Embodiments of the subject matter disclosed herein generally relate to a viscosity sensor and a method for measuring in real-time the viscosity in a tubular conduit, and more particularly, to a viscosity sensor that uses a microchannel that provides laminar flow regardless of the flow type in the tubular conduit.
Monitoring a fluid's viscosity is essential for industries transporting fluids through tubes or similar conduits, like pipes. Most of the petrochemical and chemical industries rely on transporting a variety of chemicals, having different viscosities, from one location to another location along pipes. The energy necessary for transporting a chemical through the pipe is usually provided by pumping systems. It is important to plan the pumping systems and select the required initial pressure to transfer the fluid from one location to another as the energy necessary for moving a given fluid along a certain pipe depends, inter alia, by the viscosity of the fluid. The more viscous the fluid is, the more energy is necessary to move that fluid. Not providing enough energy for the transportation process may result in loss of production, or even damaging the pumping system.
In other industries, the viscosity of a manufactured product is indicative of the quality of that product. For example, a milk in a container that has a varying viscosity is indicative of a low-quality product. Thus, a viscosity analysis is employed to ensure product consistency. The viscosity analysis serves as a quality indicator within the industrial production process, such as in petrochemical, polymers, and food industries.
Capillary, falling-object, and torque detection are various known and reliable techniques for measuring the viscosity of a fluid using an off-line workstation setup. The conventional approach for determining the viscosity of a product for many industries starts with an on-site sample collection, followed by laboratory analysis, and sometimes requiring samples preparation before the examination, and ends with sending the results' report to the site for decision making. This traditional process is time consuming and inefficient for the rapid industrial growth with their increasing demands. Continuing with the example discussed above, if the operator of the milk plant determines that the container of milk is of poor quality, only after this lengthy process has been performed, it will result in many other containers of milk being manufactured to have the same poor quality, and thus, will result in a substantial material loss for the plant.
Therefore, reliable, real-time viscosity sensors for tubular systems are desires for many industries to allow adequate production controls and reduce costs through accurate decisions, decrease production errors, and lower fluid waste.
There are many existing viscometers for real-time monitoring in tubular systems. The available viscosity sensors for this purpose are classified into three categories according to their operating principles. The viscosity sensors are based on (1) vibration or (2) rotation of a probe, or on (3) change in fluid velocity-based measurements [1, 2, 3]. The vibrational and rotational viscometers are large and rigid instruments that interfere with the flow of the liquid in the tubular system and disturb the fluid flow creating a pressure drop and energy loss. Also, some of these sensors use destructive methods that require access through the pipe to the fluid, leaving behind permanent damage to the pipe.
The viscometers based on the change in the fluid's velocity or pressure drop uses a simple and inexpensive measurement process, which is based on the Hagen-Poiseuille law. It can be a non-invasive and non-destructive method by selecting the appropriate viscosity sensors [4] to measure the change in the velocity profile, such as using probes attached to the outer surface of the pipe as the ultrasonic or electromagnetic sensors. The main drawback of this technology is the restriction of its operation to the laminar flow condition for the fluid that flows into the conduit. Hence, there is still a demand for developing reliable in-line viscometers to meet industrial needs and to be applicable to any kind of flow.
To address this need, real-time viscometers have been robustly established and well developed for microfluidic monitoring applications. MEMS, micro-resonators, and fluid velocity-based measurements are common types of real-time microfluidic viscometers [5, 6]. These sensors are optimized particularly for microfluidic applications, where the MEMS and micro-resonators are suitable for small volumes of fluid. Optical measurements, as employed by some of these sensors, require transparent materials. The fluid velocity-based viscometers, which are known as micro-capillary sensors, are limited to the laminar flows, where such flow is ensured in the microfluidics because of the small cross-section area of the microchannels. In micro-capillary viscometers, the fluid's velocity is determined by recording the time necessary for the fluid to pass from one point to another, in a channel having known dimensions, by microscopic video recording [5, 7] or using optical sensors [8]. From these measurements, the fluid flow rate is obtained based on the pressure drop approach using either micro-pressure sensors as in MEMS based sensors [9, 10] or capacitive sensors [11] distributed along the channel. Such micro-capillary viscometers have been utilized for industrial on-site analyses to provide near real-time viscosity results, and the system was supported with a pumping system, for example, the commercial handheld product Viscosity-rheometer-on-chip (VROC) for testing manually withdraw fluid samples [12]. However, even these sensors are still complex and may not provide fast enough results.
