MeOH and EtOH evaporating flow mechanisms in square and circular microchannels

Methanol and Ethanol Evaporating Flow
Mechanisms in Square and Circular
Microchannels

Laboratory of Thermofluids, Combustion and Energy Systems, LTCES
Center for Innovation, Technology and Policy Research, IN+
Instituto Superior Técnico, Technical University of Lisbon
vania.silverio@dem.ist.utl.pt
moreira@dem.ist.utl.pt

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Laboratory of Thermofluids, Combustion and Energy Systems
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels

2

MOTIVATION
•

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


3

EXPERIMENTAL APPARATUS


4

EXPERIMENTAL CONDITIONS
Properties of the fluids (Tsat, 0.1MPa)
methanol
ethanol

800

CH OH CCS
3

CH OH SCS
3

.s - 1 ]

600

521

C H OH CCS
2 5

-2

G [kg.m

542

C H OH SCS

400

2 5

542

521

200

0
0

50

100

-2

q"s [kW.m ]

CCS_543

SCS_521


5

150

200

MEASUREMENTS
𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆
40

10

8

Pressure Drop [kPa]

Pressure [kPa]

30

inlet measured pressure
20

outlet measured pressure

6

4
10
0

2

4

6

8

10
12
time [s]

14

16

18

20

0

0.5

1

1.5
Time [s]

2

2.5

3

𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆
8
400

450

380

]

6

300

.K
-2

340

h [kW.m

350

-1

360

Temperature [K]

Temperature [K]

400

320
300
280

250
0

0
2

4

6

8

10
12
time [s]

14

16

18

20

20

40

60

80

2

0

100

0

Length [mm]

20

40

60

Length [mm]


