I Scientific Objectives



Fluid Dynamics in Microgravity

Introduction

A common area of study in microgravity deals with unhindered capillarity. In the presence of gravity, fluid in a tube will rise to a specific height based on the contact angle, surface tension, and diameter of apparatus (Giancoli 1998, p. 296.). In microgravity, capillary tubes can be used to pump liquids the entire length of the tube (Stange, et al. 2003, Siegel 1961, NASA CAPL-2, 2004, ZARM 2004). In April of 2005 (Tualatin High School Physics, 2005), a group of students used capillarity with water to eject droplets into the air with limited results due to the wetting characteristics of water and glass. Therefore, we intend to use silicone fluids and small geometries to obtain more consistent results. We propose to use this capillarity to investigate three different fluid experiments dealing with liquid dynamics in microgravity, related to creating droplets in microgravity. The three experiments will deal with capillary rise in a tapered tube, capillary flow through a tube with a constriction, and splitting droplets that have already left a tube.

With a tapered tube, our first experiment, we expect the velocity of the flow to increase due to the restricted area, like a garden hose with a thumb over the end. Inertia may hinder this example of capillary action depending on the tube’s immersion depth as a greater force would be required to overcome the force of attraction between the tube and the fluid. It is our hypothesis for this experiment that the angle at which the tube tapers will cause the liquid to rise at a greater rate.

Regarding a restricted tube, like the hourglass shape, we are expecting the velocity of the liquid to increase as it approaches the point of restriction. At the point of greatest restriction, we hypothesize that the velocity will be great enough to propel a droplet into the air within the tube above the constriction.

For the standard capillary tube attempting to send a drop into a collision with a razor blade we hypothesize that the droplet that is rising out of the tube will have enough force due to its velocity to cut itself in half by the razor blade that is fixed some distance above the tube.

Our intent is to use the non-volatile fluid 3M Fluorinert Dielekrica (FC-77). The results of the ZARM experiment (Stange et al., 2003 ) show that this fluid will rise to heights of 80mm to 100mm for tube diameters of 11mm within the 2.2-second window that we have in the DIME drop tower.

We will be constructing our experiment out of clear polycarbonate plastic. It will be divide into three separate compartments with three different experiments, one in each compartment. In the bottom of each compartment they will each have their own reservoir for silicon solution. We will use the provided video camera and a backlight inside the experiment apparatus to view the results of our experiment. Experiments will be mounted on clear plastic so that they can be easily placed in their compartments, and the tubes will be easily accessible for the cleaning and the preparation of the experiment.

The purpose of this experiment is to examine the dynamics of fluids in microgravity. A benefit from this experiment would be to increase our understanding of the dynamics of fluids. Perhaps airborne droplets can be used as a form of fluid transport for packaging small amounts of liquid, or for combustion.

Method

Our apparatus consisted of three ¼ inch thick acrylic tubes with an inner diameter of 2 inches solvent welded to a 3/8 - inch base. Our test tubes consisted of an outer diameter of 2.25 in, an inner diameter of 2.0 in. and a height of 1.3 in. to contain the liquid within the pinning edge. Our apparatus is composed of a Plexiglas container with a removable lid that holds a 3/8 in. thick Plexiglas base with three separate Plexiglas cylindrical tubes, which were solvent welded to the base. Each tube will have a wetting barrier with a pinning edge approximately 1.3 in. wide and deep, each containing about 50 cc of silicone fluid. We immersed the various tube designs in the silicone fluid to about 1.3 in. The inner tubes are attached to a back plate with rubber bands. The back plate is attached to the lid that fits onto the outer tubes, which are held tight with the outer lid that is screwed down. We had three tube designs per drop (one in each chamber) in order to test a variety of theories for a fluid dynamics in microgravity, including a variety of tapered tubes, some restricted tube in an “hour glass” shape, some tubes with bubbles in the middle, some with slits on the sides, and some with a small slit on the top of the tubes.

We set up the capillary tube designs inside the plastic container filled with the designated amount of fluid (using the fixed levels and submersions). After double-checking everything to be secure before the drop, the apparatus was dropped and the provided camera captured the movement of the liquids in (and out) of the capillary tubes.

