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Heat Exchanger


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#1

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Posted 25 August 2009 - 10:43 PM

Hello,

After determining the first 3 answers for the following question, I need to be sure that I'm on the right track with the final one;

A 1:1 shell & tube heat exchanger is required to cool 10,000 kg/hof light oil from 105°C to 20°C using cooling water which is availableat 15°C and leaves at 30°C. The light oil flows inside the tubes andthe water is on the shell side.


(i) Based on the stated temperatures, show whether the flow configuration concurrent or countercurrent. What is the log mean temperature difference?
(ii) Calculate the number of tubes for a linear velocity of the oil of 0.8 m/s.
(iii) Calculate the film coefficient for the oil on the inside of the tubes.
(iv) Determine whether the number of tubes calculated in (ii) is sufficient to perform the required duty.

I assume that if I compare the following 2 transfer rates, it'll tell me that the theoretical transfer rate far outweighs the actual transfer rate.

qa = Uo x Aox ΔT x N = 256.13 x (4 x π x 0.0160) x 25.85 x 33 = 4390.362 W

qt = mass flow rate * cp * (deltaT) * 33 = 15,264,980 W

Could someone please confirm that I have the right idea?

Cheers,

Kelly

#2 breizh

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Posted 26 August 2009 - 06:43 AM

Hello,

After determining the first 3 answers for the following question, I need to be sure that I'm on the right track with the final one;

A 1:1 shell & tube heat exchanger is required to cool 10,000 kg/hof light oil from 105°C to 20°C using cooling water which is availableat 15°C and leaves at 30°C. The light oil flows inside the tubes andthe water is on the shell side.


(i) Based on the stated temperatures, show whether the flow configuration concurrent or countercurrent. What is the log mean temperature difference?
(ii) Calculate the number of tubes for a linear velocity of the oil of 0.8 m/s.
(iii) Calculate the film coefficient for the oil on the inside of the tubes.
(iv) Determine whether the number of tubes calculated in (ii) is sufficient to perform the required duty.

I assume that if I compare the following 2 transfer rates, it'll tell me that the theoretical transfer rate far outweighs the actual transfer rate.

qa = Uo x Aox ΔT x N = 256.13 x (4 x π x 0.0160) x 25.85 x 33 = 4390.362 W

qt = mass flow rate * cp * (deltaT) * 33 = 15,264,980 W

Could someone please confirm that I have the right idea?

Cheers,

Kelly


Kelly,
Energie coming from hot oil is transfered to water :
M hot oil * cp oil *(Tin hot oil - Tout hot oil ) = M water *cp water * ( Tout water -Tin water) = Q
and
Q = U*A*DTml with A = N* 2*pi *r *L ( N : number of tubes ; r = diameter/2 ;L = length of the tube ) ; DTml = log mean temperature ; U global heat transfer coefficient.

Hope it helps .
Breizh

#3 shan

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Posted 26 August 2009 - 07:15 AM

Although you satisfied velocity requirement, you did not meet heat transfer area requirement. Please increase number of tube to make qa = qt. If vlocity 0.8 m/s is critical, you may have to select smaller diameter tube to increse heat transfer area in the condition of same flow cross section.

#4 ARAZA

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Posted 04 September 2009 - 01:10 PM

Kelly,

Are you aware that you are creating a temperature cross in the H-E. Your cold side outlet temperature (30 deg C) is higher than your hot side outlet temperature (20 deg C).Conventional shell and tube may work but will require two or more shells to achieve this temperatures.

Consider U-Tube or plate and frame H-E's to handle temperature cross.

Hope this helps

ARAZA




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