WO2018138566A1

WO2018138566A1 - Compact coiled flow inverters as in-line mixers

Info

Publication number: WO2018138566A1
Application number: PCT/IB2017/057982
Authority: WO
Inventors: Krishna Deo Prasad NIGAM; Shantanu Roy; Loveleen SHARMA
Original assignee: Indian Institute Of Technology, Delhi
Priority date: 2017-01-27
Filing date: 2017-12-15
Publication date: 2018-08-02
Also published as: EP3574276A4; EP3574276A1

Abstract

Compact coiled flow inverters are proposed to be used as in-line mixers. Rectangular Spiral Pattern-Compact Coiled Flow Inverter and Crosshatch Pattern-Compact Coiled Flow Inverter employ six and fifteen flow inversions, respectively, to rotate periodically the Dean cells by 90° thereby allowing significant enhancement in transverse mixing at low shear.

Description

COMPACT COILED FLOW INVERTERS AS IN-LINE MIXERS

FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, pertains to enhanced radial mixing of fluids, and more particularly to Compact Coiled Flow Inverters (CCFIs) to be used as in-line mixers.

BACKGROUND OF INVENTION

[002] Mixing is an important operation in process industries. Therefore, various mixers are used for a range of applications such as blending, mixing of viscous fluids, heat transfer, mass transfer and chemical reactions. The level of mixing has a direct role in conversion in a chemical reaction and selectivity of desired products, and thus always plays an important role to affect the product quality. For reactions, sometimes it is good, sometimes it is bad. What is required is "controlled mixing". It is almost always desired to have good radial mixing and controlled axial mixing (or back-mixing) to obtain good reactor performance.

[003] The conventional mode of mixing (i.e. using stirred vessels) offers good mixing, but ai high shear and mixes the fluid elements of different ages which result in nonuniform transient concentration. Mixing is such conduits is desirable, but the high shear is not. It is required to have sufficient radial mixing within conduits that provide an almost similar mean residence time for all fluid elements (as against an undesirable situation in which different fluid elements have different times of residence, whether predictably different or randomly different). The commonly used techniques to enhance radial mixing within conduits involves the generation of turbulent eddies by using in-line static mixing, structures that provide better mixing performance at low operational cost due to no moving parts. In either of these two cases, high shear is encountered, which may de-nature (lie chemicals that are being mixed. Sometimes, high shear rates lead to over-heating, and the high temperature may also de-nature of chemically change the species being mixed.

[004] A static mixer is a precision engineered device for the continuous mixing of fluid materials. Normally the fluids to be mixed are liquid, but static mixers can also be used to mix gas streams, disperse gas into liquid or blend immiscible liquids. The energy needed for mixing comes from a loss in pressure as fluids flow through the static mixer. One design of static mixer is the plate-type mixer and another common device type consists of mixer elements contained in a cylindrical (tube) or square housing. Typical construction materials for static mixer components included stainless steel, polypropylene. Teflon, PVDF, PVC, CPVC and polyacetal.

[005] The in-line static mixers use the energy of flowing fluid to cause the radial mixing by redistributing the fluid in across wise direction with respect to the main flow stream. However, for very heat-sensitive fluid streams (such pharmaceutical products, polymers melts and food materials), the high shear produced by mixing structures may lead to significant viscous dissipation of mechanical energy to heat, which can cause thermal degradation of these high-value chemicals. Therefore, an ideal objective would be to achieve progressive and good radial mixing, even when the shear rate is low. i.e., in the laminar flow regime.

[006] The commonly used in-line static mixers are composed of axial ly placed multiple mixing structures that use the energy from pressure gradient of the flowing stream to mix. The choice of such a mixer is made on the basis of their superiority in operation In comparison to conventional agitator tanks. Their compact cross-section and high surface to volume ratio makes them more favourable as a mixing system. Various authors have reported these advantages by changing the channel/mixing dimensions/structure to brought streams of different concentrations to mix {for example, U.S. Pat No. 7484881 B2; U.S. Pat. No. 8696193 B2; U.S. Pat. No. 20140133268 A1; U.S. Pat. No. 20120106290 A1). However, owing to the fixtures (i.e. mixing structures) in flow cross-section, the limitations of additional pressure drop, blockage, and high shear arises while handling sensitive/viscous fluids. To overcome these limitations, the innovative designs of CCFls are developed that are capable of conducting continuous mixing of sensitive/viscous fluids in laminar flow regime without producing high shear.

