NH3 2 stage cycle question

[Kristof Papp]

Never mind this question, it was due to i couldn't get a proper NH3 logP-h diagram, but found out in coolpack i can get one which shows from 0.1 bar

Hello,
I'm studying about 2 stage cycle with NH3 refrigerant, and i don't understand some vital part about the whole thing.

I was told, that in an ice cream factory cooling tunnel there is like -40C, and to achieve that, they do the NH3 evaporation at around -45C , 0.4 bar , and the condensation is at around 40C , 10bar . ( between the 2 compressors, there is -10C and 2 bar)

But i checked the NH3 logP-h diagram (http://docplayer.se/docs-images/56/39560811/images/93-0.jpg) ,or the diagram in CoolPack program and found that it doesn't even show the 0.4 , -45 bar part, like its on the edge of the diagram and those values are rarely used.

So maybe I'm understanding something wrong, and the evaporation isn't at isobar P=0.4 bar, isoterm -45C , or why is the diagram usually always show the part above 0.5 bar?

Thanks for the answers!

[mbc]

Hi
We have gage pressure and absolute pressure

[Sandro Baptista]

Never mind this question, it was due to i couldn't get a proper NH3 logP-h diagram, but found out in coolpack i can get one which shows from 0.1 bar

Hello,
I'm studying about 2 stage cycle with NH3 refrigerant, and i don't understand some vital part about the whole thing.

I was told, that in an ice cream factory cooling tunnel there is like -40C, and to achieve that, they do the NH3 evaporation at around -45C , 0.4 bar , and the condensation is at around 40C , 10bar . ( between the 2 compressors, there is -10C and 2 bar)

But i checked the NH3 logP-h diagram (http://docplayer.se/docs-images/56/39560811/images/93-0.jpg) ,or the diagram in CoolPack program and found that it doesn't even show the 0.4 , -45 bar part, like its on the edge of the diagram and those values are rarely used.

So maybe I'm understanding something wrong, and the evaporation isn't at isobar P=0.4 bar, isoterm -45C , or why is the diagram usually always show the part above 0.5 bar?

Thanks for the answers!

If you must be carefully and take on account that on the P-h diagram and also is many tables you deal with absolute pressure. On the compressores gauges you have relative pressure (on the relative pressure the values you read are about 1 bar less...1 bar it's the atmospheric pressure).

Also you said on the post +40ºC condensing temperature (suppose you refer the saturation temperature) and you talk about 10 bar for ammonia...but that is wrong. +40ºC with R717 correspond to 14,6bar(g) or 15,6 bar(a).