26 replies to this topic

[cea]

Thanks Ankur

But i think u haven`t understood my problem.
My problem is that we cannot provide the insulation at this stage(AFC) as the pipe runs over piperack(which i have clearly mentioned"See Attached file") and to provide insulation will require space which cannot be accomodated inside piperack as it requires shifting all pipes on the piperack.

I wanted to know the heat loss through the uninsulated pipe over a length of 500m so that i can find the temperature of the fluid at exchanger inlet and the heat duty given by this fluid to heat the shell side fluid.
And the excess duty required could be provided by the other exchanger in series with this exchanger, which uses steam as heating medium.

I hope u will understand the problem now and reply asap.

Dear-

I would like to answer your query in two parts.

1) As I understood, you want to run this pipe bare, as there is no space available on pipe rack to put insulation, although temperature is as high as 220 deg C. In that case, there will be stong apprehension by your piping engineer, as running such bare pipe will cause huge amount of thermal stress on the pipe rack (considering the rack is of structural steel). Hence, I would like to request you that have a word with the stress engineer first & get approval for idea itself before proceeding for calculation.

2) In case if the idea is already frozen, you can go ahead for calculation in following way. Please note that there is no single co-relation with which you can estimate the losses. The amount of heat that can be lost depending on resistance offered during different mode of heat transfer.
In this case, there will be three modes of heat transfer that will play role, such as
a) convection - that can give you temperature at inner wall of pipe with respect to fluid body temperature
'- conduction - that will give you temperature at outer pipe wall
c) radiation - that decides amount of heat radiated from outer pipe wall. Here, I would like to highlight that radiation comes in picture only if you donot want to consider any effect due to wind velocity. Otherwise, radiation will be replaced by heat transfer due to forced convection in air.

The emperical relations for each mode of heat transfer is available in various references.

Process engineer's skill is to guess temperature at intermediates, such as at pipe inner wall, pipe outer wall so as to meet overall duty. This can be identified by itritions. The overall duty can be calculated by summing up resistance for each node, for which intermediate temperatures are not required.

Hope, this helps you.

Edited by cea, 22 January 2013 - 07:09 AM.

[mflhw]

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