| With the rapid development of micro processing technology,equipment components more and more tend to miniaturization,such as cooling for microelectronic circuit of micro heat ex-changer,for lattice chip,bio genetic engineering for EIA detection portable reactor.There are some problems of gas-liquid two-phase flow in channels with diameters less than 1mm.In order to better promote the application of engineering design to achieve the purpose of control flow process,it leads to a comprehensive understanding of the refrigerant flow characteristics in microchannel.In view of this,it is necessary to understand the characteristics of two-phase flow,such as flow pattern,pressure drop and drag reduction.Although the larger diameter relative to channel research has found many theories such as flow mechanism of two-phase flow model and some related concepts,but their applicability to the microchannel also needs to be confirmed that the micro scale effects on the flow,heat transfer and mass transfer should be further explained,and at present there are few relevant reports.In this paper,the experimental study on the Y mixed microchannel is carried out by the means of an electron microscope equipped with a high frequency industrial camera.The channel section is 100μm×200μm.In the experiment the typical flow pattern and pressure signal were recorded,the flow maps were drawn after analysis,and put forward the flow pattern transition prediction model,And the pressure signal is used to study the pressure drop.The pressure drop prediction formula based on the separated flow model and the pressure drop prediction model based on the flow pattern are proposed respectively.When the drag reduction effect is studied,it is found that the addition of the polymer or change the wall hydrophilic can achieve the effect of flow drag reduction.In the study of flow patterns,three typical flow patterns are recorded: the slug flow,the annular flow,the stratified flow.The flow pattern is plotted and compared with the existing literatures.It is found that the channel size,the cross-sectional shape,the wetting property of the wall material and the mixing mode of the gas-liquid two phases all affect the flow pattern,and the prediction model was proposed based on the above factors.In the research and analysis of the pressure drop,the influence factors of the pressure drop are analyzed,including the superficial velocity,the surface tension and the channel size.Then use the homogeneous flow model and separated and contrasted to the experiment data flow model to predict the discovery phase model experiment more accurately,and based on the separated flow model proposed correction formula application and the conditions of thisexperiment,the prediction error is smaller.At last,based on the three typical flow regimes,the pressure drop is predicted according to the different sources of flow resistance.In the analysis of the effect of drag reduction of the flow,using the existing literature analysis,validation of polymer molecules with TOMS effect,the polymer molecular chain have the ability to inhibit the emergence of resistance,and the flow resistance increases with increasing the concentration of polymer,under the experimental conditions the drag reduction effect increased.In addition,the surface wettability of the microchannel wall material was changed by the surfactant,and it was found that the pressure drop of the hydrophobic material was significantly smaller than that of the hydrophilic material. |
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