Heat Exchanger and Refrigeration Apparatus

This is a continuation of International Application No. PCT/JP2024/012112 filed on Mar. 26, 2024, which claims priority under 35 U.S.C. § 119 (a) to Patent Application No. 2023-057844, filed in Japan on Mar. 31, 2023, all of which are hereby expressly by reference into the present application.

The present disclosure relates to a heat exchanger and a refrigeration apparatus.

Japanese Unexamined Patent Publication No. 2002-267289 discloses a plate heat exchanger in which the efficiency of the heat exchange is improved by making a channel for refrigerant as a heated fluid longer by a structure that makes the refrigerant turn around several times, thereby ensuring the heat transfer area.

A first aspect of the present disclosure is directed to a heat exchanger. The heat exchanger includes: a first fluid layer having a first fluid passage through which a first fluid flows; and a second fluid layer having a second fluid passage through which a second fluid that undergoes a phase change flows, the first fluid layer and the second fluid layer being alternately stacked, the heat exchanger exchanging heat between the first fluid and the second fluid, the second fluid passage being divided into a plurality of channel sections from a first channel section to an N-th channel section by a structure that makes the second fluid turn around (N-1) times, where N is a natural number greater than or equal to two, the first channel section being near a condensation outlet or an evaporation inlet, the N-th channel section being near a condensation inlet or an evaporation outlet, a channel cross-sectional area of the first channel section being smaller than a channel cross-sectional area of the N-th channel section.

As illustrated in, a refrigeration apparatus () transfers heat between a first fluid and a second fluid that undergoes a phase change. The first fluid is, for example, water. The second fluid is a refrigerant that undergoes a phase change between a gas refrigerant and a liquid refrigerant. The second fluid is, for example, propane.

The refrigeration apparatus () includes a fluid circuit (la) serving as a fluid circuit filled with the refrigerant. The fluid circuit (la) includes a compressor (), a four-way switching valve (), a decompression mechanism (), an air heat exchanger (), and a plate heat exchanger ().

The decompression mechanism () is, for example, an expansion valve. The air heat exchanger () is, for example, a cross-fin type fin-and-tube heat exchanger. The fluid circuit (la) performs a vapor compression refrigeration cycle.

The four-way switching valve () switches the direction of circulation of the refrigerant. When the four-way switching valve () is in the state indicated by the solid curves in, the air heat exchanger () functions as an evaporator, and the plate heat exchanger () functions as a condenser. When the four-way switching valve () is in the state indicated by the dashed curves in, the air heat exchanger () functions as a condenser, and the plate heat exchanger () functions as an evaporator.

A situation where the air heat exchanger () functions as an evaporator and the plate heat exchanger () functions as a condenser will be described below.

The refrigeration apparatus () is, for example, a water heater. A water circuit () is connected to the plate heat exchanger (). The water circuit () has a tank (). In the plate heat exchanger (), heat is transferred between the refrigerant flowing through the plate heat exchanger () and water flowing through the water circuit (). The water that has undergone heat exchange in the plate heat exchanger () is stored in the tank (). An inflow pipe () and an outflow pipe () are connected to the tank (). The inflow pipe () allows water to flow into the tank (). The outflow pipe () allows the water stored in the tank () to flow out.

As illustrated in, the plate heat exchanger () includes first fluid layers () and second fluid layers (). The first fluid layers () and the second fluid layers () are alternately stacked in the thickness direction. The plate heat exchanger () transfers heat between the first fluid and the second fluid.

The first fluid layers () each have a first fluid passage (). Water as the first fluid flows through the first fluid passage (). In each of the drawings, the flow of the first fluid is indicated by the black solid arrows. The first fluid passage () extends in the vertical direction in.

The second fluid layers () each have a second fluid passage (). The refrigerant as the second fluid that undergoes a phase change flows through the second fluid passage (). In each of the drawings, the flow of the second fluid is indicated by the hollow arrows. The second fluid passage () extends in the lateral direction in.

The second fluid passage () is divided into a plurality of channel sections from a first channel section (R) to an N-th channel section (RN) by a structure that makes the refrigerant turn around (N-1) times, where Nis a natural number greater than or equal to two. In the example illustrated in, N=4. The second fluid passage () will be described in detail later.

The plate heat exchanger () is provided with a first inlet header (), a first outlet header (), a second inlet header (), and a second outlet header ().

The first inlet header () is configured as a hole extending in the stacking direction at a lower portion of the plate heat exchanger () in. A first inlet pipe () is connected to the first inlet header (). The first inlet pipe () allows water as the first fluid to flow into the plate heat exchanger ().

