looking for a design

Discussion in 'Boat Design' started by Godwinned, May 22, 2014.

  1. Rurudyne
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    Rurudyne Senior Member

    Okay.

    First off, for those in the proverbial peanut gallery that may wonder in, the organic rankine cycle is simply one that substitutes an organic fluid for water in a steam engine. As you will recall, obviously not being in said gallery, this is a very old idea having been even tried with ether (they go big boom). The lure is the sometimes mercurial promise of gained boiler efficiency because with heavier molecular weight it is generally easier to vaporize a given mass of fluid. The problems have historically included things like flammability of the working fluid, same being toxic, and while you can obtain reasonably high pressures the temperature difference over the pressure range has frequently been lower so that engine efficiency suffers as much or more than what you gain at the boiler. In fact, the classic naphtha engines were popular to the degree that they were not because they were efficient but because you didn't have to be or pay a licensed boilerman to run one. That is the short version for any folks to whom this is new.

    Now, about your request: HFE 7000 is made by 3M as an engineered fluid.

    There is an HFE 7100 that is similar in some respects, but earlier it was a typo on my part. My bad.

    Anyhoo, "engineered fluid" means that, unlike Naphtha which is really a hodgepodge of distillates within a certain range of density, it consist of isomers having nearly the same chemical formula and the same characteristics. It was invented as a cleaner and is used in the cosmetics industry as well. I came across descriptions of it in a paper about organic rankine cycles.

    Just for reference a quick summation of HFE 7000's traits are:

    Critical pressure is 2,478 kPA

    Critical temperature is 165.55 C

    Molecular weight is given as 200 g/mol

    Specific Heat is 1.3 kJ/kgK

    Latent Heat of 142 kJ/kg

    It is a dry fluid that does not wet during expansion.

    Temperature at the condenser is cited as 40 C and above atmospheric pressure

    It is considered non toxic and non volatile by EPA



    Now, water for comparison has....

    Critical pressure of 22.04 MPA

    Critical Temperature of 373.15 C

    Molecular weight is essentially 18 g/mol

    Specific Heat is 4.187 kJ/kgK

    Latent Heat is 2270 kJ/kg

    It is a wet fluid during expansion



    You will notice that it takes 3.22 times as much energy to raise a kg of water 1 C relative to a kg of HFE 7000, and that it takes nearly 16 times as much heat to vaporize it. Now, on the downside the same weight of heavier fluid will not produce as much volume of vapor ...

    ... from ideal gas law, PV = nRT, it may be seen that 1 mole of water will produce 2.5257 L of steam at 200 C and 1 mole of HFE will produce 2.2178 L of steam at 140 C: the reason for the different temperatures has to do with needing same temperature difference between inlet and condenser for both fluids, as will be seen later this yields a very similar pressure range too ...

    ... so a kg of water will give 140.3167L of steam at 200 C

    ... and a kg of HFE 7000 will give 11.0889 L of steam at 140 C

    ... to have the same volume of steam at these temperatures, their pressures being nearly the same it turns out (see below), you need to vaporize 12.6538 times as much HFE 7000, but to do so only uses about 80% of the energy needed for water.

    ... and that's where the lure of using organic compounds enters into the picture.

    But for many organic compounds, especially the early ones, the temperature difference between high pressure and low pressure isn't all that good ... so what has often seemed like gold is in fact fools gold.

    An apples to apples comparison is in order.

    Among my texts --somewhere-- is a handy little chart giving normal historical ranges of pressures for single to quadruple expansion engines ... as you can tell I can't find things when I'm looking for them. I recall, though, that the data for HFE 7000 given ...

    @ 140 C inlet pressure is 1545 kpa
    @ 40 C pressure at the condenser is 119.7 kpa

    ... or a 1425.3 kpa (206.72 psi) pressure difference

    ... does indeed fall into the range of operational pressures associated with even triple expansion -- and just barely into the lower range range of pressures associated with quadruple expansion engines -- so deciding if the fluid has real value simply comes down 1) to how the temperature range over this pressure difference compares to water over a similar pressure difference and 2) how much extra work is required from the pump the same volume of steam weighs more with the organic fluid (this second bit is more than I'm even remotely prepared to address at this time).

    Small steam engines normally do not work with vacuum, so water at atmospheric pressure (101.325 kpa) has a condensation temperature of 100 C, meaning that an apples to apples comparison, for similar thermal efficiency, would have the temperature at inlet be 200 C.

    Saturated steam at this temperature has a pressure of 1555 kpa. So the fluids do in fact compare well over the same temperature range (as had to be the case for my earlier comments to be honest).

    What is different, said a different way, is that you are not throwing away as much unusable energy at the condenser.

    And likewise the engine, boiler and all components are operating at a lower temperature as well.

    This is not a situation that applies to many organic working fluids and I will not even begin to argue that you can drive any organic fluid to the operating temps used in power plants or other turbine steam engines ... my claims, such as they are, only apply to small steam engines.

    Here is the paper with details on HFE 7000: http://www.journal-ijeee.com/content/4/1/12
     
  2. Rurudyne
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    Rurudyne Senior Member

    It should be no more rocket science than regular steam engines are. The increased mass flow rates may demand a higher power pump, but in compensation you can reap other advantages like reduced operating temperatures.

    There is, of course, no such thing as a free lunch and some of these better fluids that work in a convenient temperature range are apparently relatively expensive while others that are cheap to buy need lower temperatures than most of us can expect from where we live.
     
