Eddie Salita Posted February 14, 2005 Share Posted February 14, 2005 Thanks Merjo. My idea was based on the similarity between the two formulas. And the fact they can behave similarly when flowing along pipes/wires. I reasoned that Poiseuille's Equation would be better, to determine the maximum flow(current) possible Poiseville assumed that the flow was streamline This means it wont apply as the flow of electricity seems to be pulsing. Dang, no easy way out after all. Back to the test wire. I might try it for curiosity's sake anyway. Thankyou, Jason Link to comment Share on other sites More sharing options...
Lee Miller Posted February 14, 2005 Share Posted February 14, 2005 Wrong again Wazza, Memory is a funny thing - I can remember certain things from a million years ago - but I can't remember where I left those bloody text books Lee. PS: My calcs were VERY general and based on a perfect world. My final paragraph indicated that there is much more to it than pushing water through a hole. If nothing else we got some intelligent conversation going (and I don't mean yours Wazza ) Link to comment Share on other sites More sharing options...
gingerbeer Posted February 14, 2005 Share Posted February 14, 2005 Now, are we talking about fluid dynamics or hydordynamics? And will the flow be superviscous or subviscous??? Steve Link to comment Share on other sites More sharing options...
anchar Posted February 14, 2005 Share Posted February 14, 2005 Now we're talking Reynolds Number, Stoke's Law..... Somebody slap Stephen merjo Link to comment Share on other sites More sharing options...
CThompson Posted February 14, 2005 Author Share Posted February 14, 2005 Thanks for the effort merjo and Lee. Merjo, just to clarify, when I say the holes in the tank are drilled to allow a 40mm fitting, they are able to take both a 40 and a 32m fitting. When fitted with a 32mm fitting, there is no size difference from one end of the pipe to the other as the larger sized hole drilled in the glass is on the outside of the bulkhead, where as the water flows through the middle. So the water flow going through it will have no turbulence or eddies due to any expansion in the tunnel. Nor is there any compression of the water as the pipe is 32mm all the way through, and there are no bends. As mentioned, this is only a short section of pipe, approximately 150mm, then the water will be out into a flat tray with an egg crate bottom. Possibly as close to a "perfect word" one will come to in a plumbing situation Lee. I hope to be able to utilise a “Durso Stand Pipe” on these two inlets, but I will only be able to do so if they don’t reduce the water flow too much. Once the 2000 litre tank is filled, and the pump turned on, I now know that the water will get through two 32mm fitting. I will start from this point, and try adding the Durso Stand pipe watching the water level in the overflow box to make sure I don’t reduce the flow to a point the overflow box overflows itself… The reason I would like to use 32mm fitting instead of 40 is due to the extra size of the pipes needed when one puts together a Durso stand pipe with a 40mm, compared to a 32mm fitting. It will be much harder to get all the parts into the limited size of my overflow box. In addition, I haven't got the fittings needed to do this in 40mm, but I have in 32mm. Appreciate your help guys. Craig Link to comment Share on other sites More sharing options...
TSMill Posted February 14, 2005 Share Posted February 14, 2005 Sorry guys....everyone is making a sweeping assumption of laminar flow here..... flow becomes turbulent at Reynold's Numbers above around 2300.....for 2m/s flow in a 32mm diameter tube you are talking a Reynold's No. over 71,000....most definitely highly turbulent flow! Hence you could work backwards and determine the velocity of the flow by taking the sq. root of 2gh No you cant! Basically what you are saying is that if you increase the length of vertical pipe you will increase flow rate! If you solve the Bernoulli equation you will find that the height becomes irrelevant when applied to vertical pipe. This makes sense as water is treated as incompressible and conservation of mass dictates therefore that flowrate cannot change along the pipeline. Most flow due to gravity that you will get through these guys is about 7m/s...regardless of length/height etc. As mentioned previously, flow through fixtures (particularly horixontal) will reduce this somewhat....but 2m/s will be a piece of cake. Link to comment Share on other sites More sharing options...
anchar Posted February 15, 2005 Share Posted February 15, 2005 there is no size difference from one end of the pipe to the other as the larger sized hole drilled in the glass is on the outside of the bulkhead, where as the water flows through the middle Ok...thanks for the clarification...disregard the continuity theorem then Craig. I wasn't sure from the original wording. Millsy, you said... QUOTE Hence you could work backwards and determine the velocity of the flow by taking the sq. root of 2gh No you cant! Basically what you are saying is that if you increase the length of vertical pipe you will increase flow rate! That isn't what I said...this is what I said... Likewise, the flow rate should decrease if the viscosity of the fluid or length of the tube increases. That's why he has R (radius of the tube) and P1 - P2 (pressure difference) in the numerator and L (tube length) and n (viscosity coefficient) in the denominator. ...I also said... (all things being constant ).... Anyway...it's all too hard...Lee's formula will suffice for Craig's needs This is yet another reminder as to why I changed disciplines from Engineering to Geology merjo Link to comment Share on other sites More sharing options...
Ducksta Posted February 15, 2005 Share Posted February 15, 2005 Craig did you fill the thing up yet? I have no idea what the nerdy types are argueing about at this point. I just want to know how it went The way I see it, fill it up, if you need the bigger pipes/fittings, go to Bunnings. No science involved. Looks to me like there are so many unknown variables flying about the place nobody can give you more than a confident probably. Link to comment Share on other sites More sharing options...
Gav Posted February 15, 2005 Share Posted February 15, 2005 experimentation works much better than theory anyway, as what actually happens in practice is what matters, not what is meant to happen. I found the solution eddie suggested the best, use a bucket and a tube and measure it that way. simple answers are nearly always the best Link to comment Share on other sites More sharing options...
Eddie Salita Posted February 15, 2005 Share Posted February 15, 2005 A FDE will ask you more questions than you could ever answer, and then give you a theoretical answer which will depend on a goodly number of varable factors. Its what they do. But what would I know. Smug bugger arent I You are right ducksta and Kinerata, Practical tests are best in this situation. Cheers, Jason Link to comment Share on other sites More sharing options...
CThompson Posted February 15, 2005 Author Share Posted February 15, 2005 Ducksta, Haven’t filled the tank yet. The glass is 19mm thick, so where the patch over the join in the bottom is, I’ve got a bit over 38mm of silicon. The tank makers made the tank on the 30 Dec 2004, and wrote in very clear permanent marker on the outside of the tank “Not to be filled till the 1st of March 2005”. If I do so, any anything goes wrong due to construction, I will void my warranty. In addition, I am still constructing all the panelling that goes under the tank, above the tank, and at both ends to close the whole lot off. Not to mention I still need to get into the tank for access to some of these areas to attach wood work, and lighting fixtures for example. My light is still being constructed - it will have 8 four foot fluros, three 70 watt metal halides, and eight small halogens which I intend to install blue bulbs for a dawn/dusk simulation. I would much rather the tank was empty when I bolt this to the ceiling, as standing in a meter of water to play around with electricity is not my idea of fun….. So yes, “suck it and see” will be the ultimate answer to the question, but to be told by such persons as Lee and merjo that a key critical point/bottle neck in the water’s recirculation system is okay, is a good bit of piece of mind as I have worried at it for months. I'm not aware that places such as Bunnings sell bulk head fittings? I can purchase them elsewhere of course. And at the end of the day, if I need to put in larger fittings I have built in enough redundancy that it will be just a matter of purchasing larger plumbing fittings. Craig Link to comment Share on other sites More sharing options...
Ducksta Posted February 15, 2005 Share Posted February 15, 2005 Last time I replumbed my pool filter, my pool shop man (old family friend) sent me to bunnings for all the pvc/elbows etc, i just assumed they would sell bulkheads and the like also? This may vary from store to store? Not sure, have friends who work at bunnings from head office down to shop assistants so will find out. Link to comment Share on other sites More sharing options...
TSMill Posted February 15, 2005 Share Posted February 15, 2005 Can i quote a quote????? Likewise, the flow rate should decrease if the viscosity of the fluid or length of the tube increases. No.....length of tube is irrelevant in the case of vertical alignment. The 150mm tube could be 1500mm and you will get the same answer. So how can you work backwards taking the square root of 2gh, if you know h is irrelevant? Link to comment Share on other sites More sharing options...
phatoscarlover Posted February 15, 2005 Share Posted February 15, 2005 Now weve got 2 engineers going at each other! This will be good! Link to comment Share on other sites More sharing options...
anchar Posted February 15, 2005 Share Posted February 15, 2005 Hi Millsy, So how can you work backwards taking the square root of 2gh, if you know h is irrelevant? Told you I was rusty After all, it was 12 years ago This is only usuable in a situation such as a leaking tank ie. calculating the speed at which the water exits the hole (which is equal to the speed acquired by a body falling freely through a vertical distance). Ah well, rocks are much more interesting than water running through pipes merjo Link to comment Share on other sites More sharing options...
CThompson Posted February 15, 2005 Author Share Posted February 15, 2005 Ducksta, Someone may prove me wrong…. Where as “pvc/elbows etc” may be purchased at Bunnings, and other hardware stores. Fittings such as bulk heads (also called “tank outlets”), are not available from them also. I have only found them available at aquariums (LifeGuard stuff) at a high price, and from specialty irrigation outlets (at a much more reasonable price), where they sell bulk heads produced for irrigation purposes, which we with tanks may also use. I personally have not seen bulk heads even available at plumbing stores. Craig Link to comment Share on other sites More sharing options...
TSMill Posted February 15, 2005 Share Posted February 15, 2005 Rocks eh.....just make sure you never take your schist for granite! Link to comment Share on other sites More sharing options...
anchar Posted February 16, 2005 Share Posted February 16, 2005 Rocks eh.....just make sure you never take your schist for granite! Fat chance! Mistaking plagioclase for orthoclase without the benefit of a microscope...now that's another matter merjo Link to comment Share on other sites More sharing options...
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