Internal Natural Convection in a horizontal pipe containing Jet A
Internal Natural Convection in a horizontal pipe containing Jet A
(OP)
Looking for a correlation for internal heat transfer for a horizontal circular pipe experiencing natural convection. The pipe contains jet fuel.
Please email at michael.maixner@usafa.edu
Please email at michael.maixner@usafa.edu





RE: Internal Natural Convection in a horizontal pipe containing Jet A
Is the pipe the hot or cold fluid?
Diameter and wall thickness of the pipe?
Is the fluid flowing in the pipe?
RE: Internal Natural Convection in a horizontal pipe containing Jet A
Am also interested in calculating the heat transfer while the fluid is flowing.
Many thanks
RE: Internal Natural Convection in a horizontal pipe containing Jet A
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RE: Internal Natural Convection in a horizontal pipe containing Jet A
One reference for calculating the natural convection heat transfer coefficient inside a pipe can be found in good old Kern. it depends upon a variable called the Grashof Number.
RE: Internal Natural Convection in a horizontal pipe containing Jet A
http://www.eng-tips.com/faqs.cfm?fid=1339
This should help you to establish the threshold you're looking for
RE: Internal Natural Convection in a horizontal pipe containing Jet A
Example: You go under a runway, the thick hot sun-heated concrete above the pipe will cause that 200 feet under the runway to be changing temperature differently than the 1/4 mile going towards the runway under grass and (thin) asphalt from the tank towards the runway.
Get reasonable temperature readings of the pipe at reasonable intervals down its length.
But I'm making assumptions! I don't know enough about your conditions to really know.
Did you recently make a repair that you are trying to test with a pressure test? Is there massive leakage from unknown places you suspect? Could there be theft and pillage from people draining the tank that they are trying to cover up as a "leak in the pipe"?
RE: Internal Natural Convection in a horizontal pipe containing Jet A
Bottom line: In order to provide operators with a revised pressure drop table based on ambient temperature data (I'm recommending that a thermocouple be placed down at the pipe--they already measure the fuel temperature before isolating the system). I still need a guideline for Rayleigh/Grashof number correlations on the pipe interior for free/natural convection to use so I can back out an internal heat transfer coefficient for an analysis of the heat transfer under varying conditions--this will allow me to construct a revised set of guideliens for the operators. Hope to do some on-site testing to verify.
Many thanks!
RE: Internal Natural Convection in a horizontal pipe containing Jet A
I'm a little skeptical about convection losses though. Conduction from liquid (inside pipe) through liquid-to-wall-transition through wall through wall-to-fill-dirt-transition to final dirt temperature seems key. Seems that conduction would drive more than the convection of liquid in the pipe itself? That is, convection conditions would require a delta T to drive flow around inside the pipe .. and that delta T would have to be either bottom-of-pipe to top-of-pipe difference to drive flow in a small loop around inside the pipe, or region-of-pipe to region-of-pipe to drive flow from region to region.
"Pure" conduction would assume a stable solid mass that has no internal flow - equally unlikely in the real world, but maybe a better approximation?
How many days of topside temperature, and outside-the-pipe-at-pipe-depth temperatures do have recorded yet? Can you begin getting 12 (every two hours) hourly readings over several days when no flow in going on? Or, if you have the money and availability of people/recorders 24 hour readings for several days or weeks?
More important, do you have pressure readings of the remote end of the pipe over at least 2x 24 hour periods with no flow? If, for example, with no flow, you get equal pressure readings at 1400 each afternoon (hottest time of day), compared to consistent lower readings at 0400 (coldest time of night) then you've begun to make your case.
Things are complicated significantly if you are near-constantly flowing liquids through the pipe, since the "same volume" won';t be trapped in the pipe to cool down. (I can hear it now, "Sorry Colonel, we have to shut down all flight ops for four days to measure ground temperatures for a while .... But they could gas up at the next airfield after they takeoff if you want."
RE: Internal Natural Convection in a horizontal pipe containing Jet A
If I understand correctly, you are testing pipe with hotter than surroundings liquid over a period of time of about 1 hour.
It has been suggested that you use T probes for the fluid, which makes sense, but could be both a nightmare to implement and still leave some room for doubt, if the T varies along the length of the pipe.
Would it be possible and would it make sense to pre-condition the fuel to the ground temperature before the test? This could be done externally or by idleing the pipe for an extended period (likely not attractive). If the test is short enough, the time variation in the ground T should be less important, and you are already reducing its impact by starting with ground T fuel. You could also consider, if at all practical, shading the ground for a few feet on either side of the center line of the pipe to reduce the ground T variation. I'd suggest using a shade raised off the ground and one that is reflective, like aluminum foil.
HTH
JK
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com
RE: Internal Natural Convection in a horizontal pipe containing Jet A
RE: Internal Natural Convection in a horizontal pipe containing Jet A
TTFN
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RE: Internal Natural Convection in a horizontal pipe containing Jet A
IRStuff: I think what has happened is that a system was put in place to deliver fuel without concern for being able to hydrotest it for leaks after initial commissioning.
JK
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com
RE: Internal Natural Convection in a horizontal pipe containing Jet A
The idea of a day tank with some sort of cooling system is not a bad one.....that is, perhaps, a longer term fix. I still need to provide operators with a short term set of criteria for allowable pressure drops, albeit with relatively warm jet fuel.
RE: Internal Natural Convection in a horizontal pipe containing Jet A
My finite element analysis packages include computational fluid dynamics capability. Any analysis would need good values for the characteristics of the soil, pipe, and fuel.
JK
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
www.KleinfeldTechnical.com