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Bones
01-12-2003, 12:19 PM
Hello, after much searching and helpful advice from you guys here i have found coolpack now all i need is some helpful advise if anyone would like to help me that would be much appreciated!

When i learnt (or tryed my best) to learn pressue enthalpy charts last year at TAFE (college) here is all the information required to plot a chart was

1. suction pressure as a temp (entering comp)
2. temp of refrigerant entering RMD
3. disscharge pressure as temp (leaving comp)
4. superheat

Now i know how to work the above information out fairly easily, but finding the information i need to enter into coolpack for it to produce my pressure enthalpy chart abit confusing... (plz i'm only started my 2nd year apprentice a few months ago... so go easy on me hehe!) and i end up with something looking horribly wrong.

could you please tell me what the following is refering to, or how to work out how you get the answer from the system your workng on, perhaps we refer to these as different terms... in which case i already know how to come up with the answer just that its duble dutch explaination hehe get it? anyway...

1. Dp Evaporator?
2. Dp Suction line?
3. Dp Disscharge line?
4. Subcooling
5. Dp condenser
6. Dp Liquid line

(just for a one stage system at this stage.)

Any help would be appreciated!
ICQ: 9700240

Andy
01-12-2003, 10:25 PM
Hi Bones:)
everything you list is delta pressure drop in various parts of the system. Generally the combination of these on either the low or the highside would not exceed 2 to 3 deg C
so you could say that the Ddp tru the evaporator and the suction line would be 3 deg C (pressure drop changed to temperature, to leave the same design parameters for each type of refrigerant) and the discharge, condenser and liquid line would be a further 3 deg C.
Subcooling is a refrigerant state. If you remove energy from a liquid after it has passed it's saturation point, the liquid becomes subcooled.
Example liquid leaving you condenser will be at a lower temp than the pressure read of you head gauge fitted at this point, this is your subcooling.
Hope this helps, Regards. Andy.:)

Bones
02-12-2003, 06:18 AM
I remember reading and doing some calc's on pressure drop's through systems mid last year. But it was more related to pressure drops through elbows and bends etc in relation to pipe length...

something along the lines of a 2 metre pipe run with say 4 elbows has the same pressure drop as a straight piece of say 4 metres.

i will scour my notes again and text books again, but thanks for pointing me in the right direction andy!

so to get my presssure drop through evap (on fridge units) if i hook my low side guage to the access fitting on the coil and to the ssv at comp inlet (i know this will also include pressure drop though the suction line back...) but it would give me a rough indication though hey?

Andy
02-12-2003, 08:30 AM
Hi Bones:)
by hooking your gauges up as you stated you will be measuring the suction line dp but not the evaporator pressure drop. This can usually be for in manufacturers data, it can be measured, but this requires a little bit of investigation to find out where the injected liquid stops expanding and where evaporation starts.
Kind Regards. Andy:)

Bones
02-12-2003, 09:18 AM
so i need to solder a shreader valve at the start of my coil and at the end of my coil hehe? for both my evaporator and condenser, although this would not be practical...

so i should be able to get this information from the manufacturer for their condensing units etc... i'll see what info i can get off heatcraft tomorrow.

thanks again andy