Plate heat exchanger and refrigeration cycle apparatus including the same

A plate heat exchanger reduces the cross-sectional diameter of channels and suppresses clogging of the channels with a brazing material. First heat transfer plates each include a plurality of rows of inverse V-shaped waves formed on its surface, and second heat transfer plates each include a plurality of rows of V-shaped waves formed on its surface are alternately stacked. The intersections of the waves are joined by brazing. Further, a distance (L) between joint points in the short-axis direction of the heat transfer plates and a fillet dimension (f) in the short-axis direction of the heat transfer plates satisfy a relation 0≤((L−f)/L)×100≤40.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of PCT/JP2011/006690 filed on Nov. 30, 2011, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a plate heat exchanger and a refrigeration cycle apparatus including the same.

BACKGROUND

A so-called brazed plate heat exchanger is a multilayer heat exchanger in which a plurality of heat transfer plates are stacked while being clamped between end plates provided on two sides and are joined into one plate by brazing. Adjacent heat transfer plates each have rows of channel forming patterns of projections and recesses formed on their continuous surfaces. Peaks of crests and troughs of the channel forming patterns on the adjacent heat transfer plates abut against each other to form interspaces serving as channels for fluid. Moreover, the abutting support points are joined and fixed by brazing. Each of the end plates has an inlet port and an outlet port for fluid serving as a heat transfer medium, and the heat transfer medium flows through the interspaces to exchange heat.

As the above-described channel forming patterns, a combination of adjacent V-shaped waves and inverse V-shaped waves is known as an example (see, for example, Patent Literature 1). A pattern formed by continuous waves orthogonal to each other is known as another example (see, for example, Patent Literature 2).

In a plate heat exchanger disclosed in Patent Literature 1, waves that form channels have a wave angle θ (inclination angle) of 20° to 70° (preferably 45°), a wave height h of 1 mm or less, and a wave pitch of 4 mm or less.

In Patent Literature 2, a hydraulic diameter Dh (=2×h) is 1 to 3 mm, and a wave height h is 0.5 to 1.5 mm.

PATENT LITERATURE

Patent Literature 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-516815Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2001-056192

The wave height h or the hydraulic diameter Dh serving as one factor for specifying the cross-sectional shape of the channels has an influence on the flow velocity of fluid. The wave angle θ is also relevant to the flow velocity.

Particularly when the wave height h is set at 1 mm or less or 0.5 to 1.5 mm, the flow velocity increases and the pressure loss becomes too high, as in Patent Literature 1 or Patent Literature 2. Hence, it is necessary to reduce the pressure loss. For this reason, to reduce the pressure loss, the flow velocity is decreased by increasing the number of plates, or the channel resistance is reduced by decreasing the wave angle θ.

However, when the number of plates increases, the weight of the heat exchanger increases, and this makes the heat exchanger expensive. When the wave angle θ is simply decreased (to, for example, 50° or less), the number of joint points between adjacent heat transfer plates increases, and this causes an increase in pressure loss of the fluid and clogging of the channels. In addition, even when the wave pitch Λ is decreased (to, for example, 4 mm or less), the distance between adjacent joint points decreases. Hence, the channels are clogged with a brazing material, and an increase in pressure loss and clogging of the channels are caused. Since the increase in pressure loss generates a nonuniform flow velocity distribution in the heat transfer plates, a drift of the fluid flow decreases the effective heat transfer area and causes breakage due to freezing. Further, the increase in pressure loss increases the power consumption of a heat pump system including the plate heat exchanger, limits the type of fluid to be used, and poses other problems.

SUMMARY

The present invention has been made to solve the above problems, and has as its object to provide a plate heat exchanger that can have channels with a small cross-sectional diameter and can restrict clogging of the channels with a brazing material, and a refrigeration cycle apparatus including the heat exchanger.

