22 KB 10 SEC to download: Solar Refrigerator>>>SUN FROST




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Introduction

Refigeration is an pocess of producing low themperatures.It takes place when heat is removed fron a substance. Cooling can be achieved with ice or snow or machines.for thousands of years, people have used some kind of refrigeration to cool beverages and preserve foods. Since the mid 1800’s, refrigeration has been widely used to keep food from spoiling.

Today, people store and transport foods in home and commercial refrigerator. Also due to rapid expansion of global economy refrigeration process is emperative.Refrigeration makes it possible to store serums,vaccines ,blood plasma and other life saving medical supplies.Drug compniesuse refrigeration to make penicellium and other drugs.

Evaporative fridges are a relatively well tested, proven, low-tech approach to cooling, which cool produce, other food and beverages at about 15-20°C below ambient temperatures and subzero temperatures in freezer. They are most appropriate in hot, dry (not humid) climates where there are no other alternatives.

Principle of Refrigeration

Refrigeration removes heat from solids,liquid and gases. It is based on II law of thermodynamics. It states that the heat only flows from the warmer body to cold body, or from a subastane at certain temperature to a substance at a lower temperature.The flow of heat from warmer body to colder bodies is called heat transfer. During refrigeration, heat transfer occours when we place the substance we wish to cool near a refrigerant.

Heat Transfer:
A simple heat transfer takes place on keeping a warmer body in close contact a colder body in accord to the II law of thermodynamics.All the substaces have the ability to absorb heat . but refrigerants absord heat quickly and in large quantities.the most common types of refrigerants include air, water, brine, ice, ammonia, carbobdioxide, sulfur dioxide and such specially prepared substances as Freon and Carrene.

Endothermic Reactions:
By itself, ice could never absorb enugh heat to reduce the tremperature of a substance below its own melting point of 273K. But endothermic reactions enable ice to produce freezing temperatues . Cetrtain chemical compounds, particularly salts produce a freezing temperature action when mixed with ice or even some other compound.Such combination are called endothermic mixtures capable of producing the temperture below – 40ºC.Endothermic mixtures such combination such as calcium chloride and snow; ice, sodium chloride, ammonium chloride, pottasium nitrate and diluted nitric acid. All these substance absorb heat during their chemical reactions.

SOLAR REFRIGERATOR

PROJECTED FINAL FABRICATION DESIGN

AIM
· Most efficient refrigerator in its size range
· Rugged construction for remote service
· Reliable: Only one moving part
· Excellent temperature control
· Reserve cooling capacity: Runs only 27% (projected) of the time in a hot 43° C (110° F) environment
· Easy to defrost and clean: More convenient than chest models

DESIGN CRITERION

When selecting a refrigerator, we need to consider specific refrigeration need. Various types of refrigerators use different fuel sources and different amounts of energy. Before choosing a fridge, we should consider our requirements.
Important considerations include the following:

· How large are the items you need to refrigerate? Vaccine refrigerators need very little space, and hence require a relatively small amount of energy. A refrigerator for a restaurant, however, requires a much larger space, which will be much more expensive to cool.

· Do you need freezer space? Freezing takes more energy than simple refrigeration. We should thus consider would the unit we buy need to be a combined fridge/freezer, a simple one-compartment refrigerator or a freezer only.

· How often do we need to access the refrigerator? Frequent accessing of the cold space allows heat to enter, and will increase the size and cost of the energy system required to power it.

· How hot is your location? Warmer locations require more energy for refrigeration. We should be able to provide ambient temperatures of our site for system designers.

· Is the requirement critical? When the requirement is absolutely critical, then the power source must be 100% reliable (and over-sized), which will increase costs significantly. A refrigerator storing critical vaccines would need 100% reliability, while a household fridge storing food would not.

APPLICATIN REQUREMENT

Application Freezer (space required liters) Volume required (liters) Critical/ non-critical
Vaccine refrigeration 0-5 l 30 liters Yes
Institutional & commercial food preservation 50-550 liters 200-1000 liters Yes
Institutional & commercial drinks, etc. cooling N/A 200-300 liters No
Dedicated freezing (institutional or commercial) 500-1000 liters N/A Yes
Household refrigeration/freezing 15-250 liters 200-550 liters No

1.2 Need for solar energy

The conventional sources of energy such as oil, natural gas, fossil fuel, etc are fast depleting and becoming scarcer and scarcer. Statistics shows that oil and natural gas are likely to be consumed by the year 2020 A.D the next source of energy i.e. coal, will touch a maximum production rate between 2030 A.D. and 2060 A.D. Even the recently developed source of energy, viz., and nuclear energy utilizes consumable uranium. Even Uranium will become scarcer if we continue to use it at the present rate.

Because of the reasons mention above, there is a need to go for alternative sources of energy. Solar energy is the most promising option. Solar energy is an inexhaustible source of energy. The power from the sun intercepted by the earth is approximately 1.8 E ¹¹ MW, which is many thousands of times larger than the preset consumption rate on the earth of all commercial energy sources. Thus, in principal, solar energy could supply all the present and future energy needs of the world on a continuous basis.

