RU2328682C1 - Heat exchanger - Google Patents

Abstract

FIELD: thermal physics.

SUBSTANCE: heat exchanger consists of a matrix from two plate holders in a case, including tubelet panels made from a set of U-shaped pipes with different bending radii. The plate holders are turned 90° from each other. The straight sections of the tubelet panels of one plate holder are put in the gaps between adjacent straight sections of the tubelet panels of the other plate holder. The pipes are joined to collectors for input and output of the internal heat carrier. The collectors are fitted inside the case, are not joined to each other and are joined to the corresponding input and output channels, in the form a T-joint with separation or fusion of the stream of the internal heat carrier for two plate holders at the same time. In the U-shaped sections of the tubelet panels, between the case and the pipe matrix, there are anti-balancing devices. The anti-balancing devices used are metallic wire nets with a zigzag shape in one or more layers. Plate holders are put mutually perpendicular. The straight sections of the pipe plate holders are put between adjacent straight sections of the tubelet panels with formation of a common lattice surface.

EFFECT: intensified heat exchange and smaller dimensions of the heat exchanger.

3 cl, 6 dwg

Description

The invention relates to a power system, and in particular to devices for recovering heat from gases emitted from aggregates, in particular for heating air with combustion products coming from a compressor of a gas turbine installation for stationary and transport purposes.

The presence of tubular heat exchangers in the form of air heaters as part of gas turbine plants significantly increases their economic efficiency (efficiency), however, this leads to a significant increase in the weight and size characteristics of these plants. For example, when using a plate-type recuperative air heater, the unit mass increases by 2.5-3 times, and tubular - by 5-8 times (Arsenyev L.V. et al. "Stationary gas turbines". Directory, L .: Engineering, 1989, pg. 31, 32). Further increase in efficiency installation is possible with intermediate cooling of air in air-air heat exchangers between the stages in multi-stage compressors and the regeneration of the heat of the exhaust gases (combustion products) (Encyclopedia ", ed. advice: K.V. Frolov (previous), etc., M .: Mechanical engineering. Theoretical mechanics. Thermodynamics. Heat transfer. T.1-2, 2001, p.198.). Therefore, reducing the mass and dimensions of air heat exchangers of gas turbine plants is a very urgent task. This problem is solved, as you know, due to the intensification of heat transfer in the paths of heat exchangers (Dreitzer GA "Problems of creating compact tubular heat exchangers", Thermal Engineering, 1995, No. 3, pp. 11-18). The use of various heat transfer intensifiers not only complicates the technology and cost of manufacturing heat exchangers, but also increases the hydraulic resistance in their paths. The latter increases the energy costs for the own needs of a gas turbine installation, reduces its efficiency

Known heat exchangers containing a housing and a tubular matrix made of heat transfer tubes arranged in parallel rows with a gap, adjacent rows of tubes are arranged at an angle in alternating planes perpendicular to the direction of the medium’s movement (US patent No. 1571068, publ. 26.01.26, US patent No. 3414052, publ. 03.12.68).

Known tubular heat exchanger comprising a housing, pipes for supplying (discharging) an external coolant, collectors for supplying (discharging) a coolant, a tube matrix consisting of cassettes containing panels formed by curved pipes, each panel of one cassette being located in the gap between the panels of another cassette (certificate RU for utility model No. 19702 U1, IPC F28D 7/06, published on September 27, 2001).

The closest in technical essence to the present invention is a tubular air heater containing a housing, manifolds for supplying (removing) the internal coolant, nozzles for supplying (removing) the external coolant and a pipe matrix consisting of two cartridges containing flat panels formed by curved U-shaped pipes, moreover, the panels of one cassette are located between the panels of another cassette (patent RU No. 2154248 C1, IPC F28D 7/06, dated 01.09.1999, publ. 10.08.2000).

