The document summarizes key components and operating principles of common home appliances including refrigerators, air conditioners, washing machines, microwaves, and their basic cycles and functions. Refrigerators use a vapor compression cycle involving compression, condensation, expansion, and evaporation of a refrigerant to transfer heat from one area to cool it. Air conditioners operate similarly but in reverse to provide heating. Washing machines involve cycles of water filling, washing, rinsing, and spinning. Microwaves generate electromagnetic waves that cause dielectric heating by rotating water molecules in food to cook it from the inside out.

1. UNIT V (Home appliances)
Principles of Refrigeration
 Liquids absorb heat when changed from liquid to gas
 Gases give off heat when changed from gas to liquid.
The sequence of the refrigeration cycle is as follows:
1. Compression of the refrigerant gas.
2. Cooling and condensation of the refrigerant to
liquid.
3. Expansion and partial evaporation of the liquid into
a lower pressure which causes cooling.
4. Continued evaporation of the liquid in the 'cold
box' - further heating by removal of sensible heat
from the item being cooled, to provide the latent
heat of vaporization of the refrigerant.
Re-compression of the vapour to begin the cycle again
For an air conditioning system to operate with economy, the refrigerant must be used repeatedly. For this
reason, all air conditioners use the same cycle of compression, condensation, expansion, and evaporation in a
closed circuit. The same refrigerant is used to move the heat from one area, to cool this area, and to expel
this heat in another area.
1. The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then moves
out of the compressor as a high-pressure gas.
2. The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to
the outside air.
3. The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of
the fluid, and lowers its pressure as it leaves the expansion valve.
4. The low-pressure liquid then moves to the evaporator, where heat from the inside air is absorbed
and changes it from a liquid to a gas.
5. As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is
repeated.
THE VAPOUR COMPRESSION REFRIGERATION CYCLE
1.The principles used in a vapour compression refrigeration system are:
1.Compression of a gas causes its temperature to increase. When the gas is cooled and sensible and latent
heat removed, the temperature decreases and the gas condense to liquid which is also the boiling point of the
liquid. (The compression also increases the temperature at which the liquid boils). The liquid is then further
cooled to around atmospheric temperature.

2. 2.When the liquid is expanded (volume increased) into a lower pressure system, it will boil and cause the
liquid temperature to decrease rapidly as it gives up sensible heat to provide the latent heat of partial
vaporization of the liquid. The cold liquid and vapour, (the latent heat does not increase the vapour
temperature), now pass through the coils inside the ' Cold Box ' (or Evaporator)of the system. Exchange of
heat between the refrigerant and the material or space being cooled, adds more heat to the refrigerant liquid
which continues to evaporate. The refrigerant, on leaving the cooling system is now all cool vapour and
passes to the suction of the compressor to begin the cycle again.
Air conditioner
Every air conditioner (also pronounced as AC, A/C
or Air Cooler in certain regions of the world) has a
compressor inside it. It works to compress and pump
the refrigerant gas. Compression of refrigerant
produces heat. To dissipate this heat, compressed
refrigerant is pumped to the condenser coils where a
fan blows the heat out to outer atmosphere. During
the process, refrigerant takes the liquid form. This
liquid refrigerant is pumped towards expansion
valve. Expansion valve has a temperature sensor
connected to it which works in correlation with
thermostat settings. Expansion valve releases the
appropriate amount of refrigerant to evaporator
(cooling coils) where liquefied refrigerant takes
gaseous form. Conversion from liquid to gaseous state due to expansion produces chillness because energy is
absorbed from the surrounding. Air when passes through fins (attached to coils) gets cooled and blown to the
room. The refrigerant in cooling coils then enters the compressor and gets compressed once again. The cycle
continues unless the compressor is shut down. In a nutshell, air conditioner draws heat from the indoor and
releases it to the outdoor. Indoor acts as a source and outdoor as a sink for heat.
Air conditioner as a heater: When air conditioner is used as a heater, the process which is shown and
explained above just simply gets reversed. As a result of reverse mechanism, hot air is propelled towards
indoor and cool air towards outdoor.
Components of air conditioner
An air conditioning system may provide heating, cooling, or both. Its size and complexity may range from a
single space heater or window unit for a small room to a huge system for a building complex. Most heating
and cooling systems must have the following basic components:
1. A heating source that adds heat to a fluid (air, water, or steam).
2. A cooling source that removes heat from a fluid (air or water).
3. A distribution system (a network of ducts or piping) to carry the fluid to the rooms to be heated or cooled.
4. Equipment (fans or pumps) for moving the air or water.
5. Devices (e.g., radiation) for transferring heat between the fluid and the room.

