U.S. patent application number 13/272210 was filed with the patent office on 2012-05-03 for horizontal extraction and return extensions in liquid storage tanks.
Invention is credited to Richard Curtis Bourne, Brian Eric Lee.
Application Number | 20120104003 13/272210 |
Document ID | / |
Family ID | 45995511 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120104003 |
Kind Code |
A1 |
Lee; Brian Eric ; et
al. |
May 3, 2012 |
Horizontal Extraction and Return Extensions in liquid storage
tanks
Abstract
This invention is an improvement to the shape of liquid storage
tanks, in particular to unpressurized molded polymer tanks used for
thermal storage in solar systems. All aspects of this invention are
well suited to solar storage tanks, and individual aspects are
suited to other liquid tank applications. This invention provides a
formed horizontal extension at the bottom of the tank. From the top
of this lower extension, a hollow vertical stub provides a reliable
connection to a circulator pump. Thermal performance is enhanced by
ensuring the lowest and coolest water is delivered to the array of
rooftop solar collectors without entraining debris from the bottom
of the tank. At the top of the tank, a similar horizontal extension
is used to distribute hot water returning from the solar
collectors. Flow velocity is eliminated and a curving lower edge
allows return water to find the matching thermocline to avoid
de-stratifying.
Inventors: |
Lee; Brian Eric; (Corral de
Tierra, CA) ; Bourne; Richard Curtis; (Davis,
CA) |
Family ID: |
45995511 |
Appl. No.: |
13/272210 |
Filed: |
October 12, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61404934 |
Oct 12, 2010 |
|
|
|
Current U.S.
Class: |
220/600 |
Current CPC
Class: |
F24H 9/124 20130101;
F24D 2200/14 20130101; Y02B 10/20 20130101; F24H 1/181
20130101 |
Class at
Publication: |
220/600 |
International
Class: |
B65D 6/28 20060101
B65D006/28 |
Goverment Interests
STATEMENT REGARDING STATE OF CALIFORNIA SPONSORED RESEARCH OR
DEVELOPMENT
[0002] This invention was made with State of California support
under California Energy Commission grant number PIR-08-012. The
Energy Commission has certain rights to this invention.
Claims
1. A molded storage tank that incorporates an essentially
horizontal and hollow foot-like extension at the tank bottom, whose
outer extremity includes an upwardly-directed tank outlet.
2. Claim 1 where the tank shape is a vertical-axis cylinder.
3. Claim 1 where the tank shape is a rectangular prism.
4. Claim 1 with the outlet designed to support a circulating
pump.
5. Claim 4 where the outlet is vertical.
6. Claim 1 with the extension having two essentially vertical outer
edges that form a 90 degree angle and which extend tangentially
from a cylindrical tank.
7. Claim 1 where the underside of the extension is coplanar with
the tank bottom.
8. A molded storage tank that incorporates an essentially
horizontal and hollow extension at the tank top, whose outer
extremity includes an upwardly-directed tank inlet.
9. Claim 8 where the tank is a vertical-axis cylinder.
10. Claim 8 where the tank shape is a rectangular prism.
11. Claim 8 with the extension having two essentially vertical
outer edges that form a 90 degree angle and which extend
tangentially from a cylindrical tank.
12. Claim 8 where the top side of the extension is coplanar with
the tank top.
13. Claim 8 where there is a large radius fillet at the
intersection of the lower surface of the extension and the tank
wall.
14. Claim 8 where the top extension includes holding means for a
pipe extending vertically from the circulating pump.
15. Claim 14 where the holding means is a molded hole through the
top extension.
16. Claim 14 where the holding means is a molded slot recess in an
edge of the extension.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application does not cross-reference existing
non-provisional utility patent applications. However, it is related
to USPTO provisional application 61/404,934.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] Not applicable.
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM
LISTING COMPACT DISC APPENDIX
[0004] Not applicable.
BACKGROUND OF THE INVENTION
[0005] There are three methods commonly used in the production of
liquid storage tanks. Steel and stainless steel tanks are
fabricated from sheet material that is cut and welded, either
automated or by hand. Their resistance to elevated pressures and
temperatures makes them popular for domestic water heaters and many
commercial and industrial applications. But rising material costs
and fabrication expense result in high prices on a storage volume
basis. Steel tanks generally last less than 10 years, which can be
extended for a few years with glass lining. Stainless steel tanks
are well suited to high-purity or corrosive chemical applications,
but prices are at least double those of similar sized steel tanks.
