Why is the Heat equation solved with separation of variables but not with Fourier transformations?

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Discussion Overview

The discussion centers around the methods used to solve the unsteady state heat transfer equation, specifically why separation of variables is commonly employed in heat transfer literature instead of Fourier transformations. The scope includes theoretical considerations and potential applications of different mathematical techniques.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the preference for separation of variables over Fourier transformations in solving the heat equation.
  • Another participant suggests exploring the difficulty of solving the equation on a finite interval with initial and boundary conditions using transform methods compared to separation of variables.
  • A different viewpoint asserts that the choice of method depends on the domain, noting that infinite domains are suited for Fourier transforms while finite domains are better for series expansions. This participant claims both methods are fundamentally similar and relate to separation of variables.
  • This same participant mentions having authored a textbook that employs Fourier transforms to solve the heat equation, indicating that such methods are indeed used in practice.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of Fourier transformations versus separation of variables, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

There is a lack of clarity regarding the specific conditions under which each method is preferred, as well as the implications of domain size on the choice of solution technique.

Who May Find This Useful

This discussion may be of interest to students and professionals in fields related to heat transfer, applied mathematics, and engineering, particularly those exploring different solution methods for partial differential equations.

yaman
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Why in heat transfer books Fourier's partial differtial unsteady state heat transfer equation is solved with separation of variables but not with Fourier transformations?
 
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yaman said:
Why in heat transfer books Fourier's partial differtial unsteady state heat transfer equation is solved with separation of variables but not with Fourier transformations?

Have you tried solving it on a finite interval subject to initial and boundary conditions (the typical geometry appropriate for separation of variables) using a transform method? Is that easier or harder than separation of variables?
 
yaman said:
Why in heat transfer books Fourier's partial differtial unsteady state heat transfer equation is solved with separation of variables but not with Fourier transformations?
This is simply incorrect. The method applied will generally depend on the domain. An infinite domain will be suited for transforms such as the Fourier transform, whereas a finite domain will be more suited for series expansions. Both methods are effectively the same and amount to separation of variables.

I know at least one textbook that uses Fourier transforms to solve the heat equation (and series expansion on finite domains). I know this because I wrote it.
 
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