Refrigerating System Using Non-Azeotropic Mixed Refrigerant

This application is a Continuation of U.S. application Ser. No. 17/634,917 filed on Feb. 11, 2022 now allowed, which is a National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2020/011140, with an international filing date of Aug. 20, 2020, which claims priority to Korean Application No. 10-2019-0102341, filed on Aug. 21, 2019, all of which are incorporated by reference in their entirety herein.

A refrigerating system using a non-azeotropic mixed refrigerant is disclosed herein.

A refrigerating system is a system that provides cold air. In the refrigerating system, a refrigerant circulates through compression, condensation, expansion, and evaporation processes.

There are various types of refrigerants. A mixed refrigerant is a refrigerant in which two or more types of refrigerants are mixed. Mixed refrigerants include azeotropic mixed refrigerant and non-azeotropic mixed refrigerant.

The azeotropic mixed refrigerant is a refrigerant that changes phase without changing a composition of a gas phase and a liquid phase, similar to a single refrigerant. An evaporation temperature of the azeotropic mixed refrigerant is constant between an inlet and an outlet of the evaporator.

In the non-azeotropic mixed refrigerant, a refrigerant having a low boiling point evaporates first, and a refrigerant having a high boiling point evaporates later. Therefore, the non-azeotropic mixed refrigerant has different gas phase and liquid phase compositions during evaporation, and the evaporation temperature is low at the inlet of the evaporator and high at the outlet of the evaporator.

The non-azeotropic mixed refrigerant has a gliding temperature difference (GTD), which is a characteristic in which the temperature changes at equal pressure during phase change. Therefore, an evaporation operation of the non-azeotropic mixed refrigerant is divided into two evaporators. The first evaporator may be used for a freezer compartment, and the second evaporator through which the refrigerant having passed through the first evaporator may be used for a refrigerating compartment. The freezer compartment maintains a lower temperature than the refrigerating compartment. A multi-stage evaporator may be provided to increase a performance coefficient of the refrigerating system.

Documents that discloses such a refrigerating system are Korean Patent No. 2011-0115911 (hereinafter “Prior Art Document 1”) entitled “Refrigerating apparatus using non-azeotropic mixed refrigerant and control method thereof” and U.S. Patent Publication No. 2015/0096325 (hereinafter “Prior Art Document 2”) entitled “Refrigerators with a non-azeotropic mixtures of hydrocarbons refrigerants”, which are both hereby incorporated by reference. Prior Art Document 1 discloses a refrigerating apparatus including one compressor, two evaporators connected in series to the compressor, and a three-way valve located between the two evaporators to bypass a refrigerant introduced into a downstream refrigerating compartment evaporator.

According to Prior Art Document 1, the refrigerant that has passed through an upstream freezer compartment evaporator is introduced into the three-way valve. As the refrigerant discharged from the freezer compartment evaporator is at an extremely low temperature reaching −20° C., there are problems, such as loss of cold air through the three-way valve located at an outside and the occurrence of frost on the outer surface of the three-way valve. In addition, an operation of cooling the refrigerating compartment alone may be impossible in terms of the position of the three-way valve.

Prior Art Document 2 discloses a refrigerating apparatus including one compressor, two evaporators connected in series to the compressor, and two heat exchangers in which refrigerant discharged from the two evaporators exchange heat with capillary tubes that expand the refrigerant. According to Prior Art Document 2, the operation of the freezer compartment or the refrigerating compartment alone is impossible. That is, only simultaneous operation of cooling the freezer compartment and the refrigerating compartment is possible. In addition, the refrigerating compartment evaporator into which the refrigerant discharged from the freezer compartment evaporator is introduced may be overcooled.

Embodiments disclosed herein provide a refrigerating system using a non-azeotropic mixed refrigerant, capable of implementing various operation modes. Embodiments disclosed herein provide a refrigeration system using a non-azeotropic mixed refrigerant, capable of further increasing a performance coefficient of the refrigerating system when the non-azeotropic mixed refrigerant is used. Embodiments disclosed herein provide a refrigerating system using a non-azeotropic mixed refrigerant to stably maintain a state of a refrigerant.

According to embodiments disclosed herein, a refrigerating system may include a capillary tube configured to expand a non-azeotropic mixed refrigerant branched by a three-way valve and supply the expanded non-azeotropic mixed refrigerant to at least one of a first evaporator or a second evaporator. As the refrigerant may be supplied to any one of evaporators downstream of a three-way valve, the refrigerating system may be stably operated in various modes.

