WO2000054638A1

WO2000054638A1 - Heat pipe cookware incorporating porous material

Info

Publication number: WO2000054638A1
Application number: PCT/KR2000/000217
Authority: WO
Inventors: Young Man Chung; Byung Sook Chin
Original assignee: Young Man Chung; Byung Sook Chin
Priority date: 1999-03-17
Filing date: 2000-03-16
Publication date: 2000-09-21
Also published as: KR19990064490A

Abstract

A heat pipe cooker such as a frying pan, pot, rice cooker, etc., disposed on the heat source such as fire or an electric cooker, which is capable of improving heat transmission efficiency to thereby maintain a temperature on the whole portions thereof at a substantially same state. The heat pipe cooker of the present invention includes a completely closed space where an operation liquid and the steam therefrom are charged and inner and outer shells formed on the inner and outer sides of the closed space. In this case, the inner and outer shells are partially welded to each other. On the bottom surface of the closed space is attached a perforated plate made of a porous material such as a porous sintered metal or ceramic and drenched with the operation liquid. Therefore, upon cooking the heat is transmitted to the bottom of the outer shell and evaporates the operation liquid drenching the bottom portion of the closed space. The evaporated steam delivers the lower portion of the inner shell and is condensed. The condensed operation liquid evenly drops to the bottom surface of the closed space by the action of gravity and the capillary force of the perforated plate. Based upon the above principles, the cooker maintains a predetermined temperature, such that the cooking is completed at the uniform temperature.

Description

HEAT PIPE COOKWARE INCORPORATING POROUS MATERIAL

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat pipe cookware such as frying pan, pot, rice cooker, and etc., which is capable of improving heat transfer efficiency to thereby maintain a uniform temperature on the whole portions thereof.

2. Discussion of the Prior Art

Upon cooking, typically, it is very important to maintain the wall and bottom surfaces of the cookware at a uniform temperature. This is because the material to be cooked can be evenly heated so to obtain a satisfactory cooking result and the heat efficiency can also be maintained considerably high.

By way of example, such cooking methods as rice being boiled in a thick iron pot or pot stew being boiled in a brass chafing dish are based upon the above mentioned principle. Thus, when fabricating cookware with stainless steel which has a low thermal conductivity, it is desirable to build a multi-layer structure wherein aluminum of a high thermal conductivity is attached between two stainless steel plates. However, since even the aluminum does not have an infinitely large thermal conductivity, it fails to produce an ideal and efficient cookware. That is, the ideal cookwares can not be produced with the thermal conductivity of metal products on the market.

So I have filed Korean Patent Application No. 1997-0003257 which discloses a cookware capable of solving the conventional problem of thermal conductivity, and of maintaining a theoretically isothermal state on the whole portions thereof.

In more detail, the prior art adopts to cookwares a newly developed heat pipe technology which were developed to maintain the surface of an artificial satellite at a uniform temperature. The prior art cookware is composed of a closed space, an outer shell and an inner shell as a double structure. Both of the outer and the inner shells are made of metallic materials such as aluminum, copper, stainless steel and the like. A predetermined amount of working fluid such as distilled water is poured into the closed space, and the wire screen of 50 to 200 meshes is attached onto the outer shell side of the closed space. By using the phenomenon where the working fluid in the closed space is evaporated and condensed at a uniform temperature, the cookware can maintain the same temperature at the whole portions thereof, which exhibits the same effect as being made of an ideal material which has an infinite magnitude of thermal conductivity. In other words, even though the cookware is unevenly or locally heated by flames or electricity from the exterior thereof, it can maintain the internal surface thereof at a uniform temperature to thereby obtain an even heating, such that the material being cooked is well done to provide an excellent cooking result. Moreover, since the internal structure of the cookware contains a very small amount of working fluid, the whole thermal capacity is substantially low, with a consequence that the temperature control of the cookware is very fast and the danger of overheating is minimized by limiting the cookware temperature below that at which the whole working fluid is evaporated and the vapor functions as an insulation layer to the food therein.

The wire screen serves to naturally circulate the working fluid within the closed space to the whole surface thereof by capillary force. The material doing such action is called 'wick' as a comprehensive term.

