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Mechanical Engineering QUESTION #2432
Question 1
In natural (free) convection, the key dimensionless parameter governing the flow is the Rayleigh number \(Ra\), defined as:
  • \(Ra = Gr \cdot Pr = \frac{g\beta\Delta T L^3}{\nu^2}\cdot Pr = \frac{g\beta\Delta T L^3}{\nu\alpha}\)✔️
  • \(Ra = Re \cdot Pr\)
  • \(Ra = Nu / Pr^{1/3}\)
  • \(Ra = Gr / Pr\)
Correct Answer Explanation
Rayleigh number: \(Ra=Gr\cdot Pr=\frac{g\beta\Delta TL^3}{\nu\alpha}\) where \(\beta\) is thermal expansion coefficient, \(\nu\) is kinematic viscosity, \(\alpha\) is thermal diffusivity.