Patent Publication Number: US-2021172848-A1

Title: Viscosity sensor for real-time monitoring of tubular conduits and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/946,192, filed on Dec. 10, 2019, entitled “ONLINE MONITORING FLUID&#39;S VISCOSITY IN PIPE SYSTEMS,” the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     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. 
     Discussion of the Background 
     Monitoring a fluid&#39;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&#39; 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&#39;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&#39;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. 
     BRIEF SUMMARY OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a schematic diagram of a viscosity sensor, which is placed inside of a pipe, for measuring a viscosity of a fluid flowing through the pipe; 
         FIG. 2  illustrates various elements of the viscosity sensor; 
         FIG. 3  is a cross-section of a microchannel used by the viscosity sensor for measuring the viscosity of the fluid; 
         FIG. 4  shows a pressure sensor formed within a base of the viscosity sensor for measuring a pressure within the microchannel; 
         FIG. 5  shows a relationship between a total pressure inside a pipe and a viscosity of a fluid flowing through the pipe; 
         FIG. 6A  is a graph showing a pressure of the fluid flowing through the microchannel versus the viscosity of the fluid flowing through the microchannel, and  FIG. 6B  is a graph showing a relationship between the total, dynamic and static pressures inside the microchannel versus the viscosity of the fluid; 
         FIGS. 7A to 7D  illustrate a manufacturing process of the base and pressure sensors of the viscosity sensor, and of a bridge that is added to the base to form the microchannel, and  FIG. 7E  shows a cross-section through the obtained viscosity sensor; 
         FIG. 8  shows a setup for testing the manufactured viscosity sensor; 
         FIGS. 9A and 9B  illustrate the relationship between the measured relative capacitance of the viscosity sensor and the viscosity of the fluid within the pipe; 
         FIG. 10  illustrates a viscosity sensor system in which the viscosity sensor communicates with an external device through a wire that extends through the wall of the pipe in which the viscosity sensor is located; 
         FIG. 11  illustrates another viscosity sensor system in which the viscosity sensor communicates with an external device in a wireless manner through the wall of the pipe in which the viscosity sensor is located; 
         FIGS. 12A to 12C  illustrate the signal received from various pressure sensors of the viscosity sensor system, at the external device, using the wireless implementation; and 
         FIG. 13  is a flow chart of a method for measuring a viscosity of a fluid in a pipe with a viscosity sensor having a microchannel disposed inside the pipe. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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&#39;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  FIG. 1 , a novel fluid viscosity sensor  100  is placed inside a pipe  110  having an internal diameter D. The diameter D can be between a couple of mm (e.g., 1 cm) to any larger size. The viscosity sensor  100  has a base  102  that is placed on the internal surface  110 A of the pipe  110 , a bridge  104  attached to the base  102 , and one or more pressure sensors  106  located in the base  102 . While  FIG. 1  shows the pipe  110  having a circular cross-section, the viscosity sensor discussed herein can be configured to work in a pipe having any transverse cross-section, e.g., rectangular, square, triangular, etc. The base  102  can be made of a flexible material, e.g., polydimethylsiloxane (PDMS), so that the base  102  follows intimately the profile of the internal surface  110 A of the pipe  110 . Other flexible materials may be used as long as they can bend/deform enough to follow the profile of the internal surface of the pipe. However, in another embodiment, the base  102  may be made of a rigid material, which does not follow the profile of the internal surface  110 A, in which case a liquid pocket may be formed between the base and the internal surface of the pipe. The base may be made of a flexible material that has a high friction relative to the material of the pipe. In this way, the base may be simply placed within the pipe and the base adheres to the internal wall of the pipe so that no other means are required for attaching the sensor to the pipe. However, if desired, any type of connection means (e.g., glue, screws, etc.) can be used to attach the base of the sensor to the internal pipe of the wall. A thickness of the base may be a few mm or less. 
     The viscosity sensor  100  is shown in  FIG. 2  as extending along a longitudinal axis X 1 , which is parallel to the longitudinal axis X 2  (shown in  FIG. 1  as entering the page) of the pipe  110 . For simplicity, the pipe  110  is omitted in  FIG. 2 . The base  102  is shown in this figure as being flat, and having a footprint larger than the bridge  104 . The bridge  104  is made of a rigid material, for example, poly(methyl-methacrylate) (PMMA), so that an external pressure exerted by the fluid  112 , which flows through the pipe  110 , on the bridge, does not deform the walls of the bridge. This condition is desired because the pressure sensor  106 &#39;s readings should be indicative of only the liquid&#39;s pressure inside the bridge, and not be influenced by the liquid pressure outside the bridge. Although  FIG. 2  suggests that the length of the bridge  104  is less than the length of the base  102 , that is not required for this configuration to work as a viscosity sensor. One skilled in the art would understand that it is possible to make the bridge  104  longer than the base  102 , for which situation the bridge  104  is placed in direct contact with the internal surface of the pipe  100 , and the base  102  covers the bridge and holds it in place relative to the pipe  110 . Such arrangement still allows the fluid  112  in the pipe  110  to flow through the microchannel formed between the base and the bridge, and the base to follow the profile of the pipe. 
