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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
APPLICATIONS
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Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
EXPERIMENTAL APPARATUS
4
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
HEAT TRANSFER COEFFICIENT
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
HEAT TRANSFER COEFFICIENT
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
HEAT TRANSFER COEFFICIENT
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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
Methanol and Ethanol Evaporating Flow Mechanisms in Square and Circular Microchannels
Laboratory of Thermofluids, Combustion and Energy Systems
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