Thermodynamic Equilibrium

Equilibrium: Equilibrium is that state of a system in which the state does not undergo any change in itself with passage of time without the aid of any external agent. Equilibrium state of a system can be examined by observing whether the change in state of the system occurs or not. If no change in state of system occurs then the system can be said in equilibrium.

Examples:
Let us consider a steel glass full of hot milk kept in open atmosphere. It is quite obvious that the heat from the milk shall be continuously transferred to atmosphere till the temperature of milk, glass and atmospheres are not alike. During the transfer of heat from milk the temperature of milk could be seen to decrease continually. Temperature attains some final value and does not change any more. This is the equilibrium state at which the properties stop showing any change in themselves.

Generally, ensuring the mechanical, thermal, chemical and electrical equilibrium of the system may ensure thermodynamic equilibrium of a system.

1. Mechanical Equilibrium: When there is no unbalanced force within the system and nor at its boundaries then the system is said to be in mechanical equilibrium.
   For a system to be in mechanical equilibrium there should be no pressure gradient within the system i.e., equality of pressure for the entire system.
2. Chemical Equilibrium: When there is no chemical reaction taking place in the system it is said to be in chemical equilibrium.
3. Thermal equilibrium: When there is no temperature gradient within the system, the system is said to be in thermal equilibrium.
4. Electrical Equilibrium: When there is no electrical potential gradient within a system, the system is said to be in electrical equilibrium.

When all the conditions of mechanical, chemical thermal, electrical equilibrium are satisfied, the system is said to be in thermodynamic equilibrium.

Differentiate amongst gauge pressure, atmospheric pressure and absolute pressure.

Pressure: While working in a system, the thermodynamic medium exerts a force on boundaries of the vessel in which it is contained. The vessel may be a container, or an engine cylinder with a piston etc. The exerted force F per unit area A on a surface, which is normal to the force, is called intensity of pressure or simply pressure p.

Thus

P = F/A= ρ.g.h
It is expressed in Pascal (1 Pa = 1 Nm²),
Standard atmosphere (1 atm =1.0132 bar),
The pressure is generally represented in following terms.

1. Atmospheric pressure
2. Gauge pressure
3. Vacuum (or vacuum pressure)
4. Absolute pressure

Atmospheric Pressure (Patm):
It is the pressure exerted by atmospheric air on any surface. It is measured by a barometer. Its standard values are;
1 Patm = 760 mm of Hg i.e. column or height of mercury
= ρ.g.h. = 13.6 × 10³ × 9.81 × 760/1000
= 101.325 kN/m² = 101.325 kPa
= 1.01325 bar
when the density of mercury is taken as 13.595 kg/m³ and acceleration due to gravity as 9.8066 m/s²

Gauge Pressure (Pgauge):
It is the pressure of a fluid contained in a closed vessel. It is always more than atmospheric pressure. It is measured by an instrument called pressure gauge (such as Bourdon’s pressure gauge). The gauge measures pressure of the fluid (liquid and gas) flowing through a pipe or duct, boiler etc. irrespective of prevailing atmospheric pressure.

Vacuum (Or Vacuum pressure) (Pvacc):
It is the pressure of a fluid, which is always less than atmospheric pressure. Pressure (i.e. vacuum) in a steam condenser is one such example. It is also measured by a pressure gauge but the gauge reads on negative side of atmospheric pressure on dial. The vacuum represents a difference between absolute and atmospheric pressures.

Absolute Pressure (Pabs):
It is that pressure of a fluid, which is measured with respect to absolute zero pressure as the reference. Absolute zero pressure can occur only if the molecular momentum is zero, and this condition arises when there is a perfect vacuum. Absolute pressure of a fluid may be more or less than atmospheric depending upon, whether the gauge pressure is expressed as absolute pressure or the vacuum pressure.

Inter–relation between different types of pressure representations. It is depicted in Fig, which can be expressed as follows.
Pabs = Patm + Pgauge
Pabs = Patm – Pvace

What is heat treatment and why is it done?

Heat Treatment:

Heat treatment can be defined as an operation or  combination of different operations involving the heating and cooling of a metal or alloy in solid state for the purpose of obtaining certain required structures and  desirable properties or a combination of properties suitable for the particular applications without changing the compositions.

