JP5978094B2 - Heat exchanger and method for promoting convective heat transfer - Google Patents

Description

  The present invention relates to a heat exchanger.

  In a heat exchanger represented by a shell-and-tube type air-cooled heat exchanger, there are the following methods as methods for promoting heat transfer performance between both high-temperature and low-frequency fluids.

  That is, as shown in the following Patent Documents 1 and 2, a fin-like protrusion is provided on the heat transfer surface on the low-temperature fluid side, and a vortex is generated by the protrusion to improve the convective heat transfer coefficient, and each of the following Patent Documents As shown in FIG. 3, a convection heat transfer coefficient is improved by an oscillating flow induced by sound waves, and a piano wire that vibrates itself by a fluid flow in a heat exchanger as shown in Patent Documents 4 and 5 There are some which improve the convective heat transfer coefficient by disturbing the fluid flow by vibration of the piano wire itself or the fin portion of the cantilevered support shape on which the piano wire is mounted.

Japanese Utility Model Publication No. 56-52191 JP 2001-339113 A JP 2010-210105 A JP 54-14049 A JP-A-48-50341

As shown in the aforementioned Patent Documents 1 and 2, in order to improve the convective heat transfer coefficient by generating vortices at the protrusions on the heat transfer surface, install large protrusions to improve the convective heat transfer coefficient. If a large vortex is generated, there is a problem that the pressure loss of the fluid flow in the heat exchange increases due to the large protrusion.
When pressure loss increases in this way, a larger fluid driving force is required to maintain the same flow rate, and a large pump power is required when using a dynamic device such as a fluid driving pump. When using buoyancy due to the density difference depending on the temperature of the fluid to drive the fluid, it is necessary to set the heat transfer surface to be long in the vertical direction. The equipment becomes larger.

  As shown in the above-mentioned Patent Document 3, stirring the high-temperature fluid layer formed in the vicinity of the heat transfer surface by the vibration flow induced by sound waves improves the convective heat transfer coefficient, but the increase in pressure loss is small. Since the oscillating flow induced by the sound wave is weak, there is a problem that the flow velocity region where the effect can be exhibited is limited to a low flow velocity (about 0.1 m / s or less).

  As shown in Patent Documents 4 and 5, in the case of vibrating the vibrating piece by the flow of fluid to exchange heat, the possibility that the vibrating piece is repeatedly damaged by receiving a load is seen in Patent Document 1. There is a problem that it is larger than the protrusion.

  Accordingly, an object of the present invention is to improve the convective heat transfer coefficient over a wide flow velocity range, in a heat exchanger, in which increase in pressure loss and damage are unlikely to occur.