       FIG. 3  shows a cross-sectional view of the base  102  and the bridge  104 . The bridge  104 , when attached to the base  102 , forms an enclosed volume, which defines the microchannel  300 . The bridge  104  has two side walls  104 A and  104 B, and a top wall  104 C in this embodiment. However, the bridge may be made to have a different transversal cross-section, for example, part of a circle, ellipse, a triangle, etc. There is no bottom wall for the bridge, and thus the name “bridge” for this part of the sensor. The two side walls and the top wall define the trench or microchannel  300 . The sizes of the microchannel are the height H, the width W, and the length L. The height H is selected to obtain the microchannel  300 , i.e., a channel for fluid flow which is in the micrometer range. More specifically, the microchannel  300  has a height H between 100 and 500 μm, with a preferred size of substantially 250 μm. The term substantially is defined herein to include any variation of the height within +1-10% of the given value. The width W of the microchannel  300  is selected to be about 3 mm and the length L is selected to be between 3 to 100 mm, with a preferred length of about 60 mm. It is noted that a channel that has the height H larger than 500 μm would likely not work with the concept to be discussed later. A cross-section area A of the microchannel  300  is square in  FIG. 3 , but other shapes may be selected as discussed above. 
     The bridge  104  is made to be solid and have no openings, except for the input  105 A and the output  105 B. 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  105 A and the output  105 B. 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  FIGS. 2 and 3  to be smaller than the width w of the base  102 . In one application, the width W is much smaller than the width w, i.e., it can be a couple of times ( 2  to  10 ) smaller. This situation happens when it is desired that the width w of the base  102  to be almost the same as the internal circumference of the surface  110 A of the pipe  110 . By making the width w of the base so large, it is possible to fix the viscosity sensor to the internal surface of the pipe due exclusively to the natural adherence properties of the PDMS material, i.e., without using a glue or a mechanical means. 
     The pressure sensor  106  is shown in  FIG. 4  having a top electrode/plate  402  and a bottom electrode/plate  404  and these two plates sandwich a hole  400  formed into the base  102 . The hole  400  may be filled with air or with any other dielectric material. The two electrodes  402  and  404  and the air pocket  400  act as a capacitive pressure sensor, so that when the fluid inside the microchannel  300  has a higher pressure than the air inside the hole, it squeezes the top plate  402  toward the bottom plate  404 , which results in the dielectric air gap  400  being reduced. This change in the thickness of the dielectric material can be measured with corresponding electronics (e.g., a controller as discussed later) and can be associated with the pressure exerted by the fluid  112  on the pressure sensor  106 , as discussed later. More than one pressure sensor may be formed in the base  102  to improve the pressure reading&#39;s accuracy. Note that the pressure sensor  106  may have one electrode directly exposed to the fluid flowing through the microchannel  300  and also that electrode is fully formed within the microchannel  300 . In one application, that electrode may be protected from the fluid by being covered with a thin polymeric layer, also discussed later. 
     The viscosity sensor illustrated in  FIGS. 1 to 4  does not require an external flow path or tube contractions to prevent fluid flow interruption, pressure drop, and/or energy loss. Instead, the viscosity sensor uses the volumetric flow rate generated inside the tubular system  110  to drive a small fluidic volume inside the microchannel  300  for volumetric flow rate and/or viscosity measurements under the laminar flow condition using the microfabrication advantages. In other words, the viscosity sensor  100  uses exclusively the microchannel  300  for performing a pressure measurement of only the fluid flowing through the microchannel and from this information, estimates the flow rate and/or the viscosity of the fluid  112  flowing inside the pipe  110 . 
     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&#39;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&#39;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&#39;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 &#39;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&#39;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 P total  generated by (1) the fluid&#39;s weight and (2) the fluid flow&#39;s velocity inside the microchannel  300 . The measured pressure using the capacitive pressure sensor  106  corresponds to the total pressure P Total , which is a combination of the static pressure P Static  and the dynamic pressure P Dynamic , as expressed in equation (1). 
         P   Total   =P   Static   +P   Dynamic .  (1)
 
