Dynamic Viscosity in Reynolds Number

• George5356
In summary, for determining dynamic viscosity in heat exchanger Reynolds number/heat transfer coefficient calculations, the viscosity should be evaluated at the average of the bulk inlet and outlet temperatures and the inlet and outlet surface temperatures.
George5356
TL;DR 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

George5356 said:
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

What is dynamic viscosity?

Dynamic viscosity is a measure of a fluid's resistance to flow. It is a property of a fluid that describes how easily it can be deformed by shear stress. In simpler terms, it is a measure of how thick or thin a fluid is.

What is Reynolds number?

Reynolds number is a dimensionless number used to predict the type of flow (laminar or turbulent) in a fluid. It is calculated by dividing the product of the fluid's density, velocity, and characteristic length by its dynamic viscosity.

How does dynamic viscosity affect Reynolds number?

Dynamic viscosity is one of the factors that determine the value of Reynolds number. As dynamic viscosity increases, Reynolds number decreases, indicating a more laminar flow. As dynamic viscosity decreases, Reynolds number increases, indicating a more turbulent flow.

What is the significance of Reynolds number in fluid dynamics?

Reynolds number is an important parameter in fluid dynamics as it helps determine the type of flow (laminar or turbulent) and predict the behavior of fluids in different situations. It is used in the design of pipes, pumps, and other fluid systems.

How is dynamic viscosity measured?

Dynamic viscosity is typically measured using a viscometer, which is a device that measures the resistance of a fluid to flow. There are different types of viscometers, such as capillary, rotational, and falling ball viscometers, each with its own method of measuring dynamic viscosity.

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