JP2001141211A - Catalytic combustor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalytic combustor in which a lean mixture gas is prevented from passing through a low temperature part, generated at the inner and outer circumferential parts of a catalyst, to generate HC (hydrocarbon) rich offensive combustion gas. SOLUTION: A catalyst 7 is wound tightly around the outer circumference standing on the upper end of a pot 1 for gasifying fuel oil provided with a gasification heater 2 and a heat transfer tube 6 is covered with a bottomed guide tube 9 from the outer circumference of the catalyst 7 thus forming a reverse U-shaped mixing path 10 extending from the gasification pot 1 toward the catalyst 7. In such a catalytic combustor, inlet of the catalyst 7 is covered, in the vicinity of the inner circumference thereof, with an inner circumferential side baffle plate 14 and, in the vicinity of the outer circumference thereof, with an outer circumferential side baffle plate. Consequently, lean mixture gas does not flow into a low temperature part generated at the inner and outer circumferential parts of the catalyst 7 and generation of offensive combustion gas is prevented by suppressing generation of HC(hydrocarbon).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic combustion device constituting a combustion portion of a heater such as a domestic water heater or a fan heater.

[0002]

2. Description of the Related Art Conventionally, in this type of fuel, as disclosed in, for example, Japanese Patent No. 2646526, fuel oil is vaporized by a vaporizer provided with a vaporizing heater, and the vaporized gas and the combustion air are vaporized. The present invention provides a combustion device that generates combustion gas with a low NOx value by catalytically combusting a premixed gas in a catalyst body.

[0003] In the case of Japanese Patent No. 2646526, two heaters are required for preheating the carburetor and for heating the catalyst to the activation temperature, which is uneconomical. In the case where the mixture path through which the mixture flows is short, particularly in the case where a lean mixture having an excessive amount of air is catalytically combusted, if the mixture path is short, the lean mixture is not sufficiently mixed, and the dark and light portions are partially formed. It causes problems such as burning out of the catalyst body and incomplete combustion, and a new problem that simply increasing the length of the mixing path causes the entire appliance to become large and unsuitable for household appliances. Was.

Accordingly, the applicant of the present application has made a catalyst body having a honeycomb structure and having a large number of air passages formed in a vertical direction wound around an outer periphery of a heat transfer cylinder erected at an upper end of a vaporization pot provided with a vaporization heater so that the catalyst body is brought into close contact therewith. In addition, by covering the heat transfer cylinder from above with a bottomed cylindrical guide cylinder so that its inner circumference is in contact with the outer circumference of the catalyst body, an inverted U-shaped cross section is provided between the vaporization pot and the catalyst body. Of the present invention was previously filed as Japanese Patent Application No. 11-283631.

[0005]

In the prior application, the outer periphery of the heat transfer cylinder is in contact with the inner periphery of the catalyst body, and the inner periphery of the guide cylinder is in contact with the outer periphery of the catalyst body. The heat of the medium escapes to the heat transfer tube and guide tube,
As a result, the temperature of the central portion of the catalyst body during normal combustion is about 80
While the temperature is 0 ° C., the temperature of the catalyst body in the portion in contact with the inner circumference of the guide cylinder and the outer circumference of the catalyst body drops to about 500 ° C., and especially in the inner circumference of the catalyst body in contact with the outer circumference of the heat transfer cylinder, The range in which the temperature is reduced is larger than that in the outer peripheral portion of the catalyst body that is in contact with the inner circumference of the guide cylinder.

[0006] Therefore, the lean mixture that passes through the ventilation passage of the catalyst body in the portion where the temperature has become low is not sufficiently catalyzed while passing through the ventilation passage of the catalyst body due to the low temperature of the catalyst body. As a result, the amount of combustion gas that has been normally catalyzed and burned decreases, and HC
(Hydrocarbon) is present in a large amount, and there is a problem that combustion gas having a strong odor is generated.

