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Problem using Turbulent flow analysis

Posted Jun 6, 2010, 3:50 p.m. EDT Fluid & Heat, Battery Design 5 Replies

Hafiz Muhammad Fahid Amin
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Hi Dears, I am Fahid Amin and I am trying to solve the heat transfer problem using comsol.

I have a box enclosing a fuel cell system and in which there are sources of heat generation like stack, circuit board along with dissipator, a pump which adds heat in the box when it is running. the box which contain fuel cell system is internally cold using forced convection. the exit velocity of air is 5 m/sec, that's why i think the flow will be turbulent. But when I try to compute the solution I get an error saying singular matrix.

I have tried to solve this problem using laminar flow but i put Velocity 5cm/sec and it was done. Please guide me how can i solve it for velocity of 5m/sec or in turbulent flow.

Thanking you in advance.

Yours truly,
Fahid Amin

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5 Replies Last Post Jun 7, 2010, 5:42 a.m. EDT
Naveed Akhtar
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Posted: 1 decade ago Jun 7, 2010, 4:13 a.m. EDT
Hi Fahid

I am unable to open your model. Which version it is?

Regards
Naveed
Hi Fahid I am unable to open your model. Which version it is? Regards Naveed
Hafiz Muhammad Fahid Amin
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Posted: 1 decade ago Jun 7, 2010, 4:49 a.m. EDT

Hi Naveed,

I am using comsol 4.0 version. If you have the same version then please let me know I will try to upload the file again.
Regards,
Fahid Amin



Hi Fahid

I am unable to open your model. Which version it is?

Regards
Naveed


Hi Naveed, I am using comsol 4.0 version. If you have the same version then please let me know I will try to upload the file again. Regards, Fahid Amin [QUOTE] Hi Fahid I am unable to open your model. Which version it is? Regards Naveed [/QUOTE]
Naveed Akhtar
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Posted: 1 decade ago Jun 7, 2010, 5:11 a.m. EDT
Hi Fahid

Unfortunately not, I am still with 3.5a. By the way, the forced covection with 5m/s is too high velocity-Do you have this figure converted in air flow rate (ml/min), and to see the system efficiency of the fuel cell?How many cells are in your stack?

Regards
Naveed
Hi Fahid Unfortunately not, I am still with 3.5a. By the way, the forced covection with 5m/s is too high velocity-Do you have this figure converted in air flow rate (ml/min), and to see the system efficiency of the fuel cell?How many cells are in your stack? Regards Naveed
Hafiz Muhammad Fahid Amin
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Posted: 1 decade ago Jun 7, 2010, 5:25 a.m. EDT
Dear Naveed,

The flow rate of the fan is 110 cfm, 1900rpm and the diameter of the fan is 115mm. I calculated the velocity applying Q=AV. Also the stack have 42 cells min. I am not sure about no of cells in stack but it will not be less than 42. So, at what range of velocity do u think the flow will be laminar.
Regards,
Fahid Amin
Dear Naveed, The flow rate of the fan is 110 cfm, 1900rpm and the diameter of the fan is 115mm. I calculated the velocity applying Q=AV. Also the stack have 42 cells min. I am not sure about no of cells in stack but it will not be less than 42. So, at what range of velocity do u think the flow will be laminar. Regards, Fahid Amin
Naveed Akhtar
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Posted: 1 decade ago Jun 7, 2010, 5:42 a.m. EDT
I assume you are running a transient heat analysis for cooling fuel cell stack, so the air-flow rate depends in how much time you want a steady state temperature of the stack to be arrived. I suggest, first you calculate the exact amount of heat generated from the stack-then depending upon your requirement for steady sate arrival time, you can set the air-inlet flow rate.

You can easily calculate the Reynolds number to decide whether it is in laminar or in turbulent range. Normally internal cooled fuel cells are in laminar range, but since you are externally cooling the stack- it might go on turbulent side but you will loose your system efficiency.

I suggest do above calculations in order to decide the inlet flow range of air....

Regards
Naveed
I assume you are running a transient heat analysis for cooling fuel cell stack, so the air-flow rate depends in how much time you want a steady state temperature of the stack to be arrived. I suggest, first you calculate the exact amount of heat generated from the stack-then depending upon your requirement for steady sate arrival time, you can set the air-inlet flow rate. You can easily calculate the Reynolds number to decide whether it is in laminar or in turbulent range. Normally internal cooled fuel cells are in laminar range, but since you are externally cooling the stack- it might go on turbulent side but you will loose your system efficiency. I suggest do above calculations in order to decide the inlet flow range of air.... Regards Naveed

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