Stainless Steel Pipe - HEAT OUPUT?

Einsiedler_2

I am having difficulty finding the output in BTU's of 2" Stainless Steel Pipe.

I have been asked to determine how many feet are required to provide 50,000 btu/hr.

Running 160F Water @ 40GPM.

Can any Wallies help me out on this one?

Thanks in advance,
EINSIEDLER

Tony Conner_2

All...

... metals will be pretty much the same, for practical heat transfer purposes. I'd use the calculation for ordinary carbon steel pipe.

Einsiedler_2

Ty Tony

Thanks Tony.

My chart for Std Blk 2" shows 120Btu/ft @ 160F Temp.

I'll run with that then..

Have a good day & a BETTER weekend!!!!


EIN

Alex Giacomuzzi

Heat Transfer Of Metals

I do not agree. The heat transfer of carbon steel is better than stainless. I do not have those tables available, but if you were to contact a manufacturer of industrial/ commercial fin tube pipe, they may have data they could share with you. Typically carbon steel and cast iron are better conductors and if you are bidding or designing a system you could end up short on heat output if you use the wrong values.

Mike T., Swampeast MO

Not Only That

But, the stainless isn't a very good emitter of radiation. 18-8 has an emissivity of 0.16 compared to 0.75 - 0.90 for various iron/steel pipes in "typical" condition.

Could you possibly paint the stainless to maximize its output? Flat is MUCH better than glossy in this regard with color having much less effect. Flat black though is marginally better than other flat colors.

Tony Conner_2

Different Metals...

... do indeed have a range of heat transfer capability. However, for all practical purposes, it's pretty much irrelevant. There are several other factors that impact heat transfer FAR more than the type of metal involved. The difference that the type of metal makes is much more of a theoretical issue than a practical one.

Carl PE

well, it depends

The conduction is going to be similar, but the radiation component will be smaller. Black pipes are going to radiate more heat than shiny stainless ones.

NAIMA's 3e software says 107 btu/ft for 2" black steel and 72 btu/ft for stainless.

Tony Conner_2

The Formula...

... for heat transfer:

Q = U x A x LMTD

Q = BTU/hr

U = coefficient of heat transfer

A = area in square feet

LMTD = the log of the mean temp differences in F

There is no factor for the type of metal, in this equation.

Tim Doran

Thermal Conductivity

The thermal conductivity of stainless steel is listed as 10 btu/h/ft/f while carbon steel is listed as 30 btu/h/ft/f.
ASHRAE Systems & Equipment 2004 page 6.7 table 2. Also, as Mike T. stated the emisivity is very low.

Tim D.

hr

Doesn't the surrounding

air temperature and surface temperatures have a lot to do with the output?

Seems the cooler the temperature around the pipe the higher the output?

hot rod

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Tim Doran

Coefficient

The coefficient of heat transfer should account for the conductivity of the pipe material but would only apply as it would relate to finding the correct water temperature vs. btu required. In the original question as water temperature and flow rate was stated therefore we would have to consider the pipe wall in the calculation.

Tim D.

Tony Conner

Exactly

The inlet and outlet temps for each side of a heat exchanger are the input factors to get the LMTD. If you have a situation where you've got low delta-T's, this will drive the required surface area way up, in order to deliver the same BTU/hr.

But we need to remember that we DON'T know what's on the cold side of the SS pipe. It could be air, it could be water, it could be...?

Tony Conner

That...

..."U" factor is a REAL judgement call on the part of the designer. Take a conservative value, get a bigger HX. Take a more aggressive value, get a smaller HX. This process isn't as cut-and-dried as a lot of people assume. Things like wall thickness are usually determined by the mechanical strength required, corrosion/erosion factors, etc. Then start to look at pressure drops for both sides of the HX. Very often, you'll wind up with a lot more surface area than you need for heat transfer, so the pressure drops will stay within allowable limits.

A heat exchanger is both part of a larger system, and a smaller self-contained system when you look at it as a single component. There are MANY angles to be considered when looking at a heat exchanger. I've found that by the time all of the other factors come into play, the kind of metal employed doesn't really make a big difference at the end of the day.

Mark Eatherton1

Ein, you need to clarify...

where the btu's are going/ Are you heating air? If so from where to where (Deg F).

Are you heating another fluid? If so from where to where?

That's an open ended question...

The only correct answer is "It Depends"... But you KNEW that was coming, dintcha:-)

ME