1Copyright © 2012 Mahindra & Mahindra Ltd. All rights reserved.

Simulation of Exhaust Gas Heat Recovery System for an Automobile“Patent Pending : 2482/MUM/2013”.

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IntroductionTo recover heat from exhaust gas and used it to maintainitems temperature at 63°C (Food Safety Temperature Control,UK).

Expected Customer Benefits & Applications: Hot Water Milk, Tea, Coffee Soup Curries Keep food warm Instant food-Maggie Pop Corn ChapattisApplicationTourism Vehicles Bread Toaster Ambulance Safari rides

Hot Box

Cold Water Inlet

Hot Water Outlet

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Hot Box CircuitWater Inlet

Heat exchanger

Hot Box

Hot water Inlet

Return line

Hot Water Outlet

Pump

Switch

Hot BoxHeat Exchanger Unit

Cold Water InletHot Water Outlet

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S.No Length (mm)

Volume (L)

Temperature (o C)

1 500 4.4 2082 450 4 1983 400 3.5 1864 350 3.1 1735 300 2.6 1586 250 2.2 1407 200 1.7 1218 150 1.3 989 100 0.8 73

Table : Optimization of Heat Exchanger length

Figure : Optimization of length of Primary Heat Exchanger

Length Optimization

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Results

Initial After 15 minutesT1 34 95T2 34 90T3 31 37T4 31 34T5 31 39

whereT Temperature in degree CelsiusT1 Exhaust gas temperature before heat exchangerT2 Exhaust gas temperature after heat exchangerT3 Hot Box temperatureT4 Cold water temperatureT5 Hot water temperature

Table 1 : Results of Static testing

Initial After 15 minutesT1 36 121T2 38 111T3 36 45T4 33 35T5 36 50

Table 2. Results of Dynamic testing at 10 kmph

Initial After 15 minutesT1 36 348T2 38 336T3 36 82T4 31 33T5 36 94

Table 3. Results of Dynamic testing at Highway Driving

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Testing Condition LMTD

Static 55.85At 10 kmph 72.75

Highway driving 276.89

Log mean temperature difference (LMTD)

The Log mean temperature difference for a parallel flow double pipeheat exchanger is given by equation:

The log mean temperature difference for the three cases are as given below

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0

50

100

150

200

250

300

350

400

0 1000 2000 3000 4000 5000 6000 7000 8000

Tem

pera

ture

in d

egC

Time in Seconds

T1

T2

T5

T3

T1 T2 T3 T4 T5 LMTDInitial 117.27 112.12 35.66 32.78 32.78

Maximum 347.87 335.82 82.27 32.78 93.87 277.79

Hot Box Temperature Measurements at Highway Driving Condition

T1= Exhaust Gas Temperature before Heat ExchangerT2= Exhaust Gas Temperature after Heat ExchangerT3= Hot Box TemperatureT4= Cold Water TemperatureT5= Hot Water Temperature

AbbreviationsResults

45 minutes for Data logger preparation and Security Clearances

1st Stop2nd Stop

65 deg C Hot Box Temperature

48 minutes for Hot Box to reach 65 deg C despite two stops in between

Conclusion: The target temperature of 65 deg C at Hot Box is achievable. It is possible to achieve 65 deg C at Hot Box in less than 30 minutes in Non Stop driving at Highway Driving.

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Simulation InputInlet Boundary condition:

For Laminar Flow For Turbulent flow

Inlet velocity= 0.17 m/s Inlet velocity = 31 m/s

Inlet temperature= 313 K Inlet temperature = 390.2 K

Symmetry at boundary region Symmetry at boundary region

Wall function at pipe and gas region

No slip condition at wall

Material properties:

Substance Thermal conductivities(W/ m K)

Stainless steel 16

Water 0.58

Exhaust Gas (Carbon dioxide) 0.0146

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Hot Box Meshed model

Inlet

Outlet

Close up of boundary mesh

Mesh Statistics

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Simulation results

Fig: Contours temperature variation in Water regime & Exhaust Gas

Fig: Exhaust Pipe temperature

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Graph: Comparison of Outlet water temperature(K)

12Graph: Comparison of Outlet exhaust gas temperature(K)

COMSOL

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Way Forward The use COMSOL Multiphysics to optimize the Hot Box Design

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Conclusion The use of COMSOL Multi-physics to perform preliminary analysis of heat

transfer mechanism in Exhaust gas heat recovery system is found to give good correlation with the testing results.

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Copyright © 2012 Mahindra & Mahindra Ltd. All rights reserved.

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