KR20080102105A

KR20080102105A - Electrical heater

Info

Publication number: KR20080102105A
Application number: KR1020070048498A
Authority: KR
Inventors: 최중일
Original assignee: 최중일
Priority date: 2007-05-18
Filing date: 2007-05-18
Publication date: 2008-11-24

Abstract

An electric heater is provided to prevent boiling due to partial temperature rise of heat transfer medium by increasing the thickness of metal covering the electrical heating element and the length which contacts a heat transfer medium. An electric heater for heating a heat transfer medium in a hot water supply apparatus comprises a heater(210) in which a heater cover is covered on a hot water tank filled with a heat transfer medium; a cover(226) which is made of metal and covered outside the heater with a gap; a water inlet(222) to which the heat transfer medium returns after delivering heat by the pressure of a pump; a cavity(230) which the heat transfer medium flowing in the water inlet passes through; and a water outlet(224) through which the heat transfer medium heated by the heater surface while moving through the gap between the heater and the cover is discharged.

Description

Electric Heater {Electrical Heater}

1 is a schematic diagram illustrating a configuration of a typical hot water circulation mat,

Figure 2 is an exploded perspective view showing a hot water supply for hot water circulation mat according to the prior art,

3 is a cross-sectional view showing the internal configuration of a heater that is a main part of a hot water supply apparatus according to the prior art,

4 is a sectional view of a heater of the electric heater according to the present invention,

5 is a partial cutaway perspective view of an electric heater according to the present invention,

6 is a partially cutaway perspective view of an electric heater according to another embodiment of the present invention,

7 is a partially cutaway perspective view of an electric heater according to another embodiment of the present invention,

8 is a partially cutaway perspective view of an electric heater in another embodiment according to the present invention.

10: circulation hot water pipe 11: heat dissipation hot water pipe

101: Case 103: Supply Tank

107: operation panel 120: heater

121: hot water tank 129: bulkhead

130: pump 131: heat exchanger

200: electric heater 210: heater

211: circular groove 212: heater cover

213: heat radiation fin 214: heating wire

216 terminal 218 filling material

220: Spiral Euro 222: Inlet

224: outlet 226: cover

228: spiral bar 230: space

300: electric heater 328: spiral pin

440: pin

The present invention relates to an electric heater, and more particularly, to an electric heater for heating hot water to a hot water circulating mat and a hot water supply device for supplying hot water to a small heating device, the heat of the heater is quickly and uniformly transferred inside the heater. It is an object of the present invention to provide an electric heater that is easy to apply to the hot water circulation mat that can improve the usability and convenience of the hot water circulation mat as an embodiment.

The configuration of the present invention for achieving the above object is to form a spiral flow path on the outside of the electric heating element having a heating wire therein to efficiently transfer heat to the heat transfer medium, so that the heat transfer is not made in part By providing a configuration to increase the temperature at which the heat transfer medium boils.

Hot water circulation mats are widely used as simple heating supplies or as therapeutic and health care supplies. The heating method using hot water is the same as the purpose of heating using an electric blanket, but a commonly used electric blanket is configured to heat an electric heater wire inside a floor plate and apply electricity to the heater wire. However, since the electric field plate of this configuration emits a lot of electromagnetic waves, incidental efforts have been made to block the electromagnetic waves by inserting a metal plate inside to block the electromagnetic waves.

However, since it is not possible to fundamentally prevent electromagnetic waves shielded arbitrarily, there is a need for a configuration that does not fundamentally generate electromagnetic waves.

What was adopted as a configuration that does not generate electromagnetic waves is that the hot water pipe is inserted into the mat and the hot water is passed through the inside of the pipe to transfer heat.

As the hot water circulation mat used in the related art is schematically illustrated in FIG. 1, the heat radiation hot water through the mat 13 and the circulation hot water pipe 10 in which the heat radiation hot water pipe 11 is piped in a predetermined shape. It consists of a hot water supply device 15 connected to the pipe 11, the hot water supply device 15 is a heater 18 for heating the water introduced through the circulation hot water pipe 10 and the heater 18 Consists of a pump 17 installed at the front end or the rear end, the hot water heated by the heater 18 is supplied to the heat radiating hot water pipe 11 to heat the mat 13 to a predetermined temperature according to the user's choice. .

