What is Refrigeration?
Refrigeration deals with cooling of bodies or fluids to temperatures lower than those of surroundings. This involves absorption of heat at a lower temperature and rejection to higher temperature of the surroundings.
In olden days, the main purpose of refrigeration was to produce ice, which was used for cooling beverages, food preservation and refrigerated transport etc. Now-a-days refrigeration and air conditioning find so many applications that they have become very essential for mankind, and without refrigeration and air conditioning the basic fabric of the society will be adversely affected. Refrigeration and air conditioning are generally treated in a
single subject due to the fact that one of the most important applications of refrigeration is in cooling and dehumidification as required for summer air conditioning. Of course, refrigeration is required for many applications other than air conditioning, and air conditioning also involves processes other than cooling and dehumidification.
Applications of Refrigeration
For convenience of study, refrigeration applications may be grouped into six general categories:
1. Domestic refrigeration.
2. Commercial refrigeration.
3. Industrial refrigeration.
4. Marine and transportation refrigeration.
It will be apparent in the discussion which follows that the exact limits of these areas are not precisely defined and that there is considerable overlapping between the several areas.
1. Domestic Refrigeration
Domestic refrigeration is rather limited in scope, being concerned primarily with household refrigerators and home freezers however, because the number of units in service is quite large, domestic refrigeration represents a significant portion of the refrigeration industry.
Domestic units are usually small in size, having power input ratings of between 35 W and 375 W and are of the hermetically sealed type. Since these applications are familiar to everyone, they will not be described further here. However, the problems encountered in the design and maintenance of these units can be studied from any standard book regarding Refrigeration and Air Conditioning.
2. Commercial Refrigeration
Commercial refrigeration is concerned with the designing, installation, and maintenance of refrigerated fixtures of the type used by retail stores, restaurants, hotels, and institutions for the storing, displaying, processing, and dispensing of perishable commodities of all types.
3. Industrial Refrigeration
Industrial refrigeration is often confused with commercial refrigeration because the division between these two areas is not clearly defined. As a general rule, industrial applications are larger in size than commercial applications and have the distinguishing feature of requiring an attendant on duty, usually a licensed operating engineer. Typical industrial applications are ice plants, large food- packing plants (meat, fish, poultry, frozen foods, etc.), breweries, creameries, and industrial plants, such as oil refineries, chemical plants, rubber plants, etc. Industrial refrigeration includes also those applications that are concerned with the construction industry.
4. Marine and Transportation Refrigeration
Applications falling into this category could be listed partly under commercial refrigeration and partly under industrial refrigeration. However, both these areas of specialization have grown to sufficient size to warrant special mention Marine refrigeration, of course, refers to refrigeration aboard marine vessels, and includes, for example refrigeration for fishing boats and for vessels transporting perishable cargo as well as refrigeration for the ships stores on vessels of all kinds.
Transportation refrigeration is concerned with refrigeration equipment as it is applied to trucks, both long distance transports and local delivery, and to refrigerated railway cars. Typical refrigerated truck bodies are shown below:
What is Air Conditioning?
As the name implies, air conditioning is concerned with the condition of the air in some designated area or space This usually involves control not only of the space temperature but also of space humidity and air motion, along with the filtering and cleaning of the air.
- Comfort Air Conditioning
Any air conditioning which has as its primary function the conditioning of air for human comfort is called comfort air conditioning. Typical installations of comfort air conditioning are in homes, schools. offices, churches, hotels, retail stores, public buildings, factories automobiles, buses trains, planes, ships, etc.
2. Industrial Air Conditioning
On the other hand, any air conditioning which does not have as its primary purpose the conditioning of air for human comfort is called industrial air conditioning. This does not necessarily mean that industrial air conditioning systems cannot serve also as comfort air conditioning coincidentally with their primary function. Often this is the case, although not always so.
The applications of industrial air conditioning are almost without limit both in number and in variety. Generally speaking, the functions of industrial air conditioning systems are to
- control of moisture content by hydroscopic materials.
- govern the rate of chemical and biochemical reactions.
- limit the variations in the size of precision manufactured items because of thermal expansion and contraction.
- provide clean, filtered air which is often essential to trouble- free operation and to the production of quality products.
The preservation of perishable commodities, particularly foodstuffs, is one of the most common uses of mechanical refrigeration. As such, it is a subject which should be given consideration in any comprehensive study of refrigeration.
At the present time, food preservation is more important than ever before in man’s history. Today’s large urban populations require tremendous quantities of food, which for the most part must be produced and processed in outlying areas. Naturally, these foodstuffs must be kept in a preserved condition during transit and subsequent storage until they are finally consumed. This may be a matter of hours, days, weeks, months, or even years in some cases. Too, many products, particularly fruit and vegetables are seasonal. Since they are produced only during certain seasons of the year, they must be stored and preserved if they are to be made available the year round.
As a matter of life or death, the preservation of food has long been one of our most pressing problems. Almost from the very beginning of our existence on earth, it became necessary for us to find ways of preserving food during seasons of abundance in order to live through seasons of scarcity. It is only natural, then, that man should discovery and develop such methods of food preservation as drying, smoking, pickling, and salting long before he had any knowledge of the causes of food spoilage. These rather primitive methods are still widely used today, not only in backward societies where no other means are available but also in the most modern societies where they serve to supplement the more modern methods of food preservation. For instance, millions of pounds of dehydrated (dried) fruit, milk, eggs, fish, meal, potatoes, etc, are consumed in the United States each year, along with huge quantities of smoked, pickled and salted products, such as ham, bacon, and sausage, to name only a few. However, although these older methods are entirely adequate for the preservation of certain types of food, and often produce very unusual and tasty products which would not otherwise be available, they nonetheless have inherent disadvantages which limit their usefulness. Since by their very nature they usually bring about rather severe changes in appearance and taste, which in many cases are objectionable. They are not universally adaptable for the preservation of all types of food products. Furthermore, the keeping qualities of food preserved by such methods are limited as to where a product is to be preserved indefinitely or for a long period of time, some other means of preservation ordinarily must be utilized.
The invention of the microscope and the subsequent discovery of microorganisms as a major cause of food spoilage led to the development of canning in France during the time of Napoleon. With the invention of canning, man found a way to preserve food of all kinds in large quantities and for indefinite periods of time Canned foods have the advantage of being almost entirely imperishable, easily processed, and convenient to handle and store. Today, more food is preserved by canning than by all other methods combined. The one big disadvantage of canning is that canned foods must be heat sterilized, which frequently results in over cooking Hence, although canned foods often have a distinctive and delicious flavor of their own, they usually differ greatly from the original fresh product.
Principles of Refrigeration and Air conditioning Second Edition by Roy J. Dossat.
Lesson 3 Applications Of Refrigeration & Air Conditioning, Version 1 ME, IIT Kharagpur.