Serve Tubes

Does anyone have an image of a Serve tube, as used e.g. on the GWR's French Atlantics? They were, I believe, ribbed, and apart from seeing what one looked like, I am interested to know whether they were ribbed longitudinally or circumferentially. Thanks in advance.

 

Have you seen this? http://thierry.stora.free.fr/english/typfr_ac.htm

Tom

 

Thank you, I had not. That raises the possibility that they were ribbed internally. The heating surface specs (e.g. see Locos of the GWR) appears to take the ribs into account. Would that be legit if the ribs were internal?

 

In order to improve gas to liquid heat transfer you need to increase area and/or turbulance on the limiting gas side. Hence the use of finned tubes on the air side of steam heating tubes (eg carriage heating).

So yes, the ribbing on the flue gas side would be beneficial - though how you rib just one side I'm not sure. Also however, the cost would go up, and the tubes could be more difficult to keep clean.

 

There are numerous variants on this theme.
In Sweden so called Ess-tubes (or S-tubes) were used a lot (Swirl flow is another variant). But only on superheated engines to decrease the gas flow through the tubes and thereby increase the flow through the flues. Thus a cheap increasing the steam temperature from the superheater, and thereby power and efficiency, without changing tube plates and superheater header.
https://www.jvmv2.se/forum/index.php?id=34969

 

Thanks. That suggests that strictly the tube heating surface should be calculated as the inside surface area also on plain tubes. The GWR got rid of the Serve tubes on 102-104 within a few years, which was not a minor job as they were replaced with rather more smaller plain tubes, requiring new tube plates. Like a number of steam loco ideas, the increased efficiency probably came at too great a cost to practicality and maintenance costs.

 

Given that internal ribs are the goal, it would just be a case of having a negative of the ribs in the piercing/forming dies, assuming these would have been hot formed seamless tubes. The dies would no doubt be more expensive, I suspect the process would be less reliable, and I'd have thought the ribs would be subject to accelerated erosion compared to the rest of the tube.

However, I believe like a lot of exotic features they persisted in French practice to the end. Low axle loads, low speed limits (necessitating fast uphill running and acceleration) and expensive fuel were pretty much the perfect combination of conditions to encourage designing for maximum power and efficiency in a given package.

 

These tubes were used fairly widely on the continent and as an example, the tubes in the sectioned 4-6-4 in the French National museum at mulhouse are pretty clear so take a look at the attached photos taken back in 2006 IIRC. one of them shows quite clearly the arrangements at the end to return to a plain bore to enable expansions to be made. I would think that the tubes would undoubtedly have been extruded, but as with many other quirky features of past designs the technology and equipment to carry out such work appears to be lost.

 

Thanks Bob. I was envisaging the ribs being circumferential, not longitudinal, so that explains how it was done.

 

Yes and you can see that the plain ends have been welded to the finned portion of the tube, I suggest by gas welding in those days, probably too early for flash butt welding. Bear in mind that I think thios loco was sectioned back in around 1924 for an exhibition, a fascinating item, but apparently not one of La Belle France's finest products?
Regards Bob

 

Thank you.