Chapter 2 Main Physical Properties of Fluid.ppt

Chapter 2Properties of Fluids
Characteristic
Fluidity
Fluid Characteristic and Continuous
Medium Model (Continuum)
Definition of fluid: A Kind of Substance that deforms continuously when subjected to a shear stress.
Difference of fluidity
0 greater
Solid
Liquid
Gas
Fluid
Continuous Medium Model:
Fluid Parcel or Fluid Particle
Definition of the model
The space is full of molecules without any clearance.
Purpose
Such variables as volume, pressure, temperature, density, viscosity, velocity, acceleration and so on can be described by differential equations.
Applied condition
When the characteristic length of an object is far greater than the mean free distance of molecules.
Mean statistic law of a lot of molecules.

Density
Density and Specific Volume of Fluid
Relative Density
Specific Volume
Density of Mixed Gas
Coefficient
Bulk Modulus of Elasticity
and
Dilatability of Fluid
Dilatability
When p=constant, and T=273+t 0C
Fluid and
pressible Fluid
pressible Fluid (Simplification)
Liquid
Gas with low speed and constant pressure (. fan)
Compressible Fluid
Gas with high speed and variable pressure
Mass Force
Surface Force
ΔA
ΔFs
ΔFsn
ΔFsτ
Forces on A Fluid Parcel
Definition and Reason
Definition of viscosity
The property of showing interior friction between two adjacent flow layers for retarding their relative motions.
Reasons
Slowing down the fast flow layer
Speeding up the slow flow layer
Viscosity of Fluid
y
0
Newton’s Law of Viscosity
τ----Tangent stress, N/m2
μ----Dynamic viscosity, Pa·s
(μ/ρ)----Kinematic viscosity, m2/s
h
U
u