Page 101 - High Power Laser Handbook

70 G a s , C h e m i c a l , a n d F r e e - E l e c t r o n L a s e r s Chemical Lasers 71

(turbulent jet bubblers), various wetted-wall reactors, aerosols, and
liquid-jet reactors.
16
It is currently believed that the above reactions produce a
1
1
near-unity O ( ∆) fraction. The O ( ∆) fraction can be reduced by
2
2
several mechanisms: (1) deactivation within the liquid, leading
to the so-called detachment yield; (2) deactivation by gas-phase
surface film collisions; and (3) homogeneous deactivation in the
gas phase. In most practical devices, the dominant singlet delta
fraction loss mechanism is the homogeneous gas phase self-
1
deactivation of O ( ∆). Sophisticated SOG performance models
2
can be used to accurately evaluate these processes. Many reported
models concurrently model behavior in both the gas and liquid
film streams and predict SOG performance characteristics. One
17
such model includes an effective resistance chlorine-oxygen
–
mass transfer model; a local BHP HO diffusion model; and
2
evaluation of O ( ∆) detachment yield, surface deactivation, and
1
2
gas phase deactivation.
SOG chlorine utilization is also a function of chlorine flow rate
and BHP HO molarity. Because BHP is typically continuously
–
2
replaced by a flowing process, the surface HO concentration is
–
2
determined by the balance between reaction depletion and ion diffu-
sion from within the liquid during the residence time that the BHP
surface remains in the reaction zone. For a typical SOG, chlorine uti-
lization is usually near unity levels at the very low chlorine flow
limit but declines to values on the order of 0.8 to 0.9 at useful flow
rates. At high initial surface [HO ] levels, utilization is typically a
–
2
weak function of [HO ], and at reduced levels, it eventually decreases
–
2
–
toward zero as [HO ] tends to zero. However, because most modern
2
SOG concepts replace the BHP by flowing it in some manner, deple-
tion is only important when ion diffusion is too slow to adequately
maintain surface HO .
–
2
3.4.6 COIL Laser Performance Characterization
In addition to SOG parameters, net laser performance is frequently
characterized by chemical efficiency, which is defined as the percent-
age of power output to the power output expected if 100 percent of
the chlorine has reacted and each resultant oxygen molecule has pro-
duced one laser photon:
Chemical efficiency = P(kW)/(91 kW × X ) (3.31)
Cl2

The situation is often approximated in terms of a heuristic equation,
14
defined as follows:
η
Chemical efficiency = U × (F – N × X – F thres )η mix extract (3.32)
I2
∆