In order to solve the above problems, a heat exchanger according to the present invention includes a protrusion row in which a plurality of protrusions are provided on the heat transfer surface of the heat exchanger so as to be spaced apart in the direction of the flow of fluid to be heat exchanged. And a sound wave generation mechanism that makes sound waves incident on the fluid.
The heat exchanger according to the present invention is formed as a sensitive region that is likely to cause a vortex of the fluid at the protrusion, and when sonic vibration reaches the region as a stimulus, the region reacts sensitively to the stimulus in the region and Generation is promoted, and convective heat transfer at the heat transfer surface of the heat exchanger is promoted. As described above, a plurality of regions along the heat transfer surface are formed along the heat transfer surface where vortices are formed in response to the external stimulus sensitively from outside the heat transfer surface. When reaching the vicinity as a stimulus, the separation of the fluid flow is promoted by the protrusion and the sound wave stimulation as compared with the protrusion alone, and the separation vortex is surely caused. Convective heat transfer is promoted by stirring the flow in the vicinity of the heat transfer surface while moving along.
Preferably, of the protrusions adjacent to each other in the direction of fluid flow, a vortex formed by a protrusion on the upstream side of the fluid flow has reached a position where it can merge with a vortex formed by a protrusion adjacent on the downstream side. Sometimes, the frequency of the sound wave is set so that a new vortex is induced in the protrusion of the protrusion row by the sound wave.
In this way, when the vortex created on the upstream side arrives at a sensitive region by the protrusion adjacent to the downstream side, a stimulus is applied to the peeling portion by the downstream protrusion at the arrival timing, so there The generated vortex and the vortex arriving from the upstream side are merged with good timing to form a large vortex. In this way, by controlling the vortex generation timing at the protrusion by stimulation with the sound wave, the vortex generated from the downstream side is merged with the vortex coming from the upstream side to enlarge the vortex, and from the heat transfer surface The fluid in the far region is agitated with a large vortex and brought closer to the heat transfer surface side, contributing to heat exchange with the fluid in the region far from the heat transfer surface, further promoting convective heat transfer.
More preferably, the frequency f of the sound wave and the interval L are determined so as to satisfy the relationship of 5 / f ≦ L ≦ 100 / f.
More preferably, the sound wave generation mechanism is configured to include a speaker in which a vibration unit is in contact with the fluid, and a speaker driving device that drives the speaker.
Further, the sound wave generation mechanism may be configured by a cavity provided in a shell of the heat exchanger.
Further, as the sound wave generating mechanism, the shell may be configured so that the sound wave is generated by an acoustic resonance phenomenon in the shell of the heat exchanger.
The method for improving the convective heat transfer coefficient of the heat exchanger according to the present invention employed to solve the above-mentioned problems forms a row on the heat transfer surface in contact with the fluid to be heat exchanged with an interval in the fluid flow direction. By arranging a plurality of protrusions in this way, an environment that easily changes to a vortex flow is created when the flow is stimulated, and a wave is incident on the fluid as the stimulation under the environment.
By such a method, the environment that is likely to change into a vortex due to the projection brings a sensitive area near the heat transfer surface that is likely to cause a vortex even with a small stimulus. This makes it easy to generate vortices, and the scale of the stimulus is applied to the region sensitive to the stimulus, so that it is small. The vortex thus generated moves along the flow of the fluid along the heat transfer surface while stirring the fluid near the heat transfer surface to improve the convective heat transfer coefficient of the heat exchanger.
Preferably, the wave is generated by a sound wave, and the frequency f of the sound wave and the interval L are determined so as to satisfy a relationship of 5 / f ≦ L ≦ 100 / f.
Control for generating a large vortex by combining the vortex generated on the upstream side of the flow with the vortex generated on the downstream side by controlling the generation timing of the vortex by the protrusion by the interval and the frequency determined in this way Is surely made.
More preferably, as a method of obtaining the sound wave, a speaker is driven by a speaker driving device.
In addition, as a method of obtaining the sound wave, the fluid flow may be obtained without passing through the position of a cavity provided in the shell of the heat exchanger without using external energy.
In addition, as a method of obtaining the sound wave, external energy may be used without obtaining it by an acoustic resonance phenomenon in the shell of the heat exchanger.

  According to the present invention, in the heat exchanger, it is possible to improve the convective heat transfer coefficient without accompanying vibration of the vibrating piece by the fluid and suppressing an increase in pressure loss.

It is a longitudinal cross-sectional schematic diagram of the shell and tube type air cooling heat exchanger which concerns on Example 1 of this invention. FIG. 1 is a schematic diagram showing the vortex generation phenomenon of the fluid outside the heat transfer tube, and the diagram on the left side of the alternate long and short dash line is a diagram for explaining the situation before the vortex coalescence, and the right diagram explains the situation after the coalescence. It is a figure to do. It is a graph which shows the relationship between the flow velocity of the fluid outside a heat exchanger tube, and the convective heat transfer coefficient ratio in each structure containing the heat exchanger of FIG. It is a longitudinal cross-sectional schematic diagram of the shell and tube type air cooling heat exchanger which concerns on Example 2 of this invention. It is a longitudinal cross-sectional schematic diagram of the shell and tube type air cooling heat exchanger which concerns on Example 3 of this invention.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

