1. Design of an Improved
Bayonet Ultra Heat Exchanger
Team 11
5/1/12
2. 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
3. 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
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 3
4. Overview
• Introduction
• Proposed Solution
• Computational Fluid Dynamics Analysis
• Experimental Testing
• Energy Savings Estimate
• Cost Analysis
• Budget
• Conclusions and Recommendations
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 4
6. 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
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 6
7. Project Goals
• Increase the effectiveness of the original BU
o Robust
o Maintain pressure drops
o Easily manufacturable
o Maintain current exterior dimensions
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 7
8. • 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
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 8
10. 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
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 10
11. 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
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 11
12. 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
• Decision matrix result
• Score: 140
• Rank: 3
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 12
13. Third Concept
• 90° bends forming
rectangular loops
• Similar issues with
welding torch clearance
• Decision matrix result
• Score: 90
• Rank: 6 (worst)
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 13
15. 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
• Decision matrix result
• Score: 240
• Rank: 1 (best)
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 15
16. Final Design Concept Flow Path
Compartment at hot air outlet quickens exit
of preheated air, preventing loss of heat to
cold air inlet section
Speaker: H. D’Mello
5/1/2012 Team 11 – Heat Exchanger 16
Exhaust Out
Exhaust In
Cold Air Inlet
Hot Air Outlet
18. Design Models
• Include exchanger tubes and
exhaust gas only
• Design 3 - 45° Welded Bends
• Design 4 – Ring Manifolds
Speaker: J. Hum
5/1/2012 Team 11 – Heat Exchanger 18
21. 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
5/1/2012 Team 11 – Heat Exchanger 21
Velocity (ft/s)
Exhaust
Exhaust
24. 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
5/1/2012 Team 11 – Heat Exchanger 24
25. •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
5/1/2012 Team 11 – Heat Exchanger 25
26. Experimental Results
Average Effectiveness Overall = 22% for original BU
Average Effectiveness Overall = 26% for redesigned BU
Effectiveness
Speaker: J. Sowin
5/1/2012 Team 11 – Heat Exchanger 26
29. Assumptions
• BU heat exchanger run time
o Eight hours per day
o 365 days per year
• Propane is used as the fuel gas
o Energy content = 91,690 Btu/gal [1]
o Cost = $2.05/gal (Feb 2011) [2]
• Comparing old and new designs in terms of
o Energy saved
o Cost saved
[1] Energy Density of Propane
http://hypertextbook.com/facts/2002/EricLeung.shtml
[2] Propane Prices by Sales Type, U.S. Energy Information Administration
http://www.eia.gov/dnav/pet/pet_pri_prop_dcu_nus_m.htm
Speaker: K. Lui
5/1/2012 Team 11 – Heat Exchanger 29
30. Average Increase = 4.25%
Speaker: K. Lui
5/1/2012 Team 11 – Heat Exchanger 30
14
24
34
44
54
64
74
84
94
104
600 800 1000 1200 1400 1600 1800 2000 2200
EnergySaved(MMBtu/year)
Exhaust Inlet Temperature (°F)
Energy Saved per Year
Q_a (old) = 2000 scfh
Q_a (old) = 2830 scfh
Q_a (old) = 3500 scfh
Q_a (new) = 2000 scfh
Q_a (new) = 2830 scfh
Q_a (new) = 3500 scfh
31. Average Increase = 4.25%
Speaker: K. Lui
5/1/2012 Team 11 – Heat Exchanger 31
300
500
700
900
1100
1300
1500
1700
1900
2100
2300
600 800 1000 1200 1400 1600 1800 2000 2200
CostSaved($/year)
Exhaust Inlet Temperature (°F)
Cost Saved per Year (Propane as the fuel)
Q_a (old) = 2000 scfh
Q_a (old) = 2830 scfh
Q_a (old) = 3500 scfh
Q_a (new) = 2000 scfh
Q_a (new) = 2830 scfh
Q_a (new) = 3500 scfh
33. Original BU
• 36 total parts
• 4 subassemblies
• 46 individual welds
Overall cost estimate:
$411.22
Speaker: D. Herman
5/1/2012 Team 11 – Heat Exchanger 33
34. Redesigned BU
• 13 total parts (63% reduction)
• 2 subassemblies
• 23 individual welds (50% reduction)
Overall cost estimate:
47% reduction
Speaker: D. Herman
5/1/2012 Team 11 – Heat Exchanger 34
$215.29
38. • 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
5/1/2012 Team 11 – Heat Exchanger 38
Summary
We used CFD analysis, specifically FLUENT in Ansys Workbench, to analyze our tube designs and predict the changes in flow and key variables, namely preheat temperature and pressure drop.
