DATA PLATE ASSEMBLY FOR A HEAT EXCHANGER
20230015520 · 2023-01-19
Inventors
Cpc classification
F28F27/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28F2200/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28D9/0075
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28F2275/205
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28D9/005
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28F3/10
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28D9/0062
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28F3/083
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28G15/003
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
International classification
F28F27/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28D9/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
F28F3/08
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
Abstract
A data plate assembly for installation with a plate heat exchanger. The data plate assembly includes a monitoring device assembled with a spacer plate. The spacer plate includes inlet and/or outlet holes, and a port that extends from an outer edge of the spacer plate to one of the inlet and/or outlet holes. The port retains the monitoring device therein such that the monitoring device extends into the inlet and/or outlet holes to monitor characteristics of the process and cooling fluids flowing through the holes and the plate heat exchanger. As the performance of the plate heat exchanger degrades, the characteristics accumulated over a period of time may provide an indication that the performance of the plate heat exchanger is degrading and/or the rate in which the performance of the plate heat exchanger degrades.
Claims
1. A spacer plate for assembly with a plate heat exchanger and a monitoring device, the spacer plate comprising: one or more inlet and/or outlet holes; a port that extends from an outer edge of the spacer plate to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein; a front outer surface opposite a rear outer surface, wherein one of the front and/or the rear outer surfaces includes a gasket track, wherein the gasket track includes a plurality of legs that intersect with a circular track positioned around the one or more inlet and/or outlet holes; and one or more seals assembled with the gasket track and the circular track.
2. The spacer plate of claim 1, wherein the one of the front and/or the rear outer surfaces that includes the gasket track also includes a second gasket track that connects two of the plurality of legs of the gasket track.
3. The spacer plate of claim 1, wherein the port is positioned perpendicular to the outer edge.
4. The spacer plate of claim 1, wherein the port forms a non-perpendicular angle to the outer edge.
5. The spacer plate of claim 1, wherein the other of front and/or rear outer surfaces includes a gasket track that is similar the gasket track on the one of the front and/or rear outer surfaces.
6. The spacer plate of claim 1, further comprising: a seal positioned around the monitoring device to seal the port with the monitoring device therein.
7. The spacer plate of claim 1, wherein the monitoring device is welded to the spacer plate.
8. The spacer plate of claim 1, wherein the port includes a port for each of the one or more inlet and/or outlet holes.
9. A spacer plate for assembly with a plate heat exchanger and a monitoring device, the spacer plate comprising: a front outer surface opposite a rear outer surface, the front and the rear outer surfaces spanning between an outer edge; an inlet hole that spans through the front and the rear outer surfaces; an outlet hole that spans through the front and the rear outer surfaces; and a port that extends from the outer edge to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein.
10. The spacer plate of claim 9, wherein one of the front and/or the rear outer surfaces includes a gasket track; and a seal assembled with the gasket track.
11. The spacer plate of claim 10, wherein the gasket track includes a plurality of legs that intersect with a first circular track positioned around the inlet hole and a second circular track positioned around the outlet hole; and one or more circular seals assembled with the first and the second circular tracks.
12. The spacer plate of claim 11, wherein the one of the front and/or the rear outer surfaces that includes the gasket track further includes a second gasket track that connects two of the plurality of legs of the gasket track.
13. The spacer plate of claim 9, wherein the port includes a port for each of the inlet and the outlet holes.
14. The spacer plate of claim 9, further comprising: a seal positioned around the monitoring device to seal the port with the monitoring device therein.
15. The spacer plate of claim 9, wherein the monitoring device is welded to the spacer plate.
16. A data plate assembly for installation with a plate heat exchanger, the data plate assembly comprising: a monitoring device; and a spacer plate, wherein the spacer plate defines one or more inlet and/or outlet holes, the spacer plate further includes a port that extends from an outer edge of the spacer plate to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein.
17. The data plate assembly of claim 16, wherein the spacer plate includes a front outer surface opposite a rear outer surface, wherein one of the front and/or the rear outer surfaces includes a gasket track sized to receive a seal; and a seal assembled with the gasket track.
18. The data plate assembly of claim 17, wherein the gasket track includes a plurality of legs connected to one another and arranged along the outer edge.
19. The data plate assembly of claim 18, wherein the one of the front and/or the rear outer surfaces that includes the gasket track further includes a second gasket track that connects two of the plurality of legs of the gasket track.