Objectives:

Some of the motives or purpose of heat treatment are as follows:

• In order to improve the hardness of metals.
• For the softening of the metal.
• In order to improve the machinability of the metal.
• To change the grain size.
• To provide better resistance to heat, corrosion, wear etc.

Heat Treatment Process:

Heat treatment is generally performed in the following ways:

• Normalizing
• Annealing
• Spheroidising
• Hardening
• Tempering
• Surface or case hardening

What is thermodynamic system. Differentiate various types of thermodynamic systems.

Thermodynamics System: In thermodynamics the system is defined as the quantity of matter or region in space upon which the attention is concentrated for the sake of analysis. These systems are also referred to as thermodynamics system.

Boundary: It is bounded by an arbitrary surface called boundary. The boundary may be real or imaginary, may be at rest or in motion and may change its size or shape.

Surrounding: Everything out side the arbitrary selected boundaries of the system is called surrounding or environment.
The union of the system and surrounding is termed as universe.
Universe = System + Surrounding

Types of system
The analysis of thermodynamic processes includes the study of the transfer of mass and energy across the boundaries of the system. On the basis the system may be classified mainly into three parts.

1. Open system.
2. Closed System.
3. Isolated system

Open system
The system which can exchange both the mass and energy (Heat and work) with its surrounding. The mass within the system may not be constant. The nature of the processes occurring in such system is flow type.
For example
1. Water Pump: Water enters at low level and pumped to a higher level, pump being driven by an electric motor. The mass (water) and energy (electricity) cross the boundary of the system (pump and motor).
2.Scooter engine: Air arid petrol enter and burnt gases leave the engine. The engine delivers mechanical energy to the wheels.
3. Boilers, turbines, heat exchangers. Fluid flow through them and heat or work is taken out or supplied to them. Most of the engineering machines and equipment are open systems.

Closed System
The system, which can exchange energy with their surrounding but not the mass. The quantity of matter thus remains fixed. And the system is described as control mass system. The physical nature and chemical composition of the mass of the system may change. Water may evaporate into steam or steam may condense into water. A chemical reaction may occur between two or more components of the closed system.
For example
1. Car battery, Electric supply takes place from and to the battery but there is no material transfer.
2. Tea kettle, Heat is supplied to the kettle but mass of water remains constant.
3. Water in a tank
4. Piston – cylinder assembly.

Isolated System
In an Isolated system, neither energy nor masses are allowed to cross the boundary. The system has fixed mass and energy. No such system physically exists. Universe is the only example, which is perfectly isolated system.

Difference between Fan and Blower

Key difference: Both, fans and blowers, are mechanical devices used for circulation of air. Based on this, they are differentiated from each other, wherein a fan circulates air around an entire room, or space, and a blower only focuses on the specific or given area.

Generally, a fan is an electrical device that moves air, whereas a blower is a mechanical device that consists of a fan, and which channels the air from the fan and directs it to a specific location or point. Also, a fan circulates the air around an entire room or a large area, while a blower is only positioned to a specific direction or point.

Fan

By definition, a fan is machine that is used to create flow within a fluid, such as air. It consists of vanes or blades that rotate and act on air. This rotating assembly of blades and hub is known as an impeller, a rotor, or a runner. The impellers help in directing the air flow, and producing air at low pressure. Most fans are powered by electric motors, but other sources such as hydraulic motors and internal combustion engines can also be used.

Blower

On the other hand, a blower is defined as a machine which is used to produce large volumes of gas with a moderate increase in pressure. Similar to fans, blowers are also used to create air, but they only provide air at a specified position. It consists of a wheel with small blades on its circumference, and a casing to direct the flow of air out toward the edge. The casing in the center of the wheel uses centrifugal force to propel the air forward into the open.

	Fan	Blower
Definition	A fan circulates air around an entire room, or space.	A blower circulates the air only on the specific or pointed area.
Pressure	It is uses less pressure to produce large amounts of gas.	It is uses high pressure to produce large amounts of gas.
Pressure ratio	The ratio of pressure is below 1.1.	The ratio of pressure is from 1.1 to 1.2.
Air area	It provides air in the complete area.	It provides air in a specific location or point.
Types	Axial flow fans. Centrifugal fans. Cross- flow fans.	Centrifugal blowers. Positive-displacement blowers.
Consists of	It consists of a motor and blades, which run of electricity.	It consists of a fan, outer cover, inlet, out-let.