1. Physical Principles Flashcards
What are the three modes of transport in a fluid?
Advection, Diffusion and Convection
What is advection?
When a blob of fluid is carried along streamlines
What is diffusion?
The blob of fluid enlarges or contracts due to a concentration gradient with its surroundings
What is convection?
The blog of fluid experiences a body force compared to its surroundings e.g. buoyancy
What is momentum?
The product of mass and velocity
What is specific heat capacity, Cp?
The energy required to raise the temperature of a unit mass of material by 1K.
What is the Richardson’s number?
Ri=g’L/u^2
The ratio of stabilising stratification to destabilising shear.
Tells us how vigorous the flow needs to be to overturn the stratification.
What happens if Ri»1 ?
Insufficient kinetic energy to perturb the stratification. Flow is strongly constrained by the density field.
What happens if Ri«1
The stratification is easily overturned by vertical mixing.
Potential energy variations use up relatively little kinetic energy.
What is turbulence?
The complex, seeming random motions that result from instabilities in fluid flows.
Arises from vorticity generated at shear planes and boundaries.
What is the Reynolds number?
Re=density*u *L/ viscosity
Characterises the degree of turbulence.
Re>10^4 flow is energetic with little viscous dissipations.
Re<10^3 flow is smooth, instabilities are dampened out by viscosity (LAMINAR)
What is the formula for thermal energy?
q=mCptheta
