Nusselt number represents
the ratio of heat flux by fluid when heat is transferred
What is the physical significance of the Nusselt number how is it defined?
Nusselt number for
a flow system gives basic difference between convection and conduction heat transfer
. For a relative low Nusselt number indicates conduction heat transfer dominates convective heat transfer whereas for a large Nusselt number implies convective term dominant.
What does the Nusselt modulus or Nusselt number physical significance?
Nusselt number is an important parameter that can contribute to a better rate of heat exchange. … If the Nusselt number is about 1, it represents that
the heat transfer is conduction only
, but if the value is between 1 and 10, then it shows laminar of slug flow.
What is the significance of Nusselt number what will be the relation between conduction and convection heat transfer when the value of Nusselt number equals unity?
A Nusselt number of
Nu=1 for a fluid layer represents heat transfer across the layer by pure conduction
. The larger the Nusselt number, the more effective the convection. A larger Nusselt number corresponds to more effective convection, with turbulent flow typically in the 100–1000 range.
What does the Nusselt modulus physically signify?
the ratio of the temperature gradient at the surface [(∂T / ∂y)
y = 0
] to the reference temperature gradient [(T
w
– T
∞
) / l] 6. The Nusselt modulus or Nusselt number is a convenient measure of. a.
rate of heat transfer
.
What is L in Nusselt number?
It is defined as. where α is convective heat transfer coefficient, L is representative dimension (e.g., diameter for pipes), and λ is the thermal conductivity of the fluid. Nusselt number is
a measure of the ratio between heat transfer by convection (α) and heat transfer by conduction alone
(λ/L).
Can Nusselt number be less than 1?
Nu can not be
less than one
since it gives relation between conduction and convection of the liquid.
What is Prandtl number and its significance?
The Prandtl number is
a dimensionless quantity that puts the viscosity of a fluid in correlation with the thermal conductivity
. It therefore assesses the relation between momentum transport and thermal transport capacity of a fluid. It is defined as. (Eq. 9.13)
What is the significance of Reynolds number?
The Reynolds number, referred to as Re, is
used to determine whether the fluid flow is laminar or turbulent
. It is one of the main controlling parameters in all viscous flows where a numerical model is selected according to pre-calculated Reynolds number.
What is the physical significance of the Sherwood number?
The Sherwood number (Sh) (also called the mass transfer Nusselt number) is a dimensionless number used in mass-transfer operation. It
represents the ratio of the convective mass transfer to the rate of diffusive mass transport
, and is named in honor of Thomas Kilgore Sherwood.
What is the difference between the Biot number and the Nusselt number?
Biot number indicates how much solid temperature can change quickly based on the convection heat transfer in fluid. Biot number uses
thermal conductivity of
the body (not fluid), whereas Nusselt number uses thermal conductivity of the fluid.
What is the significance of Nusselt number Fourier number and Prandtl number?
Nusselt calculates the transference of heat relative to pure conduction
. Prandtl represents how big is the viscous boundary layer relative to thermal boundary layer.
How is Nusselt number calculated?
- Nusselt Number : Nu = hL/k.
- Convection Heat Transfer Coefficient : k = Nuk/L.
- Characteristic Length : L = Nuk/h.
- Thermal Conductivity of the Fluid : k = hL/Nu.
- Where, Nu = Nusselt Number, h = Convection Heat Transfer Coefficient, L = Characteristic Length, k = Thermal Conductivity of the Fluid.
What is K in Prandtl number?
k = thermal conductivity (W/m K, Btu/(h ft
2 o
F/ft)) The Prandtl Number is often used in heat transfer and free and forced convection calculations. It depends on the fluid properties. gases – Pr ranges 0.7 – 1.0. dry air.
What do you mean by effectiveness of fin?
2 Fin Efficiency and Surface Effectiveness. Fin efficiency is defined as
the ratio of actual heat flow of the fin to that which would be obtained with a fin of constant temperature uniformly equal to the base surface temperature
, that is, one with infinite thermal conductivity.
What is the purpose of using fins in a particular heat transfer system?
In the study of heat transfer, fins are surfaces that extend from an object
to increase the rate of heat transfer to or from the environment by increasing convection
.
