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modeling a reactor with heat exchange [syngas]

May 24, 2016, 5:47 pm
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Hello,

Actually I am doing a university project where we need to modelize a reactor for the reaction of syngas and our teacher asked if we could make three different levels of complexity

• First of all, a concentric reactor where inside of the tube we have entering ch4 and h2o and in the exterior we have water for the heat exchange
• The second is making a multi-tubular reactor where the reaction is in one side and the water in the other.
• And for the last a plate reactor
The reaction of the syngas is:
CH4+H2O=>3*H2+CO
In gaz/vap state

My problem at the time I can’t even arrive to make the first case and more simple, for each part I took:
Flows: fluid flow/single-phase flow/turbulent flow
Heat flows: heat transfer/Heat transfer in fluids
Reaction: chemical species transport/reacting flow/turbulent flow
But I can’t arrive to simulate, is there any example where I could learn how to use properly these 3 modes or the propers models for a case like the one I have.
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coupling two phase laminar flow and heat transfer in fluids

October 17, 2013, 12:44 pm
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Hi guys,

I have serious convergence problem in my case of two phase laminar flow and heat transfer in fluids. It is not a big deal. Just a box with inlet and oulet - for the flow - and one temperature boundary source and time dependent analysis.. . At the beginning there is nitrogen inside and another gas is going through the inlet and is mixing with the nitrogen. At the same time, there is a temperature at one boundary. I just want to know what is happenig with the density of the mixture in time.

Is there some trick how to couple these two analyses? It works fine separately, of course...

Thank you in advance!

Katerina
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Surface vorticity plot with angle

May 26, 2016, 3:15 am
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I am new to COMSOL. I am trying to analyze flow past a 3D sphere in steady , laminar flow case.After finding the result I am able to draw velocity and vorticity streamlines , pressure and vorticity contours. 2D plots of these quantities can be plotted by selecting the quantity from given expression.I want to draw a surface vorticity plot with angle on x-axis(along the sphere surface) and surface vorticity on y-axis.But I cannot find any expression termed as surface vorticity in COMSOL.Can any help me to plot surface vorticity plot with angle ?
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Prescribed compression of fluid

May 27, 2016, 2:04 am
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Hi,

I have a very simple model, consisting of a 1 x 1 m^2 square which is filled with Air.
I know that this problem can be solved by assuming ideal gas, and computing the area of the deformed domain. However, I want to combine this concept with more complex fluids, and therefor I want the Laminar Flow physics to solve this problem.

The study is Time Dependent.

I use the Deformed Geometry module to prescribe the deformation of my domain:
Attach Free Deformation to the whole domain, and apply a Prescribed Mesh Velocity to the top boundary, with prescribed y velocity of -0.05 m/s. The other boundaries are fixed (prescribed displacement of (0,0)).

It then fails: "Repeated error test failures. May have reached a singularity." when I try to run it.
Also, I see that the two sides of the square keep there height, but they have to shrink with the lowering of the top boundary.
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error in time dependent study

May 29, 2016, 11:00 pm
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hello
for study: range(35,0.1,95)
i am getting error: Failed to find consistent initial values.
Segregated Step 2
Attempt to evaluate real square root of negative number.
Function: sqrt
Failed to evaluate expression.

and study for range(35,0.1,70) is running fine.
and this study don't have any time dependent expression.
can anybody suggest something.

regards
Vishal Goyal
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Error : Failed to find consistent initial values

May 30, 2016, 11:46 pm
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Hi,

I have made a 3D EHL model using Thin-Film Flow, Shell and Solid Mechanics.
When computing the model, the following error is popping:
"Failed to find consistent initial values"
Maybe this error is related to the initial conditions, but I inputted some initial values for Global Equations, so I cannot understand why COMSOL cannot calculate this model.

Following is the detailed info. about my model :
1. Solid Mechanics
Boundary Load is applied to the half side surface of the cylinder( F [N]). Its direction is to the inner of the cylinder.
Fixed Constraint is applied to the half surface of the cylinder, which is the others of the side surface functioned by Boundary Load)

2.Thin-Film Flow, Shell
A cylinder is rotating (its axis is penetrating through the centre of the upper surface and the bottom surface)
This physics is applied to the side surface and its thickness is b[m], where b is time-dependent and b is calculated by Global Equation: F-forcetot = 0( Initial Values: u(0) = b0(constant), ut(0)=b0/time where time is 0.001[s])
Here forcetot is the value of the surface integration. Pfilm is integrated by this over the all side surface of the cylinder.