[0007]

The present invention focuses on this point and solves the above-mentioned drawbacks. In particular, the present invention comprises a vaporizing heater for vaporizing supplied fuel oil and premixing the vaporized gas with combustion air. A vaporizer pot that forms a lean mixture with an excess amount of air, a catalyst body provided on the outer periphery of a heat transfer cylinder erected at the upper end of the vaporizer pot, and performs catalytic combustion by flowing the lean mixture. A guide cylinder that covers the upper part of the heating cylinder, and wherein an inner peripheral portion of a lean mixed gas inlet of the catalyst body is provided in a catalytic combustion device in which a mixing path having an inverted U-shaped cross section is formed between the vaporization pot and the catalyst body. And an outer peripheral baffle that covers the outer peripheral portion of the lean mixture inlet of the catalyst body.

[0008] Further, if a recessed portion which does not contact the catalyst body is formed on the outer periphery of the heat transfer cylinder, heat near the periphery of the catalyst body is not transmitted to the heat transfer cylinder, so that a low-temperature portion generated near the periphery of the catalyst body is reduced. Thus, generation of HC (hydrocarbon) due to insufficient catalytic combustion can be prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When the vaporization heater 2 is energized to heat the vaporization pot 1 to a predetermined vaporizable temperature, this heat is transmitted to the catalyst 7 via the heat transfer cylinder 6 connected to the vaporization pot 1. Then, when the temperature sensor 13 detects the temperature of the vaporization pot 1 when the catalyst 7 reaches the activation temperature, the fuel is sprayed into the vaporization pot 1 and the combustion air of about three times the theoretical air amount is supplied. As a result, a lean air-fuel mixture with an excessive amount of air is formed.

[0010] Further, the formed lean air-fuel mixture is once converged by the upper collecting plate 11 and then satisfactorily mixed by flowing through the mixing passage 10 having an inverted U-shaped cross section. Flowing towards.

At this time, the catalyst body 7 has a honeycomb structure in which a number of ventilation paths are formed, and does not flow from one ventilation path to another ventilation path halfway between the entrance and the exit of the catalyst body 7. Even if a low temperature portion is generated in the inner peripheral portion and the outer peripheral portion of the catalyst body 7, the inner peripheral side baffle 14 is provided on the inner peripheral side of the inlet of the catalyst body 7, and the outer peripheral baffle is provided on the outer peripheral side. Since the catalyst 16 is provided, the catalyst 7 having a low temperature is provided.
The lean air-fuel mixture does not flow into the inner peripheral portion and the outer peripheral portion of the catalyst body, but passes through the low temperature portion of the catalyst body 7, so that catalytic combustion becomes insufficient and a large amount of HC (hydrocarbon) is present. This is to prevent the generation of combustion gas having a high intensity.

Even if a part of the lean air-fuel mixture flows into the inner peripheral part and the outer peripheral part of the catalyst body 7 having a low temperature, the inner peripheral baffle plate 14 and the outer peripheral baffle plate 16 become resistance and become lean. The inflow speed of the air-fuel mixture becomes slower, and the time for passing through the catalyst body 7 becomes longer than that of the lean air-fuel mixture passing through the center part of the catalyst body 7, thereby completing the passage of the catalyst body 7 having a lower temperature even in the ventilation path. This prevents the presence of a large amount of HC (hydrocarbon) due to sufficient catalytic combustion in between, that is, the generation of a highly odorous combustion gas.

Further, since the recess 8 is formed on the outer periphery of the heat transfer cylinder 6 which is in close contact with the inner periphery of the catalyst body 7, the heat of the catalyst body 7 escapes from the inner periphery of the catalyst body 7 to the outer periphery of the heat transfer cylinder 6. The range of the low-temperature portion generated in the inner peripheral portion of the catalyst body 7 is reduced, thereby increasing the number of air passages for performing normal catalytic combustion and passing through the low-temperature portion, whereby the catalytic combustion becomes insufficient. Therefore, it is possible to prevent the presence of a large amount of HC (hydrocarbon), that is, the generation of combustion gas having a strong odor.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a catalytic combustion apparatus according to the present invention will be described with reference to an embodiment shown in the drawings. Reference numeral 1 denotes an aluminum die-cast evaporating pot in which an evaporating heater 2 is cast at an upper portion, and a jet port 4 for blowing combustion air from a combustion fan (not shown) through an air passage 3 communicates with one side. , The spout 4
Is provided with a nozzle 5 which communicates with an electromagnetic pump (not shown) and sprays fuel oil. The nozzle 5 premixes the vaporized gas with about three times the theoretical air amount of combustion air to form a lean mixture.

