Re-engineering of an industrial grade heat exchanger

Design of an Improved

Bayonet Ultra Heat Exchanger

Team 11

5/1/12

Team Members

• Harshith D'mello

• Dylan Herman

• James Hum

• Kent Yee Lui

• James Sowin

Speaker: H. D’Mello

5/1/2012 Team 11 – Heat Exchanger 2

Acknowledgements• Prof. Chia-Fon Lee

• Prof. Stephen Platt

• Prof. Emad Jassim

• Lance Hibbeler

• Seid Koric and Ahmed Taha

• Jay Menacher

• Ralf Möller, Keith Parrish and their dedicated

team of machinists

• Eclipse Inc, specifically Val Smirnov, Rick

Wenger, Jason Smith and Andrew Fortener



Overview

• Introduction

• Proposed Solution

• Computational Fluid Dynamics Analysis

• Experimental Testing

• Energy Savings Estimate

• Cost Analysis

• Budget

• Conclusions and Recommendations



Introduction

Original BU



Background• Bayonet Ultra (BU) heat exchanger

o Used in industrial burners

o Typical operating temperature between

1500 - 2200 °F

o Implemented in furnaces, used to heat

ambient air

o Saves fuel in burner by recuperating heat

from exhaust gases

o Typically single tube, but BU series is

predominantly multitube



Project Goals

• Increase the effectiveness of the original BU

o Robust

o Maintain pressure drops

o Easily manufacturable

o Maintain current exterior dimensions



• Concentric tube

arrangement

• CFD on original design

showed lack of heat

transfer through inner

tube

• Complicated design and high number of parts

• Decided to abandon concentric tube design in all potential ideas

• Inlet-outlet pairs with connected ends to be underlying concept

hereafter

Original Design



Proposed Solution



Explanation of Decision Matrix

• Decision matrix created to rank design concepts

• 5 categories (weight)o No. of parts (10)

o No. of welds (10)

o Machinability (10)

o Scalability (5)

o Pressure Drop (15)

• Ranking from 1 to 5

• Maximum score of 250



First Concept

• Circular bends

• 12 tubes, 6 inlet-outlet pairs

• Min. bend radius for safe tube

bending is 1.5 times tube

diameter

• Decision matrix result

• Score: 130

• Rank: 4



Second Concept

• Compartments of four tubes

(two inlets and two outlets)

• Welding torch of 12 mm

diameter has to weld on inside

• Impossible to weld airtight


• Score: 140

• Rank: 3



Third Concept

• 90° bends forming

rectangular loops

• Similar issues with

welding torch clearance


• Score: 90

• Rank: 6 (worst)



Fourth Concept

• Inner & Outer manifold

• Outer manifold:

• 9 pipes - 4 inlet, 5 outlet

• Inner manifold:

• 3 pipes - 1 inlet, 2 outlet


• Score: 145

• Rank: 2



Final Prototype Concept

• Adapted to 8 circular tubes

• Larger bend radii leads to

increased amount of space

• High manufacturability due

to single bend radius and

pipe symmetry


• Score: 240

• Rank: 1 (best)



Final Design Concept Flow Path

Compartment at hot air outlet quickens exit

of preheated air, preventing loss of heat to

cold air inlet section



Exhaust Out

Exhaust In

Cold Air Inlet

Hot Air Outlet

Computational Fluid

Dynamics (CFD)

Analysis

Speaker: J. Hum


Design Models• Include exchanger tubes and

exhaust gas only

• Design 3 - 45° Welded Bends

• Design 4 – Ring Manifolds

Speaker: J. Hum


Design Models

Speaker: J. Hum


Computational Comparison

Speaker: J. Hum


Original BU – Symmetry

Prototype BU

Flow Profiles

• Previous designs had tubes

behind other bends

• Potential for baffles

• High pressure drop in outlet

chamber and fitting

Tube inlet: 2.2 “W.C.

Tube outlet: 1.2 “W.C.

• Similar drop at exhaust outlet

Pressure (inches-water)

1.2 “W.C.

2.2 “W.C.

