Use of STAR-CCM+ for Heat Exchanger Product Development

DENSO MARSTON LTD.

DNMN Product Development

Use of STAR-CCM+

for Heat Exchanger Product Development

Gary Yu, Martin Timmins, Mario Ciaffarafa

DENSO Marston Ltd.

DENSO MARSTON LTD.


Founded in 1904 Acquired by DENSO in 1989 Located in Shipley, West Yorkshire Designs and Manufactures engine

cooling modules for Heavy Duty Cooling applications

Product Range includes radiators, oil coolers, charge air coolers and condensers

DENSO Marston

DENSO MARSTON LTD.


1. Charge air cooler (CAC) is a typical fin-tube type cross flow heat exchanger;

very fine mesh is required in CFD model to capture inner and external fin

geometry features.

2. Further smaller mesh size is required to resolve thermal boundary layer.

3. Hundreds of millions of cells may be generated in CFD model for a conjugated

heat transfer (CHT) study on a CAC of typical size in off-highway heavy duty

vehicles.

4. Large computing resources will be required and therefore very inefficient.

Background

Core Depth

Ove

r C

ore

Tube Inner Fin

External Fin

Charge

Air

Cooling

Air

DENSO MARSTON LTD.


5. Can STAR-CCM+ single stream or dual stream heat exchanger model do the

job?

NO, it requires the input of test data and cannot be used for new product

development.

6. An in-house program has therefore been developed and validated in DENSO

Marston to build a virtual CAC prototype for prediction of heat rejection rate

and pressure drop.

7. STAR-CCM+ has been used to find the key information of heat transfer and

pressure drop in the new design.

Background

Core Depth

Ove

r C

ore

Tube Inner Fin

External Fin

Charge

Air

Cooling

Air

DENSO MARSTON LTD.


1. Use of STAR-CCM+ to study a very small section of inner and external

fins to find heat transfer and pressure drop information.

2. Based on the information from Step 1, an in-house program using C++ is

developed to build a virtual CAC prototype to predict the overall heat

rejection rate, charge air core pressure drop and cooling air pressure

drop.

3. Based on the charge air core pressure drop and overall heat rejection rate

from Step 2, STAR-CCM+ single stream heat exchanger model is used to

predict charge air pressure drop over tanks and core.

Methodology

1 2 3

DENSO MARSTON LTD.


Why STAR-CCM+ IS Required?

111 , , , hhhh PTm

222 , , , hhhh PTm

222 , , , cccc PTm

111 , , , cccc PTm

(6) D

L

2

1

c

c2 VfP cccc

)(Re ,)(Re 22hhhccc FfFf

(7) D

L

2

1

h

h2 hhhh VfP

(1) )( 21 hhhh TTmcpQ

(3) TAUQ

(4) h

hh

RT

P

hhcc AAUA 111

22

1221 cchh TTTTT

)(Re ,)(Re 11hhhccc FNuFNu

(2) )( 12c ccc TTmcpQ

(5) c

cc

RT

P

CFD is used for the solution

222222 ccchhh PTPTQ , , , , , ,7 unknowns:

Additional unknowns introduced:

hchc ffNuNu , , ,

DENSO MARSTON LTD.


Determination of Computational Domain

Assumptions:

1. Flow is uniformly distributed between each fin loop:

2. Flow and heat transfer are same in each half external fin loop

3. Flow is periodic between each inner fin loop

One loop of inner fin, 160 mm length, and half loop of external fin, 64 mm

length, are modelled in CFD

Periodic boundary

condition

Inner fin External fin

DENSO MARSTON LTD.


CFD Physics Model and Boundary Conditions

wT

• Mass flow inlet,

• Temperature inlet,

• Constant wall temperature,

• Pressure outlet

m

inT

m inT

wT

DENSO MARSTON LTD.


External fin Inner fin

Results – Y+ Value

1. Pressure drop between inlet and outlet and residuals monitored for convergence check

2. Fin wall Y+ value checked to make sure near wall viscous sub-layer resolved

DENSO MARSTON LTD.


