FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13)
A SHELL-AND-TUBE HEAT AND MASS TRANSFER
DEVICE
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R.D. Aga Road,
Chinchwad, Pune - 411 019,
Maharashtra, India.
Inventors: a) Navale Devadatta; & b) Kulkarni Sameer.
The following specification particularly describes the invention and the manner in which it is to be
performed.

FIELD OF INVENTION
The present invention relates to a heat and mass transfer device and more particularly it relates to a shell-and-tube heat and mass transfer device for use as a heat exchanger, absorber and condenser.
BACKGROUND
A vertical falling film shell-and-tube heat exchanger device comprises a shell for transmitting a first fluid and tubes placed inside the shell for conveying a second fluid. A vertical falling film device is called so since a falling film is formed on the inside or on the outside of the tubes. Such devices have been also commonly used as absorbers, condensers, evaporators, and crystallizers. In many of these applications, it is desirable to attain an even distribution of the first fluid on each of the tube so that uniform thickness film is formed. However, it is difficult to provide uniform thickness film on each tube, which results in uneven or low heat and mass transfer.
In a shell-and-tube absorber, absorption of vapors occurs in the shell and a cooling fluid is circulated through the tubes to remove the heat generated during absorption. The absorption process for a vapor-absorption refrigeration machine using ammonia-water as the refrigerant-absorbent pair comprises spraying/distributing a weak-absorbent solution (solution having less absorbent to refrigerant concentration) over a first row/column of tubes. The solution trickles under gravity over the entire set of tubes forming a film on the tube surface in the process. This film, also called the falling film, absorbs the absorbent vapors (water vapors) to give a strong-absorbent solution (solution having high absorbent to refrigerant concentration). The heat released during the absorption process is taken by the cooling fluid conveyed through the tubes.

A conventional shell-and-tube absorber device has a horizontal tube arrangement. Due to the horizontal tubes, the falling film so formed has a higher thickness and lower turbulence. This results in reduced film heat and mass transfer coefficient. Hence, a greater heat and mass transfer area is required. To overcome this drawback, multiple passes of tubes are provided. The multiple pass gives a higher fluid velocity and hence higher heat transfer coefficient on the tube side. However, multiple passes result in cross flow, a high pressure drop on the tube side, and the resultant log mean temperature difference is lower. Further, conventional shell-and-tube absorber devices need additional components like tube sheets, tube supports, baffles, pass partition plates, tube side headers, and the like, which contribute to increase in the weight and size of the absorber.
US5572885 is a typical example of a prior art device in which a vapor-liquid contact device comprising helical coil of crested tubing contained within the annular space of a shell between shrouds is disclosed. Liquid flows downwards through the annulus, vapors flow counter-currently upward, and a heat transfer fluid is made to flow through the tubing. The contact device comprises cylindrical shrouds to annularly enclose the crested tubing.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a shell-and-tube heat and mass transfer device for heat exchangers, absorbers and condensers, which gives higher heat and mass transfer and lower pressure drop, with reduced weight and size.

Another object of the present invention is to provide a vertical falling film shell-and-tube heat and mass transfer device which gives reduced/even film thickness and increased film turbulence.
Yet another object of the present invention is to provide a shell-and-tube heat and mass transfer device which gives higher solution flow per unit length of the tube.
Still another object of the present invention is to provide a shell-and-tube heat and mass transfer device which is simple, cost-effective and has fewer components.
SUMMARY OF THE INVENTION
These and other objects are dealt in the present invention by providing a new shell-and-tube heat and mass transfer device for heat exchangers, absorbers and condensers, which increases heat and mass transfer rate and eliminates the need for tube sheets, tube supports, pass partition plates, baffles, and the like.
In accordance with the present invention, there is provided a shell-and-tube heat and mass transfer device, said device comprising:
• an operatively vertical cylindrical shell having a first fluid inlet near the operative top and a first fluid outlet near the operative bottom;
• at least one set of helical tubular coils concentrically placed inside said shell for conveying a second fluid, said set of helical tubular coils being operatively connected to a second fluid inlet near the operative bottom and a second fluid outlet near the operative top, wherein said set of