In this embodiment, an example of a heat exchanger that can improve the convective heat transfer coefficient with a relatively small increase in pressure loss even in a flow velocity region used in a normal heat exchanger will be described.
As a heat exchanger using a tubular partition as a heat transfer surface, there is a shell and tube type air cooling heat exchanger as shown in FIG. In the heat exchanger, tube plates 3 for supporting a large number of heat transfer tubes 2 serving as tubular partition walls are installed on both upper and lower sides of a circular or polygonal shell 1. A large number of holes for passing the heat transfer tubes 2 are arranged in a square or a staggered manner in the tube plate 3, and the heat transfer tubes 2 are inserted into these tube holes and both ends are fixed to the tube plate 3. The heat transfer tube 2 is made of, for example, stainless steel. The thickness of the heat transfer tube 2 is determined in consideration of the pressure difference inside and outside the heat transfer tube and the heat resistance in the heat transfer tube 2.
In the upper and lower portions of the heat exchanger, a water chamber cover 6 is provided on the tube plate 3, and the water chamber cover 6 has a high-temperature fluid 4 (liquid such as water or air, water vapor, etc.) that is one fluid to be heat exchanged. Nozzle 7 is provided to allow gas in / out. Near both ends of the shell 1, nozzles 8 for passing a low-temperature fluid 5 (gas such as air), which is the other fluid to be heat exchanged, into and out of the shell 1 are provided sideways.
The high-temperature fluid 4 enters the water chamber cover 6 from the upper nozzle 7, flows into the inside of the heat transfer pipe 2, flows as a pipe-inside fluid as indicated by a downward arrow, passes through the lower water chamber cover 6, and flows into the lower nozzle. It flows out from 7.
The low-frequency fluid 5 enters the shell 1 from the lower nozzle 8, flows outside the heat transfer tube 2 and flows inside the shell 1 as a fluid outside the tube, as indicated by a broken line arrow, and upward along the heat transfer tube 2 along the way. Flowing. In this way, the heat exchange efficiency is enhanced by flowing the fluid inside and outside the pipe in the direction of the opposing flow. In this embodiment, a gas such as air is used as the low temperature fluid 5, but a liquid such as water may be used for the low temperature fluid 5.
In this embodiment, a straight pipe is used as the heat transfer pipe 2 of the heat exchanger. However, in order to alleviate the generation of thermal stress due to the temperature difference of the shell 1, both ends of the U-shaped pipe are connected to one of the tube plates 3. It is also possible to use a heat exchanger that is attached to the other and does not have the other tube sheet.

When the high-temperature fluid 4 flowing inside the heat transfer tube 2 is made into a gas such as water vapor and condensed in the heat transfer tube 2 by heat exchange, the condensation heat transfer rate by the high-temperature fluid 4 inside the heat transfer tube 2 is the low-temperature fluid outside the heat transfer tube 2. Therefore, the convective heat transfer coefficient by the low-temperature fluid 5 outside the heat transfer tube 2 is a factor that determines the surface area and the number of the heat transfer tubes 2. If the number of heat transfer tubes can be reduced, the cost can be reduced. Therefore, increasing the convective heat transfer rate by the low-temperature fluid 5 outside the heat transfer tubes 2 is an important engineering issue.
In order to increase the convective heat transfer coefficient, the structure described below is attached to the heat exchanger. That is, as shown in FIG. 2, annular projections having a projection height H (projection dimension from the outer surface of the heat transfer tube 2) are fixed to the outer surface of the heat transfer tube 2 at regular intervals L up and down. Thus, the projections 9 are arranged in the direction of the flow of the low-frequency fluid 5 and the direction along the heat transfer tube 2.
The heat exchanger is equipped with a sound wave generating mechanism. The sound wave generator 10 employed as the sound wave generating mechanism is composed of a speaker installed on the shell 1 so that the vibration surface is in contact with the low temperature fluid 5 and a speaker driving device that drives the speaker. The speaker driving device has an adjusting means for changing the frequency of the sound wave 11 and can generate a specific frequency f.

