Me 414 He Presentation

8/3/2019 Me 414 He Presentation

1/26

Heat Exchanger Design

ME 414 Design Project

Created and Designed by:Michael Stark

Joshua Keith

Billy Burdette

Brandon Mullen

Joseph Listerman


2/26

Project Goalsy Design Heat Exchanger

y Create a light weight heat exchanger

y Heat exchange must be as efficient as possible

y Cost must be kept low as possible

y The size of the heat exchanger must be under design constraint


3/26

Project Guidelinesy During the process of a liquid chemical product, its temperature needs

to be reduced by 20 degrees Celsius.y Mass flow rate is 220,000 kg/hr

y Fluid enters the heat exchanger at 45 C and should leave at 25 Cy Material properties of this chemical product can be approximated as water

y Cooling of the chemical product will be achieved by using treated citywatery City water is available at 20 C

y Mass flow rate is adjustable and one of the design parameters to be selected

y Exit temperature of city water from the heat exchanger is a function of the selected massflow rate

Professor Toksoy


4/26

Project Optimizationy Must cool the chemical from 45 C to 25 C

y Heat exchanger length can not exceed 7 meters

y

Heat exchanger shell diameter can not exceed 2 metersy Minimize heat exchanger shell and tube weight hence the cost

y Minimize heat exchanger pressure drop

Professor Toksoy


5/26

Heat Exchanger Design Inputs

for MATLAB Chemical to be cooled was set as Shell side liquid Mass flow rate of cooling water = 220 kg/sec Shell ID = .889 m Shell thickness = 5 mm Tube OD = 6.35 mm Tube thickness = .457 mm Tube Length = 2.88 m Baffle space = .6 m Helical Baffles Counter flow One shell pass and one tube pass Aluminum was used for both shell and tube materials Gnielinski equation used for tube side Nusselt correlation Square tube pitch


6/26

Heat Exchanger Design Inputs for

MATLAB Explained

Chemical to be cooled was set as shell side liquid In order to keepshell side pressure drop to a minimum we needed to keep the massflow rate in the shell low. The only way we found of doing this andgetting the desired Q was to push the chemical to be cooled through

the shell. Mass flow rate of cooling water = 220 kg/sec - For these inputs this

calculates out to an average tube side fluid velocity of ~1 m/s whichfalls within the recommended range of .9 2.4 m/s.

Tube OD = 6.35 mm - The small OD was needed to increase the

surface area for heat transfer for a given shell ID. Tube thickness = .457 mm -The small tube thickness was needed to

increase the heat transfer coefficient and also reduced the totalmaterial weight and cost.


7/26

Tube Length = 2.88 m - The tube length was increased to increase thecalculated Q.

Baffle space = .6 m - Although slightly larger then the recommended valueof 40-60% of shell ID, .6 m worked well.

Helical Baffles A helical baffle will increase the heat transfer coefficientconsiderably without dramatically increasing pressure drop due to the natureof the flows.

Counter flow - Because of the narrow band of temperatures between thetwo fluids, a counter flow arrangement was used in order to increase the logmean temperature difference between the two fluids without having toincrease the mass flow rate of the water to very high levels.


MATLAB Explained Cont.


8/26

One shell pass and one tube pass - One pass was used for both the shell andtube because currently the program does not calculate pressure drop due tomultiple passes correctly. We discovered this late into the project and didnot have time to fix the issue. If the pressures were calculated properly thewater output temperature for one shell pass and two tube passes must stay

below 28.33 deg C in order to keep the log mean temperature differencecorrection factor valid for the given temperature requirements.

Aluminum was used for both shell and tube materials - Aluminum waschosen for its excellent heat transfer properties and its reduced weight.

Gnielinskis equation used for tube side Nusselt correlation For thecalculated Reynolds number of 5800 this correlation is most applicable.Petuhkov Krillovs correlation is used for Reynolds number larger then104.


MATLAB Explained Cont.


