Yjiyji1 y yji1

where y* is what the vapour composition would be if the vapour were in equilibrium with the actual liquid on the stage and yji and yji-1 are actual vapour compositions. If the absorption factor is used, the vapour efficiency can be expressed in terms of variables already presented:

E = Vi - Vji +1( Vj/Vj + 1) MVji (KVj/m-Vj i +1( Vj/Vj + 1)

A vaporization efficiency, Eji, based on the Murphree efficiency is defined as:

yji +1 Kjixji

This can be used in the MESH equations to account for stage nonideality. This vaporization efficiency is applied to the equilibrium constant, Kji, and appears as the product EjlKji. The vaporization efficiency does solve a computational problem in placing an efficiency in the MESH equations. A major disadvantage of the vaporization efficiency is that it does vary with composition. Near the top of a high purity column, as yji +1 and Xji approach unity, Eji also approaches unity, and so a vaporization efficiency does not truly reflect stage nonidealities.

Another efficiency method is the bypass method where some of the vapour flow of a component entering the stage is sent to the next stage to account for its inefficiency in separation. The bypass method cannot be used on trays that have material leaving or entering from outside the column such as a feed tray, product draw tray, pump-around return or draw tray, or side-stripper return or draw tray. The bypass method will cause one of these trays to be out of mass balance. Some of the trays adjacent to these trays are also affected by these actions. In some columns, this eliminates a large number of trays and makes results difficult to apply.

Caution then should be used in any choice of efficiency. More often, it is usually best to perform the rigorous calculation using ideal stages and then apply an overall column efficiency based on sound engineering judgement and experience to account for stage nonideality, and calculate the number of actual trays or packing height.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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