Patent Application
20110067842
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.
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.
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:
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,
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.
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.
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.