The heater 18 has a structure in which a heater is installed inside the hot water tank so as to receive and heat the water of the heat radiating hot water pipe 11 introduced through the circulation hot water pipe 10 and resupply it if necessary. Since the conventional heater 18 has a simple structure in which the water heated by the heater is mixed with each other by natural convection, and the heat transfer is not effective, the inflowed water is changed according to the inlet and outlet of the heater or the position of the heater. Some are heated to a high temperature by receiving a lot of heat from the heater, and the other part is supplied to the heat radiating hot water pipe 11 of the mat 13 in a relatively insufficiently heated state. Accordingly, the temperature of the hot water moved through the heat radiating hot water pipe (11) is not only constant, but because the hot water is heated in part from the heater, the heat transfer medium in contact with the heater surface of the high temperature cannot prevent boiling. .

As shown in Figure 2, the hot water supply device of the prior art is a case consisting of a lower case (101b) of the plate shape and the upper case (101a) coupled to the upper portion of the lower case (101b) to form an installation space therein ( 101 and a heater 120 and a pump 130 mounted in the case 101 and sequentially connected to the circulation hot water pipe 10 connected to the heat radiating hot water pipe of the mat.

One side of the upper case 101a is provided with an operation panel 107 provided with operation and setting buttons, a display, and the like. The heater 120 and the pump ( The control unit for controlling the power supply, the operation of the display, and the like 130 is provided. In addition, the upper part of the upper case (101a) is provided with a water supply tank 103, the cover 105 is detachably coupled to the top of the water supply tank (103).

3 is a cross-sectional view showing the internal configuration of the heater 120, which is a main part of the prior art, and with reference to this, the heater 120 has the inlet 123 and the outlet 124 formed on both sides and the upper portion. A hot water tank 121 having an inlet 125 and an outlet 126 formed therein, a heater 145 installed vertically inside the hot water tank 121 to generate heat according to power supply through the controller, and a spiral Consists of a heat exchanger 131 formed of a tubular body to form a path that rotates while descending around the heater 145.

The inlet 123 and the outlet 124 of the hot water tank 121 is connected to the heat dissipation hot water pipe of the mat through the circulation hot water pipe 10, in the illustrated embodiment, the pump 130 of the heater 120 It is installed at the rear end and the inlet 123 is directly connected to the circulation hot water pipe 10, the outlet 124 is connected to the circulation hot water pipe 10 through the connecting pipe 141 and the pump 130.

In addition, the partition wall partitions the inner space into a plurality of spaces in which only a part of the internal space is communicated, for example, into two spaces having a narrow passageway 190 formed thereon as shown in the illustrated embodiment ( 129 is formed, and the inlet 125 and the outlet 126 are formed in the upper portion of the hot water tank 121 and communicate with the replenishing water tank 103, each of the inlet 125 and the outlet 126, respectively Shank valves (127, 128) are installed in the opposite direction is configured to move the water to both sides in accordance with the pressure difference between the hot water tank 121 and the replenishment water tank (103).

The heat exchanger 131 is preferably made of a material having high thermal conductivity, and the inlet 132 of the upper portion thereof is connected to the inlet 123 of the hot water tank 121, and the outlet 133 of the lower portion thereof is hot water. It is installed to communicate with the inner space of the tank 121.

The hot water supply device of the prior art configured as described above is to circulate the water of the heat radiating hot water pipe and the circulation hot water pipe 10 connected to the mat by the pump 130, and the circulated water through the heater 120 Since the water is re-supplied by heating, the heat is introduced into the heater 120 through the heat exchanger 131, so that the incoming water is preheated by the water inside the hot water tank 121, the temperature difference between the newly introduced water and the stored water. Is reduced. In particular, since the heat is exchanged while the introduced water moves along the spiral path around the heater 145 having a relatively large heat supply, the incoming water can absorb more heat in advance, and the water around the heater 145 As the temperature rise is reduced, the temperature deviation according to the position inside the hot water tank 121 may be primarily reduced.

In addition, since the water introduced through the heat exchanger 131 is rotated while being discharged into the hot water tank 121, the hot water temperature inside the hot water tank 121 is mixed by actively mixing in the hot water tank 121. Since the passage 190 is formed at a position far from the outlet 133 of the heat exchanger 131 by the partition 129, the transport path of the water passing through the hot water tank 121 becomes long and complicated. Therefore, the mixing of the water is further promoted to suggest a configuration in which the temperature of the hot water becomes uniform.

