9 replies to this topic

[KR]

Dear Engineers,

Just a quick one.

As we know the ideal velocity of water like liquid in a pipe should be between 1 to 2.65m/s [weblink: http://www.engineeri...ater-d_232.html]

What should be the ideal/acceptable velocity of the liquid whose viscocity is very high [3200cP at 0 deg C and 900cP at 20 deg C). My logic says velocity must be very low but dont know what should be the number !

Your help would be appreciated.

Thanks and Regards,
Komal

[ankur2061]

Komal,

There is no such thing as an ideal velocity. It depends upon the application and what are the objectives that you have fixed for the flow. There can be several objectives for your flow:

1. If your liquid contains some solids and you are using a pipe material which is having relatively less abrasion/erosion resistance, then your objective would be to keep the velocity below the erosional velocity of the flowing liquid.

2. If your liquid can coat the pipe wall and build a layer which can cause the C/S area of the pipe to reduce than too low a velocity will aggravate the problem.

3. If an excessive residence time of the liquid in the pipe can cause chemical degradation of the flowing liquid, then again too low a velocity is detrimental for the system.

4. If your liquid is carrying water mixed with it, then too low a velocity may cause water drop-out from the liquid which can cause corrosion if the pipe material is susceptible to corrosion by moisture e.g. Carbon Steel.

5. For a fixed viscosity of the liquid, and within the constraints of a fixed pressure drop available, too high a velocity will lead to a higher pressure drop which may not be acceptable at the terminal end of the pipe.

These are some of the generic examples of the objectives the process engineer needs to fix for his/her fluid flow and then analyze the velcoity that is acceptable to fulfill the objectives.

Thumb rules for velocity were formulated in the times when accurate analysis tools were not available and highly experienced engineers devised their own set of extremely conservative guidelines in order to have a infallible design which however were not really concerned with optimization and the economics of design.

In a nut-shell you need to arrive at what is the objective of your fluid flow before you can reach some definite conclusions about what velocity is suitable for your liquid flow.

Hope this helps.

Regards,
Ankur.

[Qalander (Chem)]

Komal,

Although our ankur has elaborated and guided you well. I add my little bit in my way.

Firstly I request more details on 'to be pumped' material as its nature has a great deal to do with plan and apply any pumping strategy.

e.g., can there be a Newtonian or non-Newtonian flow(Rod like flow; with slip at pipeline's internal walls) ?

Also, Heat tracing Plans, Insulation Plans, Pump type selection, etc. all relate to this Basic query.

Hope this helps in selecting your way forward.

[Jiten_process]

One more thing over above is....if you follow the guidlines of water you should take care the flow regime you get. Higher viscosity means lower reynold's no(density*velocity*int. dia/viscosity). That means you have to keep high velocity in order to get your flow in fully turbulant zone.

You havent mention the head ranges, just check it out coz such high viscous liquid, pressure change changes viscosity considerably.

[KR]

@Ankur,

As usual, your suggestions and guidelines are very useful and I agree what you said.
Moreover, I wanted to know recommended velocities for the pump suction and discharge for the viscous liquids.

I have got the answer but it doesn’t say about the viscosity range for which it is applicable.

Anyways, I think this guide velocities would be useful to me.


http://www.engineeri...luid-d_231.html


http://www.engineeri...luid-d_235.html

@Jiten and Qalander

Thanks for your reply as well

Regards,
Komal

[ankur2061]

Komal,

For such a high viscosity as 3200 cP you would be normally using a gear pump. Also to maintain flowability it may require some kind of heating (jacketed heated pipe) for the pumped material.

High viscous liquid flow regime is laminar and the velocities are generally low. The pipe system is designed to keep acceptable pressure drops and residence times. High pressure drops cause the frictional energy to be converted to heat energy leading to increase of temperature of the flowing material across the pipe. For certain polymeric materials, the temperature rise can lead to degradation and undesirable side reactions.

I have been personally involved a lot in the design of polymer transport pipes (dynamic viscosity: 250,000-300,000 cP) and hence have a reasonably good idea about their design fundamentals.

Regards,
Ankur.

[Qalander (Chem)]

Thanks ankur,I should say/Fairly good guidance indeed!

[Art Montemayor]

And I thank you also, Ankur - especially for your kind patience and perseverance.

Your contributions to our Forums speak for themselves.

[ankur2061]

hai Ankur

Hw r u?? Do u work in PDO??

Wn u hv been personally involved in design fundamentals, why u did not reported numbers??

Why u misled him with ur useless discussions??

Mishra,

People who have read your posts know what kind of a person you are and probably realize that you don't deserve to be even called an engineer. Keep out of my hair. I like to keep my distance from idiots like you.

Don't ever get involved with my posts again. Kapish!!!

[KR]

Hello Mishra,

I am really not happy with your post dear. It seems very offensive.

This forum is not meant for giving straight answers to one’s query. It’s always better to learn fundamentals and logic from those who have experience.

Please have a look at the link, which I posted. That is not a specific and straight forward answer to my query even.

I am pretty sure that I m bit far [no idea about you] to be compared with Ankur’s knowledge which he gained from his experience.

Once again, I am very much thankful to Ankur for his contribution and the knowledge he is sharing. I have seen his posts and they are all very impressive.

Ankur please keep it up!