helical tubular coils are secured within said shell by means of at least one coil support which is joined to said shell; and • at least one tubular distributor ring secured to said shell operatively above said set of helical coils in fluid communication with said first fluid inlet for spraying a first fluid onto said set of helical coils.
Preferably, in accordance with the present invention, a vapor inlet is located between said first inlet and said first outlet proximal to the operative bottom of said shell and said set of helical tubular coils are spaced apart from said shell to provide an upward flow path for the vapors entering at said vapor inlet.
In accordance with another aspect of the present invention, multiple set of helical tubular coils are concentrically placed inside said shell for conveying the second fluid. Preferably, multiple tubular distributor rings are secured within said shell operatively above corresponding multiple set of helical tubular coils in fluid communication with said first fluid inlet for spraying the first fluid onto said multiple set of helical tubular coils.
Typically, in accordance with the present invention, said set of helical tubular coils are selected from spaced coils and closed coils.
Preferably, in accordance with the present invention, said tubular distributor ring has the same diameter as said set of helical coils and is secured on said set of helical coils by means of at least one ring support.

Typically, in accordance with the present invention, said vapor inlet comprises a vapor distributor adapted to distribute the vapors along the circumference of said set of helical coils.
In accordance with another aspect of the present invention, there is disclosed a method for absorbing water vapors in a refrigeration system using a shell-and-tube mass transfer device, said method includes the steps of:
• conveying a first solution through a first fluid inlet located near the operative top of an operatively vertical cylindrical shell and water vapors through a vapor inlet located near the operative bottom of said shell, to obtain counter-flow;
• spraying the first solution onto at least one set of helical tubular coils by means of a tubular distributor ring to generate a vertical falling film, wherein said set of helical tubular coils are secured within said shell by means of at least one coil support which is joined to said shell;
• circulating cooling fluid through said set of helical coils;
• absorbing the water vapors in the first solution to generate a second solution; and
• discharging the second solution through a first outlet located near the operative bottom of said shell.
Typically, in accordance with the present invention, the first solution is a weak-absorbent solution and the second solution is a strong-absorbent solution. Preferably, the refrigerant-absorbent pair is ammonia-water.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with the help of the accompanying drawings, in which,
FIGURE la illustrates a schematic of the shell-and-tube device having a single set of helical spaced coils, in accordance with the present invention;
FIGURE 1 b illustrates a sectional view of the shell-and-tube device having a single set of helical spaced coils, in accordance with the present invention;
FIGURE 2 illustrates a schematic of the shell-and-tube device having multiple set of helical spaced coils, in accordance with the present invention; and
FIGURE 3 illustrates a schematic of the shell-and-tube device having a single set of helical closed coils, in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the invention. The description provided is purely by way of example and illustration.
The present invention envisages a shell-and-tube heat and mass transfer device for heat exchangers, absorbers, and condensers. The shell-and-tube device comprises tubes in the form of helical coils having a helix angle. The angular tubes give two motions to the solution flow i.e. along the angle of the tubes and downward. The multi-directional flow results in reduced and even film thickness and increased turbulence which thereby gives higher heat and mass

transfer rate, thus, reducing the heat transfer area required. Further, the helical coils provide a higher solution flow per unit length of the tube, thus further enhancing the heat and mass transfer coefficient. The device of the present invention preferably uses a single pass of tubes to prevent high pressure drop across the tubes. The device of the present invention does not require tube sheets, tube supports, baffles, pass partition plates, tube side headers, etc. This reduces the total weight and size of the device. Also, since the number of components are less, the device is easy to manufacture, cost-effective, and suitable for mass manufacturing. The device of the present invention gives Log Mean temperature difference similar to a counter-flow arrangement.
A sheli-and-tube heat transfer device of the present invention comprises: an operatively vertical cylindrical shell having a first fluid inlet near the operative top and a first fluid outlet near the operative bottom of the shell, to transmit a first heat transfer fluid; and a single or multiple set of helical tubular coils placed concentrically inside the shell for conveying a second heat transfer fluid. The helical tubular coils can be selected from closed coils or spaced coils. The set of helical tubular coils are supported in the shell by means of one or more coil supports which are joined, mostly welded, to the shell. Sufficient clearance is provided between the helical tubular coils and the shell. The second fluid enters the set of helical tubular coils at a second fluid inlet provided near the operative bottom and exits at a second fluid outlet provided near the operative top. A tubular distributor ring is secured to the shell above the set of helical tubular coils in fluid communication with the first fluid inlet for spraying the first fluid onto the set of helical coils. The tubular distributor ring has the same diameter as the set of helical tubular coils and is secured on the helical coils by means of one or more ring supports. Alternatively, multiple set of helical

