JP3404394B2 - Defrost heater and refrigerator - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a defrost heater for defrosting an evaporator of a refrigeration cycle such as a refrigerator.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 8-54172 discloses a defrost heater used in refrigerators in recent years.

The conventional defrost heater will be described below with reference to the drawings.

FIG. 15 is a vertical sectional view of a main part of a conventional refrigerator. In FIG. 15, 1 is a refrigerator main body, 2 is a freezer compartment inside the refrigerator main body 1, 3 is a refrigerator compartment inside the refrigerator body 1, 4 is a freezer compartment door, 5 is a refrigerator compartment door, and 6 is a freezer compartment 2. A partition wall that separates the refrigerator compartment 3 from the refrigerator compartment, 7 a freezer compartment inlet for sucking air in the freezer compartment 2, 8 a refrigerating compartment inlet for sucking air in the refrigerating compartment 3, 9 an outlet for discharging cold air, 10 a Evaporator, 11 is a fan for circulating cold air, 12 is evaporator 10
And an evaporator partition wall for partitioning the freezer compartment 2, 13 a trough, 14 a drain port, 15 a defrosting tube heater in which a nichrome wire is coiled and covered with a glass tube, 16 is defrosting water for defrosting A roof for preventing evaporation noise generated when it is directly dropped on and comes into contact with the pipe heater 15, 17 is a trough 13 and a defrost pipe heater 1
5 is a bottom plate made of metal which is installed between 5 and is insulated and held.

Next, the operation will be described. When cooling the freezer compartment 2 or the refrigerating compartment 3, the refrigerant flows through the evaporator 10 to cool the evaporator 10. Fan 11
Is operated to send the temperature-raising air in the freezing compartment 2 or the refrigerating compartment 3 to the cooling compartment 20 from the freezing compartment suction opening 7 or the refrigerating compartment suction opening 8 to be cooled by exchanging heat with the evaporator 10 to be cooled from the discharge opening 9. The air is sent into the freezer compartment 2, and cold air is sent from the freezer compartment 2 to the refrigerating compartment through a communication port (not shown). Here, the air that exchanges heat with the evaporator 10 is highly humidified by the inflow of high-temperature outside air due to the opening and closing of the freezing compartment door 4 and the refrigerating compartment door 5 and the evaporation of water in the food stored in the freezing compartment 2 and the refrigerating compartment 3. Since the air is air, the moisture in the air becomes frost and frosts on the evaporator 10 which has a lower temperature than the air, and heat exchange with the air that exchanges heat with the surface of the evaporator 10 as the amount of frost increases. Is impeded, and the air flow resistance is reduced, and the air volume is reduced, so that the heat transmission rate is reduced and insufficient cooling occurs. Therefore, the nichrome wire of the defrosting tube heater 15 is energized before the cooling becomes insufficient. When energization of the nichrome wire is started, heat rays are radiated from the nichrome wire to the evaporator 10 and peripheral parts. At this time, a part of the heat ray radiated to the bottom plate 17 is reflected by the heater wire due to the shape of the bottom plate 17, and the other is reflected toward the evaporator 10 and other peripheral components. As a result, the evaporator 10, the trough 13 and the drain 1
Melt frost around 4 into water. In addition, a part of the defrosted water melted in this way directly falls into the tub 13, and the other part is covered by the roof 16 to avoid the defrosting pipe heater 15 and
And is drained from the drainage port 14 to the outside of the refrigerator.

[0006]

However, in the above-mentioned conventional structure, the glass surface temperature of the defrosting tube heater 15 is, of course, very high, not to mention the surface of the nichrome wire, and the bottom plate 17 is a tube. Since the part of the heat ray radiated from the tube heater 15 is in the vicinity of the heater 15 and is reflected back to the tube heater 15, the temperature of the glass tube rises abnormally and becomes higher than the ignition temperature of the flammable refrigerant. From this, when a flammable refrigerant is used as the refrigerant, if the flammable refrigerant leaks from the pipe installed in a portion communicating with the evaporator 10 or the inside of the refrigerator, the defrosting pipe heater 15
There was a problem that there is a risk of ignition and explosion due to the energization of.

In view of the above problems, the present invention is a defrost heater capable of suppressing the risk of ignition of a flammable refrigerant even when defrosting is performed in an environment where the flammable refrigerant leaks into the installation atmosphere of the defrosting means. The purpose is to provide.

[0008]

[Means for Solving the Problems] Means for defrosting an evaporator of a refrigeration cycle in which a combustible refrigerant is sealed by functionally connecting a compressor, a condenser, a decompression mechanism and an evaporator, and a first glass A tube, a heater wire made of a metal resistor inside the first glass tube, a second glass tube located at an outermost portion of the first glass tube for covering the first glass tube with a space, and the first and the first glass tubes. Two
And a sealing means for suppressing the entry of outside air into both ends of the glass tube, and the surface of the second glass tube emits a flammable refrigerant.
The temperature is lower than the fire temperature, and an air layer is formed between the first and second glass tubes.
And the inner diameter of the second glass tube is 1.5 to 3 times the outer diameter of the first glass tube, the defrosting time is due to high heat conduction of the flammable refrigerant. If the flammable refrigerant leaks due to shortening, the outer surface temperature of the outermost glass tube is lowered to suppress ignition of the flammable refrigerant.

Further, it is possible to suppress the flame propagation from the inside to the outside of the defrost heater when the internal space sectional area of the defrost heater is regulated.

Further, it is possible to suppress the excessive temperature rise of the heater wire due to the excessive heat insulation of the space between the glass tubes.

