Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~E INVENTION
Technical ~
This invention relates generally to storage tanks
for hot fluids and, more particularly, to aip tubes for hot
water storage tanks such as water heaters.
10 Ba~kgrollnd ~
There has been a lingering problem commonly
associated with direct-fired gas and oil water heaters
having an upright storage tank in which the center gas flue
15 is surrounded by the water stored within the tank. Frequent
withdrawals of small quantities of hot water causes frequent
firing of the gas/oil burner. The gas/oil burner is
controlled by a thermostat located in the bottom of the
tank. With each draw of hot water, the burner is turned on
20 to heat the newly introduced cold water. At the same time,
the previously heated water has moved up in the tank and
gains temperature due to heat transfer from the flue. This
phenomenon continues as the water rises within the tank so
that the temperature of the water in the dome of the tank
25 reaches extremely high temperature. This high temperature
water may create an extreme safety risk. In addition, the
safety relief valve located in the tank may be opened to
drain hot water from the tank. Operation of the valve in
such a manner would waste energy by draining heated water.
This phenomenon of hot water accumulating near the
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tank dome by the aforementioned process is sometimes
referred to as "stacking". Since the thermostat is located
in the bottom of the heater, the temperature of the water in
the top can be dangerously high. To alleviate this problem,
5 present water heaters use dip tubes which terminate above
the bottom of the tank about one third of the way up. Some
heaters use a dip tube design which partially introduces
incoming cold water in the upper portion of the tank to
moderate the excessively high water temperature. To
10 accomplish this, the dip tube is provided with a hole which
opens or closes in response to the temperature of the
surrounding water. Both these solutions have an adverse
effect on the recovery rating of the heater. The invention
disclosed herein can provide a solution to the "stacking"
15 problem without adversely affecting the recovery rate.
The shorter dip tube has a second disadvantage.
It keeps the water in the tank bottom relatively stagnant.
This allows the mineral sediment to settle to the bottom of
the tank undisturbed. Over time, these sediments can
20 accumulate and reduce the usef ul gallon capacity of the
tank. Also, the sediments reduce the heat transfer from the
burner to the water through the bottom. Since the tank
bottom is the primary heat transfer area for the tank ' s
burner, this reduces heat transfer eficiency which, in
25 turn, reduces energy efficiency. This also exacerbates the
stacking problem, because more heat is transferred through
the stack rather than at the bottom. Accumulation of
sediments in the bottom also creates severe stresses on the
tank causing premature tank failure. Further, the sediments
30 block the drain valve sometimes making it inoperative or
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ineffective. All of these problems can be alleviated or
curtailed substantially if the dip tube is brought all the
way down in the bottom and the incoming water jet is used to
keep sediments in motion and in suspension so that the
5 sediments will eventually flow out the tank.
Some water heaters have appeared on market which
approach this problem in a different manner. In those
heaters, the water tank is placed inside another tank which
is filled with a captive liquid heating medium. The burner
lO heat is transferred to the liguid heating medium in the
outer tank, the liquid medium being kept in circulation.
This liquid medium transfers heat to the water. This is
extremely expensive since two tanks and an electric motor to
circulate the liquid medium and its as60ciated controls are
15 reguired for operation. The circulating medium normalizes
the temperature of the water thereby reducing the recovery
rating .
For a moderate cost, the heat exchanger dip tube
proposed here will provide a solution to the above-stated
20 problems caused by the build up of sediments, namely, loss
of heat transfer (loss of energy efficiency), reduction in
the tank's original gallon capacity, and increased safety
hazar d .
SUMMARY OF THE INVENTION
The present invention is directed to overcoming
30 one or more of the problems as set forth above.
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According to the present invention, a conventional
hot wate~ heater having a vertical storage tank with a
top wall has an inlet water dip tube with heat exchanger
means to transfer excess heat from the tank storage area top
5 to the tank storage area bottom.
Since the greater the surface area the greater the
heat transfer, the heat exchanging dip tube disclosed here
will provide more heat transfer area than a straight direct
dip tube will provide.
Exemplary embodiments of the invention provide a
heat exchanging dip tube including a reservoir, a coil,
spiral, a finned tube, or combination thereof which will
provide larger heat transfer area.
A feature of the invention is that the heater will
15 be inherently non-overheating. Other features are self-
cleaning, improved recovery, enduring energy efficiency,
longer tank life, and maintenance of original tank gallon
capa ci ty .
An advantage of the invention is that the tank
20 will deliver more hot water, in gallons, at a relatively
high temperature. A further feature of the invention is the
minimization of the mixing of hot and cold water within the
tank by the simplest and least expensive means possible.
sRIEF DES CRIPTIO~ OF TI~E DRAWINGS
The details of construction and operation of the
30 invention are more fully described with reference to the
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accompanying drawings which form a part hereof and in which
like reference numerals refer to like parts throughout.
