Liquid heaters and vaporizers – Heat transmitter
Utility Patent
1999-04-16
2001-01-02
Ferensic, Denise L. (Department: 3749)
Liquid heaters and vaporizers
Heat transmitter
C122S367300, C122S00400R
Utility Patent
active
06167846
ABSTRACT:
The disclosures of Japanese Patent Applications No. HEI 10-169339 filed on Jun. 1, 1998, No. HEI 10-152134 filed on May 14, 1998 and No. HEI 10-152133 filed on May 14, 1998, including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalytic combustion heater that causes an oxidation reaction of fuel gas using a catalyst and heats heat-receiving fluid by means of heat generated in the oxidation reaction.
2. Description of the Related Art
In a known catalytic combustion heater, combustible gas (fuel gas) is burnt using an oxidation catalyst, and a heat-receiving fluid is heated by means of the heat generated. It is expected that such a catalytic combustion heater will be applied to a variety of uses, for example, in houses, automobiles and the like. A catalytic combustion heater of this type is usually provided with a catalyst-based heat exchanger wherein tubes in which heat-receiving fluid flows are disposed in a fuel gas passage and multiple catalyst-carrying fins are integrally bonded to outer peripheries of the heat-receiving fluid passages. Carried on an outer surface of each of the catalyst-carrying fins is an oxidation catalyst such as platinum, palladium or the like. Fuel gas is brought into contact with these fins so as to cause an oxidation reaction.
FIG. 9
shows an example of such a catalyst combustion heater. Referring to
FIG. 9
, a catalyst-based heat exchanger is disposed in a container
100
. The catalyst-based heat exchanger is composed of a plurality of tubes
102
hung across left and right lateral walls and multiple fins
104
bonded to outer peripheries of the tubes
102
. An oxidation catalyst is carried on a surface of each of the fins
104
. The tubes
102
are connected with one another at their left and right end portions, and form a continuous heat-receiving fluid passage therein. Upper and lower end openings of the heat-receiving fluid passage serve as inlet and outlet ports for the heat-receiving fluid respectively. A heat-receiving fluid, which is liquid, flows through the passage formed in the tubes
102
in a top-to-bottom direction in the drawing. Meanwhile, the heat-receiving fluid is heated, reaches its boiling point and becomes gaseous.
Provided at lower and upper end portions of the container
100
are a fuel gas feed port
106
and a fuel gas exhaust port
108
respectively. Fuel gas flows among the fins provided on the outer peripheries of the tubes
102
in a bottom-to-top direction in the drawing. Upon contact with the surfaces of the fins
104
on which the oxidation catalyst is carried, the fuel gas burns due to a catalytic reaction. The heat generated by catalytic combustion is transmitted to the heat-receiving fluid flowing in the tubes
102
through the walls thereof. After catalytic combustion, exhaust gas is discharged out of the container
100
through the exhaust port
108
. A current plate
110
having multiple perforations is disposed above the feed port
106
and across the fuel gas passage. Disposed above the current plate
110
is a heater
112
for heating the catalyst to a temperature equal to or higher than its activation temperature.
In the aforementioned catalytic combustion heater, while burning, fuel gas flows in the container
100
in the bottom-to-top direction in the drawing. On the other hand, while being heated, the heat-receiving fluid in its liquid state flows in the container
100
contrary to the flow of fuel gas, that is, in the top-to-bottom direction in the drawing. Thus, in the case where fuel gas and heat-receiving fluid flow in opposite directions, on the downstream side of the fuel gas passage, the heat-receiving fluid is at a low temperature in the vicinity of the fuel gas exhaust port
108
. Therefore, the heat of combustion exhaust gas is transmitted to the heat-receiving fluid of a lower temperature with a view to utilizing the generated heat more effectively.
However, on the upstream side of the fuel gas passage, fuel gas of the highest concentration keeps flowing into the tubes
102
in the vicinity of the fuel gas feed port
106
, that is, the tubes
102
through which the heat-receiving fluid in its gaseous state flows. When the heat-receiving fluid is gaseous, it exhibits its highest temperature and a low heat transfer rate. In other words, a large amount of heat is generated in a section with the highest heat transfer resistance. Hence, the fins
104
carrying the oxidation catalyst or the tubes
102
through which heat-receiving fluid flows tend to be overheated, which may adversely affect the catalytic combustion heater.
Further, in order to enhance heat exchange efficiency, heat exchange between fuel gas and the fins
104
or the tubes
102
needs to be avoided to the maximum possible extent. However, on the upstream side of the fuel gas passage, the heat transfer resistance to the heat-receiving fluid is high. Thus, the heat generated is transmitted to fuel gas and there arises a tendency for the combustion exhaust gas to reach a high temperature. In general, on the grounds that gas and metal exhibit a low heat transfer rate and that catalytic combustion occurs at a lower temperature than flame combustion, it is difficult to recover the heat that has been transmitted to the fuel gas. An attempt to enhance heat exchange efficiency causes an inconvenience of enlarging the size of the catalytic combustion heater.
SUMMARY OF THE INVENTION
In view of the above-described background, the present invention has been conceived. It is an object of the present invention to provide a catalytic combustion heater that suitably adjusts a heat release value resulting from a catalytic reaction, prevents the fins and tubes (heat-receiving fluid passage) from being overheated, and achieves great security as well as high heat exchange efficiency.
In order to achieve the aforementioned object, according to a first aspect of the present invention, there is provided a catalytic combustion heater constructed as follows. That is, the catalytic combustion heater includes a container forming a fuel gas passage, heat-receiving fluid passages in which heat-receiving fluid flows, a catalyst-based heat exchanger and heat amount changing means. The heat-receiving fluid passages are disposed in the fuel gas passage. The catalyst-based heat exchanger is designed to heat a heat-receiving fluid by means of reaction heat of fuel gas. The catalyst-based heat exchanger is disposed in the fuel gas passage and has catalytic layers that are provided on outer peripheries of the heat-receiving fluid passages and cause an exothermic reaction upon contact with fuel gas. The heat amount changing means is designed to change an amount of heat to be supplied to heat-receiving fluid flowing in respective portions of the heat-receiving fluid passages, in accordance with a state of the heat-receiving fluid.
The aforementioned heat amount changing means may have fuel distribution means for separately supplying fuel gas to the respective portions of the heat-receiving fluid passages in accordance with a state of the heat-receiving fluid flowing inside.
The present invention focuses attention on the facts that most of the heat necessary for liquid heat-receiving fluid to be heated to a high temperature and converted into its gaseous state is evaporative latent heat and that when the heat-receiving fluid is at its boiling point, the heat transfer rate from the inner wall surface of the heat-receiving fluid passage to the heat-receiving fluid is much higher than in the case where gasified heat-receiving fluid is heated. Therefore, the aforementioned fuel distribution means is used to separately supply fuel gas in accordance with a state of the heat-receiving fluid flowing inside. Consequently, it is possible to achieve effective heat transmission without enlarging the size of the heat exchanger.
In the first aspect of the present invention, the fuel distribution means may be designed to separately supply f
Hirose Shoji
Ogino Shigeru
Yamada Tomoji
Ferensic Denise L.
Lu Jiping
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyota Jidosha & Kabushiki Kaisha
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