The flow properties of several types of liquid passing through various sizes of micro-orifices were investigated in this paper. The jet thrust and pressure drops were measured for two polyethylene glycol solutions and four surfactant solutions. Different flow properties were found for the various surfactant solutions depending on the charge of the solute. For an anionic surfactant, the results were similar to those for water, whereas in the case of a cationic surfactant, both the jet thrust and pressure decreased greatly in comparison with the other test liquids. Finally, a nonionic surfactant exhibited a steep rise in the pressure drop at a particular value of the Reynolds number. In explaining this behavior, the liquid-solid interface and alignment of the surfactant molecules are considered, and consequently, it is strongly suggested that the elastic stress on elongational flows is a contributing factor. In addition, the decreases in pressure and thrust for polyethylene glycols are attributed to viscoelastic properties, regardless of the molecular weight of PEG.

Owing to the many potential industrial and biological applications of microfluid mechanics, it has recently become an attractive research topic. However, researchers have mainly concentrated on microchannel flows and studies investigating micro-orifice flows are rare cases. In the present study, the results from experiments conducted on flows through micro-orifices with diameters of 100 μm, 50 μm, and 25 μm are presented. In these experiments, the thrust and diameter of observed outflow jets are measured. The resultant thrust and diameter of the jets for the 100 μm orifice flow agree with the numerical predictions obtained via the Navier–Stokes equations. Conversely, for an orifice with a diameter of 50 μm or less, it is found that the thrust is lower than that predicted and the existence of jet swell becomes apparent. With the estimated elastic stress proportional to squared mean velocity, a change in the elasticity of the water as it flows through a micro-orifice is strongly suggested.

Micro fluid mechanics is one of interesting fields in modern fluid mechanics, because it is applied to physical, industrial, and biological research. In the present study, pressure drops were measured for some kinds of liquids passing through various micro orifices at low Reynolds numbers. It was found that the measured pressure drops almost agree with the prediction by Navier-Stokes equation for orifices smaller than or equal to 50 micron meters in diameter for water and glycerol aqueous solution, but they increase over the prediction for orifices of 100 and 200 micron meters in diameter. Dimensionless pressure drops appear not to be correlated with Reynolds number for some surfactant solutions.

Jet thrusts of several kinds of liquids issuing through small orifices were measured and compared with the predictions from numerical simulations of the Navier-Stokes equations. Reasonable agreements for so-called Newtonian fluids were obtained between the experimental and predicted thrusts for capillaries and orifices with openings of the order of 100 μm size, but the experimental thrusts were found to be below the predictions for orifices of the order of 10 μm. It was suggested that water and glycerol solutions have an elastic property for elongational flows passing through small orifices. As to surfactant aqueous solutions, cationic surfactant(BC) and non-ionic surfactant(AE (23)) provided thrusts lower than those of water, but anionic surfactant(LAS) showed almost the same thrusts as water. Also, lower thrusts were measured for dilute polymer aqueous solutions of PEO(18). A mean elastic stress for the tested liquids was evaluated by using the measured thrusts, and discussion was made on the idea that flows near the wall are affected by an interaction between anions on the surface of orifice and charged molecules of surfactants.

No abstract