Category Archives: Thermal

Air-Conditioner | Air-Conditioning System | Window Air Conditioner


This is also called as window type room air-conditioner because it can be accommodated in window of walls. This unit is suitable for cooling the rooms in hot summer.

The window air-conditioner works on the vapour compression refrigeration cycle.



The basic components of a window air-conditioner are compressor, condenser, a capillary tube and an evaporator, in addition filters, accumulators, motors, fans and electrical controls. This unit consists of

1. A cooling system to cool and dehumidify the air which includes a condenser, a compressor and a refrigerant coil.

2. A filter to remove any impurities in the air. The filter is finished of with mesh, glass wool or fibre.

3. A fan and adjustable grills to circulate the air.

4. Controls to regulate equipment operation.

Working Principle

The high-pressure refrigerant which comes out of the compressor is condensed in the condenser using ambient air a coolant. The liquid refrigerant is expanded in a capillary tube and then enters the evaporator. Here, it evaporates and roots the refrigeration effect. Then fan blows the fresh air over the evaporator coil, which cools the air. The cool air is supplied to the room. Meanwhile, refrigerant from the evaporator enters the compressor to be compressed and the cycle repeats itself. The return air from the room is exhausted by the evaporator fan be blowing air over the condenser coil, where it picks up heat from the refrigerant.


The compressor used in a window air-conditioner is hermetic type, which is sealed in a casing with a motor. The condenser coil is a continuous copper coil with aluminium fins. The capillary tube is 40cm long, usually with 0.75mm diameter. Evaporator coil is also made of copper with aluminium fins. Dampers and louvers are provided for intake and exhaust on both sides of the air-conditioner casing.

A cone ton window air-conditioner circulated 4m³/min of air in the room. Some fraction of air is fresh, whereas some faction of air is recirculated. Filters are used to filter air entering the air-conditioning unit. The filter is plastic foam or metallic mat type. The controls used by the unit are

a) Thermostat Control: This is used to set the room air temperature. Usually it is a bimetallic strip.

b) Master Control: It is an electrical switch used to stop or start the compressor motor.

The installation of the unit is done either in the wall or by using external brackets or locating it inside the room with exhaust flush to the window. In either case, the condenser should be facing outside and the evaporator should be facing inside. It is advisable to install the unit for a minimum sun exposure as sun’s rays can diminish the efficiency of the condenser. The air louver inlets should not be blocked and provision for draining of the condensate must be provided. Maintenance of the window air-conditioner should include interrupted cleaning, replacing filters and air seals and lubrication of fans.

Domestic Refrigerator | Layout of a Typical Domestic Refrigerator


Refrigerators, once considered a luxury, are now a necessity of daily life. They have usage in homes, hotels, office, laboratories, hospitals, shops restaurants, etc. They are manufactured in several sizes and many brands are available. The different models are rated on the basis of gross volume such as 100 litres, 165 litres, 200 litres, 250 litres and so on.


The construction of household refrigerator, with location of main components.


1. Evaporator: The evaporator is located in a coil form on the freezer box. The liquid refrigerant is evaporated in the evaporator by absorbing heat from the contents of the domestic refrigerator in the cabinet. The evaporator consists of copper metal rubbing surrounding the freezing and cooling compartments.

2. Condenser: The condenser is located as zigzag tubes behind the refrigerator on a mesh. In the condenser, the heat from the refrigerant at a higher temperature is rejected to the atmospheric air.

3. Compressor: The compressor is located at the base at the rear end. It compresses the refrigerant vapour to a high pressure. Reciprocating compressor is used for low capacity domestic refrigerator.

4. Expansion Valve or Throttling Valve: An expansion valve is used to reduce the temperature and pressure of the liquid refrigerant, before it passes to the evaporator. The expansion capillary is located inside the refrigerator body hear the wall. The capillary tube is small diameter tube used as an expansion device.

5. Refrigerator cabinet: The refrigerator cabinet is thermally insulated to minimize heat flow from the atmosphere into the refrigerator. The insulation is glass fiber and the external body is of stainless steel.

Working Principle


The refrigerator works on the vapour compression refrigeration cycle. The refrigerant vapour is first compressed in the compressor. The compressor is a special one known as the hermetic compressor. In this unit, the compressor is sealed casing along with an electrical motor to run. This sealing prevents leakage of refrigerant and lubrication oil. The pressure and temperature of the refrigerant increases after compression and is subsequently condensed in a condenser. In the condenser, the refrigerant rejects heat to a coolant and cools down and finally gets condensed. The condensate is then allowed to pass through capillary to reduce temperature and pressure by expansion of refrigerant. The refrigerant is filtered before entering the capillary tube. The pressure of the refrigerant, when it leaves the capillary, is maintained above atmospheric and temperature corresponds to saturation temperature so that the refrigerant can absorb heat in the evaporator. The refrigerant enters the evaporator and is heated by the heat absorbed from the body or space thereby producing the refrigeration effect. The vapour refrigerant enters the compressor again and the cycle is completed.

When power to the compressor is switched on, a humming sound is heard and the refrigerator is functional. The refrigerant flows through its circuit and ice is produced in the freezer. Frost, i.e., moisture from ambient air, gets deposited on the evaporator coil. Defrosting removes this frost. The water from defrosting is collected in a tray to be removed manually. Articles to be refrigerated are placed on shelves. Fruits and vegetables, which contain moisture, are stored at the base. The temperature here is around 8°C. Thus there are temperature gradients in the refrigerator, negative temperature in the freezer and positive temperature at the base.