Numeral 6 denotes a hollow cylindrical heat transfer cylinder which is provided upright at the upper end of the vaporizing pot 1 and is made of aluminum and is integrally formed with the vaporizing pot 1 and has a plate-shaped palladium-based catalyst body 7 having a honeycomb structure on the outer periphery. The heat of the vaporization heater 2 for preheating the vaporization pot 1 is transmitted to the catalyst 7 and heated to 250 ° C. or more of the activation temperature before the start of combustion.

Reference numeral 8 denotes a recess provided at the center of the outer periphery of the heat transfer cylinder 6, which forms a portion where the inner peripheral surface of the catalyst body 7 does not contact the outer peripheral surface of the heat transfer cylinder 6, and the heat of the catalyst body 7 It is intended to reduce escape to the cylinder 6 and reduce a low-temperature portion generated in the inner peripheral portion of the catalyst body 7.

Numeral 9 is a bottomed cylindrical guide tube, which covers the upper part of the heat transfer tube 6 so as to cover the bottom thereof, whereby the guide tube 9
The inner peripheral portion is in close contact with the outer peripheral portion of the catalyst body 7 which is in close contact with the heat transfer cylinder 6, and the lean mixture from the vaporization pot 1 passes through the heat transfer cylinder 6 and flows to the outer peripheral catalyst body 7. Mixing path 10
By forming the mixing passage 10 having an inverted U-shaped cross section, it is possible to form the mixing passage 10 which is compact and relatively long. In this case, good catalytic combustion is carried out with a uniform mixture without air, and burnout and incomplete combustion of the catalyst body 7 can be prevented.

Reference numeral 11 denotes a collecting plate provided at a boundary portion between the vaporizing pot 1 and the mixing passage 10, which has a circulation hole 12 formed only in the center, and once concentrates the lean mixture just formed in the vaporizing pot 1. After passing through the circulation hole 12, the mixing path 10
To promote mixing.

Reference numeral 13 denotes a temperature sensor comprising a thermistor or the like for detecting the temperature of the vaporization pot 1, which detects the activation temperature of the catalyst 7 above the vaporization temperature of the vaporization pot 1 as a preset vaporization pot 1 temperature. It controls combustion start and energization of the vaporization heater 2.

Reference numeral 14 denotes a hollow disk-shaped inner peripheral baffle. The outer diameter of the inner peripheral baffle 14 is larger than the outer diameter of the heat transfer cylinder 6, and the center of the inner peripheral baffle 14 is A center hole 15 having the same inner diameter as the inner diameter of the hollow portion of the heat transfer cylinder 6 is formed, and the center hole 15 of the inner peripheral side baffle plate 14 is aligned with the hollow portion of the heat transfer tube 6. In the case of the present embodiment, since the outer diameter of the inner peripheral side baffle plate 14 is 6 mm larger than the outer diameter of the heat transfer cylinder 6, it protrudes by about 3 mm from the outer circumference of the heat transfer cylinder 6. It covers the vicinity of the inner circumference on the entrance side.

Reference numeral 16 denotes an outer peripheral baffle having a hollow disk shape and an L-shaped cross section. The outer diameter of the outer peripheral baffle 16 is substantially equal to the inner diameter of the guide cylinder 9 and the center of a horizontal plane 17 having an L-shaped cross section. An inflow hole 18 having a diameter smaller than the outer diameter of the catalyst body 7 closely contacted so as to be wound around the outer periphery of the heat transfer cylinder 6 is formed, and the guide cylinder 9 is attached to the heat transfer cylinder 6 with the catalyst body 7 closely attached. At this time, the vertical surface side 19 having an L-shaped cross section is attached to the inner periphery of the guide cylinder 9 by welding or the like so that the outer peripheral portion of the horizontal plane side 17 of the outer peripheral baffle plate 16 covers the vicinity of the outer periphery of the catalyst body 7. In the case of the present embodiment, the inner diameter of the inflow hole 18 is 6 times larger than the outer diameter of the catalyst body 7.
The outer peripheral portion of the outer peripheral side baffle 16 on the horizontal surface 17 covers the vicinity of the outer periphery of the catalyst body 7 on the inlet side.

