Solar radiation absorption

Kondrat ev, K. Y., V. I. Binenko, and I. N. Melnikova, Solar Radiation Absorption by Cloudy and Cloudless Atmospheres, Meteorol. Gidrol., No. 2, 14-23 (1996b). 

Rozanov, V.V., Yu. M. Timofeyev, A.V. Polyakov, Burrows J.P. and K.V. Chance (1992) On the possibilities of precision measurements of 03 and N02 from space by solar radiation absorption spectra. Izvestiya Akademii Nauk SSSR Fizika Atmosfery I Okeana 28 500-505. 

Calculate the heat-generation rate resulting from solar-radiation absorption in a lake with an extinction coefficient of 0.328 m and a solar altitude of 90° on a clear day. Perform the calculation for a depth of 1 ft [0.3048 m]. 

I Reconsider Prob. 7-24. Using HHS (or other) software, investigate the effects of the train velocity and the rate of ab.sorplion of solar radiation on the equilibrium temperature of the top surface of the car. Let the train velocity vary from 10 ktn/h to 120 km/h and the nite of solar absorption from 100 V/in to 500 W/m". Plot the equilibrium temperature as functions of train velocity and. solar radiation absorption rale, and discuss the results. 

This section is devoted to the results of some theoretical studies on solar radiation, absorption rates, and primary photochemical processes in smog, undertaken by Leighton (18). In work sponsored by the Air Pollution Foundation, Leighton made a critical analysis of the chemical effects that sunlight and sky radiation may have on smog formation in urban atmospheres. The radiant energy available for photochemical... 

In 1817, Josef Fraunhofer (1787-1826) studied the spectrum of solar radiation, observing a continuous spectrum with numerous dark lines. Fraunhofer labeled the most prominent of the dark lines with letters. In 1859, Gustav Kirchhoff (1824-1887) showed that the D line in the solar spectrum was due to the absorption of solar radiation by sodium atoms. The wavelength of the sodium D line is 589 nm. What are the frequency and the wavenumber for this line ... 

Most ozone is formed near the equator, where solar radiation is greatest, and transported toward the poles by normal circulation patterns in the stratosphere. Consequendy, the concentration is minimum at the equator and maximum for most of the year at the north pole and about 60°S latitude. The equihbrium ozone concentration also varies with altitude the maximum occurs at about 25 km at the equator and 15—20 km at or near the poles. It also varies seasonally, daily, as well as interaimuaHy. Absorption of solar radiation (200—300 nm) by ozone and heat Hberated in ozone formation and destmction together create a warm layer in the upper atmosphere at 40—50 km, which helps to maintain thermal equihbrium on earth. 

Sihcon cells are hundreds of micrometers ( -lm) thick in order to faciUtate handling with minimal breakage, although most solar radiation is absorbed in the first 20—30 p.m. Light penetration decreases exponentially, proportional to, where d is the absorption coefficient of a material and T is its thickness. The values of (X for a given material vary with the wavelength of incident radiation in siUcon, (X is 10 —10 /cm over most of the range of usable solar radiation. 

Because water of depths below about 2 m does not absorb much solar radiation direcdy, the radiation is absorbed and converted to heat primarily in the basin floor, which thus should have high radiative absorptance in the solar radiation spectmm. It is also noteworthy that if the stUl is designed to have low heat losses to the ambient, and if the ambient temperature drops, distillation will continue for some time even in the absence of solar energy input, because the saline water may remain warmer than the condensing glass surface and thus continue evaporating. 

During heat dissipation by radiation the colour and condition of the surface plays a similar role. Dark-coloured bodies dissipate more heat than the light-coloured ones. The amount of heat absorption and emission for the same body may therefore be assumed to be almost the same. Accordingly, Table 31.1, for selected colours, may be considered for the coefficients of absorption and emission of heat due to solar radiation and natural radiation respectively. 

In our sample calculations (Example 3 1.1) we have chosen the colour of the outdoors surface as light grey and taking the vveathering effect into account, have considered the coefficient of both absorption and emission as 0.65. The manufacturer, depending on the colour and site conditions, may choose a suitable coefficient. It is, however, advisable to be conservative when deciding the temperature rise due to solar radiation to be on the safe side. 

Table 31.1 Coefficients ol absorption (ol solar radiation) and emission (natural radiation) for a metallic surface located outdoors...

Assuming the approximate absorption coefficient of solar radiation to be 0.65, for a light-grey external surface, having collected soot and dirt over a period of time, as in ANSI-C-37-24 the approximate temperature rise on account of solar radiation... 

We have considered the emission of heat, from the surface through natural radiation, nearly the same, as its absorption of heat through solar radiation. 

Molecules and atoms interact with photons of solar radiation under certain conditions to absorb photons of light of various wavelengths. Figure 10-4 shows the absorption spectrum of NO2 as a function of the wavelength of light from 240 to 500 nm. This molecule absorbs solar radiation from... 

At angles away from the zenith, solar radiation must penetrate a greater thickness of the atmosphere. Consequently, it can encounter more scattering due to the presence of particles and greater absorption due to this greater thickness. 

Yet another alternative is the thin-film solar cell. This cannot use silicon, because the transmission of solar radiation through silicon is high enough to require relatively thick silicon layers. One current favourite is the Cu(Ga, InjSci thin-film solar cell, with an efficiency up to 17% in small experimental cells. This material has a very high light absorption and the total thickness of the active layer (on a glass substrate) is only 2 pm. 

A non-uegligible fraction of the solar radiation incident on the earth is lost by reflection from the top of the atmosphere and tops of clouds back into outer space. For the radiation penetrating the earth s atmosphere, some of the incident energy is lost due to scattering or absorption by air molecules, clouds, dust and aerosols. The radiation that reaches the earth s surface... 

The amount of solar radiation that reaches any point on the ground is extremely variable. As it passes through the atmosphere, 25 to 50 percent of the incident energy is lost due to reflection, scattering nr absorption. Even on a cloud-free day about 30 percent is lost, and only 70 percent of 1,367 W/nf, or 960 W/m, is available at the earth s surface. One must also take into account the earth s rotation and the resultant day-night (diurnal) cycle. If the sun shines 50 percent of the time (twelve hours per day, every day) on a one square meter surface, that surface receives no more than (960 W/m ) X (12 hours/day) X (365 days/year) =... 

The rate of heat conduction is further complicated by the effect of sunshine onto the outside. Solar radiation reaches the earth s surface at a maximum intensity of about 0.9 kW/ m. The amount of this absorbed by a plane surface will depend on the absorption coefficient and the angle at which the radiation strikes. The angle of the sun s rays to a surface (see Figure 26.1) is always changing, so this must be estimated on an hour-to-hour basis. Various methods of reaching an estimate of heat flow are used, and the sol-air temperature (see CIBSE Guide, A5) provides a simplification of the factors involved. This, also, is subject to time lag as the heat passes through the surface. 

Obtain an expression for the absorptivity of solar radiation as a function of surface temperature and compare the absorptivity and emissivity at 300, 400, and 1000 K. 

The total emissivity of concrete a( 330 K is 0.89, whilst the total absorptivity of solar radiation (sun temperature --- 5500 K) at this temperature is 0.60. Use the data of Problem 9.31 for aluminium. 

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

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