Talk:Magnetic Reynolds number

Distinct from the Reynolds number?
Is there a reason why this redirects to Reynolds number? The similarity in the name comes about becuase the parameters take a similar (but physically distinct) form and appear in similar places in non-dimensional versions of similarly structured (but physically distinct) equations. However, one affects the form of a fluid flow, and the other affects the behaviour of the magntic field in MHD problems. There's also no mention of "Magnetic Reynolds Number" on the "Reynolds number" page. I think there should be a separate article here. Rjw62 13:50, 1 June 2007 (UTC)

Merger proposal
The Magnetic Reynolds number is the Lundquist number when the typical velocity scale of the system is the Alven velocity.— AquaDTRS (talk) 06:17, 17 May 2016 (UTC)

The articles should not be combined. The Lundquist number $$S$$ is the ratio of the resistive diffusion time to the Alfvén crossing time, whereas the magnetic Reynolds number is the ratio of the inductive time to the resistive diffusion time. The two equations look similar, but only if one substitutes the Alfven velocity for the fluid velocity. The Alfvén velocity is the velocity of a plasma wave, and the fluid velocity is the velocity of a fluid. They're not the same. The ratio of the two quantities is
 * $$\frac{R_m}{S} = \frac{\mu_0 U L}{\eta} \cdot \frac{\eta}{\mu_0 L v_\mathrm{A}} = \frac{U}{v_\mathrm{A}}$$

Note here I've included the necessary factor of $$\mu_0$$ which many publications omit since they use normalized quantities. X4096 (talk) 16:01, 6 July 2016 (UTC)
 * Closing, given no support. Klbrain (talk) 16:43, 5 February 2018 (UTC)