Table of Contents
What is the formula for Grashof number?
For gases β = 1/T where the temperature is in K. For liquids, β can be calculated if a variation of density with the temperature at constant pressure is known. For a vertical flat plate, the flow turns turbulent for the value of Gr.Pr > 109.
What does the Grashof number represent?
The significance of the Grashof number is that it represents the ratio between the buoyancy force due to spatial variation in fluid density (caused by temperature differences) to the restraining force due to the viscosisty of the fluid.
What are the forces associated with Grashof number?
1) The grashoff number provides the relation between inertia force, buoyant force, and viscous force in flow of fluid. 2) This dimensionless number is used in the analysis of free convection heat transfer.
How does the Rayleigh number differ from the Grashof number?
The Rayleigh number is simply defined as the product of the Grashof number, which describes the relationship between buoyancy and viscosity within a fluid, and the Prandtl number, which describes the relationship between momentum diffusivity and thermal diffusivity.
What is bulk fluid temperature?
bulk temperature – in a heat transfer system, the temperature of the main stream of heat transfer fluid in the heating unit, as distinct from film temperature, which is the temperature of the slower moving layer of fluid in contact with the surface of the heating tube or coil.
What is Grashof condition?
The Grashof condition for a four-bar linkage states: If the sum of the shortest and longest link of a planar quadrilateral linkage is less than or equal to the sum of the remaining two links, then the shortest link can rotate fully with respect to a neighboring link.
What is the characteristic length in Grashof number?
The Gr number is defined for a compressible fluid as:(8.23)Gr=gLC3ρΔρμ2=inertialforce×buoyantforceviscousforce2or(8.24)Gr=gLC3Δρν2ρCompressiblefluidswhere LC is the characteristic length that is frequently chosen as the vertical distance where buoyancy occurs.
What is characteristic length in Grashof number?
How does Grashof number Gr differ from Reynolds number Re )?
In forced convection the Reynolds number governs the fluid flow. But, in natural convection the Grashof number is the dimensionless parameter that governs the fluid flow.
What is maximum film temperature?
Maximum Film Temperature is the highest temperature a fluid experiences in the system. Maximum Film Temperature normally is found adjacent to the tube wall at the heating surface, and typically averages 50°F (10°C) higher than the Bulk Fluid Temperature.
How do you calculate bulk temperature?
Substituting the temperature (T=Tc), and velocity distribution for laminar tube flow (u=u/u0) in the last equation we can get an expression for bulk temperature after integration Page 2 Heat Transfer Third Year Dr.Aysar T. Jarullah This means that Nu=4.364 (constant) for laminar flow inside tube for constant heat flux.
What is non Grashof?
A non-Grashof linkage is a planar four-bar linkage with. s + l > p + q. s = length of the shortest link. l = length of longest link. p and q are the lengths of the two remaining links.
What is beta in Grashof no?
β is the coefficient of thermal expansion (equal to approximately 1/T, for ideal gases) Ts is the surface temperature. T∞ is the bulk temperature. L is the vertical length. D is the diameter.
How does Rayleigh number differ from Grashof number?
The Rayleigh number is defined as the product of the Grashof number, which describes the relationship between buoyancy and viscosity within a fluid, and the Prandtl number, which describes the relationship between momentum diffusivity and thermal diffusivity.
Why Rayleigh number is used?
Rayleigh number is a dimensionless number that represents the ratio of buoyancy and thermal diffusivity. Difference between solid surface temperature and free stream temperature can be used as the characteristic temperature difference.
What is the purpose of film temperature?
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.