[007] Reference is made to US 733783S B2, wherein a heat exchanger for transferring heat from one fluid to another fluid is disclosed, ft comprises of a plurality of metallic tube continuously formed into four discrete helically wound coils, each coil having at least four turns, the coils being spatially placed such that axis of all the four helical coils of each bank are substantially in one common plane, the axis of each helical coil is at an angle of 90° to the adjacent helical coil, wherein number of banks is from 2 to 10 and ratio of diameter of the helical coil to the diameter of the tube is at least 10:1. [008] Reference is made to WO 2015/135844 A 1 , wherein a device and a method for continuous virus inactivation are disclosed. The device for continuous virus inactivadon in a product flow comprises a pipe or hose having an inlet and having an outlet each connected to a product-flow line for directing the product flow, wherein the pipe or the hose is curved and/or is helically wound with a number of n windings about a winding axis (h) and has one or more direction changes and/or kinks of the winding axis (h) having an angle (a) of 45° to 180° for changing the effective direction of the normal of the centrifugal force, and wherein the device is characterized by a Dean number > 0 and a torsion parameter > 0.

[009] The conventional design consists of four discrete helical arms on a common plane that are joined together in a manner that each arm is at an angle of 90° with respect to its former/successive helical arm. This arrangement of four equidistant helical arms, commonly known as one bank of Coiled Flow Inverter (CFI), provides three flow inversions to rotate the two contra-rotating Dean cells by 90°. This arrangement of helical arms results into a square duct-like structure with coiled tube wound at the boundaries and an empty interior area.

[0010] A closer look at CFI design suggests that the further improvement in the radial mixing is possible by strategically designing the flow inversions within the same floor area. Most industries today are governed by process economics and constraint on the availability of space. Thus, it is a need to develop designs that provide not only efficacy of mixing but miniaturization too. Therefore, (here is a need for innovation in die designs of CCFIs that will intensify the mixing efficiency of standard CFI within the single "frame".

[0011] It has been noted that widespread use of coiled structures in process industries in recent years point to the now accepted benefits of good radial mixing. U.S. Pat. No. 4074685 and U.S. Pat No. 4165360 discloses coiled structures for mixing and reacting component. Others present, as indicated hereinabove, employ tactically arranged helical structure as heat exchanger and device for continuous virus inactivation where different helical arms were arranged in a manner that cause the rotation of flow field by 90°, and thus provide additional performance and compactness to the helical structure. As the design of CFI does not have any additional elements that impede the flow (such as static mixing elements in the flow path and high shear), so it would be of use as commercial inline mixers if its mixing efficiency can be improved further. [0012] The proposed invention improves upon the design offered by the U.S. Pat No. 733783S B2 and W.O. App. No. 2015/135844 A1, so as to use it as an efficient mixer on a volumetric basis. For the purpose of the invention, a comparative analysis was carried out by conducting residence time distribution (RTD) and pressure drop experiments on standard CFT and innovative designs of CCFls under identical process conditions. It discloses two designs for Compact Coiled Flow Inverters (CCFIs), namely Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFI), and the Crosshatch Pattem- Coinpact Coiled Flow Inverter (CHP-CCF1), employing (as a typical case) six and fifteen flow inversions respectively to rotate periodically the Dean ceils by 90° that allow significant enhancement in transverse mixing at low shear.

[0013] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of (he invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0014] An object of the present invention is to facilitate the use of compact coiled flow inverters as in-line mixers.

[0015] Another object of the present invention is to carry out in-line mixing by using the combined action of centrifugal force and multiple flow inversions.

[0016] Another object of the present invention is to enhance further the cross- sectional mixing on a volumetric basis by utilizing the unoccupied central core of one bank CFI.

[0017] Another object of the present invention is to have two compact structures within one bank area of the CFI to significantly enhance the mixing performance in comparison to standard CFI.

[0018] Another object of the present invention is employing six and fifteen flow inversions to rotate periodically the axis of the Dean cells by 90° allowing significant enhancement in transverse mixing at low shear. [0019] Another object of the present invention is to obtaining a uniform concentration in the cross-sectional plug even in the laminar flow regime.

[0020] Yet another object of the present invention is to provide a Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFI).

[0021] Yet another object of the present invention is to provide a Crosshatch Pattern -Compact Coiled Flow Inverter (CHP-CCPI).

