heat lost to atmosphere from pump

[cams1975]

Hi

is there a way to calculate the heat lost from a pump to atmosphere

Pump data

P1 input power 2.34kw
P2 output power 1.9Kw
pump eff 63.4%
Pump and motor eff 51.7%

thanks

 

[BigInch]

Most excess energy dissipated in the pump is converted to heat and carried away by the fluid, unless the pump is recirculating that fluid in some manner. For a rough calculation, assume the pump efficiency energy loss is lost to the fluid. Most heat dumped to the atmosphere is by the driver. For a rough calculation assume the driver efficiency energy loss is dumped to atmosphere.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[waross]

What is the temperature of the fluid.
A couple of years ago a major heavy oil plant went down in a severe cold spell. It was suggested that so much heat was radiated by the pumps that the process temperatures could not be maintained.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BigInch]

Was that a news report, or an engineering study?

Pumps normally input a relatively very small amount of heat to the fluid when running at process conditions. In order for a pump to input so much that it had excess to radiate a significant amount, the flowrate would have to had been well below the minimum process flowrate, so I would suspect that the process was out of control to begin with. A likely scenario would be that perhaps someone had the pump on recycle making it appear that the pump caused the shutdown by trip of its high temperature switch. Something that could hardly be described as the root cause of the shutdown. Or the pump was damaged due to other factors, like being on fire from bearing failure, etc.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[MartinSr00]

Well said BigInch

Worked for a pump company for a lot of years, both in design and test departments. For typical flows, the temperature rise in the pumped fluid is typically a degree or so.

It's easy to do the math. Take the entire losses and divide by the flowrate knowing the heat capacity of the water. Even at flow turndowns of 5 or so, one usually finds that the temperature rise is small.

As for mechanical losses, Stepanoff, in his classic "Centrifugal and Axial Flow Pumps" (2nd Ed. published 1957 and still in print) talks of a study done "recently" at then Ingersoll Rand. Total mechanical losses, mostly bearing and stuffingbox, are typically in the 1% or less range. And remember that stuffingbox losses transfer much of their waste heat to the water -- not the surrounding air.

 

[waross]

Hi BigInch.
My source was anecdotal from some instrument technicians who were present.
The process temperature was 400 or 500 degrees. The ambient dropped to minus 30 and stayed there for a week or more. The plant had withstood similar cold spells in the past, but some of the large pumps had heated enclosures. Small sheds actually. For some reason the sheds were removed. (Possibly to eliminate confined spaces.)
The theory held by some was that although the process had withstood similar cold spells, the added system heat loss from the now unheated pumps was the straw that broke the camels back.
I was in Honduras when I saw the news report that the plant in Canada had gone down because of cold weather. This spring I worked for a time with some techs who were on-site when the plant went down.
My point was that heat transfer from the pump surface is more dependent on the temperature of the pumped fluid than on losses.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BigInch]

OK even if we're talking about total heat in the system, process heat lost by the pump surface should still be a very small fraction of the heat lost by the total surface area of the piping and equipment. There's normally a lot more surface area on just several feet of pipe than on the pump. I might believe it if the cause was ascribed to total heat lost from all pipe surface during an extreme cold spell.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[waross]

Hi Big. You may be right. The piping was insulated and heat traced. The major heat loss would be from the reactor vessels. The change in the system was the removal of the heated sheds around the pumps. The plant was built about 30 years ago and had previously survived cold spells. Most of the pumps are now insulated.
The point I was trying to make is that if the process fluid is not at ambient temperature, the heat loss or gain from the pump casing due to the fluid temperature may be large in relation to heat loss due to inefficiency.
If the OP is concerned with pump efficiency it doesn't matter.
However, if the pump is indoors in a heated or air conditioned space, heat loss or gain due to fluid temperature may be important.

Bill
--------------------
"Why not the best?"
Jimmy Carter