U.S. patent application number 12/290474 was filed with the patent office on 2009-05-28 for solar cooking pot.
Invention is credited to William H.T. La.
Application Number | 20090133688 12/290474 |
Document ID | / |
Family ID | 40668669 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133688 |
Kind Code |
A1 |
La; William H.T. |
May 28, 2009 |
Solar cooking pot
Abstract
A solar cooker in the form of a pot with double-walled body and
lid configured to collectively constitute a near-hermetic thermal
enclosure including a closed, solar radiation-absorbing and
heat-retaining vessel surrounded by a vacuum insulation shield
encased in a transparent peripheral jacket. The device intercepts
solar energy omnidirectionally, and collects and retains it with
sufficient efficiency to pasteurize water and cook food without
resorting to outside reflectors, refractors, conductors, or
insulators, thereby escaping from the dual requirements of solar
concentration and orientation that universally govern the
construction and operation of existing solar cookers. Freedom from
these restrictions enables designs that are inexpensive, simple,
compact, lightweight, sturdy, accessible, and applicable in varied
geographic, climatic, economic, social, and culinary contexts.
Inventors: |
La; William H.T.; (Stockton,
CA) |
Correspondence
Address: |
WILLIAM H.T. LA
6507 Pacific Ave. # 313
Stockton
CA
95207
US
|
Family ID: |
40668669 |
Appl. No.: |
12/290474 |
Filed: |
October 31, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61001607 |
Nov 1, 2007 |
|
|
|
Current U.S.
Class: |
126/681 |
Current CPC
Class: |
Y02E 10/40 20130101;
Y02A 40/926 20180101; A47J 41/02 20130101; Y02B 40/18 20130101;
F24S 20/30 20180501; A47J 36/02 20130101; A47J 33/00 20130101; A47J
36/36 20130101 |
Class at
Publication: |
126/681 |
International
Class: |
F24J 2/02 20060101
F24J002/02 |
Claims
1. A solar cooking pot comprising: a body and a lid, the body
comprising a first double wall defining a cavity, said wall
comprising a first inner wall, a first outer wall, a first space
therebetween, and a first closure extending between said inner and
outer walls and enclosing said space, said inner wall having a
solar selective outer surface with high absorptivity and low
emissivity, said outer wall being transparent, and said space being
evacuated; the lid comprising a second double wall defining an
inner and an outer side, said second double wall comprising a
second inner wall, a second outer wall, a second space
therebetween, and a second closure extending between said second
inner and outer walls and enclosing said second space, said second
inner wall having a solar selective outer surface with high
absorptivity and low emissivity, said second outer wall being
transparent, and said second space being evacuated; said first and
second closures being configured such that when said body and said
lid are mated through said closures, said body and said lid are
positively engaged, said first and second inner walls cooperatively
constitute a substantially closed vessel with a solar selective
outer surface, said first and second spaces cooperatively
constitute a substantially closed vacuum insulation shield
surrounding said vessel, said first and second outer walls
cooperatively constitute a substantially closed transparent jacket
surrounding said shield, and said body and said lid cooperatively
constitute a substantially hermetic thermal enclosure wherein solar
energy is absorbed and heat is retained; whereby said solar cooking
pot is enabled to function as a solar cooker when exposed to the
sun, and as a heat retention cooker in the absence of
insolation.
2. The device of claim 1 wherein said first and second closures are
integral projections of said first and second outer walls
respectively.
3. The device of claim 1 wherein said first and second closures are
composed of a material with high thermal resistance and low thermal
conductance.
4. The device of claim 1 wherein said first and second closures are
configured with nonlinear complementary cross-sectional profiles
with a centripetally downward slope, said first inner wall extends
toward said lid beyond the extent of said first closure by a first
selected distance, said second inner wall extends toward said body
short of the extent of said second closure by a second selected
distance, said first selected distance being greater than said
second selected distance; in a configuration such that when said
body and said lid are mated, said first and second inner walls come
into intimate contact, said first and second closures are separated
by a clearance gap, the thickness of said gap being equal to the
difference between said first and second selected distances, no
visual line of sight exists between any part of said inner walls
and the external environment, and any solid or liquid material
present in said gap preferentially drains to the outside.
5. The device of claim 1 wherein said first and second outer walls
are composed of polycarbonate.
6. The device of claim 1 wherein said first and second inner walls
each comprise an inner layer, a core layer, and an outer layer,
said inner layer being composed of a radiant non-stick plating or
coating with high emissivity, said core layer being composed of a
metal, and said outer layer being composed of a solar selective
plating or coating.