U.S. regulations require that pressurized vessels larger than 119
gallons be individually tested during manufacturing, and wall
thickness must increase substantially in larger sizes to maintain
the pressure rating. For these reasons and also high dry tank
weights, larger liquid storage tanks are usually unpressurized.
[0006] Although some unpressurized tanks are made from steel, such
as those used to store crude oil, most unpressurized tanks are made
from polymeric materials due to lower cost and corrosion
resistance. Polymer tanks can be broken into two basic
configurations: rigid molded tanks or flexible liner tanks that use
a site-built casing to resist hydrostatic loads. Rotationally
molded tanks are popular for large volume outdoor water storage in
residential or agricultural applications due to their durability
and low cost, and some smaller rigid vessels are blow molded.
Flexible liners are cut from roll material such as vinyl and welded
using radio frequency or ultrasonic equipment. The structural
casings are either custom built or delivered unassembled with the
liner. Flexible liner tanks make it possible to install very large
indoor tanks without the access doors that a rigid tank would
require.
[0007] The invention described herein is best suited to rigid
molded polymer tanks, which provide the most opportunity for
complex tank shapes. Tooling costs may increase, but the impact on
unit tank price of increased shape complexity is minimal. However,
there is no practical limitation preventing the incorporation of
this invention into fabricated steel vessels or tanks employing a
flexible liner.
[0008] This invention is suited to any applications of rigid molded
polymer storage tanks where a low mounted penetrating connection is
required, such as a drain, and where it is desired to avoid fouling
of this penetration by debris that may have settled out of the
stored liquid. For applications where a pump is used to move liquid
from the tank through a circuit, the weight and vibration of the
pump (usually cantilevered) result in frequent leaks at the
penetration. The most common solution is to use a multi-piece
bulkhead fitting that can be removed and a new seal fitted, but
this process requires draining the tank and accessing the
penetration from the inside of the tank. This invention is
well-suited to thermal storage tanks where it is desired to extract
the coolest, and therefore lowest, liquid from the tank. Such a
tank may or may not be designed to take advantage of stratified
thermal storage. For thermal storage tank designs that promote
stratification, it is also important to manage the return of heated
water to avoid de-stratifying the tank during certain
conditions.
[0009] This invention is ideally suited to storage tanks used in
solar thermal systems. "Active" solar thermal systems pump a liquid
from an insulated storage tank through a "collector" panel array
exposed to sunlight. The solar-heated liquid delivers heat to the
tank where it can be used for various purposes. "Closed-loop"
active systems use a water/antifreeze solution that transfers heat
via a heat exchanger to pressurized water stored in a steel tank,
while "drainback" systems circulate water directly from an
unpressurized tank through the collectors, via a circuit that
slopes so that water drains out of the circuit and back into the
tank when the pump turns off, in order to avoid freeze or overheat
damage. Instead of using a heat exchanger to charge the storage
tank during pump operation, drainback systems must use a heat
exchanger to discharge heat from the unpressurized thermal storage
water to pressurized domestic water during hot water draws. Active
solar systems usually mount a compact but relatively heavy
circulating pump to piping that extends from the wall of the tank.
The pump weight stresses the connection between the horizontal pipe
and the vertical tank wall, since the cantilevered pump is
supported only on one side.
[0010] Maintaining thermal stratification in a solar storage tank
improves system efficiency. Stratification can be promoted and
maintained by extracting liquid from the bottom of the tank and
returning it to the top; or, preferably, returning it at its
appropriate level. Liquid in a well-designed stratified tank can be
considered to comprise "thermoclines" or thin horizontal disks of
liquid that are increasingly warmer with upward position in the
vertical stack of disks.
[0011] Liquid from the tank bottom will always be coolest and thus
should be supplied to the collector to maximize their performance.