3. Split AC block diagram
Washing Machine
Push button keyboard enables the desired program to be selected. The control- the micor computer checks
firstly that the safety cut out is in the ON position. The water is then admitted( valve opened) and the water
level is constantly monitored. When the required
quantity of water has been provided the valve
closes.
The water temperature is measured and the heater is
switched until the water reaches the required
temperature. In the meantime, the washing powder
is admitted from a container and the hardness of
water is noted, at the same time the drum motor is
switched on so that the dirty washing is evenly
moved through the water. After the required time
has elapsed. According to the selected programs, the
motor is switched to high speed spinning and the
suction pump is switched on to move the washing wate3r and the rinsing water to waste. At the end of the
washing cycle the machine switches off and provides a signal to indicate this.
Speed control and measurement
One of the simplest methods of speed
measurement is to use a counting technique
shown in fig. it uses a fixed inductive sensor to
produce a pulse watch time it is passed by a
magnet which rotates with the drum. This
produces one pulse per revolution of the drum
which can be used to determine its speed.
The speed of the motor will be controlled by the
power dissipated in it. The simplest way of
speed controls is to use a triac. The power could

4. be controlled some form of electronic circuitry, but the hardware requirement can be reduced if the
microcomputer controls the power directly by firing the triac at an appropriate time during its cycle. To do
this the controller must detect the zero crossing of the ac supply. This will require circuitry to detect the
crossing point while protecting the processor from high voltages. the power directly by firing the triac
Types of washing machines
Three types, namely washer, semi-automatic and automatic. Washers are single tub machines that only wash.
Since washers don’t have the facilities for drying the clothes, these cost less than semi-automatic and fully
automatic machines.
In semi automatic the controls are not dully automatic and manual intervention is required.
In fully automatic machines, no manual intervention is required during the washing process. For automatic
machines, programs have to be selected and set by the user prior to the start of washing cycle.
Sensors sense the wash load and decide the program ideal for washing the clothes, water level time required
to wash, number of rinses and spins, type of fabric etc.
Washing Machine Hardware
1. Temperature sensor which senses the washing water temperature. (The analog/digital converter changes
the analog values to binary numbers).
2. Safety cut-out switch. 3. keyboard for program selection. 4. Water level gauge.
5. Motor for washing drum. 6. Power switches for motor, heater, etc. 7. Heater for washing water.
8. Water inlet valve. 9. Water suction pump.

