PARALLEL FLOW HEAT EXCHANGER

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priority to Korean Patent Application No. 10-2024-0202112 filed on Dec. 31, 2024, and Korean Patent Application No. 10-2025-0194246 filed on Dec. 9, 2025, the disclosures of which are incorporated herein by reference in their entireties.

BACKGROUND

1. Field

The present disclosure relates to a PF heat exchanger.

2. Description of Related Art

Heat exchangers are primarily used in outdoor air conditioner units. They come in two types: finned tube and PF coil. Recently, there has been a shift toward PF coil types, which offer superior heat transfer per unit volume. This allows for smaller and lighter air conditioners, reduces pressure loss, and reduces outdoor unit noise.

Furthermore, unlike finned tube heat exchangers made of expensive copper, PF coils are made of aluminum, reducing costs. Conventional air conditioners use air-cooling, which uses convection to dissipate heat. However, evaporative heat exchangers are increasingly used.

However, evaporative heat exchangers are prone to problems such as heat exchanger corrosion due to metal components in the water environment. Brazed PF heat exchangers, in particular, may experience corrosion due to metal components in the water spray, particularly at the contact points between the refrigerant tube and the heat transfer fins.

This corrosion causes white foreign matter, including aluminum oxide, to form on the surfaces of the refrigerant tubes and heat transfer fins. This foreign matter ultimately blocks the flow path of the heat exchanger, reducing heat exchange efficiency.

In particular, in some overseas regions, due to extensive land areas, proper water purification is not possible, and groundwater, etc., is used directly. This leads to the detection of large amounts of metal in the water.

When water containing large amounts of these metals is sprayed onto a PF heat exchanger, a potential difference between the water and the heat exchanger occurs, causing severe corrosion of the refrigerant tubes and heat transfer fins.

To prevent this corrosion, conventional evaporative heat exchangers were treated with a chemical treatment. However, this coating method, with its hydrophilic coating layer, failed to prevent corrosion due to the potential difference between the aluminum substrate and minerals in the water, particularly copper ions. This resulted in persistent corrosion even with small amounts of copper.

SUMMARY

An aspect of the present disclosure is to provide a PF heat exchanger in which corrosion of refrigerant tubes and heat transfer fins may be prevented by preventing oxidation and reduction reactions.

According to an aspect of the present disclosure, a parallel flow (PF) heat exchanger, including a header, a refrigerant tube formed of aluminum, and a heat transfer fin formed of aluminum, includes a chemical conversion layer provided on a surface layer of the refrigerant tube or the heat transfer resin coating layer provided on a surface of the chemical conversion layer; and a hydrophilic coating layer provided on a surface of the resin coating layer. The resin coating layer is formed of an epoxy acrylate resin with waterproof properties.

In an embodiment, the epoxy acrylate resin may include a hydrophilic resin.

In an embodiment, an average thickness of the hydrophilic coating layer may be 3 to 6 μm.

In an embodiment, an average thickness of the resin coating layer may be 2 to 4 μm.

In an embodiment, the chemical conversion layer may be composed of one of vanadium, titanium, zirconium, chromium, and hafnium.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a conceptual diagram illustrating the corrosion mechanism of aluminum.

FIG. 2 is a cross-sectional view schematically illustrating the layer structure and the water injection process of a heat exchanger of a comparative example.

FIG. 3 is a cross-sectional view schematically illustrating the layer structure and the water injection process of a heat exchanger according to an embodiment.

FIG. 4 is a photograph showing the state of the heat exchanger of a comparative example after water injection.

FIG. 5 is a photograph showing the state of the heat exchanger of an embodiment after water injection.

FIGS. 6 to 8 are SEM photographs showing the layer structure of the heat exchanger of a comparative example.

FIGS. 9 to 11 are SEM photographs showing the layer structure of the heat exchanger of an embodiment.

FIG. 12 is an SEM photograph showing the layer structure of the heat exchanger of a second embodiment.

FIGS. 13 and 14 are photographs comparing the corrosion resistance of the comparative example, the first embodiment, and the second embodiment.

FIG. 15 is a graph showing the increase in static pressure according to the heat exchanger blockage rate.

