(29c) A Rivulet Flow Model for Wetting Efficiency in Packed Beds

Packed towers are widely used in process industries in which a flowing gas needs to be brought into intimate contact with liquid flowing on the particles in the form films to perform unit operations such as distillation, absorption, water cooling and catalytic gas-liquid reactions. The liquid is introduced at the top of the packed bed and liquid trickles down over the particles in the form of rivulets. The width of rivulets increases with increase in liquid flow rate and eventually the liquid film spreads all over the surface of the particles.  However, it has been observed that liquid films may not cover the particle surface entirely for some operating conditions. Wetting efficiency, defined as the ratio of gas-liquid contact area to the particle surface area, can be less than one and it can adversely affect gas-liquid / liquid solid interfacial area and mass transfer coefficients. Understanding the fluid mechanics of rivulet flow on inclined and curved surfaces can be helpful in estimating wetting efficiency in packed beds. Based on simple experiments on rivulet flow on an inclined plane surface, a simple hydrodynamic model is developed relating width of the rivulet to flow rate. The concept is extended to obtain an equation for wetting efficiency in packed beds and it compares well with the literature data.