Heat exchange – Line connected conduit assemblies
Reexamination Certificate
2002-09-27
2004-06-08
McKinnon, Terrell (Department: 3743)
Heat exchange
Line connected conduit assemblies
C165S175000
Reexamination Certificate
active
06745827
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a heat exchanger using carbon dioxide as a refrigerant.
2. Description of the Related Art
In general, a heat exchanger is an apparatus for exchanging heat by transferring heat of a fluid at a high temperature to a fluid at a low temperature through a wall surface. A freon-based refrigerant has mainly been used as a refrigerant of an air conditioning system having a heat exchanger thus far. However, as the freon-based refrigerant is recognized as a major factor of global warming, the use thereof is gradually restricted. Under the above circumferences, studies about carbon dioxide as a next generation refrigerant to replace the present freon-based refrigerant is actively being developed.
The carbon dioxide is regarded as an eco-friendly refrigerant because the global warming potential (GWP) thereof is just about {fraction (1/1300)} of R134a that is a typical freon-based refrigerant. In addition, the carbon dioxide has the following merits.
The carbon, dioxide refrigerant has a superior volumetric efficiency because an operational compression ratio is low, and a smaller difference of temperature between air that flows in and the refrigerant out of a heat exchanger than that of the existing refrigerant. Since heat transferring performance is excellent, the efficiency of cooling cycle can be improved. When the temperature of the outside air is as low as in the winter time, since heat can be extracted from the outside air by only a small difference in temperature, the possibility of applying the carbon dioxide refrigerant to a heat pump system is very high.
Also, since the volumetric cooling capability (latent heat of vaporization×gas density) of carbon dioxide is 7 or 8 times of R134a that is the existing refrigerant, the volume size of a compressor can be greatly reduced. Since the surface tension thereof is low, boiling heat transfer is superior. Since the specific heat at constant pressure is great and a fluid viscosity is low, a heat transfer performance is superior. Thus, the carbon dioxide refrigerant has superior thermodynamic features as a refrigerant.
Also, in view of the cooling cycle, since the operational pressure is very high such that it is 10 times high at an evaporator side and 6-8 times high at a gas cooler (an existing condenser) side compared to the conventional refrigerant, a loss due to a pressure drop in the refrigerant inside the heat exchanger is relatively low compared to the existing refrigerant, so that a micro channel heat exchange tube exhibiting superior heat transfer performance with great pressure drop can be used.
However, since the cooling cycle of carbon dioxide is a transcritical pressure cycle, not only a vaporization pressure but also a gas-cooling pressure is high by 6-8 times compared to the existing cycle. Thus, in order to use carbon dioxide as a refrigerant, evaporator and condenser presently being used should be redesigned to endure such a high pressure.
That is, a laminate type evaporator among the conventional evaporators for cars cannot use carbon dioxide as a refrigerant because it cannot endure a high pressure. A parallel flow type condenser among the conventional condensers for cars needs to be redesigned so that it can be used as a heat exchanger using carbon dioxide as a refrigerant.
Furthermore, the parallel flow type condenser is of a single slab type designed to have one tube row and adopts a multi-pass method of a single slab in which the flow path of the refrigerant is formed in a multi-pass form by adding a plurality of baffles to improve performance. The multi-pass method exhibits a superior distribution of the refrigerant inside the heat exchanger. However, when the refrigerant is in gas cooling, the temperature of the carbon dioxide refrigerant continuously decreases without a condensing process inside the heat exchanger. Accordingly, the deviation of temperature in the whole heat exchanger becomes serious, so that a self heat flow along the surface of the heat exchanger is generated. This flow of heat prevents heat exchanging between the refrigerant and the air coming from the outside and consequently heat transfer performance is deteriorated.
In the meantime, a multi-slab method in which a plurality of tube rows are arranged through which the refrigerant passes to perform heat exchanging, unlike the multi-pass method, can block the heat flow on the multi-pass method, so that it is effective than the multi-pass method using carbon dioxide as a refrigerant.
However, in the heat exchanger in the multi-slap method, pipes to connect each slab should be installed, which is a weak structure to a high pressure. Also, the distribution of the refrigerant in the heat exchanger may be slightly lowered compared to the multi-pass method.
Conventionally, a serpentine type heat exchanger having an increased thickness has been used as a heat exchanger to endure a high operational pressure without considering a feature of the carbon oxide refrigerant. However, such a serpentine heat exchanger exhibits a great pressure drop and an irregular distribution of the refrigerant in the tubes, so that heat transfer performance is deteriorated while the manufacturing cost increases.
Also, in a heat exchanger used as a gas cooler having the same function as a condenser, the temperature of the refrigerant in the heat exchanger decreases due to the heat transfer with the outside air so that the specific volume of the carbon dioxide refrigerant decreases. In the case of the carbon dioxide refrigerant, the difference in specific volume at a heat exchanger is very great, so that the specific volume of carbon dioxide in a refrigerant inlet having a temperature of about 110° or more is approximately three times greater than the specific volume of carbon dioxide in a refrigerant outlet having a temperature of about 50°.
In the heat exchanger using carbon dioxide as a refrigerant showing a great difference in specific volume according to the temperature, maintaining a constant width of a radiating tube is ineffective in view of miniaturization in weight and size of a heat exchanger and a cost for producing parts increases.
In the meantime, in the heat exchanger in the multi-slab method, since independent refrigerant paths of header tanks of the heat exchanger should be connected separately, each path is connected by additional tubes. Thus, to manufacture a heat exchanger having additional tubes requires a lot of work steps to assemble the heat exchanger.
Japanese Patent Publication No. hei 10-206084 discloses a general configuration of a serpentine heat exchanger. The serpentine heat exchanger has a superior structure but may be damaged when the refrigerant acting at a high pressure such as carbon dioxide is used.
Japanese Patent Publication Nos. 2001-201276 and 2001-59687 disclose heat exchangers having an improved pressure resistance feature of a header pipe. These heat exchangers are not far from the serpentine heat exchanger and is limited to be used as the heat exchanger for carbon dioxide.
In addition, Japanese Patent Publication No. hei 11-304378 discloses a heat exchanger for cars in which a radiator and a condenser are integrally formed. However, such a structure is difficult to be adopted, as is, in the heat exchanger for carbon dioxide.
Also, Japanese Patent Publication No. hei 11-351783 discloses a heat exchanger in which an inner post member is further formed at an inner wall of each of header tanks so that a space formed by the inner post members is circular. However, the heat exchanger in which a single tube is connected to two or more spaces formed by the inner post members basically adopts a multi-pass method, which is not appropriate for the heat exchanger for carbon dioxide.
Japanese Patent Publication No. 2000-81294 discloses a heat exchanger by improving the above heat exchangers, in which a single tube is connected to two spaces formed by the inner post members. Since this heat exchanger has a struct
Ahn Hwang-Jae
Ahn Yong-Gwi
Han In-Cheol
Jang Kil-Sang
Lee Jun-Kang
Halla Climate Control Corporation
Lowe Hauptman & Gilman & Berner LLP
McKinnon Terrell
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