The invention according to claim 2 of the present invention is
Since the thickness of the second glass tube is greater than that of the first glass tube, it is possible to suppress the occurrence of cracks in the second glass tube during transportation or installation, and in the unlikely event that flammable refrigerant leaks. It is possible to suppress the flammable refrigerant flowing into the defrosting heater and the flame propagation to the outside air when the flammable refrigerant flows into the defrosting heater and ignites.

The invention according to claim 3 of the present invention is
A refrigerator equipped with the defrosting heater according to claim 1 or 2, wherein the defrosting time is shortened due to high heat conduction of the combustible refrigerant, and in the unlikely event that the combustible refrigerant leaks, In addition to suppressing flame propagation from the inside of the defrost heater to the outside when the outer surface temperature is reduced to suppress the ignition of flammable refrigerant and the internal space cross-sectional area of the defrost heater is regulated, Providing a refrigerator that can suppress flammable refrigerant inflow and flame propagation to the outside air when flammable refrigerant flows into the defrost heater and ignite, and suppress excessive temperature rise in the heater wire due to excessive heat insulation in the space between glass tubes it can.

The invention according to claim 4 of the present invention is
Since the centers of the diameters of the first glass tube and the second glass tube are eccentric, place the part to be defrosted most in the vicinity where the distance between the first glass tube and the second glass tube is the shortest. By installing it, the defrosting can be made uniform and the defrosting time can be shortened.

The invention according to claim 5 of the present invention is
The refrigerator according to claim 4, wherein the defrosting heater is attached so that the distance between the first glass tube and the second glass tube is larger in the upper side than in the lower side, at the outer surface temperature of the second glass tube. Since the temperature difference between the upper and lower sides can be reduced and the temperature can be made uniform around the average temperature of the upper and lower sides, the heat generation amount of the defrost heater can be increased by the maximum temperature drop of the second glass tube, and the defrost time can be shortened.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. It should be noted that the same configurations as those of the conventional one are denoted by the same reference numerals and detailed description thereof will be omitted.

(Embodiment 1) Embodiment 1 of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of a refrigeration system using a defrost heater according to Embodiment 1 of the present invention, and FIG. 2 is a sectional view of the defrost heater.

As shown in FIGS. 1 and 2, reference numeral 18 is a defrosting heater for defrosting the frost adhering to the evaporator 10.
Is a compressor, 20 is a condenser, and 21 is a decompression mechanism. The compressor 19, the condenser 20, the decompression mechanism 21, and the evaporator 10 are combustible (not shown) inside the refrigeration cycle functionally connected to each other. The refrigerant is enclosed.

Further, 22 is a glass tube which is a constituent element of the defrosting heater 18, 23 is a constituent element of the defrosting heater 18 and is a heater wire made of a metal resistor inside the glass tube 22, and 24 is a heater wire 23. A straight line portion consisting of straight lines at both ends of the
The spiral part 26 is formed in a spiral shape so that it can be stored in a predetermined length of the glass tube 22, and 26 is a polymer material that functions as a cap that suppresses invasion of outside air or defrost water into the inside of the glass tube 20. And 27 is a lead wire for conducting electricity to the heater wire 23.

The operation of the defrosting heater constructed as described above will be described below.

The operation of the compressor 19 cools the evaporator 10 of the refrigeration cycle, and the fan 11 operating at the same time as the operation of the compressor 19 ventilates the air inside the refrigerator from the cooled evaporator 10 to the evaporator 10. The cold air that has been heat-exchanged with is discharged into the refrigerator. Then, after an arbitrary operation time of the compressor 19, the operation of the compressor 19 is stopped, and at the same time when the operation of the compressor 19 is stopped, the heater wire 23 is energized through the lead wire 27 to heat the defrost heater 18. Due to the heat generated by the defrost heater 18, the glass tube 22 of the defrost heater 18 is heated to a temperature lower than the ignition temperature of the flammable refrigerant used in the refrigeration cycle to defrost the evaporator 10 and peripheral components. In the defrosting in the evaporator 10 at this time, heat is transferred from the defrosting heater 18 by the outside air, and heat is transferred from a portion of the evaporator 10 near the defrosting heater 18 to defrost the evaporator 10 from the outside. Further, the heated combustible refrigerant in the evaporator 10 carries heat to a portion having a lower temperature to defrost it.

Then, the evaporator 10 detects the completion of defrosting by detecting means (not shown) to stop the energization of the defrosting heater, and at the same time or after an arbitrary time, activates the compressor 19 to start the cooling operation. By doing so, non-cooling of the evaporator due to frost formation is regularly prevented.

Therefore, R represented by the conventional HFC refrigerant is used.
Comparing the thermal conductivities of 134a and isobutane typified by a flammable refrigerant, it is close to the temperature of the evaporator 10 at the time of defrosting.
Since isobutane is better for both liquid and gas at ℃, flammable refrigerant is better for heat transfer by the refrigerant in the evaporator 10 during defrosting, and there is a possibility that the defrosting time can be shortened. In particular, in a refrigerator or the like, a temperature increase due to the stop of cooling during defrosting causes deterioration of food that is an object to be cooled. Therefore, there is a possibility that deterioration of food can be prevented by early cooling.

In addition, in the unlikely event that the flammable refrigerant in the refrigeration cycle has an outer surface of the glass tube 22 which is the outermost space of the defrost heater 18, the temperature is lower than the ignition temperature of the flammable refrigerant, so that there is a risk of ignition. descend.

