KR910003073B1 - Shell and tube heat transfer apparatus and process therefor - Google Patents

Abstract

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Description

[Name of invention]

Shell and Tubular Heat Transfer Devices and Their Processes

[Brief Description of Drawings]

Apparatuses and processes which are preferred embodiments of the invention are described, for example, with reference to the accompanying drawings.

1 is a perspective view of a heat transfer device in which heat is transferred from a fluid flowing in the device to an atmosphere surrounding the device.

FIG. 2 is a perspective view similar to FIG. 1 with a pin, side and end wall removed to show the preferred shape of the fluid blocker structure therein; FIG.

FIG. 3 is a cross sectional view taken along line 3-3 of FIG. 2 showing the flow of fluid obtained within the apparatus.

4A, 4B, 4C and 4D are top views of small portions of other barrier structures to illustrate the respective shapes that may be taken.

5 is a schematic cross-sectional view showing a preferred form of the breaker structure.

6 is a cross-sectional view of a single tube and shell heat exchanger of the present invention.

FIG. 7 is a longitudinal sectional view taken along line 7-7 of FIG.

8 is a perspective view of a unitary breaker structure for use in the interior of a heat exchanger tube.

9 is a longitudinal sectional view taken along line 9-9 of FIG. 10 of a plurality of tube shells and tube heat exchangers of the present invention wherein the tube is a circular cross section.

10 is a cross sectional view along line 10-10 of FIG.

Figure 11 is a graph comparing the relative performance ranking of the prior art tubular and plate heat exchanger face and the heat exchanger face of the present invention.

Detailed description of the invention

[Field of Invention]

The present invention relates to novel shell and tubular devices for heat transfer and new heat transfer processes used in such devices.

[Review of the prior art]

In the field of heat transfer, continuous efforts are being made to improve the efficiency of the heat transfer process in order to improve the efficiency and to reduce the cost of the apparatus used in the improved process as much as possible. Various conventional proposals for this purpose include: (a) reducing the thickness of the boundary layer of fluid flowing in a passage by promoting turbulence in the fluid flow, for example by roughening the flow passage wall or by providing a turbulence promoter in the passage; A) the induction of boundary layer separation from the heat transfer surface by the use of curved or corrugated heat transfer surfaces; or c) the blocking of the heat transfer surface with so-called "split-pin" devices.

A major problem often encountered in this proposal is that the promotion of turbulence or the blocking of heat transfer surfaces in laminar flow increases the heat transfer per unit area, but it is necessary to maintain the fluid flow at the required rate due to the increased turbulence and inefficient laminar diffusion mixing. This results in an unbalanced increase in pumping capacity per unit area, and a significant increase in manufacturing costs in commercial use and thus, in the unfavorable case, such proposals are not adopted in most cases unless miniaturization is not essential.

As an example of the proposal, U.S. Patent No. 1,172,247 to Hugh Douz and Peter Ernest Goss, a flow passage formed between parallel plates to facilitate turbulent flow in a flow, is provided with a structure consisting of a cross woven rod or wire mesh. A heat exchanger device is described. second. M. Harrison, US Pat. No. 1,862,291, describes another structure in which expanded metal is used as a fluid deflector to weaken the boundary layer. Many other so-called "turbulence promoters" have been proposed so far for this purpose.

Another example of a proposal is A. A., located in Towana, New York. blood. V. The Company's "Heat Transfer Handbook" publication provides heat transfer pumping capability data, although improvements in heat transfer are achieved by induction of turbulent fluid flow, even at low Reynolds numbers, the induction being called "plate and A method is described which consists in the use of curved or corrugated heat transfer plates stacked with gaskets fitted to constitute a frame " exchanger. Another example is W. M. Kayes and A. L. It is described in London's 1964 New York McGraw Hill Mechanical Engineering Series 2nd Edition, "Small Heat Exchanger", pages 216 and 217.

