EP1369650B1

EP1369650B1 - Refrigerator

Info

Publication number: EP1369650B1
Application number: EP02705107A
Authority: EP
Inventors: Masahiro Nakayama; Yuji Kishinaka; Kiyonori Yamamoto; Akira Yokoe
Original assignee: Panasonic Corp
Current assignee: Panasonic Corp
Priority date: 2001-03-13
Filing date: 2002-03-13
Publication date: 2009-06-24
Anticipated expiration: 2022-03-13
Also published as: CN100439831C; JP2002267331A; CN1327177C; KR100600185B1; HK1075696A1; EP1369650A1; EP1793186A3; CN1620585A; EP1793186A2; CN1940419A; DE60232715D1; WO2002073106A1; EP1793186B1; CN1945177A; CN100513949C; EP1369650A4; TW539838B; KR20030094279A

Description

TECHNICAL FIELD

The present invention relates to defrosting for a refrigerator employing a combustible refrigerant.

BACKGROUND ART

As a prior-art refrigerator, Japanese Patent Non-examined Publication No. H8-54172 discloses a refrigerator using a combustible refrigerant. First will be described the prior-art refrigerator with reference to drawings. Fig. 8 shows a vertical sectional view illustrating the essential part of a prior-art refrigerator.
In Fig. 8, refrigerator 1 has freezer compartment 2 and cold-storage compartment 3 therein, and to which, freezer door 4 and storage door 5 are fixed, respectively. Freezer compartment 2 and cold-storage compartment 3 are separated by dividing wall 6. The air in freezer compartment 2 is captured through inlets 7, and the air in cold-storage compartment 3 is captured through inlet 8. Outlet 9 blows cold air into freezer compartment 2. The cold air is circulated by fan 11. Evaporator dividing wall 12 is disposed between freezer compartment 2 and evaporator 10. Glass-tube heater 15 for defrosting has a structure in which a coiled nichrome-wire is covered with a glass tube. Roof 16 protects heater 15 from being directly hit by a drip of melted frost that will give a sputter sound on evaporation. Metallic bottom plate 17 is disposed, in insulation, between dripping pan 13 and heater 15. Accumulator 18 is disposed at the exit of evaporator 10.
Now will be described how the aforementioned prior-art refrigerator works.
When cooling the freezer compartment 2 and cold-storage compartment 3, evaporator 10 is cooled by a refrigerant flowing through evaporator 10. At the same time, fan 11 expels warmed air in freezer compartment 2 through inlet 7, similarly, expels warmed air in cold-storage compartment 3 through inlet 8, into cooling chamber 20. The warmed air is cooled at evaporator 10 by heat exchange, and then supplied through outlet 9 to freezer compartment 2. At the same time, a portion of the cooled air is fed from freezer compartment 2 through a communication opening (not shown) to cold-storage compartment 3. The air that does heat-exchange at evaporator 10 has high moisture due to the air flown from outside into the refrigerator each time door 4 or door 5 is opened, and due to evaporation of moisture from stored foods in both compartments. Therefore, the moisture in the warmed air turns into frost on evaporator 10 where the temperature is lower than the air. Accumulator 18 works to constantly feed refrigerant in cooling cycle operations. In addition, accumulator 18 protects a compressor from damage caused by direct return of liquid refrigerant, or minimizes a flowing noise of the refrigerant.
The more increase the amount of the frost on evaporator 10, the less increase the efficiency of heat-exchange between the surface of evaporator 10 and the air to be cooled. Further, the buildup of the frost blocks a smooth airflow, inviting insufficient cooling. To eliminate said inconveniencies, the application of heat has been employed for defrosting - passing an electric current through the nichrome-wire in the glass-tube heater 15 and, with heat rays emitted therefrom, melting the frost into water around evaporator 10, dripping pan 13, and drainage hole 14.
The water is collected into dripping pan 13; the dripping water partly goes directly down into pan 13, and partly hits roof 16 as a guard of heater 15 and then down into pan 13. The water collected in pan 13 is drained through drainage hole 14 to the outside. On the application of heat, some of the heat rays radiated from heater 15 toward dripping pan 13 are reflected off bottom plate 17 and then scattered toward evaporator 10.
However, such structured conventional refrigeration cycle employing a combustible refrigerant has problems below. A combustible refrigerant has relatively large latent heat. In pipe arrangement of evaporator 10 where the combustible refrigerant stays for a period, such a property of the refrigerant invites insufficient defrosting, thereby leaving frost in the pipe arrangement. As a result, residual frost hampers heat transfer, resulting in poor refrigeration.
Besides, not only the nichrome-wire, but also the surface of the glass-tube heater has highly heated surfaces. The fact has been facing a problem; if a combustible refrigerant leaks at somewhere in the pipe arrangement of evaporator 10, the heat generated from heater 15 can trigger catching fire.
The patent application JP 2000 266450 A discloses a refrigerator comprising: a combustible-refrigerant-sealed refrigeration cycle having successive connections of following elements: a compressor, a condenser, a pressure reduction mechanism, and an evaporator; and means for defrosting the evaporator, wherein the defrosting means is formed of at least one glass-tube heater disposed below the evaporator having an out-of-contact arrangement with the evaporator.

