Following the preceding review, this review examines the influence of heat transfer models on the freezing of water and the melting of ice. The phenomenon of the freezing of flowing water in a river is discussed. In particular, the effects on freezing and melting of natural convection, forced convection and thermal radiation heat transfers under various conditions are clarified.
The phenomena occurring at a nanoscopic scale on the very surface of solid substrates are discussed, as one particular aspect of multiphase flow studies. The STM (scanning tunneling microscopy) observation as well as the newly developed total reflection X-ray diffractometry experiments revealed the nanoscopic behavior of organic molecules from vapor to solid phases (crystallization process), whichd epends greatly on the nature of the substrates, namely on the interaction between the molecules and the substrate atoms. It is suggested that such interactions, including the electrostatic intermolecular interaction, play an essential role in the aggregation process of molecules above solid surfaces, as indeed simulated by a computer calculation. Moreover, the possible correlation of these nanoscopic mechanisms to the macroscopic multiphase flow behavior is discussed.
Physical structures and properties of ice are discussed in relation to ice heat-storage technology. Ice polymorphs including Ices I, II, III, ..., IX, are mentioned, and varieties of ice growth modes in supercooled and other conditions are discussed. Physical properties of ice discussed include structures, mechanical, electrical, and thermal characteristics and others.
Unzen Volcano began to erupt in November 1990 after 198 years of dormancy and has remained active. Continuous growth of a lava dome and falls of lava rocks have resulted in frequent pyroclastic flows. Since a great volume of volcanic material has been deposited and scattered by the pyroclastic flows, debris flows have frequently occurred along the rivers around Mount Unzen, particularly along the Mizunashi River. On June 30, 1991, August 8, 1992, and April 28, 1993, large debris flows occurred in the Mizunashi River and caused severe damage in the down reach. Over a hundred houses were destroyed by each debris flow, however, no one was killed or injured as the debris flows flooded within the evacuated area. On June 3, 1991, however, 43 lives were lost as a result of a large pyroclastic flow. On June 8 and September 15, 1991, larger pyroclastic flows occurred and burned many houses along the Mizunashi River. As Unzen Volcano is still active, the possibilities of debris flows and corresponding risk to residents have risen up at the wider areas in addition to the risk of pyroclastic flows themselves.
The understanding of two-phase flow is one of the important problems for both design and safety analyses of various engineering systems. For example, the flow conditions in beer fermentation tanks have an influence on the quality of production and productivity of a tank. Numerical calculation is a powerful tool for the understanding of flow conditions because it can be easily carried out under various calculation conditions. In this study, a two-dimensional numerical calculation code based on the one-pressure two-fluid model is developed to understand the circulation structure of low quality liquid-gas two-phase flows induced by bubble plume in a tank. The simplified basic equations composed of mass and momentum balance equations for both liquid and gas phases are formulated by assuming a constant temperature and fixed liquid surface. The semi-implicit method and staggered mesh are adopted to obtain difference equations. The flow conditions are calculated by solving a matrix equation of pressure combining the time and space difference equations for all calculation cells. The developed code is evaluated by two sample calculations of rather simple flows inside tanks with different geometries.
Numerical solutions based on the two-fluid model are likely to be unstable due to its ill-posedness. The first-order upwind scheme is usually adopted for the convection terms for stabilization while high-order upwind schemes are seldom used. In this study, the applicability of high-order upwind schemes was examined by analyzing the amplification factor of finite difference equations for a single linear model equation of the two-fluid model. The numerical stability of various schemes was systematically clarified by making use of a concept of mapping in a complex plane. It was confirmed that high-order upwind schemes tend to yield unstable numerical solutions. It was also demonstrated that the inclusion of an explicit diffusion term into the basic equation can remove the numerical instability.
A two-phase flow experiment was conducted using a 200mm diameter, 100m long straight pipe with adjustable gradient. A steel pipe with transparent plastic parts was used. Superficial water and air velocities were from 0 to 1.5m/s and 0 to 10m/s. Pipe gradients were horizontal, 0.2%up, 0.8%up and 0.5%down. Test results were as follows, 1. 0bserved flow pattern in horizontal and inclined pipe was almost the same as that of the preceding 300mm pipe experiment. Flow pattern is extremely sensitive to pipe gradient. 2. Intermittent flow pressure loss was relatively low by comparison with that reported in the literature on the matter. Its pressure loss was between the mixed flow model pressure loss and the separated flow model pressure loss. An empirical formula of pressure loss was obtained. 3. Void fraction of intermittent flow was also relatively low compared with other reports. It was concluded that low up-gradient did not affect the void fraction but down-gradient did. An empirical formula of void fraction was obtained. 4. Up-gradient flow showed an air lift effect which was consistent with the void fraction.