BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front sectional view schematically showing an example of water heater according to the present invention;
FIG. 2 is a front view of a principal portion of the water heater shown in FIG. 1;
FIG. 3 is a sectional view taken along lines III-III in FIG. 1;
FIG. 4 is a side view of a principal portion of the water heater shown in FIG. 1;
FIG. 5A is a horizontal sectional view of a secondary heat exchanger of the water heater shown in FIG. 1, whereas FIG. 5B is a front sectional view thereof;
FIG. 6A is a plan view showing an example of water tube of the secondary heat exchanger shown in FIGS. 5A and 5B, whereas FIG. 6B is a sectional view taken along lines VI-VI in FIG. 6A;
FIG. 7 schematically shows the water tube shown in FIGS. 6A and 6B;
FIG. 8 is a horizontal sectional view showing another example of heat exchanger according to the present invention; and
FIG. 9 schematically shows an example of conventional structure.
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIGS. 1-6 show an example of water heater and the related structure according to the present invention. In these figures, the arrow V indicates the vertical direction, whereas the arrow H indicates the horizontal direction.
As better shown in FIG. 1, the water heater A of this embodiment includes a burner 3, a primary heat exchanger 1 and a secondary heat exchanger B. The secondary heat exchanger B is an example of heat exchanger to which the present invention is applied.
The burner 3 is arranged in a casing 30 and burns gas supplied from the outside of the casing 30 through a pipe 32. A fan 31 is arranged below the casing 30 so that air for combustion is supplied from the fan 31 upward into the casing 30. The primary heat exchanger 1 is provided for recovering sensible heat from the combustion gas generated by the burner 3. The primary heat exchanger 1 includes a water tube 11 provided with a plurality of fins 12 and penetrating through a casing 10 generally horizontally. The casings 10 and 30 may be formed integrally with each other.
The secondary heat exchanger B is provided for recovering latent heat from the combustion gas. The secondary heat exchanger B is arranged above the primary heat exchanger 1 and connected to the casing 10 via an auxiliary casing 19. The secondary heat exchanger B includes a casing 7 into which combustion gas is to be introduced, a plurality of water tubes WT each including a helical tube body 5, and headers 6A and 6B for water inflow and hot-water outflow.
The casing 7 is in the form of a generally rectangular parallelepiped and encloses the helical tube bodies 5. As shown in FIG. 3, the casing 7 includes a rear wall 70a and a front wall 70b which are formed with a gas supply port 71 and a gas discharge port 72, respectively. The gas discharge port 72 may have a generally rectangular shape as shown in FIG. 2, and the gas supply port 71 may have a similar shape. The combustion gas passed through the primary heat exchanger 1 and flowed upward enters the casing 7 through the gas supply port 71. In the casing 7, the water tubes WT recover latent heat from the combustion gas. After the latent heat recovery, the combustion gas is discharged from the casing 7 through the gas discharge port 72. When latent heat is recovered from the combustion gas, condensate water is generated at the surfaces of the water tubes WT. Therefore, a discharge port 73 for discharging condensate water is provided at the bottom wall 70d of the casing 7. With this structure, when condensate water drops from the surfaces of the water tubes WT onto the bottom wall 70d of the casing 7, the condensate water is discharged from the casing 7 through the discharge port 73.
As shown in FIGS. 5A and 5B, respective helical tube bodies 5 of the plurality of (five, for example) water tubes WT are accommodated in the casing 7. For easier understanding, the structure of a single water tube WT will be described below with reference to FIGS. 6A and 6B. The water tube WT shown in the figures may be formed by bending a single material tube. The water tube WT includes a helical tube body 5, and extensions 51 and 52 integrally connected to a lower end and an upper end of the helical tube body 5. The helical tube body 5 includes a plurality of generally ellipse loops 50 which are arranged in the axial direction of the helical tube body 5 (in the direction in which the central axis C extends) via gaps 59 and continuously connected to each other.
In this embodiment, the axial direction is the vertical direction V. In using the water heater A, the water heater A is so installed at an appropriate position that the axial direction corresponds to the vertical direction. In the width direction (the right and left direction in FIGS. 6A and 6B), each of the loops 50 is made up of an intermediate region S1 and opposite end regions 52a and 52b. The intermediate region S1 comprises a pair of straight tube portions 50a and 50b extending in parallel with each other. The straight tube portions 50a and 50b extend perpendicularly to the axial direction. The straight tube portions 50a and 50b are non-inclined tube portions which are not inclined with respect to the horizontal surface. The opposite end regions 52a and 52b comprise generally semicircular or arcuate bent tube portions 50c and 50d. The bent tube portions 50c and 50d are inclined tube portions which are inclined with respect to the axial direction and the horizontal surface.
