Aluminum/Copper Solar Fins
QUESTIONS AND ANSWERS
- General Information
- Why is the Sunstrip process so unique
- When was the process developed and by whom
- When was Sunstrip first introduced
- Can customers be serviced and supplied worldwide
- Why hasnt anybody thought of this ingenious process before
- What is the actual production capacity of Thermo Dynamics
- Who are the customers of Sunstrip Solar Fins
- What is the purchasing pattern of Sunstrip users
- How will Sunstrip be affected by inflated Al and Cu prices
- How can Sunstrip be shipped worldwide effectively
- Will Thermo Dynamics have the capacity to deliver large volumes
- Other uses of Sunstrip
- Technical Questions and Answers
- How is Sunstrip bonded
- What about dissimilar metals
- Thermal performance
- Thickness of copper tube wall
- Absorber performace
- Flattening of copper tube
- Burst pressure
- What size of coils can be shipped
- How is the fin connected to headers
- Other R and D areas of Thermo Dynamics
- Selective Surfaces Available
following is a list of questions that are frequently asked by solar collector
manufacturers about the Sunstrip technology and its applications.
IS THE SUNSTRIP PROCESS SO UNIQUE?
WHEN WAS THIS PROCESS DEVELOPED AND BY WHOM?
- Never before in the solar industry have aluminum and copper been
bonded together by a process that guarantees protection against dissimilar
metal galvanic corrosion. The Sunstrip process, involving a highly
automated rolling mill, allows mass production with minimum labour,
resulting in a highly cost effective solar absorber fin tube.
WHEN WAS SUNSTRIP FIRST INTRODUCED TO THE MARKETPLACE?
- Initial research and development work was performed in Sweden by
Granges Aluminum, a multinational aluminum company. Subsequently, Petro-Sun
International, a leading Canadian renewable energy company, acquired
the technology and manufacturing equipment and set up a production
facility in Montreal, Quebec. In 1988 Thermo Dynamics Ltd., the largest
Canadian solar equipment manufacturer, acquired the assets of the solar
division of Petro-Sun and relocated the manufacturing equipment to
Thermo Dynamics' factory in Dartmouth, Nova Scotia, Canada.
CAN CUSTOMERS BE SERVICED AND SUPPLIED THROUGHOUT THE WORLD?
- Sunstrip fin tubes were first introduced to the solar industry in
Scandinavia in 1980. Throughout 1981, Sunstrip absorbers were sold
throughout Europe, before being introduced to Canada in early 1982.
More than 600,000 m2 of Sunstrip fins have been sold for solar application
in more than 20 different countries, making Sunstrip the most widely
distributed solar absorber material in the world.
WHY HASN'T ANYBODY THOUGHT OF THIS INGENIOUS PROCESS BEFORE?
- Thermo Dynamics Ltd. is able to ship cut fin tubes as well as solar
absorbers to customers in Europe which can not justify buying large
quantities of Sunstrip in uninflated coil format direct from the Canadian
WHAT IS THE ACTUAL PRODUCTION CAPACITY OF THERMO DYNAMICS' MANUFACTURING
PLANT IN CANADA?
- A quick tour of the Sunstrip manufacturing plant in Dartmouth, Canada,
makes one realize the tremendous amount of research and development
that went into inventing and perfecting the Sunstrip aluminum/copper
solar absorber. Furthermore, as of 1981, nobody had succeeded in applying
a cost effective selective coating on aluminum, which was a major obstacle
to the use of aluminum in flat plate solar collectors.
WHO ARE THE CONSUMERS OF SUNSTRIP FIN?
- A capacity of some 225,000 m2 / year is now possible on a two shift
/ day basis.
WHAT IS THE PURCHASING PATTERN OF SUNSTRIP USERS?
- The Sunstrip cut-to-length and inflated fin tubes, as well as the
coils, are sold exclusively to solar collector manufacturers. They
in turn process the product into solar absorbers, before placing them
in their own solar collectors and systems.
HOW WILL PRICES OF SUNSTRIP FIN TUBES BE AFFECTED WITH THE INFLATION
OF ALUMINUM AND COPPER PRICES?
- Usually collector manufacturers initially purchase inflated and
pre-cut to-length fin tubes. However, as volume increases, it
cost effective for them to purchase Sunstrip in uninflated coils,
so as to be able to inflate and cut the fins to their specific
house". The Sunstrip "inflating and cut to-length equipment" is
offered to solar collector manufacturers directly from Canada.
HOW CAN SUNSTRIP COILS AND FIN TUBES BE SHIPPED AROUND THE WORLD
- Obviously, the prices will be adjusted according to the fluctuation
of raw material prices. However, since prices of aluminum have
been much more stable over time than the prices of copper, we
that the prices of Sunstrip fin tubes will fluctuate much less
than the prices of comparable "all copper" solar absorbers.
- Thermo Dynamics Ltd. has shipped on numerous occasions 20 foot ocean
containers overseas, with a high volume of products per shipment:
WILL THERMO DYNAMICS LTD. HAVE THE CAPABILITY TO DELIVER LARGE VOLUMES
IN WHAT OTHER HEAT EXCHANGER APPLICATION CAN THE SUNSTRIP FIN TUBE
Because of its current capacity of some 225,000 m2 per year delivery
for fin tubes or coils averages approximately four weeks, whereas
delivery for finished absorber plates range from four to six weeks
on the size of the order.