The disadvantages of the known heat exchangers are the low heat exchange efficiency and, accordingly, the low compactness of the apparatus when using gas as a heat carrier in both the tube and annular spaces. The low heat transfer efficiency is a consequence of the traditional layout of the tube matrix, in which adjacent panels of flat coils of different cassettes are located relative to each other at an angle equal to 0 or 180 °. When the individual fluids are washed off by individual fluxes in such staggered and corridor beams, a flat flux and turbulence, which determines the heat transfer efficiency, are generated by the irregularity of the velocity field in the plane perpendicular to the pipe axis (“Heat transfer and hydraulic resistance of tube bundles. Heat exchangers tubular ". Migai VK, Firsova EV; Response. Editor Arefyev KM; USSR Academy of Sciences. Department of physical and technical problems of energy. Scientific Council on the complex problem." Teplofi Ica and termoenergetika "," Science "Leningrad branch, 1986 str.48-50).

Such an arrangement of cassettes in the tube matrix leads to the necessity of placing collectors for supply and removal of internal coolant on one side of each cassette of the heat exchanger. The close arrangement of the collectors for supplying and discharging the internal coolant with a large difference in the temperatures of the internal coolant at the inlet and outlet of the apparatus reduces the thermoplasticity of the casing during transient conditions, causes its deformation and warpage at the junctions with the collectors due to different elongation of the latter, and, as a result, density violation connections, coolant leaks. This circumstance reduces the resource characteristics and reliability of the heat exchanger, as well as the efficiency of heat transfer.

In addition, the absence of anti-bypass devices in the heat exchangers between the body and the tube bundle also reduces the heat transfer efficiency due to the fact that the flow around the peripheral tubes is less efficient than inside the matrix. The presence of anti-bypass devices ensures the return back into the tube bundle of the bypass flow, which contributes to a significant increase in the efficiency of heat transfer in general. Since the bypass path (Handbook of heat exchangers: In 2 vols. T.2 / Transl. From English under the editorship of O.M. Martynenko et al. - M .: Energoatomizdat, 1987, pp. 41-44) has a smaller hydraulic resistance than passage through the tube bundle, the fraction of the flow flowing around the beam can reach significant values (20-30%) and reduce the heat transfer efficiency, while reducing pressure loss. This circumstance is taken into account by the introduction of correction factors for heat transfer (p. 44, ibid.), Which vary depending on the ratio of the cross-sectional area of the bypass path to the cross-sectional area of the flow cross section. So, for example, with the ratio of the area of the bypass path to the area of the flow cross section in the range of 0.1-0.3, the value of the correction coefficient can vary from 0.88 to 0.7 (in the absence of anti-bypass bands) and from 0.93 to 0, 82 (when installing anti-bypass bands), respectively.

The technical problem solved by the invention is to increase the heat transfer intensification while reducing the hydraulic resistance of the external heat carrier, accompanied by an improvement in the overall dimensions of the heat exchanger due to a decrease in the total heat transfer surface, as well as an increase in its thermoplasticity, resource characteristics and reliability.

The specified technical problem is achieved by the fact that in the heat exchanger containing the housing, the inlet (outlet) headers of the internal coolant, the inlet (outlet) of the external coolant and a tube matrix consisting of two cartridges containing flat panels formed by curved U-shaped pipes, and the panels of one cassette are located between the panels of another cassette, according to the invention, the cassettes are rotated 90 ° relative to each other, while the straight sections of the pipes of the panels of one cassette are placed in the gap x between adjacent straight pipe sections of the panels of another cassette with the formation of a common lattice surface with a corridor arrangement of pipes, the inlet (outlet) collectors of the internal coolant are connected in the input (output) section to the corresponding one input (output) channel, which is a tee with separation (merging) the flow of the internal coolant simultaneously for two cassettes, while the input (output) tees are not interconnected and are hermetically connected to the body only in sections at the input (output) of the internal heat carrier, anti-bypass devices are installed in the U-shaped parts of the tube panels, between the body and the pipe matrix, and also between the body and the inlet (outlet) pipes of the internal coolant.

Moreover, anti-bypass devices are made in the form of metal wire meshes in a zigzag shape in one or more layers.

In addition, the straight sections of the tubes of the matrix panels are twisted in an oval profile.

