How can I simulate the internal heat exchanger in ORC
Simulate chemical processes using advanced thermodynamic models
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Hello, I don't know how to simulate the internal heat exchanger(Economizer) in the organic rankine cycle. Can I fixed both outlet temperature of the working fluid at the internal heat exchanger and let other parameter vary?and Can I input the UA of internal heat exchanger and let the temperature vary?(This simulation I use to validate some of the data) Becuase when I simulate it, It's occur the error. So I can't do the simulation like this schematic diagram (picture below).
Are there any tutorial videos for internal heat exchanger in DWSIM in general? Or could someone please walk me through this problem?
best regards
Hi Tanatip,
depending upon the type of organic fluid and its conditions after the expansion in turbine, if it is still superheated vapor, the economizer should cool it down to saturated vapor (eg vapor fraction 0.99999) so that the condenser will remove only the latent heat.
So in your simulation you could try to specify the UA and hot fluid outlet temperature as the saturation temperature at discharge pressure, or alternatively specify the removed heat until the outlet hot stream becomes saturated.
Hope this helps.
Luca
Thank you Luca.
But when I input the UA it's occur that the temperature didn't converge. I don't know what to do to solve this problems.
Guys, in v6.4.0 I've added a new calculation mode to the heat exchanger where you can specify the outlet vapor fraction of one of the outlet streams.
Hello, but why I already update it in this link(https://sourceforge.net/projects/dwsim/files/) and it still version6.3 when I start the DWSIM program. Please leave the link to download the version6.4 for me thanks.
Tanatip
Last edit: Tanatip 2021-01-18
Tanatip, see if the attachment could be of help in setting your model.
Luca
Luca, I already see your attachment and get your idea that use cooler and heater instead of the internal heat exchanger model. But the result show that it's still error somewhere I don't know why. Please see the attachment below
Tanatip
Hi Tanatip. I ran your V2 model and it works well.
See attached screenshot.
Luca
Aw last night it's still error. Thank you Luca but if I want to change the input of the heat exchanger(Superheater,Economizer,Condenser) to the UA of the heat exchanger (becuase of the large relative error with the data that I want to validate) and let the temperature of both working fluid vary. It show that, it's error. Please see this attachment(V3).
Hello Tanatip,
I checked your model v3 and I have the following comments on the Economizer (the internal heat exchanger COOLER+HEAT-02) and on the Condenser.
1) My first comment is about the specified pressure drops: in the COOLER you specified a DP of 0.9 bar and on the other side HEAT-02 0.03. Considering that the vapor on the turbine discharge flows on the COOLER's shell and the feed from the pumps's discharge inside tubes, I have the impression the two DPs should be exchanged (did you get them from a Supplier?).
2) In the COOLER you specified a value of removed heat 120.32 kW. After some iterations, I calculated that this corresponds to having an outlet vapor fraction of 0.8773 and a saturation temperature of 39.64'C: therefore you enter the condenser with a wet vapor, not saturated (ie vapor fraction 1 or 0.99999).
3) As a major comment on the condenser, the specified value for UA (6.8833 kW/m2K) seems too large for the duty.
In the attached excel file, I calculated the condenser for the inlet vapor conditions.
In Case 1, considering that condenser removes only the latent heat (so the stream 7 is saturated liquid at 39.64'C), you can see that the calculated UA is much lower than the specified. Even considering an inlet vapor fraction of 1 instead of 0.877, it gives much lower UA.
This means that the condenser works a double-zone exchanger, a first section as a condenser and the remaining as a condensate cooler. This is the Case 2 in the excel. As you can see, here the condenser behaves as a series of 2 exchangers, hence no meaning to specify a single UA, due to the large difference in U coefficients between condensing and subcooling section. However, using a fictious LMTD calculated from the terminal temperatures, I found that an approx UA value of 6.8883 is obtained at condenser outlet of 22.65'C.
So if you take your model, change the Condenser calculation type to 'Cold Fluid Outlet Temperature' and enter the Hot Fluid Outlet Temperature to 22.51'C (due to approximation in my calcs), you should have the model converge to an UA of 6.883.
I repeat that this represents only a mathematical solution, because the condenser will unlikely behave in this way.
In general if your model has to validate a Supplier's design, you should be well aware of the operating conditions your Supplier took into account in his design.
Hope this helps.
Luca
Hello, Luca
Thank you alot for the recommendation and comment. I very appreciate it. You're so kind. Let me check it first and I will response you as soon as I already done it.
Thanks
Tanatip