Specifically, in FIG. 6A, the bent tube portion 50c is so inclined at an appropriate angle that the height thereof gradually reduces as proceeding from an end of the straight tube portion 50a toward an end of the uppermost straight tube portion 50b in the direction indicated by the arrow N1. The straight tube portion 50a is positioned higher than the straight tube portion 50b. The bent tube portion 50d is so inclined that the height thereof gradually reduces as proceeding from the other end of the straight tube portion 50b toward an end of the straight tube portion 50a of the subsequent loop 50 in the direction indicated by the arrow N2. It is to be noted that the straight tube portions 50a, 50b and the bent tube portions 50c, 50d of other loops 50 have a structure similar to the above.
As shown in FIGS. 5A and 5B, the helical tube bodies 5 of the plurality of water tubes WT have different sizes and are arranged generally concentrically in the casing 7. The uppermost straight tube portions 50a, 50b of the helical tube bodies 5 face the inner surface of the upper wall 70c of the casing 7 via a gap 79a and extend generally in parallel with the inner surface. The lowermost straight tube portions 50a, 50b of the helical tube bodies 5 face the inner surface of the bottom wall 70d of the casing 7 via a gap 79b and extend generally in parallel with the inner surface. With this structure, the widths L1 and L2 of the gaps 79a and 79b are constant.
An end of each of the extensions 51, 52 penetrates through the side wall 70e of the casing 7 to be positioned outside the casing 7 and is connected to the water inflow header 6A or the hot-water outflow header 6B. The header 6A includes a port 60A for water inflow, which is utilized as a water discharge port in draining water from the water tubes WT. Each of the extensions 51 is provided with a downwardly bent portion 51a positioned outside the casing 7. As will be described later, the bent portion 51a is utilized for properly draining water from the water tube WT and may comprise a bent tube formed separately from the extension 51. In this embodiment, the header 6A is slightly inclined with respect to the vertical direction V, so that the port 60A is not oriented vertically downward. This structure is convenient for connecting a pipe 80 for water inflow, for example. However, the header 6A may be oriented in a different way. Unlike the extension 51, each of the extensions 52 is not provided with a part corresponding to the bent portion 51a and directly connected to the hot-water outflow header 6B. As shown in FIG. 1, the header 6B includes a port 60B for hot-water outflow, which is connected to a water inlet 11a of the primary heat exchanger 1 via a pipe 81. In the primary heat exchanger 1, the water supplied from the secondary heat exchanger B flows through the water tube 11 to be further heated. The water heated in this way is supplied to an appropriate destination through a hot-water outlet 11b. However, the order in which water flows through the primary heat exchanger 1 and through the secondary heat exchanger B is not limitative. For instance, water may first be supplied to the primary heat exchanger 1 and then supplied to the secondary heat exchanger B.
The operation and advantages of the secondary heat exchanger B and the water heater A provided with the heat exchanger B will be described below.
In the water heater A shown in FIG. 1, when water is supplied to the water tubes WT of the secondary heat exchanger B and the water tube 11 of the primary heat exchanger 1, the burner 3 starts. Then, from the combustion gas generated by the burner 3, sensible heat and latent heat are recovered by the primary heat exchanger 1 and the secondary heat exchanger B. The hot water generated by the heat recovery is supplied to an appropriate destination through the hot-water outlet 11b.
As described before with reference to FIGS. 6A and 6B, in each loop 50 of the water tubes WT, only the opposite end regions 52a and 52b are inclined with respect to the horizontal surface, and the intermediate region S1 is horizontal. FIG. 7 schematically shows the structure of the loop 50. In this figure, the height h2 of a half region of the loop 50 is given by h2=2·L2·tan θ, and the pitch p2 of the helical tube body 5 is given by p2=2·h2=4·L2·tan θ, where L is the width of the loop 50, L1 is the width of the intermediate region S1, L2 is the width of the opposite end regions 52a, 52b, and 9 is the angle of inclination of the opposite end regions 52a, 52b. Thus, the pitch p2 is smaller than the pitch p1 of the conventional structure shown in FIG. 1. Specifically, p2 is smaller than p1 by 2·L1·tan θ. As will be understood from this, in this embodiment, the pitch of the helical tube body 5 can be reduced. Therefore, even when the number of loops 50 is increased to increase the amount of heat recovery, the overall height of the helical tube body 5 does not become so large, so that considerable increase in size of the secondary heat exchanger B can be properly prevented. Particularly, in this embodiment, the loops 50 have a generally ellipse shape in plan view. Therefore, by elongating the straight tube portions 50a and 50b, the heat transfer area of the water tube WT can be increased without increasing the height of the helical tube body 5. Therefore, the heat exchange efficiency can be increased without making the secondary heat exchanger B large.
In the secondary heat exchanger B, heat is recovered when combustion gas flows through the gaps 59 defined between the loops 50. Since the loops 50 arranged in the vertical direction V have an almost identical shape, the width (indicated by reference sign L3 in FIG. 6B) of the gap 59 is generally uniform along the longitudinal direction. Therefore, it is possible to prevent the combustion gas from flowing concentratedly through a particular portion due to the nonuniformity of the width of the gap 59. Thus, the combustion gas acts on every portion of each loop 50 generally uniformly. This is also advantageous for increasing the amount of heat recovery and enhancing the heat exchange efficiency.