The first outlet header () is configured as a hole extending in the stacking direction at an upper portion of the plate heat exchanger () in. A first outlet pipe () is connected to the first outlet header (). The first outlet pipe () allows water that has passed through the first inlet header (), the first fluid passages (), and the first outlet header () to flow out of the plate heat exchanger ().

The second inlet header () is configured as a hole extending in the stacking direction at an upper left portion of the plate heat exchanger () in. A second inlet pipe () is connected to the second inlet header (). The second inlet pipe () allows the refrigerant as the second fluid to flow into the plate heat exchanger ().

The second outlet header () is configured as a hole extending in the stacking direction at a lower left portion of the plate heat exchanger () in. A second outlet pipe () is connected to the second outlet header (). The second outlet pipe () allows the refrigerant that has passed through the second inlet header (), the second fluid passages (), and the second outlet header () to flow out of the plate heat exchanger ().

As illustrated also in, the first fluid layers () each include a pair of partition plates (), a first frame-shaped member (), and a first spacer member ().

The pair of partition plates () are spaced apart from each other in the thickness direction. The first frame-shaped member () has a rectangular first internal space () extending in the vertical direction in. The first frame-shaped member () is disposed between the pair of partition plates (). The first internal space () is sealed by the partition plates ().

The first spacer member () is disposed in the first internal space (). The first spacer member () is configured as a corrugated board. The first spacer member () is disposed in the first internal space () in such a posture that the crests and troughs of the corrugation are continuous in the lateral direction in. The tops of the crests and the bottoms of the troughs of the corrugation of the first spacer member () are in contact with the partition plates (). Thus, spaces defined by the first spacer member () and the partition plates () form the first fluid passages ().

The partition plates (), the first frame-shaped member (), and second frame-shaped member () to be described later have through holes at positions facing the first inlet header (), the first outlet header (), the second inlet header, and the second outlet header (), respectively. The partition plates () which form the outer wall surfaces of the plate heat exchanger () have no through holes. These through holes successively joined together in the stacking direction form the first inlet header (), the first outlet header (), the second inlet header, and the second outlet header (). Second Fluid Layer

The second fluid layers () each include a pair of partition plates (), a second frame-shaped member (), and a second spacer member ().

The pair of partition plates () are spaced apart from each other in the thickness direction. In this embodiment, each second fluid layer () shares the partition plates () with the first fluid layers () adjacent to the second fluid layer ().

The second frame-shaped member () has a rectangular second internal space () extending in the vertical direction in. The second frame-shaped member () is disposed between the pair of partition plates (). The second internal space () is sealed by the pair of partition plates ().

The second internal space () includes a first turnaround portion (), a second turnaround portion (), and a third turnaround portion (). The first turnaround portion (), the second turnaround portion (), and the third turnaround portion () are spaced apart from one another in the vertical direction in.

The first turnaround portion () extends rightward from the left inner wall surface of the second internal space () in. A gap is formed between the right end of the first turnaround portion () and the right inner wall surface of the second internal space (). A space between the first turnaround portion () and the lower inner wall surface of the second internal space () communicates with the second outlet header ().

The second turnaround portion () is disposed above the first turnaround portion (). The second turnaround portion () extends leftward from the right inner wall surface of the second internal space () in. A gap is formed between the left end of the second turnaround portion () and the left inner wall surface of the second internal space ().

The third turnaround portion () is disposed above the second turnaround portion (). The third turnaround portion () extends rightward from the left inner wall surface of the second internal space () in. A gap is formed between the right end of the third turnaround portion () and the right inner wall surface of the second internal space (). A space between the third turnaround portion () and the upper inner wall surface of the second internal space () communicates with the second inlet header ().

Thus, the second fluid passage () is divided into the first channel section (R), the second channel section (R), the third channel section (R), and the fourth channel section (R) by the structure that makes the refrigerant turn around and which is formed by the first turnaround portion (), the second turnaround portion (), and the third turnaround portion (). The second fluid passage () with a structure that makes the refrigerant turn around can increase the heat transfer area.

The first channel section (R) is a space between the lower inner wall surface of the second internal space () and the first turnaround portion (). Thus, the first channel section (R) is near a condensation outlet of the plate heat exchanger () functioning as a condenser. At this time, the fourth channel section (R) is near a condensation inlet of the plate heat exchanger ().

When the plate heat exchanger () functions as an evaporator, the first channel section (R) is near an evaporation inlet. At this time, the fourth channel section (R) is near an evaporation outlet of the plate heat exchanger ().

