This is a continuation of International Application PCT/JP2005/006060, with an international filing date of Mar. 30, 2005. Priority is claimed to Japan Patent Application Serial No. 2004-098476, filed on Mar. 30, 2004, which is hereby incorporated by reference. The present invention relates to a portable heat transfer apparatus equipped with an energy source in a self-contained manner and designed to supply heat to a heater or heated clothing usable in outdoor environments where any supply of electric power or fuel gas is difficult.
Heretofore, as an outdoor-type transportable heater, a gas heater and a body warmer have been widely prevalent However, these products have been inconvenient in that only a portion of user's body is warmed up or the level of warmth cannot be controlled. Further, heated clothing and a mat, each of which uses a battery and has an electrically resistive element distributed thereinside and adapted to generate heat based on electrical energy from the battery, have come into practical use. However, a mass energy density of latest batteries is still not so high, and therefore it is unable to supply required heating energy for a sufficient period of time.
With a view to solving this problem, the inventor of this application proposed an invention disclosed in Japanese Patent No. 3088127. Another invention publicly known by and disclosed in Japanese Patent Laid-Open Publication No. 09-126423 has come into practical use. These inventions are intended to use LPG as an energy source so as to overcome a disadvantage of batteries, and designed to burn LPG using a catalyst and extract resulting heat. In the former invention, the extracted heat acts to activate a heat-driven pump so as to transfer the heat by the medium of water. In the latter invention, the heat transfer is achieved by air convection.
As compared with flaming combustion, catalytic combustion is a tough combustion reaction capable of being uninterruptedly continued only by supplying fuel and air while maintaining a certain level of high-temperature environment, even if the wind blows or an air-fuel mixture ratio is slightly changed. Further, the catalytic combustion has a feature such that combustion is induced at a lower temperature than that in the flaming combustion. However, if the reaction is continued at a theoretical mixture ratio for a longer period of time, a combustion temperature will be excessively increased to cause deterioration of the catalyst. Thus, it is necessary to produce the reaction at a learn mixture ratio (excess in air). This inevitably leads to lowering of the combustion temperature to cause the need for increasing a heat transfer area required for activating the heat-driven pump and thereby increasing the size of a combustion chamber. Thus, there remains a problem in terms of portability. Moreover, it is impossible to use an atmospheric burner in view of the need for introducing air in large excess. In contrast, the flaming combustion originally has a high combustion temperature. Thus, the required heat transfer area can be reduced to facilitate downsizing, and a surface area of a heat generation section can be reduced to restrict heat leakage from the surface to the outside so as to provide enhanced heat efficiency. However, it is practically difficult to perform combustion of a fully pre-mixed mixture (fully pre-mixed combustion) within a narrow space surrounded by a peripheral wall. Such combustion is further difficult for the atmospheric burner designed to inject LPG from a nozzle and suck air based on a momentum of the injected LPG. While a flame can be maintained at a rich mixture ratio, it will be blown off before the mixture ratio reaches the theoretical mixture ratio. While a fan is typically used for forcibly supplying air (forced air supply) to achieve the fully pre-mixed combustion, such a forced-air fan cannot be used in a portable apparatus pursuing downsizing, because it has to be rotated using a motor requiring a power source, such as a battery.
It is an object of the present invention to provide a compact/lightweight portable heat transfer apparatus suitable for being carried or transported, and capable of performing flaming combustion of a fully premixed air-fuel mixture using an atmospheric burner while ensuring a stable combustion quality free of flame-out due to disturbances, and reducing heat loss to the outside so as to supply sufficient heat to a heat-driven pump.
According to the present invention, there is provided a portable heat transfer apparatus which comprises a mixture forming/supply device for producing a mixture of fuel gas and air, and a heating unit including a heat collection casing and a burner installed in the heat collection casing. The burner is formed with a combustion chamber having a flat surface. Further, the burner includes a large number of holes each formed on an upstream side thereof to extend up to the flat surface so as to serve as a burner port for injecting the mixture into the combustion chamber to perform combustion of the mixture in the combustion chamber, and a porous solid radiant-heat conversion component adapted to partly convert a heat energy of exhaust gas resulting from the combustion in the combustion chamber into a radiant heat energy. The porous solid radiant-heat conversion component defines at least a surface region of the combustion chamber located in opposed relation to a flame front to be produced close to the flat surface. The portable heat transfer apparatus further includes a heat-driven pump joined to the heat collection casing and adapted to receive heat generated by the combustion of the mixture in the combustion chamber, through the heat collection casing.
The mixture forming/supply device may comprise a venturi tube provided with an air intake duct and fluidically connected to the burner. In one embodiment of the present invention, the heat collection casing is configured to fully enclose the burner, and formed with a great number of holes constituting an upstream heat exchange section and a downstream heat exchange section. An exhaust duct is connected to the heat collection casing to establish fluid communication with the downstream heat exchange section, and a pair of wind protection plates are disposed adjacent, respectively, to an intake air inlet of the air intake duct and an exhaust gas outlet of the exhaust duct to protect against an adverse effect of disturbances of ambient air such as winds or turning upside down.
The air-gas mixture supplied from the mixture forming/supply device into the combustion chamber through the burner ports is ignited by sparks of a spark plug exposed to the combustion chamber to create flames around the flat surface of the combustion chamber. When resulting exhaust gas passes through the porous solid radiant-heat conversion component, a part of heat energy is converted into radiant heat energy by the porous solid radiant-heat conversion component, and returned toward the flame to accelerate a combustion reaction of the mixture. Thus, the flame is formed as a stable flame front resistant to “flame-out”.