In case of using the wire screen as the wick, it is found that many difficulties are encountered during cookware manufacturing process. For instance, in case of manufacturing an inner pot (container) of an electric rice cooker with a general diameter of 200 mm, two or three wire screens are overlapped and attached on the bottom surface of the closed space. At this time, spot welding process to attach the wire screens at the inside bottom of the outer shell is carried out about 300 times at an interval of 1 cm.

The time required for the spot welding is roughly 20 minutes, even to a skilled person in this field, which will of course result in a drastic reduction in the production yield. Furthermore, in case of small size cookwares, the operation in which the welding rod of the spot welding machine is inserted into the inner space of the outer shell to be welded is time consuming. As a result, this brings in the result to restrict the freedom to select the size of the cookware. In addition to that, most of the bottom surfaces of the containers do not have perfectly flat plane, but they have a concave or convex surface. Thus, when the wire screen is attached onto the bottom surface, there occurs a problem that a portion of the wire screen is undesirably warped. As a consequence, there is formed a difference in the gap between the wire screen-warped portion and the normal portions, thereby insufficient wetting or local flooding may occur. As the result, unbalance of the working fluid in operation is induced, thereby deteriorating the heat circulation efficiency.

On the other hand, if the wire screen is not attached onto the bottom surface completely in the welding process, the amount of working fluid somewhat increases to make up for the gaps. Then, the pressure in the internal closed space may be significantly increased following the liquid-vapor saturation line as far as there remains liquid. It thus causes the internal pressure of the container to be excessively high, such that there occurs a problem that the inner and the outer shells are deformed. In order to prevent the deformation, thicker metallic material must be used, which makes the container heavier.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved heat pipe cookware such as frying pan, pot, rice cooker, and etc. which is capable of improving heat transfer efficiency to thereby maintain a uniform temperature on the whole portions thereof, exhibiting an excellent capillary pumping as compared with the conventional wire screen, and enhancing heat circulation efficiency, with lower manufacturing cost.

To accomplish this and other objects of the present invention, there is provided a heat pipe cookware including: a porous plate made of porous material such as sintered metal or ceramic attached onto the bottom surface of a closed space in which only working fluid and the vapor therefrom are retained between the inner and the outer shells, the wprking fluid filled enough only to wet the porous plate, whereby the evaporation on the surface of the porous .plate occurs through a closed circulation process of the evaporation and condensation of the working fluid in the closed space and the condensed working fluid is then absorbed by the capillary force of the porous plate to be thereby circulated automatically.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:

FIG. 1 is a sectional view illustrating the heat pipe cookware having the porous plate constructed in accordance with the principles of the present invention;

FIG. 2 is a plan view of FIG. 1; and FIG. 3 is an enlarged sectional view illustrating the main parts of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an explanation on the heat pipe cookware having the porous plate constructed in accordance with the principles of the present invention will be in detail discussed with reference to FIGS. 1 to 3. FIGS. 1 and 3 are sectional views of the cookware constructed in accordance with the principles of the present invention. The cookware comprises an outer shell 1 made of a metallic material of 2-3 mm in thickness such as aluminum, copper, stainless steel, and etc., a closed space 2 of 10 mm or less formed on the inside of the outer shell 1 and an inner shell 3 formed on the inside of the closed space 2, into which the material to be cooked is disposed.

The inner and the outer shells 3 and 1 are spaced apart by means of a junction part 4 and are made by a welding or brazing process, so that they can maintain the mechanical strength, without any change, even in the case where the saturated vapor pressure of working fluid 6 in the closed space 2 differs from the atmospheric pressure. Since the junction part 4 connecting the outer and the inner shells 1 and 3 occupies only a part of the closed space 2, the working fluid 2 flows freely into the . closed space 2, without any interruption. Furthermore, the porous plate 5, made of a porous material such as sintered metal or ceramic, is provided to be attached on the outer shell 1 of the closed space 2. The porous plate 5 serves to automatically circulate the working fluid 6 within the closed space 2 to the whole surface thereof by the capillary force. As noted above, the object doing such the action is called 'wick' as a comprehensive term. The porous plate 5 is composed of a plurality of minute porosities, through which the working fluid 6 moves freely. Also, the porosities create the capillary phenomenon on the surface of the porous plate 5, so that they serve to absorb the working fluid 6, while moving from the place where the working fluid 6 overflows to the place where the working fluid 6 is evaporated and consumed.