5. 10. Control lamps and indicators.
Water inlet control valve: Near the water inlet point of the washing there is water inlet control valve. When
you load the clothes in washing machine, this valve gets opened automatically and it closes automatically
depending on the total quantity of the water required. The water control valve is actually the solenoid valve.
Water pump: The water pump circulates water through the washing machine. It works in two directions, re-
circulating the water during wash cycle and draining the water during the spin cycle.
Tub: There are two types of tubs in the washing machine: inner and outer. The clothes are loaded in the
inner tub, where the clothes are washed, rinsed and dried. The inner tub has small holes for draining the
water. The external tub covers the inner tub and supports it during various cycles of clothes washing.
Agitator or rotating disc: The agitator is located inside the tub of the washing machine. It is the important
part of the washing machine that actually performs the cleaning operation of the clothes. During the wash
cycle the agitator rotates continuously and produces strong rotating currents within the water due to which
the clothes also rotate inside the tub. The rotation of the clothes within water containing the detergent
enables the removal of the dirt particles from the fabric of the clothes. Thus the agitator produces most
important function of rubbing the clothes with each other as well as with water. In some washing machines,
instead of the long agitator, there is a disc that contains blades on its upper side. The rotation of the disc and
the blades produce strong currents within the water and the rubbing of clothes that helps in removing the dirt
from clothes.
Motor of the washing machine: The motor is coupled to the agitator or the disc and produces it rotator
motion. These are multispeed motors, whose speed can be changed as per the requirement. In the fully
automatic washing machine the speed of the motor i.e. the agitator changes automatically as per the load on
the washing machine.
Timer: The timer helps setting the wash time for the clothes manually. In the automatic mode the time is set
automatically depending upon the number of clothes inside the washing machine.
Printed circuit board (PCB): The PCB comprises of the various electronic components and circuits, which
are programmed to perform in unique ways depending on the load conditions (the condition and the amount
of clothes loaded in the washing machine). They are sort of artificial intelligence devices that sense the
various external conditions and take the decisions accordingly. These are also called as fuzzy logic systems.
Thus the PCB will calculate the total weight of the clothes, and find out the quantity of water and detergent
required, and the total time required for washing the clothes. Then they will decide the time required for
washing and rinsing.
Drain pipe: The drain pipe enables removing the dirty water from the washing that has been used for the
washing purpose.
Microwave oven
Principle: Microwave radiations generated by a magnetron pass through the exposed food, create dielectric
heating within the food, this is the basic principle on which a microwave oven works. The heart of
microwave oven is a device to generate microwaves of required frequency and wavelength called
magnetron. Microwaves generated by the magnetron are bombarded on the food, which cook the food
through a process called dielectric heating.

6. Microwave radiation is in between common radio and infrared frequencies. In common home ovens, the
frequency of microwave radiation is 2.45 gigahertz with a wavelength of 122 millimeters. It is to be noted
that, microwaves always posses an alternating electric and magnetic field around them. When microwaves
penetrate through the exposed food, they are intervened by the di-polar water molecules present within the
food. As the electric and magnetic fields associated to the microwaves alternate, the individual water
molecules also rotate to align their dipoles with respect to the changing electric field they are subjected to.
These electric and magnetic fields alternate 2.45 billion times a second in case of a microwave oven. This
causes the dipolar water molecules to rotate or simply move back and forth at a high speed.
As there are strong cohesive forces among the water molecules and between the water and other molecules,
which can be considered as the force of friction at molecular stage. The rotating water molecules generate
heat energy which is called as dielectric heating, just like the heat produced due to the force of friction
when two objects are rubbed against each other. As this process occurs in all water molecules present inside
the food, the whole mass of the food is cooked simultaneously.
Block diagram of microwave ovan
The block diagram of a microwave oven is given in Figure. The mains plug and socket are three-pin ear
thing type. The fast blow ceramic fuse is of I5A, 250 V. Interlock switches are linked with the oven door.
Power will be applied to the mains transformer only when the oven door is closed. At least one interlock
switch is in series with the transformer primary, hence even a spot of dirt in the relay or trial,
There is yet another interlock across the power supply line. It normally remains open. If the door alignment
is not correct it will be activated, putting a short circuit (crowbar) across the line and making the fuse to
melt. Thus, the microwave oven is a fail safe device.
The voltage induced in the secondary winding is about 2000 V (rms) at 250 mA for normal domestic, ovens.
The transformer also has a tertiary winding for the magnetron filaments. The high voltage return circuit is
fastened directly to the chassis through the transformer frame. A half-wave doubler configuration is used for
the rectifier, with a peak inverse voltage of about 12000 V. One end of the diode is connected to the chassis.

7. The bleeder capacitor (1 µF) should always be discharged before touching anything inside when the cover is
removed. The high value bleeder resistor is slow to discharge; further it may be open.
The thermal protector is a PTC thermistor. The primary current decreases when the temperature rises
abnormally. It senses the temperature of the magnetron as it is bolted to the magnetron case and is so
connected electrically that its resistance comes in series with the primary circuit.
The controller is a microprocessor chip with a clock. It is activated by key-pad switches and sets the cooking
time. It senses the temperature and moisture, sets the power levels and runs the display. There are; three
power levels. For HIGH the microwave generator remains on continuously; for MEDIUM it remains on for
10 seconds and off for 10 seconds; for LOW it remains on for 5 seconds and off for 15