heat transfer during boiling and condensation in microchannels · motivation volume d surfacearea 1...

HEAT TRANSFER DURING BOILING AND CONDENSATION IN MICROCHANNELS

Júlio César Passos

[email protected]

Universidade Federal de Santa Catarina

Centro Tecnológico - Departamento de Engenharia Mecânica

LEPTEN/Boiling

Laboratórios de Engenharia de Processos de Conversão e Tecnologia de Energia

Motivation

DVolume

AreaSurface 1

• High heat transfer coefficient during flow boiling and flow condensation. • The surface area to volume ratio increases with the decrease of the diameter.

• Refrigeration and air conditioning account for a significant proportion of electricity usage.

4th Brazilian Meeting of Boiling , Condensation and Multiphase Flows

UNICAMP – March 27 2015

Contents • Motivation, • Macro and micro scale, • Confined pool boiling • Two-phase flow regimes in microchannels • Flow boiling in microchannels (LEPTEN/UFSC results) • Conclusions of the Part A • Condensation in microchannels (Theoretical analysis) • Flow condensation in microchannels (LEPTEN/UFSC results) • Conclusions of the Part B



Macro and micro scale

• Criterium for considering micro and macro scale

Confinement number: Kew and Cornwell (1997)

5.0

2

1

2

h

c

vl D

L

DgCo

h

• Kandlikar and Steinke (2003) propose:

mDm h 20010 for considering micro channel.



Confinement number and transition diameter from micro to macro

Fluid Tsat

(oC) P

(bar) l

kg.m-3)

v kg.m-3)

mNm-1

Lc

(mm)

Dtran (mm)

Co=0.5

Water 99.6 1 959 0.6 59.0 2.50 5.0

FC72 55.9 1 1603 13.1 12.0 0.88 1.75

R134a - 26.4 1 1378 5.2 15.5 1.07 2.14

R134a 33 8.4 1176 41 7.02 0.80 1.60

HFE7100 59.6 1 1373 9.6 15.7 1.08 2.17

n-Pentane 35.9 1 603.6 2.9 14.3 1.56 3.11



q=20 k

W/m

2

s=0.2 mm Tw=63.1

oC s=0.5 mm Tw=64.4

oC s= 1 mm

Tw=65.5oC

q=40 k

W/m

2

s=0.2 mm Tw=75.5

oC s=0.5 mm Tw=68.1

oC s= 1 mm

Tw=69.3oC

Confined pool boiling

in Passos et al. (2005) ETFS, Elsevier, Vol. 30, pp. 1-7.

Heat

s

Heat (C)

(NC)

Flow boiling in microchannels



Two-phase flow visualization in a microchannel

Two-phase air-water test rig,

at LEPTEN-UFSC.

In Barreto, E.X., Oliveira, J.L.G., Passos, J.C., Frictional pressure drop and void fraction analysis in air-water

two-phase flow in a microchannel, IJMF/ELSEVIER, Vol. 72, pp. 1-10, 2015.



jg= 0.12 0.12 0.80 0.80 6.40 0.12 0.80 0.80 6.40 18.60 18.60 26.7 jl= 0.53 3.50 3.50 1.37 3.50 0.10 0.95 0.70 1.37 2.65 3.50 3.50

jg and jl in m/s In Barreto, E.X., Oliveira, J.L.G., Passos, J.C., Frictional pressure drop and void fraction analysis in air-water





jg and jl in m/s jg= 0.80 6.40 6.40 10.50 18.60 34.80

jl= 0.10 0.10 0.53 0.53 0.53 0.53

In Barreto, E.X., Oliveira, J.L.G., Passos, J.C., Frictional pressure drop and void fraction analysis in air-water



A

xm

A

mj

g

g

..

A

xm

A

mj l

l

)1(...



In Barreto, E.X., Oliveira, J.L.G., Passos, J.C., Analysis of air-water flow patterns in parallel microchannels: a

visualization study, ETFS/ELSEVIER, Vol. 63, pp. 1-8, 2015.

Two-phase flow visualization in

7 parallel microchannels

The gas quality in the inlet manifold is given.



Scale effects on macro and micro scale: forces per unit area

Inertia force

2

2

22'' G

D

DVFi

Surface tension force

DD

DF

2

'' cos

: specific mass of the fluid (kg.m-3)

: surface tension (N.m-1=J.m-2) : contact angle of the interface liquid-vapor

In: Kandlikar, S.G., Scale effect on flow boiling heat transfer in microchannels: A fundamental perspective, Int. J. of Thermal Sciences, vol. 49, pp. 1073-1085, 2010.



Forces per unit area (cont.)

Shear force

D

G

D

V

D

DD

V

F

2

2

''

Gravity (buoyancy) force

gD

D

gDF vl

vlg

2

3''

: fluid viscosity (Pa.s) .

