Superheater

I am about to design a coaxial superheater, with 1/2 inch outer stainless pipe and 5/16" inner copper pipe.

Question - Should the input steam go down the outer or the inner pipe?

I have seen learned discussion promoting both. Does anyone have any practical experience?

ALSO - I will use Stainless steel for the outer, copper for the inner. How do I stop them from sagging?

John A

Duplicate post deleted.

hi john,

alec farmer of Reeves fame popularised coaxial superheaters and they were adopted by don young starting with his Mountaineer 3.5"g loco.

the late jim ewins was highly critical of them and explained why they could not be as effective as ordinary superheaters with return bends.

so you might like to bear this in mind.

cheers,

julian

Normally they are set up for the steam to enter into the inner pipe and exit as superheated from the outer - one design I seen had spacer blocks soldered to the inner to give spacing and support inside the outer - the outer had end caps that had small longitudinal fins that gave positioning in the boiler tube (Design seems to originate in Spain)

They appear to work in practice, but i can understand the criticism - however, you set them up the cold steam coming in cools the hot steam as it comes back out.

There's some good stuff here http://en.wikipedia.org/wiki/Countercurrent_exchange

The optimal solution would be for cold steam to enter at the smokebox end and leave at the firebox end and find its way to the cylinders down an insulated pipe.

in practice both coaxial and standard superheater tubes are more like a countercurrent multiplier **LINK** which act to make the steam hottest at the firebox end and actively keep it's temperature down at the smokebox end.

In practice, you just don't need the levels of superheat that make this matter.

Neil

Thank you everyone for your replies.

John A