Rotating cylinder heat transfer

[adriansg95]

Hi, I'm studying the heat transfer from a rotating cylinder to static air. I use a correlation valid for Re up to 40,000
I also use CFD simulations in Fluent, but the values I get by this way are about half the ones I get with the correlation

The correlation is very simple: Nu=0.318*Re^0.571, so I don't know where the mistake is.
I've tried several domains, models and temperatures in Fluent and the results are more or less the same. The ref temp is also well set, so I think the CFD values are OK.


Could anyone check my analytic calculations (below) and tell me if they are OK? I would be very, very grateful


D=0.18; % Diameter [m]
n_rot=387 % [rpm]
T=35+273.15; % Temperature [K]
k=props(1,2,T,0) % Thermal conductivity = 0.0273 [W/mK]
vc=props(1,6,T,0) % Cinematic viscosity = 1.6377e-05 [m2/s]

w_rot=n_rot*2*pi/60 % [rad/s]
Re=w_rot*D^2/(2*vc) % Reynolds number [-]
Nu=0.318*Re^0.571 % Nusselt number [-]
h=Nu*k/D % Heat transfer coef [W/m2K]


RESULTS: Re=40.088; h=20.47 - instead of h=9.5 (Fluent)

 

[hendersdc]

My first thought is that you could simplify this by unrolling the cylinder and looking at flow over a flat plate to see how that compares.

 

[chicopee]

What you are not mentioning is the magnitutde of the convective heat transfer coefficient for free convection (or static as you called it)of the air around the cylinder .

 

[FEA way]

Is the cylinder hollow or solid ? Where did you find the formulas for Re and Nu ? In the article "Convective heat transfer inside a rotating cylinder with an axial air flow" by S. Seghir-Ouali et al. or Özerdem's paper referenced there ? They give more correlations with slightly different coefficients. What I noticed is that in various articles/books there are different formulas for rotational Reynolds number.

 

[IRstuff]

Have you checked the equations? They look like the ones for flat plates, and the equations I've seen for cylinders don't look like that.

Equating the diameter to the critical length seems to be something you might do for a cylinder in a flowing stream, rather than for a rotating cylinder

TTFN (ta ta for now)
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[chicopee]

It appears to me that the Reynold number for "static" air I too high