Flow Boiling Heat Transfer –

Fundamentals and Design of a High Heat

Flux Thermal System Including Micro

Heat Exchangers

HEXAG Meeting, 19 May 2015, Newcastle University

Mohamed M. Mahmoud and Tassos G. Karayiannis

Department of Mechanical, Aerospace and Civil Engineering

Brunel University London, UK

Applications: Cooling Computer Chips

Per chip power consumption (ITRS 2011)

Today ≈ 1.1 - 2 MW/m2

After 10 years ≈ 3.2 – 6 MW/m2

What is the challenge?

Hot spots reach 6 – 10 times the

average power, Bachmann and Bar-

Cohen (2008).

Based on that, the hot spots will reach

19 – 32 MW/m2 by 2026.

Chip temperature should be below 850C.

Processor speed decreases by 10 – 15

% due to hotspots, Yang et al. (2007).

Failure rate increases by a factor of

two, Nnanna et al. (2009).Die size is about:

• 140 mm2 for desktop computers

• 260 mm2 for high performance

computers, Flynn and Hung

(2005)

155 W2014

77 0C

Effective cooling solutions

Liquid cooled IBM iDataplex 360 Server,

Watts and Bachmaier (2012)

Example for on-chip liquid cooling

Processors

Memory cards A case study for a liquid-cooled datacentre compared to

conventional chilled air cooling, U. S. Department of

Energy (2014)

300 kW rating

Air cooling system consumed 130 kW (43 %

of the rated power consumption)

On chip microchannel liquid cooling system

consumed 50 kW (16.7 % of the rated power

consumption)

15 % efficiency improvement

Applications: Cooling Radar Antenna

Aircraft radar system Surveillance radar system

Fujitsu Transceiver Module

12 × 36 × 3.3 mm

Hundreds/thousands of miniature

transmitter/receiver modules in a

planar array.

Active phased arrays (AESAs)

Antenna elements

Efficiency of TR modules is < 45 %

High heat dissipation rate

Single phase liquid cooling is used in

AESAs

Consumes more energy

EPSRC Project

Brunel University

Edinburgh University

Selex-Galileo,

Thermacore,

Sustainable Engine Systems,

Reinforced Precision Machines300 mm

40 mm

Cooling liquid inlet Cooling liquid outlet Cold plate for radar

Failure

area

• Macro to micro transition criteria

• Dominant heat transfer mechanisms

• Flow patterns and maps

• Effect of surface characteristics

– Channel or tube material

– Manufacturing process

• Effect of heated length

• Flow Instabilities

• General heat transfer and pressure drop correlations/models for different fluids including new generation refrigerants

• Multichannel systems for industry (New EPSRC funded Research Grant with Edinburgh University and four Industrial partners)

– Manifold design

– Maldistribution

– Compressibility

– Flow reversal

– Inlet sub-cooling (control in closed-loop systems)

Some of the above could lead to inconsistencies in published data

Flow boiling at the microscale

Questions/problems still to be resolved

Macro to Micro Transition Criteria

Laplace constant (L) = 𝜎 𝑔∆𝜌 Eotvos number (Eo) = 𝑔∆𝜌𝐷2 8𝜎

Bond number (Bd) = 𝑔∆𝜌𝐷2 𝜎 Reynolds number (Re) = 𝐺𝐷 𝜇𝑙

σ: surface tension, ∆ρ: density difference, g: acceleration of gravity, D = diameter, G = mass flux, µ: viscosity

Author Criterion Transition diameter [mm] at the same Tsat

Water R134a R245fa R236fa HFE7100

Su-Griffith, 1964 D/L = 0.3 0.79 0.2 0.28 0.22 0.61

Cornwell-Kew (1993) L/D = 0.5 5.28 1.36 1.86 1.45 4.06

Triplett et al. (1999) L = D 2.64 0.68 0.93 0.74 2

Ullmann-Brauner (2007) Eo = 1.6 9.45 2.43 3.33 2.64 7.62

Harirchian-Garimella,

(2010)

Bd0.5× Re = 160 0.47 - 1.49* 0.12 – 0.38 0.2 – 0.65 0.16 – 0.49 0.46 – 1.45

Ong-Thome, (2011) L/D = 0.3 0.92 0.24 0.33 0.26 0.71

Tibrica, (2011) – I 3.74 0.96 1.32 1.05 2.87

Tibrica, (2011) – II 2.36 0.61 0.83 0.66 1.82

* The smallest value is for G = 100 kg/m2 s and the highest value for G = 1000 kg/m2 s.

