Mass flow vs Pressure at Inlet for Water Flow

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MEETG posted this 22 May 2020

Heyy, 

Here I have problem.

In this flow of water is flow from inlet at 2.04 kg/s and at pressure 20Mpa. so I found this divergence error of temperature. what it is? and why is it causing? I go for 50 iteration.

the mesh is natural. I did not change it.

I want to know outlet pressure and mass flow rate. once in past I did same experiment with 0.34 kg/s and 1MPa flow rate. so I got weird result the dynamic and total pressure at outlet is 42Mpa. How? 

The inlet diameter is 25.4mm and both outlet is 1.5 mm. the flow rate is also sometimes give me positive value and sometime negative at outlet. once it gives me 7.058 l/min at each nozzle? Is it possible at 1MPa pressure?

So basically I want to know relation between mass flow rate and static pressure at inlet boundary condition? how I can get accurate pressure and mass flow rate ? 

 

Thank you.

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MEETG posted this 03 June 2020

can anyone help me?

abenhadj posted this 03 June 2020

provide more concise but structured information and update first to a supported version.

Best regards, Amine

MEETG posted this 05 June 2020

Heyy, abenhadj

thanks for reply.

but I did not get you what you mean by structured information? what do you want? 

and how can I update supported version?

I described my problem in detail all things earlier.

abenhadj posted this 05 June 2020

Are you using a student software?

I do  not understand the details you provided in your first post.

Best regards, Amine

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MEETG posted this 05 June 2020

 

Here I describe my problem in detail.

Here the water is flow from inlet to outlet as shown in this image.

suppose for inlet the diameter is 25.4mm while the outlet diameter is 1.5mm . Now my inlet mass flow rate is 0.34kg/sec and static pressure is 1Mpa as shown in first post.

I put that all things in boundary condition, so I get weird results mass flow rate at outlet is in negative and static pressure at outlet is atmospheric, but dynamic and total pressure is 42 Mpa.

How is it possible? what is wrong with it?

when I changed the value I got "divergence detected in AMG solver: temperature" and iteration stop to run. Why is it?

So my concern is If my inlet pressure and mass flow rate is fixed and I put that both in inlet boundary condition although I get weird results of both of them. why?

I want to know outlet pressure at tip as well as mass flow rate from outlet,also I want to know that pressure and mass flow rate divided equally or not.

hope you understand my concern.

Thanks.

MEETG posted this 3 weeks ago

Any one there for help with previous problem?

Kremella posted this 3 weeks ago

I'm assuming that you are solving an incompressible flow.

You cannot specify both mass flow rate as well as static pressure at the inlet. If you are specifying the mass flow rate, then you are fixing your velocity at the inlet. The other input is only the Initial Gauge Pressure (which is used only at the time of initialization). What boundary condition are you using at the outlet?

Also, are you seeing any reversed flow at the outlet?

Thanks.

Karthik

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MEETG posted this 3 weeks ago

Heyy, thanks karthik for response

I have gauge pressure and mass flow rate of water at inlet and I want to know the mass flow rate and pressure at both outlet as shown in fig.

I also want to know the velocity of fluid at outlet if possible.

So I put inlet boundary condition in terms of mass flow rate and outlet is pressure outlet, but I got an error while calculating iteration "error: Divergence is detected in AMG solver: temperature"

yes, the fluid is water. outlet is something like nozzle so I want to know about spray.

so where am I wrong, can you help me?

Thanks again.

Meet

rahkumar posted this 3 weeks ago

Hello, 

How are you calculating Cp value? 

Regards, Rahul

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MEETG posted this 3 weeks ago

Hello, Rahul

I take default value of Cp for water that is 4182 j/kg k ..

but does it matter?

thanks.

rwoolhou posted this 3 weeks ago

OK, density is fixed, so your inlet is 0.34kg/s    

Outlet pressure (both ports) will be something.  

If the mesh is OK, and that's both the cell quality and resolution this should solve nicely. You can then report the mass flow and velocity on the outlets. 

Why is the supersonic pressure 42MPa?  Venting to atmospheric pressure? Set that to zero and see how it behaves. 

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rahkumar posted this 3 weeks ago

Can you please try with piecewise-linear? 

Regards, Rahul

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MEETG posted this 3 weeks ago

Heyy, rwoolhou

yess my inlet mass flow rate is 0.34 kg/s and pressure is 1MPa and venting to atmospheric pressure.

but only once I got outlet pressure is 42 MPa andd mass flow rate negative ,after that all I get this divergence error. I cannot run calculation now.

my mesh is natural, I have not changed it.

I cannot run iterations anymore now due to this error.

how can I remove this error?

Thanks.

 

MEETG posted this 3 weeks ago

Heyy, rahul 

I still not get it. what is piece-wise linear?

Thanks

rahkumar posted this 2 weeks ago

Look into the dropdown option beside Cp. You will find the piecewise linear option. Also, what are the operating conditions? 

Regards, Rahul

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MEETG posted this 2 weeks ago

Heyy, Rahul

Thanks.

yes the error solved.

I take input gauge pressure 1MPa and pressure output is atmospheric pressure means gauge pressure.

I get integral static pressure at inlet : 14369291 (pa)(m2)

                                                 outlet & out2 : 0.17382078

mass flow rate at inlet : 0.34 kg/sec

                            outlet & out2 : -0.28304719 kg/sec

why is the negative value of mass flow rate?

why mass flow rate at outlets is greater than input?

Thanks.

                                                  

MEETG posted this 2 weeks ago

Hello, anyone can comment on previous results?

Kremella posted this 2 weeks ago

This means you are getting reversed flow at the outlet. That is why you have a negative mass flow rate at the outlet. Can you show us the individual values at outlets 1 and 2? Also, your inlet and outlet flow rates do not match. It is very likely that your solution is not converged.

Could you please show us your convergence residuals? Also, are you running this as a steady problem? Do you have any monitors set-up at the outlet (perhaps, average outlet velocity)?

Also, please calculate the area-weighted average of static pressure at inlet and outlet boundaries. They would give you a more physical result than an integral of pressure.

 

rahkumar posted this 2 weeks ago

Hello, 

Can you also tell us the solution methods you using? 

Regards, Rahul

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