9/26

Nusselt Correlation


10/26

D.O.E. Run 1

240200

1600000

1400000

1200000

1000000

800000

42

1.50.5

1600000

1400000

1200000

1000000

800000

mdot Shell

Mean

Tube Length

Shell

Main Effects Plot for q_CalcData Means

240200

120000

100000

80000

42

1.50.5

120000

100000

80000

mdot Shell

Mean

Tube Length

Shell

Main Effects Plot for DP_TubeData Means

240200

80000

60000

40000

20000

42

1.50.5

80000

60000

40000

20000

mdot Shell

Mean

Tube Length

Shell

Main Effects Plot for DP_ShellData Means

240200

5000

4000

3000

2000

1000

42

1.50.5

5000

4000

3000

2000

1000

mdot Shell

Mean

Tube Length

Shell

Main Effects Plot for WeightData Means


11/26

D.O.E. Run 1y Factors

y Shell mass flow rate

y Tube length

y Shell internal diameter

y The most significant affect on heat transfer was tube length, aresult of increased surface area.

y Shell I.D. and tube length had the greatest affect on weight, thelarger the shell the more tubes can fit inside.

y Shell side pressure drop increases with tube length and mass flowrate. Dramatic decrease as shell ID increases.

y The only factor affecting the tube side pressure drop was tubelength.


12/26

D.O.E. Run 2

0.80.3

5600000

5400000

5200000

5000000

4800000

0.0007110.000457

0.50.1

5600000

5400000

5200000

5000000

4800000

Baffles Space

Mean

Tube Th

Baffle Cut


0.80.3

20000

18000

16000

14000

12000

0.0007110.000457

0.50.1

20000

18000

16000

14000

12000

Baffles Space

Mean

Tube Th

Baffle Cut


0.80.3

10000

8000

6000

4000

2000

0.0007110.000457

0.50.1

10000

8000

6000

4000

2000

Baffles Space

Mean

Tube Th

Baffle Cut


0.80.3

2500

2450

2400

2350

2300

0.0007110.000457

0.50.1

2500

2450

2400

2350

2300

Baffles Space

M

ean

Tube Th

Baffle Cut



13/26

D.O.E. Run 2y Factors

y Baffle Space

y Tube Thickness

y Baffle Cut

y Baffle spacing has a large affect on q and shell side pressure drop.

y Tube thickness was the only factor affect HE weight in this DOE.

y Baffle cut doesnt seem to have any affect on other parameters.

y We fixed baffle spacing because it heavily influenced shell sidepressure drop.


14/26

Final D.O.E.

42

8000000

7000000

6000000

5000000

4000000

1.5000.889

0.012700.00635

8000000

7000000

6000000

5000000

4000000

Tube Length

Mean

Shell ID

Tube OD


42

12000

9000

6000

3000

0

1.5000.889

0.012700.00635

12000

9000

6000

3000

0

Tube Length

Mean

Shell ID

Tub e OD


42

20001750

1500

1250

1000

1.5000.889

0.012700.00635

2000

1750

1500

1250

1000

Tube Length

Mean

Shell ID

Tube OD


42

6000

5000

4000

3000

1.5000.889

0.012700.00635

6000

5000

4000

3000

Tube Length

Mean

Shell ID

Tube OD



15/26

Final D.O.E.

y Final optimization factorsy Mass flow rate of the shell fluid fixed to 220 kg/s

y Tube length

y Shell internal diameter

y Tube outer diameter

y We adjusted the ranges of our chosen factors and ran the DOEagain.

y The mass flow rate only affected the shell side pressure drop atthis stage of the design. We chose the shell side mass flow ratebased on what we decided would yield reasonable shell outlettemperature using counter flow.


16/26

Factorial Design Analysis Heat Rate

y Tube length has the largestaffect on the heat rate.

y Shell ID has the smallestrelative affect on heat rate.

y Shell ID had a negative affecton heat rate.y This was a result of more

tubes decreasing the

velocity in the tube.y The result is laminar flow

inside the tube.

BC

AB

B

AC

C

A

4003002001000

Term

Standardized Effect

12.7

A Tube Length

B Shell ID

C Tube OD

Factor Name

Pareto Chart of the Standardized Effects

(response is q_Calc, Alpha = 0.05)

4003002001000

99

9590

80

70

60

50

40

30

20

10

5

1

Standardized Effect

Percent

A Tube Length

B Shell ID

C Tube OD

Factor Name

Not Significant

Significant

EffectType

AC

AB

C

B

A

Normal Plot of the Standardized Effects

(response is q_Calc, Alpha = 0.05)


17/26

Factorial Design Analysis - P Tubey We can see that tube length has the largest affect on tube side pressure

drop.

y Shell ID has no affect on tube pressure drop.

y We expected tube OD to have a larger affect on tube side pressure drop.

