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Post by marchesarosa on Dec 10, 2013 12:44:14 GMT 1
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Post by abacus9900 on Dec 10, 2013 16:01:24 GMT 1
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Post by principled on Dec 10, 2013 19:39:35 GMT 1
I think not such a good idea.
It reminds me of one of my students some years ago. As part of an assignment he brought a plan of a solar powered, concept car. I queried what would happen if the driver decided to take a night drive that was longer in duration than the available energy in the on-board batteries. The next week he returned with the solution. He placed generators on each wheel.
This idea is the same. The only time there would be a net gain of enegy from the fan would be: a) Downhill b) Where there is a headwind which is greater than the vehicle's speed (ie extracting energy from the wind). Otherwise, the blades would offer reistance to the airstream anytime we try to extract energy from it.
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Post by alancalverd on Dec 10, 2013 21:36:11 GMT 1
I queried what would happen if the driver decided to take a night drive that was longer in duration than the available energy in the on-board batteries. Thank goodness you never asked Gottlieb Daimler what would happen if he tried to drive further than the available energy in the petrol tank. Perhaps one of your predecessors wondered what would happen when the horse ran out of hay? Fortunately there are more clever inventors than smartarses in the world of engineering. |
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Post by principled on Dec 11, 2013 11:01:02 GMT 1
Au contraire mon ami.
As it happened, the assignment I took the example from was actually designed to get final year HNC students to think "out of the box". It was a complex assignment written (despite various governments' assertions that the education sector never talks to industry) jointly by R&D engineers at a vehicle manufacturer and myself. All students worked as technicians in various R&D departments.
What the student's response to my question actually showed was that WE had failed in our education programme.
I actually applaud the ingenuity of the guy who built the electric car. But that does not detract from the fact that the fan idea will only add net energy to the battery in very restricted circumstances.
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Post by abacus9900 on Dec 11, 2013 11:36:53 GMT 1
We have to remember too that despite electric cars seeming a "clean" form of transportation, the electricity itself has to be generated, which will either involve the use of fossil fuels or nuclear energy which pose their own problems.
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Post by marchesarosa on Dec 11, 2013 13:03:13 GMT 1
All the start up energy will have to come from a battery, obviously. But once a certain speed has been achieved the turbine will help to recharge the battery, partly anyway, won't it?
It's a pity the video did not go into more detail.
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Post by abacus9900 on Dec 11, 2013 14:24:16 GMT 1
All the start up energy will have to come from a battery, obviously. But once a certain speed has been achieved the turbine will help to recharge the battery, partly anyway, won't it? It's a pity the video did not go into more detail. Won't they have to be topped up every so often? They will have to provide places that permit this. |
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Post by principled on Dec 11, 2013 19:48:38 GMT 1
Marchesa,
The turbine might seem like a briliant idea on the surface, but it has a drawback. Let's see if I can explain why.
To make things simple, we'll assume that the vehicle body has no aerodynamic drag, just the normal rolling resistance and the turbine has no friction. There is no wind so at rest the fan is stationary.
As the vehicle moves forward it moves through the stationary air column and the frictionless turbine rotates freely. Because it is rotating freely, (ie without load) it does not add any reistance to the vehicle's forward motion. However, as it is spinning freely it generates no power either.
We now apply a load to the turbine (ie by connecting it to the battery). The turbine will slow because of the load and start to create a resistance to the airflow though it, thus adding more resistance to the vehicle's motion and so require more energy from the drive motors and batteries. Assuming the turbine and its associated charging system were 100% efficient, then the increased power required because of the turbine's reistance to the air flow through it would be exactly matched by the power fed into the baterry by the turbine. Obviously, nothing is 100% efficient, so the inceased power caused by the air's resistance would be more than the turbine provides to the battery.
When going downhill the turbine would supply net energy to the battery because of gravity, and in this case the turbine could act as a forrm of regenerative braking.
In the case I have outlined (where the body has no aerodyynamic drag) then if the wind was opposing the direction of travel, there may also be a net energy gain. However, I don't think this would be the case in reality because of aerodynamic drag.
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Post by alancalverd on Dec 11, 2013 19:51:48 GMT 1
What the student's response to my question actually showed was that WE had failed in our education programme. Certainly a little physics never comes amiss in an engineering program, but your student was far from alone in his delusions. Returning to the car with a fan on the front, we note that the fan is supposed to recharge the battery once the car exceeds 40 mph. Brilliant. Drive at 60 and it will keep going for ever! At 120 mph it will continue to accelerate until it reaches orbital speed! Yet another perpetual motion machine, wasted on an ignorant world. |
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Post by rsmith7 on Dec 11, 2013 20:23:43 GMT 1
Mr P,
It's amazing the number of people who have no understanding of energy. That would include every member of our government sadly. I despair here in Orkney ... not a single view free from a silly wind turbine, hundreds employed (temporarily) in tidal/wave energy stupidity and poor people dying in their beds from cold. Yet they swallow the "due to wholesale energy prices" mantra, hook line and sinker despite wholesale coal and gas prices being static for a decade. It's boring.
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Post by principled on Dec 11, 2013 21:31:58 GMT 1
RS Don't get me started on renewable energy , please. I have just sent another email to my MP based on the link supplied by Marchesa on the about turn in Germany (ie: the idea that renewables should pay for the firm spinning reserve they require) I don't expect him to reply.  P |
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Post by marchesarosa on Dec 18, 2013 13:56:58 GMT 1
Thanks for the explanation, principled.
I suppose a sail is the only genuine means of harnessing wind power for locomotion.
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Post by marchesarosa on Dec 18, 2013 13:59:24 GMT 1
Thanks for reminding me about writing to MPs, principled. I'll ask Hilary Benn what he thinks about renewable energy producers paying for the spinning reserve.
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Post by jonjel on Dec 19, 2013 16:52:06 GMT 1
Thanks for the explanation, principled. I suppose a sail is the only genuine means of harnessing wind power for locomotion. Marchesa. I worked with a company a few years ago who were developing a sail a little like a venetian blind for merchant ships. It seemed pretty good to me, but I suppose the speed the ships go at present would be difficult to duplicate with sail alone. Whether it got beyond the development stage I do not know. I also had a friend in one of the Physics departments who devised a machine that would 'sail' directly into the wind, which at first thought seems an impossibility. He had a propellor mounted on a chassis and the prop was connected via a simple belt drive to a pair of wheels at the front. The third rear wheel was on a swivel and had a large fin attached. When you blew a high speed fan at it from any direction it would turn towards the fan and rush at it like a Lemming. Very clever. All to do with lift equaling or exceeding drag, and vice-versa. |
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