DISCLOSURE OF THE INVENTION

The present invention addresses the problem above. It is therefore the object to provide a refrigerator equipped with a defrosting means capable of: not only presenting a combustible refrigerant from catching fire even if the defrosting operation is performed in an environment where leakage of the combustible refrigerant occurs at somewhere in the area having the defrosting means, but also improving a poor refrigeration due to residual frost.
The refrigerator of the present invention contains a refrigeration cycle and a defrosting means. The refrigeration cycle has successive connections of the following elements: a compressor; a condenser; a pressure reduction mechanism; and an evaporator. A combustible refrigerant is sealed in the refrigeration cycle. The defrosting means is formed of a plurality of glass-tube heaters.
The structure above can suppress an input for each glass-tube heater when the evaporator and its surroundings are heated by the glass-tube heaters in the defrosting operation. This allows the surface temperature of the glass-tube heater to maintain below a temperature at which the combustible refrigerant can catch fire. As another plus, effective heating on the area having a large amount of frost can provide a uniform defrosting, thereby enhancing the efficiency of defrosting and eliminating residual frost.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic view illustrating the refrigeration cycle of a refrigerator in accordance with a first exemplary embodiment.
Fig. 2 is a vertical sectional view showing the essential part of the refrigerator of the first exemplary embodiment, the refrigerator not being part of the invention.
Fig. 3 is a schematic view illustrating the essential part of the refrigerator shown in Fig. 2.
Fig. 4 is a sectional view of a glass-tube heater, with the essential part enlarged, of the refrigerator shown in Fig. 2.
Fig. 5 is a vertical sectional view showing the essential part of a refrigerator of a second exemplary embodiment being not part of the invention.
Fig. 6 is a vertical sectional view showing the essential part of a refrigerator of a third exemplary embodiment according to the invention.
Fig. 7 is a vertical sectional view showing the essential part of a refrigerator of a fourth exemplary embodiment according to the invention.
Fig. 31 is a sectional view illustrating the essential part of a prior-art refrigerator.

DETAILED DESCRIPTION OF CARRYING OUT OF THE INVENTION

The exemplary embodiments of the present invention are described hereinafter with reference to the accompanying drawings.