DETAILED DESCRIPTION

Hereinafter, example embodiments will be described with reference to the attached drawings. However, the embodiments may be modified in various other forms, and the scope of the present disclosure is not limited to the embodiments described below.

In addition, the embodiments are provided to more completely explain the present disclosure to those with average knowledge in the relevant technical field.

In the drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

In describing the embodiments, if it is determined that a detailed description of known technologies related to the present disclosure may unnecessarily obscure the gist of the present disclosure, the detailed description thereof will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present disclosure, and may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terms used in the detailed description are only for describing the embodiments and should never be limited. Unless clearly used otherwise, expressions in the singular form include plural meanings.

In this description, expressions such as “including” or “having” are intended to indicate certain features, numbers, steps, operations, elements, parts or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, parts or combinations thereof other than those described.

In this specification, terms such as “on,” “upper portion,” “upper surface,” “below,” “lower portion,” “lower side,” “lower surface,” “side,” “side surface” and the like are based on the drawings, and may actually vary depending on the direction in which the elements or components are disposed.

In addition, throughout the specification, when a part is said to be “connected” to another part, this includes not only cases where it is “directly connected,” but also cases where it is “indirectly connected” with another element therebetween.

Below, the present disclosure will be described in detail through each embodiment or example of the present disclosure. It should be noted that each embodiment or example described in this specification is not limited to only an embodiment or example, but may also be combined with other embodiments or examples. Therefore, the citation of claims in the patent claims is only an example of an embodiment, and the technical idea of the present disclosure should not be interpreted only as a combination with the cited claims, and combinations with various claims are also included in the scope of the technical idea of the present disclosure.

A parallel flow (PF) heat exchanger according to an embodiment includes a pair of headers, a plurality of refrigerant tubes connected to the headers, and heat transfer fins interposed between the refrigerant tubes. A brazing joint may be formed at the point where the refrigerant tubes and the heat transfer fins come into contact.

The PF heat exchanger according to an embodiment is an evaporative heat exchanger that utilizes latent heat of vaporization. Compared to conventional air-cooled heat exchangers, this significantly improves heat exchange efficiency, significantly reducing power consumption and thus reducing greenhouse gases and improving energy efficiency.

Hereinafter, the basic structure of the PF heat exchanger is based on a known structure, and therefore, a detailed description thereof will be omitted.

Hereinafter, the present disclosure will be described in detail through examples. However, it should be noted that the examples described below are only intended to illustrate and concretize the present disclosure, and are not intended to limit the scope of the rights of the present disclosure. This is because the scope of the rights of the present disclosure is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

In an embodiment of the PF heat exchanger, both the refrigerant tube and the heat transfer fin are made of aluminum.

Referring to FIG. 3, in an embodiment of the PF heat exchanger, a chemical conversion layer 111 is formed on the surface layer 110 of the refrigerant tube or heat transfer fin. A resin coating layer 140 is formed on the surface of the chemical conversion layer 111. A hydrophilic coating layer 120 is formed on the surface of the resin coating layer 140 by coating a resin composition on the surface of the resin coating layer 140.

The chemical conversion layer 111 improves the corrosion resistance of the surface layer 110 of the refrigerant tube or heat transfer fin, thereby preventing corrosion of the surface layer 110 of the refrigerant tube or heat transfer fin. Furthermore, the surface of the aluminum refrigerant tube or heat transfer fin's surface layer 110 is roughened to improve the adhesion of the resin coating layer 140. In this case, hydrophilicity refers to the property of allowing water to spread easily and facilitate evaporation.

In one embodiment, by further forming a resin coating layer 140 on the chemical conversion layer 111, corrosion of the surface layer 110 of the refrigerant tube or heat transfer fin may be double-protected, further enhancing the corrosion prevention effect.

Furthermore, the chemical conversion layer 111 may be formed of a compound containing at least one metal selected from vanadium, titanium, zirconium, chromium, and hafnium.

The metal compound may be one or more of a hydroxide, an oxide, or a composite oxide. Dehydrated oxides may be used, but the present disclosure is not limited thereto.