A plate heat exchanger according to the present invention is configured such that heat transfer plates each having a plurality of rows of wavy channel forming patterns formed on a surface thereof and heat transfer plates each having wavy patterns obtained by inverting the channel forming patterns are alternately stacked, and intersections of the channel forming patterns are joined.

The intersections of the channel forming patterns are joined by brazing, and a distance (L) between joint points in a short-axis direction of the heat transfer plates and a fillet dimension (f) in the short-axis direction of the heat transfer plates satisfy a relation 0≤((L−f)/L)×100≤40.

In the plate heat exchanger of the present invention, the intersections of the channel forming patterns are joined by brazing, and the distance (L) between the joint points in the short-axis direction of the heat transfer plates and the fillet dimension (f) in the short-axis direction of the heat transfer plates satisfy a relation 0≤((L−f)/L)×100≤40. Hence, the cross-sectional area of channels can be decreased (the cross-sectional diameter of the channels can be reduced), and clogging of the channels with a brazing material can be suppressed. Moreover, since the number of fillets can be reduced, an increase in pressure loss can be suppressed.

DETAILED DESCRIPTION

Embodiments of a plate heat exchanger according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1includes schematic structural views of a plate heat exchanger100according to Embodiment 1 of the present invention. More specifically,FIG. 1(a)is a side view of the plate heat exchanger100,FIG. 1(b)is a front view of an end plate1,FIG. 1(c)is a front view of a heat transfer plate2,FIG. 1(d)is a front view of an adjacent heat transfer plate3,FIG. 1(e)is a rear view of the other end plate4, andFIG. 1(f)is a front view of the heat transfer plates2and3superposed on each other.

As illustrated inFIG. 1, in this plate heat exchanger100, heat transfer plates2and heat transfer plates3are alternately superposed and stacked, an end plate1and another end plate4are disposed on one side and the other side, respectively, of this stack (stack of heat transfer plates)20, and these plates1,2,3, and4are joined into one plate by brazing.

A plurality of rows of inverse V-shaped waves9are formed on the surface of each heat transfer plate2as channel forming patterns in the longitudinal direction (the up-down direction ofFIG. 1). The inverse V-shaped waves9are arranged symmetrically with respect to a center line in the longitudinal direction.

On a surface of each of the heat transfer plates3, a plurality of rows of V-shaped waves10are provided as channel forming patterns in the longitudinal direction (the up-down direction ofFIG. 1). The V-shaped waves10are also arranged symmetrically about the center line in the longitudinal direction. The heat transfer plates3are obtained by inverting the heat transfer plate2.

The stack of heat transfer plates20is formed by alternately superposing and stacking the heat transfer plates2and the heat transfer plates3. When points where the inverse V-shaped waves9and the V-shaped waves10intersect with each other are joined by brazing, a heat-exchange fluid flows through interspaces formed between adjacent joint points. Also, channel forming patterns are formed in a rectangular area indicated by a dashed frame illustrated inFIG. 1(f), and serve as a heat transfer surface (heat transfer area)15for heat exchange. The channel forming patterns are formed by, for example, press working or etching.

The end plate1serves as a reinforcing plate, and is also called a side plate. The end plate1has, at the four corners of a rectangle, an inlet pipe5for a first fluid, an outlet pipe7for the first fluid, an inlet pipe6for a second fluid, and an outlet pipe8for the second fluid, respectively. Also, the heat transfer plates2and3each have a communication hole11communicating with the inlet pipe5for the first fluid, a communication hole13communicating with the outlet pipe7for the first fluid, a communication hole12communicating with the inlet pipe6for the second fluid, and a communication hole14communicating with the outlet pipe8for the second fluid.

The end plate4serves as a reinforcing plate as well, and is also called a side plate. The end plate4serves to turn one of the fluids, for example, the first fluid back from an inlet side to an outlet side.

Both of the end plates1and4reinforce the plate heat exchanger100, and this improves the pressure resistance.