[0022] Accordingly, in one aspect of the present invention, compact coiled flow inverters are used to carry out in-line mixing by using the combined action of centrifugal force and multiple flow inversions is disclosed. When liquid flow occurs through a coiled tube, it experiences the action of centrifugal force, which causes the generation of two contra-rotating Dean cells, which in turn enhances cross-secrional mixing, without adversely affecting the axial mixing. In conventional coiled flow inverters, the cross- sectional mixing in a single bank of coiled tube is further enhanced by the use of flow inversions, which cause an interchange of streamlines participating in the Dean cells which is proposed to be enhance even further, by cross-sectional mixing on a volumetric basis by utilizing the unoccupied central core of one bank CFI.

[0023] In another aspect, within one bank area of the CFI, two compact structures have been designed to significantly enhance the mixing performance in comparison to standard CFI by employing six and fifteen flow inversions to rotate periodically the Dean cells by 90° thereby allowing significant enhancement in transverse mixing at low shear and obtaining a uniform concentration in the cross-sectional plug even in the laminar flow regime.

[0024] In another aspect, a Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFI) is disclosed which employs six flow inversions to rotate periodically the Dean cells by 90°, thereby allowing significant enhancement in transverse mixing at low shear.

[0025] In another aspect, a Crosshatch Pattern -Compact Colled Flow Inverter (CHP-CCFI) Is disclosed which employs fifteen flow inversions to rotate periodically the Dean cells by 90° thereby allowing significant enhancement in transverse mixing at low shear [0026] Briefly, the use of compact coiled flow inverters to cany out In-line mixing by using the combined action of centrifugal force and multiple flow inversions is disclosed. In conventional coiled flow inverters, the cross-sectional mixing in a single bank of coiled tube is enhanced by the use of flow inversions causing an interchange of streamlines participating in the Dean cells, which will be enhance even further, by cross-sectional mixing on a volumetric basis by utilizing the unoccupied central core of one bank CFT. Two compact structures within one bank area of the CFI has been designed to significantly enhance the mixing performance in comparison to standard CFI by employing six and fifteen flow inversions for RSP-CCFI and CHP-CCF1, respectively, to rotate periodically the Dean cells by 90° thereby allowing significant enhancement in transverse mixing at low shear and obtaining a uniform concentration in the cross-sectional plug even in the laminar flow regime.

[0027] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEFF DESCRITION OF THE ACCOMPANYING DRAWINGS

[0028] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0029] Figure 1A illustrates schematic of the Coiled Flow Inverter (CFI) as disclosed in prior an.

[0030] Figure IB illustrates schematic of the Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFI) within the square frame of the CFI {Ax A) according to one implementation of the present invention.

[0031] Figure 1C illustrates schematic of the Crosshatch Pattern- Compact Coiled Flow Inverter (CHP-CCFI) within the square frame of the CFI ( A x A ) according to one implementation of the present invention.

[0032] Figure ID illustrates schematic of the Rectangular Spiral geometry within the rectangular frame { A xB) according to one implementation of the present invention. [0033] Figure 2 illustrates schematic for mixing process by using three different coiled geometries (CF1. RSP-CCFI, and CHP-CCFI) within, confined footprint (A xA) according to one implementation of the present invention.

[0034] Figure 3 illustrates generalized design model of CHP-CCFI according to one implementation of the present invention.

[003S] Figure 4A illustrates designs of (he cubical blocks to join different helical arms of CHP-CCFI according to one implementation of the present invention.

[0036] Figure 4B illustrates designs of the triangular blocks to join different helical arms of CHP-CCFI according to one implementation of the present invention.

[0037] Figure 5 illustrates typical step response curve for standard CF1, RSP-CCFI and CHP-CCFI at Reynolds number

according to one implementation of the present invention.

[0038] Figure 6 illustrates radial mixing behavior of fluid (in terms of Peclet number

through CFI, RSP-CCFI and CHP-CCFI according to one implementation of the present invention.

[0039] Figure 7 illustrates comparison of Peclet number per unit space occupied ((MvVfloor area) by CFI, RSP-CCFI and CHP-CCFI according to one implementation of die present invention.

[0040] Figure 8 illustrates coefficient of mixedness

for different coiled geometries (CFI, RSP-CCFI and CHP-CCFI) over variable

according to one implementation of the present invention.

