Experimental And Numerical Study Of Flow Field On Folded-Downward Edge Fixed Valve Tray

Folded-downward edge fixed valve tray (fixed valve tray) is a newlydeveloped tray with perfect performance. The flow field and distributionof local gas holdup are the main factors to determine the tray efficiency,therefore, it is very important to study the flow field and local gas holdupon fixed valve tray, and it is very useful for optimizing the tray andscaling-up its structure.The gas flow field and local gas holdup on fixed valve tray wereexperimentally studied in a 300mm×400mm rectangular PMMA(polymethylmethacrylate) column with plate spacing of 400mm. Theflow field of fixed valve tray was simulated by CFD, and the numericalsimulation results were compared with the experimental data.The flow field distribution of gas through the fixed valve wasstudied by hot-wire anemometer in different conditions. The experimentalresults showed that the gas pass through the side holes of the valve in thedirection of lean-up. The cross-section area of gas passing firstly increases and then decreases. In the centre of the four valves, themeasuring accuracy was decrease, because the flow field was verycomplicated as a result of the impaction of gas flow.The gas flow distribution was simulated by FLUENT6.2 based onthe Standard k-ε,RNG k-εand Realizable k-εmodels under the conditionthat the gas was passing through the fixed valve tray. The simulationresults were compared with the experimental results. It indicated that thesimulations with Realizable k-εmodel were in reasonable and inagreement with the experimental results.The time series of voltage signals of gas-liquid two-phase flow inthe fixed valve tray under different experimental conditions weremeasured by hot-wire anemometer. A wavelet multi-resolution analysismethod was used to characterize the signals and to identify the optimumtime-series data length. The main scale signals were determined by usingthe energy maxima criterion of wavelet analysis. Then, signalscorresponding to this scale were selected for an intermittent behavioranalysis. Consequently, local gas holdup was statistically determined if aproper threshold value was chosen on the local intermittency measureprofile of the major scale detail signal. By measuring the local gas holdup,we obtained the variation rule of local gas holdup on the fixed valve trayunder different conditions. The results provided theoretical references forthe tray designing, optimizing and operating.