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Transverse loss coefficient for perforated plates

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Old   October 4, 2010, 15:37
Question Transverse loss coefficient for perforated plates
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Sanyo
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Dear All,

I am trying to model perforated plate of 3mm thickness used in electrostatic precipitator. I know how to define normal loss coefficient(in the direction of flow) as I know percentage opening. But I am confused about transverse (perpendicular to the flow) loss coefficient.

CFX help says multiplier of 10 should be used. However my supervisor suggests 0.01 multiplier. I dont know what value should be used & why?

Can anybody help me please?

Thank you in advance.

--Sanyo
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Old   October 4, 2010, 18:15
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Glenn Horrocks
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The concept is simple - for cross flow, how much more (or less) is the resistance compared to the normal flow direction. If the flow is unrestricted along the plate then 0.01 sounds fair, but if there is baffling and restrictions then 10 sounds fair. You have to choose based on the situation.
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Old   October 5, 2010, 01:58
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Hello Glen,

Thanks for your reply. Our perforated plate doesnt have any baffle or restriction, so I guess it should be 0.01 in other two directions. But what about the percentage opening? I mean should I use 0.01 for 50% open plate as well as 20% open plate?

Also what about the flow direction? In one case, we have front entry ESP (electrostatic precipitator) & in other case we have top entry ESP. So angle between flow direction & plate are quite different. Will it make difference?

Thanks for your kind reply once again.

Regards,

--Sanyo
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Old   October 5, 2010, 20:10
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Quote:
But what about the percentage opening? I mean should I use 0.01 for 50% open plate as well as 20% open plate?
Obviously not. The figure you use has to be adjusted to match the ratio of the resistances. So you have to work out the normal and cross resistances and set the ratio from that.

Quote:
So angle between flow direction & plate are quite different. Will it make difference?
You have to determine that. Either experimental data or do a simulation.
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Old   October 6, 2010, 03:03
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Dear Glenn,

Thank you very much for your kind response.

It is really helpful & invaluable information. Can you please suggest any literature to decide the transverse loss coefficient & effect of flow direction?

Also one question is bugging me continuously. The transverse coefficient is assigned for plate. If we see physically, holes are punched in a solid plate. So intuitively these holes are guiding the flow by restricting the flow in other two directions. Though this will depend upon the thickness of plate & hole diameter, why do we need to assign the transverse coefficient less than the normal coefficient?

Thanks again.

Regards,

--Sanyo
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Old   October 6, 2010, 06:22
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This depends on what you define as the sub domain you set as the resistance. If it only includes the plate and then there is no way any transverse flow can happen then give it a very high resistance ratio. But if your definition includes some plates and some gaps between then the resistance to cross flow is probably low so a low ratio is required.

It all depends on your model. Have a look at what you define as the sub domain, work out forward and cross resistance and set the variables accordingly.
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Old   October 8, 2010, 01:25
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Dear Glenn,

Thank you very much for your kind & invaluable assistance.

Regards,

Sanyo
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