Radiation, solar

The glass sheet with double the thickness absorbs a somewhat larger part of the solar radiation, but still allows 65% of the incident radiation to pass through it compared to 70% with the thin sheet. The spectral reflectivity r of the thick sheet from (5.100) is 

It is increased between Ai and A2 by the multiple reflection at the edges, so that in total 6.7% instead of 4.26% of the solar energy is reflected. 

When studying the limits of solar energy conversion, either by thermal or quantum processes, the sun has traditionally been treated as a blackbody (thermal equilibrium) radiator with surface temperature 5 800 K and distance 1.5 x 1011 m from Earth. A blackbody absorbs all incident radiation irrespective of its wavelength and direction of incidence and is represented classically by a hole in a cavity. 

Its fundamental importance derives from the fact that the energy density of radiation in the cavity does not depend on the properties of the cavity, i.e., properties of the walls or the cavity size, provided it is large compared to the wavelength of the radiation. In the following we will discuss radiation not as a function of wavelength but as a function of photon energy, because it is the photons (light quanta) that are absorbed and excite electrons in matter. 

According to Planck, blackbody radiation implies a universal dependence of the energy density per photon energy interval d(huj). This results in an energy current density djV,bb per photon energy interval d(fuj) given by 

Any other body which has absorptivity a fiw) = 1 for photons with energy Hui will emit radiation according to (4.1). Although the sun consists mainly of protons, alpha particles and electrons, its absorptivity is a(Tkj) = 1 for all photon energies tiw, by virtue of its enormous size. Its temperature is not homogeneous, but emitted photons originate from a relatively thin surface layer a few hundred kilometres thick, in which the temperature is constant and in which all incident photons are absorbed. Conversely, only photons emitted within this surface layer may reach the surface of the sun. The solar spectrum observed just outside the Earth atmosphere agrees well with (4.1) 

Even more important for quantum energy converters, e.g., solar cells, than the energy current density is the photon current density, because it determines the rate at which electrons are excited. Neglecting impact ionisation effects, the excitation of one electron requires at least one absorbed photon. 

Other cases may be computed, and the influence which h and 2 have on the results is shown in the accompanying figure. 

This example illustrates how nonlinear equations with combined convection and radiation can be solved with a straightforward iterative procedure. Recognizing the uncertainties in knowledge of surface emissivity and convection coefficient, only a few iterations are necessary to achieve an acceptable solution. 

Solar radiation is a form of thermal radiation having a particular wavelength distribution. Its intensity is strongly dependent on atmospheric conditions, time of year, and the angle of incidence for the sun s rays on the surface of the earth. At the outer limit of the atmosphere the total solar irradiation when the earth is at its mean distance from the sun is 1395 W/m2. This number is called the solar constant and is subject to modification upon collection of more precise experimental data. 

It is quite apparent from Fig. 8-63 that solar radiation which arrives at the surface of the earth does not behave like the radiation from an ideal gray body, while outside the atmosphere the distribution of energy follows more of an ideal pattern. To determine an equivalent blackbody temperature for the solar radiation, we might employ the wavelength at which the maximum in the spectrum occurs (about 0.5 /im, according to Fig. 8-63) and Wien s displacement law [Eq. (8-13)]. This estimate gives 

The equivalent solar temperature for thermal radiation is therefore about 5800 K (10,000°R). 

Nichts Sufires gibt es, ah der Sonne Licht zu schaun. [Nothing is sweeter than watching the sunlight.] 

The most energetic radiation (far UV, X-rays, and y-radiation) induces ionization  

Bioinorganic Photochemistry Grazyna Stochel, Malgorzata Brindell, Wojciech Macyk, Zofia Stasicka, Konrad Szacilowski 2009 Grazyna Stochel, Malgorzata Brindell, Wojciech Macyk, Zofia Stasicka, Konrad Szacilowski. ISBN 978-1-405-16172-5 

More detailed description of stress-strain and viscoelastic behaviour can be found elsewhere [329, 653, 1579]. 

Mechanical testing (strain-stress, tensile strength, elongation at break, elastic modulus, melt flow, viscoelastic properties, etc), have frequently been used in the study of the photodegradation of polyethylene [711, 1656, 1704, 1750, 1957, 2124, 2128], polypropylene [1750, 1899, 1903], poly(styrene) [748], poly(styrene-co-carbon monoxide) [1429], poly(styrene-co-acrylonitrile) [747], EPDM [896], poly(vinyl chloride) [806,1137,1138,1232,1748,1938], impact modified poly(vinyl chloride) [761, 764,1232], nylon 6 [672, 726, 727, 1395,1396,2300,2305], polyethylene blends with nylon 6 [506], and polyurethanes and its blends with poly(vinyl chloride), poly(vinyl alcohol), poly(vinyl acetate) and poly(vinyl chloride-co-vinyl acetate) [652]. 

