MULTITUBULAR HEAT EXCHANGER

Description

TECHNICAL FIELD

The present invention relates to a multitubular heat exchanger.

BACKGROUND ART

For example, Patent Document 1 describes that “when assembling a core portion (100) for a heat exchanger in which a plurality of tubes (111) and fins (112) are alternately stacked, a wire member (10a, brazing wire) is wound around and fixed to an assembled body (110) of the core portion (100) for a heat exchanger, the assembled body (110) is integrally brazed, and then the wire member (10a) is removed”.

In addition, Patent Document 1 also describes that “the tube (111) is a pipe member through which cooling water flows, and is formed by bending a thin band plate material such that a cross section orthogonal to the longitudinal direction has a flat oval shape, and welding end portions to each other”.

PRIOR ART DOCUMENT

Patent Document

• • [Patent Document 1] JP 4492452 (Japanese Unexamined Patent Publication No. 2006-346711)

SUMMARY OF INVENTION

Technical Problem

In Patent Document 1 described above, since the fixing is performed by brazing, there is a concern that stress corrosion cracking specific to the joint portion will occur. In addition, since the wire member used in the assembly is removed, the cost of the wire member is wasted. Furthermore, the tube has a straight shape without a bent portion, and the inlet side and the outlet side of the tube needs to be fixed. However, when both sides of the tube are fixed, excessive stress may be generated in a portion where the inlet of the tube is fixed and a portion where the outlet of the tube is fixed due to thermal expansion of the tube.

In consideration of such circumstances, an object of the present invention is to suppress or prevent damage to a heat transfer tube or a peripheral member thereof due to thermal expansion of the heat transfer tube.

Solution to Problem

The present invention is a multitubular heat exchanger comprising a plurality of heat transfer tubes and performing heat exchange between a heat medium inside the heat transfer tubes and a high-temperature fluid outside the heat transfer tubes, wherein each of the heat transfer tubes has a bent portion and has a cantilever structure in which only one side in a longitudinal direction of a linear portion of the heat transfer tube is supported, and the plurality of heat transfer tubes are bundled by a metal wire.

With this configuration, it is possible to suppress or prevent the plurality of heat transfer tubes from swinging, and thus it is possible to suppress or prevent stress from being applied to the heat transfer tubes or the periphery thereof due to thermal expansion of the plurality of heat transfer tubes. Thus, it is possible to suppress or prevent damage to the heat transfer tubes and the periphery thereof due to thermal expansion of the plurality of heat transfer tubes.

The multitubular heat exchanger described above can be configured such that the metal wire is made of a material having a coefficient of linear expansion smaller than that of the heat transfer tube.

With this configuration, a difference in thermal expansion due to a temperature difference between the metal wire and the heat transfer tube can be reduced. This is advantageous in suppressing or preventing loosening of the metal wire due to the difference in thermal expansion.

The multitubular heat exchanger described above can be configured such that pretension within a certain range is applied to the metal wire in a bound state at room temperature.

With this configuration, plastic elongation of the metal wire at room temperature can be prevented, and loosening of the metal wire due to a difference in thermal expansion between the metal wire and the heat transfer tube in a high-temperature state can be alleviated or prevented. Thus, it is possible to suppress or prevent damage to the heat transfer tubes and the periphery thereof due to thermal expansion of the plurality of heat transfer tubes.

The multitubular heat exchanger described above can be configured such that a magnitude of the pretension is set within a range (pretension allowable range) in which plastic elongation does not occur in the metal wire and tension of the metal wire does not become zero during heat exchange at room temperature and at an estimated maximum temperature of the high-temperature fluid.

With this configuration, plastic elongation of the metal wire at room temperature can be prevented, and loosening of the metal wire due to a difference in thermal expansion between the metal wire and the heat transfer tube in a high-temperature state can be alleviated or prevented.

The multitubular heat exchanger described above can be configured such that a magnitude of the pretension is set within a range from an intermediate value to a maximum value of the pretension allowable range.

With this configuration, the pretension in a room temperature state can be set to the higher side of the pretension allowable range in consideration of the tendency of the tension of the metal wire to decrease in a transient state during a temperature rise or a temperature fall.

Thus, as compared with a case where the magnitude of the pretension is set within a range from the intermediate value to the minimum value of the pretension allowable range, there is an advantage in enhancing the effect of alleviating the loosening of the metal wire in a transient state during a temperature rise or a temperature fall.

