“Bring It Back” Microgravity Kit by Prashant Rao & Subra Sankaran
Prashant Rao, Ph.D., Principal Engineer, Barrios/Jacobs/
Subra Sankaran, Ph.D., Senior Thermal Specialist, MEIT/Jacobs/ESC
at NASA JSC, 2224 Bay Area Blvd, Houston TX 77058
Three experiments are described here (with suggestions for additional experiments) that use molten wax in different setups to demonstrate important principles of science and engineering. They can be performed using substantially the same equipment, making the kit quite versatile. The experiments demonstrate the dominance of surface tension and wetting effects in the absence of gravity, the lack of buoyancy and its implications, all frozen in wax. Other science concepts related to these experiments are simulated boiling, two-phase fluid flow behavior in micro-gravity, fluid flow and bubble movements induced by temperature gradients, diffusion, melting and freezing in the absence of buoyancy and natural convection, wake flow, and so on.
For these experiment you will need a small airtight container four to five milliliters in volume. Ideally it should not have a very thick wall because we are going to heat the contents with an external heater and we want to heat it up fast but the walls should be thick enough to withstand the increase in pressure due to heating and due to the expansion of the wax when it melts (about 10%). You will need to experiment with different containers or make one with acrylic sheet. We like a container with internal dimensions of 2 cm x 2 cm x 1 cm. This is pretty small but we need to heat and cool the contents fairly rapidly. Instructions for making boxes using acrylic sheets are available on the internet. The acrylic sheets used for a box of this size should be about 0.08″ (1/8 in) thick. The pressure load when the box is heated will be as much as a 1.1 kg (2.4 lb) weight on the 2 cm x 2 cm face.