2 replies to this topic

[ChemicalEngineer101]

Good afternoon, I'm a junior process engineer and I'm sizing a horizontal condenser with condensation in the shell side - vapor shell side and cooling water in tubes. I'm having trouble with the velocities.

Through Coulson and Richardson vol.4 in shell side the velocities in heat exhanger should be:

 

Gas - 15 to 30 m/s

Liquids - 0.3 to 1 m/s

 

So far, I have not been able to get both conditions straight and probably never will (difference in phase density 1000 kg m-3 to 0,75 kg m-3 ----> 1000x lower velocity with liquid compared to gas fluid for the same mass flow).

What velocity condition should I prioritize, liquid or as velocity?

 

Ty everyone in advance.

 

 

[Pilesar]

Please provide the reference from Coulson and Richardson for the 'should velocity' for your condenser. Is that velocity range quoted in a particular problem solution? I have not seen shell side velocity constraints for condensers presented like that before and I am suspicious that the rule you blame them for may be misquoted.

   Are you sizing the exchanger by hand calcs or are you using some sort of software? What is your condensing fluid? What is your exchanger configuration? Supplying more info about the heat exchanger service would help in providing a good answer to your questions. Is the shell side fluid entering at the dew point and to leave at the bubble point? If so, then the velocities in the exchanger vary considerably because of phase change.The liquid falls to the bottom of the shell and is just in the way of the heat transfer until it exits unless you have a subcooling requirement. Therefore, why would it matter to you what the liquid velocity is? Are you concerned about vapor velocity because of possible impingement damage to the tubes or for some other reason? In general when designing condensers, the pressure drop is of much higher importance than velocity. If you are designing a real piece of equipment, I suggest you have an experienced designer review your work and explain why they would make changes. If this is an academic exercise for you, then many of the details won't matter.

 

[Bobby Strain]

Sounds like a student question. Since no professional designs without software.

 

Bobby