The rotation of the cartridges at an angle of 90 ° relative to each other and the placement of straight pipe sections of one cartridge with alternation in the intervals between adjacent straight pipe sections of another cartridge leads to the formation of a common lattice surface with a corridor pipe arrangement, which helps to improve the overall dimensions of the heat exchanger, which allows it to be made more compact, to obtain a developed heat transfer surface and reduce hydraulic resistance in the external path of the heat exchanger (“Heat transfer and hydraulic e resistance of tube bundles. Tubular heat exchangers ", Migai VK, Firsova EV; Response. Editor Arefiev KM; USSR Academy of Sciences, Department of Physical and Technical Problems of Power Engineering. Scientific Council on the Complex Problem" Thermophysics and Thermal Power Engineering "." Science "Leningrad Branch, 1986, p. 48-50). The compactness of the heat exchanger in itself is the key to the high efficiency of the heat exchange surface, since it is the very nature of compact surfaces that contains the properties that determine the high heat transfer coefficient (Case VM: London A.L. “Compact heat exchangers”, M .: Energy, 1967 city, p. 13). Therefore, even with allowable pressure losses of each of the heat-exchanging media, a significant increase in the heat transfer coefficient is achieved due to an increase in flow turbulization during external flow around the tube bundles, as a result of which the heat transfer intensification increases.

In the heat exchanger with the proposed tube bundle arrangement, a periodic breakdown of the vortices and an update of the near-wall layer occur due to a change in the orientation of the axes formed near the walls of the vortex structures. According to experimental data Migaya V.K. and Novozhilova I.F. the heat transfer coefficient increases by 28%, and the hydraulic resistance decreases by 20% relative to tube bundles with a checkerboard or corridor arrangement of pipes (Migai V.K., Firsova E.V., ibid., p. 49). It is obvious that in the proposed design of the heat exchanger, part of the heat exchange surface in the places of pipe bends will have a corridor structure of the pipe matrix. Actually, the fraction of such a surface can be from 20 to 30% of the total heat transfer surface. To optimize the geometric parameters of the heat exchanger, you can vary the number of pipes in one layer and (or) in one panel. The serial connection of the proposed pipe systems in one housing creates the conditions for their further optimization.

The connection of the collectors of the supply and removal of the internal coolant of each cartridge to one input (output) channel, which is a tee with separation (merging) of the flow of the internal coolant, as well as the location of these tees inside the heat exchanger body, provides its thermoplasticity at transient operation of the heat exchanger, since the external and the internal surfaces of the walls of the collectors at start-up (shutdown) will be washed by coolants with close temperatures, i.e. practically in the absence of a temperature difference in the wall thickness. The connection of the tees of each cartridge with the housing in only one section eliminates the temperature stresses caused by the different temperature elongation of the tees and ensures their free movement in different directions regardless of the heat exchanger housing without thermal stresses.

The installation of anti-bypass devices in the U-shaped parts of the tube panels, between the case and the tube matrix, and also between the case and the inlet (outlet) pipes of the internal coolant, makes it possible to intensify the heat transfer in this zone due to the fact that the coolant flows around the peripheral pipes of the matrix as in the depths of the beam. These elements can be made, for example, in the form of metal wire meshes of a zigzag shape in one or more layers, screw tape swirlers. The characteristics of these elements are selected from the conditions for ensuring the flow around the beam in this zone, close to the flow conditions in the lattice part of the matrix and a significant reduction in the bypass flow of the external coolant in the azimuthal direction between the pipe layers. For example, for wire meshes, the parameters of the flow around the external flow around the pipes in the matrix can be provided by selecting the mesh cell and the thickness of the wire, and for screw swirls, the screw twist step. The validity of the choice in both cases is easily confirmed by aerodynamic calculation by such software systems as StarCD, CFX5, etc.

The execution of straight sections of the heat exchanger tubes by twisted oval profile contributes to a change in the direction of flow of the coolant by modifying the geometry of the surface of the pipes, changing the geometry of the channel, which leads to strong turbulization and, as a result, to high heat transfer intensity (Heat transfer and hydrodynamics in complex channels / Yu.I. Danilov, B.V. Dzyubenko, G.A. Dreitser, et al .; Edited by a member of the USSR Academy of Sciences V.M. Ievlev. - M.: Mechanical Engineering, 1986). When using pipes of a complex configuration, in particular twisted pipes, the boundary layer is destroyed from the curved surface of the pipes and swirling the flow of heat-exchanging media in the twisted channels of pipes of complex shape, which helps to increase heat transfer without increasing the speed of the coolant.

