The plumbing

Finally have some progress to report.

The wine bottle and tacky tape set up was a great way to see the cooling effect in action. I didn't have any check valves or the like in the system so I had to have the pump running all the time. Regardless, it at least demonstrated the cool effect of stimulating evaporation by lower the pressure above the liquid.

Time to move on and get a bit better set up to use as a test bed for playing around with different combinations of working fluid and desiccant material. The simplest seemed to be 1/2" copper tubing and plumbing fittings. I made a few false starts with the valves. At first I tried the type that just just push on over the pipe ( no compression fittings to tighten down). They have an o-ring seal on the inside of each end of the valve and a locking mechanism that prevents the tube from pulling out once its inserted. The problem with these is that they don't prevent the pipe from rotating and so the whole structure had to be secured to a board to stop things moving around.

The second problem I encountered is it seems that for low gas pressures these things leak. With the benefit of hindsight I'm figuring that they rely on the viscosity of water to form the seal. With gas at low pressure the air outside the valve will be about 14.5 psi higher than on the inside and that is enough for the air to get in.

Second iteration was was some gate valves, again a plumbing fitting, that secured to the pipe using compression fittings. These fittings have a nylon washer with top and bottom surfaces that taper towards the edge ( called an 'olive') that compresses as a nut is tightened over them and both squeezes in on the pipe and creates a seal. The seal around the pipe was great but these valves leaked worse than the previous ones. from the design is seems that any grit that collects in them will prevent gate from closing and allow gas to be drawn down from outside through the thread that supports the valve handle.

Finally I went to out local gas appliance repair shop and got a couple of gas shut off valves (yellow handles below) and secured them with compression fittings from the last try and the result was much better. Not perfect. It is still leaking about 0.1 psi each 15 minutes or about 6 mBar each 15 minutes. This would be way too much for a real system. according to one paper I read a change of 20 mbar in the pressure during the absorption phase was enough to almost entirely eliminate the cooling effect. However, I think that the pressure sensor connection and the plug i was using for one of the open ports is most likely the culprit.Anyhow it will do for a test bed as I will just periodically evacuate it.

I added a couple of air compressor quick connects for the vacuum pump and here is the plumbing part of the test bed. The next step will be to make the evaporator and the vessel for holding the desiccant material.

The tap on the vertical shaft is for shutting off the vacuum line and the one on the horizontal pipe is to isolate the evaporator (to go on the left) and the desiccant material (Zeolite, silica gel or calcium chloride will be the different ones I'll try)