tubular coils can be concentrically placed inside the shell, in series or parallel, for conveying the second fluid. When multiple set of helical coils are provided, multiple tubular distributor rings are secured within the shell operatively above each corresponding multiple set of helical coils, for spraying the second fluid. The shell is closed on both ends by dished ends or flat plates.
A shell-and-tube mass transfer device of the present invention is illustrated in FIGURES 1-3. FIG. la & lb show a shell-and-tube mass transfer device (absorber) having a single set of helical spaced coils; the device generally represented in FIG. la & lb by numeral 100. The shell-and-tube mass transfer device 100 comprises an operatively vertical cylindrical shell 102 having a first fluid inlet 106 at the operative top and a first fluid outlet 108 at the operative bottom, and closed from both ends by dished ends or flat plates. A single set of helical tubular coils 104 is placed concentrically inside the shell 102 for conveying a cooling fluid. The helical tubular spaced coils 104 have a gap 113 between two turns. This single set of helical tubular spaced coils 104 are supported on coil supports 116 which are joined, preferably welded, to the shell 102. The set of helical tubular coils 104 comprise a cooling fluid inlet 112 at the operative bottom and a cooling fluid outlet at the operative top 114. The device 100 is typically used in vapor-absorption refrigeration systems having ammonia-water as the refrigerant-absorbent pair, A first solution, i.e. a weak-absorbent solution is received through the first fluid inlet 106. The shell 102 further comprises a vapor inlet 110 provided proximal to the operative bottom, preferably below the set of helical coils, for conveying water vapors counter-currently upwards. The vapor inlet 110 can be provided with a vapor distributor (not shown in figure) to distribute the vapors along the entire circumference of the helical coils 104. Sufficient clearance 115 is provided between the shell 102

and the set of helical tubular coils 104 to allow free upward passage for the vapors. A tubular distributor ring 105 secured above the set of helical coils 104 is provided in fluid communication with the first fluid inlet 106 being adapted to spray/distribute the weak-absorbent solution onto the set of helical tubular coils 104. The tubular distributor ring 105 has the same diameter as the helical tubular coils 104 and is secured to the shell 102 operatively above the helical coils 104 by means of one or more ring supports (not shown in figure). The liquid-vapor counter-current contact results in absorption of the vapors in the weak-absorbent solution to form a second solution i.e. a strong-absorbent solution, which is discharged via the first fluid outlet 108.
Referring to FIG. 2, therein is illustrated a shell-and-tube mass transfer device having multiple set of helical tubular spaced coils; the device is generally represented in FIG. 2 by numeral 200. The device 200 comprises an operatively vertical cylindrical shell 202 and multiple set of helical tubular coils 204a and 204b placed inside the shell 202. The embodiment 200 is more suitable in applications where the height of the mass transfer device is restricted. The shell 202 has a first fluid inlet 206 near the operative top and first fluid outlet 208 near the operative bottom. The multiple set of helical tubular coils 204a and 204b are secured inside the shell 202, parallel to each other, by means of multiple coil supports 216, which are joined to the shell 202 preferably by welding. Each set of helical tubular coils 204a, 204b can be provided with a separate tubular distributor rings 205, which are secured to the shell 202 above the set of helical tubular coils 204a and 204b by means of multiple ring supports (not shown). The tubular distributor rings 205 are in fluid communication with the first fluid inlet 206 to receive the first solution, i.e. a weak-absorbent solution, being adapted to spray the weak-absorbent

solution on the first row of tubular coils. The multiple set of helical tubular spaced coils 204a, 204b have a gap 213 between two consecutive turns. Sufficient clearance 215 is provided between the shell 202 and the multiple set of helical tubular coils 204a and 204b to allow free upward passage for the vapors. The multiple set of helical tubular coils 204a and 204b are provided in fluid communication with a cooling fluid inlet 212 near the operative bottom of the shell 202 and a cooling fluid outlet 214 near the operative top of the shell 202, being adapted to convey a cooling fluid there through during the absorption process. A vapor inlet 210 is provided on the shell 202 near the operative bottom, preferably below the multiple set of helical tubular coils 204a, 204b, to receive water vapors. A vapor nozzle (not shown) can be provided at the vapor inlet 210 to evenly distribute the vapors over the circumference of the coils 204a, 204b in the shell 202. The water vapors are absorbed in the weak-absorbent solution to give a second solution, i.e. a strong-absorbent solution.
Referring to FIG. 3, therein is illustrated a shell-and-tube mass transfer device in accordance with the present invention, having a single set of helical closed coils; the device is generally represented in FIG. 3 by numeral 300. The device 300 comprises an operatively vertical cylindrical shell 302 and a single set of helical tubular closed coils 304 placed concentrically inside the shell 302. The shell 302 has a first fluid inlet 306 near the operative top and first fluid outlet 308 near the operative bottom. A tubular distributor ring 305 is secured to the shell 302 in fluid communication with the first fluid inlet 306 operatively above the set of helical tubular coils 304 by means of ring supports (not shown). The tubular distributor ring 305 is adapted to spray a first solution i.e. weak-absorbent solution, onto the set of helical tubular coils 304. The set of helical

tubular coils 304 are secured inside the shell 302, by means of one or more coil supports 316, which are joined to the shell 302 preferably by welding. The set of helical tubular closed coils 304 have no gap between two consecutive turns. Sufficient clearance 315 is provided between the shell 302 and the set of helical tubular coils 304 to allow free upward passage for the vapors. The set of helical tubular coils 304 are provided in fluid communication with a cooling fluid inlet 312 near the operative bottom of the shell 302 and a cooling fluid outlet 314 near the operative top of the shell 302, being adapted to convey a cooling fluid there through during the absorption process. A vapor inlet 310 is provided on the shell 302 near the operative bottom, preferably below the set of helical coils 304, to receive water vapors. A vapor nozzle (not shown) can be provided at the vapor inlet 310 to evenly distribute the vapors over the circumference of the tubular coils 304 in the shell 302. The water vapors are absorbed in the weak-absorbent solution to give a second solution, i.e. a strong-absorbent solution.
The shell-and-tube mass transfer device of the present invention can also be used as a solution cooled absorber. The solution cooled absorber can be placed above an external cooling fluid absorber in a common shell, with two additional inlet and outlet connections from the set of helical tubular coils, for solution inlet and outlet. A single tubular distributor ring, supported above the solution cooled absorber, is used in this application.
The procedure for manufacturing/assembling the shell-and-tube device of the present invention is as follow:
• joining/welding tubular coils to a required length and fabricating helical tubular coils on a coil winding machine;
• testing the helical tubular coils for any leakage;

• fabricating a tubular distributor ring having the same diameter as the helical tubular coils;
• securing the tubular distributor ring above the top most row of the helical tubular coils by using ring supports;
• placing the leak-tested helical tubular coils and distributor ring assembly inside a shell on coil supports which are welded to the operative circumference of the shell;
• connecting the coil ends to inlet and outlet nozzles provided on the shell;
• connecting shell inlet, shell outlet, and vapor inlet nozzles to the shell/end plates;
• closing the shell on both ends by flat ends/distal ends; and
• testing the shell-and-tube assembly for leakage.
TECHNICAL ADVANTAGES
A shell-and-tube heat and mass transfer device; as disclosed in the present invention has several technical advantages including but not limited to the realization of:
• provides higher heat and mass transfer and lower pressure drop, with reduced weight and size;
• provides a vertical falling film shell-and-tube device which gives reduced and even film thickness and increased film turbulence;
• provides higher solution flow per unit length of the tube;
• provides a shell-and-tube device which is simple, cost-effective and has fewer components.

