EARLY FOULING DETECTION

BACKGROUND

[0001] Some devices use liquids to perform various functions. Consider, for example, a heat exchanger 100 such as the one illustrated in FIG. 1. The heat exchanger 100 may have a first surface 110 (e.g., at 100° Celsius(C)) and a second surface 120 (e.g., at 50° C) and might use water or other liquids stored in, or moving through, internal channels or chambers to facilitate a transfer of heat.

[0002] Impurities and contaminants in the liquid may form on surfaces within the heat exchanger 100. This "fouling layer" 102 might include organic, inorganic, and/or biological material. For example, organic deposits might include polymers and inorganic materials might include Calcite.

[0003] Eventually, the fouling layer 102 may grow thick enough to substantially decrease performance of the heat exchanger 100 (e.g., the energy efficiency of the device may be substantially reduced). By this point, however, removing the relatively thick fouling layer 102 can be a time consuming and expensive process. For example, a factory might need to be shut down while a massive chemical cleaning of the heat exchanger is performed.

SUMMARY

[0004] According to some embodiments, a first capacitive element may be provided for a surface where a fouling layer is to be detected. A second capacitive element may also be provided, and a capacitance between the first and second capacitive elements may be used to detect formation of the fouling layer.

[0005] Some embodiments include: means for measuring a capacitance between a first capacitive element associated with a surface and a second capacitive element; and means for determining that a fouling layer has formed on the surface based at least in part on the measured capacitance.

[0006] Other embodiments provide a surface where a fouling layer is to be detected, and a thermal device may provide heat proximate to the surface. A

detector may detect a condition associated with the surface, and formation of the fouling layer may be determined based at least in part on the condition.

[0007] Yet other embodiments comprise: means for providing thermal energy proximate to a surface where a fouling layer is to be detected; means for detecting a condition associated with the surface; means for determining that the fouling layer has formed based at least on part on the condition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 illustrates a heat exchanger.

[0009] FIG. 2 is a side view of a system in accordance with an exemplary embodiment of the invention.

[0010] FIG. 3 is a method of detecting a fouling layer in accordance with some exemplary embodiments of the invention.

[0011] FIG. 4 is a side view of a system in accordance with an exemplary embodiment of the invention.

[0012] FIG. 5 is a top view of a system in accordance with another exemplary embodiment of the invention.

[0013] FIG. 6 is a side view of a system to detect a fouling layer in the presence of a liquid according to yet another exemplary embodiment of the invention.

[0014] FIG. 7 is a method of detecting a fouling layer in accordance with the system of FIG. 6.

[0015] FIG. 8 is a side view of a system to detect a fouling layer in the presence of a gas according to yet another exemplary embodiment of the invention.

[0016] FIG. 9 is a method of detecting a fouling layer in accordance with the system of FIG. 8.

[0017] FIG. 10 is a side view of a system to detect a fouling layer using vibration according to yet another exemplary embodiment of the invention.

[0018] FIG. 11 is a method of detecting a fouling layer in accordance with the system of FIG. 11.

DETAILED DESCRIPTION

[0019] FIG. 2 is a side view of a system 200 in accordance with an exemplary embodiment of the invention. In particular, the system 200 includes a first capacitive element 210 associated with a surface 110 where a fouling layer 102 is to be detected. The surface 110 may, for example, be an internal surface of a heat exchanger. Note, however, that the surface 110 could instead be associated with any other types of devices that use a liquid, such as a fractionation unit or a process/water system.

[0020] The first capacitive element 210 might comprise, for example, a first conducting plate mounted onto and parallel to the surface 110. Note that a bonding or insulating layer (not illustrated in FIG. 2) might be provided between the surface 110 and the first capacitive element 210. The system 200 further includes a second capacitive element 220, such as a second conducting plate mounted substantially parallel and proximate to the first capacitive element 210.

