Re: Pre-heating boiler water
Posted: Sat Apr 10, 2021 8:16 pm
1/8" copper tube offers a lot of resistance to flow even in a 3/4" model...you can do the calculations for velocity of the water and the resultant losses, but they will be substantial for a 1" or 1.5" model.
I would go with something like 1/4" copper tube (about 4x the area, or 1/4th the velocity & pumping losses).
We have fitted steam:feedwater feed heaters before- on a Stuart #9 with the 504 boiler. It was very marginal with the spirit burner without the feed heater, and a lot more comfortable with it. I would guess that as posted upthread, on a marginal boiler the added energy that you can recover with a feed heater is probably worth it. The same thing is true on full size, where a gain of a couple of .1% of n spread across all the locos could exceed the fuel costs difference. Here at work in a heating plant, we have preheaters running exhaust: water.
On the ship, running with extraction on the turbine (typically at the cross under pipe, so HP extraction not LP), the difference was about 4% _plant_ n vs using boiler steam for preheating (285F/33-38 PSI). At 10 000 hp, that was a substantial amount of fuel, and far more if we were at 21 000 shp and getting it off the LP turbine (about 5% n, from ~28-> 33% n overall)
Remember the above is on turbines running extracting steam into a pressurized hotwell, which is NOT what we would have on a railway engine.
James
I would go with something like 1/4" copper tube (about 4x the area, or 1/4th the velocity & pumping losses).
We have fitted steam:feedwater feed heaters before- on a Stuart #9 with the 504 boiler. It was very marginal with the spirit burner without the feed heater, and a lot more comfortable with it. I would guess that as posted upthread, on a marginal boiler the added energy that you can recover with a feed heater is probably worth it. The same thing is true on full size, where a gain of a couple of .1% of n spread across all the locos could exceed the fuel costs difference. Here at work in a heating plant, we have preheaters running exhaust: water.
On the ship, running with extraction on the turbine (typically at the cross under pipe, so HP extraction not LP), the difference was about 4% _plant_ n vs using boiler steam for preheating (285F/33-38 PSI). At 10 000 hp, that was a substantial amount of fuel, and far more if we were at 21 000 shp and getting it off the LP turbine (about 5% n, from ~28-> 33% n overall)
Remember the above is on turbines running extracting steam into a pressurized hotwell, which is NOT what we would have on a railway engine.
James