Code Manual for CONTAIN 2.0 - Federation of American Scientists

where h, is the convective heat transfer coefficient and is equal to N ~u(k~~), where Nu ~Uisthe
Nusselt number given below in Equation (12-19), k~~is the thermal conductivity of the boundary ~
layer, D is the drop diameter; T~is the bulk gas temperature; and T~is the drop temperature.
The second component of the total heat flux, accounting for the heat transported by the mass flux,
is given by
q.ond = j.o.dhv,b (12-15)
where jCO,~is the vapor mass flux as determined below in Equation (12-16) and &,~is the enthalpy
of water vapor at the bulk gas temperature.
The mass flux jCO.~at the spray drop surface is approximated by
.&j = ‘g”vf(pv,b - ‘v,d)
where Kgis the mass transfer coefficient (kgmole/s-m2-Pa), and
(12-16)
(12-17)
where N~~is the Sherwood number, P~is the gas pressure (Pa), B, is the diffusivity of water vapor
(m’/s), R is the universal gas constant (Pa-m3/kgmole-K), T,~ is the average of T, and T~,and
Pm= (? ,b - ‘v,d)An[(pg - ‘v,b)/(p - ‘v,d)] (12-18)
Here, Pv,~is the partial pressure of water vapor at the gas temperature T~,and PV,~is the saturation
pressure at the drop temperature T~.
For forced convection around a spherical droplet @ir60] (recall that the droplets are falling through
air), the Nusselt and Sherwood numbers used for calculating the convective and mass transfer
coefficients are given by
and
N Nu = 2.0 + o.60(NRey7NRy3
Nsh = 2.0 + o.60(NRJqNJ3
R O 12 18
(12-19)
(12-20)