[Ali_91en]

Hey guys, I wanna simulate a heat exchanger with external and internal flows, the internal flow is water that it's properties depends on temerature. My problem is I can't write suitable expression for it, and before it, is it the correct way to write an expression for it? Or there is another way?
By the way my data has been attached, help me in writing expression please



IMG_20170501_160911.jpeg

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[Opaque]

Dynamic Viscosity = ( -4.E-10 [K^-5] * T^5 + \
7.E-07 [K^-4] * T^4 + \
5.E-04 [K^-3] * T^3 + \
.... ) * 1 [Pa s]

I assumed the chart is in SI units, adjust as needed.

[Ali_91en]

Originally Posted by Opaque

Dynamic Viscosity = ( -4.E-10 [K^-5] * T^5 + \
7.E-07 [K^-4] * T^4 + \
5.E-04 [K^-3] * T^3 + \
.... ) * 1 [Pa s]

I assumed the chart is in SI units, adjust as needed.

Tnx dude I'll test it

[evcelica]

Remember to include more sig figs if needed. I usually use the "text" option for the numbers in excel to show the most digits.

You can also import a table: save numbers as "text tab delimited"
Create a user function in CFX Pre and import that table.

[Ali_91en]

ok finally i found how to write an expression
but i have another problem when i start the run it gives me an error, after struggling with CFD-pre if found i forgot to initialize the domain, the solution started but it gives me another error, can someone help to find what the problem is?

the screenshot attached
https://ibb.co/eGhr6Q
https://ibb.co/d3A00k
https://ibb.co/dXiymQ
https://ibb.co/fiY9t5
https://ibb.co/bPhPRQ
https://ibb.co/dahf0k

[Opaque]

I would run the case as Isothermal first to see if it works at the expected temperature operating range; then, I would try a more complex setup.

[Ali_91en]

Originally Posted by Opaque

I would run the case as Isothermal first to see if it works at the expected temperature operating range; then, I would try a more complex setup.

i found the problem, it's cuz of high temp that make vis negative and it isnt physical

[Ali_91en]

hey
finally i fixed the expressions but when i set everything in material i found an warning that doesnt let solution converged.
the warning is this:

Table generation controls are not set for the following materials: 'Real Water'. Please ensure that the default pressure and temperature tabulation ranges are appropriate for your setup.

maybe anyone help

[evcelica]

Set the table range in your material properties for Real Water.