In addition, the use of oval-shaped twisted pipes leads to an additional decrease in the weight and size characteristics of the heat exchanger due to the denser packing of the pipes in the heat exchanger volume with the same tube perimeters washed and the heat exchangers being compared equal heat exchange due to the use of hydrodynamic intensification of heat transfer. The spiral flow of the medium in the annulus of the heat exchanger leads to the appearance of transverse velocity components, additional turbulization, the emergence of a secondary circulation of the flow, which ensures equalization of the temperature field in the annulus and increases the efficiency of the heat exchanger. Experimental data show that, on average, the heat transfer of bundles of twisted pipes with a variable channel width is 10% greater than that of a round tube bundle. For bundles of twisted pipes with constant slotted channels, the heat transfer is on average 25-33% higher than the average heat transfer for bundles of twisted pipes with variable channels between adjacent pipes, and 30-40% higher than in a smooth tube bundle. For a given heat output and the same hydraulic losses, the use of bundles of twisted pipes instead of straight round pipes can reduce the mass and dimensions of the heat exchanger by about 20-30%. Thus, the use of oval-shaped twisted pipes due to even greater turbulence in the flow will improve the weight and size characteristics of the lattice tube bundles relative to the lattice bundles of smooth pipes and thereby increase the heat transfer.

Figure 1 shows a General view of the design of the proposed heat exchanger, in a perspective view (side segment walls of the housing are not shown);

figure 2 shows a tube matrix of a heat exchanger without a housing and anti-bypass devices, consisting of cassettes rotated 90 ° relative to each other, with tees for supplying (removing) the internal coolant, in a perspective view;

figure 3 shows the location and fastening of the collectors of the supply (exhaust) of the internal coolant to the cassettes through the tube sheet, in a perspective view (anti-bypass devices, housing and connections of the collectors of the supply (exhaust) of the internal coolant to the tees are not shown);

figure 4 - view B in figure 3, shows the location of the straight sections of the pipes of the panels of one cartridge between the straight sections of the pipes of the panels of another cartridge when the cassettes rotate 90 ° relative to each other, in a perspective view (anti-bypass devices, the housing and connections of the supply headers (outlet ) internal coolant with tees are not shown);

in Fig. 5 is a view I in Fig. 1, the arrangement of anti-bypass devices (grids) between the casing and the collectors for supplying (removing) the internal coolant (anti-bypass devices in the U-shaped parts of the pipe panels and the side segment walls of the housing are not shown);

in Fig.6 - view A in Fig.1, shows the location of anti-bypass devices (grids) in the U-shaped parts of the pipe panels (the side segment wall of the housing is not shown).

The heat exchanger contains a tubular matrix 1 located inside the housing 2 (figure 1). The housing 2 is equipped with an inlet 3 and an outlet 4 tees of the internal coolant (air), supply pipes 5 and the outlet 6 of the external coolant (gas). The matrix 1 consists of two cassettes 7, 8 (figure 2), consisting of tube panels 9 (figure 4). Pipe panels 9 are formed by a set of U-shaped pipes 10 (Fig.2-4) of different bending radius, the longitudinal axis of which is located in the same plane. Pipes 10 are the main element that provides heat transfer between the heat carriers passing inside them and in the annulus. Cassettes 7 and 8 are rotated relative to each other by 90 ° and installed in each other (figure 4). In this case, the straight sections 11 of the tubes of the cassettes 7 and 8 are located in alternating adjacent planes, so that in the zone of their joint placement, the heat exchange surface is a lattice surface with a corridor arrangement of pipes. The ends of the U-shaped pipes 10 of each cartridge 7 and 8 are fixed in the respective tube sheets 12 (Fig. 3). The tube sheets 12 are connected to the respective collectors of the inlet 13 and the outlet 14 of the internal coolant, which are connected in the inlet and outlet sections into one inlet 3 and 4 outlet channels (Fig. 2), which are a tee with a separation or fusion of the internal coolant flow, respectively. The collectors of the inlet 13 and outlet 14 of each cartridge 7 and 8 (Fig.5, 6) are located inside the housing 2 and are not interconnected. In this case, only the inlet 3 and the outlet 4 tees of the internal coolant in sections 15 are connected to the body 2 of the heat exchanger (section 1). Between the pipes 10 in the U-shaped parts 16 of the pipe panels, as well as between the housing 2 and the pipe matrix 1, anti-bypass devices 17 are installed (FIGS. 5, 6). Anti-bypass devices 17 are made in the form of metal wire meshes of a zigzag shape and are installed in the housing in one layer or several layers. The anti-bypass devices may have a different design, for example, in the form of screw tape swirlers.