As described above, the inside of the catalyst body 7 inlet, that is, the inner peripheral portion of the upper end of the catalyst body 7 abuts against the bottom surface of the inner circumferential baffle plate 14 provided at the upper end of the heat transfer cylinder 6, and the outside of the catalyst body 7 inlet That is, since the outer peripheral portion of the upper end of the catalyst body 7 is in contact with the bottom surface of the outer peripheral baffle plate 16 provided on the inner circumference of the guide cylinder 9, the catalyst body 7 moves upward with respect to the heat transfer cylinder 6. Without
The displacement of the catalyst body 7 does not hinder the mixing path 10.

Reference numeral 20 denotes a heat back portion, which is formed in a flange shape above the vaporization heater 2 of the vaporization pot 1 and in which the combustion gas sufficiently catalyzed in the catalyst body 7 passes through the catalyst body 7 and exits from the outlet. When blown out, it collides with the heat back portion 20 and blows out around the space between the heat back portion 20 and the outlet of the catalyst body 7 in a form guided by the heat back portion 20. As a result, a part of the heat of the combustion gas is transmitted to the heat back unit 20, and the transmitted heat maintains the temperatures in the vaporization pot 1 and the heat transfer cylinder 6 at the optimum temperature.

Reference numeral 21 denotes a catalyst support.
1 is in contact with the upper surface of the heat back section 20 and one side thereof is in contact with the outer peripheral surface of the heat transfer cylinder 6.
A plurality of the catalyst bodies 7 are erected radially on the upper surface, and the exit side of the catalyst body 7 contacts the upper part of the catalyst body support portion 21 to support the catalyst body 7 so that the catalyst body 7 does not move further downward. The distance between the catalyst body 7 and the upper surface of the heat back part 20 can be kept constant at an optimum distance, and the combustion gas that has passed through the catalyst body 7 can be smoothly blown out. The plate 14 and the outer peripheral side baffle plate 16 abut,
This prevents the upper and lower positions of the catalyst 7 from being displaced by the catalyst support 21 being in contact with the lower end of the catalyst 7.

Further, since the combustion gas blown from the outlet through the catalyst body 7 itself passes through the inside of the catalyst body 7, there is a heat back effect of transferring the heat of the combustion gas to the heat back section 20 and the heat transfer cylinder 6. In the case where the heat back section 20 and the catalyst support section 21 are not provided, the temperature of the wall surface in the vaporization pot 1 is set to a value such that the kerosene sprayed from the nozzle 5 vaporizes well.
In order to maintain the optimum temperature of about 0 ° C., the vaporization heater 2 must always be energized even during normal combustion. However, when the heat back unit 20 and the catalyst support unit 21 are provided, the normal combustion is performed. In some cases, heat is returned from the heat source, and the temperature in the vaporization pot 1 and the temperature in the heat transfer cylinder 6 can be maintained at an optimum temperature. Therefore, there is no need to energize the vaporization heater 2 and power consumption by the heater can be suppressed. Things.

Reference numeral 22 denotes a rod-shaped thermocouple, one end of which is fixed in the catalyst body 7 by welding or the like, and the other end of which passes through a thermocouple hole 23 provided in the heat back portion 20.
0 projecting to the lower surface, and the other end projecting to this lower surface is connected to the signal line 24.
To detect the temperature inside the catalyst body 7 by detecting the thermoelectromotive force of the thermocouple 22.

Next, the operation of this embodiment will be described. Now, the power is supplied to the vaporization heater 2 to heat the vaporization pot 1 to reach the vaporizable temperature, and the heat of the vaporization pot 1 is applied to the catalyst 7 via the heat transfer tube 6, so that the catalyst 7
When the temperature reaches the activation temperature of at least
Is detected as the temperature of the vaporization pot 1, and supply of fuel oil and combustion air is started several minutes after the start of energization.

In the vaporization pot 1, the vaporized gas of fuel oil sprayed and vaporized from the nozzle 5 and the combustion air supplied from the injection port 4 and having a volume approximately three times the theoretical air amount are mixed to form a lean air-fuel mixture. Then, the mixture is supplied to the mixing passage 10 through the flow hole 12 of the collecting plate 11, and at this time, the lean air-fuel mixture is
Is focused once to pass through and diffused after passing,
Mixing is promoted.