The shape of each protrusion constituting the protrusion row 9 is preferably a shape in which the vortex generation position becomes clear by separation of the flow of the low-temperature fluid 5. For example, as shown in FIG. Preferably there is. The height H of each protrusion in the protrusion row 9 is determined so that the pressure loss of the low temperature fluid 5 flowing in the heat exchanger becomes maximum within an allowable range.
As shown in FIG. 2, the vortex 12 generated by the protrusion moves on the flow of the cryogenic fluid 5. When the movement speed V of the vortex 12 and the interval L between the protrusions are given, the time T = L / V required for the vortex 12 to move between the protrusions, and when the vortex 12 reaches the next protrusion adjacent to the downstream side. If the sound wave 11 is incident on the surface, a new vortex is generated at the next protrusion and can be combined with the vortex 12 from the downstream side. Therefore, the frequency f of the sound wave 11 is f = V / L, and thus the protrusion interval L = V. / F. The flow velocity region targeted in each embodiment of the present invention is 5 m / s or more, where the effect is remarkable as compared with the existing examples. Therefore, the lower limit flow velocity is 5 m / s, and 5 / f ≦ L. Moreover, since the maximum flow velocity that is actually assumed is set to 100 m / s, L ≦ 100 / f.

Therefore, the interval L of the projection row 9 with respect to the flow direction of the bass fluid 5 is determined so as to satisfy the following expression (1) with respect to the frequency f of the sound wave 11 generated by the sound wave generator 10.
5 / f ≦ L ≦ 100 / f (1)
As shown in FIG. 3, it is obvious that the convective heat transfer coefficient ratio of this embodiment is more remarkable than the other cases when the flow velocity exceeds the value near 5 meters per second.

  In this embodiment, since the flow of the low temperature fluid 5 is separated at the protrusions of the protrusion row 9, a vortex 12 is generated downstream of the protrusions as shown in FIG. The vortex 12 moves to the downstream side due to the flow of the low temperature fluid 5, and reaches the vicinity 13 of the protrusion located adjacent to the downstream side.

The speaker driven by the speaker driving unit vibrates and makes the sound wave 11 having the frequency f incident on the low temperature fluid 5. Due to the incidence, the wave reaches the protrusion and the periphery thereof. When the projection f of the projection row 9 and the frequency f of the sound wave 11 incident on the projection row 9 and the interval L between the projections constituting the projection row 9 satisfy the relationship of the above equation (1), they are adjacent to each other with the interval L. When the vortex 12 formed by the protrusion on the upstream side of the flow of the low-temperature fluid 5 among the protruding protrusions reaches the vicinity 13 of the protrusion adjacent on the downstream side, a new wave is added to the protrusion of the protrusion row 9 by the sound wave 11. A vortex is induced. Since the vortex that has reached the vicinity 13 of the downstream protrusion by the flow of the low-frequency fluid 5 and the vortex induced by the wave of the sound wave 11 merge, a larger vortex 14 is formed downstream of the protrusion.
The high-temperature fluid layer formed in the vicinity of the heat transfer surface of the low-temperature fluid by heat exchange with the high-temperature fluid 5 and the low-temperature fluid layer in the main portion of the low-temperature fluid are mixed by the vortices formed in the wake of the protrusion, so that convection Heat transfer rate is improved.
The projection tube 9 is provided in the heat transfer tube to create a sensitive environment in which vortices are likely to be generated in the vicinity of the projection. Therefore, if a wave is applied as a stimulus in the vicinity of the projection or in the vicinity of the projection in that environment, the vortex is generated. It is possible to easily induce vortex generation and control the generation timing of vortices with sound waves.
Compared to the conventional means in which the projections are simply provided on the heat transfer tube, in this embodiment, the vortex formed downstream of the projections becomes larger, and the stirring effect of the high temperature fluid layer and the low temperature fluid layer can be further obtained. It is possible to further improve the convective heat transfer coefficient.
In addition, compared with a heat transfer tube provided with a protrusion, the flow of the protrusion is stimulated by the wave to induce a vortex without changing the height of the protrusion that obstructs the flow of the low-temperature fluid 5. In the embodiment, the convective heat transfer coefficient can be improved by increasing the size of the vortex without increasing the pressure loss.
In the present embodiment, the high-temperature fluid layer and the low-temperature fluid layer are not directly agitated by the oscillating flow of the sound wave 11, so that the application range is not limited by the flow velocity as compared with such a conventional example. Therefore, it is possible to improve the convective heat transfer coefficient in a flow velocity range (1 to 20 m / s) used in a normal shell and tube type air-cooled heat exchanger.

