Step 1

Acquire  refrigeration and air conditioning tools , refrigerants and components  (parts) catalogues from their suppliers and manufacturers.

Step 2

Carryout your calculations and readjust your requirements according to the parts specifications mentioned in catalogues. 

It really comes down to economics and your specific scenario. The three big components are usually the compressor and the two heat exchangers. You might also use a turboexpander in place of an expansion valve.

In small refrigeration plants, the compressor is usually an off-the-shelf component. Like a pump or fan, it has a performance curve. You normally want it to operate at one speed in the high efficiency zone. If your application has variable demand, you might consider a buffer tank, a variable speed drive, or a parallel system.

Heat exchangers are a little more interesting. With a vapour compression cycle, you probably aren't using direct contact exchangers in the main circuit, but you might in the heat exchange fluid circuits (e.g. cooling tower).

Ultimately, the design is based on cost. You need to meet the specification with the minimum NPV. The system has a capital cost and its operation has a cost in power, maintenance and replacement, and any penalty costs for failing to meet demand. Minimize the cost function and you have an optimized design.

If you need help with the Actual Fins involved for your Heat Exchangers in your refrigeration system, let me know.  that's my expertise. fins for Condensers, Evaporators, Heaters, Etc.

just get bhold of refrigeration handbook,  not the theoretical text book...inh handbokk you are given all the practical solutions, then innovate to meet your needs.

the purpose of a refrigeration cycle is to remove heat from as space. calculate/determine the heat load first. then, know the target space (heat source) and heat sink (ambient) temperatures so you may pinpoint your operating pressures. maybe then, you can start sizing up everything else, most especially the coolant type.

 Amin, I'm sorry to say,  i have bad news, we as USA Citizen's are unable to do business with the country of Iran.  unfortunately i won't be able to participate or communicate with you on this project.  my colleague also is not allowed that i mentioned on the phone.   hope you find your answers, and find help.  sorry.

You have not provided any information on what you are trying to achieve.  

The first step - is to define your end product.  i.e. - are you cooling liquid or gases and at what temperature, you want to cool it.

second step - From there you need to do you thermodynamic analysis.  How much cooling do you need to do (in BTU/HR or kW)

From this you will be able to design the evaporator or find an existing unit that will do the work.  if this is a industrial application and you are design all of the components then:

A refrigeration system has 4 main component, the evaporator, the compressor, the condenser and the TX valve.  Once you have a clear specification for the evaporator, then you find a compressor that will provide the suction for the evaporator.  Then you define your medium to reject the heat absorbed in the evaporator plus the mechanical work of the compressor.  Finally you need do get a matching tx valve.  Once you have done a first cycle, start over and optimize it.

Good luck