As a refrigerant outlet side of the first evaporator is connected to a refrigerant inlet side of the second evaporator by a connection pipe, the first evaporator and the second evaporator may supply cold air of an optimal state using a gliding temperature difference of the non-azeotropic mixed refrigerant supplied to the first evaporator. Further, as the connection pipe is provided with a check valve configured to allow the refrigerant to flow from the first evaporator to the second evaporator, reverse flow of the refrigerant may be prevented when an operation mode is switched.

The refrigerating system may include a compressor suction pipe configured to connect an outlet side of the second evaporator to an inlet side of the compressor, such that a circulating process of the non-azeotropic mixed refrigerant may be stably performed. A gas-liquid separator may be located in the compressor suction pipe, and only gas of evaporated refrigerant may be stably circulated toward the compressor. The capillary tube may include a first capillary tube configured to connect the three-way valve to a refrigerant inlet side of the first evaporator and a second capillary tube configured to connect the three-way valve to the refrigerant inlet side of the first evaporator, such that each refrigerant amount corresponding to a refrigeration capacity may be expanded.

The refrigerating system may include a regenerative heat exchanger in which at least one of at least a part or portion of the first capillary tube and at least a part or portion of the second capillary tube comes into contact with at least a part or portion of the compressor suction pipe to exchange heat with each other, thereby increasing efficiency of the refrigerating system. The regenerative heat exchanger may include a heat exchange region in which at least one of the at least the part or portion of the first capillary tube and the at least the part or portion of the second capillary tube exchanges heat with at least the part or portion of the compressor suction pipe, and a shielding region in which at least one of the at least the part or portion of the first capillary tube and the at least the part or portion of the second capillary tube is shielded not to exchange heat with the at least the part or portion of the compressor suction pipe. Therefore, optimal regenerative heat exchange may be performed according to a gliding temperature difference of the non-azeotropic mixed refrigerant, and thus, efficiency of the refrigerating system may be increased.

The shielding area may be a distance from a point (point T) to the evaporator, the point (point T) being a point at which a temperature of the non-azeotropic mixed refrigerant flowing through the capillary tube is lower than a temperature of the non-azeotropic mixed refrigerant flowing through the compressor suction pipe. Temperature reversal may be prevented to increase the heat exchange efficiency of the evaporator. As the temperature at the point T is within a range of −5° C. to 5° C., it is possible to check the heat exchange reversal point of the non-azeotropic mixed refrigerant and prevent the temperature reversal using the checked heat exchange reversal point.

As the shielding region is included within about 1 m or less from an outlet of the capillary tube and an inlet of the compressor suction pipe, regenerative heat exchange may be promoted and reduction of heat exchange efficiency due to temperature reversal may be prevented. As the non-azeotropic mixed refrigerant includes isobutane and propane, energy consumption efficiency of the refrigerating system may be improved.

According to another embodiment disclosed herein, a refrigerating system may include a compressor configured to compress a non-azeotropic mixed refrigerant, a condenser configured to condense the compressed non-azeotropic mixed refrigerant, an expander configured to expand the condensed non-azeotropic mixed refrigerant, an evaporator configured to evaporate the expanded non-azeotropic mixed refrigerant to supply cold air, and discharge the non-azeotropic mixed refrigerant to the compressor, and a regenerative heat exchanger configured to exchange heat between the non-azeotropic mixed refrigerant discharged from the evaporator and the non-azeotropic mixed refrigerant flowing through the expander, thereby improving heat efficiency of the refrigerating system. The regenerative heat exchanger may include a heat exchange region in which the evaporator and the expander contact each other and the non-azeotropic mixed refrigerant flowing through an inside of the evaporator exchanges heat with the non-azeotropic mixed refrigerant flowing through an inside of the expander, and a shielding region in which the evaporator and the expander are shielded from each other and the non-azeotropic mixed refrigerant flowing through the inside of the evaporator does not exchange heat with the non-azeotropic mixed refrigerant flowing through the inside of the expander. In this manner, heat exchange between the non-azeotropic mixed refrigerant may be controlled to improve heat efficiency of the refrigerating system.