The resin coating layer 140 includes an epoxy acrylate resin. In this case, the epoxy acrylate resin is a synthetic resin manufactured by polymerizing an acrylic monomer and an epoxy monomer.

This resin coating layer 140 may have an average thickness of 2 to 4 μm.

Furthermore, this epoxy acrylate resin may include an acrylic resin with excellent hydrophilicity.

The acrylic resin is composed of a polymer of a, B monoethylenically unsaturated monomers derived from acrylic acid or its derivatives.

Examples of α, β-monoethylenically unsaturated monomers may include acrylic acid esters (methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethyloxyl acrylate, decyl acrylate, isooctyl acrylate, 2-ethylbutyl acrylate, octyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, 3-ethoxypropyl acrylate, etc.), methacrylic acid esters (methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, n-oxyl methacrylate, lauryl methacrylate, decyl octyl methacrylate, stearyl methacrylate, 2-methyloxyl methacrylate, 3-methoxybutyl methacrylate, etc.), acrylonitrile, methacrylonitrile, vinyl acetate, vinyl chloride, vinyl ketone, vinyltoluene, and styrene, and the like.

Epoxy resins include cyclic aliphatic resins such as bisphenol, novolac, and glycidyl ether, as well as acyclic aliphatic resins. Among these, epoxy acrylate resins may include epoxy resins obtained by reacting bisphenols, due to their excellent industrial versatility and corrosion resistance.

Examples of bisphenols include bisphenol A, bisphenol F, bisphenol S, and tetrabromobisphenol A. These resins may be used singly or as mixtures of two or more. Furthermore, among bisphenols, bisphenol A type epoxy resins may be used due to their industrial versatility.

Meanwhile, the resin coating layer 140 is formed in close contact with the chemical conversion layer 110 composed of metal components. Therefore, while corrosion resistance is important, adhesion to the metal is also a crucial factor.

The above-described epoxy acrylate resin possesses excellent corrosion resistance in both the acrylic and epoxy components. Furthermore, its epoxy group provides excellent adhesion to metal, preventing separation or the formation of gaps between the resin and the chemical conversion layer when formed on the chemical conversion layer of one embodiment.

This resin coating layer 140 may be formed by applying a coating solution made by applying the synthetic resin described above as the main raw material to the chemical conversion layer 111. In addition to the synthetic resin as the main raw material, a diluent and other additives may be included.

The hydrophilic coating layer 120 serves to evenly distribute the injected water throughout the heat exchanger.

This hydrophilic coating layer 120 may have an average thickness of 3 to 6 μm.

When surface corrosion occurs in a PF-type condenser, white debris formed from aluminum particles detached from the fins and tubes of the aluminum heat exchanger may form. This debris may block the flow path of the heat exchanger, reducing heat exchange efficiency and, in severe cases, even leading to failure.

Furthermore, comparing the static pressure of a heat exchanger with one that is not corroded to one that is, a significant increase in static pressure is observed after approximately 25 days of use. Higher static pressures may lead to increased energy consumption and reduced energy efficiency.

According to one embodiment, corrosion of a PF heat exchanger may be delayed. To verify this effect, the following experimental example is presented.

Experimental Example

First, for the experiment, a 18 cupric chloride solution is diluted in water to prepare a copper chloride solution with a concentration of 0.3 ppm, and the solution is sprayed using a water injection nozzle onto a PF heat exchanger made of aluminum (comparative example) and a PF heat exchanger (exemplary example) that is additionally resin-coated to form a resin coating layer between the chemical conversion layer and the hydrophilic coating layer, and the corrosion state is checked.

As illustrated in FIG. 2, the comparative example is a PF heat exchanger without a resin coating on the surface layer 110, with a chemical conversion layer 111 and a hydrophilic coating layer 120 formed sequentially. As illustrated in FIG. 3, the exemplary example is a PF heat exchanger with a resin coating layer 140 interposed between the chemical conversion layer 111 and the hydrophilic coating layer 120.

In the comparative example, during the process of directly spraying water 130 onto the surface of the heat exchanger, some of the solids (Si) 121 of the hydrophilic coating layer 120 were removed, resulting in an uneven formation of the hydrophilic coating layer 120.

