, which moves together with a bubble. Experiments were carried out in laminar and transitional liquid flows. The wall shear stress in the liquid film around bubble averaged over the tube perimeter is presented for different flow Reynolds numbers and different lengths of the bubble.     

First results for the measurement of double-electron capture of 106Cd in the experiment TGV II

Present status of the experiment TGV II which is devoted to the measurement of double-beta decay of ¹⁰⁶Cd is given. The low background spectrometer TGV II is installed in the Modane Underground Laboratory and has been running from February 2005 with approx 10 grams of ¹⁰⁶Cd enriched at 75%. After an analysis of 3736 hours of experimental data the new improved half-life limit for 2νEC/EC decay of ¹⁰⁶Cd (0 _g.s. ⁺ → 0 _g.s. ⁺ ) is given as T ₁ ^2/2ν > 4.8 × 10¹⁹ years (90% CL). The search for 2νEC/EC decay of ¹⁰⁶Cd to the excited states of ¹⁰⁶Pd allows to determine the limits of the half-lives T ₁ ^2/2ν (0 _g.s. ⁺ → 2 ₁ ⁺ ) > 3.9 × 10¹⁹ years (90% CL) and T ₁ ^2/2ν (0 _g.s. ⁺ → 0 ₁ ⁺ ) > 5.8 × 10¹⁹ years (90% CL). Presented by I. Štekl at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

Slip velocity measurements in an upward bubbly flow by combined LDA and electrodiffusional techniques

 An experimental technique for the measurement of the local slip velocity of spherical bubbles is reported. It is based on the measurement of the local liquid velocity by an electrodiffusional method, and the bubble velocity by a specially adapted LDA (Laser Doppler anemometer) with a short measuring volume. The bubble velocity is measured taking into account the shift between the bubble centre and the centre of the LDA measuring volume. The slip velocity is obtained by subtracting the liquid velocity from the bubble velocity at the point corresponding to the bubble centre. The technique is applicable for flows with high velocity gradients. Results of the slip velocity measurements in an upward bubbly flow at laminar pipe Reynolds numbers are presented. Received: 25 July 1996/Accepted: 13 April 1998     

The problems of the upward monodispersed microbubble flow in a vertical tube

The paper presents the first experimental results concerning the wall shear stress in an upward monodispersed microbubble flow in vertical tube. A bubble generator using a microfluid focusing technique was designed to produce monodispersed submillimeter bubbles. The experimental results allow to think that there is an optimal size of the bubbles and the optimal gas fraction in the bubble sublayer that provide the maximal mass transfer coefficient beween the flow and the tube wall.     

Structural and electrical characteristics of a hyperdoped silicon surface layer with deep donor sulfur states

Inhomogeneous hyperdoping of a 100-nm-thick silicon surface layer with sulfur atoms at concentrations above 2 × 10²¹ cm^?3 was obtained via its femtosecond laser ablation in a sulfur-containing organic solvent. Infrared transmission spectroscopy reveals distinct interband absorption peaks of donor sulfur states, which are absent in the initial crystalline silicon, and a broad absorption band of free carriers with a concentration of ～10¹⁸ cm^?3. The rather low free-carrier concentration is related to equilibrium room-temperature ionization of localized donor sulfur states, preserving their nondegenerate character owing to the strong electronion binding in the donor states.     

Cadmium-loaded organic scintillators

The high value of the cross section of thermal neutron capture by the ¹¹³Cd nucleus allows us to regard cadmium-loaded organic scintillators as an alternative to gadolinium-loaded analogues. We report on new plastic and liquid scintillators with maximum metal concentrations of 2 and 1.5 wt %, respectively. Transmission spectra, scintillation characteristics, and efficiencies of the registration of thermal neutrons are given.     

Testing the Pauli exclusion principle with the NEMO-2 detector

The Pauli Exclusion Principle (PEP) was tested with the NEMO-2 detector. Limits at the 90% C.L. on the violation of PEP for p-shell nucleons in ¹²C were obtained. Specifically, transitions to the fully occupied 1s _1/2-shell yielded a limit of 4.2 · 10²⁴ y for the process with emission of a γ-quantum. Similarly limits of 3.1 · 10²⁴ y for β⁻ and 2.6 · 10²⁴ y for β⁺ Pauli-forbidden transitions of ¹²C →¹²?¹²B) are reported here. Received: 25 August 1999     

Environmental problems of finely dispersed titanium dioxide production

Finely dispersed titanium dioxide is widely used in modern technologies. Proved reserves of titanium ores in Russia are expected to meet industrial needs. However, the available facilities for the manufacture of titanium dioxide from ores are clearly insufficient, which naturally requires new plants to be put into operation. The technologies used for the production of titanium dioxide were developed as early as 1940s, when ecological aspects of the production process were almost not taken into account. The present survey analyzes environmental problems related to the titanium dioxide production according to the sulfate and chloride technologies in comparison with the fluoride process proposed for industrial implementation. The fluoride process has been examined as applied to ilmenite from the Turan deposit in Tomsk oblast, and some actions directed toward improvement of ecological parameters of this process have been proposed.