Two-Phase Flow In Rectangular Channel Research Articles

Flow regime transition criteria for vertical downward two-phase flow in rectangular channel

Narrow rectangular channels are employed in nuclear research reactors that use plate-type nuclear fuels, high heat-flux compact heat exchangers, and high-performance micro-electronics cooling systems. Two-phase flow in narrow rectangular channels is important, and it needs to be better understood because it is considerably different than that in round tubes. In this study, mechanistic models were developed for the flow regime transition criteria for various flow regimes in co-current air-water two-phase flow for vertical downward flow inside a narrow rectangular channel. The newly developed criteria were compared to a flow regime map of downward air-water two-phase flow inside a narrow rectangular channel with a 2.35-mm gap width under ambient temperature and pressure conditions. Overall, the proposed model showed good agreement with the experimental data.

Flow regime identification and classification based on void fraction and differential pressure of vertical two-phase flow in rectangular channel

Better understanding of two-phase flow in narrow rectangular channels is important because it is considerably different from that in round tubes. Two-phase flow in narrow rectangular channels is invariably employed in most of the research reactors that use plate-type nuclear fuels around the world, high-heat-flux compact heat exchangers, and high-performance micro-electronics. In this study, an objective attempt was made to identify and classify various flow regimes in co-current air–water two-phase flow for vertical upward and downward direction flow inside a narrow rectangular channel. The void fraction and differential pressure data of the flow were measured. Flow regimes were identified based on visual observation, mean void fraction, and differential pressure data. A high-speed camera was used to capture images, and the void fraction was measured and analyzed by the electrical impedance method. In addition, digital image analysis was conducted, and differential pressures were measured using differential pressure transducers. Four flow patterns were identified for the vertical upward flow, and seven flow patterns were identified for the vertical downward flow in a narrow rectangular channel.

One-dimensional drift-flux correlation for vertical upward two-phase flow in a large size rectangular channel

The study of two-phase flow in rectangular channels is of great importance due to their use in marine reactors, chemical reactors, test reactors, and neutron spallation sources. Due to the practical importance of the drift-flux correlation for two-phase flow analysis in industrial systems, distribution parameter and drift velocity have been studied for vertical upward two-phase flow in a large size rectangular channel. Due to the presence of liquid recirculation in the bubbly flow regime in large size rectangular channels, the distribution parameter, drift velocity, and flow regime transition criteria are different from those found in small or medium size rectangular channels. The use of hydraulic equivalent diameter as the characteristic length scale in channels with significant asymmetry and its effect on interfacial area concentration prediction are also discussed. Under these considerations a new drift-flux correlation has been developed for upward two-phase flow in large size rectangular channels. Comparison of the newly developed correlation with several datasets shows reasonable agreement.

902 様々な流路における沸騰二相流の乱流構造とボイド率分布の解析(GS-6 熱工学)

Analyses were carried out on turbulence structure and void fraction distribution in boiling two-phase flow for various channel geometries. Basic conservation equations of mass, mometum and energy and turbulence in boiling two-phase flow were solved couppled with basic equation of void fraction distribution. Turbulence source terms of two phase flow were considered and fully two-way coupling model between gas and liquid chases used. The results show that bubble number density and void fraction distributions in boiling two-phase flow in rectangular channel has sharp wall peak in the central region of the channel whereas it has flattened distribution near wall region which reasonably agree with experimental observation. It is indicated that multi-dimensional turbulence structure is quite important in predicting void fraction distribution in boiling two-phase flow.

Pressure Drop and Heat Transfer of Magnetohydrodynamic Annular Two-Phase Flow in Rectangular Channel

An annular two-phase flow model has been proposed to predict the pressure drop and heat transfer of magnetohydrodynamic (MHD) gas-liquid metal two-phase flow in a rectangular channel for the case of high void fraction. The model for a rectangular channel, in which the applied magnetic field is perpendicular to the short side of the channel cross-section, nearly predicts Inoue et al.’s experimental data on the MHD pressure drop. For fusion reactor conditions, the model shows calculated results that the MHD pressure drop for two-phase flow can be lowered to 10 percent of that of the single-phase liquid flow and the heat transfer coefficient can be increased by a factor of two or more over that of the single-phase liquid flow.