As a result, in the comparative example, copper ions were reduced on the aluminum surface layer 110 of the heat exchanger, resulting in aluminum corrosion as illustrated in FIG. 4 130 hours after the test. This aluminum corrosion caused by copper ions occurs according to the following

Reaction Scheme 1:

Referring to FIG. 1 and Reaction Scheme 1, copper ions with relatively high potential are reduced to copper particles 12 and separated due to a potential difference with aluminum 10. During this process, the aluminum ions are oxidized to form Al(OH)3 (11), a pitting corrosion product 13.

Conversely, in the embodiment, since the hydrophilic coating is applied over the resin coating layer 140, the hydrophilic coating layer 120 is uniform during the hydrophilic coating process and may be formed with a relatively thin thickness compared to the comparative example. Furthermore, even if a portion of the hydrophilic coating layer 120 is separated, water penetration is prevented during the water injection process, preventing corrosion even after 130 hours of testing, as illustrated in FIG. 5.

Next, the surface thicknesses of the comparative example and the embodiment were measured after the experiment. The average thickness may be measured by scanning the coating layer image in the thickness direction using a scanning electron microscope (SEM) at 5,000× magnification. More specifically, the thickness is measured at three equally spaced points on the scanned image and the average value is determined. Furthermore, measurements were performed on three specimens each for the comparative example and the embodiment.

FIGS. 6 to 8 are cross-sectional scans of the chemical conversion coating layer and the hydrophilic coating layer in a comparative example, and the results for the thickness of the hydrophilic coating layer are as illustrated in Table 1 below.

TABLE 1
	#	1 (FIG. 6)	2 (FIG. 7)	3 (FIG. 8)

	Hydrophilicity	14.99	10.13	7.69
	L1 (μm)
	Hydrophilicity	7.5	17.34	12.16
	L2 (μm)
	Hydrophilicity	4.66	10.83	11.15
	L3 (μm)
	Average (μm)	9.05	12.77	10.33

As illustrated in Table 1, in the comparative examples, the average thickness of the hydrophilic coating layer ranged from 9.05 μm to 12.77 μm, showing a large thickness dispersion. Furthermore, as illustrated in FIGS. 6 to 9, the surface of the hydrophilic coating layer is not smooth overall and is formed rough.

FIGS. 9 to 11 show cross-sectional scans of the chemical conversion coating layer, resin coating layer, and hydrophilic coating layer in the examples. The results for the thickness of the hydrophilic coating layer and the resin coating layer are illustrated in Table 2 below.

TABLE 2
#	4 (FIG. 9)	5 (FIG. 10)	6 (FIG. 11)

Hydrophilicity	3.8	6.07	3.46
L1 (μm)
Hydrophilicity	5.67	4.96	5.57
L2 (μm)
Hydrophilicity	5.66	4.79	5.19
L3 (μm)
Hydrophilicity	5.04	5.27	4.74
Average (μm)
Resin L1 (μm)	3.38	3.87	2.37
Resin L2 (μm)	3.22	2.78	2.15
Resin L3 (μm)	2.80	2.48	2.49
Resin Average (μm)	3.13	3.04	2.34

Table 2 illustrates that in the examples, the average thickness of the hydrophilic coating layer was 4.74 μm to 5.27 μm, approximately half that of the comparative examples. The average thickness of the resin coating layer was 2.34 μm to 3.13 μm.

Furthermore, the difference between the minimum and maximum average thicknesses of the hydrophilic coating layer was 0.53, indicating a relatively small thickness dispersion compared to the comparative examples. FIGS. 9 to 11 show that the surface of the hydrophilic coating layer is smooth and even throughout.

Meanwhile, during the coating process, the resin coating layer may experience pinholes, tiny, microscopic holes forming on the surface, making the surface unsmooth. This may lead to corrosion due to a reaction with copper and aluminum. In particular, if the resin coating is applied only once, the pinholes generated on the uneven surface of the material may cause concentrated corrosion in uncoated areas of the aluminum material.