In the present invention, the outer surface temperature of the glass tube 22 is lower than the ignition temperature of the flammable refrigerant, but it is preferably 360 ° C. or lower when the isobutane refrigerant is used, and the voltage to the heater wire 23 is reduced. When the fluctuation is large, it is usually desirable to design at a lower temperature in accordance with the maximum heat value of the voltage fluctuation.

(Second Embodiment) A second embodiment of the present invention will be described with reference to the drawings. The same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 3 is a sectional view of the essential parts of the defrosting heater according to the second embodiment of the present invention.

As shown in FIG. 3, 28 is a glass tube 22 having a circular cross-sectional area of 800 mm 2 in the inner diameter direction of the glass tube 22.
Is the internal space of.

The operation of the defrost heater constructed as above will be described below.

During defrosting, the temperature of the heater wire 23 rises due to the heat generated by the heater wire 23, and a part of it becomes a radiant heat ray that passes through the internal space 28 and the glass tube 22 and radiates heat directly to the outside of the defrost heater 18. To be done. Others transfer heat to the gas existing in the internal space 28 to raise the temperature of the gas, transfer the heat to the glass tube 22 and raise the temperature of the glass tube 22 to a temperature lower than the ignition temperature of the flammable refrigerant to defrost. Heater 1
The heat is radiated to the low temperature atmosphere outside the unit 8. At this time, the thermal expansion of the glass tube 22 and the heater wire 23 due to the temperature rise is absorbed by the internal space 28, the gas in the internal space 28 expands due to the temperature rise, and the expansion force causes elastic deformation of the sealing means 26 to form a gap. It may be generated and leaked to the outside.

When the defrosting is finished in such a state, when the heating of the heater wire 23 is stopped and the cooling is started, the temperature of the heater wire 23, the gas in the internal space 28, and the glass tube 22 suddenly decreases. Due to this temperature decrease, the internal space 28 is decompressed, and the outside air around the defrost heater 18 flows in.

In such a situation, in the unlikely event that flammable refrigerant exists near the defrosting heater 18, the flammable refrigerant may flow into the internal space 28 and ignite when the heater wire 23 generates heat at the start of defrosting. Becomes higher. However, the internal space 28
Cross-sectional area of the glass tube 22 is 8
Since it is 00 mm ² , the volume of gas that receives energy from the surface per unit area of the heat generating element that is the ignition source does not reach the explosive amount, so that the flammable refrigerant in the glass tube 22 burns only momentarily. The flame does not propagate from the pipe 22 to the outside, and the flammable refrigerant around the outside of the defrost heater 18 is less likely to catch fire.

From this, it is possible to suppress the deterioration of the object to be cooled by shortening the defrosting time due to the high heat conduction of the flammable refrigerant, and to set the outer surface below the ignition temperature of the flammable refrigerant should the flammable refrigerant leak. In addition to suppressing ignition of the flammable refrigerant by the glass tube 22, it is possible to further reduce the risk of fire due to suppression of flame propagation from the defrost heater 18.

In the present embodiment, as shown in FIG. 3, the spiral portion 25 of the heater wire 23 and the glass tube 22.
The center of the circle and the center of the circle are at the same position, but the same effect can be obtained even if they are eccentric.

The internal space 28 has a size of 800 mm ² , but the possibility of ignition decreases as the internal space 28 decreases below 800 mm ² . However, in order to prevent damage due to thermal expansion of the glass tube 22 and the heater wire 23 during heat generation, at least an internal space of 0.5 mm ² or more is required to absorb the thermal expansion. If the thermal expansion is not absorbed, the glass tube may be damaged and the defrost water may come into direct contact with the heater wire, and the heater wire may be deteriorated due to erosion and its life may be shortened.

(Third Embodiment) A third embodiment of the present invention will be described with reference to the drawings. The same components as those in the second embodiment will be assigned the same reference numerals and detailed description thereof will be omitted.

FIG. 4 is a cross-sectional view in the third embodiment of the present invention, and FIG. 5 is a cross-sectional view of the main part in the case of being sliced.

As shown in FIGS. 4 and 5, 29 is a first glass tube covering the heater wire 23, and 30 is a first glass tube 2
A second glass tube located at the outermost portion covering 9; a clearance, which is the distance between the outer diameter of the spiral portion 25 of the heater wire 23 and the inner diameter of the first glass tube 29; and 32, the first glass tube 29. And the second glass tube 30 is a space between glass tubes.

The operation of the defrosting heater constructed as above will be described below.

When the heater wire 23 generates heat during defrosting, a part of the radiant heat ray is directly transmitted to the outside. However, for others, the clearance 31 from the glass tube heater wire 23, the first glass tube 29, the inter-glass tube space 32, the second glass tube 3
The surface of the outermost second glass tube 30 is transmitted to 0 and the surface temperature of the second glass tube 30 rises to a temperature lower than the ignition temperature of the flammable refrigerant and radiates heat to the outside to defrost peripheral parts.

At this time, since there is the wall thickness of the second glass tube 30 and the air serving as a heat insulating layer between the first glass tube 29 and the second glass tube 30, the second glass tube is Compared to the case where the heater wire 23 does not have the same amount of heat, the outer surface temperature of the second glass tube 30 decreases, and the outer surface of the outermost glass tube has the same temperature below the ignition temperature of the flammable refrigerant. The heating value of the heater wire 23 can be increased.

