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spline

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  1. spline

    UK House prices: News & Views

    Tradition Future HPI / SPREFS chart, Jun/09 The step up clearly indicated a turn in the Halifax, but unclear whether it's done or ongoing?
  2. Hi Skipbob, The testing is slightly involved and probably best done with one of your engineering mates. You’ll probably need to beg, buy, or borrow some sort of rotary torque transducer (something like one of these, but obviously depending a lot on your setup) that can measure the torque applied to a shaft and it’s rotational speed – then you connect some sort of brake via the torque transducer to the output of your device and set everything going. Keep the flow velocity constant and measure pairs of torque and speed at various settings of the brake, i.e. at various rotary speeds of the device, and plot the graph of torque versus RPM. Then plot another graph with torque multiplied by RPM versus RPM – this is proportional to the power output and will have a peak somewhere in the middle; that’s the best operating point, i.e. maximum power for that particular flow speed. You’ll also need to convert from RPM * ft-lbs into your favourite power unit, kW, HP, etc. You would repeat the exercise at different flow speeds to build up a set of performance graphs. Another way of testing is to load the device with an electrical generator and resistive load - generally the voltage will be proportional to the RPM and the torgue to the current, so that mechanical power (torque times RPM) transmitted along the shaft roughly tracks the electrical power (volts times current) coming out coming out of the generator. This sort of test is easier to set up and do, but more tricky to interpret as some power usually gets 'lost' in various places.
  3. Hi Skiprob, So what’s happened with the super efficient windmill you invented on the other thread, and has it morphed into a water powered device? Anyway, if you're spending money on this some cautions are in order. “Not being an engineer” is fine, but you need to learn the differences between forces/moments, speed, and power, and even then it would be good idea to build a small scale model and measure the performance. At least you'd get some idea of whether the general concept was a runner or not. Tech stuff: if it has a rotary output, measure the Torque and RPM for a range of different rotational speeds while keeping the water flow constant - the power is proportional to Torque * RPM, although you’ll need to do a bit of scaling to get the units properly consistent. You'd characterise the system with two graphs: the Torque versus RPM curve, and the Power versus RPM curve; the Torque curve will typically start high and fall as the RPM is increased; the Power curve will start low, have a peak somewhere in the middle, and then fall away again. Ideally, you'd choose to operate the device at an RPM close to the maximum power point. The efficiency is given by the power measured on the shaft (see above) as a proportion of the power available in the water flow, usually something like 0.5 * water_density * swept_area * flow_speed _cubed and expressed in the appropriately consistent units.
  4. spline

    new windmill design

    Skibob, The starting point and general framework for any discussion of a wind turbine is usually the Betz limit, then how far below that the current state of the art is sitting, and finally what clever things can be done to close the gap. Now, as far as I’m aware, the ‘gap’ is somewhere around (very rough guess) 10% and the commercial WT companies are competing to close it with improvements to aerofoil section design, skin drag and boundary layer / separation control, and generally lots of other small tweaks. There is some additional scope if one considers the non-uniform wind profile seen by large WTs, and the additional energy available in the approach flow turbulence. But all this implies that the scope for a ‘multiple times’ improvement is probably not there, so the first thing you need to do is apply some sort of ‘sanity check’ to your claims before you commit to spending large amounts of money on engineering and business plans – either by making a small model and getting some performance data, or by posting a picture or the general principle of the thing (the provisional patent you already have should protect the idea) for feedback. You will get the same response whoever you talk to, so you might as well start here.
  5. Hi Karen – You have to admit, the helix is really more about German submarine periscopes and vibration/loading control than the fundamental computational mechanics of life itself, and presumably a triple helix would probably do just as well. I like the spinnaker allusion, it's a nice romantic one, but modern spinnakers work in a fundamentally different way – this is not the variation of bluff body drag with direction [and, incidentally, an eye-popping amount of energy destruction by flow separation and wake turbulence] as found in the old-fashioned cup-anemometer and the more trendy ‘eco-styled’ Bluenergy turbine, but on making sure that the flow sticks to the back and develops a decent ‘suction’. Again, nothing to do with this WT design. And trumpeting the 'good' performance at 4mph windspeed is worrying - there are hints of where the company's priorities might sit. I suppose my initial thought, based on a quick look, is that it looks more like a nice marketing concept designed to extract money from fashionable eco-nitwits rather than being good at extracting energy from wind/sun.
  6. I must admit, this bit does not sound too promising: “designed based on sailing engineering and the Double Helix of the DNA molecule”, especially from an aerodynamic point of view which, I suppose, is what matters. It looks pretty though, but, rather worryingly, more like something an advertising agency or marketing department might have dreamed up after chatting to a few greenies in a focus group than a useful machine for extracting energy.
  7. spline

