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# BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

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## BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

(OP)
hi

i'm batch heating a tank containing water
and need to raise the water temp in the
tank from 20degC to 60degC in 1 hour.

the tank water contents are not agitated.

i'm using an internal coil in the tank
as the heat exchanger. the hot water
entering is about 1.1 liters/sec at 80degC and 60degC exiting
the coil.
i've assumed an overall heat transfer coefficient
of 500 Watts/m2C for the internal coil.

what are the relevant formulas that would provide
a reasonably accurate surface area of the internal coil.

pumpmanplee

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

This has been discussed many times. Use Search (top left, under the thread title, between Forum and FAQs) with keywords batch heating. You will get good information.

Good luck,
Latexman

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

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

This is also a transient analysis as your volume of water is heating up and therefore the heat input from the static temperature of the water will decrease over time.

you need volume of water you're trying to heat, you have a heat input in terms of m2 of the coil, temperature of the heating water ( use 70C as the average heat input figure), you can calculate average heat input rate required in terms of W.

what more do you need?

This is a very basic question though - student??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

(OP)
thanks Latexman for Perry's reference...

Perry's formula (shown below) for coil in tank
isothermal heating medium
is the formula i need,
however
it is for an agitated tank,
how do you adjust the formula for
a tank that is not agitated...
that is with my tank batch heating
application, there is no mechanical
mixing inside the tank, just simply
by convection.

pumpmnanplee

= = = = =
below copied from Perry's handbook...

" and over the entire surface, (2) liquid flow rates are constant, (3) specific
heats are constant for the process, (4) the heating or cooling
medium has a constant inlet temperature, (5) agitation produces a uniform
batch fluid temperature, (6) no partial phase changes occur, and
(7) heat losses are negligible. The developed equations are as follows.
If any of the assumptions do not apply to a system being designed, new
equations should be developed or appropriate corrections made.
Coil-in-Tank or Jacketed Vessel: Isothermal Heating Medium
ln (T1 − t1)/(T1 − t2) = UAθ/Mc (11-35)
where K1 = eUA/WC "

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

You adjust the formula for a tank that is not agitated by specifying a U for an un-agitated vessel. You said, "i've assumed an overall heat transfer coefficient of 500 Watts/m2C for the internal coil." What was the basis for that? That seems a little bit low to me. I was thinking about 850 Watts/m2C. If the operation is running, you should be able to obtain a U that characterizes the performance very closely.

Good luck,
Latexman

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

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

(OP)
thanks Latexman...

yes, the U overall heat transfer coefficient
takes into account the combined conduction
& convection looking at the overall heat transfer
coefficient formula in my book),
so it takes into account the
mixing or non mixing inside the tank.

i used the 500 W/m2C from an internet reference
giving a range of 200 to 500 W/m2C
for coils immersed in water.

one other question i have in regards to Perry's handbook formula for:
Coil-in-Tank or Jacketed Vessel: Isothermal Heating Medium
ln (T1 − t1)/(T1 − t2) = UAθ/Mc (11-35)
where K1 = eUA/WC "

how come it does not take into account
the exit temperature of the fluid exiting
the coil ???
only the temperature entering the coil, T1.

pumpmanplee

### RE: BATCH HEATING OF TANK USING INTERNAL COIL - calculate surface area of internal coil

The exit temperature was eliminated by combining multiple equations during the derivation. It's basically the solution of a differential equation. If interested, see Process Heat Transfer by Donald Q. Kern, for one. It's available in many other references and early periodicals.

Good luck,
Latexman

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

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