From the above, it is possible to suppress the deterioration of the object to be cooled by shortening the defrosting time due to the high heat conduction of the flammable refrigerant, and in the unlikely event that the flammable refrigerant leaks, the outer surface of the second glass tube 30 is made to burn the flammable refrigerant. Of the flammable refrigerant when the temperature is below the ignition temperature of the defrosting heater 18, and the flame spread from the inside of the defrosting heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrosting heater 18 is regulated is reduced. In addition, the defrosting time can be further shortened by increasing the heat generation amount, so that the cooling operation can be started early and the deterioration of the object to be cooled can be further suppressed.

The first glass tube 29 and the heater wire 2
Since the same material as in the conventional defrost heater may be used for 3 and the like, the same effect can be obtained even when it is used by putting it in the second glass tube having a large inner diameter, and it is possible to further reduce the cost.

Further, in the present embodiment, the glass tube is explained as a double tube, but the same effect as above can be obtained even if more glass tubes are used.

Also, the first glass tube 29 and the heater wire 2
If the surface temperature of 3 is set below the ignition temperature of the flammable refrigerant, the risk of ignition may be further reduced.

(Embodiment 4) Embodiment 4 of the present invention will be described with reference to the drawings. The same components as those in the third embodiment will be designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 6 is a sectional view of the essential parts of the fourth embodiment of the present invention.

As shown in FIG. 6, D is the first glass tube 2
The outer diameter of 9 and D ′ are the inner diameter of the second glass tube 30, and although not shown, the value obtained by dividing D ′ by D is 3 or less.

The operation of the defrost heater constructed as described above will be described below.

At the time of heat generation of the heater wire 23 during defrosting, the heater wire 23, the first glass tube 29 and the inter-glass tube space 3
2, the heat is radiated to the outside through the second glass tube 30,
The outer surface of the glass tube 30 becomes lower than the ignition temperature of the flammable refrigerant and defrosts the peripheral parts.

At this time, the outermost second glass tube 3
If the outer surface of 0 has the same temperature and the calorific value in the glass tube heater wire 23 is the same, the outer diameter D of the first glass tube 29.
On the other hand, the larger the inner diameter D ′ of the second glass tube 30, the larger the inter-glass tube space 32, and the thicker the air layer existing in the inter-glass tube space 32. Insulation increases. From this, when the outer surface of the outermost second glass tube 30 has the same temperature lower than the ignition temperature of the flammable refrigerant, the first glass tube 29
The heating value of the heater wire 23 can be increased by increasing the inner diameter D ′ of the second glass tube 30 with respect to the outer diameter D of
Second glass tube 3 with respect to outer diameter D of first glass tube 29
If the heat insulation of the heater wire 23 is increased by strengthening the heat insulation until the size of the inner diameter D ′ of 0 exceeds three times, the heater wire 2
The temperature of 3 rises abnormally and the possibility of heater wire breakage becomes extremely high.

Further, with the outer surface of the outermost second glass tube 30 maintained at a temperature lower than the ignition temperature of the flammable refrigerant, the second glass tube 29 with respect to the outer diameter D of the first glass tube 29. In order to reduce the inner diameter D'of 30, it is necessary to reduce the heat generation amount of the heater wire 23, and D '/ D is 1.
When the heating value of the heater wire 23 is reduced to less than 5, the amount of the radiant heat ray from the heater wire 12 having a good frost absorption efficiency decreases, and the radiant heat ray directly absorbed by the frost decreases, which decreases. The remaining amount is absorbed by peripheral parts and the like, and the temperature rises to indirectly transfer heat to the frost, so that the defrosting efficiency deteriorates.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant and the increase in the amount of heat generated by the defrosting heater 18. In the unlikely event that the flammable refrigerant leaks, the second From the inside of the defrosting heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrosting heater 18 is regulated and the ignition of the flammable refrigerant is suppressed when the outer surface of the glass tube 30 is below the ignition temperature of the flammable refrigerant. In addition to reducing the risk of fire due to suppression of flame propagation, the outer surface of the second glass tube 30 can be kept below the ignition temperature of the flammable refrigerant while suppressing a decrease in defrosting efficiency, and the space 32 between the glass tubes is excessive. It is possible to suppress a decrease in reliability when the heater wire 23 is excessively heated due to heat insulation.

(Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to the drawings. The same components as those in the third embodiment will be designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 7 is a sectional view of the essential parts of the fifth embodiment of the present invention.

As shown in FIG. 7, A is the first glass tube 2
9 is the shortest distance between the glass tubes of the second glass tube 30 and A ′ is the longest distance between the glass tubes.

The operation of the defrosting heater constructed as described above will be described below.

When the heater wire 23 generates heat during defrosting, the heater wire 23, the first glass tube 29 and the inter-glass tube space 3
The heat is transferred to the second glass tube 30 through the second heat insulation layer,
The second glass tube 30 rises to a temperature lower than the ignition temperature of the flammable refrigerant, radiates heat to the outside air, and defrosts peripheral parts.

Here, the heat transfer to the second glass tube 30 of the defrosting heater 18 will be described in detail. At the shortest distance A between the glass tubes, the thickness of the air serving as the heat insulating layer is the smallest, so that the heat is transferred from the heater wire. The ratio of the amount of heat is the largest, and conversely, it is smaller in the longest distance A ′ between the glass tubes. Therefore,
The amount of heat released from the outer surface of the second glass tube 30 to the outside is the first
Since there are many cases where the distance between the glass tube 29 and the second glass tube 30 is small, defrosting becomes faster in a portion near that portion.