: accelaration due to gravity (m.s-2)

g



Forces per unit area (cont.)

Evaporation momentum force

vfg

QMh

qF

1"2

''

: heat flux on the tube surface (Wm-2) "q

: latent heat of vaporization (J.kg-1) fgh



Scale effect on flow boiling

Effect of the tube diameter on different types of forces during boiling of water

In: Kandlikar, S.G., Scale effect on flow boiling heat transfer in microchannels: A fundamental perspective, Int. J. of Thermal Sciences, vol. 49, pp. 1073-1085, 2010.



Scale effect on flow boiling (cont.) In Kandlikar (2010)

Effect of the tube diameter on different types of forces during

boiling of water

Effect of the tube diameter on different types of forces during

boiling of R-123.



Scale effect on flow boiling (cont.)

In Kandlikar (2010)

Effect of the tube diameter on different types of forces during boiling of water



Main characterisitics

Boiling flow in Microchannels

h

Dp

Surface tension force

Gravity force



Flow configurations

During flow boiling, the presence of annular flow or intermittent flow regimes are predominant due to capillary effects. The stratified flow regime is more rare.

Yan e Lin (1998), IJHMT, v. 41, pp. 4183 – 4194.



Boiling flow patterns and transitions

Bubbly flow at x=3.8%

Bubbly/Slug flow at x=4%

Slug flow at x=4.3%

Slug/Semi-Annular flow at x=7.6%

Semi-Annular flow at x= 15%

Wavy Annular flow at x=23%

Smooth Annular flow at x=23%

[U1]

In Revellin and Thome, 2007, Int. J. of Heat and Fluid Flow, Vol. 28, pp.63-71. Flow Patterns and transitions for

R245fa, d=0,5 mm, L=70,70 mm, G=500 kg/m2s and Tsat=35 oC.



Boiling flow patterns (Revellin and Thome (2007)

[U1]

In Revellin and Thome, 2007, Experimental investigation of R-134a and R-245fa two-phase flow in

microchannels for different flow conditions, Int. J. of Heat and Fluid Flow, Vol. 28, pp.63-71.

Schematic diagram of the test section



Flow regimes

[U1]

Flow patterns observed by Cornwell and Kew (1993) during

flow boiling of R113 in 2 x 0.9mm2 parallel rectangular channels.

q”=3 to 33 kW/m2

Low quality High quality



Flow visualiation by

Hara et al. (2010)



Flow maps: adapted by Revellin et al. (2006)

Bubbly Intermittent

Annular

Intermittent/Annular

Vapor superficial velocity (m/s)

Liq

uid

su

per

fici

al v

elo

city

(m

/s)

Air-Water D=1.097 mm

R-134a D=0.509 mm

Modified transition lines Transition lines (Tripplet et al., 1999)



Flow regimes: effect of the diameter on the transition lines

[U1]

Fluido: R-134a a 30º C; q”=60kW/m2 (Revellin and Thome (2007))

Vapor quality

Mass v

elo

city,

G (

kg/m

2s)

Dryout

Annular

CB IB



Case study:

Pressure drop and heat transfer coefficient during the R-134a convective

boiling inside microchannels

Results obtained in the thesis of

Evandro Rodrigo Dario

R-134a CONVECTIVE BOILING INSIDE MULTIPARALLEL MICROCHANNELS AND ANALYSIS OF THE MALDISTRIBUTION AIR-WATER MASS FLOW RATE

WITHIN THE INLET MANIFOLD CONNECTED TO MICROCHANNELS

Advisor: Júlio César Passos; Co-advisor: Lounès Tadrist POSMEC/UFSC e Aix Marseille Université



Flow boiling inside parallel microchannels forçada

Scheme of the R134a circuit, LEPTEN/Boiling, in Dario (2013).

Test section (Dario, 2013)

L=150 mm Heated length, Lheat=120 mm

Dh=0.77±0.1 mm

(1) Microchannels (copper tubes) (2) Copper plates (3) Skin heaters (4) Teflon blocks (5) Manifolds

Test section (Dario, 2013)

Thermocouple locations

(lengths in mm).

Experimental data in the flow patterns proposed by Revellin e Thome (2007)

in Dario (2013)

Annular Dryout CB

IB

Experimental data

Local quality, x

Mas

s ve

loci

ty. K

g/m

2s

The different contributions to the pressure drop

R-134a, G= 1002 Kg/m2s, Pin= 605 kPa

Thesis of Dario (2013), and Dario et al. (2015) accepted to the Int.

Conference on Boiling and Condensation , Boulder-CO/USA

Pressure drop: Comparison of experimental data with semi-empirical models

[U1]

Lee and Mudawar (2005) consider the R134-a boiling flow inside 53 parallel channels with

Dh=0.35 mm For the Homogeneous model 1

l

v

u

uS

?



