MeOH and EtOH evaporating flow mechanisms in square and circular microchannels

Methanol and Ethanol Evaporating Flow

Mechanisms in Square and Circular

Microchannels

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Laboratory of Thermofluids, Combustion and Energy Systems, LTCES

Center for Innovation, Technology and Policy Research, IN+

Instituto Superior Técnico, Technical University of Lisbon

Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels

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Laboratory of Thermofluids, Combustion and Energy Systems

APPLICATIONS

2

Devices shrink in footprint and increase in functionality

keep getting hotter

Chevrolet Equinox Fuel Cell Electric Vehicle

http://alternativefuels.about.com

Computers

http://www.treehugger.com

Photovoltaics

http://onyxgreenbuilding.wordpress.com


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MOTIVATION

3

• Microchannels

– etched directly into the component

• dielectric fluids

– thermal resistances

• integrate the microchannel structure into a layer that is closer to the heat producing device. This

removes layers of material in the thermal resistance path which can significantly improve the cooling of

the heat source

• Flow boiling

– heat removal rates

– pumping power

– €€

Macrochannel Flow Pattern Maps simply fail to apply

Instabilities are prominent


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EXPERIMENTAL APPARATUS

4


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EXPERIMENTAL CONDITIONS

5

SCS_521CCS_543

Properties of the fluids (Tsat, 0.1MPa)

0 50 100 150 2000

200

400

600

800

q"s [kW.m-2

]

G [

kg.

m-2

.s-1

]

CH3OH CCS

542

CH3OH SCS

521

C2H

5OH CCS

542

C2H

5OH SCS

521

methanol

ethanol


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MEASUREMENTS

6

0 2 4 6 8 10 12 14 16 18 2010

20

30

40

time [s]

Pre

ssure

[kPa]

0 20 40 60 80 100

280

300

320

340

360

380

400

Tem

pera

ture

[K

]

Length [mm]

0 2 4 6 8 10 12 14 16 18 2020

250

300

350

400

450

time [s]

Tem

pera

ture

[K

]

outlet measured pressure

inlet measured pressure

0 0.5 1 1.5 2 2.5 3

4

6

8

10

Time [s]

Pre

ssure

Dro

p [

kPa]

0 20 40 60 80 100

0

2

4

6

8

h [

kW

.m-2

.K-1

]

Length [mm]

𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆

𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆


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PRESSURE DROP

7

∆𝑝 inlet

stagnation

chamber

∆𝑝 outlet

stagnation

chamber

∆𝑝𝑐𝑜𝑛inlet

contraction

∆𝑝𝑒𝑥𝑝outlet

expansion

∆𝑝𝑛𝐻𝑇,𝑖𝑛non-heated

entrance length

∆𝑝𝑛𝐻𝑇,𝑜𝑢𝑡non-heated

exit length

∆𝑝𝐻𝑇= 𝑝𝑖𝑛 − 𝑝𝑜𝑢𝑡heated length

∆𝑝𝑐𝑜𝑛= 1 −𝐴𝑐𝑠𝐴𝑖𝑠𝑐

2

+ 𝐾𝑐𝑜𝑛1

2𝐺2𝜗𝐿

𝐾𝑐𝑜𝑛 = 0.0088𝛼2 − 0.1785𝛼 + 1.6027 𝐾𝑒𝑥𝑝= - 2 x 1.33𝐴𝑐𝑠

𝐴𝑖𝑠𝑐1 −

𝐴𝑐𝑠

𝐴𝑖𝑠𝑐

𝑝𝑖𝑛 = 𝑝𝑚𝑒𝑎𝑠,𝑖𝑛𝑙𝑒𝑡 − ∆𝑝𝑐𝑜𝑛 − ∆𝑝𝑛𝐻𝑇,𝑖𝑛

∆𝑝𝑒𝑥𝑝,𝑠𝑓=1

2𝐾𝑒𝑥𝑝𝐺

2𝜗𝐿,𝑜

two-phase

∆𝑝𝑒𝑥𝑝,𝑡𝑓= 𝐺2𝐴𝑐𝑠𝐴𝑖𝑠𝑐

𝐴𝑐𝑠𝐴𝑖𝑠𝑐

− 1 𝜗𝐿,𝑜 1 − 𝑥𝑒𝑥𝑖𝑡2 1 +

5

𝑋𝑉𝑉+

1

𝑋𝑉𝑉2

𝑝𝑜𝑢𝑡 = 𝑝𝑚𝑒𝑎𝑠,𝑜𝑢𝑡𝑙𝑒𝑡 + ∆𝑝𝑒𝑥𝑝 + ∆𝑝𝑛𝐻𝑇,𝑜𝑢𝑡

𝑝𝑖𝑛 𝑝𝑜𝑢𝑡

single-phase single-phase

𝑝𝑚𝑒𝑎𝑠,𝑖𝑛𝑙𝑒𝑡 𝑝𝑚𝑒𝑎𝑠,𝑜𝑢𝑡𝑙𝑒𝑡


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TEMPERATURE

8

𝑇𝑤,𝑖𝑛 = 𝑇𝑤,𝑜𝑢𝑡 −𝑞𝑠" 𝐴𝑐𝑠𝑘𝑠𝑢𝑟

𝑠𝑓𝑙𝑜𝑔𝐷𝑜𝐷𝑖

2𝜋𝐿𝐻𝑇

𝑠𝑓 = 1

𝑠𝑓 = 0.785

𝑇𝑓 = 𝑇𝑚,𝑖𝑛 +𝑞𝑠" 𝑃𝑤 𝑧

𝑉 𝜌𝐿 𝑐𝑝,𝐿

𝑇𝑓 = 𝑇𝑠𝑎𝑡

𝑇𝑠𝑎𝑡 = 1 −𝑧

𝐿𝐻𝑇𝑇𝑠𝑎𝑡 𝑃𝑖𝑛𝑙𝑒𝑡 +

𝑧

𝐿𝐻𝑇𝑇𝑠𝑎𝑡 𝑃𝑜𝑢𝑡𝑙𝑒𝑡

(Single-phase region)

(Two-phase region)𝐿𝑠𝑎𝑡 = 𝑉 𝜌𝐿 𝑐𝑝,𝐿 𝑇𝑠𝑎𝑡,0 − 𝑇𝑓,𝑖

𝑞𝑠" 𝑃𝑤

𝑻𝒊𝒏𝒏𝒆𝒓 𝒘𝒂𝒍𝒍

𝑻𝒇𝒍𝒖𝒊𝒅

one dimensional heat conduction


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HEAT TRANSFER COEFFICIENT

9

ℎ =𝑞𝑠"

𝑇𝑤,𝑖𝑛 − 𝑇𝑓

𝑞𝑠" =

𝐼2𝑅

𝐴𝐻𝑇− ℎ𝑙𝑜𝑠𝑠 𝑇𝑤,𝑜𝑢𝑡 − 𝑇𝑎𝑖𝑟 − 𝜀𝜎 𝑇𝑎𝑖𝑟

4 − 𝑇𝑤,𝑜𝑢𝑡4

60 90 120 1500

5

10

15

20C2H5OH

havg [

kW

.m-2.K

-1]

q"s [kW.m-2]

G=662kg.m-2.s

-1

G=483kg.m-2.s

-1

G=303kg.m-2.s

-1

G=214kg.m-2.s

-1

G=125kg.m-2.s

-1

SCS_521,

𝑇𝑓 = 𝑇𝑠𝑎𝑡

(Two-phase region)

square 521mm, ethanol


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10

=ℎ − ℎ𝑠𝑙ℎ𝑓𝑔

0.0 0.2 0.40

4

8

12CH3OH

havg [

kW

.m-2.K

-1]