As an example of the proposal, George W. In US Pat. No. 2,360,123 to Gersung and Hiram Walker, a heat exchanger using split corrugated fins is described, as described above in " Small Heat Exchanger " With this device a very high heat transfer coefficient is obtained and the flow becomes laminar by keeping the pin length very short through splitting and offsetting. This is very thin and close to the leading edge of the split pin, allowing for maximum heat transfer in the advancing boundary layer, and splitting and offsetting hinder the progress of the thin boundary layer. Mixing with the core layer takes place primarily by conduction through the fluid and therefore very small hydraulic radii are required for proper mixing efficiency. Some burrs are often present when transferring pins and the associated frictional resistance makes the flow turbulent at very low Reynolds numbers. As a result, the pumping capacity requirement per unit of heat transfer surface becomes high in both cases and the manufacturing cost becomes very expensive.

[Purpose of invention]

It is therefore an object of the present invention to provide a novel heat transfer process in which heat transfer can be increased without a corresponding unbalanced increase in pumping capacity.

It is a further object of the present invention to provide a novel shell and tube heat transfer apparatus in which heat transfer can be increased without a corresponding unbalanced increase in pumping capacity.

A more specific object is to provide novel shell and tubular heat transfer devices and processes which increase heat transfer while avoiding turbulence in the presence of laminar wake interferences.

According to the invention there is provided a shell and tube heat exchanger for heat exchange between two fluids, ie the shell has an inner wall, an inlet and an outlet for the passage of each fluid through the shell space inside the shell, at least one tube Is installed in a shell having an inner surface and an outer surface and having an inlet and an outlet therein for passage through an inner tube of each fluid, and each tube wall constitutes a heat exchange wall between two fluids in the inner shell and the inner tube. The fluid flow inside the tube takes the form of a non-flow boundary layer immediately adjacent the inner surface of the tube and a core layer in contact with the boundary layer, and the tube-side fluid flow blocker structure within each tube has a plurality of longitudinal extensions in contact with the passage inner wall. Comprising the rows of spheres, the structure non-disruptively blocks the complete development of at least the boundary layer at the inner surface of the tube at a number of spaced breaks, thus preventing Portions of the layer are non-disruptively separated from the inner surface of the tube between the break points and mixed with the core layer to streamline heat transfer between the inner surface of the tube, its respective boundary layer, and the core layer, and useless fluid within the tube away from the inner surface of the tube. The space between the longitudinally extending rows is filled with space filler to prevent flow.

In addition, according to the present invention there is provided a shell and tube heat exchanger for heat exchange between two fluids, that is, the shell has an inner wall, an inlet and an outlet for the passage of each fluid through the shell space inside the shell, at least one Tube is installed in a shell having an inner surface and an outer surface and having an inlet and an outlet into and through the inner wall of each fluid for passage therein, each tube wall forming a heat exchange wall between two fluids in the inner shell and the inner tube. The fluid flow in the shell space takes the form of a non-flow boundary layer immediately adjacent the inner surface of the tube and a core layer in contact with the boundary layer, and the shell-side fluid flow blocker structure in the shell space surrounds and contacts the outer wall of the tube. And the structure non-disruptively blocks the complete development of at least the boundary layer at the outer surface of the tube at a number of spaced break points, thus part of the blocked boundary layer. Non-disruptively separated from the tube outer surface between the break points and mixed with the core layer to streamline heat transfer between the tube outer surface, its respective boundary layer and core layer, preventing unwanted fluid flow in the shell inner space away from the tube outer surface In order to achieve this, the space between the shell side breaker casting sphere and the shell inner wall is filled with a space filler.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The simple convection heat transfer device 10 of FIG. 1 is adapted to transfer heat retained in a liquid such as oil or water to a gaseous atmosphere, such a device being usually used as an oil or water cooler, for example. The apparatus constitutes a hollow body 12 that provides a parallel wall flow path comprising a fluid flow blocker structure described below. Fluid is supplied to the apparatus through the inlet pipe 14 and discharged through the outlet pipe 16. The exterior of the body is provided in a manner known as parallel spaced fins 18 for more efficient heat transfer to ambient air.

