JPH04340088A - Plate fin type heat exchanger - Google Patents

Abstract

PURPOSE:To allow fluid passages to be freely movable for thermal elongation and contraction by perpendicularly crossing one or more fluid passage group to one fluid passage, and providing an elongating/contracting mechanism in a plate fin type heat exchanger in which a secondary heat transfer surface is secured only to one side of a primary heat transfer surface. CONSTITUTION:A plate fin type heat exchanger is formed of a fluid passage A and a fluid passage B perpendicular to the passage A. The passage B is sealed after an end of a plate 1 of a primary heat transfer surface is formed, and laminated to form a heat exchanger core K. The core K is contained in a casing, and the passage A is formed out of the core K. Fins 3 are respectively mounted as secondary heat transfer surfaces on the respective plates 1, and slits 9 are provided at an equal interval in the fins 3. Since the temperatures of fluids in contact with the fins 3 are different, the fins 3 are not uniformly elongated and contracted, but the elongation and contraction are absorbed by the slits 9, and a thermal stress of the contact of a slide bar which is affected by influence of the fins 3 and the atmosphere, is removed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a plate-fin heat exchanger that operates at a high temperature and a high temperature difference, such that the temperature of the fluid to be heat exchanged is 650°C to 800°C on the high temperature side and about room temperature on the low temperature side. Regarding exchangers.

0002

[Prior Art] Conventionally, a high-performance and compact type plate-fin heat exchanger F has a plate 1 with fins 3 sandwiched between them, and both sides of the fins are sealed with side bars 2, as shown in FIG. A heat exchange core K is formed by stacking and brazing a large number of such layers, and a header tank 5 that distributes fluid to each flow path is provided in the heat exchange core K.
It was welded together and had extremely high rigidity. Therefore, the temperature of the fluid to be heat exchanged is mainly between 200℃ and 3℃.
It has been used for fluids with a relatively low temperature of 50° C. and a small temperature difference between the primary and secondary fluids, or as a low-temperature industrial heat exchanger.

On the other hand, on-site fuel cells occupy an important position as a small-scale distributed energy supply source due to their high power generation efficiency and as a low-pollution and highly efficient cogeneration system. It is said that the basic conditions required for site-type fuel cells are: 1) compactness 2) low cost 3) high reliability. Therefore, there is a strong demand for heat exchangers that have a large impact on overall efficiency and occupy a large proportion of the system to be compact, high-performance, and highly reliable. In addition, in phosphoric acid fuel cells, heat exchange is required between the combustion waste gas (approximately 650°C) from the fuel reformer and air, reformed gas, and fuel gas at high temperatures and high temperature differences. there were.

[0004] Generally, heat exchangers used at high operating temperatures and large temperature differences have been limited to shell-and-tube heat exchangers equipped with an expansion/contraction mechanism (eg, a floating head).

[0005]

[Problems to be Solved by the Invention] However, as mentioned above, in the heat exchange system of a fuel cell, a shell-and-tube system equipped with an expansion/contraction mechanism (such as a floating head) is used at a high operating temperature and with a large temperature difference. When using a type heat exchanger, there were the following drawbacks.

1) The volume of the heat exchanger itself becomes about 5 to 7 times larger. Therefore, the system as a whole has to become very large. 2) The piping route for each fluid flow path becomes long.
The volume of the piping system will also be large. 3) As the piping route becomes long, the system will inevitably experience an increase in pressure loss and a decrease in thermal efficiency due to heat radiation, resulting in a decrease in overall energy efficiency. 4) System As the weight increases, the heat capacity increases proportionally. As a result, startup time becomes longer and load followability is reduced. As a result, it had no choice but to be unsuitable as a distributed small-scale energy source.

In other words, the above-mentioned shell-and-tube heat exchanger is equipped with an expansion mechanism (for example, a floating head) to allow expansion and contraction due to the temperature difference between the shell and the tube, thereby reducing thermal stress as a whole and reducing the allowable stress. However, the disadvantage is that the amount of heat exchanged is about 1/5 to 1/7 of that of a plate-fin heat exchanger, relative to the volume occupied by the heat exchanger.

[0008] For this reason, it is conceivable to apply a high-performance compact type plate-fin type heat exchanger F as shown in FIG. However, this is because the primary and secondary heat transfer surfaces that make up the flow path and the side bars that seal each flow path are laminated together with high density and high rigidity by brazing. In such a transient state, the temperature changes rapidly from the initial state within a short period of time, so the parts that make up the heat exchanger cannot expand or contract due to their high rigidity, and eventually break. The disadvantage was that large thermal stress was generated.

[0009] That is, at the time of startup, the
The high-temperature fluid at 0° C. instantaneously enters the heat exchanger flow path at room temperature and starts exchanging heat with the low-temperature fluid, but the temperature gradient at this time becomes the largest. At that time, members with relatively large heat capacity such as square bars called side bars, headers that form fluid inlets and outlets on the high temperature side and low temperature side, and plates with relatively small heat capacity as the primary heat transfer surface and secondary transfer A temperature difference occurs between the fins on the hot surface due to the difference in heat capacity, and each member has a structure that mutually restrains free expansion and contraction, resulting in large thermal stress that can lead to destruction. (The same temperature gradient occurs when the engine is stopped).