Inner Fin Correlation: Nu v Re

viscositydynamic fluid :

area through flow : rate; flow mass :

tyconductivi thermalfluid :

CAm

Inner Fin and External Fin Heat Transfer Correlations

diameter hydraulic :

tcoefficienfer heat trans averaged :

Re ,

h

h

C

h

D

D

A

mDNu

External Fin Correlation: Nu v Re

DENSO MARSTON LTD.


hD

LVfP 2

2

1

Inner Fin Correlation: Friction Factor v Re

Inner Fin and External Fin Pressure Drop Correlations

lengthfin : velocity;: density; :

factorfriction averaged : drop; pressure :

LV

fP

h

C

D

A

m

Re

External Fin Correlation: Friction Factor v Re

viscositydynamic fluid : area; through flow :

diameter hydraulic: rate; flow mass :

C

h

A

Dm

DENSO MARSTON LTD.


1. Discretise the heat exchanger core in hot flow direction by half of external fin

loop pitch and in cold flow direction by one inner fin loop pitch.

2. Carry out heat balance and pressure drop calculation on each cell to get

overall heat rejection rate and core pressure drop on both flow sides.

Assumptions:

1. Flow rate is uniform across each tube and each fin loop.

2. Both fluids are ideal gas, no tube wall thermal resistance between hot and

cold fluids.

3. No heat conduction along the tube in both flow directions.

Numerical Program for Calculation of Core Pressure Drop and Overall

Heat Rejection Rate

DENSO MARSTON LTD.


Numerical Program Output – an Example

Core Pressure Drop and Overall Heat Rejection Rate

DENSO MARSTON LTD.


Charge Air Total Pressure Drop (Tanks + Core)

Q

Outlet

Tank

Inlet

Tank

In house

program

STAR-CCM+

single stream

heat exchanger

model

Q

P over

core

DENSO MARSTON LTD.


Validation Against CAC A Test Data, Face Area 0.525 m2

- Heat Rejection Rate and Cooling Air Pressure Drop

Cooling Air Velocity m/s 4 6 8 10

Cooling Air Temp on oC 16.1 15.7 15.6 15.5

Charge Air Mass Flow kg/m 34.8 34.3 34.5 34.6

Charge Air Pressure In bar 1.9 1.9 1.9 1.9

Charge Air Temp In oC 184.4 184.0 183.4 183.0

Cooling Air P (Test) 100% 100% 100% 100%

Cooling Air P (Prediction) 97.6% 96.5% 98.9% 102.1%

Heat Rejection Rate (Test) 100% 100% 100% 100%

Heat Rejection Rate

(Prediction) 101.3% 100.3% 100.1% 100.1%

DENSO MARSTON LTD.


Validation Against CAC A Test Data, Face Area 0.525 m2 - Charge Air Pressure Drop


Cooling Air Temp on oC 16.7 16.8 16.8 16.7

Charge Air Mass Flow kg/m 42.3 36.8 34.6 30.3

Charge Air Temp In oC 185.7 187.0 187.5 185.7

Charge Air Pressure In bar 1.9 1.9 1.9 1.9

Charge Air P (Test) 100% 100% 100% 100%

Charge Air P (Prediction) 93.7% 99.3% 100.9% 106.9%

DENSO MARSTON LTD.


Validation Against CAC B Test Data, Face Area 0.074 m2 - Heat Rejection Rate


Charge Mass Flow kg/s 0.35 0.30 0.25 0.20

Charge Mean Temp In oC 182.2 182.3 181.3 178.8


Heat Rejection Rate

(Prediction) 98.1% 99.7% 99.2% 99.9%

Cooling Air velocity m/s 4 6 8 10

Charge Mass Flow kg/s 0.26 0.26 0.25 0.25

Charge Temp In oC 181.9 181.5 181.3 181.0


Heat Rejection Rate

(Prediction) 98.4% 99.3% 99.2% 100.8%

DENSO MARSTON LTD.


Summary

• An in house program has been developed to predict the charge

air cooler (CAC) thermal performance based on heat transfer

and pressure drop information obtained by two separate CFD

detailed studies on CAC inner and external fins;

• In the CFD detailed study, only a small section of external and

inner fin (one inner fin loop, half external fin loop) is modelled;

the accuracy of this study is the key to the CAC thermal

performance prediction;

• STAR-CCM+ single stream heat exchanger model is used to

predict the charge air pressure drop over CAC tanks and core;

• The developed methodology is validated against test results of

two CAC units;

DENSO MARSTON LTD.


THANK YOU

Use of STAR-CCM+ for Heat Exchanger Product Development

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