That is, the first distance between the glass tubes is set so that the shortest distance A between the glass tubes is located at the shortest position from the location where defrosting is most desired.
By decentering the centers of the glass tube 29 and the second glass tube 30 in the diameter direction of the glass tube, defrosting can be made uniform and time can be shortened.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant and the increase in the amount of heat generated by the defrosting heater 18, and in the event that the flammable refrigerant leaks, the second From the inside of the defrosting heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrosting heater 18 is regulated and the ignition of the flammable refrigerant is suppressed when the outer surface of the glass tube 30 is below the ignition temperature of the flammable refrigerant. In addition to reducing the risk of fire by suppressing flame propagation, the first glass tube 29 and the second glass tube 29
Eccentric glass tube 30 of the
The defrosting can be made uniform by installing in the vicinity of the shortest distance between the glass tube 29 and the second glass tube 30, and energy can be saved by further shortening the defrosting time and further deterioration of the object to be cooled can be suppressed.

(Sixth Embodiment) A sixth embodiment of the present invention will be described with reference to the drawings. The same components as those in the third embodiment will be designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 8 is a sectional view of the essential parts of the sixth embodiment of the present invention.

As shown in FIG. 8, 33 is the first glass tube uppermost portion located at the uppermost portion of the outer peripheral portion of the cross section circle of the first glass tube 29, and 34 is the first glass tube uppermost portion 33. The upper intersection of the inside of the second glass tube, which is the intersection of the perpendicular extending upward perpendicularly to the tangent and the inner diameter of the second glass tube 30, and 35 is the lowermost portion of the outer peripheral portion of the cross section circle of the first glass tube 29. The lowermost portion of the first glass tube is located at, and 36 is the intersection of the perpendicular line extending downward perpendicularly to the tangent line at the lowermost portion of the first glass tube 35 and the inner diameter portion of the second glass tube 30. The lower intersection point of the inside of the glass tube, B is the shortest upper distance which is the distance between the uppermost portion 33 of the first glass tube and the upper intersection point of the second glass tube, B '.
Is the shortest distance between the lowermost part 35 of the first glass tube and the lower intersection 36 of the second glass tube, and B is B '.
Is greater.

The operation of the defrost heater constructed as above will be described below.

When the heater wire 23 generates heat during defrosting, the heater wire 23, the first glass tube 29 and the inter-glass tube space 3
The heat is transferred to the second glass tube 30 through the second heat insulation layer,
The second glass tube 30 rises below the ignition temperature of the flammable refrigerant, radiates heat to the outside air, and defrosts peripheral parts.

Since the lower shortest distance B'is smaller than the upper shortest distance B, the amount of heat transfer from the first glass tube 29 to the second glass tube 30 is larger in the lower direction. In this way, heat is transferred from the second glass tube 30 to the surrounding outside air in a state where the amount of heat transferred from the lower side is higher than from the upper side, and the temperature of the warmed peripheral outside air is higher in the upper side than in the lower side due to convection. Therefore, the outer surface of the second glass tube 30 has a small amount of heat transfer from the heater wire 23 to the glass tube 30 in the upper part, but is affected by the temperature due to the convection of the outside air, and as a result, has the same temperature as the lower part. . That is, half of the temperature difference between the upper and lower portions is moved downward to make the outer surface temperature of the second glass tube 30 uniform, and the second glass tube 3
It decreases as the maximum temperature of the outer surface temperature of 0.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant and the increase in the amount of heat generated by the defrosting heater 18. In the unlikely event that the flammable refrigerant leaks, the second From the inside of the defrosting heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrosting heater 18 is regulated and the ignition of the flammable refrigerant is suppressed when the outer surface of the glass tube 30 is below the ignition temperature of the flammable refrigerant. In addition to lowering the risk of fire due to suppression of flame propagation, the upper and lower temperature differences in the outer surface temperature of the second glass tube 30 can be reduced to be uniform near the upper and lower average temperatures. The amount of heat generated by the defrost heater 18 can be increased by the maximum temperature decrease, the defrost time can be shortened, and deterioration of the cooling target due to early start of cooling operation can be further suppressed.

(Seventh Embodiment) A seventh embodiment according to the present invention will be described with reference to the drawings. The same components as those in the third embodiment will be designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 9 is a sectional view of the essential parts of the seventh embodiment of the present invention.

As shown in FIG. 9, C is the wall thickness of the outermost second glass tube 30, and C'is the wall thickness of the innermost first glass tube 29.

The operation of the defrosting heater constructed as described above will be described below.

When the heater wire 23 generates heat during defrosting, the heater wire 23, the first glass tube 29 and the inter-glass tube space 3
The heat is transferred to the second glass tube 30 through the second heat insulation layer,
The second glass tube 30 rises to a temperature lower than the ignition temperature of the flammable refrigerant, radiates heat to the outside air, and defrosts peripheral parts. When the defrosting is completed, the power supply to the defrosting heater 18 is stopped and the compressor 19 is actuated to start cooling. By this cooling, the periphery of the defrosting heater 18 is also cooled, and the temperature of the second glass tube 30 sharply drops.

At this time, since the second glass tube 30 is larger than the first glass tube 29, if the second glass tube 30 has the same wall thickness, a crack that may be difficult to determine by inspection during transportation or installation may occur. When a crack occurs in the second glass tube 30, the crack progresses due to expansion and contraction due to the temperature shock before and after defrosting. When the flammable refrigerant leaks in this state and defrosting is performed, the second glass tube 30 is damaged by the ignition due to the inflow of the flammable refrigerant from the cracks, and the flame propagates to the flammable refrigerant in the outside air, which causes a fire or the like. Increases the risk of. Here, by making the second glass tube 30 thicker than the first glass tube 29, the occurrence of cracks can be suppressed as much as possible, and the risk of ignition can be further reduced.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant and the increase in the amount of heat generated by the defrosting heater 18. In the unlikely event that the flammable refrigerant leaks, the second From the inside of the defrosting heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrosting heater 18 is regulated and the ignition of the flammable refrigerant is suppressed when the outer surface of the glass tube 30 is below the ignition temperature of the flammable refrigerant. In addition to reducing the risk of fire due to suppression of flame propagation, the inflow of flammable refrigerant into the defrost heater 18 and the combustion of flammable refrigerant into the defrost heater 18 may cause a fire due to the propagation of flame to the outside air. The risk can be reduced.

