Joint International Conference on Long-term Experiments ...

with
= +
K k
o
1 1
ka ⁄ S is much larger than 1000 cm ⁄ hour. As compared with the values of order of 10
cm⁄hour for ko, that permits us to ignore the stable film from the atmosphere, this will
give K = kO, and
Φ = − k ( C − C )
(8)
O a O
or, as a function of partial pressures, we have:
Φ = − k ( p − p )
(9)
s
with ks = kOS.
The measurements of the gas exchange constants were made in wind tunnels and
using in situ markers for a variety of gases, under various wind velocities and
temperature conditions. The measurements indicate a dependency of friction in water,
u*O, for kO of and also of Schmidt number, defined as
Sc = ν ⁄ ε (10)
where ν is the kinematic viscosity, ko of the form
kO = γ -1 Sc -n u*O (11)
and γ is a non-dimensional constant. The exponent n at the number Sc is included to
permit that the gas exchange do not comports as when it should suffer a transversal
transition to a stable film with kO = ε ⁄ Δz (e.g. with n = 1). n could be determined by
gases exchange measurements with more that a single gas and a heat exchange in the
same conditions:
log( k 1 / k 2)
n = − O O
(12)
log( Sc1
/ Sc2)
In Table nr.2 are given different models for the gases exchange coefficient. These have
a difference between them of more than a factor of 2.
4. CONCLUSIONS
There were made laboratory studies and also in situ experiments. The laboratory
studies were made in hydrodynamic tunnels, with which are analyzed the gases
exchanges and the exchange coefficients are measured by measurement of the
equilibrium for a marker mass in water. The exchange on a given period of time is the
flux. The exchange coefficient is obtained making the rapport between the flux and the
difference of concentration air-water, measured with eq.(5). Such experiments have
indicated that the gases exchange coefficients at the air-water interface varies as
functions of wind velocity, U, giving us the idea that of existence of three linear regimes
separated by the transition from a plate water surface to one with one with rugosities,
and from a rugous surface to one for which the tides begin to break up. The theory of
the micrometeorological boundary layer, that tell us that n = - 2 ⁄ 3 [1]-[4], seems to
be good when the water surface is plate. The Model of the substitution film, which
proposes the existence of a film that is periodicaly substituted by the fluid volume, gives
392
a
S
k
a
O
(7)