Science Buddies: "Ask an Expert"

Hi! My daughter has done a science project illustrating how coolant might circulate through an astronaut’s space suit.

We used a simple, hand powered, siphon pump to run blue colored water through clear tubing. With air bubbles in the tube, the concept illustrates nicely. We have an upside down "T" shaped stand we built. Holes are drilled in the wood in a staggered manner and the tubing is run through. In the back is the hand pump.

The problem comes when you connect the tubing from one end of the pump into the other. There is no air flow in to the line and the fluid won’t move. For the initial presentation we ran an open end of the tubing into a test tube... messy. Please see the attached illustration.

What piece of hardware could we add to introduce air into the line, cause the liquid to pump, and keep the system closed (and not spraying “coolant” all over the place)? Or is there something all together different that we could employ? Thanks!

This one is right up my alley. Before the advent of high speed computers and digital fluid flow models, I spent many hours working on engineering water tables studying the flow of liquids through many devices.

Your device is cleverly simple, but I think you might need to make it slightly more complex to operate as intended.

The first thing I would recommend is to replace the hand siphon pump with a simple aquarium pump, the type that pumps water, not air. Or even a small fountain pump would work. Draw the colored water from a small reservoir with the pump and drain the fluid back into that reservoir. This will establish the flow that you want.

Then to introduce air, which is a very good way to visualize the flow, use a hypodermic syringe filled with just air. Insert it into the tubing right after the pump outlet and just introduce a little air. This will just give a short burst for demonstration purposes, and will not be a continuous flow.

That should work.

Good luck, and have fun!