Calculating Charge Density in Fluids

In summary: Amps is simply V/AC, where A is the ampacity of the generator.No, voltage is simply V = B * L * u, where B is magnetic field strength in tesla's, L is width... in meters of course, and u is the current in amps. Amps is simply V/AC, where A is the ampacity of the generator.In summary, to determine the charge density of a fluid, one would need to use the equation of I = qnvA . Amperes = charge of electron * charge density * velocity * Area. Then, to determine the product of some of the factors, the charge
  • #1
Shelnutt2
57
0
How would one determine the charge density of a fluid?

I'm using the equation of I = qnvA . Amperes = charge of electron * charge density * velocity * Area. The only thing I'm not sure of is how to determine charge density. I've read several websites and I have a few textbooks here. Everything talks about it differently, and nothing specifically references a fluid. Many talk about solids, but not fluids. Are the properties between solids and fluids for charge density calculations the same? Can someone point me to a formula?

Thanks
 
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  • #2
Is this the wrong forum? Should I ask for it to be moved? I really wasn't 100% sure what forum this belonged in but I figured EE would cover it.
 
  • #3
Do you really need to know charge density, or is the product of some of your factors enough? For example,
Charge density times velocity = Coulombs / cm3 times cm/sec = Coulombs/cm2-sec = amps/cm2.
Would the electrical resistivity of the fluid be enough? What kind of fluid are you interested in? In many cases, like seawater, just knowing the resistivity is enough.
 
  • #4
I need to find amps, so it's really all or nothing for that equation. Without the charge density, I'm left with Coulomb * m2 * m/s = Coulomb m3/s or Amp * m3. I need the charge density.

As for the fluid, well I'm looking for how to find the change density for generic purposes. I don't have a specific fluid I'm working with, but I'm looking at a broad range of fluids. Water/Saltwater sure. But I really need a generic way to calculate this all.
 
  • #5
No one?
 
  • #6
Are these the units you are working with?

q Coulombs
n number of charges per cm3
v velocity cm/sec
A Area cm2

The product has to equal amps = Coulombs/sec

What kind of fluid are you talking about? plasma? seawater? Cross-field propulsion (ion currents)?
 
  • #7
Bob S said:
Are these the units you are working with?

q Coulombs
n number of charges per cm3
v velocity cm/sec
A Area cm2

The product has to equal amps = Coulombs/sec

What kind of fluid are you talking about? plasma? seawater? Cross-field propulsion (ion currents)?

Yes those are the units (expect I'm using meter not cm, but that's not overly important).

For the fluid, seawater, brack/brine water, tap water. I guess maybe it's not as generic as I though, in terms of the equation and charge density in general. I'm looking at liquids specifically.
 
  • #9
Interesting, thanks for the link, it's quite detailed so I'm going to take my time reading through it.

I guess I should explain to you exactly what I'm trying to figure out. What I want is to find the amperage of a flowing fluid. As long as there is a net charge in said fluid, and the fluid is moving, it can be said to have a certain amperage, no? I am trying to work on the theory behind a MHD generator. In all the books on it I've read, amps are the only thing that isn't really clear. Voltage is simple, based on the hall effect. Amps, however, that is conveniently left out in any detail.
 
  • #10
I thought so. First, you need a strong magnet at right angles to the current. You need reasonable sized electodes to conduct the current. You need a dc current source to get the amps needed. The current is not flowing in the fluid, but is supplied by you. The MHD force is perpendicular to BOTH the magnetic field AND the supplied current. This based on the Lorentz force law. The voltage on the electrodes depends on the conductivity of the water.brine/whatever.
 
  • #11
Bob S said:
I thought so. First, you need a strong magnet at right angles to the current. You need reasonable sized electodes to conduct the current. You need a dc current source to get the amps needed. The current is not flowing in the fluid, but is supplied by you. The MHD force is perpendicular to BOTH the magnetic field AND the supplied current. This based on the Lorentz force law. The voltage on the electrodes depends on the conductivity of the water.brine/whatever.

Yes and no. You are talking about MHD propulsion, while I am talking about a generator to produce electricity. Same principles, but by no means do I supply the amps. The amps are created by the flow/movement of the fluid. Not the movement by the amps (which is what you are talking about). When it's inside the magnetic field, we get voltage, and we have electricity. When the fluid is flowing outside the magnetic field, there is still amps, but with no volts it means nothing.

Voltage is simply V = B * L * u, where B is magnetic field strength in tesla's, L is width (meters) between anode and cathode, and u is velocity (m/s). (It starts out as an integral but everything simplifies down to straight multiplication because it's all assumed to be perpendicular).

The amperage is just something I'm not entirely sure about. After discussing it with different professors, the closest someone could help me was give me the formula of I = q * n * v * A .
 

1. What is charge density in fluids?

Charge density in fluids is a measure of the amount of charge per unit volume in a fluid. It is typically denoted by the symbol ρ (rho) and has units of coulombs per cubic meter (C/m³).

2. How is charge density calculated?

Charge density can be calculated by dividing the total charge in a given volume of fluid by the volume of that fluid. Mathematically, it is expressed as ρ = Q/V, where Q is the total charge and V is the volume.

3. What is the significance of charge density in fluids?

Charge density is an important parameter in understanding the behavior of charged particles in a fluid. It can affect the flow dynamics, electrical conductivity, and other properties of the fluid.

4. How does the charge density vary in different fluids?

The charge density in different fluids can vary depending on the type and concentration of charged particles present in the fluid. For example, a saltwater solution will have a higher charge density compared to pure water due to the presence of ions.

5. How is charge density measured in a fluid?

Charge density can be measured using techniques such as electrochemical methods, conductivity measurements, and particle tracking. These methods involve measuring the electrical properties or movement of charged particles in the fluid to determine the charge density.

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