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-   -   Propane expansion valve temperatures? (https://ecorenovator.org/forum/showthread.php?t=6591)

HugoW 03-09-18 03:10 PM

Propane expansion valve temperatures?
 
Hi,

as I am planning to make my own heat pump and I like to be in control of what I do, I am looking into the way the Expansion valve is controlled. I think I have figured out how to make an Arduino controlled valve, but I need to know values to test it. Looking at a convensional valve and the placement in the system:

http://theengineeringmindset.com/wp-...-animation.gif

I can see the capillary bulb or sensor 'steers' the throughput of the valve, based on the temperature between the outlet of the evaporator and the inlet of the pump / compressor. Is there a standard value / value range for specific refrigerants, and if so, which is it for propane / R290?

Thanks,

Hugo

jeff5may 03-12-18 10:46 PM

Yes there is. R290 is a pure substance, so it exhibits a single boiling point/dew point at any given pressure. Many refrigerants are a blend, and exhibit glide.

Ok, pictures speak louder than words.

http://www.effectspecialist.com/imag...re-diagram.png

http://ecorenovator.org/forum/attach...to-r290_pt-gif

Zwerius 04-02-18 10:38 AM

Quote:

Originally Posted by jeff5may (Post 58785)
Yes there is. R290 is a pure substance, so it exhibits a single boiling point/dew point at any given pressure. Many refrigerants are a blend, and exhibit glide.

Ok, pictures speak louder than words.

.....

Should the pressure/temperature at the exit of the evaporator not be depending on the ambient (outside) temperature?

HugoW 04-05-18 06:58 AM

I don't think so. The medium should still be in gas state after the evaporator. With the mechanical valve, the sensing bulb is the same temperature as the medium line at that point, its mechanically joined. If the medium in the line is still a liquid after the evaporator, it will also be a liquid in the sensing bulb. With the medium in the sensing bulb giving less counter pressure to the valve spring, less medium will pass through the valve and this is how the system steers itself. My system will need both a temp and pressure sensor in that position and look up the values in a table.

Hugo

jeff5may 04-06-18 07:24 PM

You two are both correct.

Hugo says that only gaseous refrigerant should be leaving the evaporator. This is a hard rule. The metering device should never allow liquid refrigerant to find its way to the compressor. Liquid slugging is a leading cause of compressor burnout.

Zwerius said that the evaporator will follow outdoor temperature. To evaporate, the low side pressure must be low enough to allow the refrigerant to exist as a gas. What that means practically is the boiling point of the refrigerant has to be colder than the heat exchanger temperature. In an air hx, the boiling point must be a dozen or more degrees below the outdoor temperature, to insure at least a few degrees of superheat in the leaving refrigerant. In a water hx, the boiling point can be closer to the entering water temperature, because water has a lot more heat capacity than air.

HugoW 04-06-18 07:57 PM

Comes natural to us Dutch folks �� I am currently working on a prototype pump with two plate exchangers, one with coolant on the cold side running through a radiator type 'heater' block, the other one with water heating up a 200 liter oil drum. If it all works I will burry a long hose in the back yard to reheat the coolant and the hot part I am still considering some options.

Hugo


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