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How stuff works??????

Discussion in 'Tech, Gadgets & Science Forum' started by Mtazamaji, Dec 28, 2010.

  1. Mtazamaji

    Mtazamaji JF-Expert Member

    Dec 28, 2010
    Joined: Feb 29, 2008
    Messages: 5,972
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    We have many appliances in our homes we use in daily lives. Have u ever asked yourself or do u know :-

    • Technically how these appliances perform their function?
    • What parts/subsystem make them?
    Tujiulize ,tudadisi, tujikumbushe na tujifunze what realy happen behind the scene.

    Naanza Na friji

    The refrigerator is one of those miracles of modern living that totally changes life. Prior to refrigeration, the only way to preserve meat was to salt it, and iced beverages in the summer were a real luxury.

    The basic idea behind a refrigerator is very simple: It uses the evaporation of a liquid to absorb heat

    The Purpose of Refrigeration
    The fundamental reason for having a refrigerator is to keep food cold. Cold temperatures help food stay fresh longer. The basic idea behind refrigeration is to slow down the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the food.

    For example, bacteria will spoil milk in two or three hours if the milk is left out on the kitchen counter at room temperature. However, by reducing the temperature of the milk, it will stay fresh for a week or two -- the cold temperature inside the refrigerator decreases the activity of the bacteria that much. By freezing the milk you can stop the bacteria altogether, and the milk can last for months (until effects like freezer burn begin to spoil the milk in non-bacterial ways)

    Refrigeration and freezing are two of the most common forms of food preservation used today.

    Parts of a Refrigerator
    You probably know that when you put water on your skin it makes you feel cool. As the water evaporates, it absorbs heat, creating that cool feeling. Rubbing alcohol feels even cooler because it evaporates at a lower temperature. The liquid, or refrigerant, used in a refrigerator evaporates at an extremely low temperature, so it can create freezing temperatures inside the refrigerator. If you place your refrigerator's refrigerant on your skin (definitely NOT a good idea), it will freeze your skin as it evaporates.

    There are five basic parts to any refrigerator (or air-conditioning system):

    • Compressor
    • Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit
    • Expansion valve
    • Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit
    • Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures
    Many industrial installations use pure ammonia as the refrigerant. Pure ammonia evaporates at -27 degrees Fahrenheit (-32 degrees Celsius).

    The Refrigeration Cycle

    In the following example, we will assume that the refrigerant being used is pure ammonia, which boils at -27 degrees F. This is what happens to keep the refrigerator cool:

    1. The compressor compresses the ammonia gas. The compressed gas heats up as it is pressurized (orange).
    2. The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure.
    3. The high-pressure ammonia liquid flows through the expansion valve.
    You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side).

    4.The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the
    inside of the refrigerator cold.

    5.The cold ammonia gas is sucked up by the compressor, and the cycle repeats.

    By the way, if you have ever turned your car off on a hot summer day when you have had the air conditioner running, you may have heard a hissing noise under the hood. That noise is the sound of high-pressure liquid refrigerant flowing through the expansion valve.

    Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak, so all home refrigerators don't use pure ammonia. You may have heard of refrigerants know as CFCs (chlorofluorocarbons), originally developed by Du Pont in the 1930s as a non-toxic replacement for ammonia. CFC-12 (dichlorodifluoromethane) has about the same boiling point as ammonia. However, CFC-12 is not toxic to humans, so it is safe to use in your kitchen. Many large industrial refrigerators still use ammonia.
    In the 1970s, it was discovered that the CFCs then in use are harmful to the ozone layer, so as of the 1990s, all new refrigerators and air conditioners use refrigerants that are less harmful to the ozone layer.

    Source: HowStuffWorks "How Refrigerators Work"

    Welcome to add any article or your knowlnge on any appliance. Iwe ni mobile phone, pasi , Jiko ,TV Radio,brender chemli, jiko la mchina , bulb, kibatari, etc


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