hey pls help me.?

Question

I am going to do a model of how refrigerator works, as a part of my project. I have to write around 150 words why I chose that subject. What am I going to write? give me ideas pls

Answer 1

google it

Answer 2

Unfortunately, nobody but you knows why you chose to make a model of a refrigerator!

However, 150 words is not much!

How about this (and it's 156 words!)


I decided to make a model of something that everybody knows and uses – a refrigerator.

All homes have one nowadays. It is an indispensible necessity and cannot be replaced by anything else. It is never thought about but used all day, every day - and by everyone in the family. It keeps food cool and fresh for longer. It stops things from spoiling longer than leaving things out on the side. Although normally white, it can be any colour. The worst thing about fridges is that it is a disaster when they goes wrong – or there is a power cut!

The fridge was first demonstrated in the 1700s but was not patented until 1895 as something for the house. The first one went on sale in 1911 and required two rooms! The first self-contained fridge went on sale in 1923, although they were not mass-produced until after World War II.

Yet nobody knows how it works!

Answer 3

In the summertime, have you ever gotten out of a swimming pool and then felt very cold standing in the sun? That's because the water on your skin is evaporating. The air carries off the water vapor, and with it some of the heat is being taken away from your skin.

This is similar to what happens inside older refrigerators. Instead of water, though, the refrigerator uses chemicals to do the cooling.

There are two things that need to be known for refrigeration.

1. A gas cools on expansion.
2. When you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics.


Old Refrigerators

If you look at the back or bottom of an older refrigerator, you'll see a long thin tube that loops back and forth. This tube is connected to a pump, which is powered by an electric motor.

Inside the tube is Freon, a type of gas. Freon is the brand name of the gas. This gas, chemically is called Chloro-Flouro-Carbon or CFC. This gas was found to hurt the environment if it leaks from refrigerators. So now, other chemicals are used in a slightly different process (see next section below).

CFC starts out as a liquid. The pump pushes the CFC through a lot of coils in the freezer area. There the chemical turns to a vapor. When it does, it soaks up some of the heat that may be in the freezer compartment. As it does this, the coils get colder and the freezer begins to get colder.

In the regular part of your refrigerator, there are fewer coils and a larger space. So, less heat is soaked up by the coils and the CFC vapor.

The pump then sucks the CFC as a vapor and forces it through thinner pipes which are on the outside of the refrigerator. By compressing it, the CFC turns back into a liquid and heat is given off and is absorbed by the air around it. That's why it might be a little warmer behind or under your refrigerator.

Once the CFC passes through the outside coils, the liquid is ready to go back through the freezer and refrigerator over and over.

Today's Refrigerators

Modern refrigerators don't use CFC. Instead they use ammonia gas. Ammonia gas turns into a liquid when it is cooled to -27 degrees Fahrenheit (-6.5 degrees Celsius).

A motor and compressor squeezes the ammonia gas. When it is compressed, a gas heats up as it is pressurized. When you pass the compressed gas through the coils on the back or bottom of a modern refrigerator, the hot ammonia gas can lose its heat to the air in the room.

Remember the law of thermodynamics.

As it cools, the ammonia gas can change into ammonia liquid because it is under a high pressure.

The ammonia liquid flows through what's called an expansion valve, a tiny small hole that the liquid has to squeeze through. Between the valve and the compressor, there is a low-pressure area because the compressor is pulling the ammonia gas out of that side.

When the liquid ammonia hits a low pressure area it boils and changes into a gas. This is called vaporizing.

The coils then go through the freezer and regular part of the refrigerator where the colder ammonia in the coil pulls the heat out of the compartments. This makes the inside of the freezer and entire refrigerator cold.

The compressor sucks up the cold ammonia gas, and the gas goes back through the same process over and over.

How Does the Temperature Stay the Same Inside?

A device called a thermocouple (it's basically a thermometer) can sense when the temperature in the refrigerator is as cold as you want it to be. When it reaches that temperature, the device shuts off the electricity to the compressor.

But the refrigerator is not completely sealed. There are places, like around the doors and where the pipes go through, that can leak a little bit.

So when the cold from inside the refrigerator starts to leak out and the heat leaks in, the thermocouple turns the compressor back on to cool the refrigerator off again.

That's why you'll hear your refrigerator compressor motor coming on, running for a little while and then turning itself off.

Today's refrigerators, however, are very energy efficient. Ones sold today use about one-tenth the amount of electricity of ones that were built 20 years ago. So, if you have an old, old refrigerator, it's better to buy a new one because you'll save money (and energy) over a long period of time.

Answer 4

How a Refrigerator Works

A refrigerator doesn't actually cool things, it removes the heat from them. But then you probably don't want a physics lesson. But you may wonder where the "cold" comes from. So here is a little bit more physics. When a gas goes from a state of high pressure to a state of low pressure, the temperature of the gas drops.

http://www.acmehowto.com/howto/appliance/refrigerator/overview.php

http://www.affordableappliance.com/Tips/HowARefrigeratorWorks.htm

How Refrigerators Work

http://www.howstuffworks.com/refrigerator.htm

http://www.mansfieldct.org/schools/mms/staff/hand/heatrefrig.htm

How Things Work Home

http://howthingswork.virginia.edu/

http://www.howstuffworks.com/

Good luck.

Kevin, Liverpool, England.

Answer 5

I would suppose like any other good student you would do your research on the functioning of a refrigerator, what its made of, and how it works. 150 words? Thats nothing.

Answer 6

This website is amazing at showing how stuff works, with pictures and animations as well. It does what the website name suggests.

http://www.howstuffworks.com

It can be a bit confusing, but look for the yellow search bar in the top right-hand corner to type in the item you wish to know how it works.

