Thin module

In order to make a multipurpose plant even more versatile than module IV, equipment for unit operations such as soHd materials handling, high temperature/high pressure reaction, fractional distillation (qv), Hquid—Hquid extraction (see Extraction, liquid-liquid), soHd—Hquid separation, thin-film evaporation (qv), dryiag (qv), size reduction (qv) of soHds, and adsorption (qv) and absorption (qv), maybe iastalled. 

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

If the index of refraction of a thin material were modulated in Heu of its absorption, the resultant transmittance function for a gra ting prepared as in the absorption case is given by equation 9 where n is the average index of the thin film. An is the amphtude of the index perturbation, and T is the thickness of the film. 

Hollow-fiber designs are being displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. Also, thin-film interfacial composite membranes, the best reverse osmosis membranes available, have not been fabricated in the form of hoUow-fine fibers. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

As with ah thin-film PV technologies, the projected manufacturing costs of a-Si H ahoy PV modules fah rapidly with annual manufacturing volume, ie, MWp /yr. The primary driver of this volume cost reduction is the volume—cost relationship of commercially available thin-film processing equipment. Thin-film coating machines often have capacities equivalent to 3—5 yr, so that manufacturing economies of scale are more fully realized at the... 

Small-area thin-film CdTe solar cells have been fabricated with sunlight-to-electricity conversion efficiencies near 16%, comparable to crystalline siUcon solar cells in large-scale manufacturing. Large-area monolithic integrated CdTe modules have been fabricated with efficiencies of ca 10%, comparable to crystalline siUcon modules commercially available. 

Copper Indium Diselenide. CuInSe2 (CIS) has proven to be one of the most promising thin-film photovoltaic materials. CIS ahoy materials have yielded smah-area (ca 1 cm ) laboratory devices with efficiencies in excess of 17% and large-area (ca 0.5 m ) monolithic integrated modules with efficiencies in excess of 11%, and have shown excehent radiation hardness. 

Compared to ingot-based and sUicon sheet technologies, thin-film modules tequke less semiconductor material and can be mote highly automated both attributes lead to lower cost. However, the performance of thin-film modules has yet to equal that of ingot-based and sUicon sheet technologies. 

The membrane material is a thin-film composite in a 20-cm module. 

Photovoltaic devices typically consist of a series of thin semiconductor layers that are designed to convert sunlight to dkect-current electricity (see Semiconductors). As long as the device is exposed to sunlight, a photovoltaic (PV) cell produces an electric current proportional to the amount of light it receives. The photovoltaic effect, first observed in 1839, did not see commercial appHcation until the 1950s when photovoltaic modules were used to power early space sateHites. Many good descriptions of the photovoltaic phenomenon are available (7). 

For applied work, an optical characterization technique should be as simple, rapid, and informative as possible. Other valuable aspects are the ability to perform measurements in a contactless manner at (or even above) room temperature. Modulation Spectroscopy is one of the most usehil techniques for studying the optical proponents of the bulk (semiconductors or metals) and surface (semiconductors) of technologically important materials. It is relatively simple, inexpensive, compact, and easy to use. Although photoluminescence is the most widely used technique for characterizing bulk and thin-film semiconductors. Modulation Spectroscopy is gainii in popularity as new applications are found and the database is increased. There are about 100 laboratories (university, industry, and government) around the world that use Modulation Spectroscopy for semiconductor characterization. 

For characterization purposes of bulk or thin-film semiconductors the features at Eq and E] are the most useflil. In a number of technologically important semiconductors (e.g., Hgi j d Te, and In Gai j ) the value of. ) is so small that it is not in a convenient spectral range for Modulation Spectroscopy, due to the limitations of light sources and detectors. In such cases the peak at E can be used. The features at Eq and are not useflil since they occur too far into the near-ultraviolet and are too broad. 

For characterization purposes the most useful form of external modulation is electromodulation, because it provides the sharpest structure (third derivative of R in bulk or thin films) and is sensitive to surface or interface electric fields. The most widely used contacdess mode of electromodulation is termed Photoreflectance (PR) 5.7.8... 

P. Jensen, B. Niemeyer. The effect of a modulated flux on the growth of thin films. Surf Sci 384 9999, 1997. 

Commercially available PV systems most often include modules made from single-crystal or poly-ciystalline silicon or from thin layers of amoiphous (non-crystalline) silicon. The thin-filni modules use considerably less semiconductor material but have lower efficiencies for converting sunlight to direct-current electricity. Cells and modules made from other thin-filni PV materials such as coppcr-indiuni-diselenide and cadmium telluride are under active development and are beginning to enter the market. 

The variable orifice of the expansion valve can be replaced, in small systems, by a long thin tube. This is a non-modulating device and has certain limitations, but will give reasonably effective control over a wide range of conditions if correctly selected and applied. Mass flow is a function of pressure difference and the degree of liquid subcooling on entry. 

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