7. The device of claim 1 wherein said first inner wall is provided
with a thermometer permanently mounted on its outer surface, said
thermometer being wholly contained within said first space.
8. The device of claim 7 wherein said thermometer is provided with
indicia for the temperatures of water pasteurization, water
boiling, and safe operating range.
9. The device of claim 7 wherein said thermometer is provided with
an indicator and a display that glow in the dark.
10. The device of claim 1 wherein said first and second outer walls
are provided with coatings or inclusions that glow in the dark.
11. The device of claim 1 wherein said body and lid each have a
density less than the density of water.
12. The device of claim 1 wherein said second outer wall is
provided with a multiplicity of circular depressions of a size
suitable for accepting fingertips.
13. The device of claim 1 wherein said first and second outer walls
are each provided with one or more groove means adapted for
securing belts, or one or more loop means adapted for securing
lanyards.
14. The device of claim 1 including a packaging system adaptable
for use as an accessory solar performance booster.
15. A solar cooking pot built from four separate parts formed from
plastic sheet material, comprising a two-part body and a two-part
lid, said body being shaped as a circular container and comprising
a body liner and a body shell enveloping said body liner and
leaving a body space therebetween, said body liner being solar
absorbent, said body shell being transparent, said body liner being
provided with an integral body liner lip, said body shell being
provided with an integral body shell lip, said body liner lip and
body shell lip being sealed together to form a body closure
enclosing said body space, and said body space being evacuated;
said lid being shaped as a circular container or disk and
comprising a lid liner and a lid shell separated from said lid
liner by a lid space therebetween, said lid liner being solar
absorbent, said lid shell being transparent, said lid liner being
provided with an integral lid liner lip, said lid shell being
provided with an integral lid shell lip, said lid liner lip and lid
shell lip being sealed together to form a lid closure enclosing
said lid space, and said lid space being evacuated; said body and
lid closures being configured such that when said body and lid are
mated, said body and lid are positively engaged, said body and lid
liners cooperatively constitute a substantially closed vessel with
a solar absorbent outer surface, said body and lid spaces
cooperatively constitute a substantially closed vacuum insulation
shield surrounding said vessel, said body and lid shells
cooperatively constitute a substantially closed transparent jacket
surrounding said shield, and said body and said lid cooperatively
constitute a substantially hermetic thermal enclosure wherein solar
energy is absorbed and heat is retained; said liners and shells
being configured to facilitate fabrication by die cutting, vacuum
forming, and heat sealing; whereby said solar cooking pot is
manufacturable with inexpensive materials and accessible
methods.
16. The device of claim 15 wherein said body liner is composed of a
black plastic sheet material.
17. The device of claim 15 wherein said body liner is coated on its
outer surface with a solar selective coating.
18. The device of claim 15 wherein said body and lid shells
collectively include one or more integral reinforcing projections
respectively engaging said body and lid liners.
19. The device of claim 15 wherein said body and lid spaces
collectively include one or more reinforcing inserts.
20. The device of claim 15 including a packaging adaptable for use
as an accessory solar performance booster.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional
application Ser. No. 61/001,607 filed Nov. 1, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention relates to cooking devices, and more
specifically to solar cookers.
[0004] 2. Description of Prior Art
[0005] Solar cookers come in a myriad of designs from different
historical eras and various geographic parts of the world, and
proponents of solar cooking have devised schemes for classifying
the many models and their variants, as discussed on the website,
solarcooking.wikia.com/wiki/compendium_of_solar_cooker_designs. At
the most basic level, among solar cooking devices in common use,
one can distinguish three types: the solar oven, the solar panel
cooker, and the solar stove. The term "solar cooker" is used to
refer to any type of solar cooking device, including the above and
less common indirect cookers.
[0006] In a solar oven, direct and, optionally, reflected solar
radiation penetrates the transparent part, or glazed aperture, of
an insulated enclosure and is converted to heat at the dark-coated
interior walls of the enclosure. The heat is trapped within the
cavity and is transmitted to one or more cookpots placed therein,
mostly by convection. Alternatively, the interior walls of the oven
are reflective and the cookpot is dark-coated, therefore heat is
evolved at the wall of the pot.
[0007] A commonly used solar oven is the Sportoven,
(www.solarovens.org), shaped to rest in two different positions,
presenting its glazed opening at a choice of two angles to
accommodate summer and winter solar altitudes. Another is the
Sunoven (www.sunoven.com) with built-in external reflectors for
increased performance, and adjustable legs for angle setting.
