Benefits of Venturi Injection versus Bubble Diffusion
Over the last twenty years, I have witnessed Ozone laundry companies come and go.
I have witnessed outlandish claims from some of these companies. Quite frankly am tired of listening to the outright lies and fallacies that some of these companies are stating.
I would like to look at the facts and help our readers make an educated decision about ozone laundry.
LET’S LOOK AT THE TWO MAJOR DESIGN DIFFERENCES.
Some ozone laundry companies use fine bubble diffusers, while others use Direct Venturi Injection. People claim that both have advantages. So, we should examine the design criteria of each and select the one that is appropriate.
Ozone gas is dissolved into the water by utilizing pressure. It does not take a lot of pressure to start dissolving ozone into water. In the industry, we call the ability to dissolve gas into water “Mass Transfer”. The efficiency of Mass Transfer is highly dependent upon the design criteria of the device.
The idea of the fine bubble diffusion injection method used on washing machines is borrowed from the bottled water industry. Bottled water plants introduce ozone to large columns (or tanks) of water. These are usually over 15 feet tall. Water flows into the top of the tank and exits the tank through the bottom. The fine bubble diffuser is placed at the bottom of the tank. Ozone is introduced through that diffuser at the bottom of the tank. Water enters the tank at the top and flows downward, eventually exiting the tank at the bottom.
Due to the water counterflow, the ozone bubbles are violently thrashed around as they rise. This turbulence lends itself to a pretty decent mass transfer of the ozone gas into the water. The tanks used in the Las Vegas water treatment plant are 32 feet tall. Remember that pressure is needed to transfer the ozone into the water solution. Every inch of the water column adds more pressure to the diffuser stone at the bottom of the tank. The taller the tank, the greater is the pressure at the bottom. So, the greater is the mass transfer of ozone in water.
Once the un-dissolved ozone reaches the top of the tank, it is removed through an air vent. Then, it is destroyed by passing through the ozone destruct system.
All in all, this is a very safe and effective way to dissolve ozone into water.
Designers of fine bubble diffusion systems implemented this type of system on a washer extractor. However, they left out a couple of key ingredients.
First, the column of water in a washer/extractor is nowhere near that of a 32-foot tall water tank. It is more like 12 inches. This allows for a much lower Mass Transfer efficiency of the ozone gas. Several ozone engineers have figured that the efficiency is somewhere in the 25-40% range at best. That means in the best-case scenario, 60% of the ozone gas does not get dissolved. This is important in that 1% of un-dissolved ozone gas can easily make a room unsafe for the laundry workers.
In the bottled water design, you can capture this un-dissolved gas and destroy it. The main problem here is that the designers somehow forgot to include this important piece of the puzzle. Common sense tells you that if you force air into an unsealed vessel, air will escape out. Some companies have tried to cover up this major design flaw. By installing an ozone monitor that, in theory, shuts off ozone generators when a certain level is reached. In reality, the ozone generator only runs for a few seconds before shutting down due to the room’s ozone oversaturation. It then takes several minutes for the room sensor to reset and let the system turn the generator back on. I have witnessed the ozone generator being in operation for all of 45 seconds during a 7-minute wash step. That’s not going to kill many “Super Bugs”.
WHY THERE ARE SO MANY BUBBLE DIFFUSERS IN THE INDUSTRY?
I recently attended an ozone conference. The guest speaker said that a fine bubble diffusion system on a washer was “So easy to build, that even a caveman could do it”. It is not only that it is easy to build, but it is also cheap to build this type of system. That is why there are so many on the market, and the low price keeps the attention of the potential uninformed buyer.
The Venturi Injection System uses the pressure of the water stream in the piping to create suction. When applied to this suction port, 85-90% of the ozone gas is instantly dissolved into the water. Since we still have this water and un-dissolved gas contained inside the water piping, it can easily be run thru an Ozone Degassing chamber that removes the un-dissolved ozone gas where it can be destroyed. The results are 100% dissolved ozonated water going to the washing machine.
This is an oversimplification of the process. But it should get the point across without going into all the hydraulic engineering facts that make this a much more reliable and stable way to dissolve ozone into water. The disadvantage of the Venturi Injection System is that it costs more to build this type of system. Another reason not to consider the fine bubble diffusion type of technology is the time it takes to build up to concentration.
Those of you operating commercial laundries know that you never want to fill up a washer with cold water then steam up the temperature to 160 degrees because it takes too long. I know there are some cases where this is unavoidable. But normally you would fill your washer up with your standard hot water usually 130-140 degrees, then add steam injection to raise the temperature in those wash steps where you need a little higher temperature.
The same is true with the fine bubble diffuser. A Venturi Injection system instantly fills the washer with highly concentrated ozonated water that instantly starts the cleaning and sanitizing process. It can take as much as 20 minutes for a fine bubble diffusion system to reach the ozone levels where the Venturi Injection system starts. None of us have that much extra time available in our wash cycle.
THE CYCLE TIME PROBLEM
Some Venturi Injection Systems on the market allow for larger than normal fill valves and water lines to be utilized. This will allow for much faster fill times. I have witnessed a 60 lb washer/extractor being filled in under 25 seconds, whereas the standard fill time was over 2 minutes. On a standard hospitality wash cycle with five fills, this would shorten your wash cycle by more than 7 minutes of total operating time. Washing an average of ten loads per day, this type of ozone laundry system would easily eliminate over one hour of processing per day.
In the graph below, you can see two identical tests that show the concentration of ozone during a complete wash cycle. Notice in the Venturi Injection System, the levels start high and slowly dissipate before the water is drained in each bath. You should also notice the effect of PH on each bath in the wash cycle. During the detergent and bleach steps, the ozone is reduced as it is counteracted by the higher PH from the wash chemistry. As the detergent and bleach are rinsed out, you can see that the ozone hangs around much longer.
In the fine bubble diffuser, you will notice that the ozone levels never reach above the 0.2 PPM of ozone in the water. It is also evident that the higher PH makes it hard for the ozone to overcome when using a Fine Bubble Diffuser.
I am not stating that the fine bubble diffusion system does not work, or does not clean laundry, but rather, it is nowhere as effective as a properly designed Venturi Injection System. Results will be more consistent with the Venturi Injection System than a comparable Fine Bubble Diffusion System.
By: Mark E. Moore