FIRST EXEMPLARY EMBODIMENT

Fig. 1 shows a schematic view illustrating the refrigeration cycle of a refrigerator in accordance with the first exemplary embodiment of the present invention. Fig. 2 is a vertical sectional view showing the essential part of the refrigerator of the first exemplary embodiment. Fig. 3 is a schematic view illustrating the essential part of the refrigerator shown in Fig. 2. Fig. 4 is a sectional view of a glass-tube heater, with the essential part enlarged, of the refrigerator shown in Fig. 2.
In Fig. 1, refrigeration cycle 301 has successive connections of the following elements: compressor 302, condenser 303, pressure reduction mechanism 305, and evaporator 306. A combustible refrigerant is sealed in refrigeration cycle 301. Besides, defrosting means 307 is disposed close to evaporator 306.
Here will be described the structure of an exemplary refrigerator having the refrigeration cycle shown in Fig. 1, with reference to Figs. 2 through 4.
In Figs. 2 through 4, the refrigerator of the first embodiment contains two glass- tube heaters 19a and 19b as an example of the defrosting means shown in Fig. 1. Each heater has a structure in which heater wire 24 made of metallic material, such as nickel chrome, is formed into a spiral shape and then inserted in a glass tube. Heaters 19a and 19b are placed below evaporator 1 in a side-by-side arrangement; more specifically, heater 19a is disposed close to lowermost pipe 21 of evaporator 10. In explanations will be given from now on, glass- tube heaters 19a and 19b may often be referred to glass-tube heater 19 as a unit.
In cooling chamber 20, as shown in Fig. 2, evaporator 10, fan 11, roof 16, and glass-tube heater 19 are disposed. A pair of supporting members 22, each one is disposed at each end of heater 19, fixes heater 19a together with heater 19b.
Hereinafter will be described the workings of a refrigerator having aforementioned structure of the first exemplary embodiment.
After the expiration of a predetermined time interval, fan 11 stops to remove frost from evaporator 10, and a refrigerant stops flowing through evaporator 10. After that, the electric current is supplied through glass-tube heater 19 for generating heat to melt the frost on evaporator 10. When a defrost-completion detector (not shown) detects the completion of defrosting, the current-supply to heater 19 is stopped, so that defrosting operation completes.
When fan 11 comes to a stop, the combustible refrigerant liquid in evaporator 10 flows down, by its own weight, to lowermost pipe 21 that collects higher amounts of the refrigerant than other pipes in evaporator 10. After that, heat generated from first glass-tube heater 19a evaporates the high amounts of the combustible refrigerant having high latent heat in the pipe.
In the process, heater 19a, which is located near by lowermost pipe 21, encourages to evaporate the high amounts of the combustible refrigerant in the pipe at the lower section of evaporator 10. With the application of heat, the combustible refrigerant is changed into hot gas, moving up toward the pipes in the upper section of evaporator 10. The pipes in the upper section of evaporator 10 are kept cool due to the frost on evaporator 10. The hot gas of the refrigerant moved from the lower section is now cooled by the pipes and the fan and changed into liquid. For turning into liquid, the hot gas radiates the heat toward frost deposited on the upper section of evaporator 10. Defrosting is thus carried out. In the process, the gaseous combustible refrigerant, due to its high latent heat, radiates a large amount of heat required for changing into liquid, whereby the defrosting is accelerated. In this way, a thermo-siphon effect facilitates the defrosting of evaporator 10. At the same time, direct radiation of the heat generated from heater 19 melts the frost on evaporator 10 and peripheral components and walls. Besides, the ambient air warmed up by the heat moves around. All the actions above contribute to a thorough defrosting of evaporator 10.
On the other hand, second glass-tube heater 19b is disposed, next to first glass-tube heater 19a, below evaporator 10. That is, by virtue of the structure having plural heaters, the application of an electric current per heater can be smaller than that in the prior-art structure. This allows the surface temperature of a glass-tube heater to keep lower than the ignition temperature of the combustible refrigerant; in the case of employing isobutane as the refrigerant, the surface temperature of the heater can be kept below 460 °C. Generally, an amount of radiation is proportional with the surface area of a hot body. Compared to a structure with a single heater, a structure formed of a plurality of heaters 19 has larger surface area, accelerating heat-transfer to evaporator 10. Furthermore, the structure with plural heaters can effectively heat the lower section of the evaporator having high amounts of frost, ensuring a uniform defrosting. This enhances defrosting efficiencies, eliminating residual frost.
As described above, the thermo-siphon effect of the combustible refrigerant in the pipes, and heat directly radiated from heaters 19a and 19b contribute to uniform defrosting the entire surfaces of evaporator 10, enhancing defrosting efficiencies, as well as eliminating residual frost. Besides, disposing a plurality of glass-tube heaters (19a, 19b) can save the operating time per heater 19a (19b); accordingly, the radiating period of each heater is shortened. This ensures that the surface temperature of the heaters 19a and 19b is kept enough below the ignition temperature of the combustible refrigerant. Furthermore, a pair of supporting members holds glass- tube heaters 19a and 19b so as to be an integrated structure, providing not only a simple structure but also easy assembling work.
The refrigerator of the first exemplary embodiment, as described above, provides a structure having a plurality of glass-tube heaters for defrosting the evaporator. Thereby, the temperature of each glass-tube heater during the passage of an electric current can be kept lower than the ignition temperature of the combustible refrigerant. That is, defrosting can be carried out at temperatures below the ignition temperature of the refrigerant, without degradation in the efficiency of defrosting. The refrigerator of the embodiment not only can prevent a combustible refrigerant from catching fire even if the defrosting operation is performed in an environment where leakage of the combustible refrigerant occurs at somewhere in the area having defrosting means, but also can improve a poor refrigeration due to residual frost.

SECOND EXEMPLARY EMBODIMENT not forming part of the invention.

