Sage-Tips

WHY is the hydrodynamic boundary layer greater than the thermal boundary layer for PR 1?

Apparently the thermal boundary layer is thicker than the hydrodynamic boundary layer for the flow situations with Pr < 1. This has to be so because Pr < 1 implies that thermal diffusivity is more than the momentum diffusivity.

How is thermal boundary layer different from hydrodynamic boundary layer?

Hydrodynamic boundary layer refers to the region close to the wall in which viscosity affects the fluid velocity. Similarly thermal boundary layer refers to the region where wall temperature affects the fluid temperature. Outside the boundary layer wall effects are negligible and free stream conditions prevail.

For which flow over a flat plate thermal boundary layer will be thicker than hydrodynamic boundary layer?

laminar flow
If Pr < 1, the thermal boundary layer thickness is greater than the hydrodynamic boundary layer thickness at a given location. Fig. 6.8 shows the hydrodynamic and thermal boundary layers for laminar flow over a flat plate.

What is the importance of hydrodynamic and thermal boundary layer in heat transfer?

Hydrodynamic and thermal boundary layers finds importance in forced convection. For fluid flowing across a horizontal plate, momentum and thermal boundary layer varies. Very near to the surface of the plate, conduction is dominant mode of heat transfer.

What do you mean by hydrodynamic and thermal boundary layer?

The thickness of the hydrodynamic boundary layer (velocity boundary layer) is normally defined as the distance from the solid body at which the viscous flow velocity is 99\% of the free stream velocity. If the Pr > 1, the thermal boundary layer is thinner than the velocity boundary layer.

What is meant by a hydrodynamic boundary layer?

Ø As we have seen earlier,the hydrodynamic boundary layer is a region of a fluid flow, near a solid surface, where the flow patterns are directly influenced by viscous drag from the. surface wall.

Which has the highest thermal conductivity from the below?

Diamond is the leading thermally conductive material and has conductivity values measured 5x’s higher than copper, the most manufactured metal in the United States. Diamond atoms are composed of a simple carbon backbone that is an ideal molecular structure for effective heat transfer.

What is meant by hydrodynamic boundary layer?

What will happen to the hydrodynamic boundary layer and thermodynamic boundary layer when Prandtl number of a fluid is equal to unity?

Prandtl Number: It is defined as the ratio of momentum diffusivity to thermal diffusivity. If Pr < 1 the thermal boundary layer will increase more compared to the momentum or hydrodynamic boundary layer. If Pr = 1 The the thermal boundary layer and momentum or hydrodynamic boundary layer will increase at the same rate.

What is meant by a hydrodynamic boundary layer explain the formation of hydrodynamic boundary layer over a flat plate?

The transition from zero velocity at the surface of the solid to the free stream velocity at some distance away from the solid surface in the V-direction (normal to the direction of flow) takes place in a very thin layer called ‘momentum or hydrodynamic boundary layer’.

What is hydrodynamic boundary layer?

This region within which the flow is disturbed is therefore larger for highly viscous fluids. This area where the flow velocity is disturbed by the influence of shear stresses between the fluid layers, is also called velocity boundary layer or hydrodynamic boundary layer.

What is the difference between hydrodynamic boundary layer and thermal boundary layer?

Hydrodynamic boundary layer is the layer defined by instantaneous velocity of fluid particles in a fluid flow wheres, Thermal boundary layer is the layer defined as the temperature profile of the moving fluids at different stages of a fluid flow.

What is a velocity boundary layer?

This area where the flow velocity is disturbed by the influence of shear stresses between the fluid layers, is also called velocity boundary layer or hydrodynamic boundary layer.

What are the characteristics of the boundary layer of a plate?

The boundary layer is normally very thin in comparison with the dimensions of the body immersed in the flow. (iv) The thickness of the boundary layer is variable along the flow direction; it is zero at leading edge of the plate and increases as the distance x from the leading edge is increased.

How do you find the pattern of flow in boundary layer?

(vii) The pattern of flow in the boundary layer is judged by the Reynolds number Re = U ∞ x/v where x is distance along the plate and measured from its leading edge. The transition from laminar to turbulent pattern of flow occurs at values of Reynolds number between 3 × 10 5 to 5 × 10 5.