GB2526861A

GB2526861A - Device for measuring the shear stress of a viscous fluid

Info

Publication number: GB2526861A
Application number: GB1410012.7A
Authority: GB
Inventors: August Peter Zurk; Christian Kukla
Original assignee: Montanuniversitaet Leoben
Current assignee: AUGUST PETER ZURK; Montanuniversitaet Leoben
Priority date: 2014-06-05
Filing date: 2014-06-05
Publication date: 2015-12-09
Also published as: GB201410012D0; WO2015185746A1

Abstract

A device 100 for measuring a shear stress of a fluid comprises an inlet section 101 through which the fluid is guidable, wherein the inlet section is formed such that the fluid streams through it along a first streaming direction 102. A tube 103 is connected to the inlet section such that the fluid is streamable from the inlet through the tube, wherein the tube comprises a transition section 104 formed such that the fluid streaming through the tube is deflected from the first direction 102 to a second different streaming direction 105. The tube 103 is deformable by deflecting the fluid from the first streaming direction to the second streaming direction within the transition section 104. A deformation sensor 106 measures a deformation of the tube indicative of the shear stress of the fluid. Several transition sections and sensors may be included.

Description

Device for Measuring the Shear Stress of a Viscous Fluid

Field of invention

The present invention relates to a device and a method for measuring a shear stress of a fluid.

Art Background

In various technical fields, such as in the food industry, in the pharmaceutical industry or in the plastics processing industry, it is an aim to analyze the condition of the fluid to be processed (such as plastic material or cream) during the manufacturing process. For example, injection molding is a manufacturing process for producing parts from thermoplastic, elastomeric and thermosetting plastic materials. Thermoplastic materials are fed into a heated barrel, mixed and forced into a mold cavity where it cools and solidifies to the configuration of the cavity. Elastomeric and thermosetting materials are injected into the heated mold cavity, where they harden by chemical reaction.

Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.

Generally, an extruder device is used for delivering a predetermined amount of plastic material into the cavity or an extrusion die. The plastic material comprises different viscosity characteristics at certain temperatures and pressures. Hence, it is an aim to determine the shear stress and with the knowledge of the flow rate, the viscosity of the used plastic material in order to provide an accurate amount of plastic material delivered by the extruder into the cavity of the injection molding device or through the extrusion die.

It is known for example to measure the pressure of the fluid which flows through a tube. Accordingly, a pressure gauge is used which is coupled to a pressure hole within the tube through which the fluid flows. However, such pressure holes may be blocked and may cause turbulences within the fluid flow inside the tube. Additionally, such holes do not allow a thorough cleaning of the channels, which is important for critical materials like PVC, food, pharmaceuticals etc.

Summary of the Invention

It may be an objective of the present invention to provide an exact determination of the shear stress of a fluid.

This objective is solved by a device for measuring a shear stress of a fluid and by a method for measuring a shear stress of a fluid according to the independent claims.

According to a first aspect of the present invention, a device (e.g. a so called shear stress sensor or rheometer device) for measuring a shear stress of a fluid is presented. The device comprises an inlet section, a tube and at least one deformation sensor. The fluid is guidable through the inlet section, wherein the inlet section is