The multitubular heat exchanger described above can be configured such that a longitudinal direction of a linear portion of the plurality of heat transfer tubes is arranged along a left-right direction, and bent portions of adjacent heat transfer tubes and/or the linear portions are arranged to be offset in an up-down direction.

With this configuration, when the high-temperature fluid flows through the plurality of heat transfer tubes from a side orthogonal to the longitudinal direction and the up-down direction of the plurality of heat transfer tubes, the heat transfer area (projected area) of the plurality of heat transfer tubes as viewed in the flow direction of the high-temperature fluid is larger than that in a case where the plurality of heat transfer tubes are not offset in the up-down direction. Thus, the heat transfer efficiency from the high-temperature fluid to the plurality of heat transfer tubes can be improved.

The multitubular heat exchanger described above can be configured such that a material of the heat transfer tube is stainless steel, and a material of the metal wire is a nickel allay containing nickel by 50 mass percent or more.

Advantageous Effects of Invention

According to the present invention, it is possible to suppress or prevent damage to a heat transfer tube and a peripheral member thereof due to heat expansion of the heat transfer tube.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an embodiment of a multitubular heat exchanger according to the present invention.

FIG. 2 is a perspective view of the multitubular heat exchanger of FIG. 1 as viewed from the side of first, third, and fifth bent portions of heat transfer tubes.

FIG. 3 is a side view of the multitubular heat exchanger of FIG. 1.

FIG. 4 is a top view of the multitubular heat exchanger of FIG. 1.

FIG. 5 is a graph showing a relationship among the temperature of a high-temperature fluid outside the heat transfer tube, the temperatures of a metal wire and the heat transfer tube, and tensile stress acting on the metal wire.

DESCRIPTION OF EMBODIMENTS

The best mode for carrying out the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 1 to 5 illustrate an embodiment of the present invention. The multitubular heat exchanger 1 of the illustrated example includes a plurality of (for example, 14) heat transfer tubes 2, an introduction-side header 3, a discharge-side header 4, a pair of introduction-side connection pipes 5, a pair of discharge-side connection pipes 6, a support member 7, and the like.

The plurality of heat transfer tubes 2 exchange heat between the heat medium inside and the high-temperature fluid outside, and are arranged side by side.

Each of the plurality of heat transfer tubes 2 is curved so as to meander from top to bottom in a side view, and has a cantilever structure in which only one side of each heat transfer tube 2 in the longitudinal direction is supported by the introduction-side header 3, the discharge-side header 4, and the support member 7.

In this embodiment, each of the plurality of heat transfer tubes 2 has a configuration in which the first to sixth linear portions 21a to 21f are connected by the first to fifth bent portions 22a to 22e.

To be specific, the first to sixth linear portions 21a to 21f are arranged in parallel to be separated from each other in the up-down direction, and the first to fifth bent portions 22a to 22e are formed in a lateral U shape.

The upstream side (the supported side or the root side) of the first linear portion 21a serves as an inlet for the heat medium, and the downstream side (the non-supported side or the free end side, the first bent portion 22a side) of the first linear portion 21a and the upstream side (the first bent portion 22a side) of the second linear portion 21b are connected to each other by the first bent portion 22a. The downstream side of the second linear portion 21b and the upstream side of the third linear portion 21c are connected by the second bent portion 22b. The downstream side of the third linear portion 21c and the upstream side of the fourth linear portion 21d are connected by the third bent portion 22c. The downstream side of the fourth linear portion 21d and the upstream side of the fifth linear portion 21e are connected by the fourth bent portion 22d. The downstream side of the fifth linear portion 21e and the upstream side of the sixth linear portion 21f are connected by the fifth bent portion 22e, and the downstream side of the sixth linear portion 21f serves as an outlet of the heat medium. The upstream side and the downstream side are described based on the flow direction of the heat medium.

The introduction-side header 3 and the discharge-side header 4 both have a hollow tube shape and are closed at both ends in the longitudinal direction.

The introduction-side header 3 and the discharge-side header 4 are arranged in parallel to be spaced apart from each other in the up-down direction in a posture along the lateral direction, and one end sides in the longitudinal direction of the introduction-side header 3 and the discharge-side header 4 are connected to each other and the other end sides in the longitudinal direction of the introduction-side header 3 and the discharge-side header 4 are connected to each other respectively by coupling members 821a.