    new windmill design

    From what I understand about windmills, there is a ‘theoretical’ aerodynamic efficiency at the Betz limit, say around 59% of the kinetic energy passing through the disk, and then you lose a bit more from skin drag and induced drag caused by the wake/tip vortices – this takes you down to maybe 45-50% (very rough guess), so the possible aerodynamic improvements are not really huge, more about tweaking the aerodynamic sections, boundary layer control, and optimising the lift distribution, etc. So at a first take, I’d say that claims of doubling or tripling the efficiency look rather fanciful - you’ll need to explain what the particular problem was that you have ‘solved’.
  8. spline

    Hydrogen

    Hi Dog – I think I agree with malco, H2 is really a container of energy and has to be “made” somewhere. I guess it’s main advantage would be no CO2 emissions at the point of use, but obviously plenty at the point of manufacture, and, quite important for urban use, there is no trace sulphur in the fuel, so that’s an huge reduction in SOX as well. But I think it’s also quite bulky per unit of energy delivered and that would impact the range or likely size of the vehicles – aeroplanes would come out looking very fat.
  9. A quick update - I’ve added about 450 pages of region / city / district graphs to HousePrices.uk.net based on the DCLG median prices from LR. At the moment it runs up to Q3/2006, but the Q4 figures should be available quite soon, and I still need to add data for NI and Scotland and tidy it up a bit. Anyway, here’s the link to house prices in Hammersmith and Fulham.
  10. They differ from HPC in one key aspect - you need to host it *externally* to get it work.
  11. spline

    Assessing Wind & Renewable Energy for the Home

    The key to making this work has to be getting the net metering tariff to be more widely implemented, and supported by a low-cost and relatively standardised mechanism for producing, aggregating, and trading those Renewable Obligation Certificates (ROCs).
  12. Interesting historical visions of the future ... The House of Tomorrow 1933-1934 Designed by: George Fred Keck + own airplane hangar + machine dishwasher + energy efficient 12-sided wedding cake shape + all-glass hermetically sealed walls + humidity controlled air-con and dust free + electric eye doors + passive solar heating Links: http://www.historiclandmarks.org/feature/feature0802.html http://www.nps.gov/indu/History/House%20of%20Tomorrow.htm
  13. I think that’s also part of the UK renewable energy “roadmap” – developing fuel cell technology is expensive, so best to start with displacing inefficient centralised generation by local CHP running on natural gas as the infrastructure is already present, then when things have got going move across to the heavy duty mobile power applications.
  14. spline

    Assessing Wind & Renewable Energy for the Home

    Abolutely, and another trick played by Windtrap is to quote a “peak output” of 200W for the FM910-3 when even at the (very high) optimum windspeed of 16m/s the current delivered into 12V is only 12A, so that’s 144W – there is a sneaky multiplication by 1.4 “justified” by a cleverly hidden peak versus RMS type misdirection. The manufacturer's website (Marlec) is quite good, though http://www.marlec.co.uk/products/products.htm
  15. spline

    Assessing Wind & Renewable Energy for the Home

    You need to be cautious with wind energy systems to avoid getting well and truly kippered. Take a look at the performance graphs, especially power versus windspeed - this £499 package includes a spectacularly appalling Rutland 503 generator that produces less than 0.1A into 12V, or only 1.2W , with a typical onshore 6-8m/s UK wind speed – so unless you live somewhere extremely windy it will be next to useless. It would take almost 1000 years to recover the costs. I would start with your average local wind speed (see below), then size your rotor/generator based on this and the performance curves. For the UK, try to get something with good aerodynamic efficiency. UK Wind Map (quesstimate) http://www.bwea.com/images/misc/noabl_c.gif DTI UK Wind speed database (and postcode converter, bit fiddly but does work, 2letters+4digits, no spaces) http://www.bwea.com/noabl/index.html http://www.dti.gov.uk/renewables/technolog...eed/online.html
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