UV-fat or skinny

[wooden_reefer]

For straight UV, is it better to have larger or smaller diameter of outside tube/pipe?

I believe many people are wrong on this issue.

Fat is better, to a reasonable limit.

 

[billsreef]

All depends on the inside diameter of the bulb and/or sleeve and what thickness of water you need to accomplish your desired results

 

[wooden_reefer]

All depends on the inside diameter of the bulb and/or sleeve and what thickness of water you need to accomplish your desired results

Every else the same; is it better to have a larger or smaller diameter outer tube?

 

[billsreef]

Are you talking in terms of the wall thickness of the outer pipe?

 

[g8gxp]

i think for UV water volume and throughput are secondary variables. Contact time seems to be the key, so bulb diameter and tube diameter are limited by each other and need to be sized together (to get max effectiveness).

 

[wooden_reefer]

i think for UV water volume and throughput are secondary variables. Contact time seems to be the key, so bulb diameter and tube diameter are limited by each other and need to be sized together (to get max effectiveness).

Actually, contact time is not something that an aquarist worries about.

Contact time is important, but it is not a primary design consideration.

When the flow is slow enough, water flows in layers (sleeves in this case of concentric ring cross-section) with little eddies. The velocity profile is not flat but V- shaped. The bacteria nearer to either wall will be killed. In other word, the contact time nearer to the wal will be longer than in the middle.

Plus, IMO many people are still confused between batch/recirculating operation of UV and thru-put operation when one wants 100% kill per pass.

In a batch operation, one is/can be only interested in drastcially reducing the pathogen cioncentration. Even a few percent kill per pass could eventually reach the goal of very low concentration after many many passes. And, even a 100% kill rate per pass will not kill all in the batch.

 

[wooden_reefer]

Are you talking in terms of the wall thickness of the outer pipe?

No, neglect wall thickness of the outside pipe.

I mean the apparant diameter of the outside pipe.

 

[billsreef]

Actually, contact time is not something that an aquarist worries about.

Actually it is when you are figuring out what size you need, even if your not aware of that fact. The designer engineered that into the unit, it goes hand in hand with the flow rate specs

Contact time is important, but it is not a primary design consideration.

Again, you can't separate out contact time from the design parameters, it's a major part of how the UV does it's thing

In a batch operation, one is/can be only interested in drastcially reducing the pathogen cioncentration. Even a few percent kill per pass could eventually reach the goal of very low concentration after many many passes. And, even a 100% kill rate per pass will not kill all in the batch.

IMO and IME, UV's are not effective when used in this manor. Good husbandry and rigorous QT of new specimens is far more effective and also more cost effective. It's that old adage, "A ounce of prevention is worth a pound of cure". Sure the batch method as you describe can cut down levels of bacteria and parasites, but it will never eliminate and will rarely cut them down sufficiently to be really an adequate control for any pathogens. It will help with algae in the water, if your having green water problems, but there are also cheaper methods that work well for that in aquaria

No, neglect wall thickness of the outside pipe.

I mean the apparant diameter of the outside pipe.

Apparent diameter of the outside pipe is totally irrelevant, assuming the piping is sized right for the internal design to function properly.

 

[wooden_reefer]

I think when you have a closed system, the only way to use the UV is by the batch/recirculating mode. How else?

The contact time adjusts itself when you are running the UV at the laminar flow region, low enough flow rate. Some distance away from the wall, the flow may become too fast for enough contact time, but nearer to either wall, the flow will be slow and enough contact time will happen.

Contact time is important during operation, but less so as a design criterium of the UV unit.

I think bacteria are not smart enough to avoid the walls and go toward the center that has high flow. IMO, where the bacteria are is ramdom; those staying close to either walls will be killed.

 

[wooden_reefer]

I think the diameter of the outside pipe is important, and the larger the better. The UV will always penetrate at the quartz sleeve/bulb side, even if not the pipe side.


This will allow lower velocity for the same overall flow rate.

 

[billsreef]

I think when you have a closed system, the only way to use the UV is by the batch/recirculating mode. How else?

With a solitary tank, recirculating is indeed the only way to use a UV. IMO they are just not efficient enough to be worth the money when it's far more efficient to simply avoid introducing pathogens via QT.

The contact time adjusts itself when you are running the UV at the laminar flow region, low enough flow rate.

Providing your running your flow rate within the design specs

Some distance away from the wall, the flow may become too fast for enough contact time, but nearer to either wall, the flow will be slow and enough contact time will happen.

If the water is flowing too fast, it's going to be the bulk of the water with that friction induced slow laminar flow near the UV being mere mm's at best. Very inefficient and a waste of resources if the flow isn't correct throughout the UV portion of the unit.

Contact time is important during operation, but less so as a design criterium of the UV unit.

How do you think recomended flow rates come about for a given sized unit? Contact time was an important part of the design criterium

I think bacteria are not smart enough to avoid the walls and go toward the center that has high flow. IMO, where the bacteria are is ramdom; those staying close to either walls will be killed.

Again, if your only zapping a minor portion of the bugs, it's a waste. Especially considering how easy it is to just buy or design a unit that will efficiently zap the entire water volume being moved through it.

I think the diameter of the outside pipe is important, and the larger the better. The UV will always penetrate at the quartz sleeve/bulb side, even if not the pipe side.


This will allow lower velocity for the same overall flow rate.

Germicidal UV wavelengths also don't penetrate water very far. So a wider diameter pipe, once past the diameter that he UV penetrates effectively, is inefficient to point of being pointless. Sure you'll have lower velocity a given flow rate, but once past the point of UV penetration, it just doesn't matter. The bigger the better idea is akin to getting seasick and barfing over the windward rail of the boat.

 

[wooden_reefer]

"With a solitary tank, recirculating is indeed the only way to use a UV. IMO they are just not efficient enough to be worth the money when it's far more efficient to simply avoid introducing pathogens via QT."

First, you cannot eradicate pathogenic bacteria, unlike for ich, because they do not have a definite lifecycle and many stick to surfaces and are infectious for a long time.

Second, it is very much worthwhile to just drastically reduce the waterborne pathogenic bacteria concentration.

I believe that fish has general defense against pathogens even without previous exposure. Against bacteria there is white blood cells but its capacity is very limited. That is why it is important to drastically reduce waterbone pathogen concentration while allowing antibodies to develop.

Emprircally this is true; after using UV correctly, bacterial infections are much less often and less virulent.

Extent of exposure to pathogen even without prior exposure is important in other animals. It is not true that any exposure is the same.

Manufacturers tend to overstate the ideal flow rate, it seems. Many people associate effectiveness with high flow.