Variation, coeflicient

The relationship between the variation coeflicient and mixer length is flow ratio dependent, as illustrated by data published for Sulzer mixers this apparently not being the case for the other two indices There is also the disadvantage, shared by most other variance based indices, of a dependence on sample size which can lead to difficulty in comparing data from different sources. 

The first step in planning an experiment to study this problem would take into consideration the choice of factors, or variables that affect the pressure drop (Ap/1) and the heat transfer coeflicient (a). As a first approach, we can consider the effects of temperature and pressure separately. In fact, the temperature variation has no direct effect on the pressure drop but has an effect on the fluid s physical properties. 

The random or indeterminate error associated with a measurement or result. Sometimes called the variability, it can be represented statistically, by the standard deviation or relative standard deviation (coeflicient of variation) (p. iS). 

The Wilson equation is very effective for dilute composition where entropy effects dominate over enthalpy effects. The Orye-Prausnitz form of the Wilson equation for the activity coeflicient, as given in Table 5.3, follows from combining (5-2) with (5-41). Values of A ij < 1 correspond to positive deviations from Raoult s law, while values of A >1 correspond to negative deviations. Ideal solutions result from A, = 1. Studies indicate that Af, and ka are temperature dependent. Values of viJvjL depend on temperature also, but the variation may be small compared to temperature effects on the exponential term. 

Although sensible heat transfer coeflicients are considerably lower than condensing coeflicients, heat transfer rates are quite high in the desuperheating zones of distillation condensers. The low heat transfer coefficient in the desuperheating zone is compensated for by the higher temperature difference between the superheated vapor and the coolants (compared to the temperature difference between the saturated vapor and the coolant). In most cases, moderate variation in superheat has little effect on condenser performance and is seldom troublesome in distillation operation. 

An important aspect of coking is its influence on the selectivity. As the product distribution or the selectivity depends on the ratios of the various rate coeflicients it is evident that the selectivity may also be affected by changes in catalyst activity, when the different reactions are not influenced in the same way by the catalyst activity decline. Froment and Bischoff [37] worked out the theory for such a situation. Figure 11.5.f-9 shows the results for a complex reaction with parallel coking scheme. The variation of the selectivity for the isomerization of n-pentane... 

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