Storage Tank Heat Losses and cooling load

[kmic]

Hi everybody
I have one question about heat losses from a milk storage tank and how to find the dimple jacket total area to hold milk temperature @ 4DegC and cooling load in order to size my chiller .
As I know the milk must be keep at 4DegC.
Tank Data:
The tank is agitated with side entry agitator.
Insulated Tank 3” insulation
Dext=3m and H=4.5m
Milk temp=4DegC ,Tamb.=27DegC
Service Water @ 1DegC Water as the Cooling medium

I try to find a Solution but i don't know if i'am correct.
I try to make some simple calculation I found the temperature difference between milk inside tank and ambient temperature Δt=23DegC and from MUELLER surface vessel heat load table page 22 i found that Wall loss factor=19 W/m2 , Tank total area = 42.4 m2 then
qw=19 x 42.4 =805.6W. I used the equation Q=U*A*ΔΤ and solve for A
A=Q/(U*ΔT) here is my issue
1)Witch Δt to be used the log mean temperature difference?
Or simply take the Δt=4-1=3DegC (Milk Temp minus Service medium temp) or something else.
2) Which overall heat transfer coefficient to used? Can I choose a “U” value from a table used Cooling as medium and an agitated product about U = 625 W / m^2 K.
3)How can I calculated the flow rate about cooling load and witch temperature difference to use?

PL’s Advice

NOTE: In my calculation I used water for product for simplicity.

 

[Latexman]

Is the in-coming milk at 4 C, or is it warmer and this tank needs to cool it to 4 C in some reasonable time? If so, this cooldown heat duty may be your design worst case.

1) The service water temperature will increase during this process. You need the service water flow rate. Then, add the heat duty removed from the milk and calculate the outlet temperature from Q = wc_pdt_sw. Then, calculate LMTD.
2) A value from a table can be used as long as it is appropriate. Otherwise, you need to get back to the basic heat transfer equations and correlations.
3) Trial and error or iteratively.

The heat added to the milk by the agitator should also be added.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[IRstuff]

How accurate do you need the solution?
What is the thermal conductivity of the insulation?
How full can the tank get?
Who determined the 3" thickness of insulation? What process did they use to determine whether it should be 3" vs 4"
What is the expected dew point of the outer surface?
What is the range of ambient temperatures?



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[kmic]

Answer to Latexman the milk is coming at 4DegC the service water is just to hold the milk temperature inside tank at constant temperature at 4DegC before process start.
Answer to IRstuff i don't want accurate solution.
If i use Δt=4-1=3DegC (Milk Temp minus Service medium temp) in my equation A=Q/(U*ΔT) i'am correct? in order to find the Area of dimple jacket.
How to find the flow rate of service fluid.

 

[Latexman]

"Δt=4-1=3DegC" is not technically correct! The water side is not an isothermal process; it is a sensible heat process. If the service water flow is very low, you could be off on the area required by a factor of 2. Is this okay? If it is okay, use it. If you have a similar installation to go by, this approach may be okay. The larger the service water flow rate, the more likely you can use "Δt=4-1=3DegC" with out being too far off.

To find the service water flow, you can measure it if this is an existing operation. If it's a design problem, you can set it at some optimum value and design to achieve that flow, within reason. I explained in my previous post how to calculate the service water outlet temperature, and that this is going to be an iterative solution (trial and error), if you want to see if the solution is realistic.

Briefly:
Assume a service water flow rate.
Calc. service water outlet temp.
Calc. LMTD.
1st pass - Get U from table. Therafter - calculate U.
Calc. A.
With this size dimple jacket, is the service water flow rate reasonable (hydraulically correct)?
With this size dimple jacket and the agitation you have, is U reasonable (use basic heat transfer equations and correlations for the dimple jacket, agitator, convective and conductive heat transfer)?
Make an adjustment to service water flow rate and repeat.

If this is the first time you have designed something like this and you do not have a good "go-by", I'd recommend not taking any shortcuts. Get into the details. Open the old textbooks.


Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[kmic]

Hi Latexman and thanks for you are reply you are answer is very useful i late a little bit sorry about that i have some personal issued.
I have on last think how i can calculated the LMTD because the milk temperature must be at 4DegC inside tank i don't have temperature difference .
I will post one similar problem i used this to figure out to solve my problem but in this problem used steam instead of Cooling Water.
See Example 3 Or is better to use Example 2.

Pl's advice

 

[IRstuff]

Is this homework? Student posting is not allowed. You can post homework questions at the engineering.com link in my signature

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[kmic]

Answer To: IRstuff you can say is homework u said student is not allowed solve my problem i don't need extra extra accuracy.

 

[IRstuff]

Students are welcome to answer questions; students are not allowed to post questions.

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