Investigation of surface tension driven flow in small capillaries

• Main Author: Li, Kunlin.
• Other Authors: Yang Chun, Charles
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/15408
• Institution: Nanyang Technological University

The surface tension driven flow is being investigated in this report. Mixtures of 4:1, 6:1 and 8:1 glycerin-Di water mixtures are the fluids used in this experiment. For the horizontal capillary tubes, 300µm, 500µm and 700µm diameters are chosen. The aim is to find out the different effects that the viscosity of the mixtures and capillary diameters have on the surface tension flow by using comparisons. A container with an outlet facing one opening of the horizontal capillary is used to create the reservoir effect. The other end is left open. A capillary holder is constructed to hold the capillary to the height of the reservoir outlet. And a CCD camera is used to capture the flowing motion of the fluid passing through the capillary. The recorded video is then analyzed using MB ruler program, the readings measured and taken down. Lucas-Washburn equation is modified for to find the displacement in open end capillary reservoir flow; the experimental data is then compared to that of the theoretical one through using Matlab. The results show that the experimental results and the theory fit closely together thus confirming the experimental data is accurate. The volume of the fluid is not fixed and allowed to flow to the maximum displacement of 10cm in the capillary tube, the time taken to complete the flow is observed for that of different diameter, then of different viscosity. Key findings show that lower viscosity fluid flows faster in the same capillary tube and reach the end in a shorter time. The larger capillary diameter also allows more fluid to pass through causing the fluid to flow faster. Furthermore, viscosity and density properties of nano-fluids are measured. The viscosity is measured with the stress-controlled rheometer. Different nano-fluid ratios of 4:1 to 8:1 with 1% and 5% particles are used to compare the viscosity against the shearing rate in the graphs. Findings show that the nano-particles are able to affect the fluids causing the viscosity to increase overall. In addition, for a single liquid capillary flow, dimensionless Pi groups are derived using the similarity analysis. It is demonstrated that using the derived Pi groups, the experimental data for the displacement of Glycerin-Di Water mixtures of viscosities Gly 6:1 and Gly 8:1 ratio in 700µm capillaries and ratio of 4:1 in diameters ,300µm and 500µm can collapse into one curve that is consistent with the Washburn equation.