While the planar shape of the above-described plates1to4is a rectangular shape in the following description, it is not limited to a rectangular shape, and may be, for example, a square shape. The plates1to4are each formed by a metal plate. In particular, the material of the heat transfer plates2and3is selected in consideration of the properties such as mechanical strength, thermal conductivity, and percentage of elongation. Suitable examples of such a material include aluminum, stainless steel, and copper.

FIG. 2schematically illustrates currents of fluid in the plate heat exchanger100. A solid arrow represents a current X of the first fluid, and a dashed arrow represents a current Y of the second fluid. Referring toFIG. 2, the stack of heat transfer plates20is illustrated in a divided state for the sake of easy understanding of the currents of two kinds of fluids.

As illustrated inFIG. 2, in the plate heat exchanger100, each of the current X of the first fluid and the current Y of the second fluid is formed on every other heat transfer plate of heat transfer plates2or3as, for example, a corresponding one of upward and downward countercurrents so that the first fluid and the second fluid do not mix with each other.

FIG. 3includes explanatory views showing definitions of variables such as a wave angle θ, a wave pitch Λ, and a wave height h.FIG. 3shows the case of the heat transfer plate2as an example.FIG. 3(a)is a plan view of the heat transfer plate2, andFIG. 3(b)is an enlarged sectional view illustrating a waveform in a direction perpendicular to a waveform ofFIG. 3(a).

Definitions of the variables inFIG. 3will be given hereinafter. The curvature of the wave illustrated inFIG. 3(b)is represented as R.

A wave angle θ is the inclination angle with respect to the center line of the inverse V-shaped waves9(or V-shaped waves10) in the direction in which these waves are aligned.

A wave pitch Λ is the distance between peaks of troughs (or crests) of adjacent waves in a direction perpendicular to the center lines of the waves9extending in the direction of the wave angle θ.

A wave height h is the distance between the crest and the trough of each wave.

A wave length s is the length of the center line of a plate thickness t of the wave.

Further, an area enlargement ratio Φ is defined as s/A.

FIG. 4(a)illustrates the positions of joint points16, a dimension f of fillets17in the short-axis direction, and a distance L between adjacent joint points16in the plate short-axis direction in Embodiment 1 of the present invention.FIG. 4(b)is an enlarged sectional view taken along a line A-A′ ofFIG. 4(a).

Note that in Embodiment 1, the plate short-axis direction refers to the direction of short sides of the heat transfer plates2and3.

As illustrated inFIG. 4(a), points (joint points)16where the inverse V-shaped waves9of the heat transfer plate2and the V-shaped waves10of the heat transfer plate3intersect with each other are joined by brazing.

At this time, in Embodiment 1, as can be seen fromFIGS. 4(a) and 4(b), at least one non-joint wave22is provided between adjacent joint points16of waves continuing in the direction perpendicular to the center lines of the waves9extending in the direction of the wave angle θ. That is, the joint points16are formed at every other intersection of the channel forming patterns in the plate short-axis direction. A wave height h2 of the non-joint wave22is set less than a wave height h1 at the joint points16(h2<h1). The first fluid and the second fluid described above flow through channels24thus formed between the fillets17.

In Embodiment 1, as described above, at least one non-joint wave22is provided between adjacent joint points16of the waves continuing in the direction perpendicular to the center lines of the waves9extending in the direction of the wave angle θ. Thus, letting L be the distance between joint points16(b-c) in the plate short-axis direction, and f be the dimension of the fillets17in the plate short-axis direction, even when the distance L between the joint points16in the plate short-axis direction is so short as to have, for example, a relation 0≤((L−f)/L)×100≤40, the cross-sectional area of the channels24can be reduced (the cross-sectional diameter of the channels can be reduced), and clogging of the channels24with the brazing material can be prevented. Therefore, it is possible to lessen reduction of the effective heat transfer area and freezing due to a nonuniform velocity distribution generated in the heat transfer plates2and3. Further, the number of joint points can be reduced, and this can reduce the amount of brazing material used. Hence, it is possible to reduce the cost and weight of the heat exchanger.