Thus, there is a need for a new viscosity sensor that overcomes the above noted deficiencies, is inexpensive, accurate, and appropriate for being located in any type of conduit.
According to an embodiment, there is a viscosity sensor for measuring a viscosity of a fluid flowing in a pipe. The viscosity sensor includes a base made of a flexible material, a bridge made of a rigid material, wherein the bridge is attached to the base to form a microchannel, a pressure sensor formed within the base, and a controller configured to receive a signal indicative of a capacitance change ΔC from the pressure sensor, and to calculate the viscosity of the fluid flowing through the microchannel based on the received capacitance change ΔC.
According to another embodiment, there is a viscosity sensor system for measuring a viscosity of a fluid flowing in a pipe. The viscosity sensor system includes a viscosity sensor having a base made of a flexible material, a bridge made of a rigid material, where the bridge is attached to the base to form a microchannel, and a pressure sensor formed within the base, a controller configured to receive a signal indicative of a capacitance change ΔC, from the pressure sensor, and to calculate the viscosity of the fluid flowing through the microchannel based on the received capacitance change ΔC, and a power source configured to supply electrical power to the pressure sensor.
According to yet another embodiment, there is a method for measuring a viscosity of a fluid flowing through a pipe. The method includes a step of attaching a viscosity sensor to an inside of the pipe, the viscosity sensor having a base made of a flexible material that directly attaches to the inside of the pipe, a bridge made of a rigid material, wherein the bridge is attached to the base to form a microchannel, and a pressure sensor formed within the base, a step of flowing the fluid through the pipe so that part of the fluid flows through the microchannel, a step of measuring a change in a capacitance associated with the pressure sensor, as the fluid flows within the microchannel, and determining the viscosity of the fluid flowing through the pipe based on the measured change in capacitance of the pressure sensor, within the microchannel.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a viscosity sensor having a flexible base and the entire sensor is placed inside a tubular pipe and measures a pressure inside the sensor. However, the embodiments to be discussed next are not limited to a flexible base viscosity sensor, or to a sensor that is placed inside a tubular pipe, but they may be applied to a rigid sensor and/or to a pipe having any profile.
Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
According to an embodiment, a new velocity-dependent viscometer or viscosity sensor using a novel design for real-time measurements with insignificant flow disruption is introduced. The viscosity sensor may use, in one implementation, a poly(methyl-methacrylate) (PMMA) microchannel bridge, that forms a microfluidic channel when attached to a mechanically flexible polydimethylsiloxane (PDMS) base, and the entire structure is connected to the inner surface of a pipe. The flexible base of the viscosity sensor naturally adapts to different pipes diameters and curvatures shapes. Forcing part of a fluid flowing in a pipe system to flow through the microchannel formed by the bridge with the base, provides a laminar flow inside the microchannel, regardless of the flow type in the pipe system. Also, this viscosity sensor uses the pipe flow's driving force to propel the fluid flow into the microchannel for measurement, without requiring a pumping system, or sample withdrawal. In one embodiment, a stand-alone viscosity sensor system is presented and the system is capable for wireless data transmission to an external device, e.g., a smartphone. The novel viscosity sensor can be developed with low-cost materials and a low-cost fabrication processes, to provide an affordable sensor. As the viscosity of a fluid is invers proportional to the microchannel flow rate for incompressible Newtonian fluids, and the microchannel flow rate is proportional to a change in pressure in the microchannel, by measuring the pressure or change in pressure in the microchannel, it is possible to calculate the viscosity of the fluid. This sensor and its operating principle are now discussed in more detail with regard to the figures. The pressure or change in pressure may be measured with one or more pressure sensors. While any kind of pressure sensor may be used, in one embodiment a capacitive pressure sensor is used for measuring the pressure inside the microchannel. Because of the small size of the microchannel (width less than 10 mm and height less than 500 μm), the capacitive pressure sensor is a good candidate. For a given pressure measurement, one or more pressure sensors may be used. For example, in one application, the readings from plural pressure sensors distributed along the length of the microchannel may be averaged and a single pressure value may be used for the calculation of the viscosity of the fluid flowing through the microchannel.
