Effects of Liquid Viscosity on Bubble Growth From Submerged Orifice Plates

Experimental investigation of bubble growth from orifice plates submerged in pools of viscous liquids has been carried out using high speed videography. Conflicting effects of viscosity on ebullience have been reported in the literature. These are addressed in the present study and their range of applicability has been identified. Furthermore, the effects of chamber volume on bubble dynamics in viscous media are examined. Orifice plates made of Acrylic glass (a hydrophilic surface) with varying orifice diameters from 0.813 mm to 1.500 mm, have been utilized. Additionally, bubble dynamics from a stainless steel capillary nozzle was captured and compared with that from orifice plates. The six different liquid pools were used, viz., pure distilled water, ethylene glycol, propylene glycol, and three different aqueous glycerol solutions. The aqueous glycerol solutions varied in viscosity from 48 cP to 128 cP. The flow rate was regulated such that the isolated bubble regime was encountered. For the smaller orifices, viscosity effects were present at all flow rates and the bubbles in water-glycerol solutions were much larger than those in pure water. However, for the larger orifice sizes, water-glycerol solutions produced bubbles that were larger than those in water only at high air flow rates. For larger orifice sizes, at low flow rates, there was no increase in bubble size in highly viscous water-glycerol solutions compared to pure water. In fact, with 1.5 mm diameter plate orifice, the bubbles for 128 cP water-glycerol solution were smaller than those in pure water at low air flow rates. When chamber effects were present, the bubbles in the more viscous medium differed in shape and size from those in pure water.