Even if the bottom of the outer shell 1 is somewhat inclined, the whole portions of the porous plate 5 is maintained wet with the working fluid 6 due to the action of the capillary force of the porous plate 5. The working fluid 6 undergoes suction in such a manner that the porous plate 5 is fully soaked with water. That is, the working fluid 6 is injected to a fixed quantity in an accurate manner in order not to block the evaporation space of the upper portion of the porous plate 5. Other gases or liquid except the working fluid 6 should be eliminated in the closed space 2.

Under the configuration as discussed above, an explanation of the operation principles of the cookware according to the present invention will be made. The closed space 2 is provided with the porous plate 5 soaked with the working fluid 6 on the bottom portion thereof. The outer shell 1 delivers the heat transmitted from the outside to the working fluid 6 soaking the porous plate 5. In this case, the working fluid 6 is evaporated on the surface of the porous plate 5 and flows through the vapor passage of the closed space 2 to each part of the inner shell 3.

The vapor is condensed on the wall of the inner shell 3 of the vapor passage and emits the condensation heat, which is transmitted to the food being cooked inside of the inner shell 3, such that the desired cooking result is obtained. The condensed liquid drops flows down to the porous plate 5 at the outer shell 1 side by the action of gravity. Once the working fluid 6 reaches the porous plate 5, it evenly wets the whole surfaces of the porous plate 5 by the strong capillary absorbing force of the porous plate 5.

The porous plate 5 exerts such the absorbing capability to prevent the outer shell 1 from being overheated, so that the outer shell 1 can maintain a uniform temperature thereof. In other words, the working fluid 6 is dynamically evaporated on the one portion of the outer shell 1 where the quantity of heat transferred is considerably large, so that the porous plate 5 is readily dried.

In this case, if the porous plate 5 does not absorb the working fluid 6 within a short period of time, a local overheating may occur, but the porous plate 5 can absorb the nearby working fluid 6 by the capillary force thereof to thereby maintain the temperature evaporation constant. In addition to that, the porous plate 5 evenly delivers the heat which is transferred from outside bottom to the working fluid 6 disposed on the bottom surface thereof, thereby preventing overheating on the bottom surface thereof and the occurrence of air bubbles thereon, such that a silent operation and a high isothermal efficiency can be ensured.

The above operation process is based upon the principles of the heat pipe cookware. The heat pipe cookware according to the present invention has the following advantages. Firstly, since the working fluid 6 is not a mixture, but a pure material, the temperature at all of the positions within the closed space 2 is uniformly the saturation temperature of the working fluid 6. In other words, even though a specific position within the closed space 2 may be cooled seriously or heated unevenly, the whole positions thereof are maintained at a uniform temperature.

Secondly, since the saturation temperature and the pressure at the state where the working fluid and vapor therefrom are contained in closed space are continuously increased following the liquid vapor saturation line from room temperature and low pressure to high temperature and high pressure, in case of using the water vapor as the working fluid 6, for example, the inner shell 3 can heat the contents in the interior thereof, not only at the temperature of 100 ^°C but also at the temperature higher or lower than 100 °C while maintaining the same temperature at all the positions within the closed space 2. Theoretically, the working fluid 6 can be any material, only if it is a pure material, but in actual application, preferably, it has to possess a high surface tension and a low viscosity for the purpose of maintaining a strong capillary force. Moreover, in order to increase the amount of heat to be transferred, the working fluid 6 should have high latent heat of evaporation while the circulation quantity of the working fluid 6 is small.

If the internal pressure of the closed space 2 is too high, a dangerous accident may occur. In order to prevent such accident, the working fluid 6 preferably has the vapor pressure of one or less atmospheric pressure at 10 O'C . On the other hand, the working fluid should have a vapor pressure of less than several atm., even when the working fluid 6 is overheated up to the temperature of 200 ^°C by mistake, for instance when the user leaves the cookware heated for a sustained period of time not putting in any material to be cooked, thereby avoiding the danger of explosion. In addition, the working fluid 6 is preferably not combustible and not poisonous, thereby preventing the danger of accidents upon the occurrence of leakage.

