FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
MULTI-TUBE HEAT EXCHANGER
THERMAX LIMITED
An Indian Company Of D-13, Midc, R.D. Aga Road,
Chinchwad, Pune - 19,
Maharashtra, India
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF DISCLOSURE
The present invention relates to heat exchangers, such as shell and tube heat exchangers. These heat exchangers facilitate an efficient heat transfer between various heat exchange media.
BACKGROUND
The object of a good configuration of an effective heat exchanger is to obtain a higher heat transfer rate at a lower pressure drop and at the same time, which has a lower weight, size and cost of construction. This is achieved by keeping the heat transfer coefficient of the shell and tube side as close to each other as possible and also to maximize the same.
TECHNICAL PROBLEMS
The conventional shell and tube heat exchangers have some of the following
limitations:
- The heat exchanger tubes are placed in a shell with a minimum pitch of 20% higher than the tube diameter. Because of this higher tube pitch, the flow area on the shell side is much higher than on the tube side. Thereby, a reduced flow velocity results on the shell side, and thus, a lower overall heat transfer coefficient is achieved. Therefore, it is quite difficult to maintain optimum flow velocities and heat transfer coefficients on the shell and tube sides in a conventional shell and tube heat exchanger because of the mismatch between the flow areas. Due to a lower overall heat transfer coefficient, the required heat transfer area is much higher.

For process conditions having a higher value of the heat duty to the mass flow rate ratio, the required heat exchanger length is higher than that used in a conventional heat exchanger. Therefore, in order to achieve the required length, multiple heat exchangers are placed in series or multiple passes are provided. However, this also results in a higher pressure drop on the shell and tube sides due to (a) losses in multiple entry and exits in nozzles of the heat exchangers arranged in series, and (b) flow reversals in case of multiple passes in the heat exchanger.
Moreover, because of such heat exchangers with multiple passes and multiple modules, the size, weight and manufacturing cost of these heat exchangers is much higher. In case of a multi-pass configuration of the heat exchangers, to optimize the flow velocities, the flow arrangement does not remain counter-current, which results in a lower effective log mean temperature difference (LMTD), thus such heat exchangers require a higher heat transfer area.
Therefore, the conventional shell and tube heat exchangers consist of various parts, such as baffles and pass partition plates, tube sheets and nozzles, if arranged in series. This also results in higher weight, higher manufacturing time and thus, higher cost of production for such heat exchangers.
OBJECTS
It is an object of the present invention to place the heat exchanger tubes very close to each other.

Another object of the present invention is to configure the heat exchanger such that it allows almost equal heat transfer areas on the shell side and tube sides. Yet another object of the present invention is to maximize the overall heat transfer coefficient at a considerably lower pressure drop than that obtained in the conventional heat exchanger.
Still another object of the present invention is to facilitate in selecting various combinations of shell and tubes diameters which achieve an equal heat transfer coefficients both on the shell and tube sides, even if the flow on the shell side and tube side are not equal.
Another object of the present invention is to maintain the maximum possible heat transfer coefficient which is equal on both the shell and tube sides in order to obtain a considerably higher overall heat transfer coefficient with a comparatively reduced heat transfer area.
A still further object of the present invention is to facilitate maintaining higher flow velocities without requiring the conventional multi-pass arrangement, which thus leads to lower pressure drops.
In yet another object of the present invention, a single heat exchanger is provided with a plurality of tubes, two tube sheets, headers and four nozzles.
SUMMARY OF THE INVENTION
Therefore, in accordance with the present invention a multi-tube shell and tube heat exchanger is provided comprising:

• a plurality of tubes,
• an outer shell having a larger diameter to accommodate said plurality of tubes,
• a plurality of expander/reducer at both the open ends of said plurality of tubes,
• a plurality of tube sheets having holes for inserting said tubes therethrough,
• a plurality of inlet/outlet nozzles,
• a plurality of tube side headers, and
wherein said plurality of tubes is inserted inside said outer shell configured as a shell and tube assembly for forming a coil, and said tubes are joined/welded to said tube sheet and said tube sheet is joined/welded to said expander/reducer, then said inlet/outlet nozzles are attached to said expander/reducer.
Typically, the coil is configured as a helical coil by a coil winding machine.
Typically, the coil is configured as a serpentine coil by a coil bending machine.
Typically, the outer shell mechanically supports to the tubes.
Typically, the expander/reducer is provided between the outer shell (S) and tube sheet in order to create a higher tube pitch at the ends.
Typically, the shell side inlet/outlet nozzle is attached to the said expander/reducer for equally distributing the shell side fluid from said nozzle into the outer shell.