Fig. 5 is a vertical sectional view showing the essential part of a refrigerator of the second exemplary embodiment.
The second embodiment differs from the first embodiment in the following points.
In Fig. 5, a plurality of glass-tube heaters is located in opposed positions, sandwiching evaporator 10 therebetween. To be more specific, first glass-tube heater 25a is disposed at a position lower than evaporator 10; on the other hand, second glass-tube heater 25b is disposed at a position higher than evaporator 10 and close to accumulator 18.
Hereinafter will be described the workings of a refrigerator having the structure above.
As is the description in the first embodiment, the combustible refrigerant liquid in evaporator 10 flows down, by its own weight, to lowermost pipe 21 that collects higher amounts of the refrigerant than other pipes in evaporator 10. After that, heat generated from glass-tube heater 25a heats up the combustible refrigerant collected in the lowermost pipe and its vicinity. With the application of heat, the combustible refrigerant is changed into hot gas, moving up toward the pipes disposed in the upper section of evaporator 10. The hot gas of the refrigerant carried from the lower section is now cooled and again changed into a liquid by the pipes and radiation fins of the evaporator. For changing into liquid, the hot gas radiates the heat toward frost deposited on the upper section of evaporator 10. The refrigerant liquid flows down to lowermost pipe 21. In this way, repeating the thermo-siphoned cycle thus carries out defrosting of the evaporator.
Due to structural difference in evaporator 10, an amount of the combustible refrigerant may not leave accumulator 18 for lowermost pipe 21. Such a position where the refrigerant tends to stay-on will be a slow-defrosted area. In the structure of the embodiment, however, heater 25b disposed above evaporator 10 can heat up the stay-on position, thereby shortening the defrosting time. In this way, the structure can uniformly remove frost from the evaporator and its surroundings, thereby enhancing the efficiency of defrosting and therefore eliminating residual frost. Furthermore, defrosting completes in a shortened operation-time of the glass-tube heater, which contributes to a power saving.
According to the refrigerator of the second embodiment, as described above, the glass-tube heaters have an opposing location via the evaporator; one is disposed above, the other is disposed under the evaporator. The arrangement of the heaters allows the evaporator to be uniformly heated up from the top and the bottom. Besides, the structure having plural heaters allows an individual heater to have small heating value, thereby keeping the surface temperature of the heater below the ignition temperature of the combustible refrigerant. The uniform defrosting enhances the efficiency of defrosting, contributing to energy conservation. Furthermore, the accumulator, which is located above the evaporator, can be properly defrosted without residual frost. In this way, the refrigerator of the embodiment not only can prevent a combustible refrigerant from catching fire even if the defrosting operation is performed in an environment where leakage of the combustible refrigerant occurs at somewhere in the area having the defrosting means, but also can improve a poor refrigeration due to residual frost.
A slow-defrosting area may vary according to the structure of an evaporator. In this case, the second glass-tube heater can be disposed close to the area where frost persists.
The glass-tube heaters can be placed in an opposite arrangement in a widthwise direction of the evaporator; one is in front of, and the other is at rear of the evaporator. The arrangement can protect glass-tube heater 25a against direct dripping-down of melted frost from evaporator 10. Thereby, roof 16 can be removed from the structure.

THIRD EXEMPLARY EMBODIMENT

Fig. 6 is a vertical sectional view showing the essential part of a refrigerator of the third exemplary embodiment.
The structure of the third embodiment differs from those of the aforementioned embodiments in the following point.
In Fig. 6, first glass-tube heater 26a is disposed below evaporator 10; on the other hand, second glass-tube heater 26b is disposed at an intermediate position in evaporator 10.
Hereinafter will be described the workings of a refrigerator having the structure above.
In the defrosting operation, an electric current is fed through heater 26b, as well as heater 26a. Most of the heat from heater 26a by the passage of electric current directly heats up, as radiant heat, evaporator 10. The hot surface of the glass-tube heater 26a warms up the ambient air to go upward, as an upward-moving stream, along evaporator 10. The upward-moving hot air warms up frosted evaporator 10 from the bottom toward the upper sections. At the same time, heat radiated from heater 26b disposed within evaporator 10 heats up a low-temperature area in the mid toward the upper sections.
Of radiant heat from heater 26a disposed below evaporator 10, upwardly radiated heat directly warms up evaporator 10; while downwardly radiated heat reaches the evaporator as reflection off dripping pan 13. On the other hand, heater 26b, since it is located inside evaporator 10, can directly heat up evaporator 10 in upward and downward (or frontward and backward) directions. The arrangement of the heaters can provide the evaporator with a rapid and uniform defrosting, allowing the surface temperature of the glass-tube heaters to keep below the ignition temperature of the combustible refrigerant. In this way, the refrigerator of the embodiment not only can prevent a combustible refrigerant from catching fire even if the defrosting operation is performed in an environment where leakage of the combustible refrigerant occurs at somewhere in the area having the defrosting means, but also can improve a poor refrigeration due to residual frost.