AB

BC

B

AC

A

C

14000120001000080006000400020000

Term

Effect

A Tube Length

B S hell ID

C Tube O D

Factor Name

Pareto Chart of the Effects(response is DP_Tube, Alpha = 0.05)


18/26

Factorial Design Analysis - P Shelly Shell ID had the largest

affect on shell sidepressure drop.

y

The affect of tube OD onthe pressure drop wassurprising.y We attribute this affect to

the 60 triangular pitchtube arrangement.

y As tube OD grows largerthere is more pressuredrop in the shell.

AC

AB

BC

A

C

B

14121086420

Term

Standardized Effect

12.71

A Tube Length

B S hell ID

C Tube O D

Factor Name

Pareto Chart of the Standardized Effects(response is DP_Shell, Alpha = 0.05)


19/26

Factorial Design Analysis HE Weight

y The shell insidediameter has the largestaffect on weight.y The larger the shell

diameter the moretubes we could fitinside, thus increasingweight.

y Because tube length

determines the lengthof the heat exchanger, ittoo has a large affect onheat exchanger weight.

BC

AC

C

AB

A

B

40003000200010000

Term

Effect

A Tube Length

B Shell ID

C Tube O D

Facto r N ame

Pareto Chart of the Effects

(response is Weight, Alpha = 0.05)


20/26

Design Optimization - 1

y The design optimized to our originaldesign.

yWe expected our final tube diameter to

be 6.35 mm with a mass flow rate of 220kg/s.

y Optimal Tube OD was 8.3mm

y The tube length was longer than ouroriginal design called for, which was aresult of maximizing the q calculated.

y We set target values for the shell andtube side pressure drops.

y We set a target range for total weightbetween 900-1100 kg.


21/26

Design Optimization - 2

CurHigh

Low1.0000D

New

d = 1.0000

MinimumWeight

y = 2288.8141

d = 1.0000

MinimumDP_Shell

y = 1805.0741

d = 1.0000

MinimumDP_Tube

y = 5865.8838

d = 1.0000

Maximumq_Calc

y = 5.454E+06

1.0000

Desirability

Composite

0.0063

0.0127

0.8890

1.50

2.0

4.0Shell ID Tube ODTube Len

[2.6263] [0.8890] [0.0096]

y The design optimized to our original design.

y We expected our final tube diameter to be6.35 mm with a mass flow rate of 220 kg/s.

y Optimal Tube OD was 8.3mm, adjusted itto 9.525 mm to coincide with standardtube dimensions.

y The tube length was longer than our originaldesign called for, which was a result ofmaximizing the q calculated.

y

We set target values for the shell and tube sidepressure drops.

y We set a target range for total weight between900-1100 kg.


22/26

Heat Exchanger Design Output from

MATLAB


23/26

Heat Exchanger Final Design

y Tube side mass flow rate of 220 kg/sec

y Tube OD set to 9.525 mm, thickness 0.889 mm

y Shell ID set to .889 meters, thickness 5 mm

y Heat exchanger is a one pass counter flow tube arrangementwith helical baffles and optimized tube length of 2.6 m.

y The ratio between desired and calculated heat rate is 1.00.


24/26

Further Analysis

y We believe that cost could be decreased by over-designingthe HE and reducing the number of tubes until we got thedesired heat ratio.

y

The tube mass flow rate was an important designconsideration because the outlet temperature of the shellfluid was completely dependent on it.

y After performing a macroscopic heat balance, counter flowwas chosen because the cold fluid outlet temp was expectedto be higher than the hot fluid outlet temp.


25/26

Matlab Program Improvements

y Create program checks in order to eliminate unrealisticdesigns.

y If multiple tube passes are used with parallel flow it is possibleto calculate a LMTD_CF that is an imaginary number.

y Provide the operator more detailed information regardingthe Nusselt correlations.


26/26

Cost Summary

y Heat Exchanger Dry Weighty 730 Kg

y Heat Exchanger & Fluid Weight

y 2287 Kg

y Costy OnlineMetals.com

y $37.00 per 8ft length of aluminum tubing

y Total estimated aluminum tubing cost $337,000.00

y

$11.00 per 8ft length of mild steel tubingy Total estimated mild steel tubing cost $100,000.00

y Instillation and Manufacturing

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Me 414 He Presentation

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