9 replies to this topic

[fatimah]

hi!
i would like to get some feedback from all about the min/max velocity for shell & tube side nozzle.
in my company, has become a practise to select nozzle size based on Rho-V2; shell = 4000 US unit & tube = 6000 US unit.
i think that is no longer correct as i believe API standard regarding Rho-V2 is not about the nozzle Rho-V2 as mentioned by some software developers.
not considering the nozzle Rho-V2 value for design, i believe we shall have limited velocity for both shell & tube side.
i welcome any suggestion ( a concrete reference is appreciated!) for the min/max velocity as here in my company, we put limit at 3 m/s.
Thanks!

[breizh]

APAK KABAR Fatimah!
You may find answers to your query :
http://www.gulleyass...ips.htm#SeptC08
Hope it helps
Breizh

[fatimah]

Thnx Breizh!

i went that path already. anyway, is it apply for all vapor/liquid or mixture phase medium?

[Srikrishna Chaitanya]

Hi Fatimah,

Let me tell you something which I knew , RHO* vel 2 is representation of kinetic energy of the fluid (hope you already know this ) .If velocity increase ( high kinetic energy ) pressure drop also increases , because pressure drop is proportional to square of the fluid velocity .At high velocities advantage is that nozzle size becomes low (but your pressure drop increasing ) and vice versa. Apart from the pressure drop we have erosion in piping according to API 14 E erosion velocity Ve = c / sqrt( rho). We have to limit velocity in piping or nozzles primarily to prevent Erosion , velocity is always kept below the erosion velocity . Once velocity is checked for erosion velocity we need to check for pressure drop . coming to RHO* vel 2 values that depends on application like nozzles are for heat exchangers or separators again they differ from code to code(codes are just guidelines, we may use different values based on experience). Actually these values are experimentally determined for different applications over a range of fluid densities . All these codes always gives max –min values because they are not just meant for a single application . so best values to be chosen based on erosion , pressure drop , type of application (like in gas liquid separators entrainment also comes into picture again that depends on kinetic energy )and last but not least experience . Hope I answered to some extent.


Regards,

Satish

[fatimah]

Thanx Satish Babu

according to API 14E, erosion velocity is Ve=c/sqrt (density). and C may vary depend on what service they are.
well, after i went through below thread;

http://www.cheresour...7342

just found out that the formula is just for mixture (can it be 3 phases?) only.
C is 100 or 125 or 150 or 200 as per service.
OK. let me understand this one first. for mixture density, the formula is;

mixture density = 1/((vapor fraction/vapor density)+(1-vapor fraction)/liquid density)) = 18.10 kg/m3

vapor fraction = 0.3
vapor density = 5.5
liquid density = 1000

then what if solid present? what C value are we going to use? assume all are as per API 660 requirement.

thanx for response, actually my company is not equipped with API 14E, my comment is based on web surfing only.

Edited by fatimah, 18 October 2009 - 09:49 PM.

[breizh]

Hi Fatimah,
additional resource :
http://books.google....page&q=&f=false

hope it helps .
Breizh

[fatimah]

Thanx again breizh

i did not get the answer from the reference. maybe my question is not clear.
do i have to use the same equation for 3 phase medium (solid/liquid/gas)? what would be the C value for this case ?

[fatimah]

Hi all

seems that i got no reply regarding this. Nevermind as there's a lot of things i believe everybody can help me. as from my experience, for shell & tube when we talked about tube velocities, we are actually referring into 2 points.

first, for tube, it's measured from (1)nozzle inlet/outlet and (2)the entrance of channel to the tube. Same thing goes to shell velocities. it refers to the (1)shell inlet/outlet nozzle and (2)areas within the shell corresponding to their location.

TEMA recommendation on Rho-V2 is referring to each point (2)s. while for API 14E, as what i understand from this forum, also referring to the same area. now i'm looking for point (1)s.

Hope anybody can help. Your experience may help.

[Srikrishna Chaitanya]

Hi ,
the C value for your case is a kinda reserch value , please see this link , purchase that document (API REPORT 91-62 Experimental Study of the Erosional/Corrosional Velocity Criterion for Sizing Multiphase Flow Lines Phase II-Experimental Results)from IHS , URL given below
http://engineers.ihs...UGJCAAAAAAAAAAA
other links may useful to you
http://www.onepetro....4485-MS&soc=OTC
http://scitation.aip...=cvips&gifs=yes

[fatimah]

Dear Satish Babu garikapati & breizh

thanx for the info. for liquid phase in tube side, for water; the value range in 1-2 m/s with max 2.5 m/s for fouling issue. most of reference agree with the max value. other liquid also about the same value.

Process Heat Transfer by Robert W. Serth gives higher range of velocities based on tube material.

while for nozzle velocity, Rules of Thumbs for Chemical Engineers by Carl Branan has the answer.

Thanx a lots!