However, even when using the configuration shown in Figure 3, rather than simply put the heater in the hot water tank 121, the temperature at which boiling occurs to raise the temperature to some extent. Since the portion of the heat transfer medium that contacts the surface of the heater is limited, the hot water is heated in part from the heater, so that the heat transfer medium in contact with the heater surface of the high temperature cannot be prevented from boiling off.

Since the noise is generated inside the hot water boiler due to the boiling, since this noise has a great effect on the water surface, it is urgently necessary to remove the cause of the noise.

The present invention relates to an electric heater, and more particularly, to a heater for heating hot water to a hot water supply device for supplying hot water to a hot water circulation mat and a small heating device. It is an object of the present invention to provide an electric heater that is easy to apply to the hot water circulation mat that can improve the usability and convenience of the hot water circulation mat in one embodiment by allowing the heat of the heater to be quickly and uniformly transferred.

According to the present invention for achieving the above object, by forming a spiral flow path on the outside of the electric heating element having a heating wire therein, it is possible to efficiently transfer heat to the heat transfer medium, and is configured so that heat transfer is not made in part It is configured to increase the temperature at which the heat transfer medium boils as the temperature rises.

More specifically, in the electric heater for heating the heat transfer medium to the hot water circulation mat and hot water supply device for supplying hot water to the small heating device,

A heater 210 installed by covering a heater cover 212 in a hot water tank 121 filled with a heat transfer medium,

A cover 226 formed of a metal on the outside of the heater 210 and covered to maintain a predetermined interval,

An inlet 222 formed at an upper side of the cover 226 so that the heat transfer medium transfers heat at the pressure of the pump and circulates back;

A space portion 230 through which the heat transfer medium introduced from the inlet 222 passes,

The outlet 210 is moved to a gap formed by the heater 210 and the cover 226, and a water outlet 224 is formed below the cover 226 through which the heat transfer medium that receives heat from the heater 210 exits. ,

The spiral bar 228 formed in a spiral on the outer peripheral surface of the heater 210 is provided,

The cover 226 which is covered in contact with the outer circumference of the spiral bar 228 and the spiral flow path 220 is formed between the spiral bar 228 and the outer surface of the heater 210 and the inner surface of the cover 226 is formed. Features,

It is characterized in that the crimped from the outside of the cover 226 to increase the contact degree of the spiral rod 228 in contact with the heater 210 and the cover 226,

The heater 210 and the cover 226 are pressed into the inner and outer circumferential surfaces of the spiral rod 228 so as to increase the contact degree of the spiral rod 228 in contact with the heater 210 and the cover 226. ,

On the outer circumferential surface of the heater 210 is provided a spiral pin 328 formed in a spiral,

It is characterized in that the crimped from the outside of the cover 226 to increase the contact degree of the spiral pin 328 in contact with the heater 210 and the cover 226,

The heater 210 and the cover 226 are press-fitted into the inner and outer circumferential surfaces of the spiral fin 328 so as to increase the contact degree of the spiral pin 328 contacting the heater 210 and the cover 226. ,

The heater cover 212 is processed to increase the contact degree of the spiral pin 328 contacting the heater 210 and the cover 226, characterized in that to form a spiral pin 328,

It characterized in that to form a female spiral of a shallow depth corresponding to the spiral pin 328 on the inner peripheral surface of the cover 226,

The spiral pin 328 is characterized in that a plurality formed to widen the contact area,

It relates to an electric heater, characterized in that a plurality of fins 440 is formed on the outer peripheral surface of the cover 226 to increase the heat transfer efficiency.

In addition, in the electric heater for heating the heat transfer medium to the hot water circulating mat and hot water supply device for supplying hot water to the small heating device,

A heater 210 installed inside the hot water tank 121 filled with the heat transfer medium,

The heating wire 214 that generates heat by energizing the inside of the heater 210,

A solid particulate filler 218 for transferring heat generated from the heating wire 214 and for electrical insulation;

A heater cover 212 that protects an internal configuration of the heater 210 outside the filler 214;

Characterized in that formed by a pair of terminals 216 protruding to supply electricity to the heater cover 212,

The lower end of the heater cover 212, characterized in that the circular groove 211 is formed to suppress the heat transfer to the portion coupled to the hot water tank 121,

Characterized in that the thickness of the heater cover 212 is formed of a metal having a thickness of 1 to 10mm to smoothly transfer heat transfer to prevent partial boiling,

The lower end of the heater cover 212, relates to an electric heater characterized in that the heat radiation fin 213 is formed to suppress the heat transfer to the portion coupled to the hot water tank 121.

