What water speed do you work with in monotube boilers?

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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fredrosse
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Re: What water speed do you work with in monotube boilers?

Post by fredrosse » Sat Jul 24, 2021 6:15 am

Bart, yes, the new monotube steam generator is based on an oil fired pressure washer "hot box", with several modifications made to generate steam at higher pressure/temperature.

The steel coil is said to be good for over 3000 PSI (207 Bar), separator and all other steam system components have been tested to 600 PSI (41 Bar). One killer issue for the Lamont setup: the feedwater pump is only good for 140F (60C) maximum temperature, and saturated steam temperature at 150 PSIG (10 Barg) is 365F (185C). That dictates various heat exchangers used to keep the water pump within its rated temperature. All of this is crammed into a 14 foot (4.25 Meter) boat, which is a very crowded arrangement.

I have developed a reciprocating Lamont circulating pump design that has no sliding surfaces (such as packings, check valve moving parts, etc.) in the high temperature steam/water (365F) circuit, and this design uses a conventional low temperature reciprocating main feedwater pump. However to build that one I need to get "a round tuit".

Later today I plan to run this steamboat plant at reduced capacity of 210,000 BTU per hour oil firing rate (61kWthermal), and if all goes well, rated firing will be increased to double that amount. At present I have the steam engine of my 1970s vintage Domestic Heat-Power Module in the boat, which is considerably smaller (350cc) than the engine I plan to eventually use. The intended final configuration will use a 3 cylinder 1000cc engine at 1000RPM. To quote a somewhat famous movie line.... We're going to need a bigger boat"
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Re: What water speed do you work with in monotube boilers?

Post by Steam Captain » Wed Jul 28, 2021 4:33 pm

Hello Fredrosse,

Your project sounds very interesting.

Concerning the diagram Cyberbadger shared with us: Is the dispersed flow the best condition the water-steam can be in inside a monotube? And to what extend would a frothing flow have an effect on steam production? Is the difference negligible? What does the horizontal axis represent?
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fredrosse
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Re: What water speed do you work with in monotube boilers?

Post by fredrosse » Wed Jul 28, 2021 9:35 pm

The data Cyberbadger shared with us (the Baker Plot), is for horizontal or vertical tubes only. For a helix type coil (such as a pressure washer "Hot Box" coil, the gravity and centrifugal forces tend to arrange for steam/water phase separation which is entirely different than the presented Baker Plot.

Fortunately, the USDOE has paid for several heat transfer studies, as well as tests, in relation to boiling heat transfer in helical coils, generally in relation to nuclear reactor steam generator coils. The USDOE allows public access to all of these technical publications, as long as they are not classified as military secrets.

Looking over some of these available documents, I did not see any term "frothing flow", could you define what you mean by this term?
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