Is Chlorine output proportional to Watts?

[mas985]

Technically the electrolytic reaction is proportional to current due to the electron reaction with the chloride ions. But in reality given a certain cell design, it turns out to be both current and power when voltage and conductance are fixed.

Chlorine production - Wikipedia

 

[JamesW]

To increase current, you can increase salinity, water temperature or voltage.

If you increase salinity or water temperature, the current should increase without any change to the voltage. This results in a power increase since the current is increased.

If the voltage is increased, the current will increase and the power usage will increase more than if the salinity or water temperature was increased because the voltage and current are increased.

If salinity and water temperature are increased, you might be able to lower the voltage such that you don't get a power increase because the lower voltage offsets the higher current.

In other words, the amount of power that it takes to make a specific amount of chlorine per unit of time depends on the salinity and water temperature.

 

[mas985]

But again, it is the electron reaction (i.e current) that generates the chlorine. Everything else is a result of ohms law.

Cathode: 2 H+ (aq) + 2 e− → H2 (g)
Anode: 2 Cl− (aq) → Cl2 (g) + 2 e−
Overall process: 2 NaCl (or KCl) + 2 H2O → Cl2 + H2 + 2 NaOH (or KOH)

e- is the current in the electrolysis equation.

However, there are side reactions that depend upon other factors. For example, oxygen is also usually created albeit in lower quantities. This too will use some current but usually not much.

 

[JamesW]

I agree that it's the current that determines the amount of chlorine produced. It's a simple relationship. Double the current and you double the amount of chlorine generated.

I was trying to answer the original question about how power relates to the production of chlorine.

That gets more complicated because it involves more factors.

For example, if you increase the voltage by 1.5 x to get the current to double, the power usage increases by 3 times.

Assuming that you are changing only the voltage, then chlorine output is proportional to power usage, but it's not a simple linear relationship.

If you change the salinity or water temperature, you might be able to lower the voltage while increasing the current, which increases the amount of chlorine generated without increasing the power used.

 

[mas985]

For example, if you increase the voltage by 1.5 x to get the current to double, the power usage increases by 3 times.

If you increase the voltage by 1.5x, the current will increase by 1.5x as well, assuming water conductivity remains a constant, so power would go up by 2.25x. But that is a good example of why one should not use power to relate to chlorine production.

 

[JamesW]

I'm not sure that it's as simple as electricity flowing through a conductor.

The electrons flow off of chlorine atoms and onto hydrogen atoms.

Increasing or decreasing the voltage should increase or decrease the reaction rate, but I'm not sure that it's a simple linear relationship. Maybe it is, but I suspect that it might be more complicated.

If the voltage is too low, the reaction won't happen at all. I suspect that there is a practical upper limit as well where you start to get a breakdown of the process.

 

[satpoolman]

Thanks for the video Costas, very interesting!

 

[mas985]

I'm not sure that it's as simple as electricity flowing through a conductor.

The electrons flow off of chlorine atoms and onto hydrogen atoms.

Increasing or decreasing the voltage should increase or decrease the reaction rate, but I'm not sure that it's a simple linear relationship. Maybe it is, but I suspect that it might be more complicated.

If the voltage is too low, the reaction won't happen at all. I suspect that there is a practical upper limit as well where you start to get a breakdown of the process.

Actually it is that simple. If conductivity remains a constant, the doubling the voltage will double the current. However, that may not mean that the CL production is double. That does depend upon the chemical reactions that occur and within a SWG, there can be over voltage and under voltage conditions which do affect the reaction. However, that should not affect the conductivity of the water. The conductivity of the water is determined by the ion content within the water and the water temperature only.

 

[JamesW]

The current isn't flowing through the water. Electrons going down one wire don't travel through the water to the other wire and back to the power supply like what would happen with a lightbulb where the electrons flow through a filament.

All electrons are used in the reactions.

Electrons flowing to the cell get pushed onto hydrogen ions. Electrons flowing from the cell back to the power supply have been removed from the chloride ions.

The conductivity of the water doesn't affect how much current the cell uses.

Only the amount of chloride affects the amount of current the cell uses. If you could remove the sodium ions from the water, the conductivity would change but the current would stay the same.

If you replaced the chloride ions with bicarbonate or sulfate or some other ions, the conductivity would stay the same but the current would be close to zero.

 

[mas985]

The current isn't flowing through the water. Electrons going down one wire don't travel through the water to the other wire and back to the power supply like what would happen with a lightbulb where the electrons flow through a filament.

The e- charges in the reaction come from the current in the wires and yes, the reaction occurs at the plates. However the H+ & CL- ions must move through the solution to get to the plates which is a measure of conductivity (i.e. ability to move charges) or more accurately specific conductivity which determines the rate of the electrolytic reaction. So again, as long as the conductivity does not change, voltage & current are linear by definition.

BTW, the definition of current is the movement of electrical charges (i.e. not just electrons).

Electric current - Wikipedia

 

[JamesW]

Ok, thanks for the explanation.

 

[tomfrh]

How does temperature affect it? How big an effect is it?

 

[mas985]

This can give you a rough idea:

 

[Costas > DownUnder]

Thanks for the graph....

Now we can see why SWG's tend to stop production of chlorine at cold temps.