Coolpack help

[marc5180]

I will have many questions to ask him next week about this.

Thanks for spending so much time trying to explain it to me, really appreciate it.

[SteinarN]

You'r welcome

[marc5180]

Hi, i went back to my tutor today and explained what you said about the line from the high stage evaporator having to be drawn vertically drawn and he disagrees totally.

He explained that it is a mixing process and not an expansion process as it leaves the EPR so the line cannot be vertical.

[SteinarN]

Hi, i went back to my tutor today and explained what you said about the line from the high stage evaporator having to be drawn vertically drawn and he disagrees totally.

He explained that it is a mixing process and not an expansion process as it leaves the EPR so the line cannot be vertical.

It is indeed an expansion process taking place in the EPR exactly similar to the expansion process in a TEV. The inlet and outlet pressure is different while the specific entalphy is the same. The specific enthalphy line is the vertical line in the log ph chart. Therefore a process line involving a change in some properties but where the entalphy is NOT changing cannot be any other than vertical.

The mixing process is the short horisontal line between the low pressure evaporator line right end coresponding to low side evaporator outlet and the lower end of the vertical line from the high side evaporator.

Where on this line the compressor line starts is determined on the relative mass flow between the high side evaporator and the low side evaporator. If the mass flow in the high side evaporator is much larger than the low side evaporator, then the compressor line should start to the right for A2, near the end point for the vertical line from the high side evaporator. If the opposite is true then the compressor line shall start where you have drawn it.

Your tutor defined the compressor suction to be -20C, therefore you have drawn it where you have and it is completely correct!

A small mass flow of say -8C gas from the EPR mix with a large flow of say -23C gas from the low side evaporator to give a mix of -20C gas entering the compressor.

Your tutor is wrong and should be educated by you in this case!

[SteinarN]

You should have three different points on the low pressure evaporator line to make the chart easier to interpret.

There should be one point, say at -23C indicating the gas leaving the low side evaporator. Another mark at -20C where the compressor line starts. You already have this mark, A2, specified by your tutor. The last mark is the low point of the vertical line from the high side evaporator, this point express the condition at the outlet of the EPR and is on the same pressure line as your low side evaporator. The vertical line from the high side evaporator is expressing the EPR in exactly same way as the vertical line at the left end of your chart is expressing the TEV.