Nonisobaric operation

If the pressure varies in a BR (nonisobaric operations), the expressions for heat capacities, CpL and CpG, should be replaced with the heat capacities for a constant volume, Cypand CyG-... 

For constant superficial velocity (zero expansion factor) and negligible pressure drop (see the subsection Nonisobaric fixed-bed operation), the general mass and thermal energy continuity equations for the catalytic fixed-bed reactor are... 

The gas-phase pressure drop is better evaluated by using the differential form of Ergun s equation and taking into account the gas density variance. However, it is easy to show that the parameter aZIPi is about 0.001, and thus the Ergun equation in its classic form can be accurately used (see subsection Nonisobaric fixed-bed operation). 

Nonisobaric conditions are accounted for through the pressure drop correlation of Eckert, for example, represented in Fig. 14.3.1-2. Nonisothermal operation will be illustrated in Example 14.3.4.A. 

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