Effects Of Surfactants On Hydrodynamic Characteristics In Pipe Flow Over Sudden Expansions/Contractions

The application of sudden expansion and sudden contraction is widely used in nuclear energy,petroleum,chemical industry,metallurgy and aviation.The paper,by setting up the experiment to study the influence rules of surfactant additive-CTAB on the hydraulic characteristics of the sudden expansion and sudden contraction pipe flow,tries to reveals the flow mechanism of CTAB solution flowing through the sudden expansion and sudden contraction,which can be applied to provide a reference for the reasonable design of the sudden expansion and sudden contraction pipe network drag reduction platform.The sudden expansion and sudden contraction pipe flow resistance text platform has been established based on fluid mechanics theory firstly.And then,through repeated water flow tests,the reliability of the experimental platform can be corroborated.Finally,with a water flow and a surfactant drag-reducing aqueous flow for the sudden expansions with two kinds of sudden expansion ratios and sudden contractions with two kinds of sudden contraction ratios flow fluids respectively,the change rule of pressure distribution,the recovery distances of the pressure,fully developed distances of the downstream flow and local loss coefficient for the sudden expansion and sudden contraction pipe flow was studied.According to the experimental results of the water flow,it is found that the pressure distribution of each position in the vicinity of the sudden expansions and sudden contractions is not changed with the Reynolds number,so is the recovery distance of the downstream pressure.Pressure distribution curves of the sudden expansions and sudden contractions raise with the increase of Reynolds,and local loss coefficient is consistent with the empirical value,which is a constant.The experimental results of CTAB solution show that the flow characteristics of the CTAB solution are related to the concentration and the critical Reynolds number.The addition of CTAB,greatly extends the fully developed distance of the downstream flow,makes the pressure distribution curve raise firstly and then decreases with the increase ofReynolds when the flow approach the critical Reynolds of the thinner pipe.Under each concentration,the recovery distance of the sudden expansion pressure is at a distance of 6D at the low Reynolds number,which is basically the same as the water flow after a certain Reynolds number.The variation of local resistance coefficient is influenced by the Reynolds number of upstream and downstream.For sudden expansions,the local resistance coefficient of CTAB solution flow is lower than the water flow and it presents drag reduction behavior in a low Reynolds number range,the maximum drag reduction rate is approximately 20%.Then,the flow exceeds the critical Reynolds number,local resistance coefficient is higher than water flow and it presents resistance increase behavior.Later on,the local resistance coefficient begins to reduce and achieves water flow level finally.For the sudden contractions,however,the local resistance coefficient of CTAB solution flow is opposite,it presents resistance increase behavior in a low Reynolds number range and drag reduction behavior in a high Reynolds number range,the maximum drag reduction rate is approximately 70%.And finally local resistance coefficient can achieve water flow level.