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Heat transfer and pressure drop of air/water mist flow in horizontal Minichannels

  • Ping-Tse Ho
  • Yao-Hsien Liu
Original

Abstract

The heat transfer, friction factor, and flow pattern of air/water mist flow in a rectangular minichannel heat sink were experimentally investigated. The channel size effect was studied using three horizontal minichannels exhibiting cross-sections measuring 0.5 mm × 3 mm, 1 mm × 3 mm, and 3 mm × 3 mm. The gas Reynolds number ranged from 1000 to 6000, and the wall temperature ranged from 40 to 60 °C. For the single-phase air flow, the flow transition was comparable with the conventional flow channel. For the mist flow, the flow patterns observed in the current minichannel were dry-wall mist flow and wavy annular flow. The mist cooling performance decreased with increase in wall temperature, mainly because of the extended dryout regions. The heat transfer from the mist flow was 1.5–4 times higher than the air flow, and higher enhancement ratios were observed in larger minichannels at lower gas Reynolds numbers. Because of droplet accumulation in the minichannel, the friction factor due to the mist flow was 2–3 times higher than the air flow. The friction factor decreased with increase in wall temperature because of the low volume of liquid in the minichannel.

Keywords

Mist flow Heat transfer Minichannel Microchannel Droplets 

Nomenclature

A

Cross-sectional area of minichannel (m)

Dh

Hydraulic diameter of minichannel (= 4A/P) (m)

EFmist

Heat-transfer enhancement ratio due to mist flow

f

Friction factor

Hch

Channel height (m)

Hw2

Distance between thermocouple and channel wall (m)

h

Heat-transfer coefficient (W/m2∙K)

ka

Thermal conductivity of air (W/m∙K)

Kc

Contraction loss coefficient

Ke

Expansion loss coefficient

ks

Thermal conductivity of copper (W/m∙K)

L

Length of minichannel (m)

m

Fin parameter

Nu

Nusselt number

P

Wetted perimeter of minichannel (m)

ΔPe

Pressure drop due to outlet expansion (Pa)

ΔPf

Frictional pressure drop (Pa)

ΔPi

Pressure drop due to inlet contraction (Pa)

ΔPmea

Measured overall pressure drop (Pa)

q″

Input heat flux (W)

q″loss

Heat loss (W)

Re

Gas Reynolds number (=ρGVchDh/μG)

Tb

Fluid bulk temperature (K)

Tw

Wall temperature (K)

Tw1

Temperature inside copper block (K)

Vch

Flow velocity in minichannel (m/s)

Wch

Channel width (m)

Ww

Half-width of fin (m)

x

Streamwise distance (m)

Greek symbols

η

Fin efficiency (= tanh(mHch)/mHch)

μG

Air viscosity (Pa∙s)

ρG

Air density (kg/m3)

Notes

Acknowledgments

This study was funded by the Ministry of Science and Technology, Taiwan, under contract MOST 104-2221-E-009-153.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringNational Chiao Tung UniversityHsinchuTaiwan

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