Sphere¶

class pychemengg.heattransfer.externalflow.Sphere[source]¶

Bases: object

Models a sphere.

Parameters

`None_required`‘None’: This class takes no parameters for instance creation.

Examples

First import the module externalflow.

>>> from pychemengg.heattransfer import externalflow as extflow 
>>> sphere = extflow.Sphere
# This will create an instance of the class 'Sphere'.
# Methods of the class 'Sphere' can then be called like so :-
# sphere.method(kwarg1=x, ...)

Attributes

`None_required`‘None’: This class does not expose any instance attributes .

__init__(*args, **kwargs)¶

Methods

`Nu_whitaker`([Re, Pr, viscosity_surface, …])	Average Nusselt number for flow over sphere.
`__init__`(args, *kwargs)

Nu_whitaker(Re=None, Pr=None, viscosity_surface=None, viscosity_infinity=None)[source]¶

Average Nusselt number for flow over sphere.

Parameters

Reint or float: Reynolds number for fluid flow over the sphere.
Print or float: Prandtl number for the fluid.
viscosity_surfaceint or float: Viscosity of fluid at surface temperature.
viscosity_infinityint or float: Viscosity of fluid at fluid temperature far from surface.

Returns

Nuint or float: Average Nusselt number for turbulent flow on sphere.

Warning

A Nusselt number is returned based on the equation even if parameters (such as Re, Pr) do not fall in their respective allowable range limits (see above under ‘Notes’). However, if this happens, a warning is issued.

Notes

The following formula is used:

\[Nu = 2 + [0.4 Re^{1/2} + 0.06 Re^{2/3}] Pr^{0.4} \left( \cfrac {\mu_{infinity}} {\mu_{surface}} \right)^{1/4} \]

where:

\(3.5 \eqslantless Re \eqslantless 8x10^4\)

\(0.7 \eqslantless Pr \eqslantless 380\)

\(1.0 \eqslantless \cfrac {\mu_{infinity}} {\mu_{surface}} \eqslantless 3.2\)

Fluid properties are at film temp (\(T_{film}\)):

\(T_{film} = (T_{infinity} + T_{surface})/2\)

\(T_{infinity}\) = temperature of fluid away from surface

\(T_{surface}\) = temperature of surface

References

[1] Yunus A. Cengel and Afshin J. Ghajar, “Heat And Mass Transfer Fundamentals and Applications”, 6th Edition. New York, McGraw Hill Education, 2020.

Examples

First import the module externalflow.

>>> from pychemengg.heattransfer import externalflow as extflow 
>>> sphere = extflow.Sphere()
# This will create an instance of the class 'Sphere'.
# Then call the method like so :-
>>> sphere.Nu_whitaker(Re=3059, Pr=0.708, viscosity_surface=2.075e-5, viscosity_infinity=1.8462e-5)
124.44556447378223