Advaned Cooling System for Heavy Vehicles

7/29/2019 Advaned Cooling System for Heavy Vehicles

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Advanced cooling system for

heavy vehicles heat exchangers/coolers

Wamei Lin


2/24

Outline

Introduction of my project

Energy distribution in vehicle

Methods for saving energy

New material for heat exchangersConclusion of graphite foam heat

exchanger

Future work


3/24

Introduction of my project The aim of my PhD project is to develop a new cooling

system for heavy vehicles, so that the fuel consumptionand CO2 emission would be reduced.

This project includes two parts:

Flow field: Chalmers University of Technology (LennartLfdahl, Lisa Larsson)

Heat transfer: Lund university (Bengt sundn, Wamei

Lin)


4/24

Energy distribution in vehicle In order to save fuel

consumption in vehicles,

what can be done?

(1)Can we reuse some energyfrom the engine coolant?

(2)Can we recover someenergy from the exhaust gas?

(3)Can we recover somemechanical energy?


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Engine cooling Radiator: to make sure the

engine works at its optimaltemperature (80-90C).

Intercooler: to cool downthe fresh air, whosetemperature is increasedafter through a

turbocharger.


6/24

Methods for saving energyEngine cooling: thermal management

14.5 kW power wassaved in a standarddiesel vehicle (Cho

2007)


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Methods for saving energyExhaust gas (vary between 250 and 680)

(1) Heatingcompartment

(2) Absorption cooling:

7.1 billion gallons ofgasoline was saved inU.S. vehicles (2002J ohnson)

(3) Thermoelectric

device:

Peltier-Seebeck effect.

3-8% of fuelconsumption can be

saved (2007 Smith)


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During the braking process, we canstore the mechanical energy and use itto drive vehicle later.

(1)Transfer the mechanical energy intoelectricity

(2)During the braking process, thekinetic energy is used to generate ahigh pressure gas, which is used todrive vehicles later.

80% of kinetic energy lost in thebraking process can be recovered

The mechanical work


9/24

With the increasing power of vehicles and the increase of electric orhybrid electric vehicles, less heat will be dissipated in the exhaust gas,more heat has to be brought away by the cooling system.

Heatingcompartment

Absorptioncooling

Thermoelectricdevice (3-10%fuel reduced)

Thermalmanagement


The regenerativebraking system (10-25% fuel reduced)


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New material for heat exchangers

The thermal management development

Aluminum and copper

heat exchanger(180 W/(m.K) for aluminum

6061 and 400 W/(m.K) forcopper)

The utilization ofmicrocellular foam materialssuch as metal or graphitefoams

(the enhancement of heat transferby huge fluid-solid contact surfacearea and the fluid mixing)

Coolingpowerincreasing


11/24

Graphite foam


An

appropriatematerial forthe thermal

management

High thermal

conductivity:(Ksolid=1700W/(m.K).

Keff=150W/(m.K) >Keff.Al=2-26W/(m.K))

Low density:0.2-0.6g/cm3,20% of that of

AluminumLarge specific

surface area:5000-50000m2/m3


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Problems

The high pressure drop

The effective area of heat transfer is reduced; A large input of pumping power, a low coefficiency of performance.

Weak mechanical properties

The tensile strength of graphite foam with porosity of 75 % is only0.69 MPa. However, the tensile strength of nickel foam with thesame porosity is 18.44 Mpa.

The dust blocking


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New material for heat exchangers In order to reduce the pressure drop of graphite foams, four different

configurations of foams (pin-finned, blind-holes, corrugated andbaffle) are analyzed.

Graphite

foam

Porosity () Pore

diameter

(Dp) (um)

Specific

surface

area

()(m2/m3)

Effective

thermal

conductivity

(keff)(W/m.K)

Permeability

() (m2)

Forchheimer

coefficient

(CF)

POCO 0.82 500 5240 120 6.13x10-10

0.4457


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Verification of the simulation model

The pressure drop values ofthe present simulation modelare justified to be comparableto experiment.

The Nusselt numbers of thepresent simulation model areslightly higher than theexperimental results.

0

5

10

15

0 0.02 0.04 0.06 0.08 0.1

Frontal velocity (m/s)

Pressuredrop(kPa)

Experiment [6]

Simulation0

20

40

60

80

100120

140

160

0 0.02 0.04 0.06 0.08 0.1


NusseltnumberN

u

Experiment [6]

Simulation


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Pressure drop of graphite foam The pressure loss through

the graphite foam is basedon the Forchheimer

extended Darcy equation

f f F

i i i

CdPu u u

dx

The corrugated and pin-finned foams have lowerpressure drop, due to theshort flow length

(corrugated) and smoothflow path (pin-finned).