While two types of wave heights have been described with reference toFIG. 4, a plurality of wave heights may be adopted, and the number of joint points may be adjusted in accordance with the type of fluid or the flow velocity distribution. Alternatively, the wave height h2 of the non-joint wave22may be set equal to the wave height h1 of a joint wave at the joint point16or more than the wave height h1 (h2>h1).

The channel forming patterns are not limited to V-shaped waves, and may be mountain-shaped, arcuate, or sawtoothed waves.

FIG. 5illustrates the positions of joint points, a fillet dimension f in the short-axis direction, and a distance L between adjacent joint points in the short-axis direction in Embodiment 2 of the present invention. A plate heat exchanger (not illustrated) of Embodiment 2 has a structure similar to that of the plate heat exchanger100illustrated inFIGS. 1 and 2.

While at least one non-joint wave22is provided between adjacent joint points16of the waves continuing in the direction perpendicular to the center lines of the waves9extending in the direction of the wave angle θ in Embodiment 1 described above, fillets17at adjacent joint points16of waves continuing in the direction perpendicular to the center lines of waves9extending in the direction of the wave angle θ are formed with different fillet dimensions f in Embodiment 2.

That is, in Embodiment 2, as illustrated inFIG. 5, fillet dimensions f1 and f2 are formed at joints points16that are adjacent to each other in the plate short-axis direction such that the fillet dimension f1 is set smaller than the fillet dimension f2 (f1<f2). This can prevent channels24from being clogged with a brazing material even when the distance L between the joint points16that are adjacent to each other in the plate short-axis direction and the fillet dimension f in the plate short-axis direction are so short as to satisfy a relation 0≤((L−f)/L)×100≤40. Therefore, an advantage substantially similar to that of Embodiment 1 is obtained.

As a method for decreasing the fillet dimension f, the brazing material used for joint points16of adjacent heat transfer plates2and3is replaced with a locally thin material, or the amount of brazing material itself is reduced. The fillet dimension f can be decreased by bringing the adjacent heat transfer plates2and3into point contact with each other, and the fillet dimension f is increased by bringing the heat transfer plates2and3into surface contact with each other. Further, the fillet dimension f is decreased by decreasing a curvature dimension R of crests or troughs of the waves (seeFIG. 3). For example, when the curvature dimension R of the crests or troughs of the waves is decreased for each of waves continuing in the direction perpendicular to the center lines of the waves9extending in the direction of the wave angle θ, a distribution of the fillet dimensions f1 and f2 as illustrated inFIG. 5can be formed.

While two fillet dimensions f are specified inFIG. 5, a plurality of fillet dimensions f may be specified, and the fillet dimension f may be adjusted in accordance with the type of fluid or the flow velocity distribution. When the fillet dimension f is partly decreased, not only clogging of the channels24can be prevented, but also the pressure loss can be reduced because the resistance applied to the fluid decreases. For this reason, a refrigerant with a low working pressure (for example, hydrocarbon or low-GWP refrigerant) can be used. Further, when fillets are completely omitted albeit locally on a heat transfer surface15, the joint strength of the heat transfer surface15decreases. Hence, a remarkable decrease in strength of the heat transfer surface15can be prevented by forming the small fillets18as in Embodiment 2.

FIG. 6illustrates a distance L between joint points in the plate short-axis direction when a wave angle θ and a wave pitch Λ are changed in Embodiment 3 of the present invention.FIG. 6(a)illustrates a case in which the wave angle θ is 65° and the wave pitch Λ is 4 mm, andFIG. 6(b)illustrates a case in which the wave angle θ is 45° and the wave pitch Λ is 4 mm. However, the wave pitch Λ is fixed in Embodiment 3. A plate heat exchanger (not illustrated) of Embodiment 3 has a structure similar to that of the plate heat exchanger100illustrated inFIGS. 1 and 2.