Figure 1 of the accompanying drawings showing a preferred embodiment according to the present invention is a schematic diagram illustrating the configuration of a typical hot water circulation mat, Figure 2 is an exploded perspective view showing a hot water supply device for hot water circulation mat according to the prior art, Figure 3 is a cross-sectional view showing the internal configuration of a heater that is a main part of a hot water supply device according to the prior art, Figure 4 is a cross-sectional view of the heater of the electric heater according to the present invention, Figure 5 is a partial cutaway perspective view of the electric heater according to the present invention. 6 is a partially cutaway perspective view of an electric heater in another embodiment according to the present invention, FIG. 7 is a partially cutaway perspective view of an electric heater in another embodiment according to the present invention, and FIG. 8 is another embodiment according to the present invention. A partial cutaway perspective view of an electric heater.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 to 3 is a configuration of a conventional hot water circulation mat and hot water supply device for hot water circulation mat according to the prior art, which has been described in the technical field of the present invention.

Figure 4 is a cross-sectional view of the heater of the electric heater according to the present invention, to form a thicker configuration of the heater cover 212 to reduce the boiling phenomenon.

Heat transfer occurring in the hot water tank 121 shown in FIG. 3 represents a very complicated phenomenon.

In order to provide a low noise hot water boiler to prevent boiling phenomenon, more efficient heat transfer, and also to transfer more heat to the hot water, the hot water circulation mat can transfer abundant heat in a short time.

In order to transfer more heat to hot water, it is usually increased the electric consumption capacity of the heater, but increasing the capacity of the heater will increase the boiling phenomenon.

In order to increase the capacity of the heater and to prevent boiling, it is necessary to take a large amount of heat from the heater and smoothly transfer the heat amount to the heat transfer medium.

The sound of water boiling in a commonly used hot or cold water heater or bidet attempts to heat a lot of heat with a heater having a narrow surface area, so the heat transfer medium that receives heat has a small amount of contact with the surface of the heater. This is because there is no configuration.

The boiling phenomenon generated in the hot water tank 121 in which the heater 145 is disposed is somewhat different depending on the hot water capacity in the hot water tank 121, but occurs when the internal warm water reaches about 60 degrees Celsius. When hot water is formed as hot water in a hot or cold water heater or a bidet, a boiling phenomenon occurs from a temperature lower than about 60 degrees Celsius.

Boiling phenomenon can be seen in our daily life. When boiling water in a thin pan, it can be partially boiled and bubbles are formed from the bottom of the pan without reaching the boiling temperature. You can see it boiling.

When boiling in a pan, even if the average temperature of the whole is low, it is thin in the area where the flame of the stove touches, so that the water contacting the part is close to the boiling temperature. As it is transmitted over, the water is heated relatively broadly so that bubbles can be seen at a higher average temperature than the pot.

This is because a bowl thicker than a pot can evenly disperse partial heat and turn it on to transfer heat to the medium.

The heater sectional view of the electric heater of FIG. 4 shows that the thickness of the heater cover 212 is thicker than the conventional heater sectional view. As the thickness of the heater cover 212 is thicker, heat can be evenly transmitted.

The heater 21 is provided with a heating wire 214 for generating heat by electric current therein, and a filler 218 for transferring heat generated from the heat transfer to the heater cover 212 and filled for electrical insulation. A pair of terminals 216 are provided to supply electricity from the outside to the inside through the heater cover 212.

The filler 218 has a particle shape in which particles are in contact with each other to facilitate heat transfer, and a space formed therein is almost no heat transfer. Therefore, the heat transferred to the outer surface of the heater cover 212 is partially transferred to the surface. The heat flows to this high part, so that partial boiling occurs like the phenomenon of the pot, so that the thickness of the surface is increased to make the non-uniform surface heat transfer homogeneous.