Answer 7

say you chose that subject as a fridge is something we all rely on and is common in all households, so you are interested in how it works.

Answer 8

INTRODUCTION


Refrigeration, process of lowering the temperature and maintaining it in a given space for the purpose of chilling foods, preserving certain substances, or providing an atmosphere conducive to bodily comfort. Storing perishable foods, furs, pharmaceuticals, or other items under refrigeration is commonly known as cold storage. Such refrigeration checks both bacterial growth and adverse chemical reactions that occur in the normal atmosphere.


The use of natural or manufactured ice for refrigeration was widespread until shortly before World War I, when mechanical or electric refrigerators became available. Ice owes its effectiveness as a cooling agent to the fact that it has a constant fusion temperature of 0° C (32° F). In order to melt, ice must absorb heat amounting to 333.1 kJ/kg (143.3 Btu/lb). Melting ice in the presence of a dissolving salt lowers its melting point by several degrees. Foodstuffs maintained at this temperature or slightly above have an increased storage life. Solid carbon dioxide, known as dry ice, is used also as a refrigerant. Having no liquid phase at normal atmospheric pressure, it sublimes directly from the solid to vapor phase at a temperature of -78.5° C (-109.3° F). Dry ice is effective for maintaining products at low temperatures during the period of sublimation.

In mechanical refrigeration, constant cooling is achieved by the circulation of a refrigerant in a closed system, in which it evaporates to a gas and then condenses back again to a liquid in a continuous cycle. If no leakage occurs, the refrigerant lasts indefinitely throughout the entire life of the system. All that is required to maintain cooling is a constant supply of energy, or power, and a method of dissipating waste heat. 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 but formerly also used for heat-operated domestic units.

II COMPRESSION SYSTEMS

Compression systems employ four elements in the refrigeration cycle: compressor, condenser, expansion valve, and evaporator. In the evaporator the refrigerant is vaporized and heat is absorbed from the material contents or the space being cooled. The vapor next is drawn into a motor-driven 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 evaporator.

III REFRIGERANTS

For every refrigerant there is a specific boiling, or vaporization, temperature associated with each pressure, so that it is only necessary to control the pressure in the evaporator to obtain a desired temperature. A similar pressure-temperature relationship holds in the condenser. One of the most widely used refrigerants for many years has been dichlorodifluoromethane, known popularly as Refrigerant-12. This synthetic chlorofluorocarbon (CFC) when used as a refrigerant would, for example, vaporize at -6.7° C (20° F) in its evaporator under a pressure of 246.2 kPa (35.7 psi), and after compression to 909.2 kPa (131.9 psi) would condense at 37.8° C (100° F) in the condenser. The resulting condensed liquid would then enter the expansion valve to drop to evaporator pressure and repeat the cycle of absorbing heat at low temperature and low pressure and dissipating heat at the much higher condenser pressure and temperature. In small domestic refrigerators used for food storage, the condenser heat is dissipated into the kitchen or other room housing the refrigerator. With air-conditioning units the condenser heat must be dissipated out of doors or directly into cooling water.

In a domestic refrigeration system the evaporator, called the freezer, is always placed in an insulated space. In some cases this space constitutes the whole refrigerator cabinet. The compressor is usually oversized, so that if it ran continuously it would produce progressively lower temperatures. In order to maintain the interior of the box within the desired temperature range, the motor driving the compressor is controlled by a thermostatic switch.

A frozen-food refrigerator resembles the household refrigerator except that its compressor and motor must be of sufficient size to handle the larger gas volume of the refrigerant at its lower evaporator pressure. For example, to maintain a temperature of -23.3° C (-10° F) an evaporator pressure of 132.3 kPa (19.2 psi) is required with Refrigerant-12.

IV ABSORPTION SYSTEM

A few household units, called gas refrigerators, operate on the absorption principle. In such gas refrigerators a strong solution of ammonia in water is heated by a gas flame in a container called a generator, and the ammonia is driven off as a vapor, which passes into a condenser. Changed to a liquid state in the condenser, the ammonia flows to the evaporator as in the compression system. Instead of the gas being inducted into a compressor on exit from the evaporator, however, the ammonia gas is reabsorbed in the partially cooled, weak solution returning from the generator, to form the strong ammonia solution. This process of reabsorption occurs in a container called the absorber, from which the enriched liquid flows back to the generator to complete the cycle.

Increasing use of absorption refrigeration now occurs in refrigeration units for comfort space cooling, for which purpose refrigerant temperatures of 45° to 50° F (7.2° to 10° C) are suitable. In this temperature range, water can be used as a refrigerant with an aqueous salt solution, usually lithium bromide, as the absorbent material. The very cold boiling water from the evaporator is absorbed in concentrated salt solution. This solution is then pumped into the generator, where, at elevated temperature, the surplus water is boiled off to increase the salt concentration of the solution; this solution, after cooling, recirculates back to the absorber to complete the cycle. The system operates at high vacuum at an evaporator pressure of about 1.0 kPa (0.145 psi); the generator and condenser operate at about 10.0 kPa (1.45 psi). The units are usually direct-fired or use steam generated in a boiler.

V REFRIGERANTS AND THE ENVIRONMENT

Refrigerant-12 and related CFCs, Refrigerant-11 and Refrigerant-22, are currently the major compounds used in the cooling and insulation systems of home refrigeration units. It has been found, however, that CFCs are posing a major threat to the global environment through their role in the destruction of the ozone layer. A search has therefore begun for replacements, and some manufacturers of CFCs have already pledged to phase out these products by the end of the century.

hope this is useful! good day