In addition to its size, solar energy had two other factors in its favor. Firstly, unlikely fossil fuels and nuclear fuels, it is an environmentally clean source of energy. Secondly, it is available free and in adequate in almost all parts of the world.

However, there are many problems associated with its use. The main problem is that it is a dilute source of energy. Even in the hottest regions on earth, the solar flux available rarely exceeds 1 KW/m², which is a low value for technological utilization in many applications and these results in excessive costs.

A second problem associated with the use of solar energy is that its availability widely varies with time. Consequently, the energy collected when the sun is shining must be stored for use during periods when it is not available. The need for storage also adds significantly to the cost of any system. Thus, the real challenge in utilizing solar energy as an energy alternative is of economic nature.

The solar energy can be used for many applications. One of them is Refrigeration.

Solar Absorption Refrigerator

Our aim is to develop a non-electric solar refrigerator-freezer. The refrigerator uses an aqua-ammonia absorption system similar to that used in propane refrigerators. The refrigerator consists of two separate units; the solar collector-generator and the refrigerator box.
The collector-generator consists of a thermal solar collector and most of the refrigeration works. It needs to be mounted in a sunny location, the same as any solar collector.
The refrigerator box is the refrigerator per se and can be placed wherever is convenient, presumably the kitchen.
When the sun shines, the collector-generator produces ammonia refrigerant, which is stored until night when the actual cooling takes place. To keep the refrigerator cold through the day and during cloudy weather, there is built-in storage. There are no moving parts.
In use, our solar refrigerator is little different from any other refrigerator. It’s designated to have automatic defrost. Currently, the drawbacks are a greater temperature variation since there is only one cycle per day.
We are also prototyping a very small unit where the refrigerator box is under the solar collector so it is all one unit that is left outside. This is meant to be used for vaccines and to be as low cost and simple as possible. We intend to include a freezer for a limited ice-making capacity, as this simplifies the design.
We have been looking seriously at auxiliary cooling for prolonged cloudy spells. We are trying an external heat pipe for colder locations and thermoelectric cooling for warmer locations. These have the advantage of being relatively inexpensive and can be offered as add-ons instead of requiring extensive redesigning.
We are also considering two technologies, which would add to the expense but make a better product. One of them is Aura vacuum panel insulation. The advantage is better insulation and thinner walls, resulting in a smaller cabinet. The disadvantages are higher cost and no guarantees that the product will be able to hold its vacuum for extended time.
The other technology we are considering is keeping the cold storage outside at the solar collector and using a pump to circulate the cold into the refrigerator. This would add significantly to the expense and require electricity, but would simplify installation and keep ammonia out of the living space.

We feel that safety; particularly in transportation and installation is a significant issue that needs to be thoroughly looked into.

Three simple factors, which will make Sun Frost an efficient refrigerator

1) It is proposed that the heating unit - and all the heat it generates -to the top of the unit. The heat from a typical refrigerator (since the compressor is on the bottom) rises and constantly creates an electric blanket of air around the refrigerator.

2) The small well designed heating unit here operating on intermittent cycle, lack of fans and the low percentage run time all contribute to Sun Frost's exceptionally quiet operation.

3) The designing aspect of the Sun Frost's includes polyurethane insulation of 3-inches thick in the refrigerator walls and up to 6-inches at the freezer top to keep the heat away from your frozen foods.

These factors combine to eliminate the reasons that most average refrigerators seem to be running all the time. Sun Frost's higher initial cost is offset by their incredible efficiency. This makes the idea of a solar refrigerator practical. Conventional AC refrigerators just take too much electricity.

ADVANTAGES:

NO FOSSIL FUELS

The SUN FROST provides a means of storing vaccines and medical supplies without the use of fossil fuels. Not only is the need for a fuel supply eliminated, but also the unit operates more reliably than kerosene-powered refrigerators.

THE MOST EFFICIENT REFRIGERATOR

The cost of a solar power system is typically more than the cost of the refrigerator, so efficiency is of prime importance in reducing system costs. As a result of the low energy consumption of the Sun Frost, the cost of the power system will be reduced

The SUN FROST refrigerator employs unique design innovations to achieve its exceptionally low energy consumption.

The top mounted condenser on the SUN FROST RFVB is accessible and easy to clean, allowing the cooling system to continue running efficiently. Eliminating the need for fans, which consume energy and generate unwanted heat and noise, further increases the efficiency of the cooling system.

ICE STORAGE FURTHER INCREASES SYSTEM RELIABILITY

The relatively large freezer in the RFVB can easily hold 4 kilograms of ice. This ice may be transferred to the refrigerator section if the cooling system is not in operation due to refrigerator failure, loss of power, or an exceptionally long overcast period.

The 4 kilograms of ice now stored in the super-insulated refrigerator section will keep the stored vaccines cold for approximately 2 days during prolonged overcast conditions.

DEFROSTING: A SIMPLE MATTER

When defrosting is needed, it is fast and easy. Just turn off the refrigerator for about 30 minutes. Since ice forms only on the flat, easily cleaned surfaces, it comes off in large pieces. There are no irregular shapes and ducts to grip and hold the ice, and no water to mop up.




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