Dynamic Viscosity in Reynolds Number

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SUMMARY

To accurately calculate the overall heat transfer coefficient in a ten-plate heat exchanger, it is essential to determine the dynamic viscosity (μ) using the Reynolds number (Re = ρuD/μ). Given that μ is highly temperature-dependent, the viscosity should be evaluated at the arithmetic average of the bulk inlet and outlet temperatures, as well as the inlet and outlet surface temperatures, as outlined in "Transport Phenomena" by Bird, Stewart, and Lightfoot, Section 14.2. This method ensures a more precise calculation of the heat transfer characteristics of the fluid, particularly when dealing with water at varying temperatures.

PREREQUISITES
  • Understanding of Reynolds number and its significance in fluid dynamics
  • Familiarity with dynamic viscosity and its temperature dependence
  • Basic knowledge of heat exchanger design and operation
  • Proficiency in using "Transport Phenomena" by Bird, Stewart, and Lightfoot as a reference
NEXT STEPS
  • Research the calculation of dynamic viscosity at varying temperatures for different fluids
  • Explore advanced heat exchanger design principles and performance metrics
  • Study the application of the Reynolds number in various fluid flow scenarios
  • Investigate software tools for simulating heat exchanger performance
USEFUL FOR

Materials students, mechanical engineers, and thermal system designers seeking to enhance their understanding of heat transfer processes in heat exchangers.

George5356
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TL;DR
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
 
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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.
 
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