Showing papers by "Kaichiro Mishima published in 2011"

Interfacial Drag Model and Numerical Analysis for Gas-Liquid Two-Phase Flow in a Large Diameter Pipe

Abstract: As the two-phase flow regime evolves from bubbly to slug flows along the flow direction in a vertical large diameter pipe, the void fraction increases first in the bubbly flow region, then decreases in the transitional region, and finally increases again in the slug flow region. The N-shaped profile of void fraction was numerically analyzed by using the one-dimensional two-fluid model. Its interfacial drag model was modified by including constitutive equations of C0 and Vgj developed by Shen et al. [2] for evolving two-phase flow from bubbly to slug flows in a large diameter pipe. The numerical calculation predicted well the N-shaped profile of the measured axial void fraction distribution from the present experiments. The predicted average gas and liquid velocities indicated that the average gas velocity increased significantly and the average liquid velocity decreased slightly when the void profile is N-shaped one. The phenomenon can be attributed to the formation and development of large bubbles of pipe size.

CHF in a Circumferentially Non-Uniformly Heated Tube under Low Pressure and Low Mass Flux Condition (Influence of the Magnitude of Heat Flux)

Abstract: Critical Heat Flux (CHF) in a non-uniformly heated tube is a very important designing factor of actual boiling two-phase flow equipments. In this series of studies, the CHF in a non-uniformly heated tube was discussed by using the re-distribution of a liquid film caused by the wave interaction. In the present investigation, in order to estimate the influence of the entrainment of droplet under the high heat flux condition on the re-distribution of liquid film, the CHF experiment was conducted. The experimental apparatus was a similar to the forced convective boiling system described in the previous paper, i.e. the eccentric tube with 20 mm I.D., 24 mm O.D., but heated length was just only 450 mm to keep the high heat flux condition. The experimental result expressed the influence of the magnitude of the heat flux as the increasing in the entrainment. The CHF was occurred at the high quality condition, i.e. liquid film dryout and at the low quality condition, i.e. departure from nucleate boiling (DNB), respectively. This obtained CHF was evaluated by using the film flow model, and the empirical correlation of the spreading coefficient of liquid film re-distribution was proposed.