1.7 PROCESS AND CYCLE

1- Thermodynamics Process is any change that a system undergoes from one equilibrium state to another.

2- Quasistatic or quasi-equilibrium process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times.

3- Process Path is the series of states through which a system passes during a process.

4- Cycle is one in which the process returns to its initial state.

5- Work and heat are not system properties because both are dependent on process.


1.8 TEMPERATURE AND THE ZEROTH LAW OF THERMODYNAMICS

The zeroth law of thermodynamics: If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.





Two bodies reaching thermal equilibrium after being brought into contact in an isolated enclosure.

The way to indicate temperature
1. Absolute zero = the lowest temperature
2. Celcius: freezing and boiling point of water Kelvin: Absolute zero
3. Fahrenheit: freezing point of brine
4. Rankine: Absolute zero


1.9 PRESSURE



 Pressure: A normal force exerted per unit area (P=F/A)

    

1 atm is equal to,
1.013 bar (English unit)
101.325kPa (SI unit)
0.1MPa (SI that is accepted to describe 1atm)
14.7 psi (lbf/in2)
760 mmHg (milimeter of mercury)
760 Torr(not SI unit)

 

•Absolute pressure: measured relative to absolute vacuum (i.e., absolute zero pressure).
•Gage or Gauge pressure: measured relative to atmospheric pressure.
•Vacuum pressures: Pressures below atmospheric pressure. Degree of vacuum is also usually used.

1.10 MANOMETER

 

Measuring the pressure drop across a flow section or a flow device by a differential manometer

 

 

 

The basic manometer

 

1.11 THE BAROMETER AND ATMOSPHERIC PRESSURE

• Atmospheric pressure is measured by a device called a barometer; thus, the
  atmospheric pressure is often referred to as the barometric pressure.
• A frequently used pressure unit is the standard atmosphere, which is defined as
  the pressure produced by a column of mercury 760 mm in height at 0°C (Hg =
  13,595 kg/m3) under standard gravitational acceleration (g = 9.807 m/s2).