Patent Publication Number: US-2011067842-A1

Title: Fluid encapsulated heat transfer vessel and method

Description:
BACKGROUND 
     The present invention relates in general to heat transfer mechanisms, and more particularly, to heat transfer vessels for containing and facilitating heating of a substance. 
     Heating of a substance, such as liquid or a solid, whether for cooking purposes or laboratory or industrial applications, consumes significant energy in the United States and worldwide. Numerous examples of commercial heating vessels exist today. Unfortunately, there are many sources of energy inefficiencies in the heating of a substance using commercially available heating vessels. These inefficiencies include: a large temperature reduction between the region where heat is applied and portions of distant vessel surfaces also being used for heating; a heat loss from the exterior sidewall surfaces of the heating vessel to the ambient air; and a lack of heating surface area in the large central volume of the substance being heated. 
     BRIEF SUMMARY 
     In one aspect, the shortcomings of the prior art are overcome and additional advantages are provided through the provision of a device comprising a heat transfer vessel to facilitate heating of a substance. The heat transfer vessel includes an at least partially hollow structure comprising a chamber formed between an outer shell and an inner shell thereof, and includes a base portion and a sidewall portion extending from the base portion, wherein the chamber is disposed within at least one of the base portion or the sidewall portion. The device further includes a heat transfer fluid disposed within the chamber of the heat transfer vessel, wherein the heat transfer fluid facilitates transfer of applied heat from the outer shell of the heat transfer vessel to the inner shell of the heat transfer vessel, and thus to the substance when disposed within the heat transfer vessel. 
     In a further aspect, a method of fabricating a heat transfer vessel is provided. The method includes: forming an at least partially hollow structure comprising a chamber defined between an outer shell and an inner shell thereof, and comprising a base portion and a sidewall portion extending from the base portion, the chamber being disposed within at least one of the base portion or the sidewall portion of the hollow structure; and disposing a heat transfer fluid within the chamber of the hollow structure, the heat transfer fluid facilitating transfer of heat applied to the outer shell of the heat transfer vessel to the inner shell of the heat transfer vessel, and thus, to a substance when disposed within the heat transfer vessel in contact with the inner shell thereof. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic of a conventional heating vessel containing a substance undergoing heating through the application of heat to the bottom surface of the heating vessel; 
         FIG. 2  is a schematic of one embodiment of a heat transfer vessel comprising a heat transfer fluid encapsulated within a chamber thereof, in accordance with an aspect of the present invention; 
         FIG. 3  is a schematic of an alternate embodiment of a heat transfer vessel comprising a heat transfer fluid encapsulated within a compartment thereof, and comprising an insulative structure surrounding the outer shell of the vessel along the sidewall portion thereof, in accordance with an aspect of the present invention; 
         FIG. 4  depicts operational heating of the heat transfer vessel of  FIG. 3 , illustrating thermal energy transfer from the outer shell of the heat transfer vessel to the inner shell of the vessel employing boiling and condensation of the heat transfer fluid within the chamber of the vessel, in accordance with an aspect of the present invention; 
         FIG. 5  is a schematic of an alternate embodiment of a heat transfer vessel comprising a heat transfer fluid encapsulated within a chamber of the vessel, in accordance with an aspect of the present invention; and 
         FIGS. 6A &amp; 6B  depict further alternate embodiments of a heat transfer vessel, each comprising a heat transfer fluid encapsulated within a chamber of the vessel, in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein is a novel three-dimensional device which addresses the above-noted drawbacks of commercially available heating vessels, and enables highly efficient heating of substances. As used herein, “substance” refers to any material to undergo heating, whether in liquid state, solid state or even gaseous state (with appropriate configuration of the device). The device disclosed herein provides high efficiency transfer of thermal energy from an externally heated surface to an inner surface (where the energy is desired) through a boiling and condensation heat transfer loop. With proper selection of the encapsulated heat transfer fluid and the encapsulation conditions (e.g., pressure) while keeping non-condensable gases within the vessel chamber to a minimum, a heat transfer vessel is attained which can operate within any desired temperature range for general heating applications, including cooking. Advantageously, the device disclosed herein uniquely provides a highly uniform, high-speed response to the external application of heat, and has many domestic and laboratory applications. 
     The heat transfer fluid employed within the heat transfer vessel is selected to possess the appropriate thermophysical properties that suit the particular heating application. Significant application parameters include the temperature of heat input via the outer shell, the heat flux of the heat input, the temperature desired at the inner shell in contact with the substance to be heated, and the expected heat transfer coefficient between the substance being heated and the inner shell of the vessel. The thermophysical fluid properties of interest for a range of temperature and pressure conditions are the boiling point of the liquid, the latent heat of vaporization, the surface tension, the specific heat, and the density in both liquid and vapor states. 
