Abstract
A heat exchanger prevents cracking in heat transfer plates while avoiding lowering heat-exchange efficiency. Heat transfer plates are arranged with a space between them, and a hollow pipe extends through the plates. A high-temperature gas flows through the space to exchange heat with a liquid in the hollow pipe. The heat transfer plates are elongated in the direction in which parts of the hollow pipe are aligned and can thus have thermal expansion accumulating in the elongation direction. The heat transfer plates each include a thermal expansion absorber between an edge of the heat transfer plate receiving inflow of the high-temperature gas and an inter-pipe portion between adjacent parts of the hollow pipe to absorb thermal expansion of the heat transfer plate. A selected one or more of the inter-pipe portions, rather than all, include the thermal expansion absorber.
Claims
1. A heat exchanger for causing heat exchange between a high-temperature gas and a liquid having a lower temperature than the high-temperature gas to heat the liquid, the heat exchanger comprising: a frame defining a part of a gas passage for the high-temperature gas; a plurality of heat transfer plates arranged within the frame with a space left between the plurality of heat transfer plates for the high-temperature gas to flow; and a hollow pipe extending through the plurality of heat transfer plates, the hollow pipe being configured to receive the liquid to exchange heat with the high-temperature gas flowing through the space between the plurality of heat transfer plates, wherein the hollow pipe extends through the plurality of heat transfer plates at predetermined N positions aligned in a direction crossing a direction in which the high-temperature gas flows through the space between the plurality of heat transfer plates, where N is an integer of at least three, the plurality of heat transfer plates each include N−1 inter-pipe portions between adjacent parts of the hollow pipe extending through the plurality of heat transfer plates at the N positions, the N−1 inter-pipe portions of each heat transfer plate include selected M inter-pipe portion(s) each of which includes a thermal expansion absorbing space configured between an edge of the heat transfer plate receiving inflow of the high-temperature gas and the selected inter-pipe portion(s) to absorb thermal expansion of the heat transfer plate, where M is an integer smaller than N−1, and no thermal expansion absorbing space is configured in each of non-selected N−1-M inter pipe portion(s) among the N−1 inter-pipe portions of each heat transfer plate.
2. The heat exchanger according to claim 1, wherein the thermal expansion absorbing space is a cut extending from the edge of the heat transfer plate receiving the inflow of the high-temperature gas to the selected inter-pipe portion.
3. The heat exchanger according to claim 1, wherein each heat transfer plate is divided by the selected inter-pipe portion into a plurality of sub-areas through which the hollow pipe extends, and the selected inter-pipe portion is positioned to allow each of the plurality of sub-areas to receive not more than three parts of the hollow pipe extending through the sub-areas.
4. The heat exchanger according to claim 1, wherein each heat transfer plate is divided by the selected inter-pipe portion into a plurality of sub-areas through which the hollow pipe extends, and the selected inter-pipe portion is positioned to allow the plurality of sub-areas to receive the same number of parts of the hollow pipe extending through the sub-areas or numbers of parts of the hollow pipe different from one another by not more than one.
5. The heat exchanger according to claim 1, wherein the selected inter-pipe portion is at least one of inter-pipe portions symmetric to each other among the N−1 inter-pipe portions.
6. The heat exchanger according to claim 1, wherein each heat transfer plate receives the hollow pipe extending through the heat transfer plate at the N positions, and receives a plurality of parts of the hollow pipe extending through the heat transfer plate at positions downstream in a direction in which the high-temperature gas flows, and the selected inter-pipe portion is selected from the N−1 inter-pipe portions between upstream parts of the hollow pipe extending through the heat transfer plate at the N positions.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic diagram of a water heater 1 including a heat exchanger 10 according to an embodiment.
(2) FIGS. 2A and 2B are schematic views of the heat exchanger 10 according to the embodiment.
(3) FIG. 3 is an enlarged partial view of the heat exchanger 10 showing heat exchanger fins 13 fitted on a hollow pipe 12.
(4) FIG. 4 is a diagram of a heat exchanger fin 13 included in the heat exchanger 10 according to the embodiment, showing the structure in detail.
(5) FIG. 5 is a diagram showing the mechanism for thermal expansion absorbers 15 to absorb thermal expansion of the heat exchanger fin 13.
(6) FIG. 6 is a diagram of a heat exchanger fin 13 including thermal expansion absorbers 15 according to another embodiment.