If you cannot understand what I try to say, please ask me.

Sincerely,
Shinnosuke Kitayama
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Coupling for heat source term from reaction enggineering.

May 31, 2016, 5:40 am
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Hi;
I am trayign to simulate chemical reactor.
I have created the following models:
1- mod1: reaction enggineering only
2- mod2: mod1 is syncronized with multiphysics having Laminar flow, Heat transfer in fluids, Diluted species module.

The temperature in the reactor depend on the chemical reaction of the species.
I added heat source to the heat transfer model, and i wand to know how Coupling for heat source term from reaction enggineering.
Best, Alain
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A.K
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Joule Heating in changed gas presser (in vacuum)

June 1, 2016, 12:08 am
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Hello!
I have such problem.
Electrical conductor connected to a DC power source. Placed in the rarefied gas.
It is necessary to see change temperature conductor, depending on the gas pressure.
I have used the module Joule Heating. In module Heat Transfer in Solids I have added the part Heat transfer in Fluids, and changed the pressure in area (cylinder of gas). But I couldn't get this depending (depend temperature conductor from pressure gas).
Who decided whether a similar problem?
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Liquid-Vapor interface drops very fast

March 18, 2016, 11:01 am
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Hi

I have encountered a problem in COMSOL when using the “laminar two-phase flow, moving mesh” physic.
A simple model indicating what I am trying to solve is provided in the attachment.

As you can see in the attached file, the liquid evaporates at a very low pressure (300 Pa) with a uniform mass flux of 1e-3 (kg/m2s). When the contact angle is 90, everything goes well. However, as I change the contact angle even a little bit from 90 (i.e. pi/2.1), the interface drops very fast, which is physically meaningless. I have had this problem with both COMSOL 4.3b and 5.1.

I could have been able to improve it by making the contact point meshes extremely fine. However, this gives me weird values of pressure (absolute negative pressures) in these regions.

I appreciate if you could help me sort out this issue.

Amin
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moving body in a fluid domain

June 2, 2016, 1:40 am
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Hello

I want to visualize the pressure variation on a solid in a predefined motion within a steady fluid(air) domain, and also see the variation of fluid around the solid body.
I am using the FSI module for the problem but am facing with an error: inconsistent initial values.

Thank You
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Flow without a channel (outlet)

June 2, 2016, 9:58 am
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I am having trouble modeling a flow in which there is no defined outlet. For example, imagine 2 hair dryers perpendicular to each other blowing air to a plate. There is an inlet, hair dryer's nozzle, but there is not an specific outlet because its an open system, without a channel for the fluid to flow.

I tried to model that using many outlets instead of not pointing any, but it did not work for laminar flow. Should I use turbulent flow instead? Which type? If the air being blew is cooling the plate, which boundary should be the outflow?

Thanks.
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Error using optimization module

June 2, 2016, 5:37 pm
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I tried to simulate a forced convective heat transfer problem: water flow through a heat sink. When I did stationary study with initial values of optimization parameters, it ran well. But if I ran optimization, the following error occurred:
Undefined variable.
- Variable: CFLCMP
- Geometry: geom1
- Domain: 2
Failed to evaluate variable.
- Variable: comp1.spf.locCFL
- Defined as: CFLCMP
Failed to evaluate expression.
- Expression: nojac(comp1.spf.time_step_inv/comp1.spf.locCFL)
Failed to evaluate expression.
- Expression: d(d((comp1.spf.rho*nojac(comp1.spf.time_step_inv/comp1.spf.locCFL)*(-(comp1.u-nojac(comp1.u))*test(comp1.u)-(comp1.v-nojac(comp1.v))*test(comp1.v)-(comp1.w-nojac(comp1.w))*test(comp1.w)))*(dvol),{test@3}),comp1.u)

Anyone got an idea how to shoot this?
Thanks in advance
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COmsol - Matlab Variable linking.