Quality [-]

G=661kg.m-2.s

-1

G=482kg.m-2.s

-1

G=302kg.m-2.s

-1

G=214kg.m-2.s

-1

Local Vapor Quality [-]

hlo

cal[k

W.m

-2.K

-1]

0.0 0.2 0.40

4

8

12C2H5OH

havg [

kW

.m-2.K

-1]

Quality [-]

G=662kg.m-2.s

-1

G=483kg.m-2.s

-1

G=304kg.m-2.s

-1

G=214kg.m-2.s

-1

G=125kg.m-2.s

-1

Local Vapor Quality [-]h

local[k

W.m

-2.K

-1]

𝒒𝒔" = 91kW.m-2, 𝑻𝒔𝒂𝒕 =343K 𝒒𝒔

" = 99kW.m-2, 𝑻𝒔𝒂𝒕 =357K

square 521mm, methanol square 521mm, ethanol


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11

-0.2 0.0 0.2 0.40

4

8

12C2H5OH

havg [

kW

.m-2.K

-1]

Quality [-]

q"

s=60kW.m

-2

q"

s=88kW.m

-2

q"

s=124kW.m

-2

Exit Vapor Quality [-]h

local[k

W.m

-2.K

-1]

-0.2 0.0 0.2 0.40

4

8

12CH3OH

havg [

kW

.m-2.K

-1]

Quality [-]

q"

s=45kW.m

-2

q"

s=66kW.m

-2

q"

s=92kW.m

-2

Exit Vapor Quality [-]

hlo

cal[k

W.m

-2.K

-1]

66 < 𝑮 < 700kg.m-2.s-1, 𝑳 = 𝑳𝑯𝑻 130 < 𝑮 < 700kg.m-2.s-1, 𝑳 = 𝑳𝑯𝑻

circular 543mm, methanol circular 543mm, ethanol


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12

Correlation Application range Comments Maximum deviation

Haynes and Fletcher(2003) R11 and R123; Copper, 𝐺= 0.11 – 1.84 kg m-2 s-1; = 0.0 – 1.0;

𝑞𝑠"= 11-170kW.m-2; 𝐷ℎ= 0.92,1.95mm

subcooled and saturated flow

boiling

+3.0%

Kandlikar and Balasubramanian (2004) R113, R134b, R123; 𝐺 = 50 – 570kg m-2 s-1; =0.00 – 0.98;

𝑞𝑠"= 5 – 91kW.m-2; 𝐷ℎ= 0.19 – 2.92mm

strong presence of nucleate

boiling

+3.3%

Saitoh et al. (2007) R134a, SUS304, 𝐺= 150-450kg m-2 s-1; = 0.2 – 1.0;

𝑞𝑠"= 5-40kW.m-2; 𝐷ℎ= 0.51, 1.12, 3.1mm

convective and nucleate boiling

contributions

+10.2%

Yu et al (2002) Water, SS, 𝐺= 50 – 200kg m-2 s-1; = 0.0 – 0.9;

𝑃= 200kPa; 𝐷ℎ= 2.98mm

nucleate boiling dominates

over a large 𝐺 and range

+21.5%

0.0 0.1 0.2 0.3 0.40

20

40

60

80C2H5OH

havg [

kW

.m-2.K

-1]

Quality [-]

Experimental

Kandlikar

Yu et al.

Saitoh et al.

