Flow In Minichannels Research Articles

ADIABATIC GAS–LIQUID FLOW IN MICROCHANNELS

This article presents a review of adiabatic two-phase flow in minichannels and microchannels. Differences between them are identified and explained based on this review and our own research. Several channels of decreasing diameter were used in our experiments to determine the effect of the channel size on the two-phase flow of nitrogen gas and water. The effect of channel geometry was examined by characterizing the two-phase flow in a circular and square microchannel of similar size. Only slug flow was observed in the microchannels. Four new sub-classes of slug flow were subsequently defined. A new correlation was developed for the time-averaged void fraction data in the microchannels. The two-phase pressure drop in microchannels was predicted by treating the two phases as being separate with a large velocity difference. Regarding the effect of microchannel geometry, the transition boundaries on the two-phase flow regime maps were shifted for the slug flow subcategories.

細管における垂直上昇気液二相流の伝熱・流動特性(沸騰,熱工学部門一般講演)

Void fraction, frictional pressure loss and heat transfer coefficient were measured for vertical upward heated air-water two-phase flow in a 1.03mm I.D. stainless steel tube to investigate heat transfer and flow characteristics of two-phase flow in minichannel. Flow regimes were observed using high speed video camera. Void fraction was correlated with drift flux model better than Smith's correlation when α>0.7, but did not agree with both correlations when α<0.7. Frictional pressure losses agreed with Chisolm-Laird's equation at relatively large liquid Reynolds number. At low liquid Reynolds number, experimental results were close to Mishima-Hibiki's modified Chisolm-Laird's equation. Pressure loss was affected by flow regime at low liquid Reynolds number. Heat transfer coefficient fairly agreed with the results of ordinary inner diameter tube except for low liquid velocities.

Friction factor and heat transfer coefficient of R134a liquid flow in mini-channels

This article presents an experimental study of friction factor and heat transfer coefficient for a vertical liquid up-flow of R134a. A flat aluminium multiport extruded tube composed of 11 parallel rectangular channels ( 3.28 mm×1.47 mm) with hydraulic diameter of 2.01 mm was used. Mass flux ranges from 28 to 800 kg m −2 s −1 and heat flux from 0.84 to 22 kW m −2. Working pressure is around 2000 kPa and inlet subcooling around 70 K. The results were compared with those found in the literature for conventional tubes and mini-channels, and discussed.

Two-Phase Flow Patterns, Pressure Drop, and Heat Transfer during Boiling in Minichannel Flow Passages of Compact Evaporators

The small hydraulic diameters employed during flow boiling in compact evaporator passages are becoming more important in diverse applications including electronics cooling and fuel cell evaporators. The high pressure drop characteristics of these passages are particularly important as they alter the flow and heat transfer, especially in parallel multichannel configurations. The pressure drop oscillations often introduce dryout in some passages while their neighboring passages operate under single-phase mode. This article presents a comprehensive review of literature on evaporation in small-diameter passages along with some results obtained by the author for water evaporating in 1-mm-hydraulic-diameter multichannel passages. Critical heat flux is not covered in this article due to space constraints.

Porous medium model for two-phase flow in mini channels with applications to micro heat pipes

In this paper the porous medium concept is adopted to build up a fundamental model for two-phase flows inside mini channels. The capillary force which appears important for those problems is rigorously included in the model by following the same treatment as for porous media. Various applications of the developed model are demonstrated, among which are adiabatic co- and counter-current flows and heated forced and natural convective flows. Some fundamental results such as the two-phase pressure drop in a downflow, the flooding limit in a counter-current flow and dryout heat flux in natural convection boiling, are achieved and compared with previous studies available in the literature. With the main emphasis on the application to micro heat pipes, the model is used to predict the capillary limit of an operating micro heat pipe, to explain the liquid holdup phenomenon and to imply the onset and origin of the plug flow pattern. Future research needs are pointed out to refine this first version of a two-phase model and to apply it to additional practical applications.