Further, according to experiments, it has been confirmed that even when the temperature difference between the fluids being heat exchanged is 300 to 400° C., destruction occurs after several hundred cycles. Furthermore, even if the temperatures of multiple fluids being heat exchanged are balanced and the temperature of each flow path is in a steady state, basically each adjacent flow path has a high temperature difference and each It consists of a complex temperature distribution curved surface, and large thermal stress is generated (Fig. 5
reference).

[0011] Furthermore, of the side bars constituting the outer part of the flow path, there is naturally a temperature difference between the inner part that is in contact with the fluid and the outer part that is in contact with the outside air or other fluid that exchanges heat, and there is A temperature difference also occurs between the plate of the surface and the fin of the secondary heat transfer surface. The difference in expansion and contraction due to this temperature difference is
Since each member is completely fixed, all of them become thermal stress, and when operated for a long time, stress concentrates at the bases of the side bars and plates, which are the weakest points in the structure, and eventually leads to fatigue failure. It will happen.

That is, since the high-performance compact type plate-fin heat exchanger F shown in FIG. 4 has high rigidity, when operated at high temperature and with a high temperature difference,
It had the disadvantage that it could easily break at the boundary between the sidebar and the plate and at the attachment point between the core and header tank after several hundred heat cycles (starting and stopping) due to thermal stress.

[0013] Regarding the structure of the heat exchanger, various laws and regulations (Electrical Industry Law, Pressure Vessel Structural Standards, etc.) require that the members used satisfy the allowable stress value of the material. In the case of the above-mentioned shell-and-tube heat exchanger, thermal stress can be reduced by, for example, having a floating head, which allows the shell and tube to expand and contract due to the temperature difference, but the conventional plate-fin heat exchanger Because of the integral structure made by brazing, it was not possible to provide an expansion and contraction mechanism.

Furthermore, calculation of thermal stress is easy in the case of a shell-and-tube heat exchanger with a simple structure, but in the case of a plate-fin heat exchanger, for example, a cross-flow type, the fluid flow path is The temperature distribution is a three-dimensional curved surface as shown in Fig. 5, and it changes transiently when the system starts and stops, so it was impossible to calculate the thermal stress value generated in each member.

[0015] The present invention is based on the property that thermal stress does not occur in an elastic body of any shape even if there is a linear temperature distribution in the absence of external restraints, and the non-uniformity that occurs in the heat exchanger body. Based on the idea of reducing temperature distribution (due to differences in fluid temperature and heat capacity of members) as much as possible, the core itself has a flexible structure, the core is housed in a casing, and an expansion and contraction mechanism is provided. prevents thermal stress,
It is an object of the present invention to provide a plate-fin type heat exchanger that is highly reliable even at high temperatures and high temperature differences.

[0016]

[Means for Solving the Problems] In order to achieve the above object, the first invention provides a plate-fin type heat exchanger in which a secondary heat transfer surface is fixed to only one side of a primary heat transfer surface.
One or more fluid flow channels are installed in one fluid flow channel in orthogonal or countercurrent directions, and an expansion/contraction mechanism is provided so that each of the flow channels can move freely in the X, Y, and Z directions against expansion and contraction due to heat. Its gist is:

[0017] The gist of the second invention is that, in the above structure, slits are provided in the fins at equal intervals to constitute a telescoping mechanism.

[0018] Furthermore, the third invention is such that the fluid inlet and outlet pipes of the heat exchange core, which serve as other fluid flow passages, are connected to the casing that covers the external fluid flow passages through expansion joints, so that they are in a floating state. The gist is that a telescoping mechanism was constructed by doing this.

[0019]

[Operation] Since the plate-fin type heat exchanger is configured as described above, the thermal stress generated in the fluid flow path having a temperature difference is eliminated in three dimensions by the expansion and contraction mechanism, so destruction due to thermal stress can be completely prevented. .

[0020]

Embodiments Next, embodiments of the present invention will be described based on the drawings. FIGS. 1 and 2 show an embodiment of the present invention, and the plate-fin heat exchanger has a fluid flow path A,
It is a cross-flow type core structure consisting of a fluid flow path B orthogonal to the fluid flow path B, and the fluid flow path B is formed by sealing the end of the plate 1, which becomes the primary heat transfer surface, after molding, and making it into a bag shape as an element. These elements are stacked to form a heat exchange core K. The fluid flow path A is formed on the outside of the heat exchange core K by housing the heat exchange core K in a casing. Each plate 1 is equipped with fins 3 that protrude into fluid channels A and B,
A telescoping mechanism is configured in the fin 3. In other words, a telescopic mechanism P that allows the fins 3 to freely expand and contract is configured.

