Some stupid questions...
Posted by steveinky
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Re: Some stupid questions... February 21, 2023 10:48AM |
Hi Steve,
Your first question regarded a 4 cylinder, triple expansion engine, such as was found in the USS Texas (BB-35) which is a New York class battleship and now a naval museum in Houston (albeit closed at the moment since Texas is undergoing a well-publicized drydocking in Galveston, you can see details on the USS New Jersey You Tube channel). A similar engine type was found on RMS Titanic -- although we can get caught in semantic knots since there was a 4th level of expansion in the Parsons turbine situated between the reciprocating engines. Since the two engines shared this expansion stage, things get a bit cloudy, terminology-wise.
There really isn't a big mystery as to why they split the third stage into a pair of cylinders, it was for mechanical convenience. This allowed the designers to keep the pistons and cylinders to a more reasonable diameter. The smaller pistons also weighed less and allowed for better engine balance and smoother operation.
Quadruple Cylinder, Triple Expansion, Engine
As for your second question, the water cooled condensers provide a vacuum that allows for expansion of steam below atmospheric pressure. The condensers work on the principle that steam occupies a far greater volume than water. If you condense the water in an air-tight chamber, nothing can fill the space occupied by steam before condensation, and you get a vacuum. Things aren't that simple, in real life, since air and other noncondensable gasses are entrained in the steam. Given time, these will gather in the condenser and raise the pressure. Therefore, some sort of air pump is fitted to the condenser to reject these gasses to the atmosphere. In earlier systems, this would be a piston pump. In modern turbine setups, such as the ones with which I worked on an aircraft carrier, they use two-stage steam ejectors (jet pumps). The ejectors also serve to establish a vacuum upon engine startup. In some instances, your steam system may also have some sort of deaerating feed tank which serves to remove the majority of entrained air and gasses before feeding the water to the boiler (in our case, it was a reactor). Submarines were too small to have DFTs, aircraft carriers had the room.
Regards,
Ken
There were a number of quadruple expansion engines built but, generally speaking, the added friction losses and low superheat temperatures tended to make these an example of diminishing returns. In some cases the quad expansion engines had five cylinders. Quadruple Expansion
Edited 1 time(s). Last edit at 02/21/2023 11:13AM by frustrated.
Your first question regarded a 4 cylinder, triple expansion engine, such as was found in the USS Texas (BB-35) which is a New York class battleship and now a naval museum in Houston (albeit closed at the moment since Texas is undergoing a well-publicized drydocking in Galveston, you can see details on the USS New Jersey You Tube channel). A similar engine type was found on RMS Titanic -- although we can get caught in semantic knots since there was a 4th level of expansion in the Parsons turbine situated between the reciprocating engines. Since the two engines shared this expansion stage, things get a bit cloudy, terminology-wise.
There really isn't a big mystery as to why they split the third stage into a pair of cylinders, it was for mechanical convenience. This allowed the designers to keep the pistons and cylinders to a more reasonable diameter. The smaller pistons also weighed less and allowed for better engine balance and smoother operation.
As for your second question, the water cooled condensers provide a vacuum that allows for expansion of steam below atmospheric pressure. The condensers work on the principle that steam occupies a far greater volume than water. If you condense the water in an air-tight chamber, nothing can fill the space occupied by steam before condensation, and you get a vacuum. Things aren't that simple, in real life, since air and other noncondensable gasses are entrained in the steam. Given time, these will gather in the condenser and raise the pressure. Therefore, some sort of air pump is fitted to the condenser to reject these gasses to the atmosphere. In earlier systems, this would be a piston pump. In modern turbine setups, such as the ones with which I worked on an aircraft carrier, they use two-stage steam ejectors (jet pumps). The ejectors also serve to establish a vacuum upon engine startup. In some instances, your steam system may also have some sort of deaerating feed tank which serves to remove the majority of entrained air and gasses before feeding the water to the boiler (in our case, it was a reactor). Submarines were too small to have DFTs, aircraft carriers had the room.
Regards,
Ken
There were a number of quadruple expansion engines built but, generally speaking, the added friction losses and low superheat temperatures tended to make these an example of diminishing returns. In some cases the quad expansion engines had five cylinders. Quadruple Expansion
Edited 1 time(s). Last edit at 02/21/2023 11:13AM by frustrated.
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Re: Some stupid questions... February 21, 2023 11:00AM |
I think you misunderstood the first question. A FOUR CYLINDER, TRIPLE EXPANSION engine limits the low pressure cylinder to a reasonable diameter with two cylinders of half the displacement. It also allows better balance than in a three cylinder engine at the expense of a longer engine.
Lohring Miller
Lohring Miller
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Re: Some stupid questions... February 22, 2023 05:17AM |
Thanks for the replies. I do see an advantage to the 4 cylinder triple expansion engine in that the low pressure cylinders have staggered crank throws. I think this would allow for greater expansion and smoother operation.
There may be little advantage to a quadruple expansion engine, but the SS Milwaukee Clipper has one. Here is a picture I took of the boat a few years ago. The tours don't include the engine room anymore for "safety" reasons.
Have a nice day
Steve
Edited 1 time(s). Last edit at 03/01/2023 02:56PM by steveinky.
There may be little advantage to a quadruple expansion engine, but the SS Milwaukee Clipper has one. Here is a picture I took of the boat a few years ago. The tours don't include the engine room anymore for "safety" reasons.
Have a nice day
Steve
Edited 1 time(s). Last edit at 03/01/2023 02:56PM by steveinky.
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Re: Some stupid questions... February 28, 2023 01:05PM |
Rick the water under a boat works great on the keel condenser.
I always ran 30 inches of vacuum on my boats.
Rolly
I always ran 30 inches of vacuum on my boats.
Rolly
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