Parts of refrigeration cycle 2

Parts of refrigeration cycle 2

2 -Condensers

In condensers the refrigerant gives up the heat that is has absorbed in the evaporator. There are three main types of condensers: air cooled condensers, water cooled condensers and evaporative condensers.

There are four main parts of refrigerating and air-conditioning systems, these are: compressor, condenser, throttling or expansion valve and the evaporator. The refrigerant leaving the compressor is in the gaseous state and at a high pressure and temperature. This refrigerant then enters the condenser where it loses the heat to the coolant, which can be air or water. 

After passing through the condenser the refrigerant gets condensed but still remains at high pressure. It comes out in a partially liquid and gaseous state and then enters the throttling or expansion valve. 

There are three types of condensers: air cooled, water cooled and evaporative. These have been described below.

1) Air cooled condensers: 

Air cooled condensers are used in small units like household refrigerators, deep freezers, water coolers, window air-conditioners, split air-conditioners, small packaged air-conditioners etc. These are used in plants where the cooling load is small and the total quantity of the refrigerant in the refrigeration cycle is small. Air cooled condensers are also called coil condensers as they are usually made of copper or aluminium coil. Air cooled condensers occupy a comparatively larger space than water cooled condensers. 

Air cooled condensers are of two types: natural convection and forced convection. In the natural convection type, the air flows over it in natural a way depending upon the temperature of the condenser coil. In the forced air type, a fan operated by a motor blows air over the condenser coil. 

2) Water cooled condensers: 

Water cooled condensers are used for large refrigerating plants, big packaged air-conditioners, central air-conditioning plants, etc. These are used in plants where cooling loads are excessively high and a large quantity of refrigerant flows through the condenser. 

There are three types of water cooled condensers: tube-in-tube or double pipe type, shell and coil type and shell and tube type. In all these condensers the refrigerant flows through one side of the piping while the water flows through the other piping, cooling the refrigerant and condensing it. 

3) Evaporative condensers: 

Evaporative condensers are usually used in ice plants. They are a combination of water cooled and air cooled condensers. In these condensers the hot refrigerant flows through the coils. Water is sprayed over these coils. At the same time the fan draws air from the bottom side of the condenser and discharges it from the top side of the condenser. The spray water that comes in contact with the condenser coil gets evaporated in the air and it absorbs the heat from the condenser, cools the refrigerant and condenses it. 

Evaporative condensers have the benefits of water cooled as well as air cooled condenser, hence it occupies less space. However, keeping the evaporative condenser clean and free of scale is very difficult and requires lots of maintenance. Hence they are not favoured by HVAC designers.

Parts of refrigeration cycle

Introduction and Parts of refrigeration cycle 

Before I talking in detail about the refrigeration cycle , we must review some physical lows which all of refrigeration cycles depends on it , its only five laws : 

Laws of refrigeration cycle 

1- Fluids absorb heat when it converted from liquid to gas and giving heat when it converted from gas to liquid . 

2- Fluid can switsh to another phase at the same temperature degree and pressure . 

3- Heat transfer only from the high temperature body to the lower one . 

4- Metal parts of condenser and evaporator must be have a good connecting to heat . 

5- Thermal energy and other form of energy can switch to another one .

Basic refrigeration cycle 

As I say the basic idea is to absorb heat which happen by converting liquid to gas or on another word evaporating liquid and after that we pump the gas by using compressor and at this point the temperature and pressure of the refrigerant raise, so we getting this raise .. out by the condenser which convert the gas to liquid by losing the heat . 

So the main parts of the refrigeration cycle will be : 

1- Compressor 

2- Condenser 

3- Expansion valve 

4- Evaporator

1] Compressor

Types of Compressors 

There are a number of different types of compressors used for refrigeration and air conditioning. Like pumps, all "heat pumps" can first be categorized as either positive displacement or non-positive displacement (centrifugal). Positive displacement compressors have chambers which decrease in volume during compression, while non-positive displacement compressors have fixed-volume chambers. This video explains visually: 

Beyond this distinction, each type differs based on its specific mechanism for fluid compression. The five main types of compressors are piston, rotary, screw, scroll, and centrifugal.

Piston Compressors

Piston compressors, also called reciprocating compressors, use a piston and cylinder arrangement to provide compressive force - like combustion engines or piston pumps. The reciprocating motion of the piston due to external power compresses the refrigerant inside the cylinder. Piston compressors have a low initial cost and a simple, easy to install design. They have a large power output range and can reach extremely high pressures. However, they have high maintenance costs, potential vibrational issues, and are not typically designed to run continuously at full capacity.

     

                  

 Rotary Compressors

Rotary compressors have two rotating elements, like gears, between which the refrigerant is compressed. These compressors are very efficient because the actions of taking in refrigerant and compressing refrigerant occur simultaneously. They have very few moving parts, low rotational speeds, low initial and maintenance costs, and are forgiving in dirty environments. However, they are limited to smaller volumes of the gas and produce less pressure than other types of compressors.

                                 Rotary vane compressor

Screw Compressors

Screw compressors use a pair of helical rotors or screws which mesh together to compress the refrigerant between them. They can produce high pressure for a small quantity of gas and consume less power than reciprocating compressors. They have low to medium initial and maintenance costs and few moving parts. However, they have difficulty in dirty environments, high rotational speeds, and shorter life expectancies than other designs.

                                             Screw compressor 

Scroll Compressors

Scroll compressors use two offset spiral disks nested together to compress the refrigerant. The upper disk is stationary while the lower disk moves in orbital fashion. Scroll compressors are quiet, smooth-operating units with few moving parts and the highest efficiency ratio of all compressor types. They also are more flexible for handling refrigerants in the liquid. However, as fully hermetic designs, scroll compressors cannot be easily repaired. They also typically cannot rotate in both directions. Scroll compressors are commonly used in automobile air conditioning systems and commercial chillers.

                                            Rotary vane compressor 

Centrifugal Compressors 

Centrifugal compressors use the rotating action of an impeller wheel to exert centrifugal force on refrigerant inside a round chamber (volute). Unlike other designs, centrifugal compressors do not operate on the positive displacement principle, but have fixed volume chambers. They are well suited to compressing large volumes of refrigerant to relatively low pressures. The compressive force generated by an impeller wheel is small, so systems that use centrifugal compressors usually employ two or more stages (impellers wheels) in series to generate high compressive forces. Centrifugal compressors are desirable for their simple design, few moving parts, and energy efficiency when operating multiple stages.

                                                             Centrifugal compressor