The combustion gas also flows into the gaps 79a, 79b defined between the loops 50 and the upper wall 70c and the bottom wall 70d of the casing 7, and heat is recovered also at the gaps 79a, 79b. The widths L1, L2 of the gaps 79a, 79b are uniform at the regions where the straight tube portions 50a, 50b exist. Therefore, also at the gaps 79a, 79b, combustion gas can be distributed generally uniformly, so that heat can be recovered efficiently.
In winter, for example, the operation of the water heater A may be stopped for a long time. In such a case, to prevent the inside of the primary heat exchanger 1 and the secondary heat exchanger B from freezing, water supply to the water tubes 11 and WT is stopped, and draining is performed. According to this embodiment, water can be prevented from remaining in the water tubes WT of the secondary heat exchanger B, as will be described below.
In the helical tube body 5, the opposite end regions 52a and 52b of each loop 50 are inclined. Therefore, because of the provision of the inclined end regions 52a and 52b, water smoothly flows from a higher portion to a lower portion of the helical tube body 5. Further, since the straight tube portions 50a and 50b of the intermediate region S1 are horizontal, accumulation of water in these portions is properly prevented. Thus, the water in the straight tube portion 50a or 50b flows to the subsequent loop 50 through the adjacent bent portion 50c or 50d. In this way, draining of the water tubes WT can be properly performed.
To increase the amount of latent heat recovery, it is preferable that each water tube WT of the secondary heat exchanger B is thinner than that of the water tube 11 of the primary heat exchanger 1. However, when the water tube WT is thin i.e., has a small diameter, a water film may be formed at the end opening of the extension 51 due to the surface tension. Such a water film hinders draining of the water tube WT. In this embodiment, however, the water film can be broken by the pressure head of the water existing in the bent portion 51a of the extension 51. Therefore, water can be smoothly discharged from the end opening of the extension 51 toward the header 6A. In this embodiment, the portion of the extension 51 which is closer to the helical tube body 5 than to the bent portion 51a is horizontal. In the present invention, however, this portion may be inclined to facilitate the water flow from this portion toward the header 6A.
The present invention is not limited to the foregoing embodiment. The specific structure of each part of the heat exchanger, the water heater and the water tube of the heat exchanger may be varied in design in various ways.
The loops of the helical tube body of the water tube may not be ellipse in plan view but may have another shape. FIG. 8 shows an example of water tube having a shape different from that of the foregoing embodiment. In this figure, the elements which are identical or similar to those of the foregoing embodiment are designated by the same reference signs as those used for the foregoing embodiment. In the illustrated example, the loop 50 of the innermost water tube WT has a structure similar to that of the foregoing embodiment, i.e., includes opposite end regions 52a and 52b which are bent to be semicircular or arcuate. However, the loops 50A of the other water tubes WT located outward are generally rectangular in plan view, and the opposite end regions 52a and 52b thereof are so bent as to include a straight portion, and the radius of curvature of the bent portions is small. With this structure, part of the helical tube body 5 can be arranged at or adjacent to the four corner portions 78 of the casing 7, so that the dead space within the casing 7 can be reduced. In the present invention, the loops may have a shape other than those described above. For example, the loops may have a generally square shape or a generally circular shape.
In the present invention, the number of water tubes is not limitative. Although not very practical, the use of only a single water tube is possible, and the present invention is also applicable to such a structure. Although it is preferable that all the loops of the helical tube body are horizontal at the intermediate region and inclined at opposite end regions, the present invention is not limited to this. In the present invention, only some of the loops may have such a structure. Also in this case, as compared with a conventional structure, the amount of heat recovery can be increased while suppressing an increase in height of the helical tube body. In the present invention, the terms “opposite end regions” and “intermediate region” of the loop in the width direction just indicate the positional relationship between portions of a loop. Therefore, the dimension or dimension ratio of these regions is not limitative.
Although the present invention is not applied to a primary heat exchanger for sensible heat recovery in the foregoing embodiment, the heat exchanger according to the present invention is not limited to a heat exchanger for sensible heat recovery or that for latent heat recovery.
As the burner of the water heater according to the present invention, a burner other than a gas burner may be used, and an oil burner may be used, for example. The system for causing combustion gas to flow into the casing of the heat exchanger and for causing the combustion gas to act on the water tubes is not limited to that of the foregoing embodiment. For example, the combustion gas may be guided to the inside of the helical tube body and caused to flow to the outside of the helical rube body through the gaps between the loops. The water heater in the present invention refers to apparatuses having a function to produce hot water and includes various apparatuses for supplying hot water for general use, use at a bath, space heating or melting snow and so on and apparatuses for producing hot water for the purposes other than the hot water supply.
Patent Application
20070289559