The fact that the heat pipe cookware according to the present invention maintains the same temperature is based upon a thermodynamic equilibrium theory where the vapor filling the closed space 2 is under a completely uniform pressure and the evaporation and condensation temperature thereof is the same at any point in the closed space 2. In addition, the evaporation and condensation process is an effective way of heat transfer even when there is very slight temperature difference therebetween.

When the working fluid 6 flows along the wall, thus to form a liquid film, and when condensation occurs on the surface of the liquid film, the temperature on the wall side of the liquid film is somewhat lower than that on the surface side of the liquid film. The surface temperature of the liquid film is naturally the saturation temperature of the vapor of the working fluid 6, but it may be expected that the wall side temperature of the liquid film is cooler slightly by the temperature difference of 0.1 °C or less.

Similarly, the upper surface of the liquid film on the porous plate 5 where the evaporation occurs maintains the evaporation temperature, but the lower surface thereof has a slightly higher temperature by about 1 °C than the upper surface thereof, that is, the lower surface maintains an over -saturated state. Accordingly, the cookware according to the present invention can operate within a temperature difference range of about 1 °C, which is practically isothermal for cooking. Therefore, it is not too much to say that the cookware according to the present invention operates while maintaining the same temperature on all the points of the cookware surfaces.

Specifically, the inner shell 3 of the cookware operates with the temperature difference range of only 0.1 "C . This ensures that the cookware according to the present invention is a most desirable cookware having an almost infinitely large thermal conductivity. On the other hand, since the porous plate 5 which is constructed according to the principles of the present invention is produced to have the shape accurately corresponding to the bottom surface of the outer shell 1 as pre-designed, in the manufacturing process of cookwares according to the present invention, the porous plate 5 which has been pre-produced by a hydraulic press machine is installed on the bottom portion of the outer shell 1 and then is fixed by means of the junction part 4 for securing the inner shell 3 and the outer shell 1.

For instance, the junction part 4 connecting the inner shell 3 and the outer shell 1 is comprised of a plate spring. In this case, the inner shell 3 is welded on the outer shell 1 in the state where the porous plate 5 is pressed down by the plate spring. Thereby, the porous plate 5 is securely fixed on the bottom surface of the outer shell 1 by the force of the plate spring. In case of this assembling process, the cookware can be assembled within a very short period of time of about 1/200 that of the conventional wire screen attaching method. That is, one cookware can be assembled in every 5 or 6 seconds.

As an another assembling method, the porous plate 5 is secured by welding on the junction part 4, and upon assembling, it is attached to the bottom surface of the outer shell 1, thereby directly welding the inner and outer shells 3 and 1 on the rims. At this time, spot welding is also carried out about 3 or .4 times on the portion where the junction part 4 and the inner shell 3 are met. Thereby, the porous plate 5 is secured on the bottom surface of the outer shell 1 in a simple manner.

Under the above securing methods of the porous plate 5, since the porous plate 5 is in a very close contact with the bottom surface of the outer shell 1, there is no need to increase the amount of working fluid and thereby, as the pressure within the closed space 2 is kept within tolerance, there is no need to increase the thickness of the inner shell 3 and the outer shell 1.

As discussed above, an improved heat pipe cookware having the porous plate according to the present invention is capable of maintaining the whole portions thereof at a substantially uniform temperature, thereby obtaining an ideal cooking result, providing a porous plate on the bottom surface of a closed space, thereby exhibiting an excellent capillary force as compared with a conventional wire screen method and enhancing a thermal circulation efficiency, and improving the assembly and productivity upon production.

Although a preferred form of the invention has been described, it will be understood by those skilled in the field that variations therefrom, and analogous uses, are within the knowledge of those skilled in the art. Accordingly, it is intended that the scope of the invention be defined, not by the scope of the foregoing description, but rather by the scope of the claims as interpreted in view of the pertinent prior art.

Claims

What Is Claimed Is:

1. A heat pipe cookware having a porous plate, comprising: said porous plate made of .a porous sintered metal or ceramic and attached on the bottom surface of a closed space into which only working fluid and the vapor therefrom are retained between an inner shell and an outer shell, said working fluid injected enough to wet said porous plate, whereby the evaporation on the surface of said porous plate occurs through a closed circulation process of the evaporation and condensation of said working fluid in said closed space and the condensed working fluid is then absorbed by the capillary force of said porous plate to be thereby circulated automatically.