Simulation of a heat reclaim water heating tank prototype using

Simulation of a heat reclaim water heating tank
prototype using ACUSOLVE
for design approach formulation
(O.Y.L Research & Development Centre)
Mohd Anuar Abd Aziz
Date – 27 Aug, 2013
SUNGAI BULOH, MALAYSIA
Background
O.Y.L R&D CENTRE SDN BHD
• People – oriented company
Purpose:
• Pledges to incorporate Innovative Technology to deliver quality products
to customers on schedule and at competitive price.
• Continual strive for design excellence that meets, and whenever
possible, exceeds customers’ expectation.
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O.Y.L R&D Presentation at the ATC2013.
Main Products –split unit
Wall Mounted
J Series
Ceiling Cassette
C Series
Ceiling Cassette
E Series
Ceiling Convertible
E Series
Ceiling Concealed
C Series
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O.Y.L R&D Presentation at the ATC2013.
Hot water tank
Heat Reclaim System
An air conditioning and centralized hot water system
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O.Y.L R&D Presentation at the ATC2013.
Simulation of a heat reclaim water heating tank
prototype using ACUSOLVE for design approach
formulation
• Objectives
1.
To develop an appropriate CFD model to design water tank geometry.
2.
The limitations and advantages of the model are to be recognized and
taken into consideration in future design/simulation.
• Statement of problem
•
A heating water tank system using waste heat from outdoor unit split unit
is currently developed in OYL R&D.
•
Experimental result has been obtained but with limited information.
•
A design methodology using CFD is pursued to provide richer design
information (fluid flow pattern, temperature distribution etc).
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O.Y.L R&D Presentation at the ATC2013.
Heat reclaim system: The concept
Standard Air-Conditioning
2 in 1 Heat Reclaim System
Cooling
Energy
Input
Standard
Unit
Energy
Input
Waste Heat
Cooling
Heat
Reclaim
Waste Heat
Tank
Hot
Water
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O.Y.L R&D Presentation at the ATC2013.
Heat reclaim system: The concept
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O.Y.L R&D Presentation at the ATC2013.
Geometry & Boundary Conditions
Temperature probes positions
Hot water outlet,
Twater, out=
?
pos
1
Coil 4,constant T4
pos
2
Coil 3, constant T3
pos
3
Coil 2, constant T2
pos
4
Coil 1, constant T1
Cold water inlet,
Twater, in≈26 oC
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O.Y.L R&D Presentation at the ATC2013.
Additional Boundary Conditions
• -Spallart-Almaras turbulence model
• -No slip, adiabatic tank wall BC
• -No heat transfer through internal pipe wall
• -Steady-state solver
• -Buoyancy model is included
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O.Y.L R&D Presentation at the ATC2013.
Point of interest
• Outlet water temperature (pos1)
• Water temperature profile at different positions (pos2, pos3, pos4)
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O.Y.L R&D Presentation at the ATC2013.
Simulation VS experiment result analysis
• Three sets of experiment results are available with three flow
conditions.
• The temperature plot is obtained for the CFD simulation for each set of
experiments 1, 2 and 3.
• The water inlet flow conditions are similar for all cases.
• The coil temperature profile is different for all cases.
Exp 1
Water inlet temperature (°C)
Exp 2
Exp 3
26
26.3
25.7
Coil 1 temperature (°C)
44.8
52.6
69.8
Coil 2 temperature (°C)
44.5
52.1
69.1
Coil 3 temperature (°C)
29
51.8
68.2
Coil 4 temperature (°C)
43.7
51
67
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O.Y.L R&D Presentation at the ATC2013.
Experiment 1: Temperature distribution
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O.Y.L R&D Presentation at the ATC2013.
Experiment 2: Temperature distribution
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O.Y.L R&D Presentation at the ATC2013.
Experiment 3: Temperature distribution
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O.Y.L R&D Presentation at the ATC2013.
Observations
• As observed:
• The average water flow speed across the tank quickly slows down due to
high tank to inlet pipe diameter ratio. Thus, the average water flow speed
across the coil is low.
• Near the coil, the temperature gradient is high but away from the coil,
temperature gradient drastically decreases. This indicates low heat
transfer from coil to fluid for this type of geometry.
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O.Y.L R&D Presentation at the ATC2013.
Comparative analysis
Temperature error (°C) Vs Positions
Temperature error, dt
2
1
0
Pos 1
Pos 2
Pos 3
-1
-2
Pos4
Exp 1
Exp 2
Exp 3
-3
-4
Sensor positions
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O.Y.L R&D Presentation at the ATC2013.
Benefits
• It is shown that the CFD constant coil temperature BC can only be used
within an error band of up to ±3oC.
• The internal flow of the water is able to be observed. This is not
possible with current experimental setup.
• While the quantitative result is judged to be having a large error margin,
the qualitative result is deemed to give a reasonable estimate on the
flow pattern inside the tank.
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O.Y.L R&D Presentation at the ATC2013.
Challenges faced and solutions presented
• This is our team’s first experience in simulating such CFD model
however we currently have ample experts supports to justify the errors
encountered.
• This is our first experience in using Acusolve’s FEA solvers, we had
more experience in using FVM based CFD codes in the past. Both Altair
and academia has been supportive for us to justify the results better.
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O.Y.L R&D Presentation at the ATC2013.
Conclusion
•
The current simple CFD model is unable to fully describes the water tank fluid
flow and heat transfer. It is shown that more complex approach is needed.
•
In general, reasonable pattern is observed. The CFD model shows suitability to
estimate flow and heat transfer pattern in the water tank, adding extra info for
design purposes. Such info is unable to be easily captured by experimental
result.
•
The CFD simulation indicates poor bypass factor of water flow through the coil.
Future design should aim to improve the bypass factor of water flow. This in turn
will increase the average heat transfer coefficient of the coil.
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O.Y.L R&D Presentation at the ATC2013.
Acknowledgements/Credits
• For in depth solver consultation:
• Steve Cosgrove, Altair.
• Prof Ng Khai Ching, Universiti Tenaga Nasional, Malaysia.
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O.Y.L R&D Presentation at the ATC2013.