[0008] In a solar panel cooker, direct and reflected solar
radiation penetrates a transparent enclosure surrounding a
dark-coated cookpot and is converted to heat at the wall of the
pot. The essential difference between the solar oven and the solar
panel cooker is that, in the former, only the sun-facing part of
the enclosure is transparent while the remaining sides are
insulated, minimizing conductive and radiative heat loss. The oven
has the advantage of retaining more heat, attaining higher cooking
temperatures, and functioning in harsher weather conditions, and
the disadvantage of being bulkier and more cumbersome to
transport.
[0009] A widely distributed solar panel cooker is the Cookit
(www.solarcookers.org), which uses a clear plastic oven bag for
enclosure. Another is the HotPot (www.she-inc.org), which uses a
borosilicate glass container to enclose the black cookpot. The
solar panel cooker with a foldable reflector system has the
advantage of smaller size and weight, and better portability than a
solar oven, and the disadvantage of lower cooking performance and
more susceptibility to ambient conditions such as cold and wind.
Inexpensive reflectors made of aluminum foil laminated over
corrugated cardboard have poor durability, while better units made
of anodized aluminum sheets are out of the financial reach of many
prospective users.
[0010] In a solar stove, focused reflected or refracted solar
radiation is converted to intense heat on a small part of the wall
of a dark-coated cookpot. Alternatively, the energy may be focused
on a plate on which a cookpot is placed, in which case heat
conversion is done at the plate. Direct solar radiation plays a
lesser part in the cooking process. The essential difference
between the stove and the above two designs is that the stove uses
focused light and no enclosure around the pot or pan. The
advantages are that the cook has unimpeded access to the food, and
the localized heat delivers elevated temperatures suitable for
frying. The disadvantages are that a focusing system is more
complex in construction, requires frequent repositioning in
operation, and presents the health hazards of skin burn and eye
damage.
[0011] Naturally, there are solar cooker designs that do not fall
neatly under one classification or another, but rather possess a
mixture of the characteristics of the basic types in different
proportions. Nevertheless, all solar cookers in common use share
two disadvantageous traits. The first universal characteristic is
the requirement for solar concentration: the total solar intercept
area of the cooker, including reflectors and glazed aperture as
applicable, is significantly greater than the intercept area of the
food container proper. The second universal characteristic is the
requirement for solar orientation: there is a preferred arrangement
of the cooker with respect to the position of the sun as a function
of geographic latitude, season of year, and time of day.
[0012] In practical terms, the property of solar concentration
implies that existing solar cookers are heavier, more complex, and
more space consuming than possible, while the property of solar
orientation implies that they are more demanding in setup and
operation, and more time consuming than possible. These dual
limitations lead to designs that incorporate manifest compromises
between cost and durability, between portability and sturdiness,
and between performance and accessibility, resulting in commercial
products that are taxing on the user's physical, intellectual, and
motivational resources.
[0013] Solar cookers have been conceived centuries ago and put to
continuous worldwide use since. They present a great potential for
countering environmental pollution, global warming, deforestation,
desertification, and fossil fuel depletion, and for mitigating
health hazards associated with wood and coal fires, and with
unsanitary drinking water. For all their promise, solar cooking
devices have achieved limited success in developing countries, and
negligible market penetration in developed economies.
[0014] Even though cultural and other societal factors may be
invoked for explaining this failure of clean energy application to
food preparation, it is probable that the right concept, with an
attractive combination of features, has yet to be presented to the
global consumer. Properly designed, a solar cooker can serve not
only as a staple appliance in daily use for the
environmentally-conscious householder, but also as a convenient
camping tool for the outdoorsman and wilderness dweller, as well as
an essential component of the emergency and disaster preparedness
kit for the survival-minded citizen.
[0015] A step in the right direction was taken by Alex Kee
(www.freewebs.com/solarkettle, or solarwyse.cjb.net), who pioneered
the cross-application of commercially-available hot water solar
collector vacuum glass tubes to solar cooking. The long and narrow
form factor is better adapted for water boiling and distillation
than food preparation, and the contraption has to be mounted at a
slant for adequate solar capture. Although this method is awkward
and unsuitable for general kitchen purposes, it demonstrates the
feasibility of eliminating the need for solar concentration.
[0016] Ashok Kundapur and J. Samalea
(solarcooking.wikia.com/wiki/Box_cookers) have similarly proposed a
solar cooker concept based on the Dewar vacuum jar, or thermos
bottle principle, in which a dark-coated inner container is
vacuum-insulated within a transparent outer container. The lid is
shown as being thermally insulated from the body of the pot. Tapani
Hakonen (www.netti.fi/.about.hakone1/cooker.htm) has also reported
on an idea for a Dewar pot with an opaque lid, used in conjunction
with a parabolic mirror reflecting sunlight onto the bottom of the
pot. Philip Fairey
(www.fsec.ucf.edu/en/publications/html/FSEC-CR-1283-01/index.htm)
has performed theoretical calculations showing the improved
performance of a vacuum jar cooker with low-emissivity greenhouse
walls. This analysis however does not examine the design of the
lid.
