difference between air refrigeration system and vapour compression system
Answers
Here are two diagrams of the vapour compression cycle..
The four processes are Vaporization (Evaporation), Compression, Condensation and Expansion.
The first diagram shows the refrigeration circuit, and the second is the T-S diagram..
The process starts with vaporisation of the refrigerant in the evaporator. This is complete at point 1. Compression is used to raise the pressure of the refrigerant, point 2 so that it can condense at a higher temperature..When all the vapour has condensed at point 3..
the pressure is reduced in an expansion device and the refrigerant is returned to its original condition 4..
Notice that Expansion is a constant enthalpy process. It is drawn as a vertical line on the T-S diagram. No heat is absorbed or rejected during this expansion, the liquid just passes through a valve, like water coming out of a tap. The difference is, that because the liquid is saturated at the start of expansion by the end of the process it is partly vapour. Point 1is on the curve..
The refrigerant at the begining of the vaporization is already partly evaporated!
How much?
This depends on the shape of the curve, and the start and end pressures.
On the other hand the Compression process is shown as a curve. It is not a constant enthalpy process. The energy used to compress the vapour turns into heat, and increases its temperature. This tends to raise the temperature of the vapour, making point 2 move further and further into the superheated part of the diagram as compression progresses. Point 2 is outside the curve and not on the curve as described in the Compression process. This means that before Condensation can start, the vapour has to be cooled down.
There are still a few more tricks to learn before this cycle can be turned into a practical ready-to-go refrigeration machine. Find out what they are by looking at the Simple Practical Cycle.
Maximum Efficiency of the Vapour Compression Cycle..
It takes a lot of heat to evaporate liquid. In other words a small amount of liquid circulating in a refrigerator can perform a large amount of cooling. This is one reason why the vapour compression cycle is widely used. The refrigeration system can be small and compact. Also from a practical point of view heat exchange is much better when using change of state - evaporation and condensation. However the expansion of the high pressure liquid, process 3-4 above is non reversible. And so the efficiency of this cycle can never even approach Carnot effciency.
Air cycle refrigeration
Air cycle refrigeration systems use air as their refrigerant, compressing it and expanding it to create heating and cooling capacity.
Air cycle is not a new technology. Air cycle or ‘cold air machines’ were available from companies 1900s. These were used on board ships and by food producers and retailers to provide cooling for their food stores.
However, the development of vapour compression cycles, based initially on ethyl ether, ammonia or sulphur dioxide, but superseded by chlorofluorocarbons (CFCs) led to the gradual replacement of the majority of air cycle systems, except in the field of aircraft air conditioning.
Environmental concerns about CFCs, ozone depletion, global warming and the resulting increasingly stringent legislation have renewed interest in alternatives to the current standard of vapour-compression refrigeration technologies.
The use of air cycle is one of these, offering a benign substitute for CFC refrigerants as well as reduced energy consumption and capital costs for targeted applications.
Why use air cycle?
Air cycle systems have specific advantages that apply to all potential applications:
The working fluid (air) is free, environmentally benign, safe and non-toxic..
Air cycle equipment is extremely reliable, reducing maintenance costs and system down-time..
The performance of an air cycle unit does not deteriorate as much as that of a vapour-compression unit when operating away from its design point
When operating in a refrigeration cycle, an air cycle unit can also produce heat at a useful temperature.. If this is used together with the cooling, highly efficient, low energy processes are possible..
Air cycle units can produce a much higher temperature difference between the hot and cold sides compared to vapour-compression units.
This means that:
o Very cold air can be produced for near-cryogenic processes
o Heat can be produced at a useful temperature, which, if used together with the cooling, can result in highly efficient, low energy processes .
plzz mark me as brainliest my dear !!!
The difference between the air refrigeration system and vapour compression system is that in the air refrigeration system, compressed air is used while in the vapour compression system, liquid refrigerant is used which is changed to vapour.
Explanation:
- The differences between air refrigeration system and vapour compression system are given below:
Air Refrigeration system:
- In this system, the compressed air is cooled in the air cooler and then passed through the cooling turbine.
- This turbine drives a fan that draws the cooling air through the heat exchanger.
- The discharge of the air from the turbine occurs at a pressure slightly above the cabin pressure.
- The additional temperature rise of the cooling air is avoided by putting a fan on the downstream.
- This system is suitable for ground cooling as the fan driven by the turbine acts as a source of cool air for the heat exchanger.
Vapour compression system:
- In this system, the circulation of a liquid refrigerant is done through the four stages of a closed system.
- The heat is absorbed as the refrigerant turns and is expelled by the system that lowers the temperature of the air-conditioned space.
- The rotation of the refrigerant through the system alternately compresses and expands it, changing it from a liquid to a vapour.
#SPJ2
