Vapour Absorption Refrigeration System | Refrigeration System

Vapour absorption refrigeration system

The vapour absorption system used heat energy instead of mechanical energy and hence compressor is not used. Instead it is replaced by an absorber, a heat exchanger and a generator. This system uses ammonia as refrigerant.

Principle

01 - VAPOUR ABSORPTION REFRIGERATION SYSTEM - REFRIGERATION SYSTEMS

The basic principle of this system is that the ammonia vapour condenses when it is dissolved in water. Further heating of the ammonia liquid converts ammonia into vapour.

Description

A simple vapour absorption system consists of the following parts.

Generator: The solution of aqua-ammonia received from the absorber is heated by some external sources such as electric heater or gas flame. Because of this heating the ammonia solution gets separated into ammonia vapour at high pressure and hot weak ammonia which mostly consists of water.

Condenser: Condenser converts the high pressure ammonia vapour received from the generator into high pressure ammonia liquid. This process is done by means of circulating cool water.

Expansion valve or throttle valve: The expansion that takes place in the expansion valve is throttling. The high pressure ammonia liquid is expanded to low pressure low temperature ammonia in the expansion valve.

Evaporator: Evaporator, also called cold chamber, is the actual freezing. The ammonia refrigerant passing through the evaporator absorbs the heat and evaporates.

Absorber: The function of the absorber is to absorb low pressure ammonia vapour from the evaporator and weak ammonia solution from the generator. The purpose of the absorber is to make this mixture into a string solution, which is pumped back to the generator.

Heat Exchanger: It is used to transfer the heat from strong ammonia solution to the weak solution.

Pump: It is used to circulate the strong ammonia through the heat exchanger. The pump increases the pressure of the solution.

01 - VAPOUR ABSORPTION REFRIGERATION SYSTEM - REFRIGERATION SYSTEM

Working Principle

The system works as follows:

The low-pressure ammonia vapour leaving the evaporator enters the absorber, where it is absorbed by cold water forming a strong solution of ammonia. This solution is known as aqua-ammonia. Due to absorption of ammonia, the pressure in the absorber reduces, which in turn, increases the temperature of the solution. The coolant removes the heat generated in the absorber. The strong solution from the absorber is pumped by a liquid pump to the generator through a heat exchanger. The pump increases pressure of the solution. The heat exchanger increases the temperature of the high pressure strong solution. The strong solution of ammonia is further heated in the generator with help of steam or a heating coil. The ammonia vapour is driven off or generated during this heating process. The hot, high-pressure ammonia vapour is then condensed in the condenser using water as a coolant. Meanwhile due to generation of vapour, weak solution remains in the generator. The weak solution at high pressure flows back to the absorber after passing through a pressure reducing valve. When the demand for refrigeration arises, the expansion valve in the circuit is opened. The ammonia in liquid passes through the expansion valve. The ammonia subsequently undergoes an expansion process and then enters the evaporator. In the evaporator, it absorbs heat and produces the refrigeration effect. The low-pressure ammonia vapour from the evaporator then re-enters the absorber, where it is again absorbed to form a strong solution and the cycle repeats itself. Thus completes the simple vapour absorption refrigerator cycle.

Advantages

· Absence of moving parts so less noise.

· Exhaust system may be used as a source of heat energy.

· Load variation does not affect the performance of the system.

· Control is easy for absorption system.

· Cost of the system is less.

Disadvantages

· COP of the system is low.

· Leakages are a problem.

· This system occupies more space.

· Costly pump is required.

Drill Tool Nomenclature | Parts of a Drill Tool

DRILL TOOL NOMENCLATURE

A drill or twist drill is a grooved end-cutting tool used for manufacturing holes in firm material. It basically consists of two parts.

· The body consisting of the cutting edges, and

· The shank used for holding purposes.

The various parts and angle of the twist drill are shown below

01 - DRILL TOOL NOMENCLATURE - PARTS OF A DRILL BIT

Body

The body of the twist drill spiral grooves cut on it. These grooves serve to offer clearance to the chips formed at the cutting edge. They also permit the cutting fluid to spread to the cutting edges.

Shank

It is a part that gets fitted into the drill chuck or sleeve. It might be parallel shank or taper shank. Smaller diameter drills have straight shank. Morse taper is generally provided for large diameter tapered drills. The taper shank brings the tang at the end of shank. This fits into a slot in the machine spindle, sleeve or socket and gives a positive grip.

Neck

It is the undercut portion between the body and the shank. Usually, size and other details are marked at the neck.

Point

It is the cone fashioned end of the drill. The point is shaped to produce lip, face, and flank and chisel edge or dead center.

Land or Margin

It is a narrow strip. It ranges back on the edge of the drill flutes. The size of drill is measured across the lands at the point end. Land retains the drill aligned.

Web

It is the central portion of drill located between the roots of the grooves and lengthening from the point towards the shank.

Chisel edge

The intersection of flank forms the chisel edge. This acts as a flat drill. It cuts a small hole in the work piece at the beginning. Therefore cutting edges removes further materials to complete the hole.

Cutting edge

The cutting edges of a drill are known as lips. Both lips should have equal length, same angle of inclination and correct clearance.

Flank

The surface behind the lip to the following flute is called flank.

01 - DRILL TOOL NOMENCLATURE - PARTS OF A DRII TOOL

Face

This is the portion of the flute surface adjacent to the lip. The chip impinges on it.

Heel

The edge which is formed by the intersection of the flute surface and the body clearance is known as heel.

Point angle

It is the angle between the cutting edges. It is generally 118 degree. Its value depends upon the hardness of the work piece to be drilled. For harder material, larger angles are used.

Point angle

It is the angle between the face and the line parallel to the drill axis. At the periphery of the drill, it is equal to the helix angle.

Helix angle

It is the angle between the leading edge of the land and the axis of the drill. It is also called as spiral angle.

Lip clearance angle

It is the angle formed by the portion of the flank adjacent to the land and a plane at right angles to the drill axis measured at the periphery of the drill.

Chisel edge angle

It is the obtuse angle between the chisel edge and the lip. Generally, this angle is 120 and 135 degree.