Temperature Rise in a Centrifugal Pump 1

[Pavan Kumar]

Hi All,

I would like to calculate the temperature rise in a Centrifugal pump under normal operation. I know it based on the pump efficiency. I would like to get the formula with the units for all the parameters involved so that I can perform a calculation. I am trying to calculate the temperature rise in Boiler Pump which takes suction at 95 Deg C. I would like to provide a minimum recirculation back to the Deaerator tank without flashing the hot water. Please reply asap.

Thanks and Regards,
Pavan Kumar

 

[EdStainless]

You know the power input to the pump, and you can calculate the hydraulic work (based on flow and pressure), so the rest of the energy must go into the fluid as heat. Sure some from friction is lost to the environment, butt his would be a worst case.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[danschwind]

https://www.engineeringtoolbox.com/pumps-temperature-increase-d_313.html

 

[Latexman]

Before the internet, the Durco Pump salesperson would give you a copy of the Durco Pump Engineering Manual which has the formula. Now, if the Durco Pump salesperson doesn't give it to you on a thumb drive or attach it in e-mail, you have to buy it from Amazon or eBay or someone.

Or, you can use Search in this forum. Top, left, between Forum and FAQs. Here's one hit I got - thread407-3427 .

Good Luck,
Latexman

 

[LittleInch]

You need to define your flow cases better than you currently describe.

You only normally get an issue when the water is in continuous circulation mode and hence the incoming feed water temperature starts to increase over time if there is no forward flow.

You don't have much room for temp rise here, but some data would help. If there is any forward flow and hence control over temperature in the degassing drum then you should be ok.

Oh and next time please don't add "Please reply ASAP". This isn't a work e-mail to a colleague, it's a request for people to help you out for free....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Pavan Kumar]

Hi EdStainless ,

I calculated the temperature rise by converting the difference between Actual Power required by the pump and the Power required when it is 100% efficient and converted this into heat energy. For my BFW that is at 95 Deg C, I am getting the temperature at the pump discharge as 114 Deg c with pump efficiency at 60%. This seems to be too high.

Please see my calculations in the attached excel spreadsheet.

We know that normally there is very small temperarure rise. I wanted to know what I can do to get a meaninful answer.


Thanks nad Regards,


Pavan

 

[LittleInch]

Nothing attached!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Pavan Kumar]

Hi Littleinch,

Here it is

https://files.engineering.com/getfi...ifugal_Pump_Temperature_Rise_Calculation.xlsx

Pavan

 

[LittleInch]

Your spreadsheet I cannot follow and appears to be meaningless I'm afraid.

There is no pump information there.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

Good Luck,
Latexman

 

[Pavan Kumar]

Hi Latexman,

What is the source for the above page?. I mean the book and the authors.

Thanks and Regards,
Pavan

 

[Latexman]

Durco Pump Engineering Manual.
The Duriron Company
Edited by R. E. Syska and J. R. Birk

Good Luck,
Latexman

 

[Pavan Kumar]

Wow that is great/ Thank You Latexman.

Thanks And Regards,
Pavan

 

[Pavan Kumar]

Hi LittleInch,

There was a conversion factor which I forgot and hence I was getting huge temperature difference. I have corrected it. The correct spreadsheet is attached with this message.

https://files.engineering.com/getfi...ifugal_Pump_Temperature_Rise_Calculation.xlsx

Thanks and Regards,

Pavan Kumar

 

[Pavan Kumar]

Hi Latexman,

Can I please post couple more pages form the Durco Engineering Manual after the page posted by you. I wanted to see the units used in the example problem.

Thanks and Regards,
Pavan

 

[LittleInch]

Well what this is a rise in temperature for a pump taking 10hp with NO FLOW.

It is a very simplistic calculation asusming all the shaft power is going into heating up the fluid (water) which is held within the pump casing.

Your original post talked about something completely different.

So what are you trying to find?

In terms of heat input into the water all you need to do is find the shaft power at whatever flowrate you want to study, find the efficiency of the pump at that flowrate and then conservatively assume that all the inefficiency is going into heating up the water.

So e.g. if you have a shaft power of say 100HP and a pump efficiency of 70% at that flowrate then asusme 30hp is going into your fluid. Your flowraste is say 100 GPM.

So I reckon this is about 0.2 F rise.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

The whole Chapter 13:

Please pardon, one of my kids drew on it a long time ago.

Good Luck,
Latexman

 

[Pavan Kumar]

Hi LittleInch,

There are three cases to the problem.

1. Temperature increase under normal pump operation.

2. Temperature increase rate under Pump Shutoff Condition.

3. Temperature increase under minimum flow rate condition.

For cases 1 and 2 I have already calculated the temperature rise and even sent the spreadsheet on this forum.

The page from Durco Manual sent by Latexman address Case 3. I have described case 3 in my plant as below.

The BFW pump in my plant pumps BFW to a Steam Drum. The Pump's VFD ramps down as the level in the Steam drum rises. The minimum the pump can ramp down is to 50% of its original RPM. Now since the Steam drum cannot take any more BFW the water pumped should be recirculated back to the Deaerator storage tank. I want to calculate the temperature rise in BFW ( which is already at 95 Deg C) for this minimum flow rate so that the water does not flash when it enters the Deaerator which is at atmospheric pressure.


Hope this clarifies the problem now.

Thanks and Regards,

Pavan

 

[Pavan Kumar]

Thank You Latexman.

Pavan

 

[LittleInch]

Case 3 though is not a steady state affair but a transient one and any temperature rise will depend on many things not allowed for.

So if you have no flow into the steam drum then the incoming temperature of the water will or could slowly rise over time. However if the heat losses from your piping and the deaerator tank exceed the heat input from the pump then it could actually fall.

Normally VFDs aren't very good for BFW supply as the pressure often stays pretty constant regardless of flow and hence once your VFD reduces in speed by a few percent, it can't actually provide the pressure required at any flow. Reducing by 50% seems like a big ask to me to actually generate the required pressure to get into the steam drum.

I've only seen case 2 as you sent in the post above and this is the first time you mention a VFD which changes everything.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.