June 3, 2016, 4:21 am
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Hi all,

I am Looping simulations over matlab with different sets of values matlab calculates.
I am looking for changing the variable values. I have found for Parameter as
model.param.set() for changing the Parameter values. I am looking a similar solution for the variable in the model. I Need to replace this with the Array of values. This variable is an time dependent function. and I am running an transient Analysis.

Suggest me some Options and solution to overcome this.
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How to Define a nonlinear elasticity Model In Comsol 4.0?

April 18, 2011, 10:26 pm
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Dear Dr. Ivar,
I want to use a nonlinear Elastic relationship called "Duncan-Chang Model " for building a model about soil deformation. I use "Linear Elastic Material Model", and fill the parameters E and nu, of cause the E and nu, which now are fuctions about principal stresses (solid.sp1 and solid sp3). and it doesn't work with err "Circular variable dependency detected."
Are there some solutions that can be used to solve my problem ? and what technique need to be used in this problem?thanks a lot.
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Matrix has zero on diagonal

January 7, 2012, 6:38 am
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Hi experts,

I mat a problem when simulate a AC/DC model.
it came out as below:

Failed to find a solution for the initial parameter.
Segregated group1

Matrix has zero on diagonal.
Returned solution is not converged.
-Feature: stationary solver2(sol1/s2)
-Error: Failed to find a solution for the initial parameter.

any suggestions and help will be highly appreciated!



--
learn COMSOL, like COMSOL
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Elliptical cylinder

November 18, 2013, 5:28 am
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I am completely new to comsol, so please forgive me for posting a problem I suspect have a simple solution. I have tried to search for a solution myself, unsuccessfully.

In a microfluidic problem I need to use a pipe with an elliptical cross section. I have attempted to use a parametric surface and then convert it to a solid, but I get a warning that the output is empty.

Any help or tips would be much appreciated.

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display probleme

June 8, 2016, 3:55 pm
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is there any one how can help me because I have comsol5.0 where subtly the display region is not very clear even for the drawing model and results display. Thank in advance
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How can i solve the problem of natural convection? and coupling of physicis?

June 9, 2016, 8:10 am
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Hi all.
I want to analyze a heat sink in natural convection.
I gave Temperature under the heat sink(80 degC), outside open boundary and volume force.

when I pushed study, I have a problem.
That is follewed,

Undefined variable.
- Variable: comp1.nitf1.T
- Geometry: geom1
- Domain: 1
(I attatched the jpg file.)

maybe, I think non-isothermal flow(nitf) have several problems, but I can't find it.
so how can I solve this?
Thank you. have a nice day!
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two phase laminar flow in 3d

June 9, 2016, 9:02 pm
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hi I m supposed to simulate two-phase laminar flow problem (moving mesh).

the size of a cyl is ,
r=5 h=5
The bottom of the cylinder is fixed and the top of the cylinder is moving with a certain speed in normal direction.
the side face of the cyl. is exposed to the air.

geometry
cyl : r=5 h=5
material water
physics
wall at h=0 : no silp and predescribed mesh velocity =0
wall at h=5 : moving wall u=0.01 m/s and predescribed mesh velocity=0.01m/s
r=5 external fluid interface predescribed mesh velocity inactive

the error mesg. :
remeshing fulfilled for initial time. or last time step of newton method is not converged.
singularity problem..etc


help.





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Mass conservation in closed fluid system

June 10, 2016, 4:56 am
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Hi Community,

I am using a Rotating Machinery, Laminar Flow, Frozen Rotor setup to simulate the liquid flow in a cylindrical container with a magnetic stirrer. To test the accuracy of my model I wanted to calculate the flux over different cut planes inspired by this blog: www.comsol.dk/blogs/how-to-cal...nservation-and-energy-balance/

However, even for the highest mesh preset (extremly fine) I get a flux of ~3% of the total volume per second over a cut plane perpendicular to the cylindrical axis (normal 0 0 1 => really simple surface integral over w). The fluid is incompressible water and the stirrer moves at 100 rpm which should be far from turbulent.

I consistantly get the highly inaccurate number 3% (0.3 cm^3/s out of 10 cm^3) for all resonable mesh presets which makes me suspect that I am doing something wrong?

Thanks,
Kristoffer
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