(Embodiment 8) Embodiment 8 of the present invention will be described with reference to the drawings. The same components as those in the second embodiment will be assigned the same reference numerals and detailed description thereof will be omitted.

FIG. 10 is a sectional view of the essential parts of the eighth embodiment of the present invention.

As shown in FIG. 10, E is the wall thickness of the glass tube 22, which is 0.5 mm or more.

The operation of the defrost heater constructed as above will be described below.

During defrosting, the temperature of the heater wire 23 rises due to the heat generated by the heater wire 23, and heat is transferred from the heater wire 23 to the glass tube 22 and the temperature of the glass tube 22 rises below the ignition temperature of the flammable refrigerant. Then, heat is radiated from the outer surface of the glass tube 22 to the outside to defrost the peripheral parts.

At this time, even if the flammable refrigerant has leaked, since the surface of the outermost glass tube 22 is usually below the ignition temperature of the flammable refrigerant, the risk of ignition is extremely low.

Even if the glass tube 22 is defrosted and ignites while the flammable refrigerant flows into the glass tube 22, the thickness of the glass tube 22 is 0.5 mm or more. Since the glass tube 22 is not damaged by the ignition force, the possibility that the flame will propagate to the outside can be reduced.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant, and in the unlikely event that the flammable refrigerant leaks, the outer surface of the glass tube 22 is ignited by the flammable refrigerant. In addition to reducing the risk of fire by suppressing the ignition of flammable refrigerant when the temperature is below the temperature and suppressing the propagation of flame from the inside of the defrost heater 18 to the outside when the cross-sectional area of the internal space 28 of the defrost heater 18 is regulated , Even if the glass tube 22 is defrosted and ignited in the state where the flammable refrigerant has flowed in, the glass tube 22 is not damaged by its ignition power, so the possibility of flame propagation to the outside is further reduced. This can reduce the risk of fire.

(Ninth Embodiment) A ninth embodiment of the present invention will be described with reference to the drawings. The same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 2 is a sectional view in the ninth embodiment of the present invention, and FIG. 11 is a temperature characteristic diagram in the same embodiment.

In FIG. 2, the heat flux of the defrosting heater divided by the outer surface area of the glass tube 22 is the outer surface heat flux of the glass tube 22, which is 1.5 W / cm ² , and FIG. The relationship between the outer surface heat flux of the tube 22 and the outer surface temperature of the glass tube 22 is shown on the vertical axis.

The operation of the defrost heater constructed as above will be described below.

During defrosting, the heater wire 23 is energized through the lead wire 27, and the heater wire 23 generates Joule heat. At this time, the outer surface heat flux of the glass tube 22 is 1.
The evaporator 10 is defrosted with a heating value of less than 5 W / cm ² . Here, the outer surface temperature of the glass tube 22 rises as the outer surface heat flux of the glass tube 22 increases, and the calorific value is 1.5 W / c.
When it is m ² or more, the ignition temperature of the flammable refrigerant becomes the temperature or more. That is, even if the dimensions of the glass tube 22 are changed, the heat generation amount is designed so that the heat flux on the outer surface of the glass tube 22 is less than 1.5 W / cm ² , so that the outer surface of the glass tube 22 is made of a flammable refrigerant. The defrost heater 18 having a temperature lower than the ignition temperature can be easily manufactured.

From the above, it is possible to suppress the deterioration of the object to be cooled when the defrosting time is shortened due to the high heat conduction of the flammable refrigerant, and to prevent the flammable refrigerant from leaking to the outer surface of the glass tube 22 when the flammable refrigerant leaks. In addition to reducing the risk of fire by suppressing the ignition of flammable refrigerant when the temperature is below the ignition temperature, it is possible to easily design objects with low risk of ignition as the defrost heater 18 for the refrigeration cycle for flammable refrigerant. Is.

Further, the heating value of the defrosting heater is controlled by the glass tube 2.
If the outer surface heat flux of the glass tube 22 which is a value divided by the outer surface area of ^{2 is} less than 0.5 W / cm ² , the temperature of the glass tube and the heater wire will drop too much even if the calorific value is the same. The amount of high infrared wavelengths decreases, and the ratio of radiant heat rays directly absorbed by frost decreases, and the peripheral components absorb the radiant heat rays and the temperature rises accordingly, resulting in indirect defrosting, resulting in poor efficiency.

Therefore, the defrosting efficiency is not lowered by setting the rate to 0.5 W / cm ² or more.

In the present embodiment, the characteristic of the outer surface temperature of the glass tube 22 with respect to the outer surface heat flux of the glass tube 22 has a linear proportional relationship, but various factors such as the volume of the heater wire 23 and the wall thickness of the glass tube 22 are required. Depending on the conditions, there may be a curved relationship.

(Tenth Embodiment) A tenth embodiment of the present invention will be described with reference to the drawings. In addition,
The same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

FIG. 12 is a sectional view of the essential parts of the tenth embodiment of the present invention.