The heating unit B includes a burner 11 formed with a combustion chamber 12, and a heat collection casing 10 configured to surround the burner 11 and made of a heat conductor, such as alumina. The burner includes a large number of holes 15 formed on an upstream side thereof in spaced-apart relation to each other in such a manner as to extend up to a flat surface 13 so as to serve as a great number of burner ports 14. The combustion chamber 12 has an extremely small internal volume of 10 cc or less. The burner B is further provided with a spark plug 16 extending to be exposed to the combustion chamber 12.
The burner 11 is provided with a porous solid radiant-heat conversion component 17. In this embodiment, the porous solid radiant-heat conversion component 17 comprises a wire mesh formed by weaving a heat-resistant metal wire having a diameter of about φ0.1 to φ0.3.
Firstly, for the ignition operation, a mixture of fuel gas and air is set at a relatively high mixture ratio by adjusting the throttle valve using the lever 5 to reduce the air volume and is injected through the great number of holes 15 into the combustion chamber 12 of the burner 11. The mixture injected from the holes is formed as mixture vortexes around the outlet openings of the holes because of suddenly enlarged flat surface 13. Then, the mixture is ignited by sparks of the spark plug 16, and the vortexes are also ignited. The resulting flames from the great number of burner ports 14 are combined together to form a single flame front, and stabilized in the vicinity of the flat surface. The combustion causes an increase in temperature of a wall surface of the combustion chamber 12, and the resulting heat acts to warm a wall region above the burner ports 14 so as to preheat the mixture. Concurrently, high-temperature exhaust gas resulting from the combustion passes through the porous solid radiant-heat conversion component 17. The wire of the wire mesh forming the porous solid radiant-heat conversion component 17 has a small diameter, and therefore a temperature of the wire mesh is quickly increased up to several hundred degrees to allow the porous solid radiant-heat conversion component 17 to emit radian heat energy in all directions as electromagnetic waves. A part of the radian heat energy acts to heat an upstream region, i.e., the flame front, to drastically accelerate the combustion. In this connection, it was proven that a position of the porous solid radiant-heat conversion component 17 is one of key factors, i.e., the heat radiation effect is deteriorated if the position is excessively apart from the flame front, and no flame can be formed during the ignition operation if the position is excessively close to the flame front. In view of this knowledge, it is preferable to arrange the porous solid radiant-heat conversion component 17 at a position apart from the flat surface of the combustion chamber by 5 to 15 mm in a downstream direction. In this manner, heat energy of the exhaust gas can be recirculated to the flame in the form of radian heat energy. The mixture is strongly heated, and therefore a combustion speed will be gradually increased. It is necessary to continue this state for a while. Thus time period corresponds to a heating time period required for increasing the respective temperatures of the porous solid radiant-heat conversion component 17 and the burner 11 to assure a combustion function. Then, the lever 5 is moved to increase the opening degree of the throttle valve 4 so as to introduce a larger volume of air. Thus, the mixture has an increased flow volume, and an increased flow rate in the combustion chamber 12. In the conventional combustion chamber, the flame front is blown off during this process. Differently, the mixture heated through the preheating and the heat recirculation has a combustion speed withstanding the above increased flow rate to allow the flame front to be stably maintained in the combustion chamber without flame-out. Further, the mixture has a mixture ratio leaner (excess in air) than the theoretical mixture ratio. Thus, a complete combustion is performed to generate larger heat energy, and the larger heat energy will be used for the preheating and the heat recirculation so as to allow the flame stability to be increasingly enhanced. As above, the combustion speed can be increased to burn a larger volume of fuel gas in the small combustion chamber. Thus, this burner can be reduced in size as compared with a conventional catalytic burner having the same output, to have an optimal size as a burner for a portable heat transfer apparatus.
Heat generated in the combustion chamber 12 is collected by the heat collection casing 10 surrounding the burner 11, and transferred to the heat-driven pump P and then to an external load.
The wire mesh for use as the porous solid radiant-heat conversion component 17 may be a single layer to obtain an intended effect. While a plurality of wire meshes may be effectively layered, the multilayer wire mesh inevitably causes increase in resistance against an exhaust gas flow. Thus, in the atmospheric burner with relative low air intake performance, the use of multilayer wire mesh should be determined with an air intake volume in mind For the same reason, as to the density of meshes, #80 to #40 wire meshes may be generally used. Further, the wire mesh may be coated with ceramic material to prevent burnout. This is also advantageous to the wire mesh because ceramics has excellent heat radiation performance. Furthermore, instead of the wire mesh, foamed ceramics may be used.
While the burner 11 for use in this embodiment is preferably formed of a heat-resistant ceramics excellent in heat radiation performance, a heat-resistant metal, such as stainless steel, may also be adequately used without problems.
This double wind protection plates and the protruded surface are also applied to the exhaust air outlet. This effect is significant, and a burner for a portable heat transfer apparatus intended to stably use outdoors without flame-out even in wind with a wind speed of about 20 m/sec.
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Number | Date | Country | |
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Parent | PCT/JP2005/006060 | Mar 2005 | US |
Child | 11528736 | US |