How do I create a contained coolant flow model for a school science project?

You need to find a way to build in a “reservoir” with an air inlet to allow air flow. A flask like container with a rubber cork you can get a a science surplus store for cheap. One tube goes to the bottom to draw up the liquid in the flask the other comes back and should stay above the fill level to return the liquid to the flask. A plastic bladder could work also and maybe even eliminate the need for an air inlet as it could expand and contract with the pump cycle.

Similar to what @Cruiser said. Obviously, you’re trying to use a simpler (cheaper) type of hand pump for the science project / demonstration than would work in a space suit (since there’s no use for a siphon pump in space, no effective gravity and no air gap) so you need to fudge your closed system to introduce the system components necessary for a siphon pump to work.

The alternative is to use a closed system (such as would actually be used) and a more expensive pump. Perhaps you can devise a way to close the system and use a non-commercial / homemade pump to accomplish your aim and to more realistically portray the system as it would be used.

@WasCy I am thinking a simple hand bulb type pump with a one way valve tubed into a bag type reservoir like you see for IV’s would work very well. Wanna get fancy a small fish tank pump would simulate the on-board pumps they do use.

Here is a simple illustration of what we made:

http://www.box.net/shared/nyzmdbt5au

All you are missing is a tube off the out flow of the bulb siphon pump back into the test tube.

We are trying to close it off. Three reasons… If she isn’t careful, the test tube will leak. If another student starts to play with it… it blasts fluid all over the place. Lastly… to make it easier for my daughter to use. More talking and less having to watch how hard she squeezes.