(7) FIG. 7 is a diagram of a heat exchanger fin 13 including symmetrical thermal expansion absorbers 15.
(8) FIG. 8 is a diagram of a heat exchanger fin 13 including through-holes 13b in rows.
(9) FIG. 9 illustrates schematic diagrams of thermal expansion absorbers 15 according to another embodiment.
(10) FIG. 10 illustrates schematic diagrams of thermal expansion absorbers 15 according to another embodiment.
(11) FIG. 11 illustrates schematic diagrams of slit-free thermal expansion absorbers 15 according to another embodiment.
DETAILED DESCRIPTION
(12) FIG. 1 is a schematic diagram of a water heater 1 including a heat exchanger 10 according to an embodiment. As shown in the figure, the water heater 1 includes a substantially rectangular body case 2 with an exhaust port 3 protruding from a side surface. The body case 2 has, on its bottom surface, a gas channel 4 for feeding fuel gas to the water heater 1, a service water channel 5 for feeding service water to the water heater 1, and a hot water channel 6 for discharging hot water generated in the water heater 1. The channels protrude from the bottom surface of the body case 2.
(13) In addition to the heat exchanger 10 according to the present embodiment, the water heater 1 also includes a combustion compartment 20, a gas manifold 30, a blower fan 40, a top cover 50, a controller 60, and a main valve unit 70 in the body case 2. The combustion compartment 20 is a hollow, prism component that is rectangular in horizontal cross section and is open at its top and bottom. The combustion compartment 20 has a lower space accommodating gas burners (not shown) that burn fuel gas. The combustion compartment 20 has an upper space without the gas burners, which is used as a combustion chamber by the gas burners for burning fuel gas.
(14) The combustion compartment 20 includes the gas manifold 30 fixed on its side surface (front surface in FIG. 1) for feeding fuel gas to the gas burners (not shown) in the combustion compartment 20, and also includes a spark plug 21 above the gas manifold 30. The combustion compartment 20 further includes the blower fan 40 fixed on its lower end for feeding combustion air to the gas burners. The combustion air is fed from the blower fan 40. While the spark plug 21 is sparking, the fuel gas is fed from the gas manifold 30 to the gas burners in the combustion compartment 20. The fed fuel gas is then burned in the combustion chamber inside the combustion compartment 20 to produce hot combustion exhaust gas. The gas channel 4 for receiving fuel gas from outside is connected to the main valve unit 70 fixed on the inner bottom surface of the body case 2. The fuel gas is fed from the main valve unit 70 to the gas manifold 30 through a fuel gas tube 71.
(15) The combustion compartment 20 includes the heat exchanger 10 according to the present embodiment fixed on its upper end. In FIG. 1, the heat exchanger 10 is hatched. Although its structure will be described later, the heat exchanger 10 allows combustion exhaust gas produced in the combustion compartment 20 to flow inside. The combustion exhaust gas flowing inside the heat exchanger 10 exchanges heat with service water to generate hot water. The heat exchanger 10 receives service water through a service water tube 73 having an upstream end connected to a connector 72 fixed on the inner bottom surface of the body case 2. The connector 72 is connected to the service water channel 5 for feeding service water to the water heater 1. The service water fed through the service water channel 5 thus flows through the connector 72 and the service water tube 73 to the heat exchanger 10. The hot water generated in the heat exchanger 10 flows out through a hot water tube 74 having a downstream end connected to a connector 75 fixed on the inner bottom surface of the body case 2. The connector 75 is connected to the hot water channel 6. The hot water generated in the heat exchanger 10 thus flows through the hot water tube 74 and the connector 75 out of the water heater 1 through the hot water channel 6.
(16) The heat exchanger 10 includes the top cover 50 fixed on its top. The top cover 50 is formed from a pressed metal plate. The combustion exhaust gas produced in the combustion compartment 20 flows through the heat exchanger 10 and is then guided by the top cover 50 to the exhaust port 3. The combustion exhaust gas in the present embodiment corresponds to high-temperature gas in one or more aspects of the present invention. The combustion exhaust gas flows through the combustion compartment 20 and the heat exchanger 10 before flowing out from the exhaust port 3 through the top cover 50. Thus, the internal spaces of the combustion compartment 20 and the heat exchanger 10 correspond to a gas passage in one or more aspects of the present invention.