[0017] Solar heated vacuum flasks are shown in U.S. Pat. No.
4,196,721 to Posnansky (1980) and U.S. Pat. No. 4,442,828 to
Takeuchi et al. (1984). These both are adapted only to the heating
of liquids, similarly to Alex Kee's solar kettle, and are
geometrically configured to operate with the help of
reflectors.
[0018] While the concept of a high-performance cooker based on the
Dewar vacuum jar principle has been described and analyzed by the
above solar pioneers over a period of time, and a specialized
tubular application has been demonstrated, no practical
implementation has been realized. In addition, these proposals
collectively do not teach all the features and benefits of the
present invention.
OBJECTS AND ADVANTAGES
[0019] An object of the present invention is therefore to provide a
solar cooker that is free from the dual constraints of solar
concentration and solar orientation.
[0020] Another object of the present invention is to provide a
solar cooker of simple and aesthetic design, in the form of a
self-contained cooking pot, requiring no additional parts or
accessories for its normal operation.
[0021] Another object is to provide a user-friendly solar cooking
pot of simple construction, requiring no assembly or setup, and
immediately usable out of the box, comprising only two separate
components: a body and a lid.
[0022] Another object is to provide a practical solar pot of simple
operation, able to function unattended, and requiring no adjustment
or planning other than the initial selection of a sunny location
for solar exposure.
[0023] Another object is to provide a universally applicable
cooking pot that has an extended range of working specifications,
delivering satisfactory performance in most geographic locations,
climatic environments, and weather conditions.
[0024] Another object is to provide a portable solar pot that is
compact, with an overall size not significantly larger than the
volume of food being cooked.
[0025] Another object is to provide an easy to handle pot that is
lightweight, its individual parts being able to float on water.
[0026] Another object is to provide a sturdy pot that is virtually
unbreakable, able to withstand the force of natural disasters.
[0027] Another object is to provide a visible solar cooker that
glows in the dark, facilitating its retrieval or recovery in
emergency situations.
[0028] Another object is to provide a secure solar pot that has
means for accepting belts and lanyards to tie the body and lid to
each other and to external objects.
[0029] Another object is to provide a self-sufficient solar pot
that incorporates an integral thermometer for confirming water
pasteurization, for monitoring food temperature, and for pushing
operation close to design limits.
[0030] Another object is to provide a versatile solar cooker that
can be safely used in multiple modes of operation at different heat
levels, with the optional assistance of external accessories.
[0031] Another object is to provide a multifunctional solar cooking
pot that doubles as a heat-retention cooker, or vacuum cooker.
[0032] Another object is to provide an inexpensive solar cooker
that is durable, affording both up-front and long-term economy for
the user.
[0033] Another object of the present invention is to provide a
packaging for a solar cooker that serves as an accessory solar
booster for the cooker, to enhance its performance under adverse
conditions.
BRIEF SUMMARY OF THE INVENTION
[0034] In accordance with the present invention, an exemplary
preferred embodiment solar cooking pot includes a body and a lid of
similar double-wall construction. The outer wall is transparent and
preferably made of polycarbonate plastic, the inner wall is
preferably made of stainless steel covered on its outer surface
with a solar selective coating and on its inner surface with a
dark-colored non-stick coating, and the space between the two walls
is closed and evacuated. When the lid is fitted onto the body, the
inner walls of these two parts effectively form a fully enclosed
solar radiation-absorbing and heat-retaining capsular vessel
surrounded by an insulating vacuum contained within a transparent
jacket.
[0035] The assembly, which we could call a "solar thermos", works
as a heat trap that captures solar light energy, converts it to
thermal energy, distributes the heat evenly within the central
compartment, and keeps it from escaping. The device is capable of
attaining moderate cooking temperatures, sufficient for
pasteurizing water and preparing food, from direct incident
sunlight without employing additional implements such as mirrors,
lenses, or thermal conductors or insulators. When a balanced form
factor is used in shaping the vessel so that it presents a nearly
constant intercept area to light beams impinging from any angle,
this energy trap is omnidirectional and obviates the need for
orientation to the sun. The present invention is thus embodied as a
cooker that is free from the dual constraints of solar
concentration and orientation. Solar cooking becomes the simple act
of loading a pot with the desired ingredients and leaving it in a
sunny spot.
