Patent application title: Solar cooking pot
William H.t. La (Stockton, CA, US)
IPC8 Class: AF24J202FI
Class name: Solar heat collector energy concentrator with support for material heated solar oven
Publication date: 2009-05-28
Patent application number: 20090133688
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.
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.
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of provisional application Ser. No. 61/001,607 filed Nov. 1, 2007.
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to cooking devices, and more specifically to solar cookers.
2. Description of Prior Art
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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/˜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.
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.
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
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.
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.
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.
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.
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.
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.
Another object is to provide an easy to handle pot that is lightweight, its individual parts being able to float on water.
Another object is to provide a sturdy pot that is virtually unbreakable, able to withstand the force of natural disasters.
Another object is to provide a visible solar cooker that glows in the dark, facilitating its retrieval or recovery in emergency situations.
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.
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.
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.
Another object is to provide a multifunctional solar cooking pot that doubles as a heat-retention cooker, or vacuum cooker.
Another object is to provide an inexpensive solar cooker that is durable, affording both up-front and long-term economy for the user.
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
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.
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.
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.
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.
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.
These novel features present unique combinations of advantages not found in the current art.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, closely related figures have the same number but different alphabetic suffixes.
FIG. 1 is a front perspective view of the preferred embodiment solar cooking pot, with the body and lid separated.
FIG. 2 is a left cross-sectional view of the preferred embodiment solar cooking pot, with the body and lid engaged.
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.
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.
FIG. 5 is a front perspective view of the preferred embodiment solar cooking pot together with an accessory packaging.
FIG. 6 is a front cross-sectional view of an alternate embodiment solar cooking pot.
FIG. 7 is a front cross-sectional view of an alternate embodiment solar cooking pot including wall inserts.
REFERENCE NUMERALS IN DRAWINGS
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
Patent applications in class Solar oven
Patent applications in all subclasses Solar oven