(17) FIGS. 2A and 2B are schematic views of the heat exchanger 10 according to the present embodiment. FIG. 2A shows the appearance of the heat exchanger 10. FIG. 2B shows the heat exchanger 10 as viewed from above in the direction indicated by arrow P in FIG. 2A. As shown in FIGS. 2A and 2B, the heat exchanger 10 includes a rectangular frame 11, multiple heat exchanger fins 13 arranged within the frame 11, and a hollow pipe 12 extending through the frame 11 and the multiple heat exchanger fins 13. The hollow pipe 12 extends through the frame 11 and the multiple heat exchanger fins 13, and is bent in a U-shape to extend again through the frame 11 and the heat exchanger fins 13 in the opposite direction. This is repeated to form a serpentine shape. As shown in FIGS. 2A and 2B, the hollow pipe 12 extends through the frame 11 and the multiple heat exchanger fins 13 nine times. The hollow pipe 12 has an upstream end connected to the service water tube 73, and a downstream end connected to the hot water tube 74. In the present embodiment, the frame 11, the hollow pipe 12, and the heat exchanger fins 13 are all formed from copper or other metal with high thermal conductivity. The heat exchanger fins 13 in the present embodiment correspond to heat transfer plates in one or more aspects of the present invention.
(18) FIG. 3 is an enlarged partial view of the heat exchanger 10 (the area indicated by A in FIG. 2B) showing the heat exchanger fins 13 fitted on the hollow pipe 12. As shown in the figure, the multiple heat exchanger fins 13 are arranged at regular intervals within the frame 11. For clarity of illustration, one of the heat exchanger fins 13 is indicated by a solid line and the other heat exchanger fins 13 by dashed lines in FIG. 3.
(19) Each heat exchanger fin 13 is an elongated plate, and mainly includes flat heat transfer portions 13a with through-holes 13b (refer to FIG. 4) to receive the hollow pipe 12. As shown in FIG. 3, each through-hole 13b has an inner periphery end surface bent up into a joint 13c to which the hollow pipe 12 is brazed. The bent joint 13c has, on its distal end, a protruding edge 13d in contact with an adjacent heat exchanger fin 13 to maintain a predetermined distance from the adjacent heat exchanger fin 13. The upper end of the heat transfer portion 13a (facing the front of FIG. 3) is also bent up into a protruding edge 13e between adjacent parts of the hollow pipe 12 to maintain a predetermined distance from the adjacent heat exchanger fin 13. The edge of the heat transfer portion 13a on each end of the heat exchanger fin 13 is also bent up into a protruding edge 13f to maintain a predetermined distance from the adjacent heat exchanger fin 13. Thus, the multiple heat exchanger fins 13 are arranged at regular intervals with a space 13g between adjacent heat exchanger fins 13. In FIG. 3, the space 13g between adjacent heat exchanger fins 13 is hatched.
(20) FIG. 4 is a diagram of a heat exchanger fin 13 showing the structure in detail as viewed in the direction indicated by arrow Q in FIG. 2B. As shown in the figure, the heat exchanger fin 13 has, at regular intervals, the through-holes 13b to receive the hollow pipe 12 at multiple (nine in the figure) positions across the length of the elongated plate member. As indicated by hatched arrows in the figure, combustion exhaust gas flows in along the width of the heat exchanger fin 13. Thus, the multiple through-holes 13b are aligned in a direction crossing the flow direction of the combustion exhaust gas. The two ends of the heat exchanger fin 13 are bent into the protruding edges 13f (refer to FIG. 3). In upstream areas facing the flow direction of the combustion exhaust gas (facing downward in FIG. 4), the edge of the heat exchanger fin 13 upstream from each through-hole 13b is bent into a protruding edge 13h to leave the space 13g from the adjacent heat exchanger fin 13.
(21) In the present embodiment, the heat exchanger fin 13 includes inter-pipe portions 14 between the through-holes 13b. As shown in FIG. 4, the upstream edge of the heat exchanger fin 13 receiving the flow of the combustion exhaust gas has the shape of a wave recessed downstream into the inter-pipe portions 14. Selected ones of the recesses on the edge include slits cut in the heat exchanger fin 13 extending from the edge of the heat exchanger fin 13 to the inter-pipe portions 14 to form thermal expansion absorbers 15. The heat exchanger fin 13 illustrated in FIG. 4 has nine through-holes 13b and thus includes eight inter-pipe portions 14, and the upstream edge of the heat exchanger fin 13 receiving combustion exhaust gas has eight recesses. The thermal expansion absorber 15 may be formed in one or more selected ones (but not all) of the eight recesses on the edge. Among the eight inter-pipe portions 14, the inter-pipe portions 14 including the thermal expansion absorbers 15 in the edge of the heat exchanger fin 13 are particularly referred to as selected inter-pipe portions 14s.