The interior of the body 12 provides a non-flow fluid flow path comprising two parallel spaced opposing heat transfer wall surfaces 20 (FIG. 3) provided with walls 22, with fluid flowing between the walls. The passage is provided with two side walls 24, and the closure is provided with two transition portions 26 which gradually change the circular cross sections of the pipes 14, 16 into rectangular cross sections of the flow path. In this embodiment, the fluid flow blocker structure disposed within the passageway constitutes a plurality of closely filled spheres 28 of a material that is not affected by fluids such as metal, glass or porcelain, and the packing is such that the spheres are in contact with each other. The diameter of the sphere is the diameter of the size of point contact with the opposing heat transfer wall surface 20, respectively. In this embodiment the spheres are in contact with each other so that they are in contact with each other at mutual contact points to take a unitary structure. In another embodiment the spheres are filled as intervening perforated plates with spheres arranged in, for example, holes in a low density apart from one another. Other changes are described later.

The fluid flowing in the passageway has a boundary layer 30 immediately adjacent to the face 20, which serves to isolate the wall surface from the fluid body flowing in the core layer 32 and in contact with the boundary layer 30. It is well known to those skilled in the art to reduce heat transfer between the wall surface 20 and the core layer 32. It is well known that the unobstructed boundary layer gradually increases in thickness in the direction of the fluid flow and increases its blocking effect. As described above, it has been proposed to collapse the boundary layer by roughening or corrugating the fluid flow surface until now, and such a proposal has the effect of increasing the pumping capacity required to an unbalanced size.

In the device of the present invention, the boundary layer 30 is spot-blocked at points 34 spaced apart by the fluid flow blocker structure interposed between the heat transfer surfaces, while maintaining the non-flow fluid flow in the core 32. Not only is the heat transfer surface 20 not coarse in the apparatus of the present invention, but in many embodiments, the surface 20 is as economically desirable as possible so as to be polished to the required smoothness. The collapse of the boundary layer 30 at a number of spaced points 34 ensures a thin hold, and the collapse method avoids turbulences that cause inadequately high frictional resistance. Polishing all surfaces, including spheres, helps minimize the required frictional resistance.

As such, the present invention improves the ratio of frictional power to convective heat transfer per unit heat transfer surface area by providing a low friction resistance special shape barrier and mixing structure directly adjacent to a smooth heat transfer surface using a hydraulic radius to ensure total laminar flow. It includes a fluid flow system. The mixed construct comprises cellular pores, the pores being longitudinally connected, in each of which fluid is helically rotated as a single laminar flow eddy. The eddy is a very efficient means of mixing laminar flow, and is preferably obtained by matching the wake eddy downstream of the break point and the advancing eddy upstream of the break point to produce a wake interference flow that provides the highest efficiency. The boundary layer 30 on the curved surface of the mixed structure is quite thick, and the boundary layer of the heat transfer surface located opposite the surface of the mixed structure is very thin on average, which is consistently and spotted at a number of contact points between the surface of the mixed structure and the heat transfer surface. This is due to the fact that it decreases, and is also exposed to the highest local velocities that occur markedly very close to the flat heat transfer surface. This allows for rapid heat flow through the heat transfer plane.

It is also believed that the efficiency is improved because the velocity gradient adjacent to the heat transfer surface is larger than the curved surface of the barrier mixing structure. In addition, the velocity gradient is largely maintained at the heat transfer surface by the uniformly spaced flow barriers occurring at multiple points of contact between the mixing structure and the heat transfer surface. The block also swirls the flow at high speed into the heat transfer plane. Because it is well known in many experimental and theoretical analyzes that temperature gradients are proportional to velocity gradients (see New York, Harper and Rowe Press, 1976, F. Craser, "Principles of Heat Transfer," 3rd 422 pages 423). For example, a barrier mixing structure that produces a rapid repetition rate gradient similar to the so-called "influence effect" also promotes increased heat transfer while the flow remains laminar.