The rugged design of the apparatus will allow it to survive the drop and be used multiple times. The use of elastics to hold the tubes in place makes them easy to mount and remount while still being strong. The elastics made it so that we were able to create more experiments without having to separately glue each one to a lid. This gave us the ability to make changes and additions to our experiment on site, which was very helpful.

In order to test the durability of the drop apparatus we took extra care in its design to ensure its stability. Before the actual drop, we checked each component of the apparatus to make sure it did what was needed and survive the drop in order to be used multiple times, as well as to ensure the stability of each tube and the precision of each experiment.

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Data

Drop 1: Bubbles

First tube: Medium size tube with one bulge in the middle. The fluid rose up around the side and almost created an air bubble but the tube was to large so the fluid just leveled out before The fluid rose much higher on the right side than the left after it passed the bulge, but that can be attributed to the fact that the bulge is not a perfect circle.

Tube 2: Large size tube with a not as drastic bulge. The fluid rose up the right side of the bulge and after it passed the bulge leveled out.

Tube 3: Medium sized tube with two bulges. As the fluid passed by the first bulge it created an air bubble that lasted until it came to the top at the second bulge, and it looked like it may have created a second air bubble had there been time.

Drop 2

Tube 1: Medium size tapered tube. When the fluid passed above the lip of the tube it wasn’t small enough to create a droplet and instead the waterwetted the lip of the tube and began crawling down the tube.

Tube 2: Large size tube with a slit in the tube. It created a very small droplet on the right side of the tube looking in.

Tube 3: Large size tube slightly tapered. This one also had too large of an opening to create a droplet, and it wetted the upper lip and began to crawl back down the tube.

Drop 3

Unleash the crane before dropping the experiment. It works better that way

Drop 3B

Tube 1: Large tapered tube with a medium sized opening. The same thing happened as in the third tube in drop 2.

Tube 2: Large slightly less tapered tube with a medium sized opening. The tube was attached to the backing and the fluid, after spurting out and looking like it would do the same thing as tube one, wetted the backing and fluid crawled all over the backing.

Tube 3: basically the same looking as tube one. Look at the notes to find out fo sho. The same thing happened as in tube one

Drop 4

Tube 1: Medium size tube tapered to be quite small. There seems to be a small air bubble just as the fluid approaches the tapered part. Because of this, the fluid spits out two bubbles right away. The rest of the fluid doesn’t have enough momentum to form a droplet so it wets the rim and rides back down the tube until the end.

Tube 2: medium sized tube tapered to be really really small. It ejects a stream right away but then the stream turns into 3 droplets and starts to go back down (the last droplet looks like it might be caught by the tube on the way back down) but it doesn’t because the time is up.

Tube 3: medium sized tube tapered to be even smaller than tube two. Creates a stream that consolidates itself into about seven little droplets.

Drop 5

Tube 1: slightly hourglass shape with a medium size tube. As the fluid goes through the narrow part, the fluid climbs the sides very high and then evens out.

Tube 2: Medium size very hourglass tube more straight on the right side than on the left side. Before the fluid goes through the narrow part another little air bubble is there. This must be due to a mistake of some sort. When the fluid is going through the wider part of the tube it climbs really high on the right side.

IV Resource Credits

Bibliography

Stange, M., Dreyer, M. E., & Rath H. J. (2003). Capillary driven flow in circular cylindrical tubes. Physics of Fluids. 15(9) 2587-2601

Siegel, R. (1961). Transient Capillary Rise in Reduced and Zero Gravity Fields. Journal of Appl. Mech. 83 165-170

Tualatin High School Physics Research (2005). Creating Isolated Droplets in Microgravity, Retrieved November 8, 2005 from



ZARM Center of Applied Space Technology and Microgravity. (2004). Capillary Rise in Tubes. Retrieved October 5, 2004, from



NASA National Space and Aeronautics Administration. (1995). Capillary Pumped Loop-2 (CAPL-2). Retrieved October 7, 2004, from



Physics – Principles with Applications. Giancoli, D. (1998). Physics – Principles with Applications. (5th ed.). New Jersey: Prentice Hall.

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