20. The data plate assembly of claim 18, further comprising: a circular track positioned around the one or more inlet and/or outlet holes, the circular track connected to one or more of the plurality of legs of the gasket track; and one or more seals assembled with the gasket track and the circular track.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The concepts described herein are illustrative by way of example and not by way of limitation in the accompanying figures. For simplicity and clarity of illustration, elements illustrated in the figures are not necessarily drawn to scale. Where considered appropriate, references labels have been repeated among the figures to indicate corresponding or analogous elements.
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DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0022] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the invention as illustrated therein as would normally occur to one skilled in the art to which the invention relates are contemplated herein.
[0023] Turning now to the present application with reference to
[0024] The spacer plate 20 includes a front outer surface and a rear outer surface which correspond to outer surfaces 30. In one embodiment, the front and the rear outer surfaces being the outer surfaces 30 are the same. In another embodiment, the front outer surface is different from the rear outer surface. The outer surfaces 30 may be smooth, corrugated, or have some other profile. In the illustrated embodiment, the spacer plate 20 includes outer surfaces 30 that are smooth. In one embodiment, the front and the rear outer surfaces 30 each includes a gasket track 32 configured to retain an O-ring or other type of gasket or seal therein. The gasket track 32 includes a plurality of legs 34 that extend along the four sides of the spacer plate 20 wherein the legs 34 intersect with a circular track 36 around each of inlet and outlet holes 40 and 42 of the spacer plate 20. In the illustrated embodiment, the gasket track 32 also includes a secondary gasket track 38 however in other embodiments the secondary gasket track 38 may not be included. The secondary gasket track 38 intersects two of the legs 34. The gasket track 32 with the gasket therein directs the hot medium as it flows through the plate heat exchanger in which the data plate assembly 10 is assembled. In another embodiment, only one of the front and the rear outer surfaces 30 includes the gasket track 32.
[0025] The spacer plate 20 includes two inlet holes 40 and two outlet holes 42 wherein one of the holes 40 or 42 is positioned at each of the corners of the spacer plate 20 to allow hot and cold fluids to pass through the holes 40 and 42 and any alternating channels 110 of the plate heat exchanger 100. In other embodiments, the inlet holes 40 can function as outlet holes and the outlet holes 42 can function as inlet holes and any combination as desired. The flow of hot process fluids and cold cooling fluids through alternating channels 110 in the plate heat exchanger 100 enables a plurality of plates 102 and the data plate assembly 10 to be in contact on one side with the hot fluid and the other side with the cold fluid.
[0026] The spacer plate 20 includes a port 24 that extends from an outer edge 46 of the spacer plate 20 to one of the inlet and outlet holes 40 and 42. In the illustrated embodiment, the port 24 forms an acute angle A with the outer edge 46. In other embodiments, the spacer plate 20 includes one of the ports 24 that extends from the outer edge 46 to each of the inlet and outlet holes 40 and 42. The port 24 is sized to receive the monitoring device 22 therein. In one form, the monitoring device 22 is inserted into the port 24 and then welded to the spacer plate 20 to prevent fluid leaks through the port 24. In other forms, the port 24 with the monitoring device 22 therein is sealed such as with a gasket, O-ring, or other sealing means.
[0027] In one embodiment, the spacer plate 20 is made of aluminum or another material however the area of the spacer plate 20 that surrounds the holes 40 and 42 and/or the ports 24 is made of a different material that is resistant to the fluid that travels through the holes 40 and 42. In this embodiment, the fluid is restricted to traveling only through the holes 40 and 42 and does not contact the remaining portions, including the outer surfaces 30, of the spacer plate 20.
[0028] One embodiment of the monitoring device 22 is illustrated in
[0029] The sensor 26 can include a single sensor or a plurality of sensors. The sensor 26 can include a temperature sensor, pressure sensor, flow sensor, positive displacement flow sensor, mass flow sensor, velocity flow sensor, and other types of sensors that will be apparent to those skilled in the relevant art(s) without departing from the spirit and scope of the disclosure.
[0030] Four of the monitoring devices 22 are shown assembled with the spacer plate 20, but in other embodiments there may be fewer or more of the monitoring devices 22. The monitoring devices 22 measure and monitor characteristics of the process and cooling fluids flowing through the holes 40 and 42. The characteristics of the process and cooling fluids may be measured directly by the monitoring devices 22 or derived from other characteristics of the process and cooling fluids that pass through the holes 40 and 42. As the performance of the plate heat exchanger 100 and the plurality of plates 102 therein degrades, the characteristics accumulated over a period of time by the monitoring devices 22 may provide an indication that the performance of the plate heat exchanger 100 and the plurality of plates 102 is degrading and/or the rate in which the performance of the plate heat exchanger 100 degrades.
