Cooling a pipe: external refrigerant flow

[cornelius]

I have to cool a steel pipe to an average temperature of 0 C. It will be a dx system. Water is passing inside. Basically it is a chiller. However i want the refrigerant flow out of the pipe. Usually and always the opposite is used so i cant find information on it. How will i design it? I am new in refrigeration business but i am good at computational fluid dynamics. I just dont know where to start.

[desA]

Try a few good heat-transfer books to assist you on the thermal design side - it's not overly difficult.

Be a little careful on the pipe size for the outer tube, due to the high pressures in refrigeration systems. This would seem to be one reason as to why the refrigerant is often (not always) contained in small diameter, inner tubes.

[cornelius]

The water side works well. I performed tests with cold water and i got what i want. This is an evaporator unit. I know that suction takes place here. How can we see high pressures?

The pipe has a diameter of 70 mm and a thickness of 1.5 mm. The evaporator should have a capacity of 6 kw. I have a design in mind for the refrigerant flow. However gravity is another issue.

[Peter_1]

The water side works well. I performed tests with cold water and i got what i want. This is an evaporator unit. I know that suction takes place here. How can we see high pressures?

The pipe has a diameter of 70 mm and a thickness of 1.5 mm. The evaporator should have a capacity of 6 kw. I have a design in mind for the refrigerant flow. However gravity is another issue.

Suction pressure: you're a EU citizen, so you must comply with EN378. Your test pressure is ways higher then your suction pressure.
Inlet of your refrigerant top or bottom? Very important for your oil return. Superheat control also in this pipe?

Why would you flow the water in the inner tube? What's the advantage?
6 kW is a lot for a single pipe, you don't have much area/surface to exchange heat.

[cornelius]

The tube in the image is covered with spiral wire. This wired tube is put in an other steel tube assuring that the surrounding tube's inner wall contacts the spiral wire. This way the refrigerant flows in the spiral channel between the wires. I want refrigerant to touch, contact the inner pipe on its entire surface. I guess this part is not that easy. However if i decrease the diameter of the wire so the height of the channel this also may be possible.

The refrigerant enters the exchanger from one side and exits from the other side. I thought that the system is very similar to a spiral tube so if i provide the right velocities there should be no oil problem.

Water side is ok. It works pretty well. 6 kw heat transfer was managed at tests. Water should flow in pipe. It has some advantages related to fouling and cleaning. I did not think much about superheat control. we ll connect a factory set txv. What do u think?

[Peter_1]

Something like this http://www.refrigeration-engineer.com/forums/misc.php?do=showattachments&t=2690

[cornelius]

Yes but only innner side of the spiral should be cooled. Any other dx evaporator design (refrigerat not in tube) like plate heat exchangers may be helpful. I think i am doing something new.

[Peter_1]

I think i am doing something new.
Oh no, all cooled drink fountains works this way.

[cornelius]

Oh no, all cooled drink fountains works this way.

Good. :D I wrote it to take this reply. how do they work? Or any image, view of them.

[Peter_1]

http://www.drinkingfountaindoctor.com/_Breakdowns_Main.html

[cornelius]

Peter,

Unfortunately, in drinkingfounatindoctor I could not find what i need. I did a literature survey on drinkingfountains and saw that evaporator is a tank like unit surrounded by coils.

I ll be happy if someone made an evaporator like mine since it is hard to design such a thing.

[chemi-cool]

Hi cornelius,

A few years ago I have installed a cooling pipes on liquid line on water chillers.

Inner pipe was 2 5\8 and wrapped around it was a 3\8 pipe and the whole thing was insulated. liquid refrigerant inside and cold water outside. If I remember right, it was about 1m long.

[sterl]

http://www.scribd.com/doc/16148849/ISHMT08

Try above, its CFD based and near what you are chasing...

There's a whole lot on the web about helical wrapped exchangers as well as using spiral finned pipes as heat exchangers, by sliding a shell over a single spiral finned pipe.