Notas de Aula Fenômenos de Transporte Aulas 1-6

Notas de Aula Fenômenos de Transporte Aulas 1-6

(Parte 3 de 4)

Boundary

A closed system is a system or a group of them where no heat or work may cross the boundaries.

You take a bottle of Coke and put it in the refrigerator that is at 3°C. Should the bottle of Coke be treated as a systemor a control volume?

Property Property

• Mass

• Temperature • Pressure

• Density

A property is a characteristic of a system to which numerical values can be assigned to describe the system.

Extensive Property Extensive Property

•Extensiveproperties are properties which can be counted and their value for the whole system is the sum of the value for subdivisions of the system.

•They depend on the extent of the system.

•Examples: Volume V, Mass M

Intensive Property Intensive Property

•Intensiveproperties are independent of the size (mass or volume) of the system.

•Examples: Density, Temperature, Pressure

Property Property m V T P

TT
PP

m/2 m/2 V/2 V/2 ρρ

Extensive propert ies

Intensive propert ies

Extensive properties per unit mass are intensive properties

Vmvolume mass mVmass volume m kg kg m

3 Specific volume density

•Decide if the following properties are extensive or intensive:

temperature, density, specific volume, pressure, energy, momentum, color.

•Decide if the following properties are extensive or intensive:

temperature, density, specific volume, pressure, energy, momentum, color.

ºCºF K R

Boiling point 100 212 373.15 671.67

Ice point0.0 32.0 273.15 491.67
Absolute Zero -273.15 -459.670 0

Triple point @ 0.006 atm, T = 0.01 ºC

We Need to Work With Temperatures We Need to Work With Temperatures

Temperature Temperature relationships relationships

•T (R) = T (ºF) + 459.67 [use 460] •T (K) = T (ºC) + 273.15 [use 273]

Pressure Pressure

•The normal force exerted on a (small) area.

•Continuum (macroscopic approach)

Atmospheric, Absolute, Gage, and Vacuum Pressures

Atmospheric, Absolute, Gage, Atmospheric, Absolute, Gage, and Vacuum Pressures and Vacuum Pressures

Gage Pressure Gage Pressure absatmvac atmabsgage −= atm atm <

In the SI system we use In the SI system we use

•SI Pressure unit is Pascal

•lbf/in2 or psi, usually with an “a” suffix or a “g” suffix, for absolute or gage.

•p sia: Absolute pressure •psig:gage pressure

In the In the BristhBristhsystem system

150 psig

Atmospheric pressure is Atmospheric pressure is

•Absolute pressure (P abs ) = gage pressure (psig) + atmospheric pressure (P atm )

Equilibrium Equilibrium are not changing at any given location in the system.

•This is also known as “thermodynamic equilibrium” or “total equilibrium.”

•Equilibrium implies balance: no unbalanced potentials (driving forces) in the system.

•We will distinguish four different types of equilibrium

Types of thermodynamic equilibrium Types of thermodynamic equilibrium :

(Parte 3 de 4)

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