Typically, the tubes are attached to the tube sheet only at the ends of the heat exchanger with the expander located between said outer shell and tube sheet.
Typically, a plurality of tubes is arranged inside said shell with a triangular pitch. Typically, a plurality of tubes is arranged inside said outer shell with a square pitch.
Further, in accordance with the present invention, a method of manufacture and assembly for the multi-tube shell and tube heat exchanger is provided, the method comprises the steps of:
• Joining/welding of tubes in the required length and testing for leakage,
• Joining/welding of the outer shell in the required length and testing for the leakage,
• Inserting the Joined/welded tubes into the outer shell for forming a shell and tube assembly of the required length,
• Coiling said shell and tube assembly into a helical coil on the coil winding machine or bending said shell and tube assembly for forming a serpentine coil by means of a bending machine,
• Joining the expander/reducer to said outer shell at both the open ends of said coil,
• Inserting the tube sheet having holes for tubes, up to the expander/reducer on said tubes at both the open ends of said coil.
• Joining of said tubes to said tube sheet and said expander/reducer to said tube sheet by welding/joining process,
• Attaching the inlet/outlet nozzles to said expander/reducer,
• Carrying out a leakage test on the shell side,

• Attaching the tube side headers on the other side of said tube sheet,
• Attaching said tube side nozzles to said tube side headers, and
• Testing for any leakage on said tube side,
wherein said method steps of tube joining/welding, shell joining/welding, tube insertion into the outer shell and winding into a helical coil or bending into a serpentine coil is done in a plurality of method steps.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will now be discussed in more detail in the following with the help of the accompanying figures.
Figure 1 - is a perspective view of a heat exchanger in accordance with the present invention in a helical coil configuration,
Figure la - is a perspective view of a shell and tube assembly of the heat exchanger in accordance with the present invention sectioned along line as A-A shown in Figure 1,
Figure 2- is a perspective view of a heat exchanger in accordance with the present invention in a serpentine coil configuration, and
Figure 2a- is a sectional view of the shell and tube assembly of the heat exchanger in accordance with the present invention sectioned along line B-B as shown in Figure 2.

Figure 3- is a perspective view of the arrangement of the expander/reducer connected to the outer shell at the both ends of the coils as shown in Figures 1, 2.
DETAILED DESCRIPTION
Figure 1 shows a perspective view of a heat exchanger including a plurality of
tubes T assembled inside the outer shell S and then, coiled in a helical coil in
accordance with the present invention. A section-line A-A is marked for showing
the detailed view of the assembly of these tubes T inside the outer shell S in the
following figure. Figure la is a perspective view in section along line as A-A
shown in Figure 1, of the assembly of the outer shell S and tube T of the heat
exchanger in accordance with the present invention. This configuration of the heat
exchanger includes a plurality of heat exchanger tubes T inserted inside an outer
shell S. The outer shell diameter is selected such that the gap between any two
adjacent tubes T and the gap between these tubes T and the outer shell S is very
small. This gap is provided such that it allows easy insertion of the tubes T into the
outer shell S. These tubes T can be disposed in a triangular or square pitch
arrangement. This results in a configuration having a tube pitch almost equal to the
tube diameter. With this reduced tube pitch, the flow area of the heat exchanger on
the shell side is substantially reduced, thereby increasing the flow velocity on the
shell side without providing multiple passes. Therefore, this new configuration can
provide a higher flow velocity, and thus, a higher heat transfer coefficient is
obtained on the shell and tube sides with just a single pass. In this new
configuration, the shell S mechanically supports to the tubes T. Therefore, baffles
or tube supports are not necessary at all.