Further, the lean air-fuel mixture after passing through the collecting plate 11 is guided by the bottomed portion of the guide cylinder 9 and flows to the catalyst 7 inlet provided on the outer periphery of the heat transfer cylinder 6 to reach the activation temperature. The catalyst is burned while passing the catalyst 7 from the upper inlet to the lower outlet through an air passage in the catalyst 7 and is blown out as a combustion gas from the outlet of the catalyst 7.

Since this combustion gas is obtained by catalytically burning a lean mixture, its combustion temperature is low, and as a result, NO
The x value is suppressed, and the NOx value in the combustion gas is almost zero, resulting in clean combustion gas.

By the way, the inner peripheral side of the catalyst body 7, that is, the portion which is in close contact with the outer periphery of the heat transfer cylinder 6 always transmits the heat of the catalyst body 7 to the heat transfer cylinder 6.
The temperature is about 500 ° C. lower than that of the central part of which is about 800 ° C., and when a lean air-fuel mixture flows in and passes through it, the catalyst is not sufficiently combusted while passing because of the low temperature, and the catalyst body A large amount of HC (hydrocarbon) is present in the combustion gas blown out from 7, and a combustion gas having a strong odor is blown out.

However, in the present invention, the inner peripheral side baffle 14 provided at the upper end of the heat transfer cylinder 6 covers the entrance near the inner periphery where the temperature of the catalyst body 7 becomes low, and prevents the lean mixture from flowing there. Since the lean mixture passes near the inner circumference where the temperature of the catalyst body 7 becomes low, a large amount of HC (hydrocarbon) is present, thereby preventing generation of a combustion gas having a strong odor. is there.

Even if the lean air-fuel mixture flows near the inner circumference where the temperature of the catalyst body 7 becomes low, the inner-circumference baffle plate 14 acts as a resistance to reduce the velocity of the lean air-fuel mixture flowing near the inner circumference. It is dropped and stays in the catalyst body 7 for a longer time than the lean mixture passing through the center portion of the catalyst body 7. Therefore, even if the temperature of the catalyst body 7 is low, the catalytic combustion proceeds sufficiently because the passage time is long and the HC combustion proceeds. (Hydrogen) is a combustion gas that is low in odor and free of odor.

The outer peripheral side of the catalyst body 7, that is, the guide cylinder 9
Since the heat of the catalyst body 7 is also transmitted to the guide cylinder 9 at the portion that is in close contact with the inner periphery, the heat is radiated to the air around the guide cylinder 9. Is low.

However, in the present invention, the outer peripheral baffle 16 attached inside the guide cylinder 9 covers the entrance near the outer periphery where the temperature of the catalyst body 7 becomes low, and prevents the lean mixture from flowing there. Therefore, the lean mixture passes near the outer periphery where the temperature of the catalyst body 7 becomes low, so that a large amount of HC (hydrocarbon) is present, thereby preventing generation of a combustion gas having a strong odor.

Even if the lean mixture flows near the outer periphery where the temperature of the catalyst body 7 becomes low, the speed of the lean mixture flowing near the outer periphery is reduced by the resistance of the outer peripheral baffle plate 16, Since the mixture stays in the catalyst body 7 for a longer time than the lean air-fuel mixture passing through the center portion of the catalyst body 7, even if the temperature of the catalyst body 7 is low, the passage time is long, so that the catalytic combustion proceeds sufficiently and HC (hydrocarbon) ) With low odor and no combustion gas.

Further, since the hollow portion 8 is provided on the outer peripheral portion of the heat transfer cylinder 6 which is in close contact with the inner periphery of the catalyst body 7, the area where the inner periphery of the catalyst body 7 and the outer periphery of the heat transfer cylinder 6 are in close contact is reduced. Heat transmitted from the catalyst body 7 to the heat transfer cylinder 6 is reduced.