As shown in FIG. 12, F is a heater wire 23.
The longest distance between the surface and the inner surface of the glass tube 22, 0.5
mm.

The operation of the defrost heater constructed as above will be described below.

When the heater 23 generates heat during defrosting, heat is transferred from the heater wire 23 to the glass tube 22 through the air existing in the clearance 31 which serves as a heat insulating layer, and the temperature of the glass tube 22 becomes lower than the ignition temperature of the flammable refrigerant. It rises and radiates heat to the outside air.

At this time, if the outer surface temperature of the glass tube 22 is the same temperature lower than the ignition temperature of the flammable refrigerant, the thickness of the air serving as the heat insulating layer is 0.5 mm. The surface temperature of a certain heater wire 23 can be increased. That is, the amount of heat generated by the defrost heater 18 can be increased.

From the above, it is possible to suppress the deterioration of the object to be cooled by shortening the defrosting time due to the high heat conduction of the flammable refrigerant and to ignite the flammable refrigerant on the outer surface of the glass tube 22 if the flammable refrigerant leaks. In addition to reducing the risk of fire by suppressing the ignition of flammable refrigerant when the temperature is lower than the temperature, the outer surface temperature of the glass tube 22 decreases due to the air serving as a heat insulating layer between the glass tube 22 and the heater wire 23 Since the calorific value can be increased by that amount, the defrosting time can be shortened, the cooling operation can be started early, and the deterioration of the object to be cooled can be suppressed.

In this embodiment, the shortest distance between the surface of the heater wire 23 and the inner surface of the glass tube 22 has been described as 0.5 mm, but if it is longer than this, the amount of heat generation can be further increased. Further effects can be obtained.

Further, due to variations in the dimensions of the glass tube 22 and the heater wire 23, the heater wire 23 can be easily accommodated in the glass tube 22 during manufacturing, and the larger the diameter of the glass tube 22, the more expensive it becomes. Therefore, the shortest distance between the surface of the heater wire 23 and the inner surface of the glass tube 22 is preferably 0.5 mm to 2 mm.

(Eleventh Embodiment) An eleventh embodiment of the present invention will be described with reference to the drawings. In addition,
The same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

In FIG. 2, the transmittance of the glass tube 22 is 60% at a wavelength of 3 to 4 μm, and the peak wavelength when the heater wire 23 generates heat is 3.5 μm.

The operation of the defrosting heater constructed as described above will be described below.

At the time of defrosting, part of the heat generated by the heater wire 23 is radiated from the heater wire 23 as radiant heat rays. Since most of this radiant heat ray has a wavelength of 3.5 μm and the transmittance of the glass tube 22 is 60% at 3.5 μm, most of the radiant heat ray incident on the glass tube 22 passes through the glass tube 22. Since the wavelength of heat radiated directly to the outside and absorption of frost is large, the radiant heat rays are efficiently absorbed by frost. The remaining radiant heat rays that do not pass through are absorbed by the glass tube 22, and the heat is transferred from the outer surface of the glass tube 22 to the outside by heat transfer / convection.

Here, if the transmittance of the glass tube 22 is less than 60%, the temperature rise due to absorption of radiant heat rays of the glass tube 22 becomes high, and in order to make the temperature below the ignition temperature of the flammable refrigerant, the defrost heater. Since the calorific value of 18 must be reduced, defrosting takes time and is uneconomical.

From the above, it is possible to suppress the deterioration of the object to be cooled by shortening the defrosting time due to the high heat conduction of the flammable refrigerant and to prevent the flammable refrigerant from leaking to the ignition temperature of the flammable refrigerant in case of leakage of the flammable refrigerant. In addition to reducing the risk of fire, the defrosting time is shortened and the cooling operation is started early to suppress deterioration of the object to be cooled.

The transmittance of the glass tube 22 is set to a wavelength of 3-4.
Although it is set to 60% in μm, a glass tube having a transmittance of more than 97% has a high production cost, so that the range of 60 to 97% is economically suitable.

(Embodiment 12) Embodiment 12 of the present invention will be described with reference to the drawings. In addition,
The same components as those in the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

At the time of defrosting, the compressor 19 is stopped and the defrosting heater 18 and the auxiliary heater 37 are energized, and both surfaces are heated to a predetermined temperature lower than the ignition temperature of the flammable refrigerant, whereby the evaporator 10 After that, the compressor 19 is activated and cooling is started.

The heat generated by the defrosting heater 18 causes the evaporator 10 to move.
Heat is transferred from a portion close to the defrost heater 18 to melt the frost, and at the same time, heat generated by the auxiliary heater 37 heats a distant portion from which heat is hardly transferred from the defrost heater 18, thereby defrosting the corresponding frost. Therefore, when defrosting is performed at the same time as in the conventional case, it is possible to reduce the heat generation amount of the defrosting heater 18, and the auxiliary heater 37 serves as the evaporator 1.
Since it is in contact with 0, the melting point of frost is 0 ° C during defrosting.
It becomes a low temperature close to the neighborhood.

From this, it is possible to maintain the defrosting ability equivalent to that of the conventional one and to lower the temperature to below the ignition temperature of the combustible refrigerant, so that it is possible to save energy by reducing the calorific value, and the combustible refrigerant is used for the defrost heater 18 Even if defrosting is performed when it leaks to the atmosphere, the risk of ignition can be further reduced.

In the present embodiment, the auxiliary heater 3
Although not specified, 7 is a heater for heating such as a pipe heater, a line heater, and a sheath heater.

