refrigerant velocity in evaporator

[patrickj]

Hi Peter,
There is adifferent angle to the oil problem. For proper oil seperation there should be sufficient discharge super heat.Ex in case of R22 more than 25 deg F.Say your compressor runs with liquid flood back or sucking wet vapour you normally end up with oil problems

[Superheatman]

Hi Peter,
There is adifferent angle to the oil problem. For proper oil seperation there should be sufficient discharge super heat.Ex in case of R22 more than 25 deg F.Say your compressor runs with liquid flood back or sucking wet vapour you normally end up with oil problems

Hi...I think this thread is about a reciprocating unit where it would be the suction superheat that is important to stop refrigerant flooding to the compressor......the discharge superheat as applicable to oil seperation is normally when there are mesh seperators on the discharge side of screw compressors.Best regards etc

[Gary]

Comming back to my original question. In attachment you will find a picture of the evaporator.
It consists of 2 coils. One coil for the refrigerant (R134a) and the second one for the fluidum to be cooled.
The refrigerant goes through the distributor, through the distibutor lines (which to me are not optimally positioned), and than the refrigerant does in to a 5/8" (smooth) horzontal tube. The length is 6 m. In the middle of the coil (at the end of the tube) the tube goes up to a next level, and in to a 2nd layer of a 6 m 5/8" tube. This 2nd level tube also stays horizontal and goes from the inside to the outside of the coil.
Comming outside it goes into a header.
So you have 18 layers of a 6 m tube, and 9 circuits. In the middle of each circuit you have a difference in height of 16 mm (5/8").
This evaporator is put into a glycol solution and the compressor is controlled by a thermostat in the glycol.
I have calculated the velocity of the gas comming out of each circuit : 0,65 to 0,8 m/s depending on the conditions and the type of compressor used on the evaporator.
I compare this to the values that i can calculate on 'standard' heat exchangers (like shell and tube heatexchangers from Heatcraft) : I get values between 2,8 and 6 m/s. Can any one confirm these values?

Is the evaporator in the picture upside down?

[BESC5240]

Is the evaporator in the picture upside down?

Dear Gary,
No it isn't.
The condensing unit is mounted under the the evaporator.

[Gary]

Seems to me that it would work much better if the flow were reversed. Each path would be downhill all the way, instead of uphill. Velocity is only important where refrigerant vapor is trying to push oil uphill.