[0036] By virtue of its well-insulated design, this solar cooker
doubles as a heat-retention cooker, or vacuum cooker, so that food
heated by other means can be transferred to the pot for
retained-heat cooking without solar energy input. By the same
token, food solarly heated in this device can continue cooking
after cessation of sun exposure, or during periods of temporary
solar interruption, such as from passing clouds. Additionally,
since the pot keeps food hot for a long time, it automatically
delivers a hot meal in the evening after being left to cook outside
for the day.
[0037] Another feature of the preferred embodiment is the inclusion
of a thermometer mounted on the outer surface of the metal capsule
within the evacuated space, with special markings for the
temperatures of water pasteurization and boiling, and the safe
range of operation. The presence of a thermometer enables safe use
of the solar pot in a push mode for frying. Additional features of
the preferred embodiment provide for safe handling, securing, and
locating in the dark. An alternate design of the vacuum space
closure extends the range of operation to higher temperatures. An
optional packaging is adaptable for use as an accessory external
solar reflector for performance boosting.
[0038] An alternate embodiment of the present invention, suitable
for occasional or disposable applications, features an inexpensive,
all-plastic construction similar to the clear plastic clamshells
and bubble packs used extensively in consumer product
packaging.
[0039] These novel features present unique combinations of
advantages not found in the current art.
BRIEF DESCRIPTION OF THE DRAWINGS
Drawing Figures
[0040] In the drawings, closely related figures have the same
number but different alphabetic suffixes.
[0041] FIG. 1 is a front perspective view of the preferred
embodiment solar cooking pot, with the body and lid separated.
[0042] FIG. 2 is a left cross-sectional view of the preferred
embodiment solar cooking pot, with the body and lid engaged.
[0043] FIGS. 3A and 3B are front cross-sectional detail views of
closures in the preferred embodiment, respectively with the body
and lid separated and engaged.
[0044] FIGS. 4A and 4B are front cross-sectional detail views of
alternate closures in the preferred embodiment, respectively with
the body and lid separated and engaged.
[0045] FIG. 5 is a front perspective view of the preferred
embodiment solar cooking pot together with an accessory
packaging.
[0046] FIG. 6 is a front cross-sectional view of an alternate
embodiment solar cooking pot.
[0047] FIG. 7 is a front cross-sectional view of an alternate
embodiment solar cooking pot including wall inserts.
REFERENCE NUMERALS IN DRAWINGS
[0048] In the reference numerals, suffixes A and B on a numeral
respectively designate homologous parts of the cooking pot body and
lid, which may also be referred to collectively by the same numeral
without suffix.
TABLE-US-00001 10 Solar cooking pot 10A Pot body 10B Pot lid 12
Liner 14 Shell 16 Insulation 18 Closure 20 Thermometer 22 Food
compartment 24 Food 26 Finger well 28 Lid loop 30A, 30C Body
grooves 30B Lid groove 32 Liner core 34 Liner outer coating 36
Liner inner coating 38 Glow strip 40 Contact 42 Gap 44 Alternate
closure 46 Reinforcement 48 Knob 50 Liner lip 52 Shell lip 54 Seal
56 Packaging 58 Body bottom insert 60 Body side insert 62 Lid
insert 64 Packaging box 66 Packaging bag
DETAILED DESCRIPTION
[0049] FIG. 1 is a front perspective view of the preferred
embodiment of the solar cooking pot 10 comprising two mating parts
shown separated, a body 10A and a lid 10B. Body 10A is a double
walled container composed of two material layers, a metal liner 12A
and a transparent plastic shell 14A, separated by a vacuum
insulation layer 16A. Lid 10B is similarly composed of two layers,
liner 12B and shell 14B, separated by insulation 16B. Lip 18A is an
inward projection or fold of shell 14A that engages liner 12A and
forms a closure for the double wall of body 10A, sealing its vacuum
space 16A. Lip 18B similarly forms a closure for lid 10B, enclosing
its vacuum gap 16B. A thermometer 20 is mounted on liner 12A,
within vacuum gap 16A. The display screen and indicator on
thermometer 20 includes glow-in-the-dark indicia for ease of
temperature reading in the absence of ambient light.
[0050] FIG. 2 is a left cross-sectional view of pot 10, with lid
10B fitted on body 10A by apposing closures 18A and 18B. Body liner
12A, shell 14A, and vacuum insulation 16A are mated to the
corresponding lid components 12B, 14B, and 16B. Body and lid liners
12A and 12B form a compartment 22 for containing food 24.
Thermometer 20 is seen in cross-section mounted on liner 12A.
