Quote:
Originally Posted by stevehull
Jeff - excellent You tube video. Thanks for posting . . .
In the current situation that Memphis has, a evaporator temperature of 65 F is far more than the typical situation where it might be 20-30 degrees less. I read the graph in the video and was surprised at the long lengths of cap tube (1/3 hp, R-22) for this temperature.
Was I reading this wrong?
I don't recall the total length of cap tube that Memphis started with.
The video makes a big point that disconnecting gauges causes a significant amount of refrigerant loss. I guess the best way to start is with a pressure at the high end of the specs, allow equilibration, make all your readings and then let out some gas and repeat.
Memphis has been doing this, but shortening the capillary length (less pressure drop) has me confused. Just taking out a few inches will make a big difference in latent heat?
Steve
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The real deal with capillary tubes, as has been stated previously, is that a small difference in diameter drives a huge change in pressure drop. As the charts depict, the mass flow at a certain delta t will get you in the right ballpark for diameter. A tiny cap tube cannot flow a large mass, no matter how short it is. A somewhat larger diameter cap tube than necessary would have to be super long to drop enough pressure.
Within the operation ballpark, the cap tube will find equilibrium with the compression ratio the compressor is working to supply. A cap tube is a fixed restriction, so as you go up in length, the resistance increases and less mass flows. This drives down your evaporator pressure with respect to discharge pressure. If you are trying to cryogenically freeze something, a long cap tube is your best bet. It might take a long time to get there, depending on how much insulation the cooler has.
With this rig, the opposite is true. The ground is massive and a much higher temperature. It has just now begun to have enough heat drawn from it to force a temperature drop. It has not been taxed enough yet to see a close approach between the exiting suction line and the borehole. Memphis has done this by driving less pressure drop with a shorter cap tube. He will soon either flood his evaporator or drop his discharge pressure too far. After all, the compressor has only so much displacement.
I have my fingers crossed, hoping he runs out of compressor before either hx reaches its limit.