Abstract
This theoretical investigation deals with the vaporization or condensation rate of a motionless liquid droplet using the quasi-steady diffusion-controlled model. A single-component liquid droplet is considered to be undergoing a phase change within a binary mixture of ideal gases (vapor plus noncondensable gas). Droplet vaporization rates corresponding to specified ambient conditions have been calculated by numerical solution of the variable-property governing equations. Results are presented for water and a series of pure hydrocarbon liquids for a range of ambient conditions of interest. A dimensionless correlation is given for the hydrocarbon vaporization and condensation rates. The pressure variation in the region surrounding a droplet undergoing vaporization or condensation has been investigated by numerical integration of the momentum equation. The resulting calculations indicate that the pressure decreases with increasing distance from the droplet for condensation as well as vaporization. Finally, criteria are given for estimating when the pressure gradient and viscous dissipation may be of significance in the energy equation.
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Abbreviations
- A, B:
-
coefficients in the vapor pressure expression, eq. (C3)
- a j , b j :
-
coefficients in dimensionless correlation, eqns. (D2) and (D3); see Table D-II
- C ji :
-
coefficients in the expression for C Pi , eq. (C2) and Table C-II
- C P :
-
specific heat at constant pressure, energy/(mass, temperature)
- D :
-
binary diffusion coefficient, D=D ij =D ji
- D 1 :
-
collection of factors in expression (C12) for the diffusion coefficient, see Table C-IV
- E :
-
relative difference between variable property and constant property calculation, see Table III
- E i :
-
modified Eucken correction to thermal conductivity
- G ij :
-
coefficient in eq. (C5)
- h :
-
enthalpy
- \(\mathop h\limits^\_\) :
-
dimensionless enthalpy, \(h/(C_{{\text{P}}_{\text{0}} } T_0 )\)
- k:
-
thermal conductivity (energy/time length temp.) or Boltzmann constant
- \( \bar k \) :
-
dimensionless thermal conductivity, k/k0
- l :
-
mean free path
- L(T):
-
latent heat of vaporization, energy/mass, evaluated at the temperature T
- L 1, L 2 :
-
coefficients in expression (C4) for the latent heat of vaporization of water
- Le :
-
dimensionless Lewis number, D ρ C P/k
- m :
-
vaporization rate, mass/time
- n :
-
number of components present in the gas phase
- P :
-
absolute pressure
- \(\hat \bar P\) :
-
dimensionless pressure, (P−P 0)/ρ 0(ν 0/r 0)2
- \(\bar P\) :
-
dimensionless pressure, P/P 0
- P 1(T):
-
vapor pressure of component 1 at temperature T
- Q :
-
heat transfer rate for quasi-steady vaporization, mL(T 0)
- Q R, Q S :
-
heat transfer rate (energy/time) due to radiative absorption or conduction via droplet support
- q :
-
heat transfer rate (energy/time area)
- R:
-
universal gas constant
- r :
-
radial coordinate
- S :
-
dimensionless radial coordinate, r/r 0
- T :
-
absolute temperature
- \(\bar T\) :
-
dimensionless temperature, T/T 0
- V i :
-
diffusion velocity of component i
- v :
-
mass average velocity
- \( \bar \upsilon \) :
-
dimensionless velocity, v/v 0
- W i :
-
molecular weight of component i, mass/mole
- X i :
-
mole fraction of component i
- Y i :
-
mass fraction of component i
- α :
-
empirical correction to eq. (C12) for the diffusion coefficient, also absorptivity
- β :
-
ratio of the rate of energy transfer by conduction from the gas phase to the rate of energy transfer required for vaporization, defined in eq. (A11)
- Δ :
-
change in vaporization rate due to change in pressure, Table I
- ε ij , σ ij :
-
intermolecular potential parameters characterizing the i–j interaction
- σ :
-
Stefan-Boltzmann constant
- η :
-
viscosity
- \( \bar \eta \) :
-
dimensionless viscosity, η/η 0
- μ :
-
dimensionless vaporization rate, m/4πr 0(D ρ)0, or micron (10−6 meter)
- ν :
-
kinematic viscosity, η/ρ
- ρ :
-
density
- \(\bar \rho\) :
-
dimensionless density, ρ/ρ 0
- Φ :
-
viscous dissipation function, eq. (A4)
- Ω (1, 1)⋆, Ω (2, 2)⋆:
-
collision integrals for Lennard-Jones potential
- 0:
-
droplet surface (gas phase)
- ∞:
-
infinitely far from the droplet surface
- B:
-
boiling point at pressure P 0
- c:
-
thermodynamic critical point
- D:
-
dew point
- i :
-
index running from 1 to n, denoting the i th component
- L:
-
liquid phase
- R:
-
reference quantity, defined in eq. (D1)
- ⋆:
-
dimensionless vaporization rate μ⋆ formed with reference value (D ρ)R, or dimensionless temperature T⋆=kT/ε
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Kent, J.C. Quasi-steady diffusion-controlled droplet evaporation and condensation. Appl. Sci. Res. 28, 315–360 (1973). https://doi.org/10.1007/BF00413076
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DOI: https://doi.org/10.1007/BF00413076