[0021] As the fouling layer 102 grows on the surface 110, it may also grow on the first capacitive element 210. This may be especially true if the thermal characteristics of the surface 110 and the first capacitive element 210 are similar (e.g., such that they will both be at similar temperatures).

[0022] According to some embodiments, a capacitance between the first and second capacitive elements 210, 220 is used to detect formation of the fouling layer 102 (e.g., that the fouling layer 102 has reached a pre-determined thickness). Note that the fouling layer 102 may have different dielectric characteristics as compared to a fluid that is normally present between the elements 210, 220 and, therefore, the capacitance between the elements 210, 220 will change as deposits accumulate (e.g., the elements 210, 220 might act as two plates of a capacitor). By monitoring the capacitance between the elements 210, 220 the formation of the fouling layer 102 can be detected.

[0023] In this and other embodiments described herein, a scaled down device may more accurately detect formation of the fouling layer 102. For example, a very small gap between the elements 210, 220 may result in a more accurate sensor (e.g., because a small layer 102 will have a greater proportional impact on the capacitance). According to some embodiments, the elements 210, 220 may be associated with

Micro-ElectroMechanical System (MEMS) devices and/or silicon micromachining technology. Such a sensor may detect a fouling layer 102 having a thickness of 1-10 micrometers or less. By sensing the fouling layer 102 at such an early stage the efficiency and maintenance costs associated with the system 200 may be improved.

[0024] Although a single pair of elements 210, 220 are illustrated in FIG. 2, note that in this and other embodiments described herein multiple systems may be used to more accurately detect formation of the fouling layer 102.

[0025] FIG. 3 is a method of detecting a fouling layer in accordance with some exemplary embodiments of the invention. At Step 302, a capacitance is measured between a first capacitive element associated with a surface and a second capacitive element. At Step 304, it is determined that a fouling layer has formed on the surface based at least in part on the measured capacitance. At Step 306, an indication that the fouling layer has formed on the surface is output. For example, a sensor might provide a binary alert signal and/or an indication of the thickness of the fouling layer.

[0026] FIG. 4 is a side view of a system 400 in accordance with another exemplary embodiment of the invention. As before, the system 400 includes a first capacitive element 410 associated with a surface 110 where a fouling layer 102 is to be detected. The first capacitive element 410 might comprise, for example, a first conducting plate mounted onto and normal to the surface 110. Note that a bonding or insulating layer (not illustrated in FIG. 4) might be provided between the surface 110 and the first capacitive element 410. The system 400 further includes a second capacitive element 420, such as a second conducting plate mounted substantially parallel and proximate to the first capacitive element 410.

[0027] According to some embodiments, the elements 410, 420 comprise two parallel conductors by wet etching into a silicon wafer. Moreover, the elements 410, 420 may be isolated from each other, and a thin silicon oxide may be grown thermally to electrically isolate the silicon plates 410, 420 from surrounding fluid.

[0028] As the fouling layer 102 grows on the surface 110, it may also grow on the first capacitive element 410 and/or the second capacitive element 420. This may be especially true if the thermal characteristics of the surface 110 and the elements

410, 420 are similar (e.g., such that they will both be at similar temperatures). Moreover, the elements 410, 420 may need to be relatively short so that the portions of the elements 410, 420 farthest from the surface 110 will be at a temperature similar to the temperature of the surface 110 (and, therefore, will accumulate the fouling layer 102 at a similar rate).

[0029] According to some embodiments, a capacitance between the first and second capacitive elements 410, 420 is used to detect formation of the fouling layer 102. Note that the fouling layer 102 may have different dielectric characteristics as compared to a fluid that is normally present between the elements 410, 420 and, therefore, the capacitance between the elements 410, 420 will change as deposits accumulate. By monitoring the capacitance between the elements 410, 420 the formation of the fouling layer 102 can be detected.

