# Dynamic Viscosity in Reynolds Number

## Summary:

Determining dynamic viscosity for heat exchanger reynolds number/heat transfer coefficient calculation

## Main Question or Discussion Point

I am trying to run a calculation to work out the overall heat transfer coefficient of an arbitrary ten plate exchanger where the fluid is not determined using Re=puD/mu where mu is dynamic viscosity. When mu is such a strong function of temperature how should I determine which valye to use, say if I assumed it was water of certain temperatures flowing in and out. I'm a materials student so haven't done too much of this.

Many thanks

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Summary: Determining dynamic viscosity for heat exchanger reynolds number/heat transfer coefficient calculation

I am trying to run a calculation to work out the overall heat transfer coefficient of an arbitrary ten plate exchanger where the fluid is not determined using Re=puD/mu where mu is dynamic viscosity. When mu is such a strong function of temperature how should I determine which valye to use, say if I assumed it was water of certain temperatures flowing in and out. I'm a materials student so haven't done too much of this.

Many thanks
According to Transport Phenomena, Bird, Stewart, and Lightfoot, Section 14.2, you evaluate the viscosity in the Reynolds number at the arithmetic average of the bulk inlet and outlet temperatures and the inlet and outlet surface temperatures. So, it is the average of the 4 temperatures.

Last edited:
• ChemAir