FIG. 3 shows the convective heat transfer coefficient ratio (ratio to the convective heat transfer coefficient without a protrusion array and sound waves) in a configuration in which only a protrusion array is provided on the heat transfer surface, and a case where sound waves are incident on the heat transfer surface. This is a comparison of the convective heat transfer coefficient ratio (ratio to the convective heat transfer coefficient with no projection row and with sound waves) and the convective heat transfer coefficient ratio according to this example. Further, as a configuration in which these comparative controls are combined, when a sound wave is incident on the heat transfer surface having the protrusion row (however, the frequency f of the sound wave and the interval L between the protrusions of the protrusion row satisfy the relationship of the expression (1)). The convective heat transfer coefficient ratio is also shown.
It can be seen from the graph of FIG. 3 that the improvement rate of the convective heat transfer coefficient according to this example is superior to any of the cases. As described above, the heat exchanger is configured as described above, so that an increase in pressure loss due to the protrusion and the adoption of a vibrating piece that vibrates in the flow of the low-temperature fluid 5 can be used. The convective heat transfer coefficient can also be improved at.

  In this embodiment, the sound wave generation mechanism of the first embodiment described above is changed to another mechanism, and the other contents are the same as those in the first embodiment. Will be described based on FIG.

A cavity 15 is provided in a portion where the nozzle 8 of the shell 1 of the shell and tube type air-cooled heat exchanger shown in FIG. The cavity 15 is a hole formed in the outer wall of the shell 1, and the hole opens only in the nozzle 8. Such a cavity 15 is provided in the mounting portion of the upper and lower nozzles 8. In the present embodiment, the cavity 15 is used as a sound wave generation mechanism that uses the hydrodynamic resonance phenomenon in the cavity 15.
When the depth of the cavity 15 is Lc and the sound velocity is Cs, a sound wave having a frequency f = Cs / (4Lc) is generated from the cavity 15 due to acoustic resonance in the cavity 15. Since the hydroacoustic resonance phenomenon in the cavity 15 is used as the sound wave generation mechanism, the sound wave 11 can be generated without a driving action from the outside like a speaker or the like.

  The configurations of the heat transfer tube 2 and the projection row 9 on the surface of the heat transfer tube are the same as in the first embodiment. The protrusion interval L of the protrusion row 9 with respect to the flow direction of the low-temperature fluid 5 is determined so as to satisfy Expression (1) with respect to the frequency f of the sound wave 11 generated by the hydroacoustic resonance phenomenon in the cavity 15.

Since the flow of the low-temperature fluid 5 is separated at the protrusion 9, the vortex 12 is generated in the wake of the protrusion as shown in FIG. The vortex 12 moves to the downstream side by the flow of the low-temperature fluid 5 and reaches the vicinity 13 of the protrusion adjacent to the downstream side. When the frequency f of the sound wave 11 generated in the cavity 15 incident on the protrusion in the protrusion row 9 or the fluid in the vicinity of the protrusion and the interval L of the protrusion row satisfy the relationship of the above equation (1), the vortex 12 is on the downstream side. When reaching the vicinity 13 of the protrusion, a new vortex is induced in the protrusion of the time train 9 by the sound wave.
The vortex that has reached the vicinity 13 of the projection on the downstream side due to the flow of the low-temperature fluid 5 and the vortex induced by the sound wave 11 merge to form a larger vortex 14 in the wake of the projection.
By forming such a large vortex, the convective heat transfer coefficient of the heat exchanger can be improved as in the first embodiment.

  Further, in this embodiment, since the sound wave 11 used in this embodiment is obtained by the hydroacoustic resonance phenomenon using the cavity 15, in order to drive the speaker as in Embodiment 1, energy such as electric power from the outside is used. Need not be introduced, and the cause of failure is reduced.

  In this embodiment, the sound wave generation mechanism of the first embodiment described above is changed to another mechanism, and the other contents are the same as those in the first embodiment. Will be described based on FIG.

