3 replies to this topic

[CHEMSTRONG]

Dear sir,

 

I have a shell and tube heat exchanger wherein in datasheet, it is mentioned that No of shells in parallel is 1 and nof of shell in series in one. We have only one Shell in heat exchanger, then why we need these details? What is the meaning of this for exchanger?

 

Also in pressure drop details of datasheet, it is mentioned that allowable/calculated pressure also. What is the diff between them?

 

Please help me understand this in lucid way.

 

Regards,

Chetan Chavan

[Technical Bard]

The datasheet has space for shells in parallel and series because some services will be greater than 1.  The one you are looking at does not, so the fields are filled with ones.

 

For pressure drop, the "allowable" is how much pressure drop the process engineer has accounted for in the hydraulics of the system, and is usually based on a rule of thumb, like 10 psi or 70 kPa for liquids, 5 psi or 35 kPa for gases, or perhaps different numbers if viscosities are high.  The calculated value is that generated from the detailed design/rating of the exchanger in software like HTRI XIST or Aspen EDR where the actual pressure drop is reported.  This is done because often the process engineer specifying the exchanger is not the same person (or even in the same company) who is doing the detailed design.

[srfish]

Specifying something for the number in series and parallel for the software used is  necessary but you can enter zeros and the software used should take it from there.

[SawsanAli311]

The allowable pressure drop is determined based on exchanger's service (fouling resistance and viscosity) and an associated pressure drop multiplier for the conversion from clean pressure drop to fouled pressure drop. It is important to maximize the use of the allowable pressure drop by manipulating the tube's length and the number of tube passes and sometimes the number of shell's in series. Maximizing the use of allowable pressure drop is important to come up with an economic exchanger design as well as enhancing system's hydraulics.