     For example, if the application is to heat a liquid substance to a temperature of 75° C. using a heat input at an outer shell temperature of 200° C., then the encapsulated fluid would have to boil at a temperature below 200° C. and condense at a temperature above 75° C., and would need to cycle between the vapor and liquid states for the application conditions (i.e., the heating and cooling heat transfer coefficients and the temperatures at heat input and heat rejection surfaces, respectively). For this example, since water under atmospheric conditions boils at about 100° C., pressurized water could be used to ensure that the boiling and condensation processes occur in the 200-75° C. temperature range, respectively, for the pressures experienced by the encapsulated fluid. If the boiling-condensation temperature range of interest is 80-40° C., then water at sub-atmospheric pressure could be used. 
     Other heat transfer fluids could be used depending on the application parameters. For example, dielectric coolants such as those manufactured by 3M Corporation under the brand names HFE-7000, HFE-7100, HFE-7200, HFE-7500, FC-87, FC-72, FC-70, FC-40 or refrigerants or oils could be used as the heat transfer fluid. Further, as noted above, pressure within the chamber can be manipulated to achieve the desired saturation conditions for a given heat transfer fluid. 
     As used herein, “heat transfer fluid” refers to any encapsulated fluid within the compartment of the vessel capable of repeated phase cycling between liquid and vapor states through boiling and condensation as explained herein. 
     Reference is made below to the drawings (which are not drawn to scale to facilitate understanding of the invention), wherein the same reference numbers used throughout different figures designate the same or similar components. 
     Briefly,  FIG. 1  illustrates a conventional heating vessel  100  which comprises a solid-walled container of any desired shape for holding a substance  120  to be heated. Traditionally, substance  120  undergoes heating via the application of heat  130  to a bottom surface of container  110 . By way of example, container  110  might comprise an aluminum, copper, stainless steel, glass, etc., cooking, laboratory or industrial processes vessel. 
       FIG. 2  illustrates one embodiment of a heat transfer vessel  200 , in accordance with an aspect of the present invention. In this embodiment, heat transfer vessel  200  comprises an outer shell  201  and an inner shell  202  spaced apart to form a chamber  203  between opposing surfaces thereof. As illustrated, chamber  203  resides, in one embodiment, in both a base portion  210  and a sidewall portion  211  of the heat transfer vessel. A heat transfer fluid  215  in liquid state partially fills chamber  203 , residing in base portion  210  of heat transfer vessel  200  as illustrated. Although not shown, one or more ports can be provided within the vessel extending into the chamber for facilitating evacuation of the chamber and disposition of the heat transfer fluid  215  within the chamber. The heat transfer fluid is a two-phase encapsulated fluid that may, at any point in time, be partially in liquid state and partially in vapor state. As noted above, various fluids could be employed for the heat transfer fluid, depending on desired thermophysical properties for a particular heating application or range of applications. 
     Heat transfer vessel  200  is thus a fluid encapsulated vessel, with enhanced energy efficient heating. In one embodiment, the vessel is cylindrical-shaped, although various shapes could be employed. As shown, the vessel is configured to hold or contain a substance  220 , such as a liquid, to undergo heating by the application of external heat  230 , for example, to a bottom surface of the vessel. With the application of heat, heat transfer fluid  215  repeatedly phase cycles transferring heat from outer shell  201  to inner shell  202 , as explained further below. The surfaces of inner shell  201 , both within chamber  203  and externally, in contact with substance  220 , are the primary surfaces for heat exchange between the heat transfer fluid and the substance, that is, between the substance being heated and the encapsulated two-phase fluid that spreads and transports the heat away from the heated surface of base portion  210  to the larger surface area of inner shell  202  in contact with substance  220 . Advantageously, the vaporized heat transfer fluid within chamber  203  efficiently and uniformly spreads this thermal energy to inner shell  202 . 
       FIG. 3  illustrates an alternate embodiment of a heat transfer vessel  200 ′, which is substantially identical to heat transfer  200  of  FIG. 2 , with the exception of a reconfiguration to provide a smaller base portion  210  and a larger sidewall portion  211 . As shown, outer shell  201  is in spaced opposing relation to inner shell  202  to define chamber  203 , within which heat transfer fluid  215  resides. With the application of heat  230  to the bottom surface of vessel  200 ′, heat transfer fluid  215  in liquid state boils and the vaporized heat transfer fluid subsequently condenses along inner shell  202 , transferring thermal energy to inner shell  202 , both along the bottom portion  210  and the sidewall portion  211  of the vessel. 
