Evaporative Condenser

https://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html

..."Type 304 is the most versatile and widely used stainless steel. It is still sometimes referred to by its old name 18/8 which is derived from the nominal composition of type 304 being 18% chromium and 8% nickel."...

You have a series of factors that limit the heat flow through your condenser, of which the thermal resistance (inverse of conductivity) of the steel pipes is one. (It's like an electrical circuit with resistors in series.) The new steel pipes have 3 times the thermal resistance of the old.

It depends on how much the thermal resistance of the pipes compares with the total thermal resistance. If it is close to the total, the reduction in heat flow would be down to 1/3. If it is a small part of the total, there would be much less reduction.

There's a good chance the wall thickness of the SS tubes will be about 1/3 of the carbon steel, so resistance is unchanged.

Also, as Rixter says, the resistance to convective transfer to and from each side of the tubes is likely to be >> resistance to conduction through the tube wall. Similar situation to heat loss through a single-glazed window. If the room is at 20°C and outside temp -10°, total ΔT 30°, there's ~ 15° ΔT between room air and inside of glass, and 15° ΔT between outside of glass and outside air. ΔT across the glass likely to be < 1°.

~10%.

So why don't you use copper tubing? It has much better thermal conductivity and better corrosion resistance. You would need to use insulated couplings where the copper joins to other metals, to avoid electrolysis.

If this evap condenser is in an ammonia system, copper would be wrong.

In general, stainless steel is probably more corrosion-resistant than copper, but it would depend on specific fluid contact conditions.

...which the original poster has withheld from the forum.

Whatever material is chosen it needs to be compatible with the fluids both sides of the wetted surface.

Whatever is driving the change in materials has not been revealed to the forum.

The change is material is being proposed to increase the life of the coil.

What is the environment? What seems to be attacking the life of the coil?

Quite - GA. This needs to be resolved before considering material change, as this has the potential to add another variable into the mix. One possibility is electrolytic corrosion between the coil materials and the materials-of-construction of the rest of the vessel, which have been withheld from the forum, as has such basic things as temperatures, pressures, and the nature of the fluids both sides of the heat exchange surface.

https://www.coleparmer.com/Chemical-Resistance

This one is at risk of becoming another one of those trickle-feed, "20 Questions" styles of thread.

There are "tricks" that can be used to increase the performance of heat exchange surfaces, depending on details of the application. Subject to <...coil...> diameter, which has been withheld from the forum:

• it may be possible to add devices inside the tubes, and
• it may be possible to add baffles to the surfaces outside the tubes

capable of creating extra turbulence at a cost of a little more pressure drop. Which approach to take depends upon which side is the limiting one in the heat-exchange performance, which may be found by engaging the original equipment manufacturer in dialogue. In fact, in all cases, advice should be obtained from the original equipment manufacturer on performance.

If the surface of the <...coil...> is becoming corroded to toe point of justifying replacement then it is quite possible that the original materials for the rest of the vessel were incorrectly selected. A written scheme of examination is mandatory is several jurisdictions, so one might reasonably also test the vessel wall thickness at intervals to satisfy the company supplying burst/collapse indemnity insurance cover on the equipment to remain lawful.

If it is found that the vessel wall is corroding similarly to the <...coil...> then a replacement vessel might prove more attractive than repairing the existing one. The replacement might benefit from newer improved materials that may have become available since the existing vessel was put into service.

If in doubt, consult a local Process Engineer.

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