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Just wondering

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Technician1002 » Fri Jun 19, 2009 9:58 am

THUNDERLORD wrote:I thought the compressor increases the pressure so right as the gas is exiting (maybe end of push(?)) it has the pressure needed to become liquid despite it's temperature???

Thanks Tech, this helps me visualize it better.
I'll check it out more tommorrow.
I have some capillary size copper and a copper (expansion chamber?) looking part on it. Was thinking of connecting bike filler to test temperature change today. 8)

Thunderlord, If this helps, take a look at the temperatures in the system while it is running. The hottest spot is the exit from the compressor. No liquid here. The first turn or so in the coil is also hotter, no liquid here either. It cools down here to the saturated vapor temperature (condensation starts). From there all the rest of the coil is the same temperature as the gas gives up latent heat and condenses. The last turn or two of the coil then are cooler as the liquid cools further (no more condensation). This prevents bubbles in the expansion valve or capillary tube entrance. Bubbles reduce system capacity as gas instead of liquid enters the evaporator.

On the evaporator, the same thing happens. Liquid sprays into the evaporator, but liquid does not expand, so cooling is only from boiling and expansion of boiled vapor. The entire evaporator is the same temperature after the coldest spot near the expansion valve or capillary tube. After the initial blast, the remaining liquid blows through the evaporator and boils off as it travels. Near the end all the liquid has boiled and the vapor is able to heat up some. The is called "Superheat" and just like superheated steam, it has no liquid in it. It is dry.

This is why the suction line to the compressor is warmer than the evaporator.

In charging a system, Too much freon floods the evaporator and there is too little Superheat and floods the condenser so there is little space for condensation. Symptoms are Frost at the compressor and only a small portion of the evaporator is hot, but it's very hot. The flooded with liquid portion doesn't condense and give up heat from condensation, thus it's cooler.

Undercharged, has no area left to cool liquid in the condenser so the expansion valve gets a large amount of vapor. Both of the above conditions reduce system capacity and efficiency.

I hope this helps. Sorry it's refrigeration 101 instead of spudding stuff. This stuff applies to boiling propane for those wishing to get high volume high pressure vapor delivery.
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Unread postAuthor: jimmy101 » Fri Jun 19, 2009 11:34 am

Knotz wrote:it says on the box its pumps 15 gallons/1.5 secs

Are you sure that's what it says?

I doubt the pump will generate more than one PSI pressure (that would all it needs to push air to a depth of two feet) but 15 gallons in 1.5 seconds (10gal/sec) is moving quite a bit of air.
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Unread postAuthor: THUNDERLORD » Fri Jun 19, 2009 12:42 pm

@jimmy101: I suspected they meant it would provide air bubbles adequate for that much water myself.

@tech: still no time to check on HVAC mechanics right now. :( 8)
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