What is Biot number and Fourier number?
The Fourier number is the dimensionless time for a temperature change to occur. The Biot number represents the ratio of heat transfer resistance in the interior of the system (L/k) to the resistance between the surroundings and the system surface (1/h).
What does Biot number mean?
The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. This ratio determines whether or not the temperatures inside a body will vary significantly in space, while the body heats or cools over time, from a thermal gradient applied to its surface.
What is the difference between Biot number and Nusselt number?
The real difference betweeh the two are; Nusselt number confirms whether conductive or convective heat transfer dominates across the fluid-solid interface while Biot number, whether significant thermal gradients will develop inside a solid by the ratio of heat transfer away from the surface of a solid to heat transfer
What is Fourier number in heat transfer?
In physics and engineering, the Fourier number (Fo) or Fourier modulus, named after Joseph Fourier, is a dimensionless number that characterizes transient heat conduction.
How is Fourier number calculated?
FormulaFourier Number : Fo = αt/L2Thermal Diffusivity : α = Fo L2/t.Characteristic Time : t = Fo L2/ αCharacteristic Length : L = √αt/Fo.Where, Fo = Fourier Number, α = Thermal Diffusivity, t = Characteristic Time, L = Characteristic Length.
What is H in Nusselt number?
Forced convection in fully developed laminar pipe flow For fully developed internal laminar flow, the Nusselt numbers tend towards a constant value for long pipes. For internal Flow: where: Dh = Hydraulic diameter. kf = thermal conductivity of the fluid.
What is critical radius of insulation?
resistance of insulation, but decreases the convection resistance of the surface because of the increase in the. outer surface area. Due to these opposite effects, a critical radius of insulation is defined as the outer radius. that provides maximum rate of heat transfer.
What is the physical interpretation of the Biot number?
Biot Number expresses the ratio of Heat Conduction Resistance through the solid mass to Heat Convection Resistance between the body and environment showing how the temperature varies from the mass interior to the atmosphere.
What does the Prandtl number mean?
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.
Can Nusselt number be less than 1?
The Nusselt number is the ratio of the heat transfer with convection to the original heat transfer with no fluid motion. Since the moving fluid always enhances heat transfer, Nusselt number can only be greater than or equal to 1.
What is temperature in forced convection flow?
The film temperature is often used as the temperature at which fluid properties are calculated when using Prandtl number, Nusselt number, Reynolds number or Grashof number to calculate a heat transfer coefficient, because it is a reasonable first approximation to the temperature within the convection boundary layer.
Which of the following is an example of forced convection?
forced convection – When a fan, pump or suction device is used to facilitate convection, the result is forced convection. Everyday examples of this can be seen with air conditioning, central heating, a car radiator using fluid, or a convection oven.
What is Reynolds number in heat transfer?
Definition. The Reynolds number is the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities. A region where these forces change behavior is known as a boundary layer, such as the bounding surface in the interior of a pipe.
What is Alpha heat transfer?
In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. Thermal diffusivity is usually denoted α but a,h,κ, K, and D are also used.