• Diameter ranges, (Mehandale et al. 2000, Kandlikar and Grande, 2003)

• The relative importance of surface tension, inertia, viscous and buoyancy forces

There is no general transition criterion

Heat flux

Vapour quality

Heat

tra

nsfe

r coeffic

ient

Bubbly Slug Churn Annular

Convective boiling

Nucleate boiling

Dominant heat transfer mechanism(s) in conventional

channels

Nucleate boiling: the

heat transfer coefficient

increases with

increasing heat flux and

independent of mass

flux and vapour quality.

Convective boiling:

the heat transfer

coefficient increases

with increasing vapour

quality and mass flux

but independent of heat

flux

Dominant heat transfer mechanism(s) in small to

micro channels

Nucleate boiling Convective boiling Nucleate-convective Thin film evaporation

Lazarek-Black, 1982

Wambsganss et al., 1993

Bao et al., 2000

Huo et al., 2004

Martin-Callizo et al., 2007

Del Col et al., 2008

Agostini et al., 2008

Bertsch et al., 2009

Karayiannis et al., 2010

Owhaib et al. 2004

Pettersen, 2004

Anwar et al., 2014

Hamdar et al., 2010

Qu-Mudawar, 2003

Boye et al. 2007

Mortada et al., 2012

Kew-Cornwell, 1997

Tran et al., 1996

Saitoh et al., 2005

Diaz et al., 2006

Choi et al., 2007

Chin-Thome, 2009

Oh et al., 2011

Lin et al., 2001

McNeil et al., 2013

Kusnetsove et al., 2013

Huh-Kim, 2006

Kuo-Peles, 2007

Thome et al., 2004

Sumith et al., 2003

In-Jeong, 2009

Balasubramanian et al., 2013

Schilder et al., 2010

Based on 33 experimental study

There is no general conclusion on the dominant heat transfer

mechanism

Mechanisms reported by different researchers

Transient liquid film evaporation, Thome et al., 2004

Also, Kandlikar and Balasubramanian (2005) reported nucleation in the liquid film.

Is nucleate boiling fully suppressed at micro scale?

Bubbles are nucleating in the liquid slug and in the liquid

film, Harirchian and Garimella (2009)

Increasing q

Thermocouple Transparent heated channel

LFDM

With simultaneous measurements

of heat transfer and liquid film

thickness the mechanism in slug

flow can be determined

Heat

transfe

r coeffic

ient

Vapour quality

Based on

thermocouple

Based on measured

thickness

If ,

there might be contribution for

nucleate boiling

lethermocoupfilmmeasured

The slug frequency can also be

measured

How can LFDM be used to infer the mechanism?

Discrepancies in the flow patterns transition boundaries

Large discrepancies among the existing models – parameters

affecting the transitions mechanism(s) are not understood

Bubbly-slugTransition to annular

0.01 0.1 1 10 1000.01

0.1

1

10

ugs, [m/s]

uls

, [m

/s]

B

C

S

A

P = 1.85 bar Chen [41]

Bubbly

Slug

ChurnChurn

Annular

R245faChen

New modified

2006

Proposed prediction method for the flow pattern transition boundaries

Surface Effects: Stainless steel cold drawn vs. welded tube, R134a

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

eff

icie

nt,

[W

/m2 K

]

q, [kW/m2]

33.733.7

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

Slug Churn Annular

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

eff

icie

nt,

[W

/m2 K

]

q, [kW/m2]

33.733.7

65.265.2

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

Slug Churn Annular

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

effic

ien

t, [W

/m2 K

]

q, [kW/m2]

12.612.6 26.426.4

33.733.7 49.249.2

65.265.2 96.596.5

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

Slug Churn Annular

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

q, [kW/m2]

33.733.7

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

q, [kW/m2]

33.733.7

65.265.2

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

eff

icie

nt,

[W

/m2 K

]

q [kW/m2]

35.335.3

P = 8 bar

G = 320 kg/m2 s

D = 1.1 mm, cold drawn

L1 = 150 mm

Slug Churn Annular

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

eff

icie

nt,

[W

/m2 K

]

q [kW/m2]

35.335.3

63.763.7

P = 8 bar

G = 320 kg/m2 s

D = 1.1 mm, cold drawn

L1 = 150 mm

Slug Churn Annular

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

D = 1.1 mm, cold drawn

L1 = 150 mm

P = 8 bar G = 312 kg/m2 s

q [kW/m2]

35.335.3

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

D = 1.1 mm, cold drawn

L1 = 150 mm

P = 8 bar G = 312 kg/m2 s

q [kW/m2]

35.335.3 63.763.7

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

effic

ien

t, [W

/m2 K

]

q [kW/m2]