The upstream side (inlet) of the first linear portion 21a of each of the plurality of heat transfer tubes 2 is connected to and communicates with the front surface of the introduction-side header 3, and the two introduction-side connection pipes 5 are connected to and communicate with the back surface of the introduction-side header 3.

The downstream side (outlet) of the sixth linear portion 21f of each of the plurality of heat transfer tubes 2 is connected to and communicates with the front surface of the discharge-side header 4, and the two discharge-side connection pipes 6 are connected to and communicate with the back surface of the discharge-side header 4. Each of the connections is, for example, welding.

The introduction-side connection pipe 5 and the discharge-side connection pipe 6 connect the plurality of heat transfer tubes 2 and a heater (not illustrated). The two introduction-side connection pipes 5, the two discharge-side connection pipes 6, and the plurality of heat transfer tubes 2 constitute a thermosiphon-type multitubular heat exchanger (reference numeral omitted) that forms a closed loop.

The support member 7 supports middle of each of the introduction-side connection pipe 5 and the discharge-side connection pipe 6 in a state in which the introduction-side connection pipe 5 and the discharge-side connection pipe 6 pass through the support member 7, and is, for example, a rectangular plate.

The heater (not illustrated) releases heat by condensing the heat medium flowing into the heater from the plurality of heat transfer tubes 2 via the discharge-side connection pipe 6, and the heat medium is introduced into the plurality of heat transfer tubes 2 via the introduction-side connection pipe 5.

Although not illustrated, for example, a thermoelectric module is attached to a surface of the heater. The thermoelectric module converts a temperature difference between one surface and the other surface into a voltage.

The even-numbered heat transfer tubes 2 of the plurality of heat transfer tubes 2 from one side in the lateral arrangement direction are arranged to be offset downward with respect to the odd-numbered heat transfer tubes 2.

Thus, the first to sixth linear portions 21a to 21f of each of the odd-numbered heat transfer tubes 2 are separated from each other by a predetermined interval, the first to sixth linear portions 21a to 21f of each of the even-numbered heat transfer tubes 2 are separated from each other by a predetermined interval, and the first to sixth linear portions 21a to 21f of each of the odd-numbered heat transfer tubes 2 are separated from the first to sixth linear portions 21a to 21f of each of the even-numbered heat transfer tubes 2 by a predetermined interval.

Then, as illustrated in FIGS. 2 to 4, the first to fifth bent portions 22a to 22e of the odd-numbered heat transfer tubes 2 and the first to fifth bent portions 22a to 22e of the even-numbered heat transfer tubes 2 are respectively bound by the metal wires 9. Thus, the first to fifth bent portions 22a to 22e of the odd-numbered heat transfer tubes 2 are brought into contact with the first to fifth bent portions 22a to 22e of the even-numbered heat transfer tubes 2, respectively.

The metal wire 9 is used to suppress or prevent the plurality of heat transfer tubes 2 from swinging, and is made of, for example, a material having a smaller coefficient of linear expansion than that of the plurality of heat transfer tubes 2. To be specific, the heat transfer tube 2 is preferably made of a metallic material such as SUS304 (coefficient of linear expansion ^˜18.4×10-6/K).

The metal wire 9 is preferably made of a material having excellent high-temperature characteristics such as heat resistance, corrosion resistance, oxidation resistance, and creeping resistance, for example, Inconel 625 (trade name, manufactured by Special Metals Co., Ltd., coefficient of linear expansion: ^˜15.6×10-6/K), nickel alloys (Hastelloy), SUS316, and titanium alloys.

The Inconel 625 is an alloy based on nickel and containing iron, chromium, niobium, molybdenum, and the like. The nickel alloy may have a composition containing 50 mass % or more of nickel.

As described above, the first, third, and fifth bent portions 22a, 22c, and 22e of the odd-numbered heat transfer tubes 2 and the first, third, and fifth bent portions 22a, 22c, and 22e of the even-numbered heat transfer tubes 2 are bound by the metal wires 9 respectively, and, for example, as illustrated in FIG. 4, a spacer 10 is interposed in an intermediate portion of the plurality of heat transfer tubes 2 in the lateral arrangement direction.

The lateral width of the spacer 10 is set to be the same as or equivalent to (including an error) a dimension obtained by adding all the separation dimensions of the plurality of heat transfer tubes 2 on the supported side (root side).

The reason why the spacer 10 is provided will be described.