As a result, compared with the case where there is no undercut 8,
The low temperature portion generated near the inner circumference of the catalyst body 7 is reduced, and the outer diameter of the inner circumference side baffle plate 14 is reduced accordingly, so that the inner circumference portion of the catalyst body 7 covered by the inner circumference side baffle plate 14 is reduced. And the amount of lean air-fuel mixture passing through the air passage of the catalyst body 7 at a normal temperature can be increased to increase the amount of combustion, and can also be a odorless combustion gas containing less HC (hydrocarbon). It is.

Further, since the heat of the catalyst 7 is prevented from being transmitted to the heat transfer cylinder 6 and the temperature of the catalyst 7 is reduced, the power supply to the vaporization heater 2 is not required, and the power consumption by the vaporization heater 2 is reduced. Energy savings.

Further, the combustion gas blown out from the outlet of the catalyst body 7 collides with the flange-shaped heat back portion 20 and changes its direction.
The air blows out around the catalytic combustor from between the catalyst body 7 and the heat back section 20.
0 and the catalyst support 21 are exposed to the combustion gas and become high in temperature, which heats back to maintain the temperatures of the vaporization pot 1 and the heat transfer cylinder 6 at appropriate temperatures. Is unnecessary, and the power consumption by the vaporization heater 2 can be reduced to save energy.

In this embodiment, the vaporization pot 1 and the heat transfer cylinder 6
And are integrally molded by aluminum die-casting or the like, but are not limited to this.
It may be one integrally formed with an adhesive or the like.

[0042]

As described above, according to the present invention, the inner peripheral portion of the entrance of the catalyst 7 which is tightly wound around the heat transfer cylinder 6 is covered with the inner peripheral side baffle plate 14, and the entrance of the entrance of the catalyst 7 is formed. By covering the outer peripheral portion with the outer peripheral side baffle plate 16, it is possible to prevent the lean mixture from flowing into the inner peripheral portion and the outer peripheral portion, which are lower in temperature than the central portion of the catalyst body 7, and to pass through the low temperature portion. The catalyst combustion becomes insufficient and the amount of HC (hydrocarbon) increases, that is, the generation of exhaust gas having a strong odor can be suppressed.

Further, since the recess 8 is provided at the outer peripheral portion of the heat transfer cylinder 6 which is in close contact with the inner periphery of the catalyst body 7 on the outer periphery of the heat transfer cylinder 6, the inner periphery of the catalyst body 7 and the outer periphery of the heat transfer cylinder 6 are in close contact. The area of the catalyst body 7 is reduced, and the heat of the catalyst body 7 is less likely to be transmitted to the heat transfer cylinder 6, so that the lower temperature portion generated on the inner periphery of the catalyst body 7 is reduced, and passes through the lower temperature portion. As a result, catalytic combustion becomes insufficient and HC (hydrocarbon)
Increases, that is, generation of exhaust gas having a strong smell can be suppressed.

Further, since the portion of the catalyst body 7 where the temperature is low can be reduced, the inner peripheral side baffle 14 can be reduced.
The combustion amount can be increased by increasing the amount of the lean air-fuel mixture passing through the portion of the catalyst body 7 at an appropriate temperature.

[Brief description of the drawings]

FIG. 1 is an external view of a catalytic combustion device to which an embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view of a catalytic combustion device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vaporization pot 2 Vaporization heater 6 Heat transfer cylinder 7 Catalyst 9 Guide cylinder 10 Mixing path 14 Inner circumference baffle 16 Outer circumference baffle

Claims (2)

[Claims] 1. A vaporization pot which is provided with a vaporization heater, vaporizes supplied fuel oil, and pre-mixes the vaporized gas with combustion air to form a lean mixture having an excess amount of air. A catalyst body provided on the outer periphery of the heat transfer cylinder and catalyzed by the flow of a lean air-fuel mixture, and a guide cylinder covering the outer periphery of the catalyst body from above the outer circumference of the catalyst body. In a catalytic combustion device having a mixture path formed in the shape of a circle, an inner peripheral side baffle plate for covering an inner peripheral portion of the lean mixture inlet of the catalyst body, and an outer peripheral side for covering an outer peripheral portion of the lean mixture inlet of the catalyst body A catalytic combustion device comprising a baffle plate. 2. The catalytic combustion device according to claim 1, wherein a hollow portion not in contact with the catalyst body is formed on an outer periphery of the heat transfer cylinder.