Coefficients definition

A direct numerical relationship between heat and momentum fluxes, as for the simple Reynolds analogy for a single phase, is not obtained in this case because of a basic and significant difference in heat transfer coefficient definitions. For singlephase flow in pipes, the mixed mean or integrated average temperature is used in... 

Although the linear mixing rule for b [Eq. (14.42)] has proved generally aceeptable, the quadratie mixing rule for a [Eq. (14.43)] is often unsatisfactory. An alternative is a mixing mle for q that incorporates activity-coefficient data. The comiection between activity coefficients and equation-of-state parameters is provided by activity-coefficient and fugacity-coefficient definitions thus. 

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