FOURTH EXEMPLARY EMBODIMENT

Fig. 7 is a vertical sectional view showing the essential part of a refrigerator of the fourth exemplary embodiment.
The structure of the fourth embodiment differs from those of the aforementioned embodiments in the following points.
In Fig. 7, first glass-tube heater 27a is disposed below evaporator 10; on the other hand, second glass-tube heater 27b is disposed either in front of or behind of evaporator 10. Evaporator 10 has indent 28 at a part of the fins to place heater 27b. Besides, heater 27a disposed below evaporator 10 has a capacity larger than that of heater 27b that is located higher than heater 27a.
Hereinafter will be described the workings of a refrigerator having the structure above.
The defrosting operation begins with the application of an electric current to heaters 27a and 27b. Heater 27a, which is disposed below evaporator 10, defrosts the evaporator upwardly from the bottom. On the other hand, heater 27b disposed at the front (or the behind) of evaporator 10 warms up a low-temperature area - the area having a slow-rise in temperature despite of the thermo-siphon effect in evaporator 10 - and effectively removes the frost from the surface of evaporator 10. In addition, by virtue of having a capacity larger than heater 27b, heater 27a can properly defrost the bottom of evaporator 10 having a large amount of frost, thereby enhancing the defrost efficiency. That is, the quick and uniform defrosting can suppress the surface temperature of glass- tube heaters 27a and 27b below the ignition temperature of the combustible refrigerant. As a result, the refrigerator of the embodiment not only can prevent a combustible refrigerant from catching fire even if the defrosting operation is performed in an environment where leakage of the combustible refrigerant occurs at somewhere in the area having the defrosting means, but also can improve a poor refrigeration due to residual frost.
Indent 28 is formed at a part of the fins of evaporator 10 so as to accept heater 27b that is placed either in the front of or behind the evaporator. The arrangement can minimize waste space caused by installing heater 27b.
In addition, the arrangement - regardless of whether heater 27b is disposed at the front, or at the behind of the evaporator - is effective in protecting heater 27b from a drip of melted frost. Accordingly, the structure can do away with the need to additional installment of the roof, which can be a barrier to air course when fan 11 is in operation.

INDUSTRIAL APPLICABILITY

The refrigerator of the present invention has a plurality of glass-tube heaters as a means for defrosting the evaporator that is disposed in a combustible refrigerant-sealed refrigeration cycle. A current-carrying period or an application of voltage to the glass-tube heater is controlled so that the temperature of the heater is kept below the ignition temperature of a combustible refrigerant. This not only protects the combustible refrigerant from the risk of catching fire, but also avoids poor refrigeration caused by residual frost. In a structure of the invention, a glass-tube heater makes contact with fins of the evaporator to decrease the surface temperature of the glass-tube heater. In another structure of the invention, the glass-tube heater has a tube-in-tube structure, and a sealing member is disposed on an end of the glass tube. Such structures can protect a combustible refrigerant from the risk of catching fire even if the defrosting operation is carried out in an environment where leakage of the combustible refrigerant occurs.

Reference numerals in the drawings

10: Evaporator
19, 19a, 19b: Glass-tube heater
25a, 26a, 27a: First glass-tube heater
25b, 26b, 27b: Second glass-tube heater

301: Refrigeration cycle
302: Compressor
303: Condenser
305: Pressure reduction mechanism
306: Evaporator
307: Defrosting means

Claims

A refrigerator comprising:
a combustible-refrigerant-sealed refrigeration cycle (301) having successive connections of following elements: a compressor (302), a condenser (303), a pressure reduction mechanism (305), and an evaporator (306); and

means (307) for defrosting the evaporator (306) including one glass-tube heater (26a) disposed below the evaporator (306),

characterized in that

the defrosting means (307) further include another glass-tube heater (26b) disposed within the evaporator (306).
The refrigerator of claim 1, wherein
said another glass-tube heater is disposed in an upper section of the evaporator; and
the glass-tube heater which is located below the evaporator has a capacity value greater than that of the another glass-tube heater.