PUMP STAND BY CASE

Dear Sir


I am analysing a pump calculation. In my calculation there are three pump, out of it two pumps are working one pump is stand by case. my question is how to find out the actual temperature (with insulation and without insulation)of stand by case pump . kindly reply.

Thank you


Regards

k.a.pillai

k.a.pillai
piping stress analysis

If I got correct you mean to ask how you will decide the temperature of the third pump which will be stand by? In that case (in my opinion) you have to considered the temperature of the third pump which will be stand by is ambient, while the two pumps will continue to work on their operating temperature.

Thanks For your reply

In pump suction line after the gate valve we can consider ambient temp. but i am asking the temp before the valve of stand by pump line considering all the heat loss .

case 1: I get one set of forces and moments in the nozzle when i consider ambient temp after the gate valve , remaining portion operating temp.

case 2: I get one set of forces and moments,when i consider ambient temp through out the pump stand by line .

In the above two cases , case 2 has less forces and moments compared to case1. so i am asking how to find the decay temperature to obtain optimal forces and moments (For Insulation line and un insulated line ).


Thanks

Regards

k.a.pillai

Hi kapillai

Different company have different practice.

Case 1: as you mention, from branch connection to block valve operating temperature then from block valve to pump nozzle ambient temperature.

Case 3: From branch connection to block valve (operating temperature+ambient temperature)/2 since flow is stagnant in this portion of pipe, then from block valve to pump nozzle ambient temperature.

Case 2: as you mention, I have not experience any such practice.

I suggest you follow your company practice.

Can you send the graphical file for my understanding showing the two load cases. My mail id is rahul_kanugo43305@yahoo.co.in

I HAVE ATTACHED THE DRG . PLEASE GO THROUGH IT AND FIND A CONCLUSION.

KAPILLAI,

You Case 1 is appropriate. You should apply the operating temperature upto the shutoff valve of pump 3 shown in your sketch (apply the operating temperature to the valve also).

Case 2 is incorrect. You cannot apply ambient temperature to the complete standby line.

Also, as the stagnant fluid in the standby line will be in direct contact with the flowing fluid at the branch connection, it may slowly gain temperature through convective heat transfer. So, it would be inappropriate to consider an average of operating & ambient temperature unless you are completely sure of the thermal profile of the stand by line.

Regards,
ASA

THANK YOU

We can not predict the stagnation of fluid inside the pipe line, when piping design, fluid does not flow through entire cross section area of the pipe. stagnation depends upon the fluid velocity,

In analysis point of view, case 1 is more conservative method. But I want to know the temperature decay of stand by case pipe line.

Any one have idea about thermal profile, please explain.

Regards

k.a.pillai

Hi kapillai
Case 1 is not the conservative method.
Try your case 2 & case 3 , you will find more difficulty to pass nozzle load.
Again if you go for case 1, I do not say it's wrong.

Since case 3 give more conservative result than case 1, I don't think we should call it inappropriate method. (in absence of more accurate data.Practical aspect there is no need also to search for appropriate data)

Dear shr


Thank you

In my experience, case 1 is more conservative than other two cases. i did one calculation , pipe size 26 ", operating temp 130 Deg c. in this calculation case 1 have more forces and moments.

same calculation considering case 2 method , the force and moments are minimize .

so i am asking . how can predict temperature decay.

i am sure using temp decay , we can eliminate all unnecessary over design.

Regards

k.a.pillai

Hi kapillai

In general model when you make more temperature difference(3 pump in series) it become more troublesome.
Can you please take a look again on nozzle load specially when middle pump is in standby condition.
If you have no problem can send me the file at habibur21@gmail.com

Dear pillai,

I suppose you were looking for something like this

Temperature distribution profile for the pump standby line you can predict well by using any of the standard FEM/CFD analysis software like Ansys.For example in Ansys you can solve this problem by usisng conjugate heat transfer method.

1)Define your model from the branch point to the pump nozzle with material thermal conductivities(Atmospheric Air+Insulation+Pipe+fluid)for steady state thermal analysis.

2)Define boundary condition as follows

a)At branch point boundary specify operating temperatre as a constant temperature boudary condition.
b)At Surface of pipe/Insulation define it as adiabatic if insulated othewise in case of un insulated and open to atmospher define a convective heat transfer coefficient of 5~10 W/m2K.You can also model atmospheric condition by defining its properties.
c)In case your line is partially filled.This effect you can consider by modelling the fluid upto that level.
d)Specify fluid velocity at the branch point and end point equal to zero.

