Zone leveling

Current mixing-type air distribution methods typically consider ventilation of the occupied zone with jets intercepting its upper boundary (e.g.. Fig. 7.6l2, c). Also, the occupied zone can be ventilated by the reverse flow produced as the supply jet degrades above the occupied zone level (Fig. 7.6h]. Mixing-type air distribution methods include air supply with jets projected vertically downward, inclined jets, jets directed vertically upward, and horizontal jets along room surfaces. 

The results of thermal building-dynamics simulation are generally referred to by zone level. They can be divided into instantaneous results and summary results. 

Space savings are not expected at the zone level. However space required for mechanical room components may be lower when compared to central heat pump system. 

Space savings arising from the smaller size of boiler and cooling tower is offset by the addition of central heat pump. Use of fan coil units at the zone level is not expected to result in space savings because of larger requirement of air flow arising from lower temperature difference across the heating coil. 

When the zone length is relatively short, k is large, and when the number of passes is small, the bulk of the specimen solidifies at very nearly a uniform composition corresponding to co- Zone solidification can be used in this manner to produce compositional uniformity, a technique known as zone leveling. 

De Kruif, C.G., Van Generen, A.C.G., Bink, J.C.W.G., Oonk, H.A.J. (1981) Properties of mixed crystalline organic material prepared by zone levelling. II. Vapor pressures and excess Gibbs energies of (p-dichlorobenzene + />-dibromobenzene). J. Chem. Thermodynam. 13, 457 163. 

Theoretical treatments have also been given to other situations of interest. In zone leveling, the impurity level is homogenized either by moving the zone back and forth along a linear rod, or by movement around a ring (1). Evaporation and condensation of a volatile impurity (17—18), as weU as decomposition of the material itself (13), have also been treated. 

DNP in the U.S. chemical industry, the urine contained 2.08 g/L of 2,4-DNP and 50 mg/L of 2-amino-4-nitrophenol (Gisclard and Woodward 1946). Workroom air levels of 2,4-DNP, determined subsequent to the death, were "normally" >40 mg/m. This may underestimate breathing-zone levels, and significant dermal absorption was thought to have occurred following deposition of the chemical on the skin. Hence, no conclusions regarding fraction absorbed can be drawn from this study, but it does provide additional evidence of absorption from the inhalation route. 

Figure 2-7. Zone leveling using a starting charge to eliminate the initial transition region.

Suppose you wanted to intentionally dope a metal with I ppm of an impurity. One way is to add a small amount of the impurity to one end of a pure ingot and make several passes. The impurity will be spread evenly throughout the ingot for a considerable length. This is called zone leveling and is excellent for making semiconductor materials where the level of impurity is critical. Refer to Figure 2-7. 

This is referred to as zone refining. If the liquid zone is passed through the charge in both the forward and reverse directions, a uniform distribution of impurities may be obtained. This is zone leveling. 

The theoretical basis of isotachophoresis has been elaborated to such an extent that relationships which permit the calculation of pH, mobilities, composition of zones, level of the separation reached etc., are available. These relationships have even been developed to routine computer procedures. Thus, not only a great deal of information on the substances to be separated can be gained but also theoretical predictions of the optimum electrolytic systems enabling successful separations can be made. 

The results from the measmements broadly confirmed the conclusions of the European study. At zone level, RDT or 30MS samples taken in a sufficient number of properties gave almost identical results. RDT is slightly more severe but, above all, it is more practical and acceptable to the consumer. 

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