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Influence of different parameters of preparing self-assembled monolayers on copper surfaces in the dropwise condensation heat transfer: an experimental study

  • Hamid Reza Talesh BahramiEmail author
  • Alireza Azizi
  • Hamid Saffari
Technical Paper
  • 28 Downloads

Abstract

Dropwise condensation (DWC) is one of the phase change heat transfer regimes, which due to its high capacity has received much attention from investigators. To produce DWC, it is necessary to have hydrophobic surfaces. Low surface energy coatings have been usually used to produce hydrophobic surfaces. These coatings due to their low thermal conductivities must have the minimum thickness. Therefore, self-assembled monolayers coatings like stearic acid or 1-octadecanethiol coatings (with thicknesses as high as a few nanometers) have been used in the literature. To create hydrophobic coatings by these materials, the surfaces are immersed in hydrophobic solutions with particular concentrations and in a specific time. There is not any general investigation on the effects of the time and concentration of these coatings on DWC in the literature. In this study, first, a proper apparatus for DWC experiments is designed and fabricated. Then, the effects of concentration and immersing time of the two mentioned materials on DWC phenomena have been studied. Between four coating times and solution concentrations of 1-octadecanethiol, concentration of 0.025 M at coating time of 30 min increases DWC heat transfer coefficient by about 4–7 times with respect to filmwise condensation in different subcooling temperatures. Concentration of 0.0025 M at coating time of 1 hour of stearic acid also increases the heat transfer coefficient by about 3–4 times. As well as the 1-octadecanethiol coating has a more uniform structure and higher heat transfer coefficient with respect to stearic acid coating.

Keywords

Dropwise condensation Hydrophobic surfaces Self-assembly 1-Octadecanethiol Stearic acid 

List of symbols

d

Diameter of a hole (m)

g

Gravitational acceleration (m/s2)

h

Heat transfer coefficient (W/(m2 K))

H

Latent heat (J/kg)

k

Thermal conductivity (W/(m K))

N

Number of temperature measurement locations

M

Molar or mole per liter

q

Heat flux (W/m2)

R

Sample forehead surface radius (m)

S

Uncertainty

T

Temperature (K)

x

Location (m)

Greek symbols

µ

Dynamic viscosity (Pa s)

ρ

Density (kg/m3)

Subscripts

FWC

Filmwise condensation

g

Gradient

i

ith thermocouple

l

Liquid (condensate)

lg

Liquid gas

q

Related to heat flux

v

Vapor

w

Wall

Notes

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Copyright information

© The Brazilian Society of Mechanical Sciences and Engineering 2019

Authors and Affiliations

  • Hamid Reza Talesh Bahrami
    • 1
    Email author
  • Alireza Azizi
    • 1
  • Hamid Saffari
    • 1
  1. 1.School of Mechanical EngineeringIran University of Science and TechnologyTehranIran

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