Designing of Evaporator

I'd start with basics on heat transfer to cover the general aspect of your question.

Then you move on to look into Absorption_refrigerator systems and its inner details.

Then you can start designing a system like this. Is this for an air conditioning system?

Answers are given in the link. Keep it low!

Yes it is air refrigeration system. I want air at 25 deg C so do I need to keep temperature of evaporator = -33 deg C at 1 bar (which is economic) or 10 deg C at 6 bar will do my work? (costly, maintaining high pressure is costly).

Now as refrigeration is caused by chilling water which passes through evaporator and gains heat from the air inside the room. Does the evaporator temperature creates any difference?

Did you read the wiki article? Water at -33 deg 1 bar is ice!

Low chance of evaporation there! You need to get your process definition right and /or your terminology.

Maybe it is not our fault! Asking an engineer something that is obvious to him might not get you any results because:

1. engineer does not understand the question

2. there is a possibility an engineer answers too complicated where an easy answer could have done (see point 1)

3. The answer will not be understood even so it covers the question quite well.

Ice evaporation is called sublimation right?

Which point you are talking about? Can you write it again. I am not able to find it.

the refrigerant is not water, it is ammonia

Refer to point one in my first post then!

You need to cover your basic heat transfer questions!

I will cover it. Can you give some solution rather than advice!

I am usually getting paid for solutions. You are not asking for a solution or do you?

You are asking for advice, right?

So my advice would be to make a schematic and then put all process parameters that you are interested in on that schematic and do the necessary calculations of what teh other parameters can and should be.
You start with the known parameters and calculate all others based on the physical processes that you know are taking place in the places called evaporator, condensor and so forth....

The thing you are looking for and helps you the most is "effort"!

The evaporating temperature should be about 10dC, maybe as low as 5dC, but definitely no lower than 0dC, or else the coil will freeze up.

"Air conditioning".

There is no need to design. One simply gives parameters to suppliers and selects.

You must get to the basics of heat...what you are concerned with is removing heat from one place and transferring it to another place....To determine the amount of heat you must convert to BTU's...To get that you must calculate heat load....

http://absorptionchiller4u.blogspot.com/search/label/absorption%20chiller

The drop of temperature across the evaporator coil is relative to the incoming air temperature, relative humidity, and volume vs the size and capacity of the coil.... so it changes...that's why we have thermostatically controlled expansion valves...typically the air temperature drop can be anywhere from 14°F to 22°F.....The size and capacity of the evaporator coil is sized to the volume of air you need to condition, typically 400cuft a minute, per ton(12,000 btu's) of cooling...the temperature of the evaporator coil needs to consistently be below the dew point of the air you are conditioning...

why plagiarize work that was figured out before you wee born?

Your question implies that you are directly cooling room air in the evaporator. You shouldn't do this, as it creates a safety hazard. In the event of a leak, you'd be leaking deadly ammonia into the closed space. That is one reason a chilled water loop is used.

No. I am not directly cooling the space. Heat is first transferred to chilling water from evaporator then it transferred to the room.

<...to chilling water from evaporator then it transferred to the room...>

That doesn't make sense. The purpose of a chilled water circuit is to remove heat, not to add it to a room.

Is this project in need of a properly-experienced local Process Engineer? If so, then do hire one.

So air conditioning is out the door. We are into heating now. Fine. Next advice is there is no evaporator needed.

Amendment to post 7.

With a secondary coolant (water) involved, the ammonia evaporating temperature can be a bit lower, say 2-4dC; with an evaporator pressure regulator to ensure it goes no lower.

Wow! Just a couple of days ago, you were wondering how a condenser worked and now you are designing a condenser!

Do you have a formal education in engineering?

You need a supply of cold water below 25C fed to an air-cooler (a heating radiator in reverse) that will take heat from the air at 40C - maybe with thermostats to regulate it to 25C.

Heat transfers at a rate proportional to the temperature difference and area of the cooler. The 'hot' water goes back to the evaporator where it is cooled down to below 25C but above 0C (to avoid ice).

You need to do heat balance calculations to work out air-cooler areas and temperature difference of the inlet and outlet cooling water, and reflect this back to the evaporator.

Providing your system is large enough to handle full load, for practical reasons it does not matter too much what the absorber temperature/pressure is, as long as the temperature controls within the absorber are set to prevent freezing of the cooling water.

Over simplified, a thermostat on the air-cooler to prevent room air going below 25C and an absorber with controls to prevent water freezing is all you need worry about. Internal temperatures and pressures will be whatever is needed to operate the system with these parameters.

Air Conditioners are highly dependent on air flow across the evaporator coil. Fan speed is essential to the evaporation process in the system. There is no set temperature for evaporator it varies the ambient air for expert's suggestions visit http://www.manta.com/c/mtplqyr/amtek-air-conditioning-inc. A good rule of thumb is a 20 degree drop between the nearest supply from the evaporator and the return air supply.