How is the heat transfer affected by the flow in the boundary layer?

How is the heat transfer affected by the flow in the boundary layer?

When the boundary layer becomes fully turbulent, the heat transfer through the boundary layer is dominated by the transport associated with the turbulent eddies. The time-averaged boundary layer equations become the incompressible constant property case without dissipation.

How does the laminar boundary layer thickness vary along a flat plate in a uniform flow?

The momentum of the flat plate is zero and the momentum of the uniform flow has a finite value. When the incoming uniform flow flows over a flat plate, the fluid particles near the plate will stick to the plate (no-slip condition). And hence the boundary layer thickness increases as the fluid moves downstream.

What is the boundary layer in heat transfer?

2.05. 4.2 Thermal Conductivity. The thermal boundary layer at the bottom of the mantle is a region where heat is transported predominantly by conduction from the core into the mantle. Conductive heat is given by the product of temperature gradient and thermal conductivity of the lowermost mantle materials.

What is the boundary layer theory of convection?

When the thermal boundary layers from adjacent cells meet they separate from the horizontal boundary and form a thermal plume on the vertical boundary between cells. The body force in the plumes drives the viscous core flow.

What causes a boundary layer?

Aerodynamic forces are generated between the fluid and the object. This creates a thin layer of fluid near the surface in which the velocity changes from zero at the surface to the free stream value away from the surface. Engineers call this layer the boundary layer because it occurs on the boundary of the fluid.

How does viscosity affect convection?

Temperature dependent viscosity effects on natural convection in a composite cavity, isothermally heated from below and cooled from the opposing surface, are analyzed. It is observed that viscosity reduction, due to temperature rising, affects heat transfer rate and fluid motion at the interface.

What do you understand by boundary layer illustrate with reference to flow over a flat plate?

The fluid flow outside the boundary layers remains effectively inviscid, whereas that inside the layers is modified by viscosity. It follows that the flow external to the layers is unaffected by the presence of the plate. Hence, the tangential velocity at the outer edge of the boundary layers is .

What is boundary layer effect?

The layer of fluid, close to the surface of a body placed in a moving stream, in which the impact pressure is reduced as a result of the viscosity of the fluid. A velocity gradient exists through the boundary layer, ranging from the velocity of the body to the velocity of the free airstream.

What does convection in the mantle cause?

Mantle convection is the very slow creeping motion of Earth’s solid silicate mantle caused by convection currents carrying heat from the interior to the planet’s surface. This subducted material sinks through the Earth’s interior.

How do you calculate convective heat transfer on a flat plate?

Convective Heat Transfer Coefficient Flat Plate Recall that convective heat transfer occurs when there is a fluid flowing over a body. To calculate the heat transfer rate the following equation would be used. (Eq 1) q = h A (T w − T ∞)

What is the mechanism of forced convection?

Mechanism of Forced Convection Convection heat transfer is complicated since it involves fluid motion as well as heat conduction. The fluid motion enhances heat transfer (the higher the velocity the higher the heat transfer rate).

What is the relationship between fluid motion and heat transfer?

The fluid motion enhances heat transfer (the higher the velocity the higher the heat transfer rate). The convective heat transfer coefficient h strongly depends on the fluid properties and roughness of the solid surface, and the type of the fluid flow (laminar or turbulent).

How does the shape of a wavy plate affect heat transfer coefficient?

With a geometry such as that of the wavy plate, the heat transfer coefficient is dependent on the temperature fields; velocity fields; and geometric parameters of the corrugations, such as the height. Hence, we can observe the enhanced heat transfer coefficient as compared to the flat plate (right image below).