Additional features kept out of in FIG. 1 for simplicity are shown
in FIG. 2. Lid shell 14B has three evenly spaced finger wells 26,
of which one is visible in the drawing, akin to a bowling ball's
grab holes, for safe handling of the lid in the presence of steam
escaping from the pot opening. Embedded loops 28A and 28B in the
body and lid shells are adapted for accepting lanyards, and
circumferential grooves 30A and 30C in the body, and 30B in the
lid, are configured to accept belts adapted for securing the body
and lid together, for carrying the pot, and for tying it to
external objects.
[0051] FIG. 3A is an enlarged cross-sectional view of the areas
surrounding lips 18A and 18B with the lid and body separated,
detailing the structure of the liners and the arrangement of the
lips. Liners 12A and 12B respectively have a central core 32A and
32B coated on its entire exterior surface with a solar selective
coating 34A and 34B, which features high absorbance and low
emissivity, and on its entire interior surface with a dark-colored
non-stick coating 36A and 36B, as is commonly done with
cookware.
[0052] Circumferential strips of glow-in-the-dark paint 38A and 38B
respectively on the inside surfaces of shells 14A and 14B in the
vicinity of lips 18A and 18B respectively render the pot visible at
night. Alternatively, body and lid shells 14A and 14B can be molded
from clear resin doped with glow dye or pigment, in which case the
entire pot is lit in the dark, at the cost of reduced solar
performance resulting from lowered shell transmittance.
[0053] FIG. 3B is a similar view with the lid and body mated. Liner
12A protrudes past the axial extent of the corresponding contiguous
part of lip 18A over a short distance, and liner 12B recesses from
the axial extent of the corresponding contiguous part of lip 18B
over a slightly smaller distance, so that when the lid is fitted
over the body, the liners form an intimate contact 40 while the
lips are held slightly apart, separated by a gap 42. Lips 18A and
18B are shaped complementarily with a nonlinear profile such that
no part of liner 12A or 12B has line-of-sight visual access to the
external environment, and with a centripetally downward slope such
that any material or water condensation that collects in gap 42
would preferentially drain to the outside. This arrangement effects
positive mechanical engagement of body 10A and lid 10B when the pot
is closed, assures shielded, intimate contact of liners 12A and 12B
for thermal continuity and sealing, and prevents foreign matter
from entering inner compartment 22 and contaminating food 24.
[0054] FIGS. 4A and 4B are similar to FIGS. 3A and 3B respectively,
showing an alternate design of closures 18A and 18B in which
integral body and lid lips 18A and 18B are respectively replaced by
annular parts, or rings 44A and 44B composed of a material selected
for high heat tolerance and low heat conductivity, such material
likely being an opaque plastic, as commonly used in the
construction of handles for cooking pots and pans. Ring 44A is
bonded at its inner edge to liner 12A and at its outer edge to
shell 14A. Ring 44B is similarly bonded at its inner edge to liner
12B and at its outer edge to shell 14B. This arrangement gives pot
10 a greater temperature range of operation.
[0055] FIG. 5 shows an optional packaging system 56 for pot 10 in
the form of a box 64 composed of reflective panels that, when
opened up and properly arranged, act as an external solar
reflector, and a clear plastic bag 66 with drawstring closure that,
when fitted around reflector 64 and pot 10, acts as an external
insulator. Packaging 56 thus serves as an accessory solar
performance booster for cooking pot 10 to enable its function under
adverse sun and weather conditions. Reflector 64 may also be
provided as a pleated aluminum foil cup that contains pot 10 in the
fashion of a cupcake paper cup, and that can be then shaped into an
advantageous geometry for capturing solar rays at the time of
use.
[0056] FIG. 6 shows a front cross-sectional view of an alternate
embodiment solar cooking pot 10 of an all-plastic construction
which is amenable to manufacturing by die cutting, vacuum forming,
and heat sealing. Liner cores 32A and 32B, and shells 14A, and 14B,
can all be made from the same clear plastic sheet material. In body
10A, lips 50A and 52A respectively of liner 12A and shell 14A are
heat-bonded to form seal 54A. In lid 10B, seal 54B is similarly
formed from lips 50B and 52B. Liners 12A and 12B respectively
include a solar selective coating, 34A and 34B. Dimples 46A in body
shell 14A and 46B in lid shell 14B represent a multitude of such
reinforcing shell projections that press against the corresponding
liners and help assure structural integrity in the presence of a
vacuum in spaces 16A and 16B and atmospheric pressure outside.
Protrusion 48 of the lid shell serves as handling knob.
[0057] FIG. 7 shows a similar sheet plastic design of pot 10 in
cross-section as well, in which structural reinforcement of the
walls is derived from the inclusion of corrugated plastic inserts
in the vacuum spaces. In this cylindrical container with discoid
lid, food volume is maximized with respect to overall cooker size.
Body 10A is strengthened with a bottom corrugated insert 58, seen
here across the flutes, and a side corrugated insert 60, seen here
along the flutes, and lid 10B is propped with a similar insert 62.
The inserts, illustrated as corrugated sheets, could be provided in
other forms as well, such as a three-wall lamination with central
corrugation, or a dimpled sheet, or a reticulated sheet, etc. This
construction allows use of thin plastic material, such as found in
disposable food containers and consumer product bubble packs and
clamshell packaging. This inexpensive design is suitable for
occasional or disposable applications, such as packaging instant
noodles, ready for in-container cooking in the sun, with a cupful
of water being the only additional requirement, and with the added
advantage that the soup stays hot until the end of the meal. Liners
12A and 12B may be made of black plastic sheet material, obviating
the need for painting or coating in the manufacturing process. In
this case, solar booster packaging 56 plays an important role.
Principle of Operation
[0058] When body 10A and lid 10B of solar pot 10 are mated, liners
12A and 12B form a substantially continuous and closed solar
selective capsule 12, shells 14A and 14B form a substantially
continuous and closed transparent jacket 14, spaces 16A and 16B
form a substantially continuous and closed vacuum shield 16, and
the whole assembly acts as a vacuum-insulated capsule. Selective
coatings 34A and 34B form a substantially continuous and closed
skin 34 that allows radiative heat to flow only in the inward
direction through liner core 32 formed by 32A and 32B, non-stick
coating 36 formed by 36A and 36B, to compartment 22. To achieve an
even distribution of energy within cooking chamber 22, coating 36
is preferably a radiant material with high emissivity. From a
thermal perspective, cooking pot 10 is thus a near-hermetic solar
heat valve, or heat trap. It can be conceptualized as a Dewar
vacuum jar, or Thermos bottle, that will absorb heat from the sun
but not release it. When exposed to the sun, this device acts as a
solar energy collector to cook food and boil water. In the absence
of insolation, it can function as a retained-heat cooker after an
initial load of thermal energy.
[0059] Short-wave solar light penetrates clear shell 14 and gets
converted to heat at the dark exterior surface of capsule 12, which
then gets transmitted through the capsule wall to food 24 contained
within. Dark non-stick coating 36 on the interior surface of the
capsule facilitates internal radiation and even distribution of the
captured energy. Selective coating 34 on the exterior surface of
the capsule keeps the energy from being radiated back outward as
long-wave infrared, thus preventing heat loss through radiation.
Vacuum 16 between the two solid walls prevents heat loss through
convection. Heat loss from the capsule through conduction is
limited to the lines of contact with the shell in the area of the
opening, at body lip 18A and lid lip 18B. Body liner 12A protrudes
past the axial extent of lip 18A over a short distance, and lid
liner 12B recesses from the axial extent of lip 18B over the same
distance, to assure positive engagement of lid and body, and to
prevent foreign matter from entering the food compartment.
[0060] The performance of pot 10 depends chiefly on the quality of
the selective coating, the level of vacuum, and the extent of
liner-shell contact. Perfect insulation is not desirable: total
heat loss must be sufficient to keep the stagnant temperature at a
safe level, so that the pot does not self-destruct when left to sit
empty in the sun.
Fabrication
[0061] This solar cooking pot is a specialized vacuum jar, and the
manufacturing techniques used in the production of thermos bottles,
well-known to the art, can be applied to this device as well. The
double wall structure is inherently sturdy, therefore the metal
liner can be thin, drawing on the strength of the plastic shell,
and yielding a low total weight. Stainless steel thermos bottles
use liner wall thicknesses down to 0.5 mm. Conventional cookware
use thicker walls to better distribute the applied energy,
typically the intense heat of a flame localized to the bottom. This
is less of an issue for a solar cooker, where the energy influx is
milder and more diffuse. The liner wall thickness can therefore be
closer to that of a thermos bottle than that of a regular cooking
pot.
[0062] The transparent shells can be made from molded or vacuum
formed clear polycarbonate, a commonly used plastic that is very
strong, has good optical properties and chemical resistance, can be
UV-protected, and can withstand relatively high temperatures.
Multi-walled polycarbonate sheets are used extensively in
greenhouse glazing applications. A 6 mm shell wall imparts
exceptional toughness to a 3 liter solar cooking pot of the
proposed design.