4

6

80

100

PRESSURE DROP
𝑝 𝑖𝑛 = 𝑝

𝑚𝑒𝑎𝑠,𝑖𝑛𝑙𝑒𝑡

− ∆𝑝 𝑐𝑜𝑛 − ∆𝑝 𝑛𝐻𝑇,𝑖𝑛

∆𝑝 𝐻𝑇 = 𝑝 𝑖𝑛 − 𝑝 𝑜𝑢𝑡

𝑝 𝑜𝑢𝑡 = 𝑝

𝑚𝑒𝑎𝑠,𝑜𝑢𝑡𝑙𝑒𝑡

+ ∆𝑝 𝑒𝑥𝑝 + ∆𝑝 𝑛𝐻𝑇,𝑜𝑢𝑡

heated length

𝑝

𝑝 𝑖𝑛

𝑚𝑒𝑎𝑠,𝑖𝑛𝑙𝑒𝑡

∆𝑝 inlet
stagnation
chamber

∆𝑝 𝑐𝑜𝑛
inlet
contraction

∆𝑝 𝑛𝐻𝑇,𝑖𝑛
non-heated
entrance length

∆𝑝 𝑛𝐻𝑇,𝑜𝑢𝑡
non-heated
exit length

single-phase
∆𝑝 𝑐𝑜𝑛 = 1 −

𝑝

𝑝 𝑜𝑢𝑡

𝑚𝑒𝑎𝑠,𝑜𝑢𝑡𝑙𝑒𝑡

∆𝑝 𝑒𝑥𝑝
outlet
expansion

single-phase
𝐴 𝑐𝑠
𝐴 𝑖𝑠𝑐

2

+ 𝐾 𝑐𝑜𝑛

1 2
𝐺 𝜗𝐿
2

∆𝑝 𝑒𝑥𝑝,𝑠𝑓 =

𝐾 𝑐𝑜𝑛 = 0.0088𝛼 2 − 0.1785𝛼 + 1.6027

1
𝐾
𝐺 2 𝜗 𝐿,𝑜
2 𝑒𝑥𝑝

𝐾 𝑒𝑥𝑝 = - 2 x 1.33
two-phase
∆𝑝 𝑒𝑥𝑝,𝑡𝑓 = 𝐺 2

𝐴 𝑐𝑠
𝐴 𝑖𝑠𝑐

𝐴 𝑐𝑠
−1
𝐴 𝑖𝑠𝑐

𝜗 𝐿,𝑜 1 − 𝑥 𝑒𝑥𝑖𝑡


7

𝐴 𝑐𝑠
𝐴 𝑖𝑠𝑐

2

1−

1+

𝐴 𝑐𝑠
𝐴 𝑖𝑠𝑐

5
1
+ 2
𝑋 𝑉𝑉
𝑋 𝑉𝑉

∆𝑝 outlet
stagnation
chamber

TEMPERATURE
𝑻 𝒊𝒏𝒏𝒆𝒓

𝒘𝒂𝒍𝒍

one dimensional heat conduction

𝑇 𝑤,𝑖𝑛 = 𝑇 𝑤,𝑜𝑢𝑡 −

𝑞 "𝑠 𝐴 𝑐𝑠
𝑘 𝑠𝑢𝑟

𝑠 𝑓 𝑙𝑜𝑔

𝑠𝑓 = 1

𝐷𝑜
𝐷𝑖

2𝜋𝐿 𝐻𝑇

𝑠 𝑓 = 0.785

𝑻 𝒇𝒍𝒖𝒊𝒅
𝑇 𝑓 = 𝑇 𝑚,𝑖𝑛 +
𝑇 𝑠𝑎𝑡 = 1 −

𝐿 𝑠𝑎𝑡 =

𝑞 "𝑠 𝑃 𝑤 𝑧
𝑉 𝜌 𝐿 𝑐 𝑝,𝐿
𝑧
𝐿 𝐻𝑇

𝑉 𝜌 𝐿 𝑐 𝑝,𝐿 𝑇 𝑠𝑎𝑡,0 − 𝑇 𝑓,𝑖
𝑞 "𝑠

𝑃𝑤

(Single-phase region)

𝑇 𝑠𝑎𝑡 𝑃𝑖𝑛𝑙𝑒𝑡 +

𝐿 𝐻𝑇

𝑇 𝑓 = 𝑇 𝑠𝑎𝑡


𝑧

8

𝑇 𝑠𝑎𝑡 𝑃 𝑜𝑢𝑡𝑙𝑒𝑡

(Two-phase region)

HEAT TRANSFER COEFFICIENT

-1
-1

-2

-1

-2

-1
-1

G=662kg.m .s
G=483kg.m .s
G=303kg.m .s

-1

15

G=214kg.m .s

-2

(Two-phase region)

-2

-2

20

havg [kW.m .K ]

𝑇 𝑓 = 𝑇 𝑠𝑎𝑡

squareSCS_521, C2H5OH
521mm, ethanol

-2

𝑞 "𝑠
ℎ=
𝑇 𝑤,𝑖𝑛 − 𝑇 𝑓

G=125kg.m .s

10
5
0

60

90
120
-2
q"s [kW.m ]

150

𝑞 "𝑠 =

𝐼2 𝑅
− ℎ 𝑙𝑜𝑠𝑠 𝑇 𝑤,𝑜𝑢𝑡 − 𝑇 𝑎𝑖𝑟 − 𝜀𝜎 𝑇 4 − 𝑇 4
𝑤,𝑜𝑢𝑡
𝑎𝑖𝑟
𝐴 𝐻𝑇


9


𝒒"𝒔 = 91kW.m-2, 𝑻 𝒔𝒂𝒕 =343K

𝒒"𝒔 = 99kW.m-2, 𝑻 𝒔𝒂𝒕 =357K

square 521mm,CH3OH
methanol
-2

-1

-2

-1

-2

-1

-1

-2

-1

G=302kg.m .s
G=214kg.m .s

4

0

0.0

0.2
Quality [-]
Local Vapor Quality [-]

-2

-1

-2

-1

-2

-1

-2

-1

-2

-1

G=662kg.m .s
hlocal [kW.m-2 -1]
havg [kW.m.K.K ]

G=482kg.m .s

-2

-1

h
[kW.m-2 -1]
hlocal [kW.m.K.K ]
avg

G=661kg.m .s

8

square 521mm,Cethanol
2H5OH

12

-2

12

0.4

G=483kg.m .s

8

G=304kg.m .s
G=214kg.m .s
G=125kg.m .s

4

0

0.0

0.2
0.4
Quality [-]
Local Vapor Quality [-]

 =


10

ℎ − ℎ 𝑠𝑙
ℎ 𝑓𝑔


66 < 𝑮 < 700kg.m-2.s-1, 𝑳 = 𝑳 𝑯𝑻

130 < 𝑮 < 700kg.m-2.s-1, 𝑳 = 𝑳 𝑯𝑻

circular 543mm, methanol
CH3OH

12

circular 543mm, ethanol
C2H5OH

12

"

-2

"

-2

"

-2

q s=60kW.m

"

-2

q s=88kW.m

"

-2

q s=92kW.m

4

0
-0.2

0.0

0.2
Quality [-]
Exit Vapor Quality [-]

-1

8

"