- Because of it's exceptionally high heat transfer characteristics
the Sunstrip fin tubes are used more and more in other "conventional" heat
exchange process: · In Scandanavia, Sunstrip is used extensively
in radiant heating and cooling systems, where the Sunstrip fins
are installed on either vertical walls or on the ceilings.
B. Technical Questions and Answers
HOW ARE THE ALUMINUM
SHEETS BONDED TO THE COPPER TUBE IN THE ROLLING MILL OPERATION?
WHAT ABOUT DISSIMILAR METAL OR GALVANIC CORROSION EFFECT BETWEEN THE
ALUMINUM AND COPPER?
- Through a "cold welding" process, commonly known as
cladding, the aluminum sheets and the copper tube are metallurgically
resulting in the molecular bonding of both the aluminum and copper.
WAS THERE A TRADE-OFF IN THERMAL PERFORMANCE VS COST WITH THE USE OF
ALUMINUM INSTEAD OF THE CONVENTIONAL ALL-COPPER FIN?
- Because of the perfect metallurgical bond, there is absolutely no
possibility of air nor water being introduced between the aluminum
and copper at any time during the life of the product. Unlike mechanical
or pressure fits, where the aluminum fins are mechanically bonded to
the copper tube, the Sunstrip process results in a perfect and continuous
weld between the two metals, thus eliminating any galvanic corrosion
SHOULD THE THICKNESS OF THE COPPER TUBE WALL BE INCREASED FOR ADDED
- No. The Sunstrip fin tube has achieved consistently better overall
performances than conventional all copper and stainless steel absorbers
with selective surfaces such as black chrome.
WHY IS THE THERMAL PERFORMANCE OF SUNSTRIP ABSORBERS CONSISTENTLY HIGHER
THAN THOSE OF OTHER ALL COPPER, BLACK CHROME SOLAR ABSORBERS?
- In order to reach the optimum cost/performance ratio, the research
engineers have determined that a copper tube wall thickness of
0.30 is adequate for both long term corrosion protection as well
burst pressure ratings. These conclusions were based on three
year actual "in-the-field" testing, where solar collectors
installed in different locations in Europe were brought back
to the laboratory
to be carefully analyzed and monitored, to see if any erosion
or corrosion had occurred within the copper waterway risers and
thermal and pressure cycling had any effect on the mechanical
integrity of the Sunstrip fin tubes.
DURING THE FLATTENING OPERATION OF THE COPPER TUBE AND THE SUBSEQUENT
ROLLING MILL PROCESS, ISN'T THERE ANY "WORK HARDENING" OF THE
- Even though aluminum is not as good a heat conductor as copper,
independent laboratory testings are formal and clearly show the
of the Sunstrip fin tubes. These results are mainly due to the
perfect heat transfer metallurgical bond that exists between
the aluminum fin
and the copper waterway as well as the fin configuration which
yields a complete 360° "wrap-around" heat transfer
profile between the fin and the heat transfer fluid.
HOW CAN A THIN WALL COPPER TUBE SUSTAIN HIGH OPERATING AND BURST PRESSURES?
- The use of annealed copper tube ensures a finished product where
residual corner stresses and the possibility of subsequent crevice
corrosion have been eliminated. Examination of an inflated Sunstrip
fin, with a sophisticated electron-microscope, clearly shows the stress
free rearrangement of the copper molecules in the corners of the rhombic
shape copper tube.
WHAT SIZE OF COILS CAN ACTUALLY BE SHIPPED TO MANUFACTURERS?
- The combination of the copper tube and its aluminum cladding result
in a tube with a burst pressure in the order of 6 MPa (870 psi), which
is more than sufficient to guarantee the long life durability of any
solar absorber, which in most instances would be operating between
0.2 MPa (30 psi) and 0.6 MPa (90 psi).
HOW IS THE FIN TUBE CONNECTED TO THE SOLAR ABSORBER HEADERS?
- Coils range from 520 to 620 meters in length and weigh approximately
WHAT OTHER AREAS OF R and D IS THERMO DYNAMICS LTD. INVOLVED IN?
- Using a simple and conventional brazing operation, a copper "nipple",
round at one end, rhombic at the other end, is brazed to a copper header
or manifold. The Sunstrip fin is then soldered to the rhombic end of
the copper nipple. This nipple ensures the transfer from the fin tube
to the absorber header. The fact that a transfer "nipple" has
to be used with the Sunstrip fin tubes is inherent to the nature
of the continuous Sunstrip rolling mill operation.
WHAT KIND OF INVESTMENT SHOULD ONE CONSIDER TO PURCHASE THE
SUNSTRIP INFLATING AND CUTTING-TO-LENGTH EQUIPMENT"?
- Thermo Dynamics Ltd. has developed continuous "serpentine type" solar
absorbers for solar domestic hot water applications. These conventional
2 or 3 m2 solar absorbers are made from one continuous Sunstrip
fin tube, thus eliminating the need for any brazed connection
riser tube and the two end headers. These absorbers have now
been produced in large quantities and have undergone thermal performance
and market evaluation.
- For a solar collector manufacturer that produces an average of
15,000 to 20,000 m2 of solar absorbers/month, it becomes advantageous
a Sunstrip inflating and cutting-to-length equipment. Prices
for this equipment range from $20,000 to $35,000, depending on the
C. What Type of Selective Surfaces are Available for Sunstrip?
- Thermo Dynamics offers a painted selective surface coating.
The painted surface has an absorptivity of 98% and an emissivity
of 25%. The painted surface can be applied to cut and inflated
lengths of Sunstrip up to 7.6 m (25 ft) long.
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