Thesis of Dario (2013), and Dario et al. (2015) accepted to the Int.

Conference on Boiling and Condensation , Boulder-CO/USA

Onset of nucleate boiling

(a) Heat flux;

(b) Inlet pressure;

(c)Mass velocity; (d) Pressure drop; (e) Wall

temperature.

Time (s)

Two phase flow Single phase flow



Boiling curves

ONB

Hea

t fl

ux,

”

At T 7



Boiling curves

ONB

At T 7

Hea

t fl

ux,

kW

/m2K



Boiling curves

smkgG 2/1001

smkgG 2/503

smkgG 2/252

Hea

t fl

ux

At T7



Heat transfer coefficient as function of quality on the flow pattern map of

Revellin and Thome (2007)

Dry

ou

t

HT

C, CB

IB

Vapor quality, x



Experimental points obtained by

Dario (2003) in his thesis.



Dryout

CB IB

HT

C,

Vapor quality, x



Experimental points obtained by

Dario (2003) in his thesis.



Dario (2013)

HT

C,

Dryout

IB CB

Vapor quality, x



BOILING FLOW INSIDE AN ANNULAR CROSS SECTION MICROCHANNEL

The next results were obtained in the Master of Science of Evandro Rodrigo Dario

Advisor: Júlio César Passos LEPTEN/POSMEC/UFSC – March 2008.



Convective boiling in microchannels

n-Pentane G=253 kg/m²s q”= 25 kW/m2

n-Pentane G=169 kg/m²s q”= 12.5 kW/m2

MSc of Dario (2008)



Test section



Location of the thermocouples in the test section.

Copper tube

Test section

Boiling flow visualization (1)

G = 148 kg/m2s

Liquid-vapor interface



G = 190 kg/m2s


On increasing the mass velocity and the heat flux the liquid-vapor interface becomes less defined. On increasing the heat flux increase the number of active nucleation sites. Occurs the trend to stratify the flow with big bubbles on the upper region of the channel.



G = 232 kg/m2s


G = 274 kg/m2s




Conclusions

• The flow regime maps needs to be improved in order to predict dryout heat fluxes for a wide operational conditions and fluids;

• There is still insufficient data for heat transfer coefficient in

convective boiling inside microchannels of organic fluids, in particular CO2.

• Inlet two-phase flow represents a typical condition in the evaporators of a refrigerant system and can affect the heat transfer coefficient because the early dryout caused by the maldistribution of mass flow rate.



Flow condensation in microchannels



Chiller condenser

http://www.carriercca.com

MPE-MultiPort Extruded Aluminium tubes

used in microcondensers

www.hydro.com



State of the art

Condensers employing microchannel (MC) in aluminum profiles MPE have been used successfully in automotive

air condicioners for around 25 years.

Available experimental heat transfer data for condensation in MC are widely scattered.

A great number of researchers obtained the HTC by using the Wilson plot methods, such data have high

uncertainty.

In: Wang and Rose (IJHMT, vol. 54 (2011), pp. 2525-2534) 4th Brazilian Meeting of Boiling , Condensation and

Multiphase Flows UNICAMP – March 27 2015

Results of Wang and Rose (2006) Effect of the microchannel shape

Literature review – Effect of the

channel shape

• Numerical solution for annular regime, Wang and Rose (2006).

53

Wang and Rose (2006, 2011) is based on the

assumptions of Nusselt (1916) but includes the

streamwise shear stress on the condensate film

surface as well as the transverse pressure

gradient due to surface tension in the presence

of change in condensate surface curvature. The surface tension has negligible effect.

Nusselt (1882-1957)

Ernst Kraf Vilhelm Nusselt

Published, in 1916,

“Die Oberflachenkondensation des

Wasserdampfes”, Z. Ver. Deut. Ing., Vol.

60, 541, 1916.

4th Brazilian Meeting of Boiling , Condensation and


The Nusselt model for film condensation

gρρμ

1

dy

udvl

l

2

2

y=0, u=0 ,

y=d,

Boundary conditions

2

l

2

vl

δ

y

2

1

δ

y

μ

δρρgu(y)

0dy

du

y

Laminar =

smooth interface

30deR

Laminar

with waves

1800deR

Turbulent region

1800Re30 d

30deR

(1)

(2)



The Nusselt model (2)

.

md

.

mdhdq lv

..

mdm

.

m

dxbq ."

sup

.

mdhdq lv

dxbqdq ."

sup

lv

satl

lv h

TTk

h

q

dx

d

.

sup

"

sup

d

.

mdhdq lv

dxbqdq ."

sup

dx

dg

dx

d

l

vll d

d 2

4

1

sup4

lvvll

atll

hg

xTTkx

d

s

xd x;

Jahh lvlv 68,01'

correction

Ja: Jakob number

dxx

x



The Nusselt model (3)

dl

x

kh

4

1

sup

'3

4

xTT

hkgh

atl

lvvll

xl

s

sup

"

sup ssatx TThq

The local hx

decrease with x.