     The dynamic pressure P Dyamic  is proportional to the square of the volumetric flow rate Q of the fluid, as expressed in equation (2), while the static pressure P static  is proportional to the high of the microchannel  300 . 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       
                         T 
                          
                         otal 
                       
                     
                     = 
                     
                       
                         ρ 
                          
                         g 
                          
                         H 
                       
                       + 
                       
                         
                           1 
                           2 
                         
                          
                         ρ 
                          
                         
                           
                             Q 
                             2 
                           
                           
                             A 
                             2 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where ρ is the fluid&#39;s density, H is the microchannel  300 &#39;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): 
     
       
         
           
             
               
                 
                   
                     C 
                     = 
                     
                       
                         
                           ɛ 
                           0 
                         
                          
                         
                           ɛ 
                           r 
                         
                          
                         
                           A 
                           1 
                         
                       
                       d 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     where d is the thickness of the base  102  (see  FIG. 4 ), which also coincides with the thickness of the dielectric pocket of air  400 , ε r  is the dielectric relative permittivity of the material (air in this case), ε 0  is the permittivity of the free space (8.854×10 12  F/m), and A 1  is the area of the conductive parallel plates  402 ,  404 , which have the sizes of 3 mm×3 mm in this embodiment. Other sizes and shapes may be used. 
     When the pressure exerted by the fluid  112  inside the microchannel  300  increases, the dielectric layer&#39;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: 
     
       
         
           
             
               
                 
                   
                     Q 
                     = 
                     
                       
                         Δ 
                          
                         P 
                          
                         
                           W 
                           2 
                         
                          
                         
                           H 
                           3 
                         
                       
                       
                         1 
                          
                         2 
                          
                         μ 
                          
                         
                           l 
                            
                           
                             ( 
                             
                               W 
                               + 
                               H 
                             
                             ) 
                           
                         
                       
                     
                   
