Contents
What is constant wall temperature?
constant wall temperature is defined to be the case of boundary when constant temperature process occurred for example : Boiling or condensation but constant heat flux is when the boundary exposed to a constant power or heat flux like a heating power from a resistive load heating element .
Does Nusselt number change with temperature?
) due to temperature change between the bulk fluid average temperature and the heat transfer surface temperature, respectively. The Sieder-Tate correlation is normally solved by an iterative process, as the viscosity factor will change as the Nusselt number changes.
What does Nusselt number represent?
The Nusselt number is defined as the ratio of convection heat transfer to fluid conduction heat transfer under the same conditions.
What is adiabatic boundary condition?
Adiabatic conditions refer to conditions under which overall heat transfer across the boundary between the thermodynamic system and the surroundings is absent. The flow of a viscous liquid or gas through a heat-insulated channel is often referred to as adiabatic.
Is Reynolds number affected by temperature?
For the same concentration, the critical Reynolds number increases as the temperature increases, and thus the heat transfer reduction range is enlarged. However, the critical Reynolds number starts to decrease with temperature when the temperature exceeds critical value depending on the corresponding concentration.
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)
Is the Nusselt number of a flow constant?
The Nusselt number in the fully developed laminar flow is constant and depends on the channel geometry and the wall heat transfer boundary condition. Table 3.1 presents the Nusselt numbers for commonly used geometries under axially constant heat flux and circumferentially constant wall temperature (H1) boundary conditions with four-sided heating.
How to find the Nusselt number of the wall?
Constant wall temperature, T-boundary condition: Constant circumferential wall temperature, uniform axial heat flux, H1 boundary condition: (3.44) NuH1 = 8.235(1 − 2.0421αc + 3.0853α2c − 2.4765α3c + 1.0578α4c − 0.1861α5c)
How is Nusselt number used to describe convective heat transfer?
The Nusselt number can therefore be interpreted as a measure of a dimensionless temperature gradient on the wall. And the greater this temperature gradient, the higher the heat flow. Later we will show that for fully developed pipe flows this dimensionless temperature gradient is constant under certain boundary conditions.
How is the Nusselt number of a channel determined?
For a rectangular channel, the Nusselt number depends on the channel aspect ratio αc = a / b and the wall boundary conditions. Three boundary conditions are identified in the literature; the Nusselt number for each one is given below. Constant wall temperature, T-boundary condition: