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Recent content by chrisjc

  1. chrisjc

    Calculation of laminar / viscous sublayer

    Hi thanks guys. btrueblood... i need to calculate friction factor in spreadsheet so cant use charts... I still cant find a reference for that equation (using massey mechanics of fluids)! katmar... sure i figured it would be kind of approximate. I only need to estimate whether rough because...
  2. chrisjc

    Calculation of laminar / viscous sublayer

    Hi there, I'm interested in determining whether or not a pressure pipe can be considered to hydraulically smooth or not however i've only found one unreferenced equation for calculating the laminar sublayer thickness: http://wiki.answers.com/Q/What_is_meant_by_Hydraulic_smooth_pipe...
  3. chrisjc

    Estimating/modelling catchment discharge

    Hi there, Sorry this is a really vague question but i figure it's worth putting my query out there. I am tasked with assessing hydro power feasibility for a tropical rainforest region, however my background in hydrology is rather minimal. What I am hoping for from this forum is some pointers...
  4. chrisjc

    Gurgling Battery Normal, Bad, Dangerous?

    Hi, Thanks for posting. It's kind of weird i dont think its charging problem... if anything, they arent gassing and fizzing as much as they should on a good bulk charge. This is more like battery indigestion noises... like large amounts of gas trapped which suddenly moves at once but like a...
  5. chrisjc

    Paramatising a solve block with multiple unit types

    Thanks, This approach occurred to me but I like my units and thought I was missing something fundamental!
  6. chrisjc

    Paramatising a solve block with multiple unit types

    Hi there, I have set of equations that I need to solve numerically (colebrook-white, darcy, and bernouli equations). I express these equations in a solve block and use find to solve. Explicit matrix form works fine: {x, y, z} = find(x,y,z) However, I want to paramatise this solve block i.e...
  7. chrisjc

    Gurgling Battery Normal, Bad, Dangerous?

    Hi there, I have a pair of 250ah 6V lead acid traction batteries which are a couple of years old now... they have been permanently connected to a solar panel in series, but I have just brought them indoors and keep them topped up from time to time. The batteries... im not sure if it is one or...
  8. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Many thanks Katmar, Your post has greatly clarified the problem. The velocity head and pressure drop terms were separated purely because that is how I dug the equations out of my textbook. Joining the terms into one energy balance equation makes a lot more sense. As it happens what I'm really...
  9. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Hi IRstuff, No MathCad's solve block black-artiness solves the lot in one go. I am using excel because I must solve for many different values and I couldn't work out how to parametrize the solve block in mathcad. It works fine when assigning the Find(x,y,z,...) results to an explicit matrix...
  10. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Hi Prex, Yep absolutely, i did try this for starting values but unfortunately the head-loss is quite significant for some of the various pipe diameters that my model must consider... I am looking at small capacity rural hydroelectric system that will have relatively long penstock pipework which...
  11. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Hi BigItch Thanks for the help, it would be good to know if ive got the theory backward and inside out! Perhaps it is my poor use of terminology leading to confusion though, i think i meant hydrostatic head,potential head,differential head or whichever one it is! The way i understand the...
  12. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Hi thanks for the link, Sorry, for obscure post! My objective is to calculate head-loss for a given pressure head and set of pipe dimensions so velocity, reynolds number, fiction factor and head loss are all unknown. From Bernoulli i have velocity = sqrt(2 g (h - headloss_friction)) But...
  13. chrisjc

    Numerical solution of Darcy equation for headloss and velocity

    Hi Im having problems with a numerical solution to these equations, and i think it relates more to the process of iterative solutions rather than to the fluid theory. For some initial values a convergent solution is found, but often the Darcy frictional headloss equation returns a value greater...
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