[0031] For example, the temperature of the process fluid or the cooling fluid as it passes the holes 40 and/or 42 may be indicative of the performance of the plate heat exchanger 100 and the plurality of plates 102. Other characteristics of the process fluid and/or the cooling fluid that may be monitored by the monitoring devices 22 include flow rates of the process fluid and/or cooling fluid, temperature differentials such as temperature drops or temperature spikes, pressure differentials of the process fluid and/or cooling fluid as these fluids travel through the holes 40 and 42, and/or any other type of characteristic that may be an identifiable parameter that will be apparent to those skilled in the relevant art(s) without departing from the spirit and scope of the disclosure. Other characteristics of the process fluid and/or the cooling fluid that may be monitored by the monitoring devices 22 include cross-contamination of the process fluid with the cooling fluid or the cooling fluid with the process fluid. Other characteristics of the process fluid and/or the cooling fluid that may be monitored by the monitoring devices 22 include flow measurement (e.g., volumetric, mass, or velocity), media operating conditions (pressure, temperature, external vibration levels, and other conditions), properties of the media (acidity, corrosiveness, Reynold's number, viscosity, electrical conductivity, magnetic properties, etc.), amount of pressure loss that is tolerable, and/or flow rate range (the minimum and maximum values over which a measurement is needed).
[0032] Turning now to
[0033] The data plate assembly 300 includes a spacer plate 200 and one or more of a monitoring device 22 assembled with the spacer plate 200. The spacer plate 200 is configured similarly to the spacer plate 20, however the spacer plate 200 includes a plurality of ports 224 that are substantially perpendicular to an outer edge 246 of the spacer plate 200. Each of the ports 224 extends from an outer edge 246 of the spacer plate 200 to one of inlet and outlet holes 240 and 242. In the illustrated embodiment, the port 224 is substantially perpendicular to the outer edge 46. The port 224, similar to port 24, is sized to receive the monitoring device 22 therein. In one form, the monitoring device 22 is inserted into the port 224 and then welded to the spacer plate 200 to prevent fluid leaks through the port 224. In other forms, the port 224 with the monitoring device 22 therein is sealed such as with a gasket, O-ring, or other sealing means.
[0034] Turning now to
[0035] The spacer plate 400 includes outer surfaces 430 that are smooth. In one embodiment, each of the outer surfaces 430, i.e., the front and rear outer surfaces, includes a gasket track 432 configured to retain an O-ring or other type of gasket or seal therein. In one form, the gasket track 432 is a milled gasket groove. The spacer plate 400 has a thickness sufficient to accommodate a thermos weld to mount and seal the monitoring device 22 in the ports 424. In another embodiment, only one of the outer surfaces, i.e., one of the front and rear outer surfaces, includes the gasket track 432.
[0036] The plate heat exchanger 100 is one illustrative example of a plate heat exchanger and one of ordinary skill in the art would appreciate that other types of plate heat exchangers can be used with the data plate assemblies 10, 300, and 500. The plate heat exchanger 100 includes a plurality of plates 102 that have outer surfaces 104 that are corrugated. In other embodiments, the outer surfaces 104 are flat or have a different profile.
[0037] In the illustrated embodiment in
[0038] The plurality of plates 102 and the data plate assembly 500 slide on a pair of carry bars 111 and are pressed together such as between a pair of outer frames 112. The pair of outer frames 112 can include a movable frame and a fixed frame or cover. The pair of outer frames 112 can be attached to the plurality of plates 102 and/or the data plate assembly 500 with one or more bolts and/or tie bars or rods 114. Each of the plurality of plates 102 includes a gasket 120 placed on one side or face of the plate 102 wherein the gasket 120 directs the flow of the fluids and to seal the channels 110 between the plurality of plates 102. The gaskets 120 are placed along grooves 122 at the outer edges of the plates 102 on one side of the plate 102. The gaskets 120 are also placed around inlet holes 140 and outlet holes 142 of the plurality of plates 102. The gaskets 120 ensure that the cold fluid and the hot fluid do not mix.