With these set of boundary condition the software will calculate heat flux and convective heat transfer coefficient at the fluid-solid boundary and will give temperature distribution in the entire model.
I hope this will be of information to you.
If you want simplified mannual calculation then I can send you a copy.

You can solve this problem by simlifying it and making some meaningfull assumsions.

1)Flow through the total crossection of the pipe
2)One dimentional steady state heat conduction trough fluid and metal pipe.

After taking actual values of variable for this case you will be surprised to know that the temperature will saturate to ambeint value after say 400 mm from branch point in your case.

I suppose this exersise you can do yourself.If you want me to show you this I will explaine you latter.

Therfore I see there is absolutely no need to go for calculating temperature profile in the stand by line of pump or any other such instance.

All the three possible cases for defining temperature in standby line disscussed previously are practised in all measure companies.

Regards,

Aslam

Thanx Aslam


i did the manual calculation considering all the heat loss ( conduction and convection ). but with insulation line i dont have formula,my manual calculation, i consider the pump has standby inside ther is no fluid ,

i dont have clear idea, when the pump has standby, after the gate valve and pump casing , upto dischage line gate fluid has stagnent, before the gate valve upto the standby line connected to header i thing very less fluid or no fluid. this stagnent fluid depens upon fluid velocity, do u have any clear idea, please inform. so i am not considering inside fluid heat transfer. do u have any manual calculation please forward to me.


Regards

k.a.pillai

Dear Pillai,

You can use simple formulla derived and attached with this message for calulating steady state temperature of any body.

Remember your case is somwhat different.The lumped capacity analysis assumption made is not fully applicable for this case.

But still this will give you a feel of the system.

Regards,

Aslam

Dear Aslam

Thank u so much for u r reply

i know, its transient heat transfer formula. we cant use this formula.
i used fins ( short length ends are uninsulated )heat transfer formula, then i find out uninsulated line temp distribution (with out considering stagnent of fluid) but insulated line how can find out the temp distribution.

Dear pillai,

Its steady state formula and you can use it but you first need to understand lumped capacity analysis assumption.(One clue for you- calculate biot number for your system and decide on the use of this formulla)

However, This is not a textbook formulla and you will not find this formulla in textbook.If you could find it somewhere please give me reference.

This case does not fit into fins category.

I will try this weekend to make another mathematical model for this case.

Regards,
Aslam

Dear Pillai,

This attached sheet shows simplyfied calculation and comparison of results with earlier given formulla.

Regards,
Aslam

Mr.Appavoo Pillai,

There is no need to go so deep in calculation for getting the Actual temp of Fluid.its better to take the Avaerage temp. of Design & Operating,and go with it for analysis.

Dear Pillai,

There is some correction to be made for the above statement.In place of Design & operating, it should be average temperature of Design & Ambient or Operating & Ambient.

Hi Jeba
I agree with you.
That is quick & enough reasonable conservative calculation as far as pipe stress is concern.

Dear Jeba & Habib,

The easiest way to answer a technical question is "NO NEED"
We say "no need" to calculate/understand/learn a concept when we really do not know it and try hard to show as you know it fully.

Pillai had asked a valid question and he is aware of engineering practice followed in different companies relating to this issue as he makes it very clear in his previous posts.

An engineering practice is adopted after decades of successful run,engineering judgement and spending scientific efforts to understand theory behind it.

I am not sure, but somebody around some corner of the world at some point of time must have done this study.

Pillai was curious and just wanted to know the science and maths behind those numbers.

It will be good effort instead If you can encourage and help with your knowledge.

Regards,
Aslam

Dear Aslam


Thank You so much.



Regards

k.a.pillai

Dear Aslam,

thanks lot for your effort. your calculations help me a lot and please i have some comments needed your and other friends:

- Assumption of value 100w steady state heat flow for piece of 1 m depend on what?
- If i need to calculate the length L to can define it at CAESAR II with assumption of Q=100w that mean L=1 m not 400mm as you mentioned in above post.
-Where L=1m (or L=400 mm)is too small, so can neglect it and then CASE#2 by Pillai that consider ambient temp through out the pump standby line is the most real case.

best regards