                   . 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     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&#39;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&#39;s length.  FIG. 5  shows the effect of the pipe diameter on the measured pressures at the selected position, with different viscosity ranges. Each tube diameter has a different diagram performance that varies with the viscosity and the pressure ranges because the static pressure increases with the pipes&#39; depths. Therefore, using the microchannel  300  in the tube  110  provides uniform pressure range and behavior with the viscosity depending only on the microchannel flow rate and its constant depth. 
     In contrast to the results of  FIG. 5 , the measurements illustrated in  FIG. 6A  indicate the microchannel  300 ′ depth effect on the viscosity sensor&#39;s performance at a measured point located in the center of the microchannel. The base  102  of the microchannel  300  was connected, for this simulation, to the internal wall of a 4 cm diameter pipe  110 , with a fixed flow rate of the fluid. The results in  FIG. 6A  show a consistent viscosity sensor performance for different microchannels heights H (150, 250, and 450 μm), with a dramatic decrease in the measured pressure with the viscosity of the fluid. At higher fluid viscosities, the volume of the fluid driven in the microchannel decreases, as well as the absolute pressure, for which the dynamic pressure dominates over the static pressure. At high viscosities, the flow rate and the dynamic pressure become too low, and the static pressure becomes dominant particularly for the higher channels, as shown in the graph for the microchannel having the 450 μm height. The microchannel  300  may have any height between 100 and 500 μm. 
       FIG. 6B  illustrates the absolute pressure  600  measured in the microchannel  300 , at the same conditions as in  FIG. 6A , but using a 250 μm channel depth. The total pressure  600  is almost equal to the dynamic pressure  610  and thus, the static pressure  620  measurements are negligible compared to the dynamic pressure  610 . Also, the dynamic pressure behavior is following the trend of the microchannel flowrate  640 , as illustrated in the inset of  FIG. 6B . The inset also shows the flow rate  630  through the pipe  110 . 
     Note that for these measurements, the viscosity sensor  100  was placed into the tube  110  so that the microchannel  300  has its longitudinal axis X 1  parallel to the longitudinal axis X 2  of the tube  110 . This arrangement is also used when the actual viscosity sensor  100  is placed into an actual tube or pipe.  FIG. 6A  shows, at scale, the extremely low profile (i.e., height) of the microchannel  300  relative to the pipe  110 . 
     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  FIGS. 7A and 7B , using three PDMS layers  700 ,  702 , and  704 . In one application, each of the PDMS layers  700 ,  702 , and  704  has a 500 μm thickness. Other values may be used for the thickness. Kapton tape may be used as a shadow mask on the first and third layers  700  and  704 . The Kapton tape is placed to cover the entire surface of the layer and then it is patterned using a CO 2  laser to form 3 mm squares, which may be aligned along a longitudinal line X 3  formed in the middle of the layers  700  and  704 . These squares correspond to squares  710  on the first and third layers as shown in  FIG. 7A . The patterned squares of Kapton tape are then peeled off from the surfaces of the two layers to form corresponding active areas for the capacitance pressure sensors  106 . 
     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  FIG. 7A . The Kapton tape was then completely removed from the PDMS layers  700  and  704 , leaving the active areas with a thin coated layer  712  and  714  of copper, which correspond to plates  402  and  404 . 
     The second PDMS layer  702  was patterned all the way through the PDMS layer thickness using the CO 2  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  FIG. 7A  and then the layers were assembled and bonded together, as shown in  FIG. 7B , using an oxygen plasma technique by exposing the surfaces to oxygen plasma for 60 seconds followed by bringing the surfaces together. The bonds were enhanced by baking the bonded layers for 60 seconds at 80° C. Copper electrodes  722  and  724  were bonded to the flexible plates  712  and  724 , respectively, using a silver paste  726 . After curing the silver paste, the entire assembly was packaged using a PDMS layer  730  to protect the copper electrodes  712  and  714 , and to fix the positions of the layers  700 ,  702 , and  704  to prevent air leaking. 
     Next, the microchannel bridge  104  was fabricated, as shown in  FIG. 7C . The microchannel bridge  104  was fabricated using a 1 mm thickness PMMA sheet. The sheet was patterned using the CO 2  laser to form a 250 μm trench depth into the rectangular shaped piece of the sheet, the rectangular shaped piece having a 3 mm width and a length of up to 60 mm, as also shown in  FIG. 7C . Then, the rectangular shaped piece was cut off from the sheet to obtain the bridge  104  with the trench. After that, the microchannel bridge  104  was attached to the prepared, flexible sensory base  102  using the oxygen plasma bonding method, to obtain the microchannel  300 , and essentially the viscosity sensor  100 , as shown in  FIG. 7D . To ensure a good bonding between the bridge  104  and the base  102 , the viscosity sensor  100  can be repackaged with a thin PDMS coat  740 . A transversal cross-section of the viscosity sensor  100  obtained with the method discussed herein is shown in  FIG. 7E . 
     For characterizing the viscosity sensor  100 , a transparent polyvinyl chloride (PVC) pipe system  800  was built with a 3.8 cm inner diameter D 2  and a 60 cm total system&#39;s length L 2 , as shown in  FIG. 8 . The viscosity sensor  100  was attached to the inner wall  110 A of the pipe  110 . The viscosity sensor  100  was characterized using a pump controller  810  (Catalyst FH100DX Pump), which generates a precise flow rate. The pump was connected to the pipe system and to a fluid reservoir  820 . The viscosity sensor  100  was tested with different fluid  112  viscosities at a steady flow rate of 2,000 ml/min. For each fluid, the system was run for 1 minute to stabilize the selected viscosity before collecting data. At each viscosity, the capacitance was recorded from the pressure sensors  106  using a general-purpose source meter  830 , for example, a Keithley 2400A-SCS. 
