Day Two

Yep, there are a couple of catches in the system. First, today is really cold for this area. It is under 32 degrees Celsius. A cold wave, complete with thunderstorms. We watch a wall of water cross mountains and sheet across desert valleys. Lightning is seen from miles away. Yes, we were told we were coming to one of the hottest and driest places on Earth and I am in a long sleeve shirt under my rain jacket.

The weather is affecting our challenge. The plastic tubing we have is pretty stiff in this temperature. Yesterday, when it was warmer, the tubing was quite malleable. In this “cold”, our motorized pump isn’t strong enough to smush the plastic tubing sufficiently to squeeze the water through it. When we heat the tubing briefly over Mike B's fire, the system pumps the water just fine… it better be warm tomorrow!

We also needed to test to see if the pump was strong enough to force water through a long system of tubing. This is where things get fuzzy - my botany and ecology training don’t provide much insight. (I run into these types of situations regularly, so I have been taking physics-related courses on things like light, sound, electricity, magnetism, and astronomy for the past couple years in order to better understand how the world works. I still didn’t know how to think about this situation, though.)

Questions:
Does the length of tubing, thus the length of the water column, affect the amount of force needed to make the water circulate?
What matters more, the total volume of water in the loop or the length of the water column?
Is there a critical tube diameter for which water adhering to the tube will over take cohesion of water molecules, thus keeping the water from moving?
Does the system need “priming”? In other words, is an exceptional amount of force needed to start the water circulating, compared with the amount of force needed to maintain the system once it is started?
How many air bubbles are too many? How much air in the system is too much?

Unless someone just knows the answers to questions like these while we are doing the project, we have to experiment to find out. We dealt with question 1, which quickly lead to others...

We didn’t know if the pump could circulate water through a long length of tube, so we mocked up a long tube, about 10 m, and tried to completely fill it with water. With Kate at our side we turned the pump on. Nothing. The pump wheel went around, but the water didn’t move. There were lots of air bubbles, however. Some were quite large. Jonathan wondered if an airlock was preventing water movement. We took the connecting piece out of the loop. It was easy to suck water through the tube, but quite hard to get the water moving by blowing into the tube. Our pump was equivalent to blowing into the tube.

We refilled the tube, this time ensuring as few air spaces as possible by keeping the funnel feeding water into the tube constantly full and having one of us sucking on the other end of the tube. (Don’t ever put your mouth on something unless you are sure of what it is and where it’s been. In this case, we were using tubing we had washed. We were filling it will drinking water and food colouring, so we felt it was safe.) We basically flushed water through the tubing until the person sucking on the tube encountered no more air spaces. We also inspected the tubing, which was intentionally transparent, for air bubbles. We ended up with one air bubble about two centimetres long. Good enough. Having one relatively small air bubble allowed us to easily determine if water was moving through the system when the pump was on. Yes, indeed, with a full tube of water and a warm tube, the pump circulated water without issue. So we learned if we minimised the amount of air in the tube, our pump was forceful enough to pump water through a long tube (about 10 meters of tubing).

We then tested to see if tight coils restricted water circulation—they didn’t as long as flow was restricted. We also tested to see if the pump could pump water upwards against gravity. The water would, after all, have to travel against gravity at least a couple of feet as I am 6 feet tall before heading back down into the fridge. No problem.

As we ended up with a working system, we didn’t delve much farther into our questions or try to tease out the different components. There just wasn’t time.

With extra screwdriver batteries recharging, we went on to design the actual tubing system for the fridge and spacesuit. We ended up with a long series of copper tubing coils in the fridge, so the water would have lots of time to cool. We connected this by short sections of clear plastic tubing covered by a second plastic tube wrapped in aluminium foil to a set of zigzagging copper tubing designed to cool the astronaut’s body core - the trunk. We chose the core of the body because the extremities have a lot of surface area and thus release heat to the atmosphere quite quickly anyway. Plus, it is the body core that really needs to function effectively to keep the astronaut alive and well. If you take a look at how we positioned the zigzags, we avoided areas of fat and concentrated contact between lean parts of my body core and the cooling system. This should make the cooling system more efficient, because fat is a great insulator and that’s not what we want in this situation.

Also, if the fridge had been likely to produce freezing temperatures, we would have probably set the system up differently and cooled the core slowly by reducing the heat in the body extremities first. But since the fridge wasn’t working at all as a fridge at the end of day two, we weren’t particularly worried about shocking the astronaut’s system or causing hypothermia. Though Kathy, Iain, and Mike had a good vacuum seal and honest-to-goodness zeolite, no real cooling is taking place in the fridge.

(I was chosen as the astronaut to test the spacesuit and cooling apparatus merely because I fit into the spacesuit materials we were given. Who planned this? Thus, I am wondering if I should be slightly concerned about keeling over with heat stroke in Death Valley tomorrow. I am counting on K, I, and M to figure out something!)