Page 149 - Design of Solar Thermal Power Plants

P. 149

134 3. GENERAL DESIGN OF A SOLAR THERMAL POWER PLANT

during the sandstorm was more than 20 times of that after the
sandstorm; whereas the concentration of ﬁne particles (d < 2 mm) is
seven times that after the sandstorm. Optical thickness, extinction
efﬁciency factor, scattering efﬁciency factor, and absorption
efﬁciency factor of aerosols are major physical parameters to
describe the conditions of atmospheric aerosols, as well as the
crucial factors to evaluate the energy ﬂow transmission of
atmospheric concentration.
Extinction efﬁciency factor Qe refers to the ratio of the light
extinction section to geometric section of the respective particle.
According to the Mie-Debye scattering theory, extinction efﬁciency
factor Qe has the important features of ﬂuctuating along with the
attenuation of sand dust particle radius r and approaching 2.
According to Fig. 3.6, position of the primary main peak of Qe falls
in a range of 0.1e1.0 mm. Along with the increase of wavelength l,
position of the primary main peak moves toward the direction of the
increase of r. According to the measured data from both home and
abroad, it is exactly within the above-mentioned main peak area, in
which aerosol spectrum normally has sharp peak values. However,
along with the increase of particle radius r, variation amplitude of
extinction efﬁciency factor gradually decreases; when r > 5.0 mm,
the extinction efﬁciency factor Qe gradually loses its sensitivity
against the particle size r, and gradually approaches 2, that is, solar
energy eliminated by large particles from the incident beam is
exactly two times of the optical energy prevented by its section.

5
440nm
4.5 670nm
870nm
936nm
4
Extinction efficiency factor Qe 2.5 3 2
1020nm
3.5

1.5

0.5 1
0
1 2 3 4 5 6 7
Particle size r /μm
FIGURE 3.6 Variation of extinction efﬁciency factor Qe over particle size r.

144 145 146 147 148 149 150 151 152 153 154