[0041] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers arc used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0042] The following description with reference to the accompanying drawings is provided lo assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0043] Accordingly, those of ordinary skill in the art will recognize mat various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0044] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for Illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0045] Tt is to be understood that the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

[0046] By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including/or example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0047] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0048] Tt should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0049] The subject invention lies in Compact Coiled Flow inverters (CCFIs) being used as in-line mixers. [0050] Most industries today are governed by process economics and constraint on the availability of space. Thus, it is desirable to develop a design that provides not only efficacy of mixing but miniaturization too. Therefore, the proposed CCFIs have been developed to intensify the mixing efficiency of standard CFI within the single "frame". The Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFI) and Crosshatch Pattern -Compact Coiled Plow Inverter (CHP-CCFI) are made by analysing the parameters that affect the performance of the conventional CFT, that includes:

(a) ratio of the volume in each helical arm;

(b) angle of inversion between successive helical arms; and, (c) number of inversions.

The values of design parameters in (a), (b) and (c) were optimized to maximize the extent of radial mixing.

[0051] In the present invention, compact coiled flow inverters carry out in-line mixing by using the combined action of centrifugal force and multiple flow inversions. In conventional coiled flow inverters, the cross-sectional mixing in a single bank of the coiled tube is enhanced by the use of flow inversions which causes the rotation of Dean cells, which is further enhanced by cross-sectional mixing on a volumetric basis by utilizing the unoccupied central core of the CFI bank. Two compact structures within the bank area of a CFT significantly enhance the mixing performance by employing six and fifteen flow inversions for RSP-CCFI and CHP-CCFI, respectively, to rotate periodically the Dean cells by 90°, thereby allowing significant enhancement in transverse mixing at low shear and obtaining a uniform concentration in the cross-sectional plug even in the laminar flow regime.

[0052] In one implementation, compact coiled flow inverters as in-line mixer is provided for.

[0053] In one implementation, cross-sectional mixing on a volumetric basis is enhanced by utilizing the unoccupied central core of one bank CFI is provided for.

[0054] In one implementation, two compact structures within one bank area of the CFI is provided for that significantly enhances the mixing performance.

[0055] In one implementation, a Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCFl) employing six flow inversions to rotate periodically the Dean cells by 90°, thereby allowing significant enhancement in transverse mixing at low shear is provided for.

[0056] in one implementation, a Crosshatch Pattern -Compact Coiled Flow Inverter (CHP-CCFl) employing fifteen flow inversions to rotate periodically the Dean cells by 90° thereby allowing significant enhancement in transverse mixing at low shear is provided for.

[0057] Tn one implementation, specially designed cubical and triangular blocks are required to join different helical arms such that these blocks have not only joined the two helical arms but also retained the square shape for the CCJFIs so as to fit it within the frame of standard CFT is provided for.

[0058J Tn one implementation, the number of inversions per bank is variable as it dependents upon the outer enclosure area of the one bank is provided for.

[0059] The proposed CCFTs exhibits very high radial mixing performance at low shear by restructuring the design of standard colled flow inverter (CFT) whose potential applications as micro-reactor for various applications including polymerization, in-line mixer, heat exchanger, microfluidic device for process intensification, microfluidic device for nanofluid processing, milli/micro-structured heat exchanger, microfracture device for nanofluid processing, membrane module for enhanced mass transfer, liquid-liquid extractor, two-phase flow application, potential device for food processing, reactor for continuous protein refolding, reactor for continuous precipitation of clarified cell culture supernatant, suitable reactor for continuous flow chemical processes, reactor for continuous biopharmaceutical processing, reactor for continuous viral inactivation and continuous operated modular reactor design for the multiphase reaction system are well documented.

[0060] The RSP-CCFI and CHP-CCFI provide improved mixing in all the above applications in which CF1 have been demonstrated or reported to work. This is achieved by improving the radial mixing by strategically designing the flow inversions within the same floor area.

[0061] The present invention utilizes the unoccupied central core of the standard design of CFI to get enhanced mixing performance within the same floor area occupancy. The strategy of ''filling" the coil volume within the specified dimension of the CFI frame ( Ax A), referring to Figures 1 A-1C, are based on two concepts, viz., (1) amassing as maximum as possible mixing volume without altering the footprint of the CFI, so to get enhanced mixing per unit occupied floor area; and

(2) reorganizing the volume enclosed in one bank of the CPlby using the optimum values of all parameters, that would maximize the mixing performance of the CCPI embodiment.

[0062] The RSP-CCF1 and CHP-CCF1 have been developed within the identical footprint of the CFI. Figure 1 A illustrates a conventional coiled flow inverter (CF1) while Figure IB and 1C illustrate the Rectangular Spiral Pattern-Compact Coiled Flow Inverter (RSP-CCPI) within the square frame of the CFI ( A x A ) and Crosshatch Pattern-Compact Coiled Plow Inverter (CHP-CCFI) within the square frame of the CFI (Ax A), respectively. Three coiled structures have identical dimensions such as coiled tube inner diameter

curvature diameter

curvature ratio (λ) and frame area (Ax A). Moreover, the RSP-CCF1 is meant to include ail tube bank arrangements within a three- dimensional flat, cuboidal structure, as illustrated in Figure ID. However for the sake of comparative analysis the two innovative designs, viz. RSP-CGFI and CHP-CCFI, are accommodated within the square frame (A x- A) of standard CFI.

