heat transfert between pipes and ambiant air

[lomli]

Hi, it is my first partcipation,
i have to design a seaw water network used for cooling in several heat exchangers, the old network was underground, and we want to make it outside, but i need to calculate the water temperature change due to air temperature which can reach 47 °C,

is the heat transfert is

Q1 : forced convection inside the pipe ( Re, Pr) h = (k/d)*Nu
Q2 : forced convection betwen air and external pipe wall ??? how?
Q3 : conduction against wall pipe (ks(T1-T2)/e)

with q1=q2=q3

is it right and what relation must be used for air coefficient

 

[chicopee]

what the heck is a seaw?

 

[25362]

It's probably a typo from "sea water" by typing w twice.

 

[gr2vessels]

Here is a free Insulation Design Guide, I found it very useful.
cheers,
gr2vessels

 

[lomli]

sorry, i mean sea water,
thanks

 

[chicopee]

Is the piping to be insulated?

 

[lomli]

no, it's in direct contact with air, sea water is at 25°C and air is estimated at 47 °C, the temperatume must not reach 28.5°C at the inlets of heat exchangers, this is what i want to confirm.

 

[gr2vessels]

lomli,
The only way to prevent the heat absorbtion in the pie and overheating the sea water is to insulate the pipe. The Insulation Design Guide I sent you will help you to calculate the insulation thickness, but I would leave it in your case to the insulation contractor to design and install the most suitable insulation and at a cost you may negotiate with them. This way you can ask the contractor to guarantee his work, to ensure the termal isolation of your pipe.
cheers,
gr2vessels

 

[lomli]

thank you very much gr2vessels

I am agree with you Mr, but if the sea water temperature don't exceed 28.5 °c at the XCHgrs inlets ,I prefer avoid insulating (cost) if I will be sure that it reaches the 28.5 °C, so i will not have choice,

(sorry my english is bad)
thank you