While different fillet dimensions f are specified in Embodiment 2 above, a wave height h is 0.8 to 1.4 mm and a wave angle θ is 40° to 50° in Embodiment 3.

Since the wave height h is set as low as 0.8 to 1.4 mm in Embodiment 3, if the wave angle θ exceeds 50°, the pressure loss becomes too high, and the flow velocity needs to be decreased by increasing the number of plates to increase the cross-sectional area of channels. Hence, the weight of the heat exchanger cannot be reduced. For this reason, the pressure loss is reduced by decreasing the wave angle θ. For example, the wave angle θ is set small, as illustrated inFIG. 6.

When the wave angle θ is decreased, for example, from 65° to 45°, the distance L between the joint points16in the plate short-axis direction satisfies L1>L2, as illustrated inFIG. 6(b). When the wave angle θ is 45°, and the wave pitch Λ is less than 4 mm, fillets17made of a brazing material formed at joint points c and d are combined and the channels are thereby clogged.

FIG. 7is a graph showing the relationship between the wave angle θ and the amount of weight reduction of the plate heat exchanger. As can be seen fromFIG. 7, to reduce the weight of the heat exchanger, a great weight reduction effect can be obtained when the wave angle θ falls within the range of 40° to 50° (especially 45°) for a wave height h that falls within the range of 0.8 to 1.4 mm. Therefore, it is preferable to form a heat transfer surface15such that the wave angle θ falls within the range of 40° to 50°. However, if the wave pitch Λ is 4 mm or less, the distance L between adjacent joint points16in the plate short-axis direction and the fillet dimension f in the plate short-axis direction satisfy a relation 0≤((L−f)/L)×100≤40, and the channels are clogged with the brazing material. For this reason, practicing Embodiments 1 and 2 in combination makes it possible to form the heat transfer surface15free from clogging of the channels with the brazing material even when the distance L between adjacent joint points16in the plate short-axis direction and the fillet dimension f in the plate short-axis direction satisfy a relation 0≤((L−f)/L)×100≤40. Thus, in Embodiment 3, the weight of the plate heat exchanger can be greatly reduced, in addition to weight reduction of the heat exchanger by reducing the amount of brazing material used in Embodiments 1 and 2.

In Embodiment 4, a refrigeration cycle apparatus including the plate heat exchanger100described in Embodiments 1 to 3 above will be described.

The plate heat exchanger100is utilized in refrigeration cycle apparatuses mounted in apparatuses for, for example, air conditioning, hot-water supply, floor heating, electric power generation, and heat sterilization of food.

FIG. 8is a circuit diagram of a refrigeration cycle apparatus (air-conditioning apparatus) according to Embodiment 4 of the present invention.

An air-conditioning apparatus200according to Embodiment 4 includes one outdoor unit101serving as a heat source unit, one indoor unit102, and a heat medium relay unit103that transfers cooling energy of a heat-source-side refrigerant flowing through the outdoor unit101to a heat medium flowing through the indoor unit102.

The outdoor unit101and the heat medium relay unit103are connected by a refrigerant pipe120, which conducts a heat-source-side refrigerant (first fluid), to constitute a refrigerant circuit A. The heat medium relay unit103and the indoor unit102are connected by a heat medium pipe121, which conducts a heat medium (second fluid), to constitute a heat medium circuit B.

At least a heat-source-side heat exchanger110, a compressor118, and an expansion unit111are mounted in the outdoor unit101.

At least a use-side heat exchanger112is mounted in the indoor unit102.

At least the plate heat exchanger100according to Embodiment 1 and a pump119are mounted in the heat medium relay unit103.

While an example in which the plate heat exchanger100is mounted in the heat medium relay unit103will be given, the plate heat exchanger100need only be adopted as a heat exchanger in at least one of the outdoor unit101, the indoor unit102, and the heat medium relay unit103.