Alternatively, the straight sections 11 of the pipes 10 of the cassettes 7 and 8 in the zone of their joint placement can be made twisted oval profile (not shown), providing a transverse flow around the medium and intensifying heat transfer.

The heat exchanger operates as follows.

The external heat carrier of the heat exchanger is a heated medium, in which the products of combustion from gas turbines (gases) are used. The combustion products enter the supply pipe 5 of the housing 2, pass through the lattice structure of the cassettes 7, 8 of the pipe matrix 1, wash the outer surface of the U-shaped pipes 10 from all sides and give their heat to the air passing inside the pipes 10, as a result of which they cool and exit heat exchanger through branch pipe 6.

The internal coolant is a heated medium, in which air is used. Air is supplied through the inlet tee 3 of the housing 2, is divided by two flows through the supply manifolds 13 of the cassettes 7 and 8, and is distributed through the tube sheets 12 through the U-shaped pipes 10. Moving along the internal channels of the pipes 10, the air receives heat from the combustion products (gas), heats up and enters the headers of the outlet 14 of the cassettes 7 and 8 through the tube sheets 12 and then is discharged by the common stream through the outlet tee 4 from the heat exchanger. Thus, heat exchange occurs between the two media during their circulation through the heat exchanger.

As anti-bypass devices 17 in the example of a specific embodiment, metal wire meshes of a zigzag shape in one layer are used. The grids intensify the heat exchange process by eliminating leakages in the transverse flow of combustion products in the annulus, provide almost the same flow around the combustion products of the peripheral pipes 10 of the matrix 1, as in the depth of the tube bundle.

The execution of the straight sections 11 of the pipes 10 of the matrix 1 in the form of oval-shaped twisted pipes leads to additional intensification of heat transfer by increasing the specific heat transfer surface, which is achieved by denser packing of the pipes 10, modification of their geometry, changes in the channel geometry and the creation of additional eddy flows, as well as interaction multidirectional screw flows caused by their rotation during the transition from one row of pipes 10 of panels 9 to another due to the mutually perpendicular arrangement of these panels in trice 1.

The use of gas turbine combustion products as an external coolant allows to reduce the mass of the heat exchanger body 2, since the latter is practically unloaded from the mechanical pressure of the external coolant. Since the combustion products have a pressure close to atmospheric, therefore, the elements of the housing 2 can be made of sheet material.

The calculated comparative characteristics of the claimed heat exchanger with a lattice matrix and a heat exchanger with a W-shaped tube bundle with a checkerboard arrangement of pipes according to RU patent for utility model No. 31838 are carried out.

The results are presented in the table. Assessment of heat transfer and hydraulic resistance of the lattice structure of the matrix was performed for the corridor arrangement of pipes (Fig. 10.90, Case VM, London A. L. “Compact heat exchangers”, M .: Energy, 1967, p. 179). Calculations of heat transfer and hydraulic resistance in the zone of pipe bends are performed as for corridor flow around pipes with external coolant according to the recommendations (Heat-exchange equipment for nuclear power plants. Calculation of heat and hydraulic. RTM 108.031.05-84). When calculating the hydraulic resistance for the internal coolant in all cases, the table shows the following components of the pressure loss:

- friction losses in the tube matrix;

- losses due to flow turns in pipe bends;

- losses at the inlet and outlet of the matrix pipes.

In addition, in the calculations, the safety factors for the heat exchange surface, correction factors taking into account bypass flows, and the approximation error by the recommended dependences of the hydraulic resistance and heat transfer were taken into account and taken equal for the compared options.

The calculations showed that with the same parameters of the coolant at the inlet of the apparatus, the heat transfer coefficient of the external coolant (p. 1.7 of the table) of the proposed heat exchanger is significantly higher (133.4 W / m ² · C) heat transfer coefficient (99.7 W / m ² · C) of the known apparatus with lower relative pressure losses of a given medium. Taking into account that the total pressure loss of the external and internal coolants in the tube bundle (p. 1.1 and 1.12 in the same place) and the degree of regeneration are approximately the same, we can conclude that the proposed heat exchanger is more compact, since it has a smaller heat exchange surface (p. 2.13 and 2.10 there).

