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

  • Ping-Tse Ho
  • Yao-Hsien LiuEmail author


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.


Mist flow Heat transfer Minichannel Microchannel Droplets 



Cross-sectional area of minichannel (m)


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


Heat-transfer enhancement ratio due to mist flow


Friction factor


Channel height (m)


Distance between thermocouple and channel wall (m)


Heat-transfer coefficient (W/m2∙K)


Thermal conductivity of air (W/m∙K)


Contraction loss coefficient


Expansion loss coefficient


Thermal conductivity of copper (W/m∙K)


Length of minichannel (m)


Fin parameter


Nusselt number


Wetted perimeter of minichannel (m)


Pressure drop due to outlet expansion (Pa)


Frictional pressure drop (Pa)


Pressure drop due to inlet contraction (Pa)


Measured overall pressure drop (Pa)


Input heat flux (W)


Heat loss (W)


Gas Reynolds number (=ρGVchDh/μG)


Fluid bulk temperature (K)


Wall temperature (K)


Temperature inside copper block (K)


Flow velocity in minichannel (m/s)


Channel width (m)


Half-width of fin (m)


Streamwise distance (m)

Greek symbols


Fin efficiency (= tanh(mHch)/mHch)


Air viscosity (Pa∙s)


Air density (kg/m3)



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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