Bejan number
Encyclopedia
There are two Bejan numbers (Be) in use, named after Duke University
professor Adrian Bejan
in two scientific domains: thermodynamics and fluid mechanics.
, the Bejan number is the ratio of heat transfer
irreversibility to total irreversibility due to heat transfer and fluid friction:
where
and heat transfer
. the Bejan number is the dimensionless
pressure drop along a channel of length
:
where
The Be number plays in forced convection the same role that the Rayleigh number
plays in natural convection.
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 thermodynamicsThermodynamics
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 mechanicsFluid 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 BejanAdrian BejanAdrian Bejan is an American professor and proponent of the constructal theory of design and evolution in nature. He is J. A...
- EntropyEntropyEntropy 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...
- ExergyExergyIn 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...
- ThermodynamicsThermodynamicsThermodynamics 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 theoryConstructal theoryThe 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...