12.9 12.9

25.225.2

35.335.3

49.849.8

63.763.7

78.578.5

95.895.8

102102

P = 8 bar

G = 320 kg/m2 s

D = 1.1 mm, cold drawn

L1 = 150 mm

Slug Churn Annular

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

D = 1.1 mm, cold drawn

L1 = 150 mm

P = 8 bar G = 312 kg/m2 s

q [kW/m2]

12.9 12.9

25.225.2

35.335.3

49.849.8

63.763.7

78.578.5

95.895.8

102102

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

55000

60000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r c

oe

ffic

ien

t, [

W/m

2 K

]

q, [kW/m2]

12.612.6 26.4 26.4

33.733.7 49.249.2

65.265.2 96.596.5

D = 1.16 mm, L = 150 mm

G = 312 kg/m2 s

P = 8 bar

Welded tube

Limited number of nucleation sites not uniformly distributed in welded tube may explain non-uniformity of HTC and small heat

flux effect

Cavity

Effect of Surface Characteristics

10 µm

Welded tube

Cold drawn tube Cold drawn tube

Scanning Electron Microscope

analysis – Stainless Steel Tubes

This explains in part the

discrepancies across various

laboratories in the world

debris

10 µm2 µm

Surface Roughness /peak to valley : Cold Drawn 1.27 µm; Welded 0.52 µm and 4.2 µm

Surface Effects: Cold Drawn Brass, Stainless Steel and copper tubes,

R245fa

MaterialAverage

Roughness, Ra (μm)

Root mean

square

deviation , Rq

(μm)

Maximum profile peak height, Rp

(μm)

Lowest point from Mean

Line, Rv (μm)

Maximum height, Rt

(μm)

Brass 1.249 1.743 5.465 6.409 11.874

Stainless steel 0.716 0.928 2.696 2.992 5.688

Copper 0.524 0.722 2.406 2.260 4.666

Stainless steel Brass

Surface characteristics of tubes made from

different metalsScanning Electron Microscope results

Copper

Cut-off of 0.025mm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

2000

4000

6000

8000

10000

12000

14000

16000

18000

Local vapour quality, [-]

Lo

ca

l H

ea

t T

ran

sfe

r C

oe

ffic

ien

t, [W

/m2 K

]

q, kW/m2

13.513.5

25.625.6

35.9 35.9

49.949.9

64.164.1

78.678.6

95.795.7

102.4102.4

P = 6 bar

G = 300 kg/m2 s

D = 1.1 mm

L = 150 mmSlug Churn Annular

Cold drawn

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.160

2000

4000

6000

8000

10000

12000

14000

16000

18000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r co

effic

ien

t, [W

/m2 K

]

D = 1.1 mm, cold drawn L = 150 mm

q, kW/m2

13.513.5

25.625.6

35.9 35.9

49.949.9

64.164.1

78.678.6

95.795.7

102.4102.4

P = 6 bar

G = 300 kg/m2 s

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

2000

4000

6000

8000

10000

12000

14000

16000

18000

Local vapour quality, [-]

Lo

ca

l h

ea

t tr

an

sfe

r co

effic

ien

t, [W

/m2 K

]

q, [kW/m2]

55101017.217.2

25.325.3303035.435.4

Seamless cold drawn tube

D = 1.1 mm L = 450 mm

G = 300 kg/m2 s P = 6 bar

AnnularChurnSlug

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Axial distance, [m]

Lo

ca

l h

ea

t tr

an

sfe

r co

effic

ien

t, [W

/m2 K

]

Seamless cold drawn tube

D = 1.1 mm L = 450 mm

G = 300 kg/m2 s P = 6 bar

q, [kW/m2]

55101017.217.2

25.325.3303035.435.4

Effect of heated length: cold drawn stainless steel tube, R134a dryout

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

2000

4000

6000

8000

10000

12000

14000

16000

x = 0.51

x = 0.48

x = 0.52

Lo

ca

l H

ea

t T

ran

sfe

r C

oe

ffic

ien

t, [

W/m

2 K

]

Local vapour quality, [-]

L = 150 mmL = 150 mm

L = 300 mmL = 300 mm

L = 450 mmL = 450 mm

P = 6 bar

G = 300 kg/m2 s

q = 64.1 kW/m2

q = 30.5 kW/m2

q = 20.8 kW/m2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

2000

4000

6000

8000

10000

12000

14000

16000

Lo

ca

l H

ea

t T

ran

sfe

r C

oe

ffic

ien

t, [

W/m

2 K

]