Typically used thickness is about 1mm to protect the internal configuration of the heater 210, the present application has limited the thickness to 1 ~ 10mm for more smooth heat transfer. It is sufficient that the thickness is such that the thickness of the heating wire 214 and the filling material 218, which are not necessary, can be in contact with the heat transfer medium with a uniform distribution of heat transferred to the surface.

Increasing the thickness more than necessary increases the capacity containing heat only.In the case of a bidet, the remaining water is boiled when the flow of water stops after heating with hot water. 121) to increase the temperature of the portion where the heater 210 is coupled to the bottom to bring the result of melting the case.

The lower portion of the heater cover 212, the terminal 216 portion is fitted in contact with the case and the lower portion of the heating wire 214 is a configuration that is not arranged for safety, the heating wire that is the upper end of the heater cover 212 The thickness of the portion 214 is installed is thick and the lower portion is formed relatively thin, or the circular groove 211 around the outer circumference of the heater cover 212 in order to transfer less heat transferred from the upper end to the lower end of the heater cover 212 ) To reduce the thickness of heat transfer, or to form a heat radiating fin 213 smooth heat transfer at the lower end to configure the heat transfer relatively less at the lower end corresponding to another embodiment.

Figure 5 shows a partial cutaway perspective view of the electric heater 200 according to the present invention, the electric heater 200 is in contact with the configuration of the heater 210 described in Figure 4 in the center, the outer peripheral surface of the heater 210 The spiral rod 228 wound in a spiral shape, the cover 226 covered in contact with the outer circumference of the spiral rod 228, the spacing between the spiral rod 228 and the heater 210 outer surface and the inner surface of the cover 226 The continuous spiral flow path 220 formed therein, and an inlet 222 through which a heat transfer medium flows are formed on an upper side of the cover 226, and a lower outlet port 224 is formed in the lower part.

The spiral rod 228 is wound in a spiral shape in contact with the outer circumferential surface of the heater 210 to be in contact with the heater 210 and the heat transfer medium for a longer time through the continuous spiral flow path 220 to transfer heat from the heater 210. In order to increase the amount, the heat is directly transmitted through the spiral bar 228 in contact with the heater 210 surface, and heat is directly transmitted to the cover 226 in contact with the spiral bar 228 to provide a larger area. It is to transfer heat to the heat medium.

The thickness of the spiral bar 228 may be changed depending on the required flow rate and the diameter of the heater, it is determined according to the cross-sectional area of the spiral flow path 220 required.

The spiral flow path 220 is a cover 226 which is covered in contact with the outer circumference of the spiral bar 228, the gap between the spiral bar 228 and the outer surface of the heater 210 and the inner surface of the cover 226 is formed, the heat transfer As the medium moves rapidly on the outer surface of the heater, the higher the amount of heat delivered, the greater the amount of heat transferred from the heater, which results in intensive or localized heat transfer to prevent boiling.

The heat transfer medium flows through the water inlet 222 and finishes the heating role to transfer the heated amount of heat, and the return water cooled and returned returns to the space portion 230, which is the upper portion of the heater 210, and is continuously and continuously formed in a spiral shape. It moves through the spiral flow path 220, receives heat from the heater 210, rotates in a spiral direction through the water outlet 224, is discharged, and is uniformly mixed with hot water remaining in the passage 190 to form a uniform temperature. do.

The heated hot water is circulated again through the pump.

Compression may be performed on the outside of the cover 226 so as to increase the contact degree between the heater 210 and the cover 226 in contact with the spiral bar 228. This is because the heat transfer rate is higher in heat transfer efficiency between metals due to metal contact than through the heat medium.

In addition, in another embodiment, a configuration in which the spiral rod 228 is lacking also forms a fast flow path on the surface of the heater 210 from the water inlet 222 to the water outlet 224, thereby achieving heat transfer more efficiently than the prior art. This is a configuration that can be simply used when there is no need to raise the temperature to a high temperature (near the boiling temperature, about 80 degrees Celsius).

FIG. 6 shows a partially cutaway perspective view of an electric heater in another embodiment according to the present invention, the difference from FIG. 5 being that it is formed of a spiral pin 328 having a thickness instead of being formed of a spiral rod 228. Since the spiral pin 328 having a thickness has a thickness, the heat transfer efficiency is increased because the degree of contact between the heater 210 and the cover 226 in contact with the spiral pin 328 can be further increased.