Through a typical daytime cycle, the liquid returning from the
collector is usually warmer than stratified liquid at the top of
the tank until late in the collection cycle, when solar input is
reduced, or when clouds obstruct the sun. At these times the return
liquid, though valuably warmer than the tank bottom liquid entering
the collector, can be cooler than other recently-returned liquid at
the top of the tank. Returned to the top, it could de-stratify the
tank top down to the thermocline whose temperature matches that of
the return liquid. Thus, it is preferable to admit the return
liquid at the thermocline that matches its temperature.
[0012] Optimal performance results when collector flow rates are
relatively low, thus saving pump energy and allowing smaller piping
that minimizes heat losses. In polymeric tanks, which have very
modest vertical heat conduction through the tank walls, thermal
stratification of 20 to 40 degrees C. can be maintained if liquid
velocities entering and leaving the tank are limited to prevent
mixing. But typical, piping flow velocities of 1 m/sec or more
cause mixing that damages stratification, and the impact is
particularly damaging when there are vertical components to the
return velocity.
[0013] Since the varying temperature of liquid returning from the
collector has obvious impact on stratification, much prior effort
has been devoted to perfecting devices that return liquid at the
appropriate level, and that slow the return velocity and direct it
horizontally. Two publicized examples (apparently unpatented) are
the "large perforated vertical return tube" and the
"gravity-gradient return hose." The perforated return tube is a
fixed vertical pipe in the tank, of larger diameter than the return
piping from the collector, with large perforations that allow slow
outward return flow into the tank at various levels. Presumably the
liquid slows enough to exit the pipe at its appropriate temperature
level, thanks to buoyancy effects. The gravity-gradiant hose is of
a neutrally-buoyant plastic. It also relies on varying density (and
therefore buoyancy) with temperature, so that the return liquid
temperature causes the open end of the hose to float to the right
thermocline and discharge the liquid in a horizontal stream.
[0014] The value of these stratification-enhancing devices has not
been widely confirmed, and less effort has been devoted to limiting
flow velocities than to discharging heated liquid at the
appropriate thermocline. This application discloses new art that
incorporates into the design of molded polymeric tanks valuable and
economical features to promote stratification. More specifically,
it discloses ledge-like extensions at the tank top and/or bottom
that slow and disperse inlet and outlet flows.
BRIEF SUMMARY OF THE INVENTION
[0015] This invention consists of geometric features that can be
added to the shape of existing liquid storage tanks. The larger
tank to which this invention is a.sub.pplied can be of any shape,
such as cylindrical or rectangular prismatic. All aspects of this
invention are well suited to thermal storage tanks used for solar
thermal systems, and individual aspects are suited to many other
tank applications, such as domestic water heaters, or water and
chemical storage tanks.
[0016] When applied to various basic tank shapes, this invention
provides a formed horizontal extension at the bottom of the tank.
From this lower horizontal extension, a stub is directed upwardly
to provide a secure and easily-maintained connection to a
circulator pump. Because the stub is oriented vertically, the
structural load of the pump is well transmitted to the tank with
minimal stresses within the tank material.
[0017] At the top of the tank, a similar horizontal extension is
used to distribute hot water returning from the array of rooftop
solar collectors (or some other heating process such as a boiler).
This extension acts like a baffle to reduce or eliminate the flow
velocity and enhance thermal stratification within the tank. A
curving lower edge to the upper horizontal extension allows return
water to find the thermocline with matching temperature. This
allows useful heat to be added to the storage tank without
disrupting stratification even if the return water is cooler than
the water at the top of the tank.
[0018] The ideal embodiment of this invention incorporates both
lower and upper horizontal extensions. Used in a solar thermal
system, the upper horizontal extension would include a cylindrical
through passage to support a riser pipe mounted to the discharge
side of the pump. This places both connections together at the top
of the tank for convenient connection to the collector array, and
also makes it easy to deliver tanks to the site with pumps
pre-installed at the factory. With careful design of the tank, the
pump can be contained entirely within the footprint of the
tank.