Local vapour quality, [-]

q = 25 kW/m2

P = 6 bar

G = 300 kg/m2 s

L = 150 mmL = 150 mm

L = 300 mmL = 300 mm

L = 450 mmL = 450 mm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

2000

4000

6000

8000

10000

12000

14000

16000

Z/L

Lo

ca

l H

ea

t T

ran

sfe

r C

oe

ffic

ien

t, [

W/m

2 K

]

L = 150 mmL = 150 mm

L = 300 mmL = 300 mm

L = 450 mmL = 450 mm

P = 6 bar G = 300 kg/m2 s q = 25 kW/m

2

Effect of heated length on the magnitude of the heat transfer coefficient

High heat flux hence more active nucleation sites

Comparison at constant exit quality

Comparison at constant heat flux

Short Tubes: Nucleate boiling dominates (operate

at higher heat flux).

Longer tubes: Nucleate boiling at low quality &

convective boiling at intermediate and high quality .

Short tubes preferred because of lower pressure

drop per unit heating power.

Similar

magnitude

Similar magnitude

Increases

with x

Discrepancies in prediction of heat transfer rate

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Chen, 1966

Shah, 1982

Gungor-Winterton, 1986

Kandlikar, 1990

Liu-Winterton, 1991

Steiner-Taborek, 1992

Lazarek-Black, 1982

Tran et al., 1996

Kew-Cornwell, 1997

Warrier et al., 2002

Kandlikar-Balasu, 2004

Zhang et al., 2004

Lee-Mudawar, 2005

Saitoh et al., 2007

Bertsch et al., 2009

Mikielewicz, 2010

Li-Wu, 2010

Cooper, 1984

Thome et al., 2004

Consolini-Thome, 2010

Percent of data within 30 % error bands

1.1 mm (L = 450 mm)

1.1 mm (L = 300 mm)

1.1 mm (L = 150 mm)

0.52 mm

Cooper pool boiling

correlation predicted the

data of the shortest tube

much better than the

flow boiling

correlations.

Saitoh et al., 2007,

Mikielewicz, 2010 and

Thome et al., 2004

predicted the data of the

shortest tube

reasonably well.

The performance of the

correlations depends on

the heated length.

Design Correlations Correlation I: Based on dimensionless groups

D

k

Co

WeBoh LLL

tp 6.0

1.02.0625.0 Re3414

For D = 4.26 – 1.1 mm before dryout

For D = 0.52 mm up to x ≈ 0.3

D

k

N

WeBoh L

Co

Ltp

79.1

25.0

25.03.0

5324

For D = 0.52 mm up to x > 0.3

5.08.0

1

g

LCo

x

xN

L

L

GDx

)1(Re

Convection number proposed by Shah (1982)

Liquid Reynolds number

DgCo Confinement number, Kew and Cornwell (1993)

fgGh

qBo

L

L

DGWe

2

Boiling numberAll liquid Weber number

CoWeBofk

DhNu LL

L

tp,Re,,

,exp

exp

Assessment of the correlation using

the experimental data of Anwar et al.

(2014), R134a and R152a, D = 1.6 mm

β = 99.14 % for R152a

β = 96.11 % for R134a

The performance of the correlation

using the experimental database at

Brunel University

Correlation II: Based on Chen (1966) correlation

LnewCoopernewtp hFhSh

1.0213.035.2

1.01

1736.01

1

tttt

ttF

17.125.16 Re1056.21

1

newL

new

FS

LZFtp FhShh

17.125.16 Re1056.21

1

FS

L

CofFnew , 444.02

,exp HMLF

64.0

1

AFNew

408.0812.2 CoA

Where:

S: Nucleate boiling

suppression factor

F: Convective boiling

enhancement factor

hF-Z: Forster-Zuber pool

boiling correlation,

Co: Confinement number

hL : Single phase liquid

heat transfer coefficient,

ReL: Liquid Reynolds number

hCooper: Cooper pool boiling

correlation

0 10000 20000 30000 40000 50000

0

10000

20000

30000

40000

50000

Measured HTC (W/m2 K)

Pre

dic

ted

HT

C(W

/m2K

)

+30%

-30%

G=50 kg/m2s

G=100 kg/m2s

G=200 kg/m2s

G=300 kg/m2s

Mohamed and karayinnis 2013

MAEP=19.%

R134a data in multi-microchannel heat sink, Dh = 0.42

mm, Fayyadh et al. (2015)Brunel University database

Flow Boiling of R134a in Multi-microchannels:

Experimental system

Subcooler

Condenser

R134a

Microscope

Coriolis flow meters

Test section

Inlet

outlet

Micro channel

Cartridge heater

O-ring groove

Inlet manifold

Inlet plenum

O-ring groove

Pressure Tape

Thermocouple Tape

Housing

Outlet manifold

Thermocouple Tape

Pressure Tape

Outlet plenum

Wch Wth

Hch

Dimensionl Measured by

Microscope, [µm]