Haynes and Fletcher

𝒒𝒔" = 55kW.m-2; 130 < 𝑮 < 700kg.m-2.s-1

Exit Vapor Quality [-]

hlo

cal[k

W.m

-2.K

-1]

square 521mm, ethanol


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FLOW PATTERNS

13

• Definitions adapted from Collier and Thome (1994) and Carey (2007)

– Determined from simultaneous measurements of ∆𝑝, 𝑇𝑤,𝑜𝑢𝑡 and high speed imaging

Bubbly flow

Confined flow

Elongated flow


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FLOW PATTERN MAPS

14

𝐼 𝐵 𝐶𝐵 = 0.763𝑅𝑒𝑙𝑜𝐵𝑜

𝑊𝑒𝑙𝑜

0.41

𝐶 𝐵 𝐴 = 0.00014𝑅𝑒𝑙𝑜1.47𝑊𝑒𝑙𝑜

−1.23

Revellin and Thome (2007)Revellin and Thome (2007)

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800CH3OH, CCS

Bubbly flow

Confined flow

Elongated flow

IB/CB

CB/A

Mass

Flu

x, G

[kg.m

-2.s

-1]

Quality [-]Exit Vapor Quality [-]

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800CH3OH, SCS

Bubbly flow

Confined flow

Elongated flow

IB/CB

CB/A

Mass

Flu

x, G

[kg.m

-2.s

-1]

Quality [-]Exit Vapor Quality [-]

𝒒𝒔" = 81kW.m-2, 𝑻𝒔𝒂𝒕 =342K 𝒒𝒔

" = 73kW.m-2, 𝑻𝒔𝒂𝒕 =360K

square 521mm, methanolcircular 543mm, methanol


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CLOSURE

15

∆𝒑

𝒉

𝑻𝒘,𝒐𝒖𝒕

• inlet contraction and outlet expansion as well as non–heated lengths were quantified and subtracted from the total two-phase

flow pressure drops

• determination of local 𝑻𝒔𝒂𝒕 and 𝑻𝒇 and of flow pattern regimes

• 𝑇𝑤,𝑜𝑢𝑡 varies non-linearly along the channel

• determination of local 𝑻𝒘,𝒊𝒏,𝑻𝒇, 𝒉 and of flow pattern regimes

• 𝒉𝒍𝒐𝒄𝒂𝒍

• is higher for low and independent on 𝐺 incipience of boiling

• is lower for high and independent on 𝐺 dry patches on the wall causing heat transfer decline

• 𝒉𝒍𝒐𝒄𝒂𝒍,𝒐𝒖𝒕𝒍𝒆𝒕

• is higher for low 𝑞𝑠" and dependent on 𝐺 (𝐺 =662kg.m-2.s-1) reduced space for convective flow to develop

• is lower for low 𝐺 and independent on 𝑞𝑠" dominance of nucleate boiling and annular evaporation; the effect of 𝑞𝑠

" on

ℎ overcomes the effect of 𝐺

• comparison of the experimental results with correlations for subcooled boiling and flow boiling show similar trends, but the

experimental values are below prediction


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CLOSURE

16

𝑭𝒍𝒐𝒘 𝒑𝒂𝒕𝒕𝒆𝒓𝒏𝒎𝒂𝒑𝒔

• flow patterns and flow pattern transitions for diabatic evaporation of ethanol and methanol obtained from 𝑻, 𝒑 and high speed

imaging

• flow patterns are qualitatively identical for both fluids and cross sections

• similar trends with the model proposed by Revellin and Thome (2007)

• deviations Instabilities occurring inside the channel, due to pressure fluctuations, explosive boiling and long dryout periods that

degrade the heat transfer

• further experimental research is needed to generate more data at higher vapor qualities and different heat fluxes and mass

fluxes, for the developing of more accurate flow pattern maps


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Professor Nunes de Carvalho and his team for thin film deposition.

Financial support:

Project “SURWET-COOLS”, PTDC/EME-MFE/109933/2009

Portuguese Science and Technology Foundation, grant SFRH-BD-76596-2011

QUESTIONS

17

Simultaneous measurements of Temperature, pressure and high-speed imaging

in well defined homogeneous transparent channel walls with constant wall heat flux

is a major asset to assist in the comprehension of fluid flow behavior in microscale flows

Acknowledgements

Date post:	17-Jul-2015
Category:	Technology
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