The general flow direction of the fluid is indicated by arrow 36, and the flow blocker structure produces the generation of laminar flow eddys 38 having a shape and a number of revolutions depending on the geometry of the structure. Wake eddy is produced around the blocking downstream point of the flow, and tremor eddy is produced upstream of the flow. If the shortness of the breaking point 34 is such that the advancing and wake eddy of the immediately continuous point are coincident, the wake interference flow is obtained and thus the highly efficient non-flow mixing, due to the presence of turbulent frictional resistance, is blocked by the boundary layer 30. ) And the adjacent core layer 32. The laminar flow to be avoided can be distinguished from Eddy in that the laminar flow is irregular and there is no observable form as Eddy. Thus Eddy and the vortex are not turbulent. Laminar eddys or vortices are defined by entity boundaries or laminar flows, and turbulent eddies or vortices are surrounded by turbulent eddies or other eddys and vortices that interact with the vortices. Specially structured laminar flow retention conditions can be observed, for example, by providing a suitable window in the experimental structure or by adding a visible fluid to the fluid stream as needed.

The intervening structure does not need to contact the passage wall as long as it is close enough to provide the barrier layer with the required size. Thus, in the embodiments described above, the portion of each sphere around the seal contact that is submerged in the boundary layer is effective for this blocking action. Thus, the breaker structure is suspended in the closure and is in contact with the wall at a point that is not actually in contact with the wall or is less than where the break is present.

4A is a plan view of the contour of the concrete breaker structural element of FIGS. 1 to 3 taken along the direction of fluid flow in the passage, the contour being a circle. Other contours may be used, and the fluid flow is designed to provide a smooth contour surface, to minimize frictional losses and to ensure laminar flow. Figure 4b shows, for example, an ellipsoidal contour, Figure 4c shows an oval contour, and Figure 4d shows a droplet contour, with the largest radial plane in the latter contour facing upstream.

5 shows that the elements of the breaker structure do not need to contact the heat exchange surface, the dashed line contour 40 does not correspond to this but the vertex of the contour is at a minimum distance d from the face 20 and the plane 20 In the case of a convex curved surface away from it, the distance d indicates that it should not exceed about 10% of the effective diameter of the curved surface.

The pyramidal face 42 is also shown as a dashed line ending at the contact point 34 and is not satisfactory for use in the flow block structure of the present invention, which mainly results in a drastically reduced settling opportunity of high fluid flow velocity in the boundary layer. This is because there is less collapse of the layer and heat exchange in the plane is not effective. The good shape of the contour is characterized by convex curved surfaces and arranged to provide the maximum possible speed as close as possible to the smooth surface of the heat transfer while maintaining laminar flow.

For example, special situations arise when the fluid has great viscosity, such as viscous oil to be heated. The spaced spacing of the parallel walls 20 of the passages when the fluid is high viscosity can be significantly increased without setting turbulence, but such fluids typically have low thermal conductivity, and the thermal boundary layer is closer to the heat transfer thinner than each boundary layer. Is set. The intervening structure should be arranged to block the thin thermal boundary layer regardless of the thickness of the boundary layer. The main factor in determining the thickness of the thermal boundary layer is the number of prandlets that becomes high when the viscosity is high and the thermal conductivity is low.

One of the main variables to be considered in determining the laminar and non-flow factors of a special fluid stream is the Reynolds number obtained from

Classically, Reynolds numbers of less than 4,000 were thought to be laminar, and more than about 6,000. It is not possible to determine the fluid velocity in the breaker structure in the apparatus of the present invention, but it is possible at full speed, and the only evidence that the fluid is in laminar flow is to draw a so-called J factor curve that shows a sharp change in slope at the onset of turbulence.

Thus, the presence of a constant slope J factor curve demonstrates that laminar flow is occurring, which can occur at Reynolds numbers of around 15,000.

