 # Validation of holding time in a tube

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### #1 harrypr

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Hi every one, I need assistance to recheck Validation of Holding Time of Product in heating Tubes, Can any one assist for the formula,

The Tube length - 114 Ft, ID - 2 Inches , Flow Rate 1200 Liters /Per hour, Density of Product -1.5

### #2 Charles.C

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Posted 09 July 2017 - 07:01 AM

Hi every one, I need assistance to recheck Validation of Holding Time of Product in heating Tubes, Can any one assist for the formula,

The Tube length - 114 Ft, ID - 2 Inches , Flow Rate 1200 Liters /Per hour, Density of Product -1.5

Hi harry,

i assume a liquid.

Can see this thread although it does not categorically answer yr query -

http://www.ifsqn.com...r-pasteurizers/

Or maybe the general calculation methodology detailed here -

(eg pgs 12-15)

PS - A trivial answer to yr query could be as below but I doubt this is what you are actually asking ?

(assuming value given is inside diameter / laminar flow)

mean velocity of the product is calculated from the following equation:

V = F/A

Where: V = Velocity (m/s).

F = Flow rate (m3/s).

A = Area (m2)

(Use the inside diameter of the tube to calculate the area)

Maximum velocity (center line) for laminar flow is assumed = 2V (m/s)

So shortest theoretical residence time for laminar flow presumably = L/(2V) sec where L is in metre

Kind Regards,

Charles.C

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### #3 Charles.C

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Posted 09 July 2017 - 07:33 AM

some more related info -

Kind Regards,

Charles.C

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### #4 harrypr

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• India Posted 09 July 2017 - 10:37 AM

Hello, Many Thanks,

i was struggling to find the exact Formula to find the Holding Time in seconds,

Some one shared the Mathematical concept to find the Holding Time = V X D / Flow Rate

V= VOLUME

D = DENSITY

F= Flow rate

regards

### #5 Charles.C

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Posted 09 July 2017 - 11:34 AM

Hello, Many Thanks,

i was struggling to find the exact Formula to find the Holding Time in seconds,

Some one shared the Mathematical concept to find the Holding Time = V X D / Flow Rate

V= VOLUME

D = DENSITY

F= Flow rate

regards

Well, the simplest formula for the average time for an incompressible fluid would presumably be (total internal volume)/(volume flow rate) but this ignores the factors brought in due to the possible velocity profiles.

I also noticed another (dairy) (laminar flow) formula for the US legal minimum holding time -

L = 588 Qt

D 2

Where,

L = holding tube length

Q = pumping rate(gallons)

t = holding time standard (second)

D = inside diameter of holding tube

Not sure where the 588 comes from or the (missing) US units for length, diameter.  (plus Q must logically be gallons/sec).

(PS,added - see Post 7 for partial explanation)

Kind Regards,

Charles.C

### #6 Ryan M.

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Posted 12 July 2017 - 03:05 PM

Check the 2015 Pasteurized Milk Ordinance (PMO).  Is the US Dairy guidance book/manual for dairy manufacturing operations.

https://www.fda.gov/...k/ucm513508.pdf

On page 321 (starting) it discusses how to calculate the flow rate and holding time.  However, be aware that this is for laminar flow.  Depending on your product(s) you may not have laminar flow and in that case you'l have to get outside help from food processing engineers that specialize in this.

### #7 Charles.C

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Posted 12 July 2017 - 04:02 PM

Check the 2015 Pasteurized Milk Ordinance (PMO).  Is the US Dairy guidance book/manual for dairy manufacturing operations.

https://www.fda.gov/...k/ucm513508.pdf

On page 321 (starting) it discusses how to calculate the flow rate and holding time.  However, be aware that this is for laminar flow.  Depending on your product(s) you may not have laminar flow and in that case you'l have to get outside help from food processing engineers that specialize in this.

Hi Ryan,

Thanks for above.

The formula given on Pg323 looks offhand likely to be derived from the simplest formula I suggested in Post 5 (ie = average time) and is probably the source of the one I speculatively quoted at end but with the latter now displaying the missing units etc which i had previously noted, namely

Alternate Procedures for the Determination of the Holding Tube Length for Non-Standard Pipe Size: The holding tube length may be accurately calculated from the following equation:

L = 588 Qt/D2

Where:   L = Holding tube length (inches)

Q = Pumping rate (gallons per second)

t = Pasteurization holding time standard (seconds)

D = Internal diameter of the holding tube (inches)

( above formula looks to give results matching data in PMO tables14/15).

(Note that there is another formula shortly after which has an additional factor of 1.2 for steam. Meaning unknown [to me])

My only comment is that this basic PMO formula appears to ignore all the "velocity" caveats I quoted in Posts 2, 3 and 5. I am not expert enough this area to analyse  further why the discrepancy (maybe it's in the 588 ) .

PS - note that non-laminar flow is discussed in Post 2's attachment

Kind Regards,

Charles.C

### #8 PowderQM

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• Germany Posted 13 July 2017 - 04:14 PM

Hello Harry, hello to all

last year I had to calculat varius holding tubes and I constructed an Excel-Sheet for it.

All dimensions are in the metric system (European ). But I put allready the correct data in the Sheet.

You can change the calculation for other holding tubes by filling the correct data into the yellow fields.

If you wish to see all the data for the calculation you have to remove the soreadsheet protection (no password needed).

Below the calculation is a table with various flow rates so you can easily see the change in the holding time by chang in the flow rate.

I hope some find this helpfull

PowderQM

### #9 Charles.C

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Posted 14 July 2017 - 04:10 AM

Hello Harry, hello to all

last year I had to calculat varius holding tubes and I constructed an Excel-Sheet for it.

All dimensions are in the metric system (European ). But I put allready the correct data in the Sheet.

You can change the calculation for other holding tubes by filling the correct data into the yellow fields.

If you wish to see all the data for the calculation you have to remove the soreadsheet protection (no password needed).

Below the calculation is a table with various flow rates so you can easily see the change in the holding time by chang in the flow rate.

I hope some find this helpfull

PowderQM Holding Tube Calculation.xlsx

Hi Powder,

Thks for the attachment.

I deduce the factor F=2 allows for the velocity profile in laminar flow so as to calculate the shortest theoretical residence time as compared to a mean value ?.

If so, yr formula looks probably identical to the one at end of Post 2. (may or may not = the one in Post 7 [a lot of unit manouevring is required to check])

I'm sure Harry would also like an Excel using L/hr, feet and inches  (apparently Indian Standard )

Thanks again.

Kind Regards,

Charles.C

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