Table Parameter Name GTU with a capacity of 6 MW, regenerator W-shaped bundle, staggered arrangement of pipes (patent for PM 31838) Lattice bundle, corridor arrangement of pipes, series connection of two pipe systems 1 Heat exchanger parameters 1.1 Temperature of the cooled medium, ° C: - at the entrance; 647.0 647.0 - at the exit 359.3 358.1 1.2 Temperature of the heated medium, ° C: - at the entrance; 234.0 234.0 - at the exit 566.3 568.3 1.3 Consumption of the cooled medium, kg / s 26.3 26.3 1.4 Consumption of heated medium, kg / s 24.1 24.1 1.5 Pressure of the cooled medium (abs.), KPa 106.0 106.0 1.6 Pressure of the heated medium (abs.), KPa 586.0 586.0 1.7 Coeff. heat transfer of an external heat carrier, W / m ² ° С 99.7 133.4 1.8 Coeff. heat transfer of the internal heat carrier, W / m ² ° С 139.6 166.6 1.9 Heat transfer coefficient, W / m ² ° С 55.7 71.1 1.10 Correction for cross travel 0.932 0.929 1.11 Relates. loss of pressure of the external coolant,% 2,31 1.8 1.12 Relates. pressure loss of the internal coolant,% 0.821 1,54 1.13 Degree of regeneration 0,800 0.804 2 Tubing matrix parameters 2.1 The outer diameter of the pipe, m 0,025 0,025 2.2 Inside diameter of pipes, m 0.023 0,023 2.3 Relative transverse pipe pitch, m 1.18 1,571 2.4 Relative longitudinal pitch of pipes, m 0.952 1,0 2.5 the Number of layers of pipes along the flow, pcs 4 × 9 72 2.6 Number of rows of pipes along the front of the stream, pcs 72 70 2.7 Porosity of the lattice beam - 0.5 2.8 Number of strokes on the internal coolant four four 2.9 Length of the straight pipe section in the matrix panel, m 2.7 2.74 2.10. The length of the matrix along the external coolant, m - 2x0.925 2.11 The proportion of the heat exchange surface of the lattice structure, m ² - 0.786 2.12 The proportion of the heat transfer surface in the zone of pipe bends, m ² - 0.214 2.13 The total heat transfer surface, m ² 1713 1378 2.14 Material of heat transfer tubes - 1 and 2 moves 08X18H10T 08X18H10T - 3 and 4 moves 15XM 15XM 2.14. Overall dimensions, m 3.47 × 3, 10 × 4.40

Thus, with the location of the heat exchange tube bundle in the proposed manner, the heat transfer intensification is significantly increased, and the mass and size characteristics of the heat exchanger are improved, allowing it to be made as compact as possible.

Claims (3)

1. A heat exchanger comprising a housing, manifolds for supplying (discharging) the internal coolant, nozzles for supplying (discharging) the external coolant and a tube matrix consisting of two cassettes containing flat adjacent panels formed by curved U-shaped tubes, the panels of one cassette being located in the gap between the panels of another cassette, characterized in that the cassettes are rotated relative to each other by 90 °, while the straight sections of the pipes of the panels of one cartridge are placed in the spaces between adjacent straight sections of the pipes of the pan another cassette with the formation of a common lattice surface with a corridor arrangement of pipes, the collectors for supplying (discharging) the internal coolant are connected in the input (output) section to the corresponding one input (output) channel, which is a tee with separation (merging) of the internal coolant flow simultaneously for two cassettes, while the input (output) tees are not interconnected and hermetically connected to the housing only in sections at the inlet (outlet) of the internal coolant, in the U-shaped parts of the pipe panels, anti-bypass devices are installed between the body and the tube matrix, as well as between the body and the inlet (outlet) pipes of the internal coolant. 2. The heat exchanger according to claim 1, characterized in that the anti-bypass devices are made in the form of metal wire meshes in a zigzag shape in one or more layers. 3. The heat exchanger according to claim 1, characterized in that the straight sections of the pipes of the matrix panels are made in the form of twisted pipes of an oval profile.

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