[0063] Figure 2 illustrates the mixing process by using the three different coiled structures of Figures 1 A-IC, where all three geometries are accommodated within the same floor area described by Ax A. POT the purpose of demonstrating the design procedure, a CFI of specified dimensions was fabricated as standard, that uses die optimal values of all parameters that would provide the best performance of CFI, that includes:

(a) an equal ratio of the volume of the tube in each helical arm;

(b) the angle of inversion - 90°; and

(c) number of inversions = three (maximum obtained by designing the one bank).

[0064] Figure 1A illustrates the standard CFI of 64 coil turns on a 6 cm cylindrical base using 1 cm {inner diameter,

PVC tubing with 0.3 cm wall thickness, wherein a curvature ratio

of 7.6 was maintained throughout the design. The four discrete helical arms (shown by 1, 2, 3 and 4) were arranged at an angle of 90* with respect to their successive/former helical arm to obtain three equidistant 90° ilow inversions at point 5, 6 and 7 within a square of 42.4 cm x42.4 cm.

[0065] Figure IB illustrates the proposed Rectangular Spiral Pattern- Compact Coiled Flow Inverter (RSP-CCF1) that amasses the maximum possible mixing volume without altering the footprint of the CFI, to enhance the mixing per unit occupied floor area based on current dimensions of standard CFI (A* A). The square frame of RSP-CCFI, as illustrated in Figure IB, can be considered as a special case of the more general rectangular spiral geometry within a rectangular frame, as illustrated in Figure 1 D, where six 90° bends (shown as 8-13) join the seven discrete helical arms (marked as 14, 15. 16, 17, 18, 19 and 20) to accommodate as maximum as possible 90° inversions. In this case, the decision on the number of coil turns and number of 90° bends was made on the basis of occupied floor area(j4x J4).

[0066] Each helical arm is labeled as q. For q≤ 3 , coiling is performed in traditional CFT fashion where equal length dimension of helically coiled arm, is formed for standard CFI) so as to cover available outer dimensions (Ax A). Fot q > 3, coiling was stopped when a distance equal to the outer diameter of coil was left between

helical arm, and then a 90' bend was introduced to form helical arm till there is no

further space left for the coiling in the available area. For demonstrating the design using current dimensions of occupied floor area by standard CFI (A x A = 42,4 cmx42.4 cm), Figure IB is outlined, where after coiling on first three successive helical arms (indicated as 14, IS and 16), the coiling on fourth helical arm (indicated as 17) is continued until a distance after which distance equal to outer diameter of helical arm is left

from the first helical arm (indicated as 14). From this point, the continuing coiling onhclical arm 17 was inverted at 90" to another helical arm indicated by 18, which is further made to Invert on helical arm 19 when a distance equal to the outer diameter of helical aim was left again. The similar procedure was followed till helical arm 20, after which no further space is available for coiling.

[0067] Therefore, depending on the outer diameter of the contributing helical arm and available empty internal area of CFI, variable non-equidistant 90° inversions can be obtained to form RSP-CCFI. It is of importance that in the RSP-CCFI of Figure 1 B, there is an increase of 23% (approx.) of mixing volume in contrast to standard CFI, owing to increased number of helical arms, and this is achieved within the same floor area. The percentage increase in the volume per unit space may vary depending upon the dimensions of CFI. Nonetheless the design procedure will remain same irrespective of the dimensions of the standard CFI as well as the type of frame (square/rectangular).

[0068] Figure IC that illustrates the CHP-CCFI is based on the generalized design model as illustrated in Figure 3, where the entire occupied floor area (Ax A) is divided into various sub-squares, indicated by 1, 2, 3....so on, in Figure 3. The sides of each sub- square(s) represent the axis for coiling. The projected view of one such sub-square is also indicated in Figure 3. In this design, coiling can be started from any edge of any sub-square and can be continued in any direction. For illustration, the starting edge of coiling is shown, in Figure 3 along with the manner in which coiling is to be continued from the starting edge for a first round of coiling, indicated by the direction of arrows. On completion of coiling on the outer edges, coiling is shifted to the immediate inner edge for the second round, as indicated in Figure 3 and continued in a similar manner.