According to another embodiment disclosed herein, a refrigerating system may include a compressor configured to compress a non-azeotropic mixed refrigerant, a condenser configured to condense the compressed non-azeotropic mixed refrigerant, an expander configured to expand the condensed non-azeotropic mixed refrigerant, at least two evaporators configured in series to evaporate the expanded non-azeotropic mixed refrigerant to supply cold air, and a three-way valve configured to branch the refrigerant condensed by the condenser to at least two branches and supply the branched refrigerant to the expander. Therefore, as the non-azeotropic mixed refrigerant flows through an optimal passage according to an operation mode of the refrigerating system, it is possible to appropriately cope with the operation mode. The three-way valve may perform a mode in which the non-azeotropic mixed refrigerant is supplied to an upstream evaporator of the at least two evaporators, such that the at least two evaporators supply cold air. Therefore, a flow rate of the refrigerant circulating through the refrigerating system is controlled such that a large amount of refrigerant flows, thereby operating the refrigerating system in response to the freezing/refrigerating mode.

The upstream evaporator of the at least two evaporators supplies cold air of a temperature lower than a downstream evaporator of the at least two evaporators. Therefore, irreversible loss during heat exchange may be reduced to obtain higher operating efficiency of the refrigerating system.

The downstream evaporator of the at least two evaporators may not supply cold air, and only the upstream evaporator may supply cold air. In this case, the refrigerant may flow through the downstream evaporator, but may not be used for supply of cold air.

The three-way valve may be operated such that only one of the at least two evaporators supplies cold air. Therefore, it may be operated in a freezing mode, a refrigerating mode, or a freezing/refrigerating mode.

The three-way valve may perform only a freezing mode by directly supplying the non-azeotropic mixed refrigerant to the downstream evaporator. The expander may be placed on a refrigerant inlet side of each of the at least two evaporators. The non-azeotropic mixed refrigerant may be expanded in response to each mode of the refrigerating system.

According to embodiments disclosed herein, it is possible to satisfy various operation modes required in a refrigerating apparatus, such as simultaneous operation of a freezer compartment and a refrigerating compartment and operation of the refrigerating compartment alone.

According to embodiments disclosed herein, a coefficient of performance may be improved by arranging a multi-stage evaporator, and the coefficient of performance may be further improved using flow of a non-azeotropic mixed refrigerant. According to embodiments disclosed herein, in response to a phase change of the refrigerant generated when the multi-stage evaporator is arranged, a state of refrigerant may be stably formed in a liquid phase and a gas phase in accordance with specifications required by the refrigerating system.

Hereinafter, embodiments will be described with reference to the accompanying drawings. The embodiments are not limited to the embodiments discussed hereinafter, and those skilled in the art who understand the spirit will be able to easily propose other embodiments falling within the scope by adding, modifying, and deleting components. However, this also falls within the spirit.

First, a non-azeotropic mixed refrigerant that is preferably applicable is presented. In the description related to the selection of the non-azeotropic mixed refrigerant, contents of the present disclosure are divided into technical elements and described in detail. First, a process of selecting a type of a non-azeotropic mixed refrigerant will be described.

Refrigerants to be mixed, which are suitable for the non-azeotropic mixed refrigerant, are proposed. As the refrigerant to be mixed, a hydrocarbon-based (HC-based) refrigerant may be selected. Hydrocarbon-based refrigerant is an eco-friendly refrigerant having a low ozone depletion potential (ODP) and a low global warming potential (GWP). The criteria for selecting a refrigerant suitable for the non-azeotropic mixed refrigerant among hydrocarbon-based refrigerants may be summarized as follows.

First, from a viewpoint of compression work, when a difference (pressure difference (ΔP)) between a condensing pressure (Pd or p1) and an evaporation pressure (Ps or p2) is smaller, compression work of the compressor is further reduced, which is advantageous for efficiency. Therefore, refrigerants having a low condensing pressure and a high evaporation pressure may be selected. However, considering reliability of compressors, an evaporation pressure of 50 kPa or more may be selected.

Second, from a viewpoint of utilization of production facilities, refrigerants may be selected which have been used in the past for compatibility of existing facilities and components. Third, from a viewpoint of purchase costs of refrigerants, refrigerants obtainable at low cost may be selected. Fourth, from a viewpoint of safety, refrigerants that are not harmful to humans when refrigerant leaks may be selected.

Fifth, from a viewpoint of reducing irreversible loss, reduction of a temperature difference between a refrigerant and cold air so as to increase efficiency of a cycle is desirable. Sixth, from a viewpoint of handling, refrigerants that can be conveniently handled at a time of work and may be conveniently injected by handlers may be selected.

