Turbulence modulation of the upward turbulent bubbly flow in vertical ducts

The present paper aims at improving the modeling of turbulence for the upward turbulent bubbly flow through the use of experimental databases that contain data on small and large vertical ducts. First, the role of bubble-induced turbulence was analyzed, which indicated the dominant role of the bubble-induced turbulence in the duct center for relatively high void fraction cases. Therefore, the turbulence therein was mainly focused on, which indicated that the stronger turbulence could be induced by bubbles in large ducts with similar void fractions as compared to that in small ducts. Next, the turbulence of upward turbulent bubbly flow near the wall is discussed to understand the interaction between the wall-induced and bubble-induced turbulence. It showed that the existence of a wall could suppress the bubble-induced turbulence given the same void fraction, and the existence of bubbles could also suppress the solely wall-induced turbulence as compared to the single-phase turbulent flow, even though the total turbulence is enhanced. The above characteristics indicated that the current turbulence modeling method needs to be modified, especially when the bubble-induced turbulence plays a dominant role

Viscoelastic fluid behaviors around a rising bubble via a new method of mesh deformation tracking

The deformation of a hydrogen microbubble line and/or mesh in a viscoelastic fluid around a rising bubble was tracked from the original static position in order to discuss the mechanism of the typical phenomena such as the negative wake or the cusp shape. This new experimental method is essentially important because of the hysteresis-dependent nature of the viscoelastic fluid. This new method makes this study distinctive from a number of conventional studies of viscoelastic fluids focusing on the non-Newtonian properties and/or the instantaneous flow field. According to our experimental results, the flow mechanism responsible for the negative wake or cusp shape was attributed to the accumulation and release of the shear strain energy. Some residual displacements were observed after the bubble rising, which were almost completely reproduced as the internal dissipations in a Maxwell model modified with a non-linear spring

Measurements of liquid film and droplets of annular two-phase flow on a rod-bundle geometry with spacer

Measurements have been conducted to simultaneously consider both liquid films and droplets of the annular flow on a 3 × 3 simulating BWR fuel rod-bundle test-section with spacers. The optical system of a high speed camera and a tele-microscope was used to record the backlight images at the gap between a corner rod and a side rod of the bundle at high time and space resolutions. The data obtained from the liquid film showed that the mean film thickness, wave height, power spectral density, and wave velocity at the corner rod are larger than those at the side rod, and that the influences of the spacer are different in the cases of low and high gas superficial velocities. Simultaneously, the data containing size and spatial distributions as well as the axial velocity distribution of liquid droplets were obtained. In the case of lower gas flow rates, the spacer generates not only a large number of small droplets but also big droplets whose size exceeds the maximum droplet diameter at upstream. At further downstream, the spatial distribution of the droplets indicates an asymmetry characteristic, which emphasizes the contribution of the droplet impingement mechanism to the entrainment phenomena. Moreover, a close-up observation at right up- and downstreams of the spacer was conducted to describe the interactions between the two-phase flow and this structure. By using these new experimental arrangements, the interaction mechanisms among the wavy liquid film, droplets and spacer were discussed

Experimental study on chemical behaviors of non-metal impurities in Pb, Pb-Bi and Pb-Li by temperature programmed desorption mass spectrometer analysis

The chemical behaviors of non-metal impurities such as O2, H2, N2, H2O, CO2 and CO in lead (Pb) metal,lead-bismuth (Pb-Bi) alloy and lead-lithium (Pb-Li) alloys were experimentally investigated by means of temperatureprogrammed desorption mass spectrometer (TPD-MS) analysis. Desorption of H2O and CO2 from thePb metal and the Pb-Bi alloy was clearly detected by TPD-MS analysis. However, desorption of H2O and CO2from the Pb-Li alloys was much less than that from the Pb metal and the Pb-Bi alloy, since these molecules arechemically unstable and react with Li in the Pb-Li alloys. Then, oxygen and hydrogen must be dissolved in Pb-Lialloys as they form the chemical compounds of Li (i.e., Li2O, LiOH and LiH). Large desorption of hydrogen fromsolid Pb-Li alloys by their heating was detected. The possible mechanism for the large desorption of hydrogenfrom the Pb-Li alloys is based on the decomposition of LiH and Pb-Li-H at high temperature. The chemicalbehaviors of the non-metal impurities in the Pb-Li alloys was modeled based on the thermodynamic stability.The methodologies for the fabrication of high-purity Pb-Li alloys and the control of the impurity condition arediscussed