(22) The heat exchanger fin 13 including the thermal expansion absorbers 15 in the upstream edge receiving the flow of the combustion exhaust gas can be prevented from cracking when the heat exchanger 10 is used over a long time under thermally severe conditions for the reasons below. For convenience of explanation, a heat exchanger fin 13 with no thermal expansion absorber 15 will be described first. When heated by combustion exhaust gas, the heat exchanger fin 13 reaches a higher temperature and expands. The expansion due to heat will be simply referred to as thermal expansion. The coefficient of thermal expansion of metal (in other words, thermal expansion per unit length for a unit increase in temperature) is constant in all directions. However, for the elongated heat exchanger fin 13 as shown in FIG. 4, the thermal expansion is larger in the elongation direction (horizontal direction in FIG. 4) than in the transverse direction (vertical direction in FIG. 4). The larger thermal expansion in the elongation direction is restricted by the multiple parts of the hollow pipe 12 extending through the heat exchanger fin 13, and the resultant larger thermal stress on the heat exchanger fin 13 may cause cracking. Thus, cracking in the heat exchanger fin 13 may result from the heat exchanger fin 13 thermally expanding more in the elongation direction, rather than simply from the heat exchanger fin 13 reaching a higher temperature.
(23) Although the heat exchanger fin 13 illustrated in FIG. 4 can receive the nine parts of the hollow pipe 12, the two thermal expansion absorbers 15 formed as slits divide the hollow pipe 12 into three sub-areas Ra, Rb, and Rc each including three parts of the hollow pipe 12. The sub-areas Ra, Rb, and Rc, each of which is much shorter than the entire heat exchanger fin 13, greatly reduce thermal expansion in the elongation direction. The heat exchanger fin 13 is thus prevented from cracking. This will be described in more detail.
(24) FIG. 5 is an enlarged diagram of a sub-area Rb (refer to FIG. 4) of the heat exchanger fin 13. As shown in the figure, the sub-area Rb has three through-holes 13b, which are referred to as a through-hole 13bC for the central through-hole 13b, a through-hole 13bL for the left through-hole 13b, and a through-hole 13bR for the right through-hole 13b for convenience. When the heat exchanger fin 13 is heated, the heat transfer portion 13a surrounding the central through-hole 13bC (hatched in the figure) thermally expands to push the left through-hole 13bL to the left and the right through-hole 13bR to the right. In the figure, the through-holes 13bL and 13bR pushed to the left and the right are indicated by dashed lines. Moreover, the heat transfer portion 13a surrounding the left through-hole 13bL thermally expands to the right and the left from the position pushed to the left together with the through-hole 13bL (indicated by the dashed line), pushing the through-hole 13b (not shown) on the left of the left through-hole 13bL further to the left. In this manner, the heat exchanger fin 13 accumulates thermal expansion in the elongation direction. A longer heat exchanger fin 13 thus accumulates more thermal expansion.
(25) However, the thermal expansion absorbers 15 in the heat exchanger fin 13 absorb the accumulating thermal expansion. More specifically, as shown in FIG. 5, the thermal expansion of the heat transfer portion 13a surrounding the through-hole 13bL pushed to the left (indicated by the dashed line in the figure) is absorbed by the thermal expansion absorber 15 formed as a slit on the left of the through-hole 13bL. The thermal expansion merely shifts an edge 15tR on the right of the slit leftward and does not reach the adjacent left through-hole 13b (not shown). In FIG. 5, the edge 15tR of the thermal expansion absorber 15 shifted leftward by the thermal expansion is indicated by a dashed line.
(26) The same applies to the through-hole 13bR on the right of the central through-hole 13bC. More specifically, the thermal expansion of the heat transfer portion 13a surrounding the through-hole 13bR pushed to the right (indicated by the dashed line in the figure) is absorbed by the thermal expansion absorber 15 on the right of the through-hole 13bR. The thermal expansion merely shifts an edge 15tL on the left of the slit rightward and does not reach the adjacent right through-hole 13b (not shown). In FIG. 5, the edge 15tL of the thermal expansion absorber 15 shifted rightward by the thermal expansion is indicated by a dashed line.