To address this issue, another embodiment (hereinafter, a single resin coating is referred to as the first embodiment, and a two-layer resin coating is referred to as the second embodiment) utilizes two resin coatings to mitigate or prevent pinholes and, thus, corrosion. In this case, the resin coating layer formed by the first resin coating and the resin coating layer formed by the second resin coating may be separated by a boundary layer, or they may become a single layer as the boundary layer disappears during the drying process.

FIG. 12 illustrates a cross-section scan of the resin coating layer and the hydrophilic coating layer in the second embodiment. The average thickness of the hydrophilic coating layer was 5.25 μm, and the average thickness of the resin coating layer was 6.26 μm.

Furthermore, Energy Dispersive X-ray Spectroscopy (EDS) analysis using an SEM×80 (scale 1 mm) compared the aluminum detection levels from surface analysis tests of the comparative example, example 1, and example 2. The aluminum content in the comparative example was approximately 19. 12%, the aluminum content in example 1 was approximately 0.97%, and the aluminum content in example 2 was approximately 0.02%. This indicates that two coats may further reduce the corrosion rate.

Furthermore, even with two coats of resin, the adhesion to the hydrophilic coating layer remains as excellent as with a single coat.

Furthermore, two coats of resin increase the thickness of the resin coating layer compared to a single coat. Performance testing was conducted to determine whether heat exchange degradation occurs. The test was conducted on a 640×900 condenser with two rows and 91 coils, and the results are illustrated in Table 3.

TABLE 3
	Whether or not	Capacity	Total
	to inject water	(kW)	Input (kW)	EER2

Example 1	Non-Water	33161.7	2768	11.98
	Injection
	water	336786.6	1878	17.93
	injection
Example 2	Non-Water	33552.3	2775	12.09
#1	Injection
	Water	33580.9	1887	17.79
	Injection
Example 2	Non-Water	33474.8	2790	12.00
#2	Injection
	Water	33166.6	1918	17.29
	Injection
Example 2	Non-Water	33133.7	2770	11.96
#3	Injection
	Water	33199.8	1884	17.63
	Injection

Capacity: Capacity, Total Input: Total input power, EER2: Energy Efficiency Ratio 2

Table 3 illustrates that there is no significant difference in performance between single and double resin coatings. Therefore, it may be seen that performance is not significantly affected by coating thickness when applying two coats of resin.

FIG. 13 is a photograph comparing the corrosion resistance of the Comparative Example, Example 1, and Example 2, using a CuCl2 water injection test. Water was injected into the heat exchanger through a 0.1 1 μm nozzle, and the Cu concentration was 0.3 ppm. The test results show that corrosion occurred after 69 hours for the Comparative Example, 648 hours for Example 1, and 1, 752 hours for Example 2. This demonstrates that resin coating improves corrosion resistance, and that two coats may further enhance this resistance.

FIG. 14 is a photograph comparing the corrosion resistance of the comparative example, the first embodiment, and the second embodiment through a continuous immersion test in a CuCl2 aqueous solution. The Cu concentration was set at 100 ppm. As illustrated in FIG. 14, a visual comparison after 920 hours illustrates that corrosion resistance is improved by the resin coating, and that the second coating further improves corrosion resistance.

FIG. 15 is a graph showing the increase in static pressure according to the heat exchanger clogging rate. At this time, water injection to the heat exchanger is done through a 0.1 1 μm nozzle, the concentration of Cu is 0.3 ppm, and when only hydrophilic coating is done, the static pressure increase rate of the heat exchanger was 202.1%, when only resin coating is done, the static pressure increase rate of the heat exchanger was 19.8%, when resin coating was done once, the static pressure increase rate of the heat exchanger was 5.28, and when resin coating was done twice, the static pressure increase rate of the heat exchanger was 0%. As such, when resin coating was done twice, the static pressure value was also the best, and it may be confirmed that when resin coating was done twice, the performance was also the best.

As set forth above, a PF heat exchanger according to an embodiment has the effect of suppressing corrosion of the refrigerant tube and heat transfer fin even when water containing a metal component is injected into the heat exchanger by forming a hydrophilic coating layer with an even and thin thickness.

While example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present disclosure as defined by the appended claims.