Bejan number
Encyclopedia
There are two Bejan numbers (Be) in use, named after Duke University
Duke University
Duke University is a private research university located in Durham, North Carolina, United States. Founded by Methodists and Quakers in the present day town of Trinity in 1838, the school moved to Durham in 1892. In 1924, tobacco industrialist James B...

 professor Adrian Bejan
Adrian Bejan
Adrian Bejan is an American professor and proponent of the constructal theory of design and evolution in nature. He is J. A...

 in two scientific domains: thermodynamics and fluid mechanics.

Thermodynamics

In the context of thermodynamics
Thermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

, the Bejan number is the ratio of heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 irreversibility to total irreversibility due to heat transfer and fluid friction:


where
is the entropy generation contributed by heat transfer
is the entropy generation contributed by fluid friction.

Fluid mechanics and heat transfer

In the context of fluid mechanics
Fluid mechanics
Fluid mechanics is the study of fluids and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion...

 and heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

. the Bejan number is the dimensionless
Dimensionless quantity
In dimensional analysis, a dimensionless quantity or quantity of dimension one is a quantity without an associated physical dimension. It is thus a "pure" number, and as such always has a dimension of 1. Dimensionless quantities are widely used in mathematics, physics, engineering, economics, and...

 pressure drop along a channel of length :


where
is the dynamic viscosity
is the thermal diffusivity


The Be number plays in forced convection the same role that the Rayleigh number
Rayleigh number
In fluid mechanics, the Rayleigh number for a fluid is a dimensionless number associated with buoyancy driven flow...

 plays in natural convection.

See also

  • Adrian Bejan
    Adrian Bejan
    Adrian Bejan is an American professor and proponent of the constructal theory of design and evolution in nature. He is J. A...

  • Entropy
    Entropy
    Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...

  • Exergy
    Exergy
    In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its...

  • Thermodynamics
    Thermodynamics
    Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

  • Constructal theory
    Constructal theory
    The constructal law puts forth the idea that the generation of design in nature is a physics phenomenon that unites all animate and inanimate systems, and that this phenomenon is covered by the Constructal Law...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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