We created design models to directly compare impact of new tube arrays. As you can see we ignored the housing and inlet/outlet fittings, focusing only on the exchanger tubes and exhaust domain. Here we have the performance for the original BU, design 3 which is the 45deg welded bends and Design 4 which had inner and outer manifolds. Preheat air temperature, which is the most important number, what we send to the burner, is on the left axis, burner input on the lower axis. The typical range of 200 to 400 thousand btu/hr is directly related to the flow rates on both exhaust and air sides.
We see a 5 to 8% increase in preheat air temperatures, with decreasing gains at high flow rates for the manifold design.
These are the pressure drops associated with those two designs. You’ll note that the square bend design has significantly increased air pressure drop and much lower exhaust drop. This is because this design required smaller diameter tubes, shifting the greater pressure drop towards the air side. The manifold design had higher pressure drop on both sides. So these charts are why we didn’t like the designs from a pressure drop aspect.
One thing to note is that looking at the original design, the pressure drops in air and exhaust are very close, where as the actual numbers youd find on the datasheet show the air drop higher by 2 to 5 times. This is because these models only contain the tubes, and I’ll explain this further in a few slides.
So now we have the full models of the original BU and the prototype. You can see that the original design had a symmetry plane that we took advantage of. So here’s the combined performance chart, preheat temperature on the left axis corresponding to the red curves, pressure drop on the right. We vary over the operating range of 100 to 400 KBTU/hr. Again solid lines are the original, dashed are the prototype. We have a 4 to 12% increase in preheat temperature, 20% decrease in air pressure drop, and up to 10% increase in exhaust pressure drop, although as I stated before, the exhaust numbers are much lower than the air numbers, and because this is a closed loop system we can say that these offset to an overall reduction in pressure drop.
Here we see the flow profiles in the exhaust section and pressure drop in one of the exchanger tubes. The flow here is colored by velocity. We see two zones with low flow velocity. The one behind the tube bends here does not affect our design since we have removed the central set of 3 tubes. This zone here is due to positioning of the exhaust outlet, and existed in the original design as well. This creates a potential for adding a baffle before the exhaust outlet to eliminate this zone. We also note that for the majority of the interaction region there is high velocity flow at the edges of the radiant tube where our exchanger tubes are located, always a good sign.
Here we see the pressure contour in one of the exchanger tubes. As I alluded to earlier, the pressure drop in the tubes themselves is not a clear majority of the overall pressure drop. We see a pressure drop here of 1 “WC. This means the remaining 1.2 “WC drop is due to the rapid expansion and compression as the heated gasses enter the chamber and are forced through the outlet. A similar pressure drop occurs in the exhaust region heading into the 90deg exhaust outlet. While we had to keep the exterior dimensions and fittings the same, we believe this is a key area to look at redesigning the outlets and chambers to further reduce the pressure drop.
For tests, exhaust inlet increases with increasing flow rate (approaches set point)
22 individual parts costed as well as 4 sub assemblies which served as a baseline comparison for the new design. A painting finishing process was then added. the same methodology was used for both analyses
Costing the original BU with aPriori serves as a baseline comparison for the new design
