Stream content in a closed loop

[HenkF]

Hi all,
I'm simulating a heat pump loop. Setup : condensor, expander, evaporator and compressor, with at the evaporator side as the heat source, to be transported to the condensor to heat a water stream. The heatpump fluid is water/steam. Initially it ran quite well, but when switching evaporator and condensor outside streams (water <=> air) the inner closed loop also changed from water/steam to air content. I tried to fix this (clearing all stream content), however no success. Could anyone give me a clue on how to change the closed loop to keep the intended water/steam content? Please find the flowsheet attached.

Thanks, Henk

[jasper]

If there is not supposed to be any air in the inner loop I suggest you set up a different material type that contains only water (and the steam tables would be the most reliable thermodynamics in this case). Model the loop with stream objects that use your dedicated material type.

If some air is to be present in this loop you have to find a way to fix the composition. One option could be inserting a custom unit operation (e.g. excel, matlab, scilab, home brewn) that copies feed flow rate to product, but sets the product composition to the desired one. As there is no other unit in the loop affecting composition, this will converge such that the feed stream of this unit will have the same flowrate and composition. You can optionally control the flow rate as well from this unit.

[nrgeng]

I really like your flow diagram with the color accent to show heat source and sink. Great idea!

In trying to understand your problem, do you want to use water/steam in inner Loop 1-2-3-4, and air in the outer loops, Loop 21-22 and Loop 31-32? If so, I may be able to help because I have run a similar simulation. Let me know where you stand in solving the problem. Are you finished or do you still want/need help?

[HenkF]

Hi Jasper,
Regarding this question. You present a nice and clean solution. Great!
Thanks for your offer! This is just a trial, I'm still digging in the possibility of using heatpumps at our location. We do have a lot of waste heat available, which could be upgraded to process heat.
When I need a hand, I'm glad to contact you.
regards,
Henk