Nominal,

[µm]

Wch 297±3 300

Hch 695±3 700

Wth 209±3 200

Flow Boiling of R134a in Multi-microchannels:

Test Section Details

Material: oxygen free copper

Manifold length: 16 mm

Channel length: 20 mm

Channels number: 25

Bubbly flow, q = 11.1 kW/m2 Slug flow, q = 19.3 kW/m2Bubbly flow, q = 15.8 kW/m2

Churn flow, q = 29.3 kW/m2 Wavy flow, q = 58.3 kW/m2

Flow direction

Flow Boiling of R134a in Multi-microchannels:

Flow Patterns at G = 100 kg/m2 s and P = 6.5 bar

Camera location

Inlet

manifold

Outlet

manifold

G = 50 kg/m2 s

Flow reversal occurred for all heat

fluxes, q = 8.5 kW/m2

Flow direction

Flow Boiling of R134a in Multi-microchannels: Effect of G

and q on Flow Reversal at P = 6.5 bar

Inlet manifold

Camera

location

Inlet manifoldOutlet

manifold

G = 300 kg/m2 s

Flow reversal started at q = 149 kW/m2

Inlet manifold

0 50 100 150 200 2500

5

10

15

20

q" [kW/m2]

htp

[k

W/m

2 K

]

G=50G=50G=100G=100G=200G=200

G=300G=300

0 0.2 0.4 0.6 0.8 10

5000

10000

15000

20000

25000

x [-]

htp

[W

/m2 K

]

G=50G=50G=100G=100G=200G=200

G=300G=300

0 1 2 3 4 5 6 70

50

100

150

200

250

300

350

Tw-Tsat [° C]

q"

[kW

/m2]

G=50G=50

G=100G=100

G=200G=200

G=300G=300

Flow Boiling of R134a in Multi-microchannels: Heat Transfer Results

• The heat transfer coefficient increases

with heat flux, vapour quality and mass

flux.

• Based on the conventional criterion – no

clear dominant heat transfer mechanism

HFE-7100 Integrated Microchannels Cooling system

Photograph of the HFE-7100 Cooling System

Coriolis flow

meters Pre-heater

Test section

power meter

Evap. thermocouplesCond. thermocouplesTurbine flow meter

Micro-gear

pump

Degassing port

heater

Reservoir

Condenser

SCXI data

logger

Labview

program

Microscope

Microchannel Evaporator

Flow

inlet

TInletTout

Flow

outlet

PInletPout

∆P

Hch = 1 mm

Wch = 0.3 mm

Wfin = 0.1 mm

Lch = 25 mm

Wch = 20 mm

N = 50 channel

W × L × H = 26 × 51 × 2.5 mm

Aht = 0.00275 m2

Microchannel Condenser

Hch

mm

Wch

mm

Wfin

mm

Dhyd

mm

L

mm

W,

mm

W × L × H,

mm

N HT area,

m2

1 0.4 0.1 0.57 160 45 51 × 216 × 22 90 0.035

Top view: Refrigerant side

bottom view: water side

Water

inlet

Water

outlet

T_c_out

T_w_in

T_c_in

T_w_out

HFE-7100

inletHFE-7100

outlet

∆P PinPout

Experimental plan

1. Conduct a complete flow boiling test including heat transfer, flow

patterns, pressure drop and flow instability over a wide range of

operating conditions.

Optimum operating range of the evaporator

2. Conduct a complete test for the microchannel condenser with a

directly heated tubular evaporator in order to control the vapour quality

at the condenser inlet (x ≈ 1).

Optimum operating range of the condenser

3. Conduct a system performance test including the microchannel

evaporator and condenser.

Condenser

Evaporator

Pump

Receiver

122`3

3` 4

Qamb

QEvap

Qcond

WPump

Schematic of the Real Thermal Management system

www.micropumps.co.uk

Dimensions: 70 × 32 × 30 mm

Weight: 104 g

Material: Aluminium CNC

Flow rate: 850 ml/min

Pressure: 6 bar

Temperature: -20 to 100 0C

Conclusions

The understanding of two-phase flow in small and micro channels is still limited and calls for more research work

In particular it is still necessary to discuss and clarify or develop:

Definition for small/mini/micro diameter

Geometry effects

Flow patterns in small/micro tubes - General flow pattern map

Mechanisms for heat transfer

General design heat transfer and pressure drop correlations

Different behaviour between single and multi-channel arrangements

Thank You for Your Attention