Flow Over Weir Plate in Kettle Reboiler 2

[dygorane]

I want to calculate flow over weir plate for kettle reboiler, process fluid is C3+Hydrocarbon (Density:474.9kg/m3 & viscosity: 0.086cP).
I found following formula from internet, but this is for water.

Horizontal, sharp edged weirs (Bazins formula)
Q = 0.66 x cB x (2g)0.66 x H1.5

where;

Q = water flow rate, m3/sec

B = width of the weir, metres*

c = discharge coefficient, average 0.62

g = gravitational constant, 9.81

H = Height of the water over the weir, measured behind the weir edge, m
* Note’; if the weir is narrower than the channel feeding it, shorten B by 0.2xH

I am not very sure how different hydrocarbon will behave than water.

Is there any other method to calculate this.

In above formula units are not cancelling out,

m3/s = m x m/s2 x m

Any views?

Thanks
Dinesh

 

[vpl]

You might take a look at thread378-182281. In particular the paper referenced 3/4 of the way down "Simple Discharge Relations for Sharp-crested Rectangular Weir and
Right-angled Triangular Weir at Low Heads" is not specific to water. If the link doesn't work, let me know as I kept a copy of this document.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[25362]

If the formula looked like the following:

Q = 0.66 c B (2g)^0.5H^1.5

the units would cancel out: m³/s = m.m^0.5m^1.5/s.

 

[25362]

Although not the same type baffle or weir, a visit to thread124-150588 may be of interest.
You may notice that both sides of the quoted equations are not necessarily equidimensional.
Besides, in a kettle reboiler the height-over-weir may be altered by the possible presence of a froth.

 

[dygorane]

Thanks everybody for replying to post. Patricia I did looked at that thread before posting this but thought that was not relevent reading first couple of replies.

Anyway I got that paper from thread. Thanks for your help.

Dinesh

 

[mbeychok]

dygorane:

This is not an answer to your specific question. I am simply curious as to why you want to calculate the flow over the weir in a kettle reboiler.

The liquid feed into a kettle reboiler will be partially vaporized. The vapor will return to the fractionation column and the residual liquid will flow over the weir and exit the reboiler. When you submit your process specifications to the reboiler manufacturer, the manufacturer will leave adequate vapor space above the weir and will account for the height of liquid above the weir.

I must have written process specifications for more than a thousand kettle reboilers handling liquids of many types ... and not a single one failed to operate correctly.

Why invent the wheel again? Any reputable heat exchanger manufacturer will furnish you a kettle reboiler that will function properly.

Milton Beychok
(Visit me at www.air-dispersion.com)
.