Speaker: J. Hum


Velocity (ft/s)

Exhaust

Exhaust

Prototype Experimental Comparison

Speaker: J. Hum


Experimental

Testing

Speaker: J. Sowin


Test Procedure•Exhaust air simulating 200-350 kBtu/hr with 12% excess air

•Three flow rates varying the exhaust temperatures from 700-1100°F

•Temperatures measured at all inlets, outlets and on tubes with thermocouples

•Flow rates measured for exhaust and pre-heat air by an orifice plate pressure drop

•Pressure drops measured for exhaust and pre-heat air with manometers

Electric

Heaters

Pre-Heat Air

Blower

Insulated BU

Recuperator

Orifice Flowmeter

K-type

Thermocouple

Wires

Speaker: J. Sowin


•9 K-type thermocouples: spaced throughout the BU

•Temperature read out from electric heater

•2 Orifices : placed 4 feet from blowers, pressure drop measured by

manometer

•2 Static pressure manometers: placed at exhaust inlet and pre-heated air inlet

Thermocouple Placements

Speaker: J. Sowin


Experimental Results

Average Effectiveness Overall = 22% for original BU

Average Effectiveness Overall = 26% for redesigned BU

Effectiveness

Speaker: J. Sowin


Experimental ResultsAir Pressure Drop

Speaker: J. Sowin


Energy Savings

Estimate

Speaker: K. Lui


Assumptions

• BU heat exchanger run time o Eight hours per day

o 365 days per year

• Propane is used as the fuel gaso Energy content = 91,690 Btu/gal [1]

o Cost = $2.05/gal (Feb 2011) [2]

• Comparing old and new designs in terms ofo Increased energy savings (energy saved)

o Reduced cost (cost saved)

[1] Energy Density of Propane

http://hypertextbook.com/facts/2002/EricLeung.shtml

[2] Propane Prices by Sales Type, U.S. Energy Information Administration

http://www.eia.gov/dnav/pet/pet_pri_prop_dcu_nus_m.htm

Speaker: K. Lui


Average Increase = 4.25%

Speaker: K. Lui


14

24

34

44

54

64

74

84

94

104

600 800 1000 1200 1400 1600 1800 2000 2200

En

erg

y S

ave

d (

MM

Btu

/ye

ar)

Exhaust Inlet Temperature (°F)

Energy Savings Increased per Year

Q_a (old) = 2000 scfh



Q_a (new) = 2000 scfh



Average Increase = 4.25%

Speaker: K. Lui


300

500

700

900

1100

1300

1500

1700

1900

2100

2300

600 800 1000 1200 1400 1600 1800 2000 2200

Co

st

Sa

ve

d (

$/y

ea

r)

Exhaust Inlet Temperature (°F)

Reduced Cost per Year (Propane as the fuel)







Cost Analysis

Speaker: D. Herman


Original BU

• 36 total parts

• 4 subassemblies

• 46 individual welds

Overall cost estimate:

$411.22

Speaker: D. Herman


Redesigned BU

• 13 total parts (63% reduction)

• 2 subassemblies

• 23 individual welds (50% reduction)

Overall cost estimate:

47% reduction

Speaker: D. Herman


$215.29

Budget

Speaker: D. Herman


Cost BreakdownSpeaker: D. Herman


$1,153.53

$493.12

$566.10

$1,002.49

$2,252.67Final Project Costs

Total Experimental Testing Costs

Total Cost of Final Build

Total Travel Costs

Estimated Project Costs

Machining Time 3 18 $50.00 $900

Pipes 1 3 $35.78 $107.34

FedEx Shipping 2 2 $60.00 $120.00

Sheet Metal 12" X 24 " 12" X 24 " $26.19 $26.19

Machining Time 3 7 $50.00 $350.00

Pipes 4 4 $35.78 $143.12

Travel Plant visits 2 3 $188.70 $566.10

Cost

Experimental Testing

Final Design Build

Quantity $/UnitType Original Quanity

Conclusions and

Recommendations

Speaker: D. Herman


• Average effectiveness increased from 22%

to 26%

• Cost of manufacturing decreased by 47%

o 1/3 of the original number of parts

o 50% fewer individual welds

• Air pressure drop reduction of 27%

• Future recommendations

o Determine the optimum tube diameter and number

of tube pairings

o Redesign exhaust and air outlets

o Further test the implementation of external fins

Speaker: D. Herman


Summary

Thank You

Questions?

Comments?

Re-engineering of an industrial grade heat exchanger

Technology

dmello512012 team

heat exchanger8

lack of heat transfer

concentric tube design

inner tubecomplicated

safe tube bending

single bend radius

inletoutlet pairsmin