[0069] Conversely, if coiling is started from any innermost edge, then it is to be continued to immediate outer edge in a similar manner. It is evident that for this kind of design the number of sub-squares along the diagonal of outer square with the area (Ax. A) as indicated by m in Figure 3 should be an odd number. In order to estimate the number of sub-squares along the diagonal (m), dimensions of each sub-square (sxs) and number of 90° bends (n) within occupied floor area (Ax A), equations 1 to 4 are used. If coil diameter , pitch (A), number of helical turns per arm and floor area (Ax A) ate known,

then the possible number of sub-squares along the diagonal (m) and their dimension (s xs ) are calculated by using equations 1-2. The value of m thus obtained by using equation 1 is round-off up to zero decimal place to report an integer for m. Based on the obtained integer value of m. the dimension of floor area (A) is recalculated by using equation I ; which is then used in the subsequent calculations of number of 90' bends (n) by using equations 3 and 4:

where r represents the total number of sub-squares of area

that can be fitted in door area (A x A) without leaving any unoccupied space in area (Ax A) .

[0070] In order to illustrate CHP-CCFI within the outer dimensions of standard CFI

Figure 1C is sketched for which four helical turns per arm

are used so that secondary flow can become fully developed even at higher values of Reynolds number

Therefore, based on the given floor area (i.e. Ax A= 1798cm³ approx.), number of helical turns per arm curvature diameter and

pitch

m came out to be 3 (in round Figure) and number of 90º bends (n) came out to be 15 by using equations I to 4. Consequently, sixteen different helical arms, represented by numbers 21-36 in Figure 1C are arranged within the similar outer "/-erne" that offer fifteen equidistant 90º flow inversions, that are shown as 37 to 51 in Figure 1C. However, while coiling it was not possible to have exactly same helical turns per arm

rather some arms contains

number of helical turns, some contain

half more or half less number of helical turns as per coiling demands. If each helical arm would contain the same number of helical turns,

then various helical coiled arms will intersect with each other, and the coiling cannot be done properly. Thus, for fabricating CHP-CCFI with fifteen 90° bends, an error of approx.7% was obtained in the value of A (found by back calculations from this design model using the value of m = 3) on comparing the fabricated and theoretically outlined CHP-CCFI. Nevertheless, one may incorporate more number of 90° bends within the same area by choosing lesser number of helical turns on each arm

by using design protocol explained by equations 1 to 4.

[0071] Figure 1C also illustrates the placement of specially designed cubical, indicated as 52-55 and triangular, indicated as 56-63 blocks amid different helical arms of the CCFT. This is because of the high-density packed structure of CCFI that makes coi ling a challenging task. Therefore, by using specially designed blocks, it is possible to attach the successive arm after the completion of coiling on the former arm. The positioning of the cubical and triangular blocks is decided on the basis of accompanying helical arms. Consequently, the triangular blocks were used to attach the two helical arms at the outer edges of the structure; while the cubical blocks were used to attach four helical arms in the central area.

[0072] Figures 4A and 4B illustrate the cubical and triangular blocks with extended cylindrical provisions at 64 to position hollow cylindrical base for coiling. The dimensions of the blocks were decided on the basis of the dimensions of the hollow cylindrical base used for die coiling. Based on the outer diameter of the cylindrical base pipe used in the present study (0 = 6 cm), it was required to have the dimensions of 6 cm x 6 cm x 6 cm for the central cubical part so as to obtain a precise touch between two adjacent helical arms. Therefore, cubical blocks were fabricated by using 10 cm x 10cmx 10 cm cuboid, from which a central cube of 6 cm x 6 cm x 6 cm was formed, as indicated by 55 m Figure 4A with four cylindrical extensions of 5.4 cm diameter and 2 cm height as indicated by 64 in Figure 4A. The diameter and height of each cylindrical extension were kept in accordance with the inner diameter of the cylindrical base pipe (0=5.4 cm) and support required to fit the helical arms on it respectively. Further, from these completed cubical blocks, the fabrication of triangular blocks was achieved by cutting them diagonally, as illustrated in Figure 4B. The triangular blocks not only join the two helical arms at the outer edge but also retain the squared shape for the CHP-CCFI so as to fit it within the frame of standard CFI.

