FIELD

The present disclosure relates to the field of heat exchangers.

DEFINITIONS As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

The expression‘pass’ used hereinafter in this specification refers to, but is not limited to, a singular passage of a fluid through an enclosed space (i.e., a shell or a tube) of a heat exchanger, relative to the flow of another fluid flowing through the heat exchanger in an adjacent enclosed space (i.e., a tube or a shell respectively). The pass may be made in parallel, anti-parallel, circumferential or any other manner.

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Heat exchangers of the shell- and- tube type are known for efficiently carrying out transfer of heat from one fluid to another, thereby heating one fluid and cooling the other. One fluid is made to flow through the tubes and the other, through the space in the shell exterior to the tubes. A shell-and-tube heat exchanger can be used in a wide range of pressure and temperatures, and is preferred in high pressure applications such as for feedwater heating with steam, in power plant condensers, in oil refineries and in chemical industries. Amongst the vast variety of applications of a shell-and-tube heat exchanger, is a multiple-effect evaporator system for different applications such as treatment of municipal waste and industrial effluents, use in food industry, etc. In multiple-effect evaporator systems, preheaters use the non-condensed steam from the evaporator as heat source (only latent heat) and use it to preheat the incoming feed solution. The preheaters are of shell-and-tube type with steam in the shell side and the feed solution in the tube side. The preheater tubes usually get choked first due to evaporation of feed solution inside the tubes resulting in formation of hard scales, especially during turn-down operating conditions. The steam condenses at a constant temperature and the wall temperature will not change due to flow turn-down conditions. Since the flow is reduced through tubes at turn down, the fluid will start to evaporate especially near tube wall due to high source temperature (i.e. steam temperature) resulting in formation of suspended solids and hard scale formation.

To avoid the problem as mentioned above, hot condensate water can be used as the heat source (sensible heat recovery) by ensuring complete condensation of steam in the evaporator itself instead of non-condensable steam (latent heat recovery). The source temperature will also decrease during preheating of the feed solution at full and turn-down operating conditions resulting in avoidance of evaporation inside the tubes. However, the flow rate of hot source fluid (i.e. condensate water) is significantly small (for example, almost 1/3 to l/10 ^th of feed solution) when compared to the feed flow, based on the number of stages to effect the evaporation. It is difficult to get high heat transfer coefficient for such applications (i.e. liquid-to-liquid heat exchanger applications) where the flow of one liquid is much smaller than the other liquid resulting in big and costly heat exchangers.

The compaction of the heat exchanger can be done if plate heat exchangers are used. However, the plate heat exchangers will get frequently choked even if the feed solution contains less suspended solids. The plate heat exchangers then have to be frequently cleaned by opening the frame and all gaskets have to be replaced resulting in high down time and high gasket replacement costs.

The shell-and-tube heat exchangers are very good in terms of resistance to scale formation, ease of cleaning and less cost for gasket replacement. Therefore, a heat exchanger which is compact and capable of achieving high heat transfer coefficient is required. Compact heat exchangers of the shell-and-tube type have been designed where a reversal chamber is required for added compactness. However, the use of a reversal chamber leads to the usage of an additional element in the fabrication process, thereby increasing cost, possibly increasing size, and at the same time, not utilizing the fluid reversal process part for heat exchange. This design also leads to unfavorable liquid velocity variation if used for liquid-liquid heat transfer applications. Thus, the prior art design fails to provide an optimum heat transfer efficiency. There is, therefore, felt a need of a heat exchanger which eliminates the shortcomings of the arrangements as described hereinabove. OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

An object of the present disclosure is to provide a heat exchanger. Another object of the present disclosure is to provide a heat exchanger, which is compact.

Yet another object of the present disclosure is to provide a heat exchanger, which gives highly efficient heat transfer.

Still another object of the present disclosure is to provide a heat exchanger, in which pressure drop is low. Yet another object of the present disclosure is to provide a heat exchanger, in which velocity variations are optimum.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY The present disclosure envisages a heat exchanger. The heat exchanger comprises an outer tubular wall, an inner tubular wall and a plurality of tubes. The inner tubular wall is spaced apart from the outer tubular wall. The inner tubular wall defines a vacant tubular space on its inner side. An annular space defined between the outer tubular wall and the inner tubular wall defines a shell side of the heat exchanger for transmitting a first fluid therethrough. The plurality of tubes is disposed in the annular space, which transmit a second fluid therethrough. Temperature of the second fluid is different from temperature of the first fluid.

According to an embodiment, the outer tubular wall and the inner tubular wall have similar cross-sectional contours. Alternatively, in another embodiment, the outer tubular wall and the inner tubular wall have different cross-sectional contours. According to another embodiment, the first fluid flows along longitudinal axis of the heat exchanger through the space between the outer tubular wall and the inner tubular wall exterior to the tubes, defining a single shell-side passes. According to an embodiment, a plurality of transverse baffles is placed longitudinally between the outer tubular wall and the inner tubular wall, defining a plurality of shell-side passes.