[0030] FIG. 5 is a top view of a system in accordance with another exemplary embodiment of the invention. As with previously described systems, the system 500 includes a first capacitive element 510 associated with a surface 110 where a fouling layer 102 is to be detected. The first capacitive element 510 might comprise, for example, a first set of conducting fingers mounted onto an parallel to the surface 110. Note that a bonding or insulating layer (not illustrated in FIG. 5) might be provided between the surface 110 and the first capacitive element 510. The system 500 further includes a second capacitive element 520, such as a second set of conducting fingers interdigitated with the fingers of the first conducting element 510. In this configuration, a fouling layer may grow on the surface 110 and the elements 510, 520 (e.g., on the surface of FIG. 5).

[0031] Note that this configuration may result in mostly fringe fields away from the plane of the elements 510, 520 (e.g., into and out of the page of FIG. 5) with a range approximately equal to the gap between the fingers. According to some embodiments, a capacitance between the first and second capacitive elements 510, 520 is used to detect formation of a fouling layer. Note that the fouling layer may have different dielectric characteristics as compared to a fluid that is normally present above the elements 510, 520 and, therefore, the capacitance between the elements

510, 520 will change as deposits accumulate on them. By monitoring the capacitance between the elements 510, 520 the formation of the fouling layer can be detected.

[0032] FIG. 6 is a side view of a system 600 to detect a fouling layer 102 growing on a surface 110 in the presence of a liquid according to yet another exemplary embodiment of the invention. The system 600 includes a thermal device 610 to provide heat proximate to the surface 110 and a detector 620 to detect a condition associated with the surface 110. The thermal device 610 might comprise, for example, a membrane heater that is able to provide a pulse of heat to the surface 110. The detector 620 might comprise, for example, a thermometer that can determine the temperature of the surface 110. According to other embodiments, the detector 620 might measure other thermal characteristics (e.g., heat capacity and/or heat flux). As will now be described, formation of the fouling layer 102 may be determined based at least in part on the detected condition.

[0033] Referring to FIG. 7, which is a method of detecting the fouling layer 102 in accordance with the system 600 of FIG. 6, at Step 702 thermal energy is provided proximate to the surface 110 where the fouling layer 102 is to be detected. For example, the thermal device 610 may provide a pulse of heat while the surface 110 is in the presence of flowing water. At Step 704, a condition associated with the surface 110 is detected. For example, the detector 620 might measure the current temperature of the surface 110.

[0034] It may be determined if the fouling layer 102 has formed (e.g., is of at least a certain thickness) based at least in part on the detected condition. In particular, note that the fouling layer 102 may act as an insulator that reduces the amount of heat that may be transferred from the surface to the liquid. As a result, increasing the thickness of the fouling layer 102 will cause the surface 110 to retain more heat from the pulse generated by the thermal device 610. Thus, at Step 706 it is determined if the temperature is above a pre-determined threshold. If so, an indication that the fouling layer 102 has formed on the surface 110 is output at Step 708. The process may then be repeated (e.g., rapid pulses of heat may be applied the surface and analyzed to reduce the impact of moving liquid in the system 600).

[0035] Note that the presence of moving liquid in the system 600 may make it difficult to accurately determine small temperature changes. FIG. 8 is a side view of a system 800 to detect a fouling layer 102 growing on a surface 110 in the presence of a gas according to yet another exemplary embodiment of the invention. The system 800 includes a thermal device 810 to provide heat proximate to the surface 110 and a detector 820 to detect a condition associated with the surface 110. The thermal device 810 might comprise, for example, a membrane heater that is able to provide a pulse of heat to the surface 110. The detector 820 might comprise, for example, a thermometer that can determine the temperature of the surface 110. According to other embodiments, the detector 820 might measure other thermal characteristics (e.g., heat capacity and/or heat flux). As will now be described, formation of the fouling layer 102 may be determined based at least in part on the detected condition.

