Abstract
Simulations have been performed for water vapor condensation underneath a horizontal and an inclined textured substrate. A horizontal surface having unidirectional wettability gradient has also been considered. Here, the effect of thermophysical properties, physico-chemical properties of the substrate, promoter layer thickness, nucleation site density, saturation temperature, degree of subcooling, effect of wettability gradient and angle of inclination are parametrically explored. Quantities such as the contact angle and contact angle hysteresis play an important role. We have used a nucleation site density of 106 cm−2 in most of the simulations reported. The simulation data is presented in the form of condensation patterns, area coverage as a function of time, and area-averaged heat transfer coefficient as a function of time. The cycle time and the maximum drop size at instability are tabulated. Based on numerical data, heat transfer coefficients of water vapor condensation are expressed as correlations. In order, the horizontal, inclined, and the graded surface experience (a) larger to smaller drop sizes, (b) longer to shorter cycle times, and (c) lower to higher heat transfer coefficients.
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Abbreviations
- C p :
-
Specific heat at constant pressure, W/kg K
- h lv :
-
Latent heat of vaporization, J/kg
- h :
-
Heat transfer coefficient, W/m2 K
- k :
-
Thermal conductivity of the condensate, W/m K
- N :
-
Number of nucleation sites, cm−2
- r :
-
Radius of drop, m; suffix b is for base radius
- r cap :
-
Capillary length, \( \sqrt{\sigma /g\left({\rho}_{\mathrm{l}}-{\rho}_{\mathrm{v}}\right)} \), m
- r crit :
-
Size of the drop at instability due to slide-off, m
- r max :
-
Size of the drop at instability due to fall-off, m
- r min :
-
Radius of thermodynamically smallest drop, m
- T :
-
Temperature, K; subscripts w and sat are for wall and saturation
- ΔT, (Tsat − Tw):
-
Temperature difference between the saturated vapor and condensing wall, K
- Ja:
-
Jakob Number, (Cp/hlv)ref(Tsat − Tw)
- Nu:
-
Nusselt number, hrcap/k
- Pr:
-
Prandtl number
- α :
-
Inclination angle of the substrate from horizontal, radians
- θ :
-
Contact angle, radians or degrees; adv, rcd and avg are advancing, receding and average angles
- Δθ, (θadv − θrcd):
-
Contact angle hysteresis, °
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Sikarwar, B.S., Somwanshi, P., Muralidhar, K., Khandekar, S. (2020). Simulation: Dropwise Condensation of Water. In: Drop Dynamics and Dropwise Condensation on Textured Surfaces. Mechanical Engineering Series. Springer, Cham. https://doi.org/10.1007/978-3-030-48461-3_9
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DOI: https://doi.org/10.1007/978-3-030-48461-3_9
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