Researchers at Purdue University have...
Coiled Tubes vs. Quartz Sleeves in UV Applications
The use of quartz sleeves in ultraviolet (UV) light's
treatment of water has been the medium of choice for many years. Quartz sleeves
always have been cleaned off and replaced at intervals recommended by product
Now there seems to be an upheaval in the ranks, which brings
into light compact system designs, longer contact times, less shadowing, cost
savings and easier, safer change outs. Coiled fluoropolymer tubes are not
new--they have been used in the Asian market for more than eight years. They
may not be as time tested as their quartz counterpart, but the coiled tubes
offer a very promising change in UV water treatment.
The coils can give the system designer more contact time to
the UV light source. With more turbulent water flow caused by the coil, there
also is less shadowing of contaminants. This enables the designer to produce
more compact water treatment systems such as above and below counter units.
These coiled tubes are used successfully in the Asian market, and nearly 1
million of the tubes were sold for above-the-counter water treatment systems.
Coiled tubes will become a mainstay in an industry looking for new and more
cost-effective ways for production while allowing easier maintenance for end
users and, of course, compact designs for use in labs, recreational vehicles,
under-the-counter units and portable systems.
Looking at UV light from a professional water treatment
specialist's point of view reveals possibilities overlooked before in this
application and other uses to be mentioned later. UV light transmission is
essential for destroying bacteria in water treatment, but whether a quartz
sleeve or plastic tube is the best choice for protection of the bulb,
effectively controlling bacteria is what needs to be determined. Different
applications and influent water changes to some degree the end result needed by
the user. Maintenance costs and ease of use in the field are other factors that
determine the choice of bulb protection. Pretreatment of the influent water
also is another factor in using such a system to prevent premature system
failure. Many times point-of-use (POU) and point-of-entry (POE) water treatment
designs neglect pretreatment and this allows for the scaling of the sleeves
whether they are plastic or quartz. This scaling prevents the proper
transmission of the UV light and, in turn, reduces
the effectiveness of the system's bacterial reduction
abilities. Turbidity is another factor that often is missed, and the shadowing
of the particles can compromise effectiveness. The particles causing the
turbidity also can scale the sleeves. In applications requiring UV light or
reverse osmosis (RO), a pretreatment of the water is recommended to reduce
maintenance costs and prevent premature failure of the system.
The pros of using a coiled tube are numerous, with the
number-one advantage being compact design. Cost also is significant, not only
for production reasons but also for replacement costs and ease of maintenance.
The coil's ability to achieve longer contact times because of its design and
longer travel of water flow by the UV lamp is what makes using the coil
something that water system designers can appreciate. The coiled tube causes
the water to become more turbulent, which decreases the chances of shadowing or
hiding of bacteria, thus increasing effectiveness. Coiled tubing helps
designers save room and enables compact designs for water treatment where space
is essential. Systems for labs where tabletop units need to be employed and
under-the-counter systems where space is limited can be addressed easier and
more cost effectively.
One of the advantages is durability and safety when
changing, handling or shipping coiled tubes as compared to quartz sleeves.
Breakage or damage from touching coupled with sensitive handling of the quartz
sleeve is no longer an issue. The coiled tubes are easy to work with, thus
enhancing compact design. Elongated tubes for other applications also are
manufactured for uses where compact design is not essential, but the cost of
tube replacement is a factor.
Periodic changing of the sleeve is a moot point when
comparing quartz or plastic protective coverings. Both must be changed or
cleaned at intervals that are caused by UV light breakdown or scaling. A recent
study revealed and proved the reduction of UV light transmission in quartz
sleeves caused by solarization or the breakdown of quartz from the UV light
radiation. The degradation of the quartz sleeve proves that a sleeve cannot be
used forever with just cleaning or wiping and replacement is necessary at
various intervals depending upon operation. The UV lamp itself suffers from
this solarization degradation and must be changed based on hours of use. The
impurities in the glass and quartz cause the solarization--a darkening of the
glass or quartz--which reduces the clarity, resulting in the UV light
transmission loss. The coiled tubes do not suffer breakdown from this
UV dosage rates equal UV lamp intensity multiplied by
contact time multiplied by transmission value. This dosage rate is measured in
microwatt seconds per square centimeter (µW-s/cm2). An example would be a
UV lamp with an intensity of 4,000 µW-s/cm2 multiplied by a contact of 10
seconds gives a theoretical dosage of 40,000 µW-s/cm2. Manufacturers usually
rate this dosage against distilled water, which usually has a transmission rate
of 100 percent. A transmission rate of 90 percent is more practical in the real
world, and this dosage rate of 40,000 µW-s/cm2 translates into a
theoretical 36,000 µW-s/cm2. An industry standard for UV light dosage to
provide germicidal control in a typical application generally is 30,000
µW-s/cm2. Most common waterborne organisms can be destroyed with 15,000
µW-s/cm2 or less. This additional built-in dosage rate, therefore, can be
compensated by any UV loss in most systems, whether the reduced rate was
affected by plastic tubing or quartz sleeves. Total organic carbon
applications, however, would need to be examined to be sure the loss of
transmittance would not affect the high-purity water needed for the
application, thus, reducing the water quality. This loss could have
consequences that may be devastating in certain manufacturing processes. Again,
no matter which type of sleeve is selected, there is inherent possibilities of
UV light transmission loss that will occur.
Applications for the use of these coiled or elongated tubes
are numerous. Although tested and sold in the Asian market, these coils have
not been widely used in the U.S. market. Systems using UV light for
under-the-counter water treatment are a viable marketplace for low flow rates,
especially in an industry where POU/POE water treatment is in the limelight
because of public health issues and concerns. Commercial and industrial
applications also are being developed and tested. Other arenas that could be
pursued would be contact tubing for ozone systems and de-chlorination units.
The possible uses and applications for these coiled and elongated tubes are
unlimited in the water treatment industry.