     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.  2 L 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/C 0  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 C 0  being the capacitance values with and without the applied pressure. 
       FIGS. 9A and 9B  present the viscometer characterization results for a capacitor sensor located in the center of the microchannel base. The results for the diluted glycerol solutions (shown in  FIG. 9A ) and for the lubricant oils (shown in  FIG. 9B ) show similar behaviors. The capacitance pressure sensor  106 , representing the microchannel flow rate, is inversely proportional to the fluid&#39;s viscosity, as the numerical analysis indicates. The viscous fluids have a lower drive force to flow the fluids into the microchannel  300  at a steady pipe flow, causing a decrease in the microfluidic flowrate, which is translated into a reduction in the capacitive measurements. For these measurements, the capacitive sensor&#39;s readings were calibrated prior to the measurements with known pressures so that a unique mapping can be established between a capacitive reading and a corresponding pressure. The capacitive pressure sensors were characterized using the multisource  830  for different water depths. From these measurements, it can be seen that by reading the change in the capacitance of the sensor  106  while within the microchannel  300 , it is possible to uniquely calculate the corresponding viscosity of the fluid flowing inside the microchannel  300 . 
     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  FIGS. 10 and 11 .  FIG. 10  shows the wired implementation of a viscosity sensor system  1000  in which one or more wires  1010  extend through the wall  111  of the pipe  110 , from the viscosity sensor  100  to a connection box  1012 . The connection box  1012  may include electronics for facilitating data exchange between the viscosity sensor and an external controller  1020 . The figure also illustrates the fluid flow A through the microchannel  300  and the fluid flow B through the pipe  110 . If the connection between the pressure sensor  106  and the controller  1020  (which can include a processor  1022  and a memory  1024 ) is fully wired, then additional wires  1014  electrically connect the connection box  1012  to the controller  1020 . Alternatively, it is possible that the connection box  1012  includes a transmitter or transceiver  1016  that communicates in a wireless manner with a corresponding transceiver  1026 , which is part of the controller  1020 . The two transceivers may use any protocol and any frequency spectrum (FM, Wi-Fi, Bluetooth, etc.) for communication and data exchange. One or more of these devices may also be fitted with an appropriate power source to supply electrical energy to the transceivers. The embodiment illustrated in  FIG. 10  can be implemented in any type of pipe, i.e., even a type made of a material that suppress electromagnetic waves from passing through the wall. 
     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.  FIG. 11  shows the viscosity sensor system  1000  including the viscosity sensor  100 , the microcontroller  1020  and a battery  1120  attached to the base  102 . The battery  1120  is configured to supply power to the pressure sensor  106  and/or to the various elements of the microcontroller  1020 . The figure also show one pressure sensor  106  and one of its terminal  722 . Wires  1130  are visible and they are configured to link the pressure sensor  106  to the microcontroller  1020 . For this embodiment, the viscosity sensor  100  was integrated with commercially available electronics to create a standalone functional system installed inside a pipe. In one application, a Bluetooth Low Energy (BLE) enabled Programmable System on Chip (PSoC) from Cypress™ can be used as the controller  1020 . This controller has an internal capacitance to digital convertor (CDC) to connect one or more capacitive pressure sensors  106  to the controller without the need for additional Integrated Circuits (ICs), or passive components. The raw CDC values from the pressure sensors  106  can be converted into a capacitance unit using a calibration plot that is obtained prior to deploying the viscosity sensor. Furthermore, the PSoC has the BLE functionality built-in to enable sending the data wirelessly through the pipe  110 . The viscosity sensor system  1000 , which includes the viscosity sensor  100  and the controller  1020 , is powered using a coin cell battery  1120  due to the advantage of the low power consumption of the chip. The battery  1120  can be replaced with an energy generation device that uses the fluid flow or other means to generate energy. The controller was connected to the pressure sensors with the wires  1130  and everything was packaged via a PDMS layer  1140  for insulation. 
     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  FIGS. 12A to 12C , respectively. It is noted that the three curves are similar to each other. It is also noted that only one pressure sensor is needed for measuring the flow rate through the pipe  110  and/or for determining the viscosity of the fluid. In this embodiment, three pressure sensors are used to improve the accuracy of the estimated flow rate and/or viscosity, and for redundancy. 
     A method for measuring a viscosity of a fluid now discussed with regard to  FIG. 13 . The method includes a step  1300  of attaching a viscosity sensor  100  to an inside of a pipe  110 , the viscosity sensor  100  having a base  102  made of a flexible material that directly attaches to the inside of the pipe  110 , a bridge  104  made of a rigid material, where the bridge  104  is attached to the base  102  to form a microchannel  300 , and a pressure sensor  106  formed within the base  102 , a step  1302  of flowing a fluid  112  through the pipe  110  so that part of the fluid flows through the microchannel  300 , a step  1304  of measuring a change in a capacitance associated with the pressure sensor  106 , as the fluid  112  flows within the microchannel  300 , and a step  1306  of determining the viscosity of the fluid  112  flowing through the pipe  110  based on the measured change in capacitance of the pressure sensor  106 , within the microchannel  300 . 
     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&#39; viscosity in pipe systems. The sensor&#39;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&#39;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. 
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