(27) Although the sub-area Rb at the center of the heat exchanger fin 13 (refer to FIG. 4) has been described with reference to FIG. 5, the same applies to the sub-area Ra on the left of the sub-area Rb and the sub-area Rc on the right of the sub-area Rb. Thus, when the heat exchanger fin 13 is heated to cause thermal expansion of the sub-areas Ra, Rb, and Rc, the rightward shift of the edge 15tL of the thermal expansion absorber 15 and the leftward shift of the edge 15tR of the thermal expansion absorber 15 absorb the thermal expansion to prevent accumulation of thermal expansion across the thermal expansion absorbers 15. This structure prevents the heat exchanger fin 13 from cracking.
(28) As clearly described above, the slit of each thermal expansion absorber 15 has a width h large enough to prevent contact between the edge 15tL shifted rightward by thermal expansion and the edge 15tR shifted leftward by thermal expansion. The heat exchanger fin 13 has a part (upstream part) receiving the inflow of the combustion exhaust gas reaching higher temperatures than a downstream part. The heat exchanger fin 13 thus has a larger thermal expansion in the upstream part than in the downstream part. Thus, each heat exchanger fin 13 may include the thermal expansion absorber 15 as a cut extending from the upstream edge as illustrated in FIG. 4.
(29) As shown in FIG. 4, the heat exchanger fin 13 includes the thermal expansion absorbers 15 at positions to divide the heat exchanger fin 13 covering the nine through-holes 13b into the sub-areas Ra, Rb, and Rc each covering three through-holes 13b. However, the thermal expansion absorbers 15 may be formed at positions that form multiple sub-areas with different lengths, and the number of thermal expansion absorbers 15 may not be two. For example, a heat exchanger fin 13 illustrated in FIG. 6 includes three thermal expansion absorbers 15. The thermal expansion absorbers 15 are formed at positions to divide the heat exchanger fin 13 into a sub-area Ra covering five through-holes 13b, a sub-area Rb covering one through-hole 13b, a sub-area Rc covering two through-holes 13b, and a sub-area Rd covering one through-hole 13b, which are arranged in this order from left to right.
(30) Also in such a configuration shown in FIG. 4, thermal expansion of the sub-areas Ra, Rb, Rc, and Rd is absorbed by the thermal expansion absorbers 15 without accumulating largely, for the same reasons as described above with reference to FIG. 5. The sub-area Ra, covering five through-holes 13b, accumulates thermal expansion. However, the sub-area Ra is shorter than the entire heat exchanger fin 13 and thus accumulates less thermal expansion. Thus, this structure generates less thermal stress when the hollow pipe 12 extending through the through-holes 13b restricts the thermal expansion than the structure including no thermal expansion absorber 15, and thus reduces cracking.
(31) As illustrated in FIG. 6, with a short sub-area (having fewer through-holes 13b) and a long sub-area (having more through-holes 13b), the accumulating thermal expansion is larger in the long sub-area than in the short sub-area. Thus, as illustrated in FIG. 4, the thermal expansion absorbers 15 are positioned in the heat exchanger fin 13 to allow multiple sub-areas to have the same length (have the same number of through-holes 13b) or to have numbers of through-holes 13b different from one another by not more than one.
(32) Although more thermal expansion absorbers 15 formed in the heat exchanger fin 13 allow a sub-area to be shorter (have fewer through-holes 13b), the surface area of the heat transfer portions 13a in the heat exchanger fin 13 may decrease and lower the efficiency of heat exchange. However, to prevent thermal expansion of sub-areas from accumulating, a sub-area having one through-hole 13b (e.g., sub-areas Rb and Rd in FIG. 6) is not largely different from a sub-area having three through-holes 13b (e.g., sub-areas Ra, Rb, and Rc in FIG. 4). This is because a sub-area having three through-holes 13b actually receives no accumulation of thermal expansion as described above with reference to FIG. 5. Thermal expansion of the heat transfer portion 13a surrounding the central through-hole 13bC may reach the left and right through-hole 13bL and 13bR. In addition to the thermal expansion, thermal expansion of the heat transfer portions 13a around the left and right through-holes 13bL and 13bR may be added, thus accumulating the thermal expansion. However, the thermal expansion is absorbed by the thermal expansion absorbers 15 adjacent to the left and right through-holes 13bL and 13bR.
