# An identity derived by a 90° turn of a classical fluid-mechanics problem

## Document Type

Article

## Publication Date

12-1-2020

## Abstract

We take the classical problem of laminar flow in a rectangular duct and turn the duct 90°. Driven by the same pressure gradient, the volume flow rate should remain the same. This leads to an identity that relates a polynomial to infinite series of tanh functions. We discuss the mathematical properties of this identity and verify it by two different methods.

## Publication Source (Journal or Book title)

Applied Mathematics E-Notes

## Recommended Citation

Wong, H.
(2020). An identity derived by a 90° turn of a classical fluid-mechanics problem.* Applied Mathematics E-Notes*
Retrieved from https://repository.lsu.edu/mechanical_engineering_pubs/427