[0063] The solar selective material coating the liner may be a
plating, such as black chrome, or a coating, such as Solkote
(www.solec.org). The plastic and metal parts can be made separately
and then bonded together with a suitable adhesive. The intervening
space can then be evacuated through a small passage in the shell,
which is then sealed. The vacuum gap serves primarily as
insulation, but has the positive side effect of lowering the
overall density of the part. With proper sizing of the gaps, both
body and lid can be made light enough to float in water, an
appealing quality for boaters and residents of flood-prone
areas.
User Operation
[0064] In normal or regular operation mode, the user loads the pot
body with food to cook, closes the lid, and sets the cooker out in
an area that will remain sunny for the duration of the cooking
operation. The selective coating and vacuum insulation features
maximize energy capture and minimize loss, thereby obviating the
need for solar concentration under typical weather conditions. The
capsular shape of the food container ensures even exposure to the
sun under different angles of insolation, thereby obviating the
need for solar orientation.
[0065] The food will cook and stay hot for a long time after the
sun has disappeared. It is possible to exploit the heat retention
property of the device to extend cooking time beyond the period of
solar exposure. This is useful when one has limited access to the
sun, in which case the minimum requirement is the time it takes to
bring the food up to cooking temperature. For example, a cook
concerned about the security of her food left unattended can bring
the cooker inside as soon as the desired temperature has been
reached.
[0066] In push or overdrive mode, the user places the solar pot in
a field of concentrated sunlight, such as produced by a
conventional solar oven, solar panel cooker, or solar stove. He
then monitors the temperature to ensure that the safe limit is not
exceeded. Thanks to its construction, this pot will attain higher
temperatures than a regular cookpot, or will achieve faster cooking
times, depending on the type of food. In weak solar conditions,
this device will still cook when a regular pot will not. In
unfavorable geographic or climatic situations, the solar pot can be
used regularly in the place of an ordinary utensil.
[0067] For service as a conventional heat-retention cooker or
vacuum cooker, the user heats food in a regular oven or stove, then
transfers the hot food into the solar pot, letting it continue
cooking from the retained heat without need for solar exposure.
This unit can also function as a thermos bottle in storing hot
contents.
[0068] In the regular or normal cooking mode, the unit operates
unattended and independent from any accessories, with moderate heat
and self-limited temperature, suitable for pasteurizing water and
cooking most foods. In the high heat mode, with the assistance of
concentrated solar radiation such as provided by a panel reflector,
the unit can achieve active boiling of water, or can perform
cooking under unfavorable solar situations such as low angle, or
under adverse atmospheric manifestations such as smoke, haze and
clouds. In the operator-monitored extra high heat mode, or push
mode, the boost of focused solar energy such as provided by a
parabolic reflector enables the unit to attain heat levels
sufficient for frying food.
Applications
[0069] Aside from its obvious role in household cooking, the solar
pot of this invention is also well suited for transitory and mobile
applications, being small, light, securable to a variety of
objects, and operable in the presence of motion. For the student or
office worker with access to a sunny spot, it can deliver a green
hot lunch. For the camper, it can be hung from a tree or pole to
gain a better insolation or to shield the food from undesirable
ground circumstances. For the hiker, it can be mounted on the
outside of a backpack for direct heating, or tucked inside for
retained heat cooking on the trail. For the boater, it can swing
over an unsteady deck, and floats if dropped overboard. For the
city dweller who prefers the convenience of a microwave oven, it
can be left in the closet and ignored until a power disruption
happens, or until utility rates reach the financial pain threshold.
The glow-in-the-dark paint or resin inclusion is a useful feature
for campers and disaster victims.
CONCLUSION, RAMIFICATIONS AND SCOPE
[0070] Thus, the reader will see that the present invention
provides an unique solar cooking pot that achieves full freedom
from the dual constraints of solar concentration and solar
orientation that govern solar cookers of the current art. It does
so while presenting simplicity in design, construction, and
operation, coupled with universal utility, versatile functionality,
and clean aesthetics. This device fits various applications in
daily, recreational, and emergency situations, and will appeal to
disparate categories of consumers. Being comparable to a thermos
bottle in affordability, durability, and merchantability, this
product holds the promise of breaking through in many markets so
far unpenetrated by solar cooking devices, aided by the urgency of
global environmental, climate, and energy changes.
[0071] While the above description contains many specificities,
these should not be construed as limitations on the scope of the
invention, but rather as an exemplification of preferred
embodiments thereof. Many other variations are possible. As an
example, the solar cooker may be sized and shaped as a coffee mug,
with the addition of a handle to the body. As another example, to
minimize the weight for a backpacker, aluminum may be used for the
liner. Accordingly, the scope of the invention should be determined
not by the embodiments illustrated, but by the appended claims and
their legal equivalents.
* * * * *