The configuration hasimportant effect on thepressure drop of foams.

15times

Frontal air velocity (m/s)

0

50

100

150

200

250

300

350

400

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Pressuredrop(P

a)

corrugated

blind-holes

baffle

pin-finned


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Thermal performance of graphite foam

Nusselt number (Nu) is calculatedby

Np h removed

f f b base inlet

h D D Qu

k k A T

Due to the low flow resistancethrough the corrugated and the

pin-finned foams, more cold air canreach the surface inside the foamand bring away the heat from thefoam.Thus, the effective heat transfersurface is larger in the corrugatedand the pin-finned foams

removedQ . .effhA T

The corrugated and pin-finnedfoams have higher Nu

Frontal air velocity (m/s)

0

20

40

60

80

100

120

140

160

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Nus

seltnumberNu

corrugated

blind-holes

baffle

pin-finned


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Comparison between graphite foam and

aluminium louver fin

Lp(mm)

(degree)

Fp(mm)

Tp(mm)

Lw(mm)

FL(mm)

1 29 2.5 14 12 50

removed removed

pum in in

Q QCOP

P u A P

1000

removed

HEX

QPD

m

1000

removed

HEX

QCF

V

(1) coefficient of performance (COP,how much heat can be removed bya certain input pump power)

(2) power density (PD, how muchheat can be removed by a certainmass of fins)

(3) compactness factor (CF, howmuch heat can be removed in acertain volume)

Aim of comparison


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Comparison of COP (coefficient of

performance)

The louver finheat exchanger

has a largerCOP valuethan thecorrugated andpin-finned foamheat

exchangers atlow velocity.


10

60

110160

210

260

310

360410

460

510

5 6 7 8 9 10 11 12 13 14 15

COP

pin-finned

louver fin

corrugated

At highvelocity,the COP

values aresimilar

Thus, by applying an appropriate configuration for graphitefoam, it is possible to reduce the input pumping power, andhave similar COP value as aluminium louver fin.


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Comparison of PD (power density)


20

30

40

50

60

70

80

90

100

5 6 7 8 9 10 11 12 13 14 15

PD(kW/kg

pin-finned

louver fin

corrugated The corrugatedand pin-finnedfoams havehigher PD valuesthan the louver

fin

This means that the corrugated or pin-finned graphitefoamheat exchanger is lighter than the louver fin heatexchanger, when the removed heat is the same.(Because of the low density)


20/24

Comparison of CF (compactness factor )

When the removed heat is the same, the volume of thecorrugated or pin-finned foam is much smaller than that of thelouver fin.

Because of the open cells in the foam, the heat transfer surface is

larger in the corrugated or pin-finned foam than in the louver fin.

The CF value of

the corrugated orpin-finned foam ishigher than that ofthe louver fin.


2000

4000

6000

8000

10000

1200014000

16000

18000

5 6 7 8 9 10 11 12 13 14 15

CF(kW/m3

pin-finned

louver fin

corrugated

Highcompactness in graphite

foam


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Conclusion of graphite foam heat

exchanger Low pressure drop and high thermal performance have

been provided by the corrugated and pin-finned graphitefoams.

The corrugated and pin-finned graphite foams have

higher PD and CF values than the aluminium louver fin.This implies a light or compact cooling system in vehicles.

By using an appropriate configuration of the graphitefoam, it is possible to have the similar COP value as thealuminum louver fin.


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Future work New structure for heat exchangers

Due to space limitation, it might be good to change the position of heatexchanger. But when the position of the heat exchanger is changed,maybe a new structure of the heat exchanger is appropriate for the newposition.

1) Maybe a countercurrent exchanger is good for the radiator which is on thetop of driver compartment.

2) Designing a new configuration of heat exchanger, first the aluminum heatexchanger will be considered and analyzed. Later the graphite foam heatexchanger will be considered.

radiator 2

compartment

radiator 3

Radiator 1:

countercurrent

exchanger


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Ideas about countercurrent HEX

a.Louverfin(crossflow) b.Louverfin(countercurrentflow)

d.Wavefin(countercurrentflow)c.Pinfin(countercurrentflow)


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Thank youDiscussion and Questions

Documents

Advaned Cooling System for Heavy Vehicles