The invention is applicable to shell and tubular heat exchangers, as shown in FIGS. 10 and 11 showing a single tube and shell exchanger, where one fluid passage with inlet 14 and outlet 16, respectively, is provided. Is formed as an annular space between the outer shell 54 and the inner circular tube 22, and another fluid passage having an inlet 48 and an outlet 50 is also formed of the tube 22. The annular shell space has a sufficient radial dimension to accommodate the sphere 28, and is completely filled with the appropriate cementitious material 56 between the sphere and the inner wall of the outer shell so as to allow the fluid flow to be consumed therethrough. The breaker system used in the tube 22 consists of a row of small spheres used to provide the required flow capacity to and from a sufficient number of break points 34 along and around the length of the tube. In shell-side breaker systems, the useless spaces between the columns are filled with cementitious or other suitable material 58 such as concrete or ceramic cement.

As shown in the perspective view of FIG. 8, the individual spheres 28 and the cement 58 sandwiched therebetween may constitute a unitary structure 60 formed by, for example, a casing, thus protruding from the central matrix. 28 couples with the inner tube wall. Such unitized structures can be manufactured more easily and can be assembled and disassembled in the device more easily. Note that continuous spheres are disposed around the length of the structure, giving the same effect as the rows of spheres are arranged in a helical manner. Similarly, the space filler 56 and the cylinder of the spheres disposed relative to the shell inner wall may constitute a cylindrical unitary structure that slides and is removed as a unit.

9 and 10 show the tubes in a shell type heat exchanger in which a number of parallel tubes 22 are arranged in a single outer cell 54. Each tube 22 is lined up and surrounded by spheres 28, with circles and spirals in some spheres contacting two adjacent tubes, thus disrupting the boundary layer of both tubes. This tube 22 replaces the cement 58 of FIGS. 6 and 7 structures, and only the facet 56 is required between the outermost sphere and the shell 54.

Although it is difficult to evaluate the performance of the heat exchanger surface because of the large number of variables, it is a satisfactory method that was obtained in August 1978. G. Solland, W. M. Mac II and W. M. It is described in Roseno's paper, "Router Ranking of Plate Fin Heat Exchanger Faces." FIG. 11 shows the order of faces according to the above method, comparing the face of the present invention with the face of a 1.2 cm diameter tube and a 0.5 cm plate heat exchanger. The vertical axis thus represents the heat exchanger core and the number of heat transfer units (NTU) per unit volume (V), and the horizontal axis represents the pumping capacity (E) required to move the fluid through the core per unit volume of the heat exchanger core (V). . The improvement in heat exchanger performance is indicated by a high line on the vertical axis, and the increase in improvement can be measured along any vertical line.

The test fluid is water and the bottom dashed line A is heat transfer in a 1.2 cm diameter tube using data obtained from the above papers from Solland, Mac and Roseno. Dotted line B is for an "APV" plate heat exchanger with a plate pitch of 0.5 cm using data obtained from the second edition of the APV Heat Transfer Handbook, published by AV V. Incorporated, Tonawanda, New York. It can be seen that Line B shows a 28% improvement in performance over Line A. The lower solid line C shows the performance of the heat exchanger of the present invention using a densely packed sphere having a diameter of 6.35 mm between the plates of the space, and the upper solid line D shows the maximum performance that can be obtained as the heat exchanger of the present invention. It can be seen that line C represents 100% and 52% improvement over line A and line B, respectively, and line D represents improvement of 415% and 290%, respectively.

Claims (12)