More specifically, as shown in
The viscosity sensor 100 is shown in
The bridge 104 is made to be solid and have no openings, except for the input 105A and the output 105B. This means that the bridge 104 is attached to the base 102, for example, with a glue 210 or other materials or methods, so that no fluid enters or exits the microchannel 300 except for the input 105A and the output 105B. The bridge 104 may be attached to the base 102 by other means, e.g., mechanical means, thermal means, etc. The width W of the bridge is shown in
The pressure sensor 106 is shown in
The viscosity sensor illustrated in
As previously discussed, the base of the viscosity sensor is made as a physically flexible platform to adapt to different pipe diameters and curved architectures. The designed viscosity sensor's base, which is made of PDMS in this embodiment, has excellent physical and chemical properties since it is compatible with the microfabrication process, provides high flexibility, thermal stability, and is a low-cost material. The PDMS base contains one or more pressure sensors 106, which are based on a capacitive mechanism. The capacitive pressure sensor 106 was selected among other pressure sensing technologies because of the high stability and reliability even under mechanical deformations and it can be tailored easily for different sizes as appropriate for a variety of sensing pressure ranges. Therefore, it can provide good sensitivity to the flow's pressure for different pipe diameters and bending radii. The PDMS base may be patterned to include the encapsulated air 400, which is used as the dielectric material for the pressure sensor, and which is sandwiched between sputtered copper layers 402 and 404 on the PDMS base, which act as the conductive parallel plates for the capacitive structure.
The rigid microchannel bridge 104 is installed on top of the capacitive pressure sensor 106 on the base 102 to form the fluidic microchannel 300 because it is not possible, in large scale cross-section areas, i.e., for pipes, to measure the flow rate directly using the pressure change in the pipe. Because the static pressure generated by the fluid's weight inside the pipe 110 is much higher than the dynamic pressure generated by the fluid flow, by creating the microchannel 300, the size of the static pressure term is reduced, to be less than the dynamic pressure term. Note that the static pressure is multiplied by the microchannel height (which is less than 500 μm), and the dynamic pressure is divided with the square of the cross-section area A of the microchannel 300 (the area is very small, which makes the dynamic pressure large). Therefore, the bridge 104 provides a small cross-section area A regardless of the pipe 110's dimensions, which makes the dynamic pressure to dominate over the static pressure. For this reason, the microchannel 300 is made of a solid material, e.g., PMMA but other materials may also be used, to avoid channel deformation under different applied pressures from the surrounding fluidic environment. Also, the PMMA material is compatible with the PDMS base and the microfluidic fabrication processes.
The design of the microchannel 300 with micro-sized height H and a rectangular cross-section area offers a negligible flow disturbance in the pipe, compared to the existing technologies that generate large pressure drops and/or energy losses due to their large size. Another advantage of the microchannel 300 is the formation of a constant cross-section area A regardless of the pipe's dimensions. This means that no special correction of the measured viscosity is needed for measurements performed in pipes with different diameters. Moreover, the Reynold number is small for the microchannel 300 because it is proportional to its height. Therefore, the microchannel provides a laminar flow irrespective of the flow type in the pipe 110. The laminar flow simplifies the overall system physics and mathematical equations used for calculating the flow rate and/or the viscosity.
The operating principle of the viscosity sensor 100 is now discussed in more detail. The capacitive pressure sensor 106 inside the microchannel 300 is placed to measure the absolute pressure Ptotal generated by (1) the fluid's weight and (2) the fluid flow's velocity inside the microchannel 300. The measured pressure using the capacitive pressure sensor 106 corresponds to the total pressure PTotal, which is a combination of the static pressure PStatic and the dynamic pressure PDynamic, as expressed in equation (1).
P
Total
=P
Static
+P
Dynamic. (1)
The dynamic pressure PDyamic is proportional to the square of the volumetric flow rate Q of the fluid, as expressed in equation (2), while the static pressure Pstatic is proportional to the high of the microchannel 300.
where ρ is the fluid's density, H is the microchannel 300's height, and g is the gravity acceleration.