While the air-conditioning apparatus200for performing cooling operation will be described as an example of a refrigeration cycle apparatus in Embodiment 4, heating operation can also be performed with, for example, a four-way valve being added in the refrigerant circuit A, as a matter of course.

The heat-source-side heat exchanger110functions as a condenser, and exchanges heat between the heat-source-side refrigerant flowing through the refrigerant pipe120and the outdoor air. The heat-source-side heat exchanger110is connected on its one side to the plate heat exchanger100, and is connected on its other side to the discharge side of the compressor118.

The compressor118compresses and conveys the heat-source-side refrigerant to the refrigerant circuit A. The compressor118is connected on its discharge side to the heat-source-side heat exchanger110, and is connected on its suction side to the plate heat exchanger100.

The expansion unit111decompresses and expands the heat-source-side refrigerant flowing through the refrigerant pipe120. The expansion unit111is connected on its one side to the heat-source-side heat exchanger110and is connected on its other side to the plate heat exchanger100. It is desired to form the expansion unit111by, for example, a capillary or a solenoid valve.

The use-side heat exchanger112exchanges heat between the heat medium flowing through the heat medium pipe121and the air in an air-conditioned space. The use-side heat exchanger112is connected on its one side to the plate heat exchanger100and is connected on its other side to the suction side of the pump119.

The plate heat exchanger100exchanges heat between the heat-source-side refrigerant and the heat medium. The plate heat exchanger100is connected to the suction side of the compressor118and the expansion unit111via the refrigerant pipe120. The plate heat exchanger100is also connected to the use-side heat exchanger112and the pump119via the heat medium pipe121. That is, the plate heat exchanger100is cascaded to the refrigerant circuit A and the heat medium circuit B.

The pump119conveys the heat medium to the heat medium circuit B. The pump119is connected on its suction side to the use-side heat exchanger112and is connected on its discharge side to the plate heat exchanger100.

Flow of the heat-source-side refrigerant in the refrigerant circuit A will be described.

A low-temperature and low-pressure heat-source-side refrigerant is compressed by the compressor118, and is discharged as a high-temperature and high-pressure gas refrigerant. The high-temperature and high-pressure gas refrigerant discharged from the compressor118flows into the heat-source-side heat exchanger110. Then, the high-temperature and high-pressure gas refrigerant turns into a high-pressure liquid refrigerant while rejecting heat to the outdoor air in the heat-source-side heat exchanger110. The high-pressure liquid refrigerant that has flowed out of the heat-source-side heat exchanger110is expanded by the expansion unit111into a low-temperature and low-pressure two-phase refrigerant. The low-temperature and low-pressure two-phase refrigerant flows into the plate heat exchanger100functioning as an evaporator. Then, the low-temperature and low-pressure two-phase refrigerant turns into a low-temperature and low-pressure gas refrigerant while cooling the heat medium circulating in the heat medium circuit B by removing heat from the heat medium. The gas refrigerant that has flowed out of the plate heat exchanger100is sucked into the compressor118again.

Flow of the heat medium in the heat medium circuit B will be described next.

The heat medium pressurized by the pump119and flowing out therefrom flows into the plate heat exchanger100, and cooling energy of the heat-source-side refrigerant in the plate heat exchanger100is transferred to the heat medium. After flowing out of the plate heat exchanger100, this heat medium flows into the use-side heat exchanger112. Then, the heat medium cools the air-conditioned space by removing heat from the indoor air in the use-side heat exchanger112. The heat medium that has flowed out of the use-side heat exchanger112is sucked into the pump119again.

According to Embodiment 4, it is possible to provide the highly-reliable inexpensive air-conditioning apparatus200that can reduce power consumption and can reduce the amount of CO2emissions because the above-described plate heat exchanger100is mounted therein.