The above criteria for selecting refrigerants is variously applied in selecting the non-azeotropic mixed refrigerant.

Based on evaporation temperature (Tv), candidate refrigerants suggested by the National Institute of Standards and Technology are classified into three (upper, middle, and lower) groups in descending order of evaporation temperature. A density of refrigerant is higher as evaporation temperature increases.

A combination of candidate refrigerants capable of exhibiting an evaporation temperature of −20° C. to −30° C. suitable for the environment of refrigerating apparatuses may be selected. Hereinafter, classification of the candidate refrigerants will be described.

The candidate refrigerants are classified into three types based on boundary values of evaporation temperature, that is, −12° C. and −50° C. The candidate refrigerants classified into the three types are shown in Table 1. It can be seen that the classification of the evaporation temperature changes greatly based on the boundary values.

Referring to Table 1, refrigerants that may be mixed as the non-azeotropic mixed refrigerant may be selected and combined in each region. First, which group is selected among the three groups will be described. There may be one case in which refrigerants are selected from the three groups and three refrigerants are mixed, and three cases in which refrigerants are selected from two groups and two refrigerants are mixed.

When at least one refrigerant is selected from each of the three groups and three or more refrigerants are mixed, the temperature rise and drop in the non-azeotropic mixed refrigerant may be excessively great. In this case, design of the refrigerating system may be difficult.

Thus, the non-azeotropic mixed refrigerant may be obtained by selecting at least one refrigerant from each of two groups. At least one refrigerant may be selected from each of the middle group and the lower group, from each of the upper group and the middle group, and from each of the upper group and the lower group. Among them, a composition in which at least one refrigerant selected from each of the upper group and the middle group is mixed may be provided as the non-azeotropic mixed refrigerant.

When at least one refrigerant selected from each of the middle group and the lower group is mixed, the evaporation temperature of the refrigerant is excessively low. Thus, a difference between interior temperature and the evaporation temperature of the refrigerant is excessively great in a general refrigerating apparatus. Therefore, efficiency of the refrigeration cycle deteriorates and power consumption increases.

When at least one refrigerant selected from each of the upper group and the lower group is mixed, a difference in evaporation temperature between the at least two refrigerants is excessively great. Therefore, unless a special high-pressure environment is created, each refrigerant is classified into a liquid refrigerant and a gaseous refrigerant under actual use conditions. For this reason, it is difficult to inject the at least two refrigerants together into a refrigerant pipe.

Which refrigerant is selected from the upper group and the middle group will be described hereinafter.

First, the refrigerant selected from the upper group will be described. At least one refrigerant selected from the upper group may be used as the non-azeotropic mixed refrigerant.

As isopentane and butadiene have a relatively high evaporation temperature, the inner temperature of the evaporator of the refrigerating apparatus is limited and freezing efficiency deteriorates. Isobutane and N-butane may be used without changing components of the refrigeration cycle, such as the compressor of the refrigerating apparatus, currently used. Therefore, their use is most expected among the refrigerants included in the upper group.

N-butane has a smaller compression work than isobutane, but has a low evaporation pressure (Ps), which may cause a problem in the reliability of the compressor. For this reason, isobutane may be selected from the upper group. As described above, selection of at least one from the other hydrocarbons included in the upper group is permissible.

The refrigerant selected from the middle group will be described hereinafter. At least one refrigerant selected from the middle group may be used in the non-azeotropic mixed refrigerant.

As propadiene has a smaller pressure difference (ΔP) than that of propane, efficiency is high. However, propadiene is expensive and harmful to respiratory systems and skin when humans inhale due to leakage. Propylene has a greater pressure difference than that of propane, and thus, compression work of the compressor is increased.

For this reason, propane may be selected from the middle group. As described above, selection of at least one from the other hydrocarbons included in the middle group is permissible.

For reference, isobutane may also be referred to as R600a, and propane may also be referred to as R290. Although isobutane and propane may be selected, other hydrocarbons belonging to the same group may be applied in obtaining properties of the non-azeotropic mixed refrigerant, even where there is no specific mention in the following description. For example, if it is possible to obtain a similar gliding temperature difference of the non-azeotropic mixed refrigerant, other compositions than isobutane and propane may be used.

As the refrigerant to be mixed in the non-azeotropic mixed refrigerant, isobutane is selected from the upper group and propane is selected from the middle group. Ratios of the refrigerants to be mixed in the non-azeotropic mixed refrigerant may be selected as follows.