The inventors of the present application have found that since the supported sides (root sides) of the plurality of heat transfer tubes 2 are separated from each other by a predetermined interval, when the free end sides of the plurality of heat transfer tubes 2 are bound by the metal wire 9, stress is applied to portions of the supported sides (root side) of the plurality of heat transfer tubes 2 welded to the introduction-side header 3 and the discharge-side header 4, and thus stress corrosion cracking is likely to occur in the welded portion. Therefore, the present inventors have found that when the spacer 10 is used as described above, the stress applied to the welded portion is reduced or prevented, and thus the stress corrosion cracking can be prevented.

Next, in the multitubular heat exchanger having the above-described configuration, for example, as illustrated in FIG. 4, a high-temperature fluid (high-temperature gas) is caused to flow in a direction orthogonal to the longitudinal direction of the first to sixth linear portions 21a to 21f of each of the plurality of heat transfer tubes 2, and thus the heat medium in the plurality of heat transfer tubes 2 is boiled by receiving heat from the high-temperature fluid.

Generally, in a transient period in which the temperature of the heat medium in the plurality of heat transfer tubes 2 rises, the temperature rise of the external high-temperature fluid propagates from the metal wires 9 to the heat transfer tubes 2 with a time delay, and thus the temperature of the metal wires 9 tends to be relatively higher than the temperature of the heat transfer tubes 2.

In a transient in which the temperature of the external high-temperature fluid falls, the heat transfer tubes 2 are cooled from the inside by the low-temperature heat medium, and thus the temperature of the metal wires 9 tends to be relatively higher than the temperature of the heat transfer tubes 2.

That is, since “the temperature of the metal wires 9 is equal to or more than the temperature of the heat transfer tubes 2” in the transition period during the temperature rise and the transition period during the temperature fall, the binding of the plurality of heat transfer tubes 2 by the metal wires 9 is likely to be loosened due to the thermal expansion of the metal wires 9.

In consideration of this point, when the plurality of heat transfer tubes 2 are bundled with the metal wire 9 at room temperature, it can be said that it is preferable to apply a pretension within a range in which the metal wire 9 does not plastically elongate and within a range in which the metal wire 9 does not loosen during heat exchange. The above-described range is referred to as a “pretension allowable range”.

Next, the pretension allowable range will be described with reference to FIG. 5.

In FIG. 5, “gas” is the high-temperature fluid, “wire” is the metal wire 9, “pipe” is the heat transfer tube, “T” is the temperature, and “a” is the tensile stress.

In FIG. 5, the solid line indicates “T_wire”, the broken line indicates “T_pipe”, the one dot chain line indicates “σ_wire at 520 MPa and room temperature”, and the two dot chain line indicates “σ_wire at 280 MPa and room temperature”.

σ wire = σ wire ( 0 ) - E * ( α wire ⁢ Δ ⁢ T wire - α pipe ⁢ Δ ⁢ T pipe ) Δ ⁢ T wire = C wire ⁢ Δ ⁢ T gas , Δ ⁢ T pipe = C pipe ⁢ Δ ⁢ T gas E * = E wire / ( 1 + ( E wire ⁢ A wire ) / ( E pipe ⁢ A pipe )

Note that “σ_wire(0)” represents the stress at room temperature, “E_wire” represents the Young's modulus of the metal wire 9, “E_pipe” represents the Young's modulus of the heat transfer tube 2, “A_wire” represents the cross-sectional area of the metal wire 9, “A_pipe” represents the cross-sectional area of the heat transfer tube 2, “α_wireΔT_wire” represents the thermal expansion of the metal wire 9, and “α_pipeΔT_pipe” represents the thermal expansion of the heat transfer tube 2.

In FIG. 5, the region where the plastic elongation of the metal wire 9 occurs (see hatching) is defined by “σ_wire is equal to or more than 0.2% Yield Strength”, and the region where the loosening of the metal wire 9 occurs (see cross-hatching) is defined by “σ_wire is equal to or lower than 0”.

Between the region where the plastic elongation occurs and the region where the loosening occurs, a region between σ_wire at room temperature and 520 MPa (see one dot chain line in FIG. 5) and σ_wire at 280 MPa and room temperature (two dot chain line in FIG. 5) is the pretension allowable range.

