Simulation of Exhaust Gas Heat Recovery System for an Automobile

Transcription

1 Simulation of Exhaust Gas Heat Recovery System for an Automobile Patent Pending : 2482/MUM/2013. Copyright 2012 Mahindra & Mahindra Ltd. All rights reserved. 1

2 Introduction To recover heat from exhaust gas and used it to maintain items 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 Chapattis Application Tourism Vehicles Bread Toaster Ambulance Safari rides Cold Water Inlet Hot Water Outlet Hot Box 2

3 Water Inlet Hot Water Outlet Hot Box Circuit Hot water Inlet Hot Box Return line Hot Water Outlet Cold Water Inlet Swi tch Pump Heat Exchanger Unit Hot Box Heat exchanger 3

4 Length Optimization Table : Optimization of Heat Exchanger length S.No Length (mm) Volume (L) Temperature (o C) Figure : Optimization of length of Primary Heat Exchanger 4

5 Results Table 1 : Results of Static testing Initial After 15 minutes T T T T T Table 2. Results of Dynamic testing at 10 kmph Initial After 15 minutes T T T T T where T T1 T2 T3 T4 T5 Temperature in degree Celsius Exhaust gas temperature before heat exchanger Exhaust gas temperature after heat exchanger Hot Box temperature Cold water temperature Hot water temperature Table 3. Results of Dynamic testing at Highway Driving Initial After 15 minutes T T T T T

6 Log mean temperature difference (LMTD) The Log mean temperature difference for a parallel flow double pipe heat exchanger is given by equation: The log mean temperature difference for the three cases are as given below Testing Condition LMTD Static At 10 kmph Highway driving

7 Hot Box Temperature Measurements at Highway Driving Condition Temperature in degc st Stop 2 nd Stop T1 T2 T5 T deg C Hot Box Temperature Time in Seconds 45 minutes for Data logger preparation 48 minutes for Hot Box to reach and Security Clearances 65 deg C despite two stops in between Results T1 T2 T3 T4 T5 LMTD Initial Maximum Abbreviations T1= Exhaust Gas Temperature before Heat Exchanger T2= Exhaust Gas Temperature after Heat Exchanger T3= Hot Box Temperature T4= Cold Water Temperature T5= Hot Water Temperature 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. 7

8 Simulation Input Inlet Boundary condition: For Laminar Flow Inlet velocity= 0.17 m/s Inlet temperature= 313 K Symmetry at boundary region Wall function at pipe and gas region For Turbulent flow Inlet velocity = 31 m/s Inlet temperature = K Symmetry at boundary region No slip condition at wall Material properties: Substance Thermal conductivities (W/ m K) Stainless steel 16 Water 0.58 Exhaust Gas (Carbon dioxide)

9 Hot Box Meshed model Inlet Close up of boundary mesh Mesh Statistics Outlet 9

10 Simulation results Fig: Contours temperature variation in Water regime & Exhaust Gas Fig: Exhaust Pipe temperature 10

11 Graph: Comparison of Outlet water temperature(k) 11

12 COMSOL Graph: Comparison of Outlet exhaust gas temperature(k) 12

13 Way Forward The use COMSOL Multiphysics to optimize the Hot Box Design 13

14 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. 14

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