ReadFamily wrote: > > Are we fooling ourselves a little with pretending that there is a difference > between removing kinetic energy from a flowing stream and > driving a turbine > with a high head using the potential energy of the water. > > In a stream there is a relationship between speed of flow and difference in > height. It may be complex, but its there, and we know it > intuitively to > some extent.
You are alluding to a useful concept known as the "velocity head". This is the height that an object is required to fall solely under the influence of gravity, without any friction or other losses so as to reach the given velocity. The relationship is NOT complex, the velocity head (H) = V^2/(2*g), where g is the gravitational constant, which in the metric system has a value of 9.8. So for example, if V = 2 meters/sec the associated velocity head is 0.204 metre. > If the stream is level then its a lake - it doesnt move - as the difference > in height grows, so does the horizontal component of gravity and > so the > horizontal force applied to the water, hence its acceleration. NO - part 1. Imagine water exiting a tank through a hole in the side, with water being replaced at the same rate by being piped in through a second hole on the other side of the tank. Clearly water is moving, but provided there is not turbulence the water in the tank remains level. NO = part 2 Our sense of what up and what is down is due to gravity. By definition, gravity cannot have a horizontal component. I have previously argued through this eGroup that hydraulics is far from being intuitively obvious, except for a gifted few. Once again, intuition fails. > The water accelerates to the point where the forces holding it back are the > same as the forces pulling it downstream... ... The ideas you are expressing here form part of classical hydraulics - this had been systematically studied and the quantitative relationships determined by the middle of the 19th century. It is all available on the internet - put the following keywords into your favourite search engine "hydraulics, Manning's equation, Bernoulli's equation, critical flow, super critical flow" and you will find much to interest and challenge you. Regards, Max Enfield Planetary Power ------------------------ Yahoo! Groups Sponsor --------------------~--> $9.95 domain names from Yahoo!. Register anything. http://us.click.yahoo.com/J8kdrA/y20IAA/yQLSAA/FGYolB/TM --------------------------------------------------------------------~-> Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! NOTE: The advertisements in this email are added by Yahoogroups who provides us with free email group services. The microhydro-group does not endorse products or support the advertisements in any way. More information on micro hydropower at http://microhydropower.net To unsubscribe: send empty message to [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/microhydro/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
