Patent Application
20120047940
The present subject matter relates generally to refrigeration systems, and more particularly to heat exchangers used in sealed refrigeration systems.
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.
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:
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.
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
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
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:
Various evaporator tube combinations are presented in Table 1, with the first two columns (“Comp”) corresponding to known conventional evaporator configurations and provided for comparison purposes. Table 1 provides outside diameter (OD) values and refrigerant side (inside) diameters (D1) for thin and thick wall variations of the same (OD) tube diameters.
The First Component of Table 2 provides the refrigerant side areas (in square inches) for the tubes of Table 1 over three lengths of tube (20 ft., 34.25 ft., and 40 ft.). For purposes of a range of residential refrigerator spine fin evaporators, the evaporator tube 74 would likely fall within the range of 20 to 40 ft. (All ranges expressed herein are inclusive of the end values and include all intermediate values and ranges. For example, the range of 20 ft. to 40 ft. includes the range of 25 ft. to 35 ft.).
The Second Component of Table 2 provides a calculated R-134a refrigerant charge for evaporators having the tube dimensions and lengths set forth in the First Component. Likewise, the Third Component of Table 2 provides a calculated R-600a refrigerant charge for evaporators having the tube dimensions and lengths set forth in the First Component.
It can be appreciated from Tables 1 and 2 that an evaporator placed within a system 60 in accordance with aspects of the invention may have a refrigerant side diameter (D1) of less than 0.30 inch and a refrigerant side area (A1) determined by (L1) and (D1). The system 60 may have the corresponding charge masses provided in the Second Component such that a ratio (R1) of the charge mass to refrigerant side area (A1) is less than 0.10 for the various combinations set forth in Table 2. With these evaporators and charge masses, the refrigerant pressure drop across the evaporator can be maintained at 0.7 psi. or less.
In a particular embodiment supported in Table 2, the evaporator tube has an outside diameter (OD) of 5/16 inch (or 0.3125 inch), with (D1) from 0.2525 to 0.2725 inch. The refrigerant charge masses with R-134a refrigerant provide a ratio (R1) in this embodiment may be from 0.086 to 0.094.
In another embodiment, the evaporator tube has an outside diameter (OD) of ¼ inch (or 0.25 inch), with (D1) from 0.19 to 0.21 inch. The refrigerant charge masses with R-134a refrigerant provide a ratio (R1) in this embodiment may from 0.063 to 0.070.
In still another embodiment, the evaporator tube has an outside diameter (OD) of 3/16 inch, with (D1) from 0.1275 to 0.1475 inch. The refrigerant charge masses with R-134a refrigerant provide a ratio (R1) in this embodiment from 0.041 to 0.048.
In an embodiment supported in Table 2 wherein the refrigerant is R-600a and the evaporator tube length (L1) is from 20 to 40 ft., the evaporator tube may have an outside diameter (OD) of 5/16 inch, with (D1) from 0.2525 to 0.2725 inch. The refrigerant charge provide a ratio (R1) in this embodiment from 0.031 to 0.034.
In another embodiment wherein the refrigerant is R-600a, the evaporator tube has an outside diameter (OD) of ¼ inch, with (D1) from 0.19 to 0.21 inch. The ratio (R1) is from 0.022 to 0.026.
In still a further embodiment with R-600a refrigerant, the evaporator tube has an outside diameter (OD) of 3/16 inch, with (D1) from 0.1275 to 0.1475 inch. The ratio (R1) is from 0.015 to 0.017.
It should be appreciated that a refrigeration system 60 incorporating any of the evaporator configurations discussed above may also include a spine fin condenser in accordance with the principles discussed herein.
Tables 3 and 4 relate to various condenser embodiments in accordance with aspects of the invention:
Table 3 is similar to Table 1 discussed above and provides various condenser tube configurations. The First Component of Table 4 provides the refrigerant side areas (in square inches) for the tubes of Table 3 over three lengths of tube (30 ft., 66 ft., and 80 ft.). For purposes of a range of residential refrigerator spine fin condensers, the condenser tube 74 would likely fall within the range of 30 to 80 ft. (all ranges expressed herein are inclusive of the end values and include all intermediate values and ranges).
The Second Component of Table 4 provides a calculated R-134a refrigerant charge for condensers having the tube dimensions and lengths set forth in the First Component. Likewise, the Third Component of Table 4 provides a calculated R-600a refrigerant charge for condensers having the tube dimensions and lengths set forth in the First Component.
It can be appreciated from Tables 3 and 4 that a spine fin condenser placed within a system 60 in accordance with aspects of the invention may have a defined length (L2) of tube with a spine fine material configured around at least a portion of said tube, with the tube having a refrigerant side diameter (D2) of less than 0.2 inch and a refrigerant side area (A2) (square inches) defined by (L2) and (D2). The refrigeration system may have a refrigerant charge mass (grams) such that a ratio (R2) of the charge mass to refrigerant side area (A2) is less than 0.23.
In a particular embodiment wherein the refrigerant is R-134a, the condenser may have a length (L2) from 30 to 80 ft. The condenser tube may have an outside diameter (OD) of ¼ inch, with (D2) from 0.17 to 0.19 inch. The ratio (R2) in this embodiment may be from 0.198 to 0.220.
In a different condenser embodiment with R-134a refrigerant, the condenser tube has an outside diameter (OD) of 3/16 inch, with (D2) from 0.1315 to 0.1475 inch. The ratio (R2) is from 0.153 to 0.172.
In a particular embodiment wherein the refrigerant is R-600a and the condenser has a length (L2) from 30 to 80 ft., the condenser tube may have an outside diameter (OD) of ¼ inch, with (D2) from 0.17 to 0.19 inch. The ratio (R2) in this embodiment may be from 0.071 to 0.079.
In a different condenser embodiment with R-600a refrigerant, the condenser tube has an outside diameter (OD) of 3/16 inch, with (D2) from 0.1315 to 0.1475 inch. The ratio (R2) is from 0.055 to 0.062.
It should be appreciated that a refrigeration system 60 in accordance with the present invention may utilize a condenser as described herein regardless of the evaporator configuration.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
