Turbulent Flow In Long Pipes

Unless specifically indicated, all fluid properties are evaluated at the mixing-cup temperature of the fluid  

The subscript w indicates the property is to evaluated at the wall temperature  

Experimentally, one finds that heat transfer coefficients can be different for heating and cooling over the same temperature range. The reason, is that the viscosity at the wall is very important in determining transport and p can be very different from p. This is accounted for in the p/pw factor. 

When the inlet and outlet T s differ, what T do you use to evaluate the properties at Use arithmetic mean values for T and 

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