The terminology ‘dry-cell’ came into the public domain (I haven’t tracked down the originator) during the explosion of on-board electrolyzer experimentation that happened during 2008.
The originator popularized the term ‘dry-cell’ to differentiate the ‘recirculating-electrolyte‘ electrolyzer designs (dry-cell) from the original electrolyzers that did not recirculate the electrolyte (wet-cell).
The ‘dry-cell’ is a misnomer. Dry-cells do NOT use dry (no liquid) electrolyte. In fact, they usually use MORE liquid electrolyte than the original simple design; that they re-named a ‘wet-cell’.
A so-called ‘dry-cell’ is simply a full flooded wet-cell with an additional reservoir for electrolyte and a means to circulate the electrolyte fluids, (liquid and gas mixture) between the electrolyzer and the reservoir.
I think they were named ‘dry’ because they, theoretically, could have a smaller portion of the liquid electrolyte in the cell-pack at any given time. This is actually not true in a lot of cases.
The dry-cell’s fluid reservoir is usually mounted higher than the cell-pack and is connected to the cell-pack so that the natrual ‘rising’ action of convection (heated liquid electrolyte) and gas bubbles will ‘pump’ the electrolyte/gas mixture up out of the electrolyzer, allowing fresh electrolyte to flow into the bottom of the electrolyzer.
A ‘dry-cell’ is simply an ‘electrolyte circulating electrolyzer system’. The electrolyzer portion of the system can be, and usually is, EXACTLY the same design as the original (now ‘re-named’ wet-cell).
Typically the dry-cell’s reservoir is used to separate the BG (aka HHO) and electrolyte fluid, allowing the BG to exit from the system and the de-gassed electrolyte to re-enter the bottom of the electrolyzer.
Dry-cells can be designed using parallel-plate or series-plate configurations; exactly the same as the original wet-cells. I say again… Nearly ANY electrolyzer can be converted to be a ‘dry-cell’ just by adding a reservoir tank and recirculation hoses. BUT just because it’s a dry-cell DOESN’T make it more efficient, most often just the opposite is true.
Some advantages of the dry-cell concept include:
1. An increased ability to control the temperature of the electrolyte. For any given electrolyzer design, frequency, pulse (width and shape), electrolyte and electrolyte concentration there will be an ideal or optimum temperature.
Sometimes the BG production increase can be dramatic if the optimum temperature is maintained; so all electrolyzers should have temperature control, allowing heating or cooling as needed.
Our HyZor is designed to be heated or cooled and is more efficient when HOT (so doesn’t need cooling)!
2. The ability to mount the reservoir tank separately from the electrolyzer, supposedly allowing easier filling with water and easier placing of components within the vehicle. Easier filling may not be actually true, depending on the electrolyzer and the location of the reservoir tank.
Our HyZor is designed to be filled remotely and includes electronics to monitor fluid level.
3. The ability to remove bubbles from the electrolyzer faster than natural convection, particularly if using a pump. Using a pump to increase ‘dry-cell’ efficiency is highly recommended.
4. The ability to ‘treat’ all the electrolyte, filtering out solids and/or changing the electrolyte density easily and quickly. In some cases, this can be a practical advantage.
The usual concept is to have the BG, generated in the electrolyzer, lift itself and some electrolyte out of the electrolyzer using bubble-assisted convection or pump assisted convection. The upper tank then allows the BG to separate from the electrolyte fluid (at it’s own convenience) and the, now clear, electrolyte then falls back (through a separate tube) to the bottom of the electrolyzer, to continue the process.
The dry-cell may also cause more ExW to form, as cations and anions can be ‘pushed’ out of the electrolyzer with the BG before they have a chance to complete their chemical dance.
My advise would be to provide a pump for positive circulation of the electrolyte. Maximizing the advantages above (particularly as I’m finding that temperature control may be a major factor in finding the peak performance point) and minimizing the inevitable ‘surging’ that happens with passive bubble-assisted circulation (surging causes portions of plate surfaces to become inactive).
Also, it is VITAL to remove bubbles from the active electrode surfaces ASAP to raise electrolyzer efficiency. Every bubble that is stuck to a surface is preventing that portion of the surface from participating in the electrolysis process. Less surface area causes a higher amperage density and higher cell voltages; both of which reduce wattage efficiency. A pump forces the fluids, including the bubbles formed on the plates, to be ejected from the cells; allowing the electrolysis process to be more efficient.
Also, most dry-cells are miss-designed for maximum efficiency, because they enter and exit the fluid through the side-plates. This causes flow, surging and ‘shorting’ issues.
Fluid for each cell should enter from directly below each cell and exit directly above each cell, using manifolds (like these people did). If fluids from one cell can access another cell, electricity can ‘short’ between the cells and cause lower efficiency.
Our HyZor, as currently designed, is a compact, integrated hybrid wet/dry electrolyzer wherein the bulk of the electrolyte is separate from the (dual) electrolyzers and electrolyte CAN circulate in and out of the cells.
I have not yet seen a dry-cell that can match or exceed the efficiencies of our current HyZor design, which has achieved 20+ MMW.