Investigation Of Outflow Through Orifices Of Trough-type Liquid Distributor

It is well known that the uniformity of liquid distribution is crucial for theseparation performance of packed columns. Therefore, liquid distributor is theimportant column internals of packed column. In this paper, outflow through orificesof trough-type liquid distributor is investigated by experiment and CFD simulation.Firstly, outflow through single orifice is researched by experiment. Theexperimental results show that the orifice coefficient decreases with increase of orificediameter while the wall thickness is same. The decreasing trend of orifice coefficientwith increase of orifice diameter is obvious when the diameter is small; however, thedecreasing trend is unobvious when the diameter is large especially the diametergreater than10mm. The orifice coefficient increases with increase of wall thicknesswhile the orifices have same diameter. According to different aspect ratio, the orificescan divided into thick wall orifices and thin wall orifices. The orifice coefficient oftwo kind orifices has different variation trend. The experimental results also show thatthe orifice coefficient of punched orifices is greater than it of bored orifices while thegeometric size of orifices and liquid height are same. The difference of orificecoefficient between punched orifices and bored orifices gradually decreases withincrease of orifice diameter. The above conclusions that are drawn by the experimentof the orifices located in side wall are also applied to the orifices located in bottombecause the location of orifices has little influence on outflow through orifices.Subsequently, outflow through single orifice is numerically investigated by CFDsimulation. The orifice coefficient of two orifices is calculated by the CFD models ofhigh turbulent Reynolds number and low turbulent Reynolds number. Geometric sizesof the two orifices are orifice diameter of4mm and wall thickness of2mm, orificediameter of8mm and wall thickness of2mm respectively. Calculation results showthat simulated orifice coefficient of the high turbulent Reynolds number CFD modelsis closer to experimental results, which means that the CFD models of high turbulentReynolds number are suitable to investigate outflow through orifices of relativelysmall diameter. On the contrary, the CFD models of low turbulent Reynolds numberare suitable to research outflow through orifices of large diameter because of theadvantages of this CFD models in predicting separated flow. Finally, the influence of flow characteristics in trough on outflow through orificesof trough-type liquid distributor is investigated by CFD simulation. In this paper, flowpast the flow region in front of orifices is firstly proposed to explain the reason whylateral flow in trough influence on outflow through orifices. The relationship betweenthe orifice coefficient and lateral velocity is researched and discussed based on flowpast the flow region in front of orifices. After the investigation for the influence oflateral flow on outflow through orifices, relationship between the orifice coefficientand vertical velocity of inlet is also researched. Characteristics of vertical flow andflow past the flow region in front of orifices are applied to explain the influence ofvertical flow on outflow through orifices. In order to improve outflowsnon-uniformity of trough-type liquid distributor, two strategies of optimized structureare proposed in this paper. The structure of trough-type liquid distributor is optimizedby increasing trough width and distance from orifice center to trough bottom, which isproved to improve liquid distribution performance by CFD simulation.