I n th e d rawi ngs:
Fig. 1 is a side elevational sectional view of a
5 first embodlment of the present invention showing the use of
a dip tube constructed in accordance with the present
invention;
Fig. 2 is a side elevational view of another
embodiment of a dip tube constructed in accordance with the
10 present invention;
Fig. 3 is a side elevational view of another
embodiment of a dip tube constructed in accordance with the
present invention;
Fig. 4 is a side elevational view of another
l~ embodiment of a dip tube constructed in accordance with the
present invention; and,
Fig. 5 is a cross-sectional view of the dip tube
taken along line 5-5 of Fig. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
~arryinQ ~ ~ Inv~ntion
Referring to Fig. l of the drawings, a
conventional, non-compartmentalized hot water heater,
generally designated 20, has a storage tank 21 with an
upright, vertical axis. The internal hot water storage
chamber of the tank 21 is defined by a cylindrical side wall
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23, a bottom wall 24 and an outwardly concave top wall 26.
The bottom wall 24 is located at the upstream end of the
tank 21 and the top wall 26 is located at the downstream end
of the tank 21. The tank 21 has a cold water inlet 30 and a
5 hot water outlet 31 in the downstream portion of the tank 21
generally adjacent the top thereof. Both the inlet 30 and
the outlet 31 are radially spaced from the tank axis.
Heating means, such as the gas/oil burners or the electric
heating elements are not shown. The tank 21 may also have
10 an opening (not shown) for a temperature-pressure relief
valve .
When in operation, hot water is withdrawn from the
top of the tank 21 by way of the outlet 31. Cold water
replacing the water withdrawn is introduced to the tank 21
15 by way of the inlet dip tube 35.
In a first embodiment of the invention as shown in
Fig. 1, the dip tube is provided with a heat exchanging
means 37, which in this embodiment is defined by a small
reservoir, that provides for a large heat transfer area.
20 The dip tube 35 is in communication with the inlet 30 and
extends downward through the heated water within the tank's
internal storage area. The dip tube 35 has an open end 38
in the upstream portion of the tank 21 near the bottom wall
24 for delivering water therethrough to the tank storage
25 area. Herein, the open end 38 is shown facing the bottom
wall 24 so that any sediment settling on the bottom wall 24
is flushed by the incoming water and placed in suspension
within the tank.
The reservoir 37 is disposed in the upper portion
30 of the dip tube 35 and is defined by increasing the diameter
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of the dip tube 35. Water flowing through the dip tube 35
and into the reservoir 37 will absorb heat from the hotter
water found in the top of the tank 21 thereby reducing the
temperature of the stored water. When the water exits the
5 open end 38, it will have an increased temperature so that
cold water is not introduced directly into the tank 21
without some degree of preheating. Further, the temperature
of the water in the top of the tank 31 is reduced slightly.
Because the external surface area of the dip tube
10 with a reservoir is greater than the external surface area
of a straight dip tube with a constant external diameter,
more heat is transferred to incoming cold water before it is
introduced into the tank. While the shape and relative size
of the reservoir 37 may vary, it should be understood that
15 the external surface area of the reservoir 37 should be
greater than the product to the internal circumference of
the inlet 30 times the vertical distance betwee~n the inlet
30 and the open end 38 of the dip tube 35 so that the
effective heat transfer area is greater than that of a
20 typical straight dip tube of conventional design.
In Fig. 2, another embodiment of a dip tube
constructed in accordance with the invention is shown. The
upper portion of the dip tube 45 is coiled, the coil 47
having a spiral form and a relatively large radial diameter.
25 selow the coil 47, the dip tube 45 straightens. The
increased surface area presented by the coil 47 increases
the heat exchanged between the tank water and the dip tube
water. Since the spiral coil 47 extends radially across the
tank in a circular fashion, the probability that rising
30 water will come in contact with the dip tube is lncreased.
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In Fig. 3, another embodiment of a dip tube
constructed in accordance with the invention is shown. The
upper portion of the dip tube 55 is bent and looped back and
forth to define a wound or sinuous shape. Below the coil
5 57, the dip tube 55 straightens. The increased surface area
presented by the coiL increases the heat exchanged between
the tank water and the dip tube water.
In Figs. 4 and 5, a f urther embodiment of a dip
tube constructed in accordance with the invention is shown.
10 Extending radially outward from the upper portion of the dip
tube 65 are a series of circumferentially spaced heat
exchanging fins 67. The fins 67 extend out into the tank
water and effectively increase the surface area of the dip
tube and thereby increase the amount of heat exchanged.
Note that in modif ications of the embodiments of
the dip tubes shown, combinations of the heat exchanging
methods shown herein may be employed. For example, heat
exchanging fins may be used around the reservoir or formed
as part of the dip tube coils.
Tndll~trial A,l~plici~hility
From the foregoing, it should be apparent that the
6torage tank described herein is simple and inexpensive, yet
25 provides a convenient and reliable means for delivering more
hot water from the tank outlet at a relatively higher
temperature over an extended period of time.
other aspects, objects and advantages of this
invention can be obtained from a study of the drawings, the
30 disclosure and the appended claims.
