Heat tracing pipe with hot oil 1

[MJO15]

I am working on a problem that involves heat tracing a product with hot oil. Ultimately I would like to calculate the GPM requirement of hot oil to maintain a product temperature.

The pipe is located outdoors (let's say 1000 ft long). The product (300°F) is in a 6" pipe and is traced with two 2" hot oil (<500°F) lines and everything will be enclosed in 2" insulation. The hot oil will pass a given section of pipe twice (hence two tracer lines), once as a main supply, second as oil return.

I would first calculate the heat loss of the 6" pipe with 2" insulation. This loss must be replaced by the heat delivered by the hot oil. However, how do I get from knowing the tracing heat requirement to an oil flow given there are two tracing lines at different temperatures which vary along the pipe run. If anyone has a suggestion on how I could simplify the calculation I would love to hear your input.

Thanks.

 

[TD2K]

Try using the Q you calculate to come up with a dT of the hot oil tracer. You should be able to estimate the oil flow through the tracing given your supply and return pressures. If the hot oil doesn't actually cool that much, you have your answer. if it does, you might have to go through a couple of iterations.

 

[vonbad]

I believe that you are trying to determine the GPM in order to size the pump correctly. Is this correct?

I maybe mistaken but I think there is another approach.
If you have the heat tranfer oil (specs), you maybe able to work the GPM from another angle. As you want a turbulent flow for maximum heat transfer, determine Re number based on the fluid characteristics and pipe size. From here you should be able to work it back to a GPM.

Do you know the pressure drop for the piping?

The Q will aid in determining the heating system size(heater).

Althought it's insulated, you may want to consider extreme ambients (cold) weather since it's outside.

Also, with hot oils it's recommended to filter the oil for maximum life fluid and heat tranfer. As well as, protecting the pump, heater etc. Run a google on hot oil filtration.

 

[Montemayor]

MJO15:

Regardless of how much -or how efficiently- you pump the hot oil, you will fail to trace your process line in accordance with your needs if you fail to install the two, 2" hot oil lines correctly. By correctly, I mean that you must comply with the basis of your heat transfer calculations: you are totally reliant on transferring the hot oil heat into your 6" line through the application of CONDUCTION heat transfer across both the 2" pipe walls and the 6" pipe wall. In order to follow through with this basis, you must ensure that there is 100% physical metal contact between the 2" pipes and the 6"pipe. In order to have (& maintain) the kind of physical contact you require, you need to affix a heat transfer cement between the 2" pipes and the 6" process pipe. "Thermon" is one industrial heat transfer cement that I have had repeated success with in doing this type of application. This medium allows for the heat flow through the length of the trace pipes - in accordance with the calculation basis.

I urge you to employ this; otherwise all your calculations and installation work will be be for naught.

 

[unclesyd]

If you are not going to use full jacketed pipe here is an option that full fills montemayer’s
recommendation of metal to metal contact.

http://www.csiheat.com/Products/Bolt-On/ControTrace/ControTrace.htm