[0073] The comparative analysis of geometries (i.e. CFT and CCFTs) was carried out by conducting step response residence time distribution (RTD) experiments by using water as a flowing media and Congo red dye as a tracer for the range of Reynolds number from 10- 145. The dispersion model was fitted to the experimentally obtained response curves (F-curve), as all of them follow the Gaussian distribution. Figure 5 illustrates the typical step response curve (F-curve) for three geometries at

It is apparent that RSP-CCFI and CHP-CCFI offer narrower RTD as compared to standard CFI while CHP- CCFI offers the narrowest RTD in-spite of using same tube length, and consequently same coil volume, as in the case of standard CFI. A closer examination of the designs of three flow inverters (i.e. CFI and two CCFIs) indicate that for standard CFI only three 90°inversions takes place while in RSP-CCFI and CHP-CCFI there are six and fifteen 90° inversions (i.e. five times of CFI), respectively, within the identical floor area The RSP- CCFT offers better radial mixing performance over standard CF1 due bo increased mixing volume and 90° inversions. However, CHP-CCFI offers the best radial mixing performance than RSP-CCFI and CFI owing to fifteen equidistant 90° inversions, and equal volume carried in each helical arm that provides an effective flow inversion.

[0074] From Figure 5, it is apparent that although all three coiled geometries, viz., CFI, RSP-CCFI, and CHP-CCFI have followed the applicability of Axial Dispersion Model (ADM), the CHP-CCFI offers maximum closeness to plug flow condition. This is stated on the basis of dimensionless time

corresponding to the first appearance of F

value on threshold line (defined at slightly above zero value) at Reynolds number

The definition of threshold line has been made to avoid the violation of ADM solution that postulates the zero start time of all concentration measurements. The dimensionless time

for first appearance of F value on threshold line by CFI, RSP- CCFI and CHP-CCFI is 0.70, 0.73 and 0.80, respectively, while for ideal plug flow conditions this value is 1.0. Therefore, CHP-CCFI is suitable as mixers that express significantly enhanced radial mixing in the laminar flow regime, compared to CFI designs, by utilizing an identical floor area.

[0075] Moreover, the intensity of radial mixing of fluid over variable flow

velocity

was measured to present the evolution of improvement made by CFI and two CCFIs. Figure 6 illustrates the compiled values of

against the

which illustrates that the innovative designs of CCFIs have significantly higher value of

as compared to CFI. It is also observed that the radial mixing performance of the CCFIs is improving with increasing Reynolds number

which is due to the inversion of more intense secondary flow field (due to centrifugal force) produced at higher Reynolds number

Further, the magnitude of radial mixing achieved by RSP-CCFI at Reynolds number

of SO (significantly laminar conditions) is almost equivalent to the magnitude of radial mixing achieved by CFI at Reynolds number (Λ¾) of about 75, and similarly the magnitude of radial mixing achieved by CHP-CCFI at Reynolds number

of 10 is almost equivalent to the magnitude of radial mixing achieved by CFI at Reynolds number

of about SO.This shows that die proposed CCFIs help in providing enhanced radial mixing to fluid even at remarkably lower flow rates that will also reduce the operational cost (in terms of pumping energy required for such fluids). However, on comparing the performance of three designs, it has been observed that CHP-CCFT offers superlative performance over entire flow range and this is achieved by utilizing the same floor area as occupied by CFI. This aspect of Improvement is plotted in Figure 7, which illustrates the relative increase in radial mixing

per unit floor area, assessed by calculating dimensionless

area occupied, for all designs and concluded that the proposed CCFTs provide significantly improved performance.

[0076] The cost of offered advantages by CCFTs fs assessed by measuring the pressure drop across the coiled geometries. To measure their aptness as an in-line mixer, it is very important to measure the combined effect of induced mixing and offered pressure drop. Consequently, the coefficient of mixedness is evaluated for each coiled geometry over entire flow regime

by using equation S.The coefficient of mixedness gives the relative contribution of axial dispersion coefficient {D) and friction factor

with respect to fluid properties (v).

[0077] Figure 8 illustrates the comparison between three coiled geometries on this basis, which indicates that CHP-CCFI gives prime performance over RSP-CCFI and CFI. It is noteworthy that CHP-CCFI and RSP-CCFI provide nearly 39%-83% higher and 10%- 19% lower value of the coefficient of mixedness

in contrast to standard CFI, respectively. The reason for such an observation is explained by examining the Peclet number

and pressure drop data prudently, which provide highest value of Peclet number

and friction factor

for CHP-CCFI; and higher value of Peclet number

and friction factor

for RSP-CCFI with respect to standard CFT. However, there exist a marginal difference in the magnitude of Peclet number

between standard CFI and RSP-CCFI than between standard CFI and CHP-CCFI; and similarly a marginal difference lies in the magnitude of friction factor

between CHP-CCFI and RSP-CFI than between standard CFI and CHP-CCFI. [0078] Therefore, on evaluating coefficient of mixedness

by using friction factor (f) and overall dispersion coefficient (D), based on these measurements and

pressure drop), the lowest value for RSP-CCFI is obtained owing to the involvement of higher tube length. While the CHP-CCF1 gives the significantly higher magnitude of the coefficient of mixedness

over entire flow range despite having a higher pressure drop. This implies that a relatively higher radial mixing is produced with respect to the offered pressure drop penalty by CHP-CCFT.