(33) Thus, for a heat exchanger fin 13 having the number of through-holes 13b that is a multiple of three, as illustrated in FIG. 4, thermal expansion absorbers 15 may be positioned to cause each sub-area to have three through-holes 13b. For the number of through-holes 13b that is not a multiple of three, thermal expansion absorbers 15 may be positioned to cause some sub-areas to have three through-holes 13b, and the other sub-areas to have two or four through-holes 13b. This structure minimizes the number of thermal expansion absorbers 15 formed in the heat exchanger fin 13, enabling each sub-area to avoid accumulation of thermal expansion. This heat exchanger thus prevents the heat exchanger fin 13 from cracking and avoids lowering the efficiency of heat exchange.
(34) In other examples, thermal expansion absorbers 15 that form sub-areas in different lengths may be positioned to cause the sub-areas to be symmetrical with respect to the inflow of the combustion exhaust gas into the heat exchanger fin 13. For example, the heat exchanger fin 13 illustrated in FIG. 7 has eight through-holes 13b, with sub-areas Ra and Rc each having three through-holes 13b and a sub-area Rb having two through-holes 13b. In this case, the thermal expansion absorbers 15 are positioned to cause the sub-area Rb to have two through-holes 13b at the center, and the sub-areas Ra and Rc each to have three through-holes 13b on the right and the left. This structure prevents the heat exchanger fin 13 from having thermal stress biased rightward or leftward, and thus avoids warping of the heat exchanger fin 13.
(35) As illustrated in FIGS. 4, 6, and 7, each heat exchanger fin 13 in the above embodiment has multiple through-holes 13b aligned in a direction crossing the flow of the combustion exhaust gas (lateral direction). However, as illustrated in FIG. 8, a heat exchanger fin 13 may have the multiple through-holes 13b arranged upstream in the flow direction of the combustion exhaust gas as well as multiple through-holes 13i aligned downstream. The heat exchanger fin 13 has an upstream part reaching a higher temperature than a downstream part in the flow of the combustion exhaust gas. As shown in FIG. 8, for the through-holes 13b and 13i in rows in the flow of the combustion exhaust gas, thermal expansion absorbers 15 may be formed for the through-holes 13b that are aligned upstream.
(36) Each thermal expansion absorber 15 in the above embodiment is planar (more specifically, a slit cut in a part of the flat heat transfer portion 13a). However, the thermal expansion absorber 15 may be three-dimensional (more specifically, a slit cut in a part of the flat heat transfer portion 13a, with the heat transfer portion 13a bent at either or both of its edges along the slit).
(37) FIG. 9 illustrates a heat exchanger fin 13 including three-dimensional thermal expansion absorbers 15. FIG. 9(c) shows the entire heat exchanger fin 13. FIG. 9(b) is an enlarged view of a thermal expansion absorber 15. FIG. 9(c) shows the thermal expansion absorber 15 as viewed in the direction indicated by arrow R in FIG. 9(b). The thermal expansion absorber 15 illustrated in FIG. 9 is formed by cutting a slit in a heat transfer portion 13a of the heat exchanger fin 13 (refer to FIG. 9(b)), bending the heat transfer portion 13a on the left of the cut toward the facing side of FIG. 9(b), and bending the heat transfer portion 13a on the right of the cut toward the opposite side of FIG. 9(b).
(38) In this manner, an edge 15tL on the left and an edge 15tR on the right of the slit forming the thermal expansion absorber 15 are positioned on different planes (refer to FIG. 9(c)). When the left edge 15tL of the thermal expansion absorber 15 largely moves rightward, and the right edge 15tR largely moves leftward to absorb thermal expansion as indicated by arrows in FIG. 9(c), the left edge 15tL and the right edge 15tR do not come in contact with each other. The thermal expansion absorber 15 may thus have a smaller slit width h (refer to FIG. 5). The thermal expansion absorber 15 with the small width thus is less likely to reduce the surface area of the heat exchanger fin 13 or is less likely to lower the heat-exchange efficiency.
(39) The thermal expansion absorber 15 illustrated in FIG. 9 is formed by bending the heat transfer portions 13a on the right and the left of the slit cut from the edge of the heat exchanger fin 13. However, the edge 15tL on the left and the edge 15tR on the right of the thermal expansion absorber 15 may be positioned on different planes, and both the heat transfer portions 13a on the right and the left of the slit may not be bent. Thus, the heat transfer portion 13a on one edge of the slit may be bent, and the heat transfer portion 13a on the other edge may not be bent.