Further, in the present embodiment, the auxiliary heater is in contact with the entire evaporator 10, but may be installed without contacting the evaporator 10, and it is not necessary to install it in the entire evaporator 10 and defrosting is not necessary. Should be installed so that

[0115]

As described above, the present invention is a means for defrosting the evaporator of the refrigeration cycle in which the compressor, the condenser, the decompression mechanism and the evaporator are functionally connected to each other and the flammable refrigerant is enclosed. There is a first glass tube, a heater wire made of a metal resistor inside the first glass tube, and a second glass tube located at the outermost contour of the first glass tube to cover the first glass tube with a space. A sealing means for suppressing outside air from entering both ends of the first and second glass tubes, and
The surface is below the ignition temperature of the flammable refrigerant, and the first and second
Since it is a defrost heater in which an air layer is present between glass tubes and the inner diameter of the second glass tube is 1.5 to 3 times the outer diameter of the first glass tube, it is a flammable refrigerant. The defrosting time can be shortened due to the high heat conduction, and in the unlikely event that the flammable refrigerant leaks, the outer surface temperature of the outermost glass tube is lowered and the ignition of the flammable refrigerant can be suppressed.

Further, it is possible to suppress the flame propagation from the inside to the outside of the defrost heater when the internal space sectional area of the defrost heater is regulated.

Further, it is possible to suppress the excessive temperature rise of the heater wire due to the excessive heat insulation of the space between the glass tubes.

Further, since the thickness of the second glass tube is larger than that of the first glass tube, it is possible to suppress the occurrence of cracks in the second glass tube during transportation and installation, and in the unlikely event that a flammable refrigerant is used. When the flammable refrigerant leaks, it is possible to suppress the flammable refrigerant flowing into the defrosting heater and the flame propagation to the outside air when the flammable refrigerant flows into the defrosting heater and ignites.

Further, since the centers of the diameters of the first glass tube and the second glass tube are eccentric, the portion to be defrosted most is the shortest distance between the first glass tube and the second glass tube. Defrosting can be made uniform by installing it in the vicinity of a distance, and defrosting time can be shortened.

If the first glass tube and the second glass tube are installed so that the distance between the first glass tube and the second glass tube is larger in the upper side than in the lower side, the difference between the upper and lower temperatures of the outer surface temperature of the second glass tube is reduced. Since the temperature can be made uniform near the upper and lower average temperatures, the heat generation amount of the defrosting heater can be increased by the amount of decrease in the maximum temperature of the second glass tube, and the defrosting time can be shortened.

[Brief description of drawings]

FIG. 1 is a refrigeration system diagram according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the defrost heater according to the first, ninth, and eleventh embodiments of the present invention.

FIG. 3 is a sectional view of a defrosting heater according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a defrost heater according to Embodiments 3 and 12 of the present invention.

FIG. 5 is a sectional view of a main part of a defrosting heater according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a main part of a defrosting heater according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a main part of a defrost heater according to a fifth embodiment of the present invention.

FIG. 8 is a sectional view of a main part of a defrosting heater according to a sixth embodiment of the present invention.

FIG. 9 is a sectional view of a main part of a defrosting heater according to a seventh embodiment of the present invention.

FIG. 10 is a sectional view of essential parts of a defrost heater according to an eighth embodiment of the present invention.

FIG. 11 is a temperature characteristic diagram of a defrost heater according to the ninth embodiment of the present invention.

FIG. 12 is a sectional view of essential parts of a defrost heater according to a tenth embodiment of the present invention.

FIG. 13 is a refrigeration system diagram in Embodiment 12 of the present invention.

FIG. 14 is a sectional view of a main part of a refrigerator according to a twelfth embodiment of the present invention.

FIG. 15 is a sectional view of a main part of a conventional refrigerator.

[Explanation of symbols]

10 evaporator 18 Defrost heater 19 compressor 20 condenser 21 Decompression mechanism 22 glass tube 23 heater wire 26 sealing means 28 Internal space 29 First glass tube 30 Second glass tube 37 Auxiliary heater

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikihiro Nakayama 2-3-3 Noji Higashi, Kusatsu City, Shiga Matsushita Refrigerating Machinery Co., Ltd. (72) Kenji Takaichi 2 Noji Higashi, Kusatsu City, Shiga Prefecture No. 3 1-2, Matsushita Refrigerator Co., Ltd. (56) Reference JP 2000-329447 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F25D 21/08

Claims (5)

(57) [Claims] 1. A means for defrosting an evaporator of a refrigeration cycle in which a compressor, a condenser, a pressure reducing mechanism, and an evaporator are functionally connected to each other and a flammable refrigerant is enclosed, and a first glass tube, and A heater wire made of a metal resistor inside the first glass tube, a second glass tube positioned at the outermost portion of the first glass tube for covering the first glass tube with a space, and the first and second glass tubes. ends and a sealing means for suppressing ambient air enters the front
Note that the surface of the second glass tube is below the ignition temperature of the flammable refrigerant.
Then, an air layer is present between the first and second glass tubes,
A defrost heater in which the inner diameter of the second glass tube is 1.5 to 3 times the outer diameter of the first glass tube. 2. The defrost heater according to claim 1, wherein the thickness of the second glass tube is larger than that of the first glass tube. 3. A refrigerator provided with the defrost heater according to claim 1 or 2. 4. The defrost heater according to claim 1, wherein the centers of the diameters of the first glass tube and the second glass tube are eccentric. 5. The refrigerator provided with the defrost heater according to claim 4, wherein the distance between the first glass tube and the second glass tube is larger at the upper side than at the lower side.