Shell & Tube Evaporators – Common Misunderstanding
Shell & tube evaporators are nothing more than a vessel with numerous tubes internally designed to transfer heat into the mechanical refrigeration system from a liquid source. There are vertical shell & tubes that commonly make tubed ice, horizontal shell & tubes referred to as chillers, and even some used on the high side to cool compressor oils that are simply referred to as oil coolers.
Looking to the steam industry and stationary boilers, we have fire-tubed boilers and water-tubed boilers. Both of these designs are simple shell & tubes. One method the water is in the shell while the fire is in the tubes (Fire-tube), and the other method the water is in the tubes and the fire is in the shell (water-tube). Seeing that these common industrial devices can be designed either or, I ask you to consider the same to industrial ammonia refrigeration evaporators acting as a shell & tube by function.
Sometimes design engineers will plumb the refrigerant to be in the shell while the liquid secondary coolant to be cooled in the tubes, and in other applications withing the same system you will see just the opposite.
- Misconception #1
- Some have stated that is it is called a “shell & tube” the refrigerant is in the shell, and if it is called a “tube-in-shell the refrigerant is in the tubes. I would try to stay away from identifying the two as far as I possibly could between those specific play on words.
- Misconception #2
- The refrigerant is always in the shell.
- Misconception # 3
- If flooded by design the refrigerant is the shell and if DX by design the refrigerant is the tubes.
- Misconception #4
- That all shell and tubes are open shells, some have baffle plates and with this design only allows the refrigerant changing state to be in the tubes.
The science is this. Whatever fluid is plumbed through the end caps is the only fluid in the tubes. Whatever fluid is plumbed into the shell is the only fluid in the shell. So, an operator needs to not to assume one or the other because sometimes the refrigerant is in the shell, sometimes the refrigerant is in the tubes, and in cascade refrigeration designs you might even have a refrigerant in the shell and another refrigerant in the tubes.
You as an operator must walk up to each and every shell & tube and make distinctive evaluations of what it is. If the refrigerant is in the end caps – then refrigerant is in the tubes. Some shells are baffled. Baffled shells must have the refrigerant in the tubes. However, one cannot determine the shell & tube is baffled by looking at the unit or name plate.
Shell & Tube – Refrigerant in the Shell
Shell & Tube – Refrigerant in the Tubes
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