In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments 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 invention and not as a limitation.

We Claim:
1. A shell-and-tube heat transfer device comprising:
• an operatively vertical cylindrical shell having a first fluid inlet near the operative top and a first fluid outlet near the operative bottom;
• at least one set of helical tubular coils concentrically placed inside said shell for conveying a second fluid, said set of helical tubular coils being operatively connected to a second fluid inlet near the operative bottom and a second fluid outlet near the operative top, wherein said set of helical coils are secured within said shell by means of at least one coil support which is joined to said shell; and
• at least one tubular distributor ring secured to said shell operatively above said set of helical coils in fluid communication with said first fluid inlet for spraying a first fluid onto said set of helical coils.

2. A shell-and-tube device as claimed in claim 1, wherein multiple set of helical tubular coils are concentrically placed inside said shell for conveying the second fluid.
3. A shell-and-tube device as claimed in claim 2, wherein multiple tubular distributor rings are secured within said shell operatively above corresponding multiple set of helical tubular coils in fluid communication with said first fluid inlet for spraying the first fluid onto said multiple set of helical tubular coils.

4. A shell-and-tube device as claimed in claim 1, wherein said set of helical tubular coils are selected from spaced coils and closed coils.
5. A shell-and-tube device as claimed in claim 1, wherein said tubular distributor ring has the same diameter as said set of helical coils and is secured on said set of helical coils by means of at least one ring support.
6. A shell-and-tube mass transfer device comprising:

• an operatively vertical cylindrical shell having a first fluid inlet near the operative top, a first fluid outlet near the operative bottom, and a vapor inlet located between said first fluid inlet and said first fluid outlet proximal to the operative bottom;
• at least one set of helical tubular coils concentrically placed inside said shell for conveying a cooling fluid, said set of helical tubular coils being operatively connected to a cooling fluid inlet near the operative bottom and a cooling fluid outlet near the operative top, wherein said set of helical coils are secured within said shell by means of at least one coil support which is joined to said shell, such that, said set of helical coils are spaced apart from said shell to provide an upward flow path for vapors entering at said vapor inlet; and
• at least one tubular distributor ring secured to said shell operatively above said set of helical tubular coils in fluid communication with said first fluid inlet for spraying a first solution onto said set of helical tubular coils.

7. A shell-and-tube device as claimed in claim 6, wherein multiple set of helical tubular coils are concentrically placed inside said shell for conveying the cooling fluid.
8. A shell-and-tube device as claimed in claim 7, wherein multiple tubular distributor rings are secured within said shell operatively above corresponding multiple set of helical coils in fluid communication with said first inlet for spraying the first solution onto said multiple set of helical tubular coils.
9. A shell-and-tube device as claimed in claim 6, wherein said set of helical tubular coils are selected from spaced coils and closed coils.
10.A shell-and-tube device as claimed in claim 6, wherein said tubular distributor ring has the same diameter as said set of helical coils and is secured on said set of helical coils by means of at least one ring support.
11.A shell-and-tube device as claimed in claim 6, wherein said vapor inlet comprises a vapor distributor adapted to distribute the vapors along the circumference of said set of helical tubular coils.
12.A method for absorbing water vapors in a refrigeration system using a shell-and-tube mass transfer device, which includes the steps of:
• conveying a first solution through a first inlet located near the operative top of an operatively vertical cylindrical shell and water

vapors through a vapor inlet located near the operative bottom of said shell, to obtain counter-flow;
• spraying the first solution onto at least one set of helical tubular coils by means of a tubular distributor ring to generate a vertical falling film, wherein said set of helical tubular coils are secured within said shell by means of at least one coil support which is joined to said shell;
• circulating cooling fluid through said set of helical coils;
• absorbing the water vapors in the first solution to generate a second solution; and
• discharging the second solution through a first outlet located near the operative bottom of said shell.
13.The method as claimed in claim 12, wherein the first solution is a weak-absorbent solution and the second solution is a strong-absorbent solution,
14.The method as claimed in claim 12 & 13, wherein the refrigerant-absorbent pair is ammonia-water.