Effect of Orifice Surface Roughness on the Liquid Weeping in Bubble Columns

Abstract

Liquid weeping at the orifices of a gas distributor plate is one problem commonly encountered in bubble column operations. The effect of orifice surface roughness on the liquid weeping phenomenon in a bubble column is investigated over a superficial orifice gas velocity range of 143−703 cm/s. High-speed images of the bubbling and liquid weeping process are analyzed using a computer-aided image analysis algorithm. Pressure fluctuation in the plenum is also monitored. The liquid weeping rate is found to decrease with an increase in orifice surface roughness at low superficial orifice gas velocities while it increases with an increase in surface roughness at high superficial orifice gas velocities. Analysis indicates that the orifice surface roughness affects liquid weeping indirectly by changing the bubbling behaviors at the orifice. At low superficial orifice gas velocities, an increase in orifice surface roughness reduces the bubble size at bubble detachment. The reduction in pressure fluctuation in the plenum thus decreases the liquid weeping rate. On the other hand, as the superficial orifice gas velocity is approaching the bubbling/jetting regime transition, an increase in orifice surface roughness increases the transition velocity and hence the liquid weeping rate increases. Nonetheless, a modification of the orifice surface roughness is a viable solution to the liquid weeping problem in industrial bubble columns.

Experimental study and modeling of weeping rate in rectangular large‐scale valve trays

“…However, at a relatively high gas velocity of ~6.0 m s −1 , our experimental data are consistent with the experimental data of Banik and Zarei. The experimental results of Fasesan illustrate the consistency of weeping data at a high gas velocity, that is, for a gas hole velocity of 6.0–8.5 m s −1 , the data obtained by different researchers are basically consistent in terms of change trend.…”

“…Under the same vapor and liquid flow rates, the larger the weir height is, the larger the weeping flux is. This relationship is due to an increase in h w increasing the liquid height, which is the weeping's driving force . However, from Equation , the driving force of weeping is ( h co ‐ h cl ), and the effect of h w on this value is not evident.…”

Effects of Orifice Angle and Surface Roughness on the Bubbling-to-Jetting Regime Transition in a Bubble Column

“…The difference in the regime-transition velocity is expected to arise from the difference in frictional losses in the orifice. A rough orifice surface can give rise to higher frictional losses and reduce the instanteous orifice gas velocity . As a result, larger bubbles emerging at a lower bubbling frequency are formed at a rough orifice compared to a smooth orifice.…”

“…Few studies have taken into account the effects of the surface roughness of the orifice and the orifice angle on the regime transition. Both orifice surface roughness and orifice angle were found to have significant impacts on the liquid weeping rate in previous studies. , It is highly possible that the two parameters will also affect the bubbling/jetting regime transition.…”

“…Average roughness ( R a ) is defined as the arithmetic mean of the roughness of the surface measured on the length scale. The treatment of the orifice surfaces and the measurement of the surface roughness were reported in a separate study . Compressed air was used as the gas phase, whereas tap water was used as the liquid phase for all experiments.…”