[0079] Hence, (he proposed compact coiled flow inverters to be used as in-line mixers offers improved performance for the applications such as microrcactor for various applications including polymerization, heat exchanger, microfluidic device for process intensification, microfluidic device for nanofluid processing, milli/microstructured heat exchanger, microstructure device for nanofluid processing, membrane module for enhanced mass transfer, liquid-liquid extractor, two-phase flow application, potential device for food processing, reactor for continuous protein refolding, reactor for continuous precipitation of clarified cell culture supernatant, suitable reactor for continuous flow chemical processes, reactor for continuous biopharmaceulical processing, reactor for continuous viral inactivation and continuous operated modular reactor design for the multiphase reaction system.

[0080] Although compact, high efficiency and high-performance inline mixers using compact coiled flow inverters have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices/apparatus described. Rather, the specific features are disclosed as examples of implementations of compact coiled flow inverters carrying out in-line mixing by using the combined action of centrifugal force and multiple flow inversions.

Claims

1. A compact in-line mixer for mixing of fluids in laminar regime on a volumetric basis comprising a rectangular frame with six 90° bends joining seven discrete helical arms to accommodate maximum possible inversions.

2. The mixer as claimed in claim 1, wherein the number of coil turns per arm and number of 90° bends is based on occupied floor area (Ax. A).

3. The mixer as claimed In claim 1, wherein the rectangular frame has equal sides.

4. The mixer as claimed in claim 1, wherein for q > 3, coiling is stopped when a distance equal to the outer diameter of coil

is left between helical arm,

followed by a 90º bend to form

helical arm till no further space for coiling is left in available area, where q is the number of helical arms.

5. A compact in-line mixer for mixing of fluids in laminar regime on a volumetric basis comprises of a frame with fifteen equidistant 90° flow inversions.

6. The mixer as claimed in claim 5, wherein the number of helical turns per arm is not constant.

7. The mixer as claimed in claim 6, wherein some arms contains numberof helical

rums and others contain

and a half more or half less helical turns as per coiling demands.

8. The mixer as claimed in claim 6, comprising specially designed cubical and triangular blocks amid the helical arms.

9. The mixer as claimed in claim 8, wherein successive arms are attached after coiling using the specially designed blocks.

10. The mixer as claimed in claim 8, wherein the triangular blocks are adapted to attach the two helical arms at the outer edges of the structure.

11. The mixer as claimed in claim 8, wherein the cubical blocks are adapted to attach four helical arms in the central area.

12. The mixer as claimed in claim 8, wherein dimensions of the blocks are based on the dimensions of the hollow cylindrical base used for coiling.

13. The mixer as claimed in claim 10, wherein triangular blocks are obtained by cutting the cubical blocks diagonally.

14. The mixer as claimed in claim 10, wherein the triangular blocks aids in retaining the squared shape of the frame.

15. A method for in-line mixing of fluids in laminar regime on a volumetric basis involves rotating periodically the Dean cells by 90° for significant enhancement in transverse mixing at low shear.

16. Hie method as claimed in IS, wherein flow inversions facilitate rotation of the Dean cells.

17. The method as claimed in 16, wherein the number of flow inversions is six or fifteen.

18. The mixer as claimed in any of the preceding claims adapted to use as micrareactor for various applications including polymerization, heat exchanger, microfiuidic device for process intensification, microfiuidic device for nanofluid processing, milli/microstructured heat exchanger, microstructure device for nanofluid processing, membrane module for enhanced mass transfer, liquid-liquid extractor, Iwo-phase flow application, potential device for rood processing, reactor for continuous protein refolding, reactor for continuous precipitation of clarified cell culture supernatant, suitable reactor for continuous flow chemical processes, reactor for continuous biopharmaceutical processing, reactor for continuous viral Inactivation and continuous operated modular reactor design for the multiphase reaction system and the like.