Notas de Aula Fenômenos de Transporte Aulas 1-6

Notas de Aula Fenômenos de Transporte Aulas 1-6

(Parte 2 de 4)

Write out allunits in allequations to the bitterest of detail!

Example (1)Example (1)

mkgWb s mkgs

An object at sea level has a mass of 400 kg. (a)Find the weight of this object on earth.

(b)Find the weight of this object on the moon where the local gravitational acceleration is one-sixth that of earth.

Example (2)Example (2)

smkg msmmkg

The Pipe Reynolds Number, Re, is dimensionless quantity defined as:

Re = rVD/m

Evaluate Re for water flowing at an averaged velocity of 1 m/sand pipe with diameter of 50 m. The transport properties of the water are: density (r)1 g/cm3and the viscosity (m)is of 10-3 Ns/m2.

Whenever you work with a formula BE CONSISTENT with your units.

DO NOT MIX (cm) with (m), (g) with (kg). Always use the same unit for mass, length, time, temperature and so forth.

Chapter 2 : Topics Chapter 2 : Topics

••System definition System definition

•• Properties Properties

•• Thermal Equilibrium Thermal Equilibrium

••State and Process State and Process

••Heat and Work modes Heat and Work modes

Thermodynamic System Thermodynamic System

•System is a region of space with a FIXED amount of MASS.

•The system’s boundary separates the system from the surroundings.

•The boundary can be deformable or not, stationary or not;

•The boundary can exchange: work, heat, BUT NOT MASS

Example of a System Example of a System

Example of a SystemExample of a System Example of a System

Energy (Heat or Work), not mass,crosses system boundaries

Fluid Flowing

•Very often there are applications where fluid is flowing in and out of a region (not a system).

•Tracking the system boundaries is not a easy task, since the fluid is a continuously deformable matter…

Pipe

Boundary of the system

V o t = t0t = t0 +dt

Fluid Flowing: Emptying a Tank tank is a classical example of a region of space loosing/gaining mass.

•How the system boundary behaves? t = t 0 t = t0 +dt

•Control Volume: Mass and energy can cross the boundary.

•System concept necessary to physical Laws. Control Volume concept necessary to experiments.

Control Volume:

Control Volume:

Chapter 5 Chapter 5

•Reynolds Transport Theorem relates the two concepts.

•Control surface can be stationary or not, deformable or not.

•We are just interested in the region bounded by the dashed lines.

Isolated System Isolated System

Isolated System Boundary

Mass System

Surr 2 Surr 3

Surr 4 Mass

Heat

Work Surr 1

Heat = 0 Work = 0 Mass = 0 Across Isolated

(Parte 2 de 4)

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