PHOENICS USER CONFERENCE 2004 The Supercomputing People CFD ANALYSIS OF CROSS FLOW AIR TO AIR TUBE TYPE HEAT EXCHANGER Vikas Kumar 1* , D. Gangacharyulu 2* , Parlapalli MS Rao 3 and R. S. Barve 4 1 Centre for Development of Advanced Computing, Pune University Campus, Pune, India 2 Thapar Institute of Engineering & Technology, Patiala, India 3 Nanyang Technological University, Singapore 4 Crompton Greaves Ltd, Kanjur Marg,
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CFD ANALYSIS OF CROSS FLOW AIR TO AIR TUBE TYPE HEAT EXCHANGER
Vikas Kumar1*, D. Gangacharyulu2*, Parlapalli MS Rao3 and R. S. Barve4
1 Centre for Development of Advanced Computing, Pune University Campus, Pune, India2 Thapar Institute of Engineering & Technology, Patiala, India3 Nanyang Technological University, Singapore4 Crompton Greaves Ltd, Kanjur Marg, Mumbai, India
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Introduction• Closed Air Circuit Air Cooled (CACA) electrical motors are used in
various industries for higher rating (500 kW and above) applications
• Heat generation due to the energy losses in the windings of motors at various electrical loads under operating condition
• Cold air is circulated in the motor to remove the heat generated
• The hot air generated in the motor is cooled by using an air to air tube type cross flow heat exchangers
• The motor designers are interested to know the temperature distribution of air in the heat exchanger and pressure drop across the tube bundle at various operating parameters, e.g., different hot & cold air temperatures and fluid (hot & cold) flow rates
Large Electrical Motor
Heat exchanger
Source: M/S Crompton Greaves Ltd. Mumbai, India
Heat Exchanger Geometry
External cold air
Internal hot air
External hot air
cooled air
cooled air
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OBJECTIVE
Predictions of
Pressure Air flow and Temperature distributions
in the heat exchangers
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Sl. No.
Description Unit
Value/Type
1. Overall dimension mm
1760 x 100 x 765
2. Tube inner diameter
mm
22
3. Tube outer diameter
mm
26
4. Tube length mm
1610
5. No. of tubes - 27
6. Transverse pitch mm
61
7. Longitudinal pitch mm
41
Table 1: Geometrical details of the heat exchanger
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Modeling Considerations1. Geometry has symmetry in width wise.
2. A section of heat exchanger consisting of 9 rows & 3 columns has been considered for analysis. Each column has 9 tubes.
3. Tube is modeled as solid blockage, whereas, the inner volume of the tube has been modeled as blockage with gaseous properties to allow the ambient air to pass through it by using PHOENICS CFD Software.
4. Conduction takes place from the tube wall & convection takes place from the surface of the tube.
5. The partition plate and baffle participate in heat transfer.
6. Temperature & flow distributions have been considered to be three dimensional in nature.
7. k-ε turbulence model has been considered.
8. Hybrid difference scheme has been used.
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The distribution of cells in the three directions are given below:X Direction : 55 Y Direction : 48 Z Direction : 232 The total number of cells in the computational domain is 612,480.
Grid generation for heat exchanger
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Fig. 3: Side view of the grid
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Sl. No. Input parameters Unit Value
1. Temperature of cold air
oC 35
2. Temperature of hot air oC 63
3. Volumetric flow rate of cold air
cfm (cu.m/m)
388 (10.98)
4. Volumetric flow rate of hot air
cfm (cu.m/m)
228.80(6.48)
Table 2: Operating boundary conditions of the heat exchanger
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Results & Discussions
• The highest pressure region has been observed nearby the top of the separating plate, which may be due to the large change in the
momentum of the cold fluid caused by the plate. • Hot fluid recirculation has been observed at the
top corner of 1st & 4th section. • The temperature drop of the hot air in the 1st
section of the heat exchanger is higher than 4th section because of the high temperature difference between the cold air and the hot air.
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Fig. 4: Pressure distribution in the heat exchanger
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Fig. 5: Velocity distribution in the heat exchanger
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Fig. 6: Temperature distribution in the heat exchanger
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Fig. 7: Temperature distribution in the tube bundle of the heat exchanger
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Sl. No.
Inlet temperature, oC
Outlet temperature, oC
Remarks
Cold air
Hot air 2nd section
Hot air 3rd section
Hot air1st section
Hot air4th
section
Cold air
1. 34.4
63 63 41.9 51.8 46.8 Experimental
2. 34.4
63 63 44.70 49.55 43.68
PHOENICS Simulation
3. 34.4
61 65 43.68 50.9 44.32
PHOENICS Simulation
Table 3: Comparison of air temperature prediction at various outlets
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Fig. 8: A comparison between CFD simulation & experimental result
41.9
51.8
46.844.7
49.55
43.68
0
10
20
30
40
50
60
Hot air outlet temperature(Ist section)
Hot air outlet temperature(4th section)
cold air outlet temperature
Different position of outlets
Ou
tlet
tem
per
atu
re,
Deg
.C
Experimental
Simulated
Boundary conditions: cold air temperature : 34.4 Deg.C
hot air temperature: 63 Deg.C cold air flow rate : 0.18316 cum/s
hot air flow rate: 0.108 cum/s
Fig. 8: A comparison between the results of CFD simulation & experiments
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Fig. 9: Temperature distribution in the heat exchanger – a case study
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Fig. 10: Temperature distribution of the heat exchanger (after modification of central partition plate)
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Figure 10 : Effect of processor on computation time using parallel PHOENICS
316.5
219
136
92.5
7260
0
50
100
150
200
250
300
350
0 2 4 6 8 10 12
Number of processors
Com
puta
tion
time
per
swee
p, s
(Sun Ultra SPARC-450, 300 MHz)
Fig. 11: Effect of number of processors in computing time using parallel PHOENICS
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Conclusions• A method for predicting the pressure, velocity &
temperature distributions in the tube type heat exchanger associated with CACA large motor has been developed using PHOENICS CFD software.
• The simulated results predict the temperature distribution reasonably at different locations of the heat exchanger.
• The CFD model may be used to optimize its thermal performance by varying the location of the baffles & the partition plate in the heat exchanger and in turn to improve the performance of electrical motors.
• The parallel PHOENICS can be used to reduce the design cycle of the equipment due to fast computation.
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1. M/S Thapar Centre for Industrial Research & Development, Patiala, India for providing the necessary facilities to carry out this project
2. M/S Crompton Greaves, Mumbai, India for providing the funds in addition to drawing, design data and experimental results
3. M/S CHAM, U.K (support team) for technical help
4. M/S Centre for Development of Advanced Computing (C-DAC), Pune, India for providing the facility to use PARAM 10000 for running parallel PHOENICS and funding for presenting this paper
Acknowledgements
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THANK THANK YOUYOU
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