According to yet another embodiment, a channel header is provided at each longitudinal end of the heat exchanger. According to an embodiment, a plurality of partition plates is placed in the channel header. According to an embodiment, the tubes passing through the channel header are configured to permit at least one tube-side pass. According to yet another embodiment, the flow of the first fluid and the second fluid on the shell-side and the tube-side respectively can be either a co-current flow or a counter-current flow.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING The heat exchanger of the present disclosure will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates a schematic cross-sectional view of tube-side and shell-side flow of a heat exchanger to depict counter-current flow, having multiple (four) shell-side passes and multiple (four) tube-side passes, according to an embodiment of the present disclosure; Figure 2 illustrates a schematic cross-sectional view of a multi-pass shell-side flow and single tube-side pass in a heat exchanger according to another embodiment of the present disclosure;

Figure 3 illustrates a schematic cross-sectional view of a heat exchanger with multiple passes on tube side and single pass on shell side, according to yet another embodiment of the present disclosure;

Figure 4 illustrates a schematic cross-sectional view of a heat exchanger with a single pass on tube side and a single pass on shell side, according to still another embodiment of the present disclosure; and

Figure 5 illustrates a schematic cross-sectional view of tube-side and shell-side flow of a heat exchanger to depict co-current flow, having multiple (four) shell-side passes and multiple (four) tube-side passes, according to an embodiment of the present disclosure.

LIST OF REFERENCE NUMERALS

100 Heat exchanger of the present disclosure 10 Outer tubular wall

20 Inner tubular wall

15 Annular space between outer tubular wall and inner tubular wall 25 Vacant tubular space

30 Tube

40 Baffle

1 First pass on the tube side

2 Second pass on the tube side

3 Third pass on the tube side

4 Fourth pass on the tube side

I First pass on the shell side

11 Second pass on the shell side

III Third pass on the shell side

IV Fourth pass on the shell side DETAILED DESCRIPTION

When an element is referred to as being "mounted on,"“engaged to”,“connected to”, or “coupled to” another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements. The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure. Terms such as“inner”,“outer”,“beneath”,“below”,“lower ”,“above”,“upper” and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.

The shell-and-tube heat exchanger 100 of the present disclosure comprises an outer tubular wall 10, an inner tubular wall 20 and a plurality of tubes 30. The inner tubular wall 20 is spaced apart from the outer tubular wall 10. The inner area of the inner tubular wall 20 defines a vacant tubular space 25. An annular space 15 is defined between the outer tubular wall and the inner tubular wall. The plurality of tubes 30 is disposed between the outer tubular wall 10 and the inner tubular wall 20 in the annular space 15. A first fluid flows through the annular space 15 between the outer tubular wall 10 and the inner tubular wall 20 exterior to the tubes 30 and a second fluid flows through the tubes 30.

According to an embodiment of the present disclosure, the flow of process fluids in the heat exchanger 100 is“straight flow through path” both on the shell-side which includes the annular space 15 and on the tube-side. In other words, the first fluid and the second fluid flow along the longitudinal axis of the heat exchanger 100 through the annular space 15 and through the tubes 30 respectively.

According to an embodiment of the present disclosure, transverse baffles 40 are placed end- to-end along the length of the tubular walls 10 and 20, wherein the length of baffles 40 is lesser than the tubes 30 such that it facilitates multiple shell-side passes. According to an embodiment, one or more channel headers are provided at each longitudinal end of the heat exchanger 100. According to another embodiment, partition plates are placed in the channel headers of the heat exchanger 100. Based on design requirements and optimization, the number of tube-side passes and shell-side passes can be determined. The number of passes on the shell side is maintained by the transverse baffles 40, whereas the number of passes on the tube side is maintained by the partition plates in the channel headers of the heat exchanger 100. The number of tube-side passes is one more than the number of the partition plate(s) in the channel headers. The number of shell-side passes is equal to the number of baffles.

The shell-side passes are marked as T, TG, TIG and TV’ in Figure 1, 2 3, 4 and 5 and the tube-side passes are marked as T’,‘2’,‘3’ and‘4’. In one embodiment of the invention, as illustrated in Figure 1, the arrangement is a shell and tube heat exchanger 100 which is configured to permit four passes on shell side and four passes on tube side. The tube-side passes and the shell-side passes are such that the first tube-side pass (pass 1) is associated with the fourth shell-side pass (pass IV), the second tube-side pass (pass 2) is associated with the third shell-side pass (pass III), third tube-side pass (pass 3) is associated with the second shell-side pass (pass II) and a fourth tube-side pass (pass 4) is associated with the first shell- side pass (pass I). The arrangement in Figure 1 depicts counter-current flow on tube side and shell side of the heat exchanger 100.

