MeOH and EtOH evaporating flow mechanisms in square and circular microchannels

transcript

Methanol and Ethanol Evaporating Flow

Mechanisms in Square and Circular

Microchannels

vania.silverio@dem.ist.utl.pt

moreira@dem.ist.utl.pt

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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Photovoltaics

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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

EXPERIMENTAL APPARATUS

EXPERIMENTAL CONDITIONS

SCS_521CCS_543

Properties of the fluids (Tsat, 0.1MPa)

0 50 100 150 2000

q"s [kW.m-2

CH3OH CCS

CH3OH SCS

5OH CCS

5OH SCS

methanol

ethanol

MEASUREMENTS

0 2 4 6 8 10 12 14 16 18 2010

time [s]

0 20 40 60 80 100

Length [mm]

0 2 4 6 8 10 12 14 16 18 2020

time [s]

outlet measured pressure

inlet measured pressure

0 0.5 1 1.5 2 2.5 3

Time [s]

0 20 40 60 80 100

Length [mm]

𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆

𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆

PRESSURE DROP

∆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

+ 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 +

𝑋𝑉𝑉+

𝑋𝑉𝑉2

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

𝑝𝑖𝑛 𝑝𝑜𝑢𝑡

single-phase single-phase

𝑝𝑚𝑒𝑎𝑠,𝑖𝑛𝑙𝑒𝑡 𝑝𝑚𝑒𝑎𝑠,𝑜𝑢𝑡𝑙𝑒𝑡

TEMPERATURE

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 +

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

HEAT TRANSFER COEFFICIENT

ℎ =𝑞𝑠"

𝑇𝑤,𝑖𝑛 − 𝑇𝑓

𝑞𝑠" =

𝐼2𝑅

𝐴𝐻𝑇− ℎ𝑙𝑜𝑠𝑠 𝑇𝑤,𝑜𝑢𝑡 − 𝑇𝑎𝑖𝑟 − 𝜀𝜎 𝑇𝑎𝑖𝑟

4 − 𝑇𝑤,𝑜𝑢𝑡4

60 90 120 1500

20C2H5OH

havg [

.m-2.K

q"s [kW.m-2]

G=662kg.m-2.s

G=483kg.m-2.s

G=303kg.m-2.s

G=214kg.m-2.s

G=125kg.m-2.s

SCS_521,

𝑇𝑓 = 𝑇𝑠𝑎𝑡

(Two-phase region)

square 521mm, ethanol

=ℎ − ℎ𝑠𝑙ℎ𝑓𝑔

0.0 0.2 0.40

12CH3OH

havg [

.m-2.K

Quality [-]

G=661kg.m-2.s

G=482kg.m-2.s

G=302kg.m-2.s

G=214kg.m-2.s

Local Vapor Quality [-]

0.0 0.2 0.40

12C2H5OH

havg [

.m-2.K

Quality [-]

G=662kg.m-2.s

G=483kg.m-2.s

G=304kg.m-2.s

G=214kg.m-2.s

G=125kg.m-2.s

Local Vapor Quality [-]h

local[k

𝒒𝒔" = 91kW.m-2, 𝑻𝒔𝒂𝒕 =343K 𝒒𝒔

" = 99kW.m-2, 𝑻𝒔𝒂𝒕 =357K

square 521mm, methanol square 521mm, ethanol

-0.2 0.0 0.2 0.40

12C2H5OH

havg [

.m-2.K

Quality [-]

s=60kW.m

s=88kW.m

s=124kW.m

Exit Vapor Quality [-]h

local[k

-0.2 0.0 0.2 0.40

12CH3OH

havg [

.m-2.K

Quality [-]

s=45kW.m

s=66kW.m

s=92kW.m

Exit Vapor Quality [-]

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

circular 543mm, methanol circular 543mm, ethanol

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

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

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

80C2H5OH

havg [

.m-2.K

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 [-]

square 521mm, ethanol

FLOW PATTERNS

• 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

FLOW PATTERN MAPS

𝐼 𝐵 𝐶𝐵 = 0.763𝑅𝑒𝑙𝑜𝐵𝑜

𝑊𝑒𝑙𝑜

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

800CH3OH, CCS

Bubbly flow

Confined flow

Elongated flow

Quality [-]Exit Vapor Quality [-]

0.0 0.2 0.4 0.6 0.8 1.00

800CH3OH, SCS

Bubbly flow

Confined flow

Elongated flow

Quality [-]Exit Vapor Quality [-]

𝒒𝒔" = 81kW.m-2, 𝑻𝒔𝒂𝒕 =342K 𝒒𝒔

" = 73kW.m-2, 𝑻𝒔𝒂𝒕 =360K

square 521mm, methanolcircular 543mm, methanol

CLOSURE

∆𝒑

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

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

CLOSURE

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

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

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