Study On Film Foam Flow Characteristics In A Straight Tube

Foam has been widely used as a mobility control agent for enhanced oil recovery and carbon dioxide geological storage,therefore the study on its rheology is especially important.This paper presents the research work on film foam flow characteristics in a vertical tube with Sodium Dodecy Benzene Sulfonate,Sodium Dodecyl Sulfonate and Triton X-100 as surfactant.The experimental apparatus is built to measure the surface tension of the above three surfactant solutions and their variation with concentration is studied.Then the flow characteristics and its influencing factors are investigated for the film foam flow in a vertical tube.Experimental results show that:(1)Flowing film foam shows a typical shear-thinning behavior.The apparent viscosity decreases rapidly with increasing shear rate and keeps almost unchanged at further shear rate increment.The foam made of above 90%of gas in quality,but the apparent viscosity is 0.050 Pa·s and 0.038 Pa·s,at shear rates 20s-1 and 50s-1 respectively,which is 50 times and 38 times of water.When the shear rate increases,the apparent viscosity tends to a fixed value,but its value is always greater than the apparent viscosity of water’ 0.001 Pa·s.(2)The concentration and foaming agent of surfactant solution have a significant effect on the apparent viscosity of the foam film liquid.The higher the surfactant concentration,the higher the apparent viscosity under the same shear rate for the film foam flow.In a tube of 5.9mm in diameter and 94cm in length,the apparent viscosities at the shear rate of 50s-1 are 0.021Pa·s,0.027Pa·s,0.034Pa·s and 0.038Pa·s under the surfactant concentrations of 3.2g/L,4.8g/L,6.4g/L and 14g/L respectively.Although they are close to each other at surface tension values,the foam generated under higher surfactant concentration has higher bubble numbers,which leads to higher foam apparent viscosity.On the other hand,surfactant type also shows important impact on the foam flwo behavoir.In the same shear rate of 30s-1,the apparent visocity for SDS foam is 0.10Pa·s,which is 0.05Pa·s higher than that of SDBS foam.(3)The type of foam inner phase also has great effect on foam flow behavoir in a vertical tube.The apparent viscosity for the foam with carbon dioxide as the inner phase has apparent viscosity of 0.10Pa·s at the shear rate of 15s-1,which is 0.04Pa·s lower than the air foam.The variation can be reasonalby contribtued to the water solubility of CO2.(4)The foam generated with the same surfactant solution shows different flow characteristics in tubes of different diameters.The apparent viscosity increases with the increase of diameter under the same shear rate.(5)Force balance is carried out for a certain set of data for film foam flow in a vertical tube.For a film foam flow with total pressure drop of 85OPa,the contribution of gravity,wall boundary layer flow and the surface tension are calculated as 11.05Pa,67.56Pa and 724.80Pa respectively.It can be concluded that,the pressure drop for a flowing film foam is mainly caused by the surface tension,while the contribution of boundary layer can not be ignored.The data analysis gives an error of 46.59Pa,which is not more than 6%of the total pressure drop.(6)Dimensionless analysis is carried out for film foam flow behavior in a verticle tube.The foam flow can be calculated by the fitting equation of AP=4.08(3μU/σ）0.45σ/r in the range of 0.01<μU/σ<0.06,and our results generally agree well with the data predicted by Bretherton model.Due to the fact that Bretherton theory is only valid in the region of less than 0.01.Our work can be expected to fill the blank for its application on foam flow in higher shear rate region.(7)Numerical studies are carried our for film foam flow in a verticle tube.The film foam is treated as a single phase non-Newtonian fluid,and the curve of the pressure along pipeline under different inlet velocities is numerically obtained through the software of FLUENT with the constitutive equation of power law fluid modeling.It is found the pressure drop increases rapidly with the increment of fluid velocity in the beginning stage,while its increment rate becomes slower and slower with further increase of flow velocity,showing obvious shear thinning behavior.Numerical results agree well with experimental ones,validateding the simulation and assumptions.(8)Error analysis is carried out on experimental data.The maximum relative error of surface tension is 1.25%,the maximum relative error of apparent viscosity is 4.41%,which are in a reasonable range.It is expected our research work can provide some theoretical guidance for film foam application in practice,and lay a good theoretical basis for further analysis of the rheological behavior of foam flow in porous media in the near future.