OBJECTS OF THE INVENTION
[0019] 1. To provide the lowest possible horizontal exterior tank
surface from which an upward, vertically-directed flow stream can
enter the circulator pump after being drawn slowly and horizontally
from the lowest level of the tank without entraining any debris
that may have settled out of solution and collected on the tank
bottom. [0020] 2. To form a molded tank that maximizes
stratification in solar heating applications by incorporating
extensions designed to slow and disburse liquid flow streams
leaving and entering the tank. [0021] 3. To provide the highest
possible horizontal exterior tank surface from which a downward,
vertically-directed flow stream can enter the tank slowly and
horizontally at the highest level of the tank, and entering along
an outer tank wall, allowing, the slow-moving return liquid to ooze
downward toward its own temperature level when return liquid is
cooler than tank-top liquid. [0022] 4. To locate an upper "return
liquid" tank extension directly above a lower "pump support"
extension to permit the upper extension to support an upward riser
from the pump.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0023] This application includes three figures, all of which show
the same preferred embodiment of the invention.
[0024] FIG. 1 is an isometric view indicating the shape of the
lower and upper horizontal extensions. The invention is shown on a
tank of generic cylindrical shape, along with representative pump
and plumbing connectors.
[0025] FIG. 3 is a cross-section of the molded tank at the
sectional line indicated in FIG. 2. Features are identified by
number, with many features indicated on both FIG. 1 and FIG. 3.
(FIG. 2 does not contain feature numbers, but is included only to
shown the orientation of the cross section in FIG. 3.)
DETAILED DESCRIPTION OF THE INVENTION
[0026] The tank 1 is a vertical-axis cylinder with planar top 2 and
bottom 3; and with relatively thin, hollow bottom and top
extensions 10 and 20. The bottom extension 10 has its bottom
surface 11 co-planar with the tank bottom 3. The extension 10
comprises vertical surfaces 13 that extend tangentially from the
circumference of the tank 1 and meet approximately at a right angle
at a vertical extension corner 12. From the upper horizontal
surface 14 of the bottom extension 10 extends a vertical pipe
connection 15 that flares smoothly from flat to an upward vertical
cylindrical shape that allows connection to the circulating pump
30. The radius of the corner 12 may vary but will normally be less
than the radius of the flared pipe connection 15. This design
allows the pump 30 to draw water smoothly upward with minimal
pressure drop, minimal tendency to draw debris into pump 30, and
with transition flow characteristics that minimize the tendency of
the pump inlet flow stream to mix the tank water. The extension 10
is preferably formed integrally with the tank in a molding
process.
[0027] At the top of the tank 1 is a second possible extension that
minimizes the mixing potential of water entering the tank. The
upper extension 20 is an independent feature that can be anywhere
on the upper circumference of tank 1, but is conveniently placed
directly above a lower extension 10, if used. The upper extension
20 has its upper surface 28 co-planar with the tank top 2. The
extension 20 comprises vertical surfaces 23 that extend
tangentially from the circumference of the tank 1 and meet
approximately at a right angle at a vertical extension corner 22.
From the upper horizontal surface 28 of the upper extension 20
extends a vertical pipe connection 24 near the corner 22.
Connection 24 receives water from return pipe 27 and helps the
return water spread smoothly across upper extension 20 and into the
tank 1. The radius of the corner 22 may vary but will conveniently
equal the radius of the pipe connection 24. The underside 21 of
upper extension 20 can curve slightly downward as it approaches the
wall of the tank cylinder 1, to allow inlet water to flow downward
along the tank wall without mixing the tank water. Since this
return water may or may not be warmer than water on top of the
tank, the slowing and smoothing of inlet water caused by the
features of the upper extension 20 allow water to move downward to
its own temperature-based thermocline. At this point the water will
move laterally from buoyancy effects without de-stratifying the
water layers above. The extension 10 is preferably formed
integrally with the tank in a molding process.
[0028] If upper extension 20 is located directly above lower
extension 10, the upward supply pipe 31 from pump 30 to the supply
connection 26 can be held in proper vertical alignment by securing
it to the upper extension 20. In a preferred embodiment, the pipe
31 is held in position by passing through hole 25 formed in upper
extension 20. Alternately a slot recess can be molded into the side
of the upper extension 20 to hold the pump discharge pipe. Hole 25
can be molded into a polymeric tank if a rotational molding process
is used. Tank 1 can also be blow molded with extensions 10 and
20.
* * * * *