MEC203 Chapter 6 Definitions Flashcards
Define Convection heat transfer coefficient
The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference
Define No-slip condition
A fluid in direct contact with a solid “sticks” to the surface due to viscous effects, and there is no slip
Define Boundary layer
The flow region adjacent to the wall in which the viscous effects (and thus the velocity gradients) are significant
Define Nusselt number
Dimensionless convection heat transfer coefficient
Define Viscous flows
Flows in which the frictional effects are significant
Define Inviscid flow regions
In many flows of practical interest, there are regions (typically regions not close to solid surfaces) where viscous forces are negligibly small compared to inertial or pressure forces
Define External flow
The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe
Define Internal flow
The flow in a pipe or duct if the fluid is completely bounded by solid surfaces
Define Laminar flow
The highly ordered fluid motion characterized by smooth layers of fluid. The flow of high-viscosity fluids such as oils at low velocities is typically laminar
Define Turbulent flow
The highly disordered fluid motion that typically occurs at high velocities and is characterized by velocity fluctuations. The flow of low-viscosity fluids such as air at high velocities is typically turbulent
Define Transitional flow
A flow that alternates between being laminar and turbulent
Define Forced flow
A fluid is forced to flow over a surface or in a pipe by external means such as a pump or a fan
Define Natural flow
Fluid motion is due to natural means such as the buoyancy effect, which manifests itself as the rise of warmer (and thus lighter) fluid and the fall of cooler (and thus denser) fluid
Define Velocity boundary layer
The region of the flow above the plate bounded by δ in which the effects of the viscous shearing forces caused by fluid viscosity are felt
Define Boundary layer region
The viscous effects and the velocity changes are significant
Define Irrotational flow region
The frictional effects are negligible and the velocity remains essentially constant
Define Thermal boundary layer
The flow region over the surface in which the temperature variation in the direction normal to the surface is significant
Define Reynolds number
The ratio of inertia forces to viscous forces
Define Critical Reynolds number
The Reynolds number at which the flow becomes turbulent