[0039] Each of the plurality of plates 102 includes two inlet holes 140 and two outlet holes 142 wherein one of the holes 140 or 142 are positioned at each of the corners of the plates 102 to allow hot and cold fluids through the alternating channels 110. The flow of hot and cold fluids through the alternating channels 110 in the plate heat exchanger 100 enables the plurality of plates 102 and the data plate assembly 500 to be in contact on one side with the hot fluid and the other side with the cold fluid.
[0040] The number of the plurality of plates 102 can vary from 3 to several hundred. The size of the plurality of plates 102 can vary from a few square centimeters to 3 or 4 square meters. The plates 102 are commonly made of steel, aluminum alloy, titanium, nickel, graphite, or other metal materials. The plurality of plates 102 are arranged in a cold-hot-cold-hot fluid flow pattern to maximize the thermal mixing between each fluid. One fluid 160 enters an upper inlet 162 of the outer frame 112 and successively flows down every even-numbered plate, while the other fluid 170 enters through the bottom lower inlet 172 and is pumped up every odd-numbered plate.
[0041] The data plate assembly 500 is operatively connected to a controller 200 structured to perform certain operations to control the monitoring devices 22. In certain embodiments, the controller 200 forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller 200 may be a single device or a distributed device, and the functions of the controller 200 may be performed by hardware or by instructions encoded on computer readable medium. The controller 200 may be included within, partially included within, or completely separated from other controllers (not shown) associated with the plate heat exchanger 100 and/or the data plate assembly 500. The controller 200 is in communication with the monitoring device 22 of the data plate assembly 500, including through direct communication, communication over a datalink, and/or through communication with other controllers or portions of the processing subsystem that provide sensor and/or other information to the controller 200.
[0042] In certain embodiments, the controller 200 is described as functionally executing certain operations. The descriptions herein including the controller operations emphasizes the structural independence of the controller, and illustrates one grouping of operations and responsibilities of the controller. Other groupings that execute similar overall operations are understood within the scope of the present application. Aspects of the controller may be implemented in hardware and/or by a computer executing instructions stored in non-transient memory on one or more computer readable media, and the controller may be distributed across various hardware or computer based components.
[0043] Example and non-limiting controller implementation elements include sensors providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements.
[0044] The listing herein of specific implementation elements is not limiting, and any implementation element for any controller described herein that would be understood by one of skill in the art is contemplated herein. The controllers herein, once the operations are described, are capable of numerous hardware and/or computer based implementations, many of the specific implementations of which involve mechanical steps for one of skill in the art having the benefit of the disclosures herein and the understanding of the operations of the controllers provided by the present disclosure.
[0045] In one embodiment, the controller 200 may communicate with the monitoring device 22 to obtain the fluid data generated from the monitoring of the characteristics of the process fluid and/or the cooling fluid flowing through the plate heat exchanger 100 and the data plate assembly 500. The controller 200 may then analyze the fluid data to generate different types of analytics for the plate heat exchanger 100. The controller 200 may then communicate the analytics of the plate heat exchanger 100 to a second monitoring device (not illustrated) that is operated by a user so that the user may monitor the performance of the plate heat exchanger 100 via the analytics provided to the user via the controller 200.
[0046] One of skill in the art, having the benefit of the disclosures herein, will recognize that the controllers, control systems and control methods disclosed herein are structured to perform operations that improve various technologies and provide improvements in various technological fields. Certain operations described herein include operations to interpret one or more parameters. Interpreting, as utilized herein, includes receiving values by any method known in the art, including at least receiving values from a datalink or network communication, receiving an electronic signal (e.g. a voltage, frequency, current, or PWM signal) indicative of the value, receiving a software parameter indicative of the value, reading the value from a memory location on a non-transient computer readable storage medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted parameter can be calculated, and/or by referencing a default value that is interpreted to be the parameter value.
[0047] As is evident from the figures and text presented above, a variety of aspects of the present disclosure are contemplated. A first aspect of the present disclosure includes a spacer plate for assembly with a plate heat exchanger and a monitoring device, the spacer plate comprising: one or more inlet and/or outlet holes; a port that extends from an outer edge of the spacer plate to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein; a front outer surface opposite a rear outer surface, wherein one of the front and/or the rear outer surfaces includes a gasket track, wherein the gasket track includes a plurality of legs that intersect with a circular track positioned around the one or more inlet and/or outlet holes; and one or more seals assembled with the gasket track and the circular track.
[0048] In one embodiment of the first aspect, the one of the front and/or the rear outer surfaces that includes the gasket track also includes a second gasket track that connects two of the plurality of legs of the gasket track.