The sound wave generation mechanism in the present embodiment utilizes the acoustic resonance phenomenon in the shell 1 of the shell-and-tube type air-cooled heat exchanger shown in FIG. When the height of the shell 1 is Ls, the sound speed is Cs, and n is a natural number, a sound wave 11 having a frequency f = (n / 2) · (Cs / Ls) is generated in the shell.
Since the acoustic resonance phenomenon in the shell 1 is used as the sound wave generation mechanism, the sound wave 11 is generated without adding a structure such as a sound wave generator using a speaker as in the first embodiment or a cavity 15 as in the second embodiment. It is possible.

The protrusion interval L of the protrusion row 9 with respect to the flow direction of the low-temperature fluid 5 is determined so as to satisfy Expression (1) with respect to the frequency f of the sound wave 11 generated by the acoustic resonance phenomenon in the shell 1.
Also in this embodiment, as in the first and second embodiments, as shown in FIG. 2, the vortex 12 that has reached the vicinity 13 of the protrusion on the downstream side by the flow of the low temperature fluid 5 and the vortex induced by the sound wave are combined. Thus, a larger vortex 14 is formed in the wake of the protrusion.
By forming such a large vortex, it is possible to improve the convective heat transfer coefficient of the heat exchanger as in the first and second embodiments.

  Further, in the present embodiment, since the sound wave 11 used in the present embodiment is obtained by the acoustic resonance phenomenon in the shell 1, there is no need to introduce energy such as electric power or the cavity 15 from the outside.

  The present invention is used for a heat exchanger of a type in which each fluid to be heat exchanged exchanges heat through a heat transfer wall surface.

DESCRIPTION OF SYMBOLS 1 ... Shell, 2 ... Heat exchanger tube, 3 ... Tube plate, 4 ... High temperature fluid, 5 ... Low temperature fluid, 6 ... Water chamber cover, 7, 8 ... Nozzle, 9 ... Projection row | line | column, 10 ... Sound wave generator, 11 ... Sound wave .

Claims (9)

A projection rows formed by providing a plurality of projections spaced in the direction of the heat exchanged fluid flows through the heat transfer surface of the heat exchanger, the heat exchanger and a sound wave generating mechanism incident sound waves to the fluid ,
Of the protrusions adjacent to each other in the direction of fluid flow, when a vortex formed by a protrusion on the upstream side of the fluid flow reaches a position where it can merge with a vortex formed by a protrusion adjacent on the downstream side, The heat exchanger is characterized in that the frequency of the sound wave is set so that a new vortex is induced at the protrusion of the protrusion row by the sound wave. Oite to claim 1, the frequency f of the acoustic wave, the heat exchanger is characterized in that it is determined such that the distance L satisfies the relation of 5 / f ≦ L ≦ 100 / f. 3. The sound wave generation mechanism according to claim 1, wherein the sound wave generation mechanism includes a speaker in which a vibration unit is in contact with the fluid, and a speaker driving device that drives the speaker. Heat exchanger. 3. The heat exchanger according to claim 1, wherein the sound wave generating mechanism includes a cavity provided in a shell of the heat exchanger. 3. The shell according to claim 1, wherein the sound wave is generated by the acoustic resonance phenomenon in the shell of the heat exchanger as the sound wave generating mechanism. Heat exchanger. By arranging a plurality of protrusions on the heat transfer surface in contact with the fluid to be heat exchanged so as to form a row at intervals in the flow direction of the fluid, an environment that easily changes to a vortex when the flow is stimulated is created. In the method for promoting convection heat transfer of a heat exchanger that makes a vortex by making a sound wave incident on the fluid as the stimulus under the environment, and stirs the fluid with the vortex ,
The relationship between the frequency f of the sound wave and the interval L is set and used so that the relationship between the frequency f of the sound wave and the interval L becomes a relationship of 5 / f ≦ L ≦ 100 / f. Method for promoting convective heat transfer in a heat exchanger. 7. The method according to claim 6 , wherein the sound wave is obtained by driving a speaker with a speaker driving device. In claim 6, a method of obtaining the sound wave, before Symbol heat exchanger method convective heat transfer accelerating which is characterized in that to obtain in flow force acoustic resonance phenomenon using a cavity provided in the heat exchanger of the shell . 7. The method of promoting convective heat transfer in a heat exchanger according to claim 6 , wherein the sound wave is obtained by utilizing an acoustic resonance phenomenon in a shell of the heat exchanger.