Figure 2 is a perspective view of a heat exchanger in accordance with the present invention, in a serpentine coil configuration. It can be used for very long heat exchangers.
Figure 2a is a cross-sectional view of the assembly of the shell S and tube T of the heat exchanger in accordance with the present invention along line B-B as shown in Figure 2.
Figure 3 is a perspective view of the expander/reducer arrangement, which is connected to the outer shell S at one end and to a tube sheet TS at the other end. This expander/reducer EX/RED is provided between the outer shell and tube sheet TS in order to create a higher tube pitch at the ends.
This higher tube pitch provides additional space for joining the tubes T to the tube sheet TS. The shell side inlet/outlet nozzle SNP is attached to this expander/reducer EX/RED, which equally distributes the shell side fluid from nozzle SNP into the outer shell S. The tubes T are attached to the tube sheet TS only at the ends of the heat exchanger with the expander/reducer EX/RED located between the shell and tube sheet TS.
Both these embodiments (both the helical coil and serpentine coil configurations) make it possible to make the heat exchanger length as per the requirement, which can be as high as a few kilometers.
The heat exchangers in accordance with this invention can be disposed in series or in a parallel arrangement. Their positioning can be one above the other or in a side by side arrangement or it can be in the form of parallel coils. The proposed heat

exchangers have a continuous geometry. These can be used for all the applications having heat exchange between any combination of liquid, vapor, gas, two phase fluid, boiling fluid, and condensing fluid.
While considerable emphasis has been placed herein on the specific configuration of the preferred embodiments, it will be appreciated that many modifications may be made without departing from the basic principles of the invention. These and other modifications in the preferred embodiment as well as other possible embodiments of the invention 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 present invention and not in any way construed as a limitation thereof.

We claim:
1. A multi-tube shell and tube heat exchanger comprising:
• a plurality of tubes (T),
• an outer shell (S) having a larger diameter to accommodate said plurality of tubes (T),
• a plurality of expander/reducer (EX/RED) at both the open ends of said plurality of tubes (T),
• a plurality of tube sheets (TS) having holes for inserting said tubes (T) therethrough,
• a plurality of inlet/outlet nozzles (SNP, TNP),
• a plurality of tube side headers (TH), and
wherein said plurality of tubes (T) is inserted inside said outer shell (S) configured as a shell and tube assembly for forming a coil, and said tubes (T) are joined/welded to said tube sheet (TS) and said tube sheet (TS) is joined/welded to said expander/reducer (EX/RED), then said inlet/outlet nozzles (SNP, TNP) are attached to said expander/reducer.
2. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said coil is configured as a helical coil by a coil winding machine.
3. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said coil is configured as a serpentine coil by a coil bending machine.

4. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said outer shell (S) mechanically supports the tubes (T).
5. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said expander/reducer (EX/RED)is provided between the outer shell (S) and tube sheet (TS) in order to create a higher tube pitch at the ends.
6. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein shell side inlet/outlet nozzle (SNP, TNP) is attached to the said expander/reducer (EX/RED) for equally distributing the shell side fluid from said nozzle into the outer shell (S).
7. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said tubes (T) are attached to the tube sheet (TS) only at the ends of the heat exchanger with the expander/reducer (EX/RED) located between said outer shell (S) and tube sheet (TS).
8. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said plurality of tubes (T) is arranged inside said shell (S) with a triangular pitch.
9. Multi-tube shell and tube heat exchanger as claimed in claim 1, wherein said plurality of tubes (T) is arranged inside said outer shell (S) with a square pitch.
10. A method of manufacture and assembly for the multi-tube shell and tube heat exchanger as claimed in any one of claim 1 to 9, comprising the following steps:

• Joining/welding of tubes (T) in the required length and testing for leakage,
• Joining/welding of the outer shell (S) in the required length and testing for the leakage,
• Inserting the Joined/welded tubes (T) into the outer shell (S) for forming a shell and tube assembly of the required length,
• Coiling said shell and tube assembly into a helical coil on the coil winding machine or bending said shell and tube assembly for forming a serpentine coil by means of a bending machine,
• Joining the expander/reducer (EX/RED) to said outer shell (S) at both the open ends of said coil,
• Inserting the tube sheet (TS) having holes for tubes up to the expander/reducer (EX/RED) on said tubes (T) at both the open ends of said coil.
• Joining of said tubes (T) to said tube sheet (TS) and said expander/reducer (EX/RED) to said tube sheet (TS) by welding/joining process,
• Attaching the inlet/outlet nozzles (SNP, TNP) to said expander/reducer (EX/RED),
• Carrying out a leakage test on the shell side,
• Attaching the tube side headers (TH) on the other side of said tube sheet (TS),
• Attaching said tube side nozzles (TNP) to said tube side headers (TH), and
• Testing for any leakage on said tube side,
wherein said method steps of tube (T) joining/welding, shell (S) joining/welding, tube (T) insertion into the outer shell (S) and winding into a

helical coil or bending into a serpentine coil is done in a plurality of method steps.