     In this embodiment, an insulator  300  is attached to at least partially encircle outer shell  201  at the sidewall portion thereof. This insulator significantly reduces heat loss along the outer shell of the heat transfer vessel due to radiation cooling to ambient surroundings, natural air convection, or forced air convection in cases where there is a mechanically induced draft in the ambient surroundings. In one example, insulator  300  is an insulating jacket that is applied separately to outer shell  201 , or alternatively, is an insulative structure that is integrated with outer shell  201 . Insulator  300  would be most effective when heat transfer vessel  200 ′ is relatively tall, that is, has a relatively large sidewall portion  211 , and the ratio of the surface area exposed to potential heat loss to the total external surface area is relatively large. 
       FIG. 4  is an operational example of heat transfer vessel  200 ′ of  FIG. 3 . When no heat source is applied, heat transfer vessel  200 ′ is non-operational, and the heat transfer fluid  215  exists in an equilibrium condition, with the liquid portion within chamber  203  remaining liquid and the vapor portion within chamber  203  remaining vapor. When the base of the heat transfer vessel  200 ′ is heated  230  (using some form of a heat source such as an electrical heater coil, or a flame), heat transfer fluid  215  in liquid state that was in equilibrium starts to boil, and its vapor travels through chamber  203 , contacting the inner surfaces of inner shell  202  (within both base portion  210  and sidewall portion  211 ). As illustrated by arrows  400  in  FIG. 4 , a portion of this vaporized heat transfer fluid rises within chamber  203  into sidewall portions  211  of heat transfer vessel  200 ′. The substance  220  within the vessel being heated cools one side of inner shell  202 , thus condensing the encapsulated vaporized heat transfer fluid on the other side of inner shell  202 , that is, the surface of inner shell  202  exposed to chamber  203 . This condensate forms a film  410  over the horizontal and vertical surfaces of the inner shell. The condensate film  410  flows as illustrated by arrows  411  along the inside surface of inner shell  202  and falls as droplets (not shown) back to the pool of boiling heat transfer fluid  215  in liquid state in base portion  210  of the vessel. The process continues until the desired amount of heat has been transferred to substance  220  from applied heat  230 . Note that the result is a superior, more uniform spreading of heat  420  into substance  220  contained within the vessel. 
       FIG. 5  illustrates an alternate embodiment of a heat transfer vessel  500 , in accordance with an aspect of the present invention. Heat transfer vessel  500  is similar to the vessels described above in connection with  FIGS. 3 &amp; 4 , however, includes the addition of one or more protrusions  510  in inner shell  202  into the central region of the vessel holding substance  220 . As shown, chamber  203  defined between inner shell  202  and outer shell  201  extends in this embodiment within sidewall portion  211 , base portion  210  and a protrusion portion(s)  511 . This vessel configuration advantageously enhances the available surface area of inner shell  202  for heating substance  220  employing heat transfer fluid  215  and the application of heat  230  to the vessel. As illustrated, insulator  300  is provided at least partially surrounding the exposed exterior surface of outer shell  201  to limit parasitic heat loss to the ambient environment. Advantageously, the heat transfer vessel configuration of  FIG. 5  allows a larger volume of substance  220  to be in contact with the hot surface of inner shell  202 . 
       FIGS. 6A &amp; 6B  depict further alternate embodiments of heat transfer vessels, in accordance with aspects of the present invention. In  FIG. 6A , a heat transfer vessel  600  is illustrated in cross-sectional plan view as comprising a circular-shaped vessel (presented by way of example only). Heat transfer vessel  600  includes outer shell  201  and inner shell  202  in spaced opposing relation to define chamber  203 , within which is located a two-phase heat transfer fluid (not shown) such as described above. An insulator  300  surrounds the sidewall portion of outer shell  201 , and in this embodiment, a rib-shaped central protrusion is provided within inner shell  202 , resulting in chamber  203  also having a central protrusion portion  511  into which vaporized heat transfer fluid can rise, such as illustrated in  FIG. 5 . The result is an increased surface area of inner shell  202  exposed to substance  220  contained within the vessel. 
       FIG. 6B  depicts a further embodiment of a heat transfer vessel  600 ′, wherein multiple protrusions  610  in inner wall  202  are shown in cross-sectional plan view. Each protrusion  610  is a cylindrical-shaped protrusion extending from a lower portion of inner shell  202  upwards into the central region of the vessel holding substance  220  to be heated. The cylindrical-shaped protrusions  610  in inner shell  202  result in multiple protrusion portions  611  being defined within chamber  203  (i.e., defined between outer shell  201  and inner shell  202  of the vessel). Heat transfer fluid in vapor state rises, in part, within the protrusion portions and is condensed upon contacting the surfaces of the inner shell, which are in thermal contact with the cooler substance  220 , to then drop back down in liquid state into the base portion of the vessel for further boiling. Advantageously, the multiple protrusions  610  in inner surface  202  enhance the heat transfer surface area of inner shell  202 . In this embodiment, an insulator  300  again at least partially encircles the sidewall portion of outer shell  201  to limit parasitic heat loss through the outer shell. 
     Although embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.