In another embodiment of the invention, as illustrated in Figure 2, the arrangement corresponds to a shell and tube heat exchanger 100 which is configured to permit four passes on shell side and one pass on tube side. Thus, the tube-side pass 1 is associated with four shell-side passes i.e. pass I, pass II, pass III and pass IV.

In another embodiment of the invention, as illustrated in Figure 3, the arrangement corresponds to a shell and tube heat exchanger 100 which is configured to permit one pass on shell side and four passes on tube side. Thus, the tube-side passes 1, 2, 3 and 4 are associated with single shell-side pass I.

In yet another embodiment of the invention, as illustrated in Figure 4, the arrangement corresponds to a shell and tube heat exchanger 100 which is configured to permit a single tube-side pass 1 associated with a single shell-side pass I.

In yet another embodiment, as illustrated in Figure 5, the arrangement corresponds to a shell and tube heat exchanger 100 which is configured to permit four passes on shell side and four passes on tube side. The tube-side passes and the shell-side passes are such that the first tube- side pass (pass 1) is associated with the first shell-side pass (pass I), the second tube-side pass (pass 2) is associated with the second shell-side pass (pass II), third tube-side pass(pass 3) is associated with the third shell-side pass (pass III) and a fourth tube-side pass (pass 4 ) is associated with the fourth shell-side pass (pass II). The arrangement in Figure 5 depicts co current flow on tube side and shell side of the heat exchanger.

Figures 1, 2, 3, 4 and 5 illustrate few of the various possible configurations of having either a single pass or a multiple pass of both tube-side and shell-side process fluids. Since provision of the inner tubular wall 20 allows having a relatively smaller flow area in the shell side, the process fluid with less flow rate can be allotted to the shell side, in a preferred embodiment of the present invention.

In an embodiment of the invention, velocity of the process fluid allotted in the shell side is further increased by increasing the number of baffles 40 in the shell side. In another embodiment, feed solution with scaling tendency is passed through the heat transfer tubes. In yet another embodiment, the number of tube-side passes is increased based on compaction requirements and pressure drop penalty. The allocation of process fluids in the annular space 15 and the tube 30 is done based on process requirements and design optimization. Diameter of heat transfer tubes 30, number of heat transfer tubes 30, number of tube side -passes, number of longitudinal baffles 40 (or shell-side passes), diameter of outer tubular wall 10 and diameter of inner tubular wall 20 are variables and are designed based on process requirements on a case-to-case basis. Also, in the exemplary embodiments of the invention, the flow configuration of the hot and the cold fluid is either“co-current” or“counter current” based on process requirements.

In general, pressure drop in the heat exchanger of the present disclosure is within an acceptable range. Even stringent pressure drop constraints of vacuum systems can also be achieved by means of“straight flow through path” and appropriate selection of diameters of tubes, inner tubular wall 20, outer tubular wall 10, number of tube-side and shell-side passes.

Since the flow area is reduced due to provision of the inner tubular wall 20, efficiency of heat transfer is significant even at turn-down operating conditions. The sensible heat recovery process ensures that evaporation of feed solution does not take place inside the heat transfer tubes during rated and turn-down operating conditions.

Thus, the inner tubular wall 20 enhances the heat transfer by reducing the available flow area in the shell-side and maintaining a“straight flow through path” for very less pressure drop resulting in a compact and energy-efficient heat exchanger.

The heat exchanger of the present disclosure also provides an optimum heat transfer efficiency especially for liquid-to-liquid heat exchange applications. Since the flow area is reduced due to the inner tubular wall, the heat transfer efficiency is quite good even at turn down operating conditions. Thus, the heat exchanger has a good turndown operating capability. The heat exchanger of the present disclosure is also resistant to scale formation, on both shell and tube sides. The sensible heat recovery process will ensure that evaporation of feed solution will not take place inside the heat transfer tubes during rated and turn down operating conditions. Since the evaporation of the feed solution does not occur, scale formation will also be very less as compared to prior art. Moreover, the walls (i.e., shells) or tubes can be cleaned easily, as compared to the conventional shell-and-tube heat exchangers, in which the shell cannot be easily cleaned due to transverse baffles). The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms“a”,“an” and“the” may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms“comprises”,“comprising”,“including” and“having” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

TECHNICAL ADVANCEMENTS

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a heat exchanger which gives:

• Optimum heat transfer efficiency:

o Liquid-to-liquid heat exchange applications;

o Good turndown operating capability;

• Very less pressure drop:

o Gas flows where very less head loss is available; o In systems operating under vacuum;

• Resistance to scale formation:

o The heat exchanger of the present disclosure is highly resistant to scale formation on both shell and tube sides;

o Walls (i.e., shells) or tubes can be cleaned easily (in conventional design the shell cannot be easily cleaned due to transverse baffles);

• Compactness; and

• Cost-efficiency.

The foregoing disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. The use of the expression“at least” or“at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.