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Electric field generation between anode and cathode

  1. Aug 11, 2017 #1
    Electric experiment.jpg Hi

    I'm running an experiment where I want to see the electrical field generated when I energise a submerged anode (an array consisting of 4 x stainless steel tubes spaced equidistance apart) and cathode array (similar to the anode) upstream and downstream of the flowing water tank (glass sided, concrete bottom).
    The generated electrical field (v/cm) is shown in the attached image? Can anyone explain to me why this type of field is generated? There is a high v/cm at both the anode and cathode but a marked tail off between the two?
     
  2. jcsd
  3. Aug 12, 2017 #2

    Baluncore

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    Welcome to PF.

    The diameter of the electrodes is small compared with their separation. For that reason the field will be stronger closer to the electrodes. Parallel plates would have a more linear field.

    Colours are quite meaningless without a scale and some real numbers.

    Is that a numerical simulation or the plot of real experimental measurements?
    How do you measure the field, what is the relative size and orientation of the 1D, 2D or 3D sensor?
    You only show two electrodes in the plan or cross section, which picture is which?
    Where are the grids of electrodes you write about but do not show?
    Does the sensor change the field?
    How conductive is the water?
     
  4. Aug 12, 2017 #3
    Hi thanks for the comments

    The graphs are from real tests we conducted. Computer simulations showed that this was suppose to be able to produce a more linear electrical field but alas empirical work show otherwise.

    The colour scales show the observed field from blue to red it's between 0 to 0.61v/cm respectively for the top image and 0 to 0.34v/cm for the image below. The squares on the image just represent the rough position of the electrodes. To be honest I'm more interested in the generated field than the actual values. I'm really trying to generate an linear field without the large drop in voltage in between the electrodes.

    The pipes we used are 10mm diameter 316 grade stainless. There are 4 pipes mounted equidistance apart from one side wall to the other this is the same configuration for both electrodes. The left hand side in the graph is the anode and the right hand side is the cathode.

    The lower image shows only a single set of pipes being energised which caused the observed flow field (just for interest)

    Essentially we wired an oscilloscope with a pair of wires at a 3cm distance apart mounted on a wooden pole. This measures the horizontal voltage across a known distance. I was hoping this measurement method is passive but i might be wrong? On average the conductivity of the running water was 0.05 microsiemens.

    With the plates would you place them parallel to the flow and in the same position as the tubes or would it need to be an entirely new configuration?

    Thanks for your help
     
  5. Aug 13, 2017 #4

    Baluncore

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    You need to reduce turbulence. Use a strip of thin stainless steel sheet, edge-on to the flow. Fold the strip like a cookie cutter so it makes an electrical wall across the flow that is also a flow collimator.

    How do you measure conductivity of the running water as 0.05 microsiemens? Is that 20 Meg ohm? The input impedance of an oscilloscope is probably 1 Meg ohm, so measurement will load the field you are trying to measure. Maybe add salt to the water to lower resistance?

    You have not understood the importance of reporting scale. I find it difficult to identify the field since there is no scale for colour. It is your loss.
     
  6. Aug 14, 2017 at 3:27 AM #5
    Thanks for replying again,

    Ok, so placing metal strips edge on the flow. Are you talking about replacing the 4 x tubes with the 4 x steel strips, what sort of widths of strips do you think we will need? I can imagine that we can cut a longer piece of metal for each electrode and concertina it so we can increase surface area, hopefully won't take up too much space, we want to minimise the impact on the hydrodynamics as the water flows through the electrodes so don't want to narrow the gap between the tubes which would increase flow.

    I think I added one too many zero's to the conductivity measurement. The measurement was around 0.5microsiemens, so converting conductivity to resistance, its around 2Mohm/cm2. Would lowering the resistance/conductivity of the water make the generation of a linear field much more difficult to achieve? (That's just me talking about the novice).

    Also I didn't mean to come across rude about the colour scheme, I don't have the data for the graph that I posted. I can only really give you the range that was observed in each trial, the blue colour is the lowest (0) and the red the highest values (0.61). I will try and get the colour scale in the meantime.

    Thanks
     
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