That is, it can be said that the magnitude of the pretension is preferably set within a range (pretension allowable range) in which the plastic elongation does not occur in the metal wire 9 at room temperature and the estimated maximum temperature of the high-temperature fluid and the tension of the metal wire 9 does not become zero during the heat exchange at the estimated maximum temperature of the high-temperature fluid.

In addition, as illustrated in FIG. 5, it can be seen that the stress change in the transition period during the temperature rise (see the thick one dot chain line) and the stress change in the transition period during the temperature fall (see the thick solid line) have hysteresis, but both the stress changes are present within the range from the intermediate value to the maximum value of the pretension allowable range. The thick broken line in FIG. 5 indicates the stress change of the metal wire 9 when the temperature of the high-temperature fluid is changed constantly (infinitely slowly).

According to the above, it can be said that the magnitude of the pretension is more preferably set within the range from the intermediate value to the maximum value of the pretension allowable range, that is, on the upper limit side.

As described above, according to the embodiment to which the present invention is applied, it is possible to suppress or prevent the plurality of heat transfer tubes 2 from swinging, and thus it is possible to suppress or prevent stress from being applied to the heat transfer tubes 2 or the periphery thereof due to thermal expansion of the plurality of heat transfer tubes 2. Thus, it is possible to suppress or prevent the heat transfer tubes 2 and the periphery thereof, that is, the joint portions of the plurality of heat transfer tubes 2 to the introduction-side header 3 and the discharge-side header 4 from being damaged due to the thermal expansion of the plurality of heat transfer tubes 2.

In particular, in this embodiment, since the plurality of heat transfer tubes 2 are not brazed as in the conventional example, a problem such as stress corrosion cracking of the joint portion as occurring in the conventional example does not occur.

In this embodiment, since the pretension in the room temperature state is set to the pretension allowable range in consideration of the tendency of the tension of the metal wire 9 to decrease in the transient state during the temperature rise or the temperature fall, the plastic elongation of the metal wire 9 at room temperature can be prevented, and the loosening of the metal wire 9 due to the thermal expansion difference between the metal wire 9 and the heat transfer tube 2 in the high temperature state can be alleviated or prevented.

Since the pretension in the room temperature state is set on the higher side of the pretension allowable range in this embodiment, the effect of alleviating the loosening of the metal wire 9 in the high temperature state can be advantageously enhanced as compared with the case where the magnitude of the pretension is set within the range from the intermediate value to the minimum value of the pretension allowable range.

In this embodiment, since the odd-numbered heat transfer tubes 2 and the even-numbered heat transfer tubes 2 are offset in the up-down direction, when the high-temperature fluid flows through the plurality of heat transfer tubes 2 from the side orthogonal to the longitudinal direction and the up-down direction of the first to sixth linear portions 21a to 21f, the heat transfer area (projected area) of the plurality of heat transfer tubes 2 as viewed in the flow direction of the high-temperature fluid is increased as compared with the case where the plurality of heat transfer tubes 2 are not offset in the up-down direction. Thus, the heat transfer efficiency from the high-temperature fluid to the plurality of heat transfer tubes 2 can be improved.

The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the claims and within a scope equivalent to the scope of the claims.

(1) Although an example in which the spacer 10 is provided has been described in the above embodiment, the present invention is not limited thereto.

For example, although not illustrated, a form in which the spacer 10 is not used is possible. The other configurations are basically the same as those of the embodiment shown in FIG. 1. This embodiment can also obtain actions and effects comparable to those of the above-described embodiment.

(2) Although the example in which the number of times of bending of the heat transfer tube 2 is five has been described in the above embodiment, the present invention is not limited thereto, and, for example, although not illustrated, the number of times of bending of the heat transfer tube 2 can be arbitrarily set.

INDUSTRIAL APPLICABILITY

The present invention can be suitably used for a multitubular heat exchanger.

REFERENCE SIGNS LIST

• • 1 multitubular heat exchanger
  • 2 heat transfer tube
  • 21a first linear portion
  • 21b second linear portion
  • 21c third linear portion
  • 21d fourth linear portion
  • 21e fifth linear portion
  • 21f sixth linear portion
  • 22a first bent portion
  • 22b second bent portion
  • 22c third bent portion
  • 22d fourth bent portion
  • 22e fifth bent portion
  • 3 introduction-side header
  • 4 discharge-side header
  • 5 introduction-side connection pipe
  • 6 discharge-side connection pipe
  • 7 support member
  • 8 coupling member
  • 9 metal wire
  • 10 spacer