4

1

sup

'3

943.0

LTT

hkgh

atl

lvvll

Ll

s

After integration

4

1

sup

3'

943.0

TTk

LhgNu

atll

lvvll

L

s

Properties at:

2

supTTT

sat

f

satlvv Tathand

'

sup

'

.

lv

satL

lv h

TTAh

h

qm



Advisor: Júlio César Passos; Co-Advisor: Saulo Güths LEPTEN/POSMEC/UFSC – defended in March 06 2015.

CONVECTIVE CONDENSATION WITHIN AN ALLUMINIUM PROFILE-MPE CONTAINING

EIGHT PARALLEL MICROCHANNELS

The next results were obtained in the Master of Science of Guilherme Piazza Zanette



Experimental setup: R-134a condensation loop

Main elements of the experimental set up

1 Heat chamber 6 Filter

2 Superheater 7 Micro-pump

3 Mass flowmeter 8 Thermal baths

4 Test section A Test section bypass

5 Post-condenser B Experimental setup bypass

Schematic diagram of the test section

1 – MPE profile (Multi-Port Extruded);

2 – Manifolds;

3 – Copper Plates;

4 – Heat Fluxmeters;

5 – Heat Sinks;

6 – Plexy Glass Structure.



Test section – MPE profile

• Multi-Port Extruded

• Commercial Profile

• Aluminium 3003

• Eight Microchannels



Dimensions of the test section – MPE

LABMETRO/CERTI

Central Channels

Lateral Channels

Average Deviation

Hydraulic Diameter

Total Length

Mean Roughness

Thickness

m



MPE test section welded to the manifolds

93.5 mm

Heat flux meter

Copper plate

Aluminium

profile-MPE

Heat

Flux

meter

Heat Flux meter



Flow regimes 76.060.0 Co



Vapor quality

Average heat transfer coefficients



ha

vera

ge (W

/m2K

)

Advisor: Júlio César Passos LEPTEN/POSMEC/UFSC –May 24 2011.

HEAT TRANSFER AND PRESSURE DROP DURING THE CONDENSATION OF R-134a IN PARALLEL

MICROCHANNELS

The next results were obtained in the Master of Science of Gil Goss Jr.

GOSS Jr., G.;PASSOS, J.C. Heat transfer during the condensation of R134a inside eight parallel microchannels, International Journal of Heat and Mass Transfer, v.59, p. 9–19, 2013.



Test section



(1)Microchannels

(2) Copper plate

(3) Cooler Peltier

(4) Copper plate (5) Heat sink

Experimental uncertainty of the

hcond

Calibration curve (Peltier cooler)

Flow regimes

Test conditions

230 kg.m-2.s-1 < G < 445 kg.m-2.s-1

17 kW.m-2 < q” < 53 kW.m-2 0.55 < xv < 1

7.3 bar < p < 9.7 bar 28 oC < Tfluid < 38 oC

0 < Rel < 616 6621 < Rev < 28145

Eo=50 and Co=1.1

Condensation flow regime map of Coleman and Garimella

Annular/Mist Mist

Annular

Disperse



Vapor quality

Comparison with semi-emprirical models

Heat Transfer Coefficient

MAE=19.5%

MAE=40 %

Condensation of the R134a

Test section: microchannel with 0.8 mm diameter

Cooling flow: ethylene-glycol

in the annular space LEPTEN-UFSC



Visualization: R-134a flow condensation (Microchannel with 0.8 mm diameter), LEPTEN/UFSC results

a) Annular flow (p=6.0 bar; m=183 g/s)

b) Annular flow with waves (p=6.7 bar; m=217 g/s)

c) Intermittent flow (p=6.6 bar; m=182 g/s)

d) Bubbly flow (p=6.4 bar; m=177 g/s) Liquid slug Taylor bubble

Liquid ring

Liquid rings



Video (LEPTEN-UFSC)

R-134a flow condensation



Conclusions

• Experimental heat transfer data for condensation in microchannels are widely scattered (Wang and Rose, 2011)

• The Wilson-plot technique is not appropriated for determining the HTC, in microchannels;

• The experimental determination of HTC for condensation

presents additional challenges; • For the heat transfer phenomenon, the formulations developed

for conventional channels do not work with the same precision in microchannels (Goss Jr. and Passos, 2013);

• Further research is need.

4th Brazilian Meeting of Boiling , Condensation and


Thank you very much for your attention!



Many thanks to the organizers of the JEM-2015 for the invitation!

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heat transfer during boiling and condensation in microchannels · motivation volume d surfacearea 1...

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