First, the fins 3 are formed in advance by fusing corrugated plates 4 that alternately repeat U-shapes to the plate 1, and have a U-shaped or U-shaped cross section with the inverted portion as the tip. 3 and the fins 3, alternating up and down, and by providing a space 7 between the opposing corrugated plates 4 and disconnecting them from the adjacent plate 1, they can freely expand and contract. It is now possible to do so.

The telescopic mechanism P according to the second invention of the present application is constructed by providing slits 9 in the fins 3 at equal intervals. In other words, the fins 3 protruding from the plate 1 have different fluid temperatures in contact with each other, and the fins 3 have different temperatures.
There is also a temperature difference in the height direction, and the material does not expand and contract uniformly.
The expansion and contraction due to this temperature difference is absorbed by the slits 9. As a result, the temperature generated at the plate 1 as the primary heat transfer surface, the fins 3 as the secondary heat transfer surface, and the connection with the side bar or header tank that is affected by the outside air, as in a conventional plate-fin heat exchanger. Thermal stress due to the difference is eliminated and fatigue failure is prevented.

The structure of the fins 3 described above was similarly applied to a counterflow type plate-fin type heat exchanger in which the fluid channels face each other in parallel, and similar effects could be obtained.

FIG. 3 shows the telescopic mechanism P according to the third invention.
The cores laminated as described above are provided with an external inlet/outlet (not shown) so that the entire core forms a fluid flow path C, and a casing 17 surrounding the entire core is provided with an internal fluid inlet/outlet (not shown). An opening 15 larger than the diameter of the inlet/outlet pipe 13 is provided, the fluid inlet/outlet pipe 13 is passed through to the outside of the casing 17, and the casing 17 and the fluid inlet/outlet pipe 13 are connected via an expansion joint 19. A telescoping mechanism P is configured. In other words, the heat exchange core is provided with a telescoping mechanism P inside the casing 17 so as to be in a floating state.

A ring 20 is fitted and fixed to the fluid inlet/outlet pipe 13, and the expansion joint 19 has its proximal end welded to the casing 17 at the opening 15, and its distal end welded to the ring 20, respectively.

When the expansion/contraction mechanism P is configured in this way, the heat exchange core is in a floating state within the casing, and the external fluid flow path C in the casing 17 and the internal fluid flow path in the fluid inlet/outlet pipe 13 are connected to each other. The difference in expansion and contraction of the member due to the temperature difference between D and D is absorbed by the expansion joint 19, and as a result,
Thermal stress between them is eliminated, and problems such as cracks occurring at the connection between the heat exchange core and the header tank, which are conventional, can be prevented.

[0027]

[Effects of the Invention] As explained above, according to the present invention,
In a plate-fin heat exchanger, even if a large temperature difference or temperature gradient occurs in each fluid flow path, the expansion and contraction mechanism allows the expansion and contraction difference between the members between the fluid flow paths with the temperature difference to be freely adjusted in three dimensions. Since it is absorbed, expansion and contraction are not mutually constrained, thermal stress is eliminated, and there is an excellent effect that destruction due to thermal stress can be completely prevented.

Furthermore, since it is possible to increase the temperature difference between the fluid flow paths, it is possible to provide a high-performance and compact plate-fin type heat exchanger that can be effectively used at high temperatures and high temperature differences. It was made.

[0029]

[Brief explanation of drawings]

FIG. 1 is a partially exploded perspective view showing the core structure of a plate-fin heat exchanger showing an embodiment of the second invention.

FIG. 2 is an assembled sectional view of the same.

FIG. 3 is a partially cutaway plan view of a plate-fin heat exchanger showing an embodiment of the third invention.

FIG. 4 is a configuration diagram of a conventional brazed plate-fin heat exchanger.

FIG. 5 is a three-dimensional graph showing fluid temperature distribution in a cross-flow plate-fin heat exchanger.

[Explanation of symbols]

F Plate fin heat exchanger K Heat exchange core A, B, C, D　Fluid flow path P　Expansion mechanism 1 Plate as primary heat transfer surface 3. Fins as secondary heat transfer surfaces 7 Space 9 Slit 13 Fluid inlet/outlet pipe 15 Opening 17 Casing 19 Expansion joint

Claims (3)

[Claims] Claim 1: In a plate-fin heat exchanger in which the secondary heat transfer surface is fixed to only one side of the primary heat transfer surface, one or more fluid flow path groups are arranged in one fluid flow path in orthogonal or countercurrent directions. 1. A plate-fin type heat exchanger, characterized in that the plate-fin heat exchanger is equipped with an expansion and contraction mechanism so that each flow path can move freely in the XYZ directions against expansion and contraction due to heat. 2. The plate-fin heat exchanger according to claim 1, wherein the fins are provided with slits at equal intervals to constitute an expansion and contraction mechanism. [Claim 3] The expansion and contraction mechanism is achieved by connecting the fluid inlet and outlet pipes of the heat exchange core, which serve as other fluid flow paths, with an expansion joint interposed in the casing that covers the external fluid flow path so that the pipes are in a floating state. The plate-fin type heat exchanger according to claim 1, characterized in that the plate-fin type heat exchanger comprises: