Low charge heat exchanger in a sealed refrigeration system   

FIELD OF THE INVENTION

The present subject matter relates generally to refrigeration systems, and more particularly to heat exchangers used in sealed refrigeration systems.

BACKGROUND OF THE INVENTION

Consumer refrigerators generally utilize a relatively simple vapor compression refrigeration cycle that includes a compressor, a condenser, an expansion device, and an evaporator connected in series. The system is charged with a refrigerant such as R-134a. The type and amount of refrigerant are important considerations in the cost, efficiency, and safety aspects of the refrigerators.

Essentially all available refrigerants have environmental and safety concerns. For example, it has been found that CFC and HCFC refrigerants are a significant contributor to depletion of the stratospheric ozone layer. As a result, the use of CFC refrigerants was discontinued in most countries by 1996, and the use of HCFC refrigerants is being curtailed.

In addition to the environmental concerns, when a refrigerant containing chlorine or fluorine is burned, poisonous gases are generated and released.

R-600a is a known refrigerant that has a dramatically lower Greenhouse Warming Potential (GWP) than R-134a, and has replaced R-134a in much of the world outside of the U.S. R-600a also tends to reduce the energy use of conventional refrigerators by as much as four percent (4%). Unfortunately, the refrigerants with the least environment impact (such as R-600a) also tend to be the most flammable or toxic. Besides R-600a, R-600, R-152a, and HFO-1234ze are alternative refrigerants, but are also flammable. Ammonia has excellent refrigerant characteristics, but is toxic in large charge amounts. Thus, it is desired to minimize the charge requirements of these refrigerants.

Accordingly, it would be desirable to provide a sealed refrigeration system particularly suited for residential consumer refrigerators that reduces the refrigerant charge without a significant impact on cooling capacity or efficiency.

Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

The present invention provides heat exchangers, such as evaporators and condensers, for a sealed refrigeration system, wherein the heat exchangers have a unique combination of refrigerant side (inner) diameter, tube length, and refrigerant charge mass that provides balanced efficiency between cooling capacity of the system and reduced refrigerant charge.

In this regard, an exemplary embodiment of a consumer refrigeration appliance, for example a refrigerator, includes at least one compartment configured for storage of items to be refrigerated, such as a fresh food or freezer compartment. A sealed refrigeration system within the appliance is charged with a refrigerant and further includes a compressor, a condenser, an expansion device, and an evaporator. Either or both of the condenser and evaporator may be configured in accordance with aspects of the invention. For example, in a particular embodiment, the evaporator is a spine fin heat exchanger having a defined length (L1) of tube with a spine fin material configured around at least a portion of the tube. The tube may have a refrigerant side diameter (D1) of less than 0.3 inch and a refrigerant side area (A1) determined by (L1) and (D1). The refrigeration system has a refrigerant charge mass such that a ratio (R1) of the charge mass to refrigerant side area (A1) is less than 0.10 and a refrigerant pressure drop across the evaporator is less than 0.7 psi.

In certain evaporator embodiments, the refrigerant may be R-134a and (L1) is from 20 to 40 ft. In other embodiments, the refrigerant may be R-600a with the same (L1).

Different combinations of evaporator tube dimensions and refrigerant charge masses can provide the benefits of the present invention, and certain non-limiting embodiments are descried in greater detail below.

The refrigeration appliance may also include a spine fin condenser in alone or in combination with the spine fin evaporator discussed above. For example, in particular embodiments, a spine fin condenser may be provided with a defined length (L2) of tube and a spine fine material configured around at least a portion of the tube. The condenser tube may have a refrigerant side diameter (D2) of less than 0.2 inch and a refrigerant side area (A2) determined by (L2) and (D2). The refrigeration system may have a refrigerant charge mass such that a ratio (R2) of the charge mass to refrigerant side area (A2) is less than 0.23.

As with the evaporator, different combinations of condenser tube dimensions and refrigerant charge masses can provide the benefits of the present invention, and certain non-limiting embodiments of the condenser are also descried in greater detail below.

The invention also encompasses a consumer refrigeration appliance wherein the condenser is configured in accordance with aspects described herein regardless of the evaporator configuration.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a perspective view of a consumer refrigeration appliance, in particular a refrigerator, that may incorporate aspects of the present invention;

FIG. 2 is schematic view of a refrigeration system within a refrigeration appliance;

FIG. 3 is a cross-sectional view of a tube component of a spine fin heat exchanger in accordance with aspects of the invention; and

FIG. 4 is a perspective and partial cut-away view of a length of tube from a spine fin heat exchanger in accordance with aspects of the invention.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 depicts a consumer refrigeration appliance 10 in the form of a refrigerator that may incorporate a sealed refrigeration system in accordance with aspects of the invention. It should be appreciated that the term “consumer refrigeration appliance” is used in a generic sense herein to encompass any manner of refrigeration appliance, such as a freezer, refrigerator/freezer combination, and any style or model of conventional refrigerator. In the illustrated embodiment, the refrigerator 10 is depicted as an upright refrigerator having a cabinet or casing 12 that defines a number of internal storage compartments. In particular, the refrigerator 10 includes upper fresh-food compartments 14 having doors 16 and lower freezer compartment 18 having upper drawer 20 and lower drawer 22. The drawers 20, 22 are “pull-out” drawers in that they can be manually moved into and out of the freezer compartment 18 on suitable slide mechanisms.

FIG. 2 is a schematic view of refrigerator 10 including an exemplary sealed refrigeration system 60. A machinery compartment 62 contains components for executing a known vapor compression cycle for cooling air. The components include a compressor 64, a first heat exchanger or condenser 66, an expansion valve 68, and an evaporator 70 connected in series and charged with a refrigerant. Evaporator 70 is also a type of heat exchanger which transfers heat from air passing over the evaporator to a refrigerant flowing through evaporator 70 thereby causing the refrigerant to vaporize. As such, cooled air is produced and configured to refrigerate compartments 14, 18 of refrigerator 10.

From evaporator 70, vaporized refrigerant flows to compressor 64, which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the gaseous refrigerant through condenser 66 where heat exchange with ambient air takes place so as to cool the refrigerant. A fan 72 is used to pull air across condenser 66, as illustrated by arrows A, so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant and the ambient air.

An expansion device (e.g., a valve, capillary tube, or other restriction device) 68 further reduces the pressure of refrigerant leaving condenser 66 before being fed as a liquid to evaporator 70. Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through refrigeration compartments 12, 14. The refrigeration system 60 depicted in FIG. 2 is provided by way of example only. It is within the scope of the present invention for other configurations of the refrigeration system to be used as well.

The sealed refrigeration system 60 includes heat exchangers in the form of the evaporator 70 and the condenser 66. Either or both of these heat exchangers may be constructed in accordance with aspects of the invention. In particular embodiments, one or both of the evaporator 70 and condenser 66 is a spine fin heat exchanger. Referring to FIGS. 3 and 4, a spine fin heat exchanger includes a tube or conduit 74 having a defined length 76 that will vary depending on a number of factors, such as system capacity (size), whether the heat exchanger is a condenser or evaporator, and so forth. The tube 74 has a refrigerant (inside) side diameter 78 and an outside diameter 79. The outer surface of the tube 74 is covered with a spine fin material 80 that has multiple, pin-like elements or fins 84 that project from a base 82 that wraps around the tube 74 such that the fins 84 project radially from the tube 74. These radial spine fins 84 increase the area available for heat transfer with the surrounding air. The spine fin material 80 is typically in the form of a ribbon that is readily wrapped around the tube 74. The spacing (“pitch”) between adjacent wraps of the ribbon base 82 may be varied to change the heat transfer characteristics of the heat exchanger for particular applications within the refrigeration system 60.

In the case of an evaporator 70, the spine fins 84 enhance the ability of the evaporator to absorb and transfer heat from the refrigerator compartments 14, 18 to the refrigerant. In the case of a condenser 66, the spine fins 84 enhance the ability of the condenser 66 to transfer heat from the refrigerant to air drawn across the condenser tubes. Preferably, the tubing 74 and radial spine fins 84 are constructed from a thermally-conductive material, such as one or more metals.

Spine fin evaporators 70 are widely used in the refrigeration and air conditioning arts, and a detailed explanation of the operation and construction of these heat exchangers is not necessary for those skilled in the art. Reference is made to the following U.S. patents for a description of spine fin evaporators used in commercial refrigerators: U.S. Pat. No. 5,067,322; U.S. Pat. No. 5,214,938; U.S. Pat. No. 5,241,840; U.S. Pat. No. 5,255,535; and U.S. Pat. No. 5,720,186. Spine fin condensers 66 have not been widely used in residential refrigeration systems.

Spine fin heat exchangers are advantageous in that they possess a large ratio of secondary (fin) area to primary (tube) area. The heat exchangers of the present refrigeration system 60 are preferably spine fin heat exchangers that have a modified tube diameter and length to reduce the internal capacity of the sealed system 60 while balancing efficiency losses associated with higher pressure drops. Conventional wisdom has been that an increased internal tube area is necessary for efficient heat transfer, which resulted in greater refrigerant charge mass. For example, work has been done in the art to increase internal tube area with internal partitions or other structure, as discussed in U.S. Pat. No. 5,967,228. In accordance with certain aspects of the present invention, it has been found that a reduced tube area is advantageous when combined with a carefully selected tube diameter, tube length, and type of refrigerant, resulting in a decreased refrigerant charge and corresponding increase in heat transfer coefficient.

A decreased refrigerant charge typically requires higher refrigerant velocity through the circuit, which increases concerns of detrimental pressure drop. It has, however, now been found by computer modeling and actual device testing that a reduction in tube diameter with associated reduction in refrigerant charge can achieve significant benefits with only a moderate pressure drop across the heat exchangers. In the case of an evaporator 70, this pressure drop can be maintained at less than about 0.7 psi. Pressure drop across the condenser 66 is less of a concern and a much larger pressure drop (i.e., up to about 3.0 psi) can be tolerated in a spine fin condenser 66 with modified diameter without a noticeable change in energy usage

Besides the environmental and economic benefit, a reduced refrigerant charge also reduces energy use by limiting transient losses. When the refrigeration system 60 is shut off, a portion of the warm refrigerant migrates from the condenser to the evaporator and carries heat into the cabinet 12. This occurs for approximately three minutes in most residential-sized refrigerators. In addition, at the beginning of a subsequent compressor on cycle, there is a period of time when the system is less efficient because the refrigerant is not optimally distributed through the circuit. When a smaller refrigerant charge is used, these losses are minimized.

Tables 1 and 2 below relate to various evaporator embodiments in accordance with aspects of the invention:

TABLE 1 Evaporator Tube Dimensions Comp Comp “1” “2” “3” “4” “5” “6” Outside Tube 0.375 ⅜ 0.3125 5/16 0.25 ¼ 0.1875 3/16 diameter (inches) Wall thickness 0.03 0.02  0.03 0.02  0.03 0.02 0.03 0.02  (inches) Inside diameter 0.315 0.335 0.2525 0.2725 0.19 0.21 0.1275 0.1475 (inches) (D1)

TABLE 2 Length ft. (L1) First Component: Evaporator Refrigerant side area (A1) in square inches 20 237.5 252.6 190.4 205.5 143.3 158.3 96.1 111.2 34.25 406.7 432.6 326.0 351.9 245.3 271.2 164.6 190.5 40 475.0 505.2 380.8 410.9 286.5 316.7 192.3 222.4

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