The second channel section (R) is a space between the first turnaround portion () and the second turnaround portion () in the second internal space (). The third channel section (R) is a space between the second turnaround portion () and the third turnaround portion () in the second internal space (). The fourth channel section (R) is a space between the upper inner wall surface of the second internal space () and the third turnaround portion ().

The second spacer member () is disposed in the second internal space (). The second spacer member () is configured as a corrugated board. The second spacer member () is disposed in the second internal space () in such a posture that the crests and troughs of the corrugation are continuous in the vertical direction in. The tops of the crests and the bottoms of the troughs of the corrugation forming the second spacer member () are in contact with the partition plates (). Thus, spaces defined by the second spacer member () and the partition plates () form the second fluid passages ().

The second spacer member () is disposed in the first channel section (R), the second channel section (R), the third channel section (R), and the fourth channel section (R). In the second spacer member (), the refrigerant flows in the lateral direction in.

Thus, the refrigerant that has flowed in from the second inlet pipe () and the second inlet header () passes through the second fluid passage () in the fourth channel section (R), and then passes through the gap between the third turnaround portion () and the inner wall surface of the second internal space () toward the third channel section (R).

The refrigerant that has passed through the second fluid passage () in the third channel section (R) passes through the gap between the second turnaround portion () and the inner wall surface of the second internal space () toward the second channel section (R).

The refrigerant that has passed through second fluid passage () in the second channel section (R) passes through the gap between the first turnaround portion () and the inner wall surface of the second internal space () toward the first channel section (R).

The refrigerant that has passed through the second fluid passage () in the first channel section (R) passes through the second outlet header () and the second outlet pipe () to flow out of the plate heat exchanger ().

When the plate heat exchanger () is used as a condenser, the refrigerant as a heated fluid condenses as it is closer to the downstream side, and hence the refrigerant has a lower degree of dryness. This means that the density changes from a gas refrigerant to a liquid refrigerant, causing a reduction in the flow velocity of the heated fluid on the downstream side. As a result, the heat transfer coefficient decreases.

To address this problem, in this embodiment, it is possible to reduce a decrease in the heat transfer coefficient due to a decrease in the flow velocity of the refrigerant at the condensation outlet of the second fluid passage ().

Specifically, as illustrated in, the first channel section (R) has a smaller channel cross-sectional area than a channel cross-sectional area of the second channel section (R) different from the first channel section (R). For example, it is preferable that the first channel section (R) has a channel cross-sectional area that is 25% or less of the channel cross-sectional area of the second channel section (R).

The first channel section (R) has a plurality of first unit passages (r). Each of the first unit passages (r) has a substantially constant channel cross-sectional area, and extends along the direction of flow of the refrigerant. The first unit passages (r) are formed in a space surrounded by the corrugated second spacer member () between the tops of adjacent crests and by the partition plate (), and a space surrounded by the corrugated second spacer member () between the bottoms of adjacent troughs and by the partition plate ().

The second channel section (R) has a plurality of second unit passages (r). Each of the second unit passages (r) has a substantially constant channel cross-sectional area, and extends along the direction of flow of the refrigerant. The second unit passages (r) are formed in a space surrounded by the corrugated second spacer member () between the tops of adjacent crests and by the partition plate (), and a space surrounded by the corrugated second spacer member () between the bottoms of adjacent troughs and by the partition plate ().

The channel cross-sectional area of the respective first unit passages (r) is substantially equal to the channel cross-sectional area of the respective second unit passages (r). The number of the first unit passages (r) is less than the number of the second unit passages (r).

As can be seen, the channel cross-sectional area of the first channel section (R) is smaller than that of the second channel section (R), thereby making it possible to increase the flow velocity of the refrigerant flowing through the first channel section (R), and reduce a decrease in the heat transfer coefficient in the first channel section (R).

In this embodiment, the passage is divided to include the first channel section (R), the second channel section (R), the third channel section (R), and the fourth channel section (R) by the structure that makes the refrigerant turn around two or more times. Thus, it is preferable that the channel cross-sectional area of the first channel section (R) is 25% or less of the channel cross-sectional area of the fluid section having the largest channel cross-sectional area among the second channel section (R), the third channel section (R), and the fourth channel section (R).

According to a feature of this embodiment, the channel cross-sectional area of the first channel section (R) is small, thereby making it possible to increase the flow velocity of the second fluid flowing through the first channel section (R) and reduce a decrease in the heat transfer coefficient in the first channel section (R).

According to a feature of this embodiment, the channel cross-sectional area of the first channel section (R) is appropriately set, thereby making it possible to increase the flow velocity of the second fluid flowing through the first channel section (R) and reduce a decrease in the heat transfer coefficient in the first channel section (R).