The total pressure is measured using the capacitive pressure sensor 106, where its capacitance value is proportional to the applied pressure, as shown by equation (3):
where d is the thickness of the base 102 (see
When the pressure exerted by the fluid 112 inside the microchannel 300 increases, the dielectric layer's height d decreases, and thus the capacitance C value of the pressure sensor 106 increases. Thus, based on the readings from the capacitor, it is possible to calculate the pressure inside the microchannel 300 or the flow rate of the fluid, as these quantities are related to each other through the equations (1) to (3). Knowing the exact profile of the microchannel 300 and also the profile and sizes of the pipe 110, it is then possible to link the pressure readings to the flow rate Q within the pipe 110.
The change in the microfluidic flow rate Q is measured using the capacitive pressure sensors 106 in the microchannel 300. The capacitance measurements and the absolute pressure are proportionally related, as recognized from the capacitive pressure sensors [13]. Therefore, a change in the fluid viscosity is inversely proportional to the capacitance measurements due to the variation in the fluid flow rate.
In this regard, the fluid viscosity p in the pipe 110 is inversely proportional to the microfluid flow rate Q in the microchannel 300. Equation (4) expresses the relationship between the viscosity and the flow rate using the Hagen-Poiseuille law for the microchannel having a rectangular cross-section, where W is the microchannel width, H is the microchannel depth, and ΔP is the pressure difference between two points separated by a length l:
Thus, by measuring the pressure difference ΔP and the flow rate Q through the microchannel 300, it is possible to calculate the viscosity μ of the fluid flowing through the pipe 110. The pressure difference ΔP can be measured by placing two pressure sensors 106 in the base 102. The fluid flow rate Q through the microchannel 300 can be calculated based on equation (2) based on a single pressure reading (as the dynamic pressure is directly related to the dynamic pressure). Alternatively, as all these quantities are related to each other by equations (1) to (4), it is possible to expose the sensor 100 to various fluid flows and map the pressure readings inside the microchannel 300 to the viscosity of the fluids run through the microchannel and store this correspondence in tables associated with the various fluids. Then, when the viscosity sensor 100 is distributed in an actual piping system, the controller that receives the pressure readings from the sensor uses these tables to identify the actual viscosity for a given fluid that corresponds to the measured pressures. This approach was tested as now discussed.
The simulated capabilities of the viscosity sensor 100 were studied using a numerical analysis performed with a commercially available tool. The numerical analysis was performed to understand the microchannel's effect on the readings, to consider the effect of its depth on the device performance, to assure fully developed flow conditions inside the microchannel, and also to understand the relationship between the fluid viscosity in the tubular system 110 and the flow rate and associated pressures in the microchannel 300. For this analysis, first, the pressure behavior of various pipes was analyzed without the microchannel 300. Tubes having a length of 30 cm and various diameters have been tested using a variety of fluid viscosities at a fixed flow rate equal to 2,000 ml/min. The pressure measurements were recorded at an individual point located on the base, at the middle point of the tube's length.
In contrast to the results of
Note that for these measurements, the viscosity sensor 100 was placed into the tube 110 so that the microchannel 300 has its longitudinal axis X1 parallel to the longitudinal axis X2 of the tube 110. This arrangement is also used when the actual viscosity sensor 100 is placed into an actual tube or pipe.