[0036] Refer to FIG. 9, which is a method of detecting the fouling layer 102 in accordance with the system 800 of FIG. 8. At Step 902, thermal energy is provided proximate to the surface 110 where the fouling layer 102 is to be detected. For example, the thermal device 810 may provide a pulse of heat after water has been removed from a chamber (and now the chamber contains only air). At Step 904, a condition associated with the surface 110 is detected. For example, the detector 820 might measure the current temperature of the surface 110.

[0037] It may be determined if the fouling layer 102 has formed (e.g., is of at least a certain thickness) based at least on part on the detected condition. In particular, note that the fouling layer 102 may act as thermal load that absorbs some of the heat received from the thermal device 810. As a result, increasing the thickness of the fouling layer 102 will cause the surface 110 to retain less heat from the pulse generated by the thermal device 810. Thus, at Step 906 it is determined if the temperature is below a pre-determined threshold. If so, an indication that the fouling layer 102 has formed on the surface 110 is output at Step 908.

[0038] Note that conditions other than temperature changes might be monitored to detect a fouling layer. FIG. 10 is a side view of a system 1000 to detect a fouling layer 102 growing on a surface 110 according to yet another exemplary embodiment of the invention. The system 1000 includes a thermal device 1010 to

provide heat proximate to the surface 110 and a vibration detector 1020 to detect a condition associated with the surface 110. The thermal device 1010 might comprise, for example, a membrane heater that is able to provide heat pulses to the surface 110. The vibration detector 1020 might comprise, for example, a device that can determine vibration-related characteristics of the surface 110. As will now be described, formation of the fouling layer 102 may be determined based at least in part on the detected condition.

[0039] Refer to FIG. 11, which is a method of detecting the fouling layer 102 in accordance with the system 1000 of FIG. 10. At Step 1102, thermal energy is provided proximate to the surface 110 where the fouling layer 102 is to be detected. For example, the thermal device 1010 may provide pulses of heat while the surface 110 is in the presence of either a liquid or a gas. Assuming the surface 110 and fouling layer 102 have different thermal coefficients of expansion, these pulses may cause the surface 110 to vibrate. According to other embodiments, an oscillator (not illustrated in FIG. 10) may be used to induce vibration of the surface 110 instead of the thermal device 1010.

[0040] At Step 1104, a condition associated with the surface 110 is detected. For example, the vibration detector 1020 might measure information associated with a resonant frequency and/or a damping behavior of the surface 110.

[0041] It may be determined if the fouling layer 102 has formed (e.g., is of at least a certain thickness) based at least on part on the detected condition. In particular, note that the fouling layer 102 may act alter the resonant frequency and/or damping behavior of the surface 110. Thus, at Step 1106 it is determined if certain vibration-related conditions are met. If so, an indication that the fouling layer 102 has formed on the surface 110 is output at Step 1108.

[0042] By detecting a fouling layer at an early stage of build up in accordance with any of the embodiments described herein, a maintenance frequency associated with a heat exchange or other types of devices may be reduce. Moreover, the need for factory shut downs may be avoided and/or the energy efficiency of such devices may be improved.

[0043] The following illustrates various additional embodiments of the invention. These do not constitute a definition of all possible embodiments, and those skilled in the art will understand that the present invention is applicable to many other embodiments. Further, although the following embodiments are briefly described for clarity, those skilled in the art will understand how to make any changes, if necessary, to the above-described apparatus and methods to accommodate these and other embodiments and applications.

[0044] Several approaches to early fouling detection have been provided, and any of the embodiments described here may be used together with other approaches. For example, a sensor may use both capacitance detection (e.g., as described with respect to FIG. 2) and thermal detection (e.g., as described with respect to FIG. 6). Moreover, although particular layouts and configurations have been provided, embodiments described herein may be implements using any number of other layouts and configurations.

[0045] The present invention has been described in terms of several embodiments solely for the purpose of illustration. Persons skilled in the art will recognize from this description that the invention is not limited to the embodiments described, but may be practiced with modifications and alterations limited only by the spirit and scope of the appended claims.