0.4

4

0
-0.2

0.0

0.2
Quality [-]


-2

q s=124kW.m

-2

8

h
hlocal [kW.m-2.K-1] ]
[kW.m .K
avg

q s=66kW.m

-2

-1

h
hlocal [kW.m-2.K-1] ]
[kW.m .K
avg

q s=45kW.m

11

0.4

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

square 521mm,C2H5OH
ethanol
Experimental
Kandlikar
Yu et al.
Saitoh et al.
Haynes and Fletcher

60

-2

-1

hlocal [kW.m-2 .K
havg [kW.m .K-1] ]

80

40
20
0
0.0

0.4

Comments

Maximum deviation

R11 and R123; Copper, 𝐺= 0.11 – 1.84 kg m-2 s-1;  = 0.0 – 1.0;
𝑞"𝑠 = 11-170kW.m-2; 𝐷ℎ = 0.92,1.95mm

subcooled and saturated flow
boiling

+3.0%

R113, R134b, R123; 𝐺 = 50 – 570kg m-2 s-1;  =0.00 – 0.98;
𝑞"𝑠 = 5 – 91kW.m-2; 𝐷ℎ = 0.19 – 2.92mm

strong presence of nucleate
boiling

+3.3%

R134a, SUS304, 𝐺= 150-450kg m-2 s-1;  = 0.2 – 1.0;
𝑞"𝑠 = 5-40kW.m-2; 𝐷ℎ = 0.51, 1.12, 3.1mm

convective and nucleate boiling
contributions

+10.2%

Water, SS, 𝐺= 50 – 200kg m-2 s-1;  = 0.0 – 0.9;
𝑃= 200kPa; 𝐷ℎ = 2.98mm

Haynes and Fletcher(2003)
Kandlikar and Balasubramanian (2004)

Yu et al (2002)

0.2
0.3
Quality [-]

Application range

nucleate boiling dominates
over a large 𝐺 and  range

+21.5%

Correlation

Saitoh et al. (2007)

0.1


12

FLOW PATTERNS
•

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

Determined from simultaneous measurements of ∆𝑝, 𝑇 𝑤,𝑜𝑢𝑡 and high speed imaging

Bubbly flow
Confined flow

Elongated flow


13

FLOW PATTERN MAPS

𝒒"𝒔 = 81kW.m-2, 𝑻 𝒔𝒂𝒕 =342K

circular 543mm, methanol
CH3OH, CCS

600
400
200
0

0.0

𝐼 𝐵

0.2

0.4
0.6
Quality [-]

𝐶𝐵

Revellin and Thome (2007)

= 0.763

𝑅𝑒 𝑙𝑜 𝐵𝑜
𝑊𝑒 𝑙𝑜

0.8

Bubbly flow
Confined flow
Elongated flow
IB/CB
CB/A

-1
-2

-2

-1

Bubbly flow
Confined flow
Elongated flow
IB/CB
CB/A

square 521mm,OH, SCS
CH3 methanol

800

Mass Flux, G [kg.m .s ]

800

Mass Flux, G [kg.m .s ]

𝒒"𝒔 = 73kW.m-2, 𝑻 𝒔𝒂𝒕 =360K

1.0

600
400
200
0

0.0

0.2

0.4
0.6
Quality [-]
Exit Vapor Quality[-]

0.8

0.41

𝐶𝐵

𝐴

= 0.00014𝑅𝑒 1.47 𝑊𝑒 −1.23
𝑙𝑜
𝑙𝑜

Revellin and Thome (2007)


14

1.0

CLOSURE
∆𝒑
•

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 𝑻 𝒔𝒂𝒕 and 𝑻 𝒇 and of flow pattern regimes

𝑻 𝒘,𝒐𝒖𝒕
•

𝑇 𝑤,𝑜𝑢𝑡 varies non-linearly along the channel

•

determination of local 𝑻 𝒘,𝒊𝒏 , 𝑻 𝒇 , 𝒉 and of flow pattern regimes

𝒉
•

𝒉 𝒍𝒐𝒄𝒂𝒍
•
•

•

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

𝒉 𝒍𝒐𝒄𝒂𝒍,𝒐𝒖𝒕𝒍𝒆𝒕
•
•

•

is higher for low 𝑞 "𝑠 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 𝑞 "𝑠  dominance of nucleate boiling and annular evaporation; the effect of 𝑞 "𝑠 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

15

CLOSURE

𝑭𝒍𝒐𝒘 𝒑𝒂𝒕𝒕𝒆𝒓𝒏 𝒎𝒂𝒑𝒔
•

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


16

QUESTIONS

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
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


17

MeOH and EtOH evaporating flow mechanisms in square and circular microchannels

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