Heat Loss Through Uninsulated Stainless Tubing-Laminar Flow 1

[RJB32482]

I was looking to find the heat loss through a pipe with a fluid flowing and also just sitting in the pipe. For forced convection, I could not find the method to determine this if the flow is Laminar. Is forced convection neglectible is the flow is laminar or does someone know a method to determine this?

Any help with finding these two values out would be appreciated.

Thanks

 

[roker]

hello,

the controlling heat transfer is from the pipe outside surface to the air,
the heat transfer with no wind is ~10 kcal/hr-m2-C.

regards,
roker

 

[sailoday28]

What is the Reynolds number? What is the Prandtl number?

 

[RJB32482]

Flow of silicone in pipe is 0 so no flow. Would there need to be a convection heat loss taken in account in the fluid?

Thanks.

 

[25362]

Convection in a static fluid can only take place if there are density changes (buoyancy forces) arising from the cooling/heating process. If there is no fluid movement there is -by definition- no convection. But conduction is indeed possible.

If the biggest resistance to heat flow is on the non-moving silicone, the overall coefficient of heat transfer would per force be smaller than the HT coefficient in the silicone itself.

The cooling of the pipe and its contents is time-dependent, namely it is an unsteady state process. Thus the heat loss to the surroundings will change with time, as the [Δ]T becomes smaller. So would the combined "convection + radiation" external coefficient.

A simplified formula for natural (free) convection in air as given by Holman:

h_c = 1.32([Δ]T/d)^0.25​

Where:

h_cis in W/(m².K)
d, the diameter of the pipe, in m
[Δ]T, in [up]o[/sup]C

This doesn't include yet a radiation coefficient that depends on the emissivities of pipe and surroundings as well as on their temperatures.

To estimate the temperature of a solid cylinder or rod upon time, given the starting temperature and the outside surface temperature taken as constant, one can use the Gurney-Lurie graphs published in the IEC issue 15, 1170-1172 (1923).