Based on these observations, the viscosity sensor 100 has been manufactured as now discussed. In this embodiment, the viscosity sensor 100 was manufactured with a lithography-free process making it a low cost, simple and affordable device. Other processes may be used to manufacture the viscosity sensor. The viscosity sensor has two parts, which are the rigid PMMA microchannel bridge 104 and the PDMS mechanically flexible base 102, with at least one capacitive pressure sensor 106 as discussed above. The physically flexible base 102 was fabricated as shown in
The exposed PDMS surfaces were treated with oxygen plasma to modify the surface from hydrophobic to hydrophilic, to increase the surface roughness to provide better metal adhesion on its surface. Then, the patterned squares on the two PDMS layers 700 and 704 were sputtered with 200 nm thickness of copper to form conductive plates 712, 714 for the capacitance sensors. Note that the plate 712 is formed on the top square 710 of the PDMS material for the layer 704 while the plate 714 is formed on the bottom square 710 of the PDMS material for the layer 700, in
The second PDMS layer 702 was patterned all the way through the PDMS layer thickness using the CO2 laser to form trenches or holes 720. These trenches are filled by air, which performs as a dielectric material for the capacitance sensors 106. The three prepared PDMS layers 700, 702, and 704 were arranged in the order shown in
Next, the microchannel bridge 104 was fabricated, as shown in
For characterizing the viscosity sensor 100, a transparent polyvinyl chloride (PVC) pipe system 800 was built with a 3.8 cm inner diameter D2 and a 60 cm total system's length L2, as shown in
The viscosity sensor 100 was tested with diverse fluids viscosities. Volume-diluted glycerol solutions and lubricant oils, with the international standards organization viscosity grade (ISO VG), were used to characterize the sensor at the different viscosities with pre-known values. 2L of liquid samples were applied for each viscosity test to fill the pipe, pumping tubes, and leave some liquid in the reservoir for pumping. The capacitance of the pressure sensor was measured with the multimeter 830 at each running fluid, and a switch 832 was used to alter between different capacitor sensors 106 present in the base 102. A quantity ΔC/C0 was calculated for each measured capacitance to determine the change in the capacitance in response to the difference in the microfluidic flow rate due to the transformation of the fluid viscosity, with C and C0 being the capacitance values with and without the applied pressure.
The viscosity sensor 100 has been shown in the above embodiments as being placed inside the pipe 110 with no wires leaving the sensor. However, for the viscosity sensor to exchange data (capacitive readings) with an external controller, either a wired communication or a wireless communication needs to be established between the one or more pressure sensors 106 and the controller. Both implementations are possible and both are now discussed with regard to
However, if the pipe 110 is made of a material that allows electromagnetic waves propagation through its walls, e.g., PVC, than it is possible to have the viscosity sensor 100 made to include a power source, the controller (e.g., a microcontroller) and a transmitter so that no wires are piercing the wall of the pipe.
For a plastic pipe with 4 cm in diameter and filled with the fluid 112, the BLE can easily communicate with a mobile device 1150, e.g., laptop, tablet, smartphone, etc., up to 10 m in range. A test was performed with the viscosity sensor 100 being connected to the controller 1020, and the viscosity sensor was submerged in water up to 50 cm depths. The data measured by the pressure sensor was sent in real-time from three pressure sensors, placed in the microchannel, to the smartphone 1150. The curves 1200 to 1220 corresponding to the readings from the three pressure sensors 106 are shown in
A method for measuring a viscosity of a fluid now discussed with regard to
The above embodiments disclose a new usage of a microfluidic viscometer that depends on the flow rate change to allow real-time monitoring of fluids' viscosity in pipe systems. The sensor's novel design provides a negligible pressure drop or fluid disturbance when compared to the bulky monitoring sensors due to (1) the microchannel and (2) the mechanically flexible base, which matches different pipes diameters and surfaces. The microchannel ensures the laminar flow in the sensing area regardless of the pipe flow type. Also, the bridge design for the microchannel uses the fluid drive force from the pipe to drive the same fluid into the microchannel, without the need for a pumping system or manual withdrawal samples. In addition, the viscosity sensor's fabrication process was developed with low-cost materials and lithography-free procedures to make the sensor inexpensive. The experimental results show that the viscosity of the fluid flowing through the microchannel is inversely proportional to the measured pressure, at constant pipe flow, due to the change in the microfluidic flow rate. A stand-alone system was integrated with the viscosity sensor for real-time monitoring using wireless communication between the viscosity sensor and a smartphone or a similar device, for a plastic pipe up to 50 cm in diameter.
The disclosed embodiments provide a viscosity sensor that is capable of accurately measuring the viscosity of a fluid flowing through a pipe, by estimating a pressure inside a microchannel formed within the pipe. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.
Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.
This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.
This application claims priority to U.S. Provisional Patent Application No. 62/946,192, filed on Dec. 10, 2019, entitled “ONLINE MONITORING FLUID'S VISCOSITY IN PIPE SYSTEMS,” the disclosure of which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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62946192 | Dec 2019 | US |