The spiral pin 328 may be inserted by pressing the heater 210, may be welded and bonded for a higher heat transfer rate, and may be formed by cutting the heater cover 212 by cutting, or correspondingly spirally. Lower than the height of the pin 328 may be formed inside the cover 226 in the form of a female screw so as to secure the space of the spiral flow path 220.

7 is a partial cutaway perspective view of an electric heater according to another embodiment of the present invention, which is different from FIG. 6 in that a plurality of spiral fins 328 are formed to contact heat transfer between metals by a plurality of spiral fins 328. The efficiency is increased, and a pin is formed outside the cover 226 to transfer a large amount of heat from the heater 210 to the heat medium to effectively prevent boiling.

Due to these embodiments, the capacity of the heater 210 is increased, and even when the temperature of the heat medium reaches 80 degrees Celsius, it is possible to effectively prevent local boiling.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, but the hot water is described as an embodiment, but it is applicable to all heat transfer fluids, and various modifications may be made without departing from the spirit of the present invention. It will be apparent to those skilled in the art that branch substitution, modification, and alteration are possible.

As described above, according to the present invention, the electric heater increases the thickness of the metal surrounding the electric heating element, increases the length of the heat transfer medium contact, prevents the heat transfer medium from boiling due to the partial temperature rise, quiet and quiet An electric heater can be provided.

Claims

In the electric heater for heating the heat transfer medium to the hot water circulation mat and hot water supply device for supplying hot water to the small heating device,

The outlet 210 is moved to a gap formed by the heater 210 and the cover 226, and a water outlet 224 is formed below the cover 226 through which the heat transfer medium that receives heat from the heater 210 exits. Electric burner.

The method of claim 1,

The cover 226 which is covered in contact with the outer circumference of the spiral bar 228 and the spiral flow path 220 is formed between the spiral bar 228 and the outer surface of the heater 210 and the inner surface of the cover 226 is formed. Electric burner characterized by the above.

The method of claim 2,

An electric heater, characterized in that the compression of the outside of the cover 226 so as to increase the contact degree of the spiral bar (228) in contact with the heater 210 and the cover 226.

The method of claim 2,

The heater 210 and the cover 226 are pressed into the inner and outer circumferential surfaces of the spiral rod 228 so as to increase the contact degree of the spiral rod 228 in contact with the heater 210 and the cover 226. Electric burner.

The method of claim 1,

The method of claim 5,

Pressed from the outside of the cover 226 so as to increase the contact degree of the spiral pin 328 in contact with the heater 210 and the cover 226.

The method of claim 5,

The heater 210 and the cover 226 are press-fitted into the inner and outer circumferential surfaces of the spiral fin 328 so as to increase the contact degree of the spiral pin 328 contacting the heater 210 and the cover 226. Electric burner made.

The method of claim 5,

An electric heater, characterized in that for forming a spiral fin (328) by processing the heater cover (212) to further increase the contact degree of the spiral fin (328) in contact with the heater (210) and the cover (226).

The method of claim 8,

An electric heater, characterized in that to form a female spiral of a shallow depth corresponding to the spiral pin (328) on the inner peripheral surface of the cover (226).

The method of claim 8,

The spiral fin 328 is an electric heater, characterized in that formed in plural to widen the contact area.

An electric heater, characterized in that formed by a pair of terminals 216 protruding to supply electricity to the outside of the heater cover (212).

The method according to any one of claims 1 to 11,

An electric heater, characterized in that the circular groove (211) is formed in the lower end of the heater cover (212) in order to suppress the heat transfer to the portion coupled to the hot water tank (121).

The method according to any one of claims 1 to 11,

An electric heater, characterized in that the thickness of the heater cover 212 is formed of a metal having a thickness of 1 to 10mm to smoothly transfer heat transfer to prevent partial boiling.

The method according to any one of claims 1 to 11,

An electric heater, characterized in that the heat dissipation fin (213) is formed in the lower end of the heater cover (212) in order to suppress the heat transfer to the portion coupled to the hot water tank (121).

The method according to any one of claims 1 to 10,

Electric heater, characterized in that a plurality of fins (440) is formed on the outer circumferential surface of the cover (226) to increase the heat transfer efficiency.