In a shell and tube heat exchanger for heat exchange between two fluids, the shell has an inner wall, an inlet and an outlet for the passage of each fluid through the shell space inside the shell, and at least one tube has an inner surface and an outer surface. It is installed in a shell having an inlet and an outlet for each passage of fluid through the inside of the tube, and each tube wall constitutes a heat exchange wall between two fluids inside the shell and inside the tube, and fluid flow inside the tube. Takes the form of a non-flow boundary layer immediately adjacent the inner surface of the tube and a core layer in contact with the boundary layer, wherein the tube-side fluid flow blocker structure in each tube constitutes a row of multiple longitudinally extending spheres in contact with the passage inner wall. In other words, the structure non-disruptively blocks the complete development of at least the boundary layer at the inner surface of the tube at a number of spaced break points, thus blocking the point of part of the blocked boundary layer. Is discontinuously separated from the inner tube surface and mixed with the core layer for efficient heat transfer between the inner surface of the tube, its respective boundary layer, and the core layer, and to prevent unwanted fluid flow inside the tube away from the inner tube surface. Shell and tube heat exchanger, characterized in that the space between the columns extending to the filling with space filler. In a shell and tube heat exchanger for heat exchange between two fluids, the shell has an inner wall, an inlet and an outlet for the passage of each fluid through a shell space inside the shell, and at least one tube has an inner surface and an outer surface. It is installed in a shell having an inlet and an outlet into each of the fluid for passage through the inner tube of each fluid, and each tube wall constitutes a heat exchange wall between the two fluids in the inner shell and the inner tube, and the fluid flow in the shell space. Is in the form of a non-flow boundary layer immediately adjacent to the inner surface of the tube and a core layer in contact with the boundary layer, and the shell-side fluid flow blocker structure in the shell space constitutes a plurality of spheres surrounding and contacting the outer wall of the tube. Non-disruptively blocking the complete development of at least the boundary layer at the outer surface of the tube at spaced intercept points, so that the portion of the intercepted boundary layer is Shell-side breaker structure to prevent unwanted fluid flow in shell inner space away from tube outer surface, mixed with core layer to streamline heat transfer between tube outer surface, each boundary layer and core layer Shell and tube heat exchanger, characterized in that the space between the sphere and the shell inner wall is filled with a space filler. 3. The fluid flow of claim 2 wherein the fluid flow within the tube takes the form of a non-flow boundary layer immediately adjacent the inner surface of the tube and a core layer in contact with the boundary layer, wherein the tube-side fluid flow blocker structures in each tube contact the inner wall of the passageway. The structure constitutes a row of a plurality of longitudinally extending spheres, the structure non-disruptively blocking the complete development of at least a boundary layer at the inner surface of the tube at a plurality of spaced break points, so that the portion of the blocked boundary layer is a tube between the break points Non-discharged from the inner surface and mixed with the core layer to streamline heat transfer between the inner surface of the tube, its respective boundary layer, and the core layer, and between the rows to prevent useless fluid flow in the inner tube space away from the inner tube heat transfer. The space of the shell and tube heat exchanger is characterized by being filled with a space filler. The shell and tubular heat exchanger according to claim 1, wherein the interval of immediately continuous spaced breaking points in the flow direction is such that a wake interference flow is set to be between the continuous points. 3. The shell and tubular heat exchanger according to claim 2, wherein the interval of immediately continuous spaced break points in the flow direction is such that a wake interference flow is set between the continuous points. 4. A shell and tube heat exchanger as claimed in claim 3, wherein the spacing of immediately continuous spaced breaking points in the flow direction is such that a wake interference flow is set between the continuous points. 3. The shell and tubular heat exchanger of claim 2, wherein the shell and tubular heat exchanger constitute a plurality of tubes installed inside the shell parallel to each other, and some spheres of the shell-side blocking structure contact the outer surfaces of the one or more tubes. 4. The shell and tubular heat exchanger according to claim 3, wherein installations within the shell parallel to each other constitute a plurality of tubes, and some spheres of the shell-side blocking structure contact the outer surfaces of the one or more tubes. The shell and tube heat exchanger according to claim 1, wherein the tube side fluid flow block structure comprises a singular body constituting a row of the plurality of longitudinal extension protrusions protruding from the space charge body. 4. The shell and tubular heat exchanger of claim 3, wherein the tube-side fluid blocker structure includes a singulated body that constitutes a row of the plurality of longitudinally extending spheres protruding from the space filler. 10. The shell and tube heat exchanger according to claim 9, wherein the concrete elements are arranged in a helical shape. The shell and tube heat exchanger according to claim 10, wherein the concrete elements are arranged in a helical shape.

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