[0049] In a second embodiment of the first aspect, the port is positioned perpendicular to the outer edge.
[0050] In a third embodiment of the first aspect, the port forms a non-perpendicular angle to the outer edge.
[0051] In a fourth embodiment of the first aspect, the other of front and/or rear outer surfaces includes a gasket track that is similar the gasket track on the one of the front and/or rear outer surfaces.
[0052] In a fifth embodiment of the first aspect, further comprising: a seal positioned around the monitoring device to seal the port with the monitoring device therein.
[0053] In a sixth embodiment of the first aspect, the monitoring device is welded to the spacer plate.
[0054] In a seventh embodiment of the first aspect, the port includes a port for each of the one or more inlet and/or outlet holes.
[0055] A second aspect of the present disclosure includes a spacer plate for assembly with a plate heat exchanger and a monitoring device, the spacer plate comprising: a front outer surface opposite a rear outer surface, the front and the rear outer surfaces spanning between an outer edge; an inlet hole that spans through the front and the rear outer surfaces; an outlet hole that spans through the front and the rear outer surfaces; and a port that extends from the outer edge to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein.
[0056] In one embodiment of the second aspect, one of the front and/or the rear outer surfaces includes a gasket track; and a seal assembled with the gasket track.
[0057] In a second embodiment of the second aspect, the gasket track includes a plurality of legs that intersect with a first circular track positioned around the inlet hole and a second circular track positioned around the outlet hole; and one or more circular seals assembled with the first and the second circular tracks.
[0058] In a third embodiment of the second aspect, the one of the front and/or the rear outer surfaces that includes the gasket track further includes a second gasket track that connects two of the plurality of legs of the gasket track.
[0059] In a fourth embodiment of the second aspect, the port includes a port for each of the inlet and the outlet holes.
[0060] In a fifth embodiment of the second aspect, further comprising: a seal positioned around the monitoring device to seal the port with the monitoring device therein.
[0061] In a sixth embodiment of the second aspect, the monitoring device is welded to the spacer plate.
[0062] A third aspect of the present disclosure includes a data plate assembly for installation with a plate heat exchanger, the data plate assembly comprising: a monitoring device; and a spacer plate, wherein the spacer plate defines one or more inlet and/or outlet holes, the spacer plate further includes a port that extends from an outer edge of the spacer plate to one of the inlet and/or outlet holes, the port configured to receive the monitoring device therein.
[0063] In one embodiment of the third aspect, the spacer plate includes a front outer surface opposite a rear outer surface, wherein one of the front and/or the rear outer surfaces includes a gasket track sized to receive a seal; and a seal assembled with the gasket track.
[0064] In one embodiment of the third aspect, the gasket track includes a plurality of legs connected to one another and arranged along the outer edge.
[0065] In a second embodiment of the third aspect, the one of the front and/or the rear outer surfaces that includes the gasket track further includes a second gasket track that connects two of the plurality of legs of the gasket track.
[0066] In a third embodiment of the third aspect, further comprising: a circular track positioned around the one or more inlet and/or outlet holes, the circular track connected to one or more of the plurality of legs of the gasket track; and one or more seals assembled with the gasket track and the circular track.
[0067] In the above description, certain relative terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” “proximal,” “distal,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object.
[0068] Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. Similarly, the use of the term “implementation” means an implementation having a particular feature, structure, or characteristic described in connection with one or more embodiments of the present disclosure, however, absent an express correlation to indicate otherwise, an implementation may be associated with one or more embodiments.
[0069] The described features, structures, advantages, and/or characteristics of the subject matter of the present disclosure may be combined in any suitable manner in one or more embodiments and/or implementations. In the following description, numerous specific details are provided to impart a thorough understanding of embodiments of the subject matter of the present disclosure. One skilled in the relevant art will recognize that the subject matter of the present disclosure may be practiced without one or more of the specific features, details, components, materials, and/or methods of a particular embodiment or implementation. In some instances, the benefit of simplicity may provide operational and economic benefits and exclusion of certain elements described herein is contemplated as within the scope of the invention herein by the inventors to achieve such benefits. In other instances, additional features and advantages may be recognized in certain embodiments and/or implementations that may not be present in all embodiments or implementations. Further, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the subject matter of the present disclosure. The features and advantages of the subject matter of the present disclosure will become more fully apparent from the following description and appended claims, or may be learned by the practice of the subject matter as set forth hereinafter.
[0070] The present subject matter may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.