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The Junkers turbine was to run at 550°C.
Steam Pressure 100 atm
Steam Temperature 550 °C
Saturation Temperature 312 °C
Degrees Superheat 238 °C
Specific Enthalpy of Water (hf) 1413020 J/Kg
Specific Enthalpy of Evaporation (hfg) 1309080 J/Kg
Specific Enthalpy of Superheated Steam (h) 3499570 J/Kg
Density of Steam 28.4626 kg/m³
Specific Volume of Steam (v) 0.0351338 m³/kg
Specific Entropy of Water (sf) 3368.61 J/kg.K
Specific Entropy of Evaporation (sfg) 2237.17 J/kg.K
Specific Entropy of Superheated Steam (s) 6748.84 J/kg.K
Specific Heat of Steam (cv) 1833.7 J/kg.K
Specific Heat of Steam (cp) 2505.54 J/kg.K
Speed of sound 674.232 m/s
Dynamic Viscosity of Steam 0.0000310333 Pa.s
Isentropic Coefficient (k) 1.27931
Compressibility Factor of Steam 0.937066
You only have to look at some WW2 strafing films to see how vunerable boilers are to even .50 cal fire.
About 10 years later when the USA was researching nuclear powered aircraft, steam turbines would have been the power source in that case. They even had a B-36 with a reactor, but conventional power. But they couldn't get the weight of the reactor, and it's necessary shielding down enough.
If you were to ask an engineer how big a 100hp steam turbine would be he would tell you it would be about the size of an rugby or gridion football.
If you asked about the boiler the answer would be about the same size (eg a tube boiler.)
If you asked how big the condensor would be then you would have asked the key question: it would by far be the largest part.
The energy in the combustion gas of an piston or jet engine that could not be expanded further is simply dumped into the atmosphere. However the unutilised energy of the steam engine must be transfered via highly stressed condensor wall to the air. The radiator of an piston engine only gets rid of heat that was removed fom vital parts to keep them cool and strong ie about 30%.
The way around this is to increase the efficiency of the engine which can be done via opperating at as high a temperature as possible, this increases efficiency (See Carnot cycle) and means the radiator can be smaller as there is less heat to dispose of and what there is to dispose is quite hot and will conduct easily. Opperating at high temperatures (and 550C is very high) means special materials that don't corrode and suffer from hydrogen embrittlement. I believe 550C is supercritical?
They key is also where are the radiators/condensors going on this aircraft? Will evaporative skin cooling be used?
The condenser's job is not to bring the water temp back down to ambient, but to convert it from steam to water.
IMO cost was a greater factor. Synthetic fuel plants are very expensive to build. The 1939 Gelsenberg hydrogenation plant cost 208 million RM to build. Over ten times the cost of the Genshagen DB601 engine factory constructed during 1936. More then a Bismarck class battleship cost to build during the late 1930s. With a price tag that high it's easy to understand why Goering didn't build a few more hydrogenation plants as part of the German 4 year economic plan.major problem was that the Bergius Hydrogenation plants, which were efficient and produced high grade fuel, had to be big and and thus were targets
A steam power aircraft could relieve the pressure on supplies of high grade fuels. Given the quoted sfc of 190 grams per kilowatt hour which works out at a stunning 0.32 lbs/hp/hour it would be suited to long maritime patrol missions, raids on the USA and transfers of technology and strategic materials between Germany and Japan.
@wuzak
The heat rejection of 100C seems a little low to me, I suspect a higher temperature would improve heat transfer from the condenser to the atmosphere and thereby reduce its size considerably. There will be a cost in efficiency but weight and drag is a very important issue.
The question for me are
1 What materials are to be used (I assume high chrome refractory steals)
2 What size the condensers, where to mount them.
3 What is the power to weight ratio?
A twin engine design is best from a structural point of view, I am inclined to put the turbine and boiler in the one nacelle while the condenser is in a turbofan engine like pod outboard of the wings where it can be designed to exploit the so called Meredith effect. Residual steam pressure can operate a small inductor fan to keep airflow up while the aircraft is stationary. Parts of the wing leading edge can be used for cooling and to provide a de-icing function. The engine would be smooth, vibration free which should keep weight of the propeller, gearbox and mountings down.
The nuclear powered aircraft was to use jet propulsion.
A turbojet was modified for this use - the compressor and turbine remained, but the combustion chambers were raplced by heat exchangers. The air would be compressed bythe compressor, then heat from the reactor transferred to the air in the heat exchangers, and the air would then expand through the turbine, which would drive the compressor, and exit out the back to create thrust.
The XB-36H carried an operating 1MW nuclear reactor. The B-36 was powered by 6 2.8MW R-4360s, yet was thought to be underpowered. A 1 MW reactor wasn't going to power the plane. What it did show is the viability of such an installation, and how th eradiation affected systems etc. IIRC the crew compartment was fully shielded, but the reactor was not.
IMO cost was a greater factor. Synthetic fuel plants are very expensive to build. The 1939 Gelsenberg hydrogenation plant cost 208 million RM to build. Over ten times the cost of the Genshagen DB601 engine factory constructed during 1936. More then a Bismarck class battleship cost to build during the late 1930s. With a price tag that high it's easy to understand why Goering didn't build a few more hydrogenation plants as part of the German 4 year economic plan.