Category Applied Science and Technology

     Air conditioning system is the system which keeps on control and maintains the particular condition (that is required temperature and humidity of air) in the closed space.

            It is technically defined as a system which controls temperature, humidity, purity and motion of air to produce desired effects upon the occupants of the space. In case of air cooler, which has the capability to cool the air inside the space does not maintain particular temperature and humidity of the air. In response to atmospheric seasons we can have winter, or summer air-conditioning system, but any air cooler will not do so.

            A so-called air cooler or desert cooler is basically a humidifier (Humidity is the moisture or water content of air). An “air-cooler” mixes water vapour with air by means of a rolling pad of moist cloths of fibre, and makes the air seem cool, but actually more humid (high moisture content).

            An Air conditioner/refrigerator, basically a dehumidifier, works as follows:

            A fluorocarbon refrigerant gas (such as “a Freon”) is compressed. On compression it is pressurized and heated. The extra heat is removed by air (from a fan) or by cooling water as in the case of large (Central A/c) units.                                                                            

            The high-pressure refrigerant is expanded. In contrast to heating on compression the refrigerant, on expansion by sudden reduction in pressure, becomes very cold due to Joule Thomson effect.

            By heat exchange with the very cold refrigerant (which has now become liquid) passing through tubes (that have fins for good heat exchange) the air paning ore, becomes cold and is circulated in the space (room etc) to be cooled. Because the air is cooled considerably, extra moisture content on humid days may be seen dripping from the air conditioner.

            For efficient operation the room in which an air conditioner is used will have to have its doors & windows closed. On the other hand, when direct cooler are in use, at least one window should be kept open as otherwise the humidity will become very uncomfortable.

            P.S.: When humidity in the atmosphere is more, curcating will be more as the sweat will not dry fast enough. In contrast, when humidity is very less as in very cold days when all the moisture in the air would have condensed leaving the atmospheric air “dry”, lips and body skin may be seen getting cracks.

            The water for frost formation comes from the articles placed in the refrigerator and the occasional air that gets into the gadget when it is opened and closed.

            Refrigeration is the process of lowering the temperature and maintaining it in a given space. In mechanical refrigeration, constant cooling is achieved by the circulation of a refrigerant in a closed system, in which it evapourates to a gas and then condenses back into a liquid in an evapourates to a gas and then condenses back into a liquid in a continuous cycle.

            The two main types of mechanical refrigeration systems used are the compression system (used in domestic units for large cold-storage applications and for most air conditioning) and the absorption system (now employed largely for heat-operated air-conditioning units).

            In the compression systems four elements – compressor, condenser, expansion valve, and evapourates are involved in the refrigeration cycle. In the evapourator the refrigerant is vapourized and heat is absorbed from the material contents or the space being cooled. The vapour is next drawn into a compressor and elevated to high pressure, which raises its temperature. The resulting superheated, high-pressure, gas is then condensed to liquid in an air-or-water-cooled condenser. From the condenser the liquid flows through an expansion valve, in which its pressure and temperature are reduced to the conditions that are maintained in the evapourator. The cycle thus continues. The amount of water vapour in the atmosphere is termed as humidity. Air at a given temperature can contain only a certain amount of water vapour. This amount increases as the temperature rises and decreases as temperature falls. In air containing a given amount of water vapour, the temperature at which dew (water that condenses on cool objects from the water vapour in warm air) begins to form is known as the dew point. If the dew point is below the freezing temperature of water, frost is formed.

            When the air surrounding the evapourator coil is cooled the moisture present in the air condenses and sticks on to the coil in the form of water droplets. These droplets are cooled in the subsequent cycle and results in frost.

            The moisture present in the items placed is absorbed by the air and carried to the evapourated coil. The condensation takes place as explained earlier.

   To understand refrigeration, pour a small quantity of petrol in your hand and expose it to the atmosphere. The petrol evaporates leaving a cooling sensation. This is because the petrol has taken the heat from the hand and transformed it into vapour. (This is known as latent heat of vaporization).

            The working substance in the refrigerator is called a refrigerant. It compressed to a high pressure and then pressure and then allowed to condense by rejecting its heat to the atmosphere surrounding it. The liquid is then allowed to expand at a low pressure. During this process it absorbs heat from the spaced inside the refrigerator and become a vapour. The above cycle is repeated in vapour-compression refrigerator which differs fundamentally from vapour absorption system.

            The major compounds in a refrigerant are halocarbon compounds (which includes halogens: chlorine, fluorine and bromine); hydrocarbons (such as methane, ethane and propane); inorganic compounds (such as ammonia, water and air) and unsaturated organic compounds (hydrocarbon with ethylene and propylene base).

            Refrigerant is the working fluid in a fridge. It should have a low boiling point so that it vaporizes at low temperatures and absorbs the heat from a substance. Some of the common refrigerants are ammonia, carbon-dioxide and Freon. Ammonia is often used as it is cheap and easily available. But it is toxic and explosive at high temperatures. Carbon-dioxide was one of the first refrigerants used but presently its use is limited. It is non-toxic and non explosive but causes suffocation when its concentration is high. Freon 12 has a boiling point of -30 degree Celsius. This refrigerant is fluorocarbon of methane and ethane series. It is a combination of halogens, chlorine and fluorine. It is the most commonly used refrigerant. Its chemical name is dichloro-difluoro-methane. It condenses at a moderate pressure under normal atmospheric temperature. This property makes it the most suitable refrigerant.

   Our retina can only respond to stimuli in one way: by sending a signal along optic nerve to the brain, which interprets this signal as light. Normally, the stimulus is light impinging on the retina, but other stimuli work too.

            One of the commonest is a mild trauma to the eyeball. If you close your eyes in a dark room and press gently on the front of your eye will see a faint flow in your peripheral vision.

            This can also happen when a blow to the head causes you to close your eyes hard for a moment. You sometimes see stars or flashes when you sneeze, which is again the result of eyeball compression as the eyelid is forced closed. The retina will also send a light signal response to the brain if it becomes torn or detached. This is a serious condition requiring treatment by an ophthalmologist. Another potential source of problem is the jelly-like vitreous humour that fills the rear two-thirds of the eye. It is attached to the retina at several points, and tugging on it can result in the sensation of light when, for example, you move your eyeball around rapidly under your lid.

            These attachments can fail as we age, which is normally not a problem unless the vitreous pulls some retina with it. This, incidentally, is the cause of floaters, the little bits of matter you can sometimes see floating about inside your eye. Light flashes can also be associated with migraine headache and central nervous system disorders, which can act on the vision centres of the brain to produce the sensation of light.

            This effect is the result of a marked increase in intra-ocular pressure (IOP) caused by the blow. This pressure is exerted on the eye by the vitreous humour – the fluid within the eye that gives it its shape.

            The increase in IOP triggers the rods and cones that make up the retina, sending an electrical signal via the optic nerve to the visual cortex at the back of the head. The visual cortex is where we perceive what we see, and hence we think we are seeing a star for a few second nicely matches the timescale of the temporary rise in IOP.