  3. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    Check the Cyclone type steam engine. It should generate as much power as you will ever need!. Best of all it has max torque right at the bottom where you need a prop to bite.

    http://www.cyclonepower.com/
     
  4. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    Organic Rankine Cycle (ORC) and Cyclone Engines

    "It (building an ORC Engine Cycle) should be no more rocket science than regular steam engines are. "

    In theory this may be true, but in the actual practice of building machines, putting together an ORC will be far far more complicated than using the tried and true steam cycles, that have been around for about 200 years now. Many "armchair engineers" read a news bite about some great new technology, and imagine how easy it would be to make the machine. These people do not have the experience of actually building these types of machines, so it is easy to imagine their success.

    As to the Cyclone Engine Technology, from what I have seen so far (very little to nothing about the real performance of these machines, and annual promises that the Cyclone engines will be powering everything from lawn mowers to automobiles, very "soon"), this technology is really nothing new, and the promoters know that the performance of their engine design is at a dead end, yet they continue to seek investors. Again many "armchair engineers" read a news bite about Cyclone technology, and imagine the coming of a new steam engine break-thru. I have spent 50 years as an engineer in the steam power and steam cycle design arena, I love steam engines and would love to see more applications, but I don't see Cyclone Technologies going anywhere realistically.

    BTW, lets not steal this thread, the originator is looking for a boat, for his own use, and he is not going to be building a new ORC, etc., lets move the engine/cycle discussion to "Propulsion and Engines" if anyone wishes to continue this.
     
  5. Rurudyne
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    Rurudyne Senior Member

    I wasn't hijacking. I made a suggestion and he asked for further clarification (and I hope I provided it).

    One thing I must confess, though, is that when I first glanced at the thread I missed the word "plans" in "plans budget" and actually ... well, you know, got the wrong impression about his budget. Then I came back and there was a discussion about building a steam engine. Kinda threw me for a loop and resulted, GIGO style, in a comment about expense in that first post of mine.

    BTW, I would just like to mention that if Godwinned wants to use steam power he needs to look at varied State regulations if he wants to travel down the Ohio or upper Mississipi. For example, I believe that Ohio won't let you get by without certification (who, wanting just to sail a few miles, wants to waste time arguing that because of US Coast Guard rules there is no regulation for steam power on boats under 40'?) if your steam engine is greater than 30 HP. Interestingly they permit, IIRC, 30 HP boilers ... so I guess you could have two 30 HP engines... ;)
     
  6. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Some states have state licenses for engineers and pilots. Personally have known men who worked on Mississippi river pushing big tows, with only state licenses. As long as they don't cross state lines. Feds regulate interstate commerce, not internal state regulations.
     
  7. Yobarnacle
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    Yobarnacle Senior Member holding true course

  8. Godwinned
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    Godwinned Junior Member

    all I can say to that is- I completely hope your right...;)!!
     
  9. Godwinned
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    Godwinned Junior Member

    excellent explanation. Thanks. I still like water better. I just suck it into the boiler from the lake. But in theory it sounds good.
     
  10. Godwinned
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    Godwinned Junior Member

    yep, that's not going to happen. Ill stick to what's known. and the engineering is beyond me anyway. water works. and has, for a long time. why complicate it? ill let others with the knowledge and experience handle the theory. please back to a boat hull.
     
  11. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Ten or 15 years ago saw the first deep water drilling. Before that, a few hundred feet water depth was best they could do. Now they are drilling in more than a thousand feet of water. Primarily, improvements in dynamic positioning made it not only feasible, but reality. maybe in another ten years or so, they'll be drilling in MILE deep water. I predict it will happen. the world isn't abandoning crude oil simply because it's difficult to get at. we'll get it.
     
  12. Godwinned
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    Godwinned Junior Member

    no worries. I just want to find a good, simple way to have a boat within my budget. One that isn't overly complicated. I figure a 26- 30 ft boat built over a few years is not unreasonable. I do like radius chined or round bilge but worry about the roll periods. chined hulls are simpler. But not as good with steam from my understanding. As mentioned I could go for a small diesel. economy is important to me.
     
  13. Godwinned
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    Godwinned Junior Member

    from my understanding, costs of drilling deeper is reaching a point where the costs of getting the oil are no longer viable for what is earned by getting it. Thus increases in o.p.e.c. prices.

    wont there be a time when oil runs low enough that the cost benefit will be stoplossed?

    I hope I am wrong.

    But you cannot argue that oil is finite.

    The earth only has so much of it. and judging by the prices today, its getting harder and harder to find, drill and produce.

    my question is, what are the costs of production ? since diesel is needed to produce diesel. Isn't there a limit to how much can be spent, without losing money on it? this seems to me like a vicious cycle??

    Anyway back to the boat.

    what about chined hulls vs. round bottoms or radius chined?

    I know there are probably lots of threads on it here but in a nutshell what are the pros and cons of either?
     
  14. Yobarnacle
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    Yobarnacle Senior Member holding true course

    you didn't mention flat bottomed. many original steamers were flat bottomed, and the most stable hull form, is a flat bottomed barge.
     

  15. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Another form might be a pontoon boat style hull. You could install a split paddle wheel at the stern, and perhaps make steam engines from double acting rams. Thus the engines located on or at the paddle wheels, saving space and complexity.
     
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