(40) FIG. 10 illustrates a heat exchanger fin 13 including three-dimensional thermal expansion absorbers 15 according to another modification. FIG. 10(a) shows the entire heat exchanger fin 13. FIG. 10(b) is an enlarged view of a thermal expansion absorber 15. FIG. 10(c) shows the thermal expansion absorber 15 as viewed in the direction indicated by arrow S in FIG. 10(b). The thermal expansion absorber 15 illustrated in FIG. 10 has an edge 15tL, which is parallel to its unbent surface, formed by cutting a slit in a heat transfer portion 13a of the heat exchanger fin 13 (refer to FIG. 10(b)) and bending the heat transfer portion 13a on the left of the cut. The edge 15tL on the left and an edge 15tR on the right of the slit forming the thermal expansion absorber 15 are positioned on different planes (refer to FIG. 10(c)). When the left and right edges 15tL and 15tR of the thermal expansion absorber 15 largely move to absorb thermal expansion as indicated by arrows in FIG. 10(c), the left and right edges 15tL and 15tR do not come in contact with each other. The thermal expansion absorber 15 may thus have a smaller slit width h (refer to FIG. 5), and the thermal expansion absorber 15 with the small width is less likely to reduce the surface area of the heat exchanger fin 13 or is less likely to lower the heat-exchange efficiency.
(41) In the above embodiment, the thermal expansion absorbers 15 are formed by cutting slits in the heat exchanger fin 13. However, the thermal expansion absorbers 15 may have any shape that deforms easily to absorb thermal expansion and may not be slits in the heat exchanger fin 13.
(42) FIG. 11 illustrates a heat exchanger fin 13 including slit-free thermal expansion absorbers 15. FIG. 11(a) shows the entire heat exchanger fin 13. FIG. 11(b) is an enlarged view of a thermal expansion absorber 15. FIG. 11(c) shows the thermal expansion absorber 15 as viewed in the direction indicated by arrow Tin FIG. 11(b). The thermal expansion absorber 15 in this shape also absorbs thermal expansion. When the heat transfer portion 13a on the left of the thermal expansion absorber 15 moves rightward and the heat transfer portion 13a on the right moves leftward due to thermal expansion of the heat exchanger fin 13 as indicated by arrows in FIG. 11(c), a left side wall 15c and a right side wall 15d forming a rib of the thermal expansion absorber 15 bend to absorb thermal expansion. This structure prevents the heat exchanger fin 13 from cracking.
(43) As shown in FIG. 11(c), the left side wall 15c and the right side wall 15d forming the rib of the thermal expansion absorber 15 are parallel and connected to each other with an arched ceiling. However, as illustrated in FIG. 11(d), the right and the left side walls 15c and 15d may be placed closer to form a rib with a ridge-shaped cross section. The thermal expansion absorber 15 formed in this manner also prevents the heat exchanger fin 13 from cracking. When the heat transfer portions 13a come closer from the right and the left of the thermal expansion absorber 15 as indicated by arrows in FIG. 11(d), the right and the left side walls 15c and 15d forming the rib of the thermal expansion absorber 15 bend to absorb thermal expansion, thus preventing the heat exchanger fin 13 from cracking. As shown in FIG. 11, the slit-free thermal expansion absorber 15 does not reduce the surface area of the heat exchanger fin 13, and the heat-exchange efficiency may not be lowered.
(44) Although the heat exchanger 10 according to the present embodiment has been described, the embodiment disclosed herein should not be construed to be restrictive, but may be modified variously without departing from the scope and the spirit of the invention.
REFERENCE SIGNS LIST
(45) 1 water heater 2 body case 3 exhaust port 4 gas channel 5 service water channel 6 hot water channel 10 heat exchanger 11 frame 12 hollow pipe 13 heat exchanger fin 13a heat transfer portion 13b through-hole 13c joint 13d protruding edge 13e, 13f protruding edge 13g space 13h protruding edge 13i through-hole 14 inter-pipe portion 14s selected inter-pipe portion 15 thermal expansion absorber 15c, 15d side wall 15tL, 15tR edge 20 combustion compartment 21 spark plug 30 gas manifold 40 blower fan 50 top cover 60 controller 70 main valve unit 71 fuel gas tube 72 connector 73 service water tube 74 hot water tube 75 connector Ra to Rd sub-area