The sun is the most influential radiation source in the sky having approximately the spectral radiation distribution of a black-body with a distribution temperature (T ) of 6200 K. Energy is received from the sun on the outside of the earth s atmosphere at an average rate of about 0.135 W cm On a 

The light that reaches the earth s surface from the sun consists of two components [926, 1436, 1762, 2000, 2209, 2293]  

Sunlight, i.e. radiation that comes directly from the sun, and 

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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 ... 

Solar evaporation Solarization Solar panels Solar ponds Solar power systems Solar radiation Solar salt... 

Stratospheric Depletion. In the stratosphere, is formed naturally when O2 is dissociated by uv solar radiation in the region 180—240... 

The average daily incident solar radiation, or insolation, that strikes the earth s surface worldwide is about 220 W/m (1675 Btu/ft ). The annual insolation on 0.01% of the earth s surface is approximately equal to all energy consumed (ca 1992) by humans in one year, ie, 321 x 10 J (305 X 10 Btu). In the United States, the world s largest energy consumer, annual energy consumption is equivalent (1992) to the insolation on about 0.1 to 0.2% of U.S. total surface. 

The maximum efficiency with which photosynthesis can occur has been estimated by several methods. The upper limit has been projected to range from about 8 to 15%, depending on the assumptions made ie, the maximum amount of solar energy trapped as chemical energy in the biomass is 8 to 15% of the energy of the incident solar radiation. The rationale in support of this efficiency limitation helps to point out some aspects of biomass production as they relate to energy appHcations. 

Table 22. Daily Solar Radiation in the United States ...

Ozone, which occurs in the stratosphere (15—50 km) in concentrations of 1—10 ppm, is formed by the action of solar radiation on molecular oxygen. It absorbs biologically damaging ultraviolet radiation (200—300 nm), prevents the radiation from reaching the surface of the earth, and contributes to thermal equiHbrium on earth. 

Ozone is formed rapidly in the stratosphere (15—50 km) by the action of short-wave ultraviolet solar radiation (<240 nm) on molecular oxygen,... 

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. 

At 25°C, pH 7.5, 1.5 ppm FAC, and 25 ppm cyanuric acid, the calculated HOCl concentration is only 0.01 ppm. Although the monochloroisocyanurate ion hydrolyzes to only a small extent, it serves as a reservoir of HOCl because of rapid hydrolysis. Indeed, this reaction is so fast that HClCy behaves like FAC in all wet methods of analysis. Furthermore, since HClCy absorbs uv only below 250 nm, which is filtered out of solar radiation by the earth s atmosphere, it is more resistant to decomposition than the photoactive C10 , which absorbs sunlight at 250—350 nm and represents the principal mode of chlorine loss in unstabilized pools (30). As Httie as 5 ppm of bromide ion prevents stabilization of FAC by cyanuric acid (23) (see also Cyanuric and ISOCYANURIC acids). 

Factors considered to affect pond performance are air temperature, relative humidity, wind speed, and solar radiation. Items appearing to have only a minor effect include heat transfer between the earth and the pond, changing temperature and humidity of the air as it traverses the water, and rain. 

TABLE 12-5 Maximum Expected Solar Radiation at Various North Latitudes ... 

Table 12-5 presents typical values of solar radiation on a horizontal... 

Thermal expan sion. Equipment and pipehues which are liquid-full under normal operating conditions are subject to hydrauhc expansion if the temperature increases. Common sources of heat that can result in high pressures due to thermal expansion include solar radiation, steam or other heated tracing, heating coils, and heat transfer from other pieces of equipment. 

The initial gas temperature in a tank can reach a value of 55°C (131°F) as a result of strong solar radiation. Ambient rainfall is assumed to be 15°C (59°F). The maximum flow rate of air into the... 

The ocean is an integral part of the climate system. It contains almost 96% of the water in the Earth s biosphere and is the dominant source of water vapour for the atmosphere. It covers 71% of the planet s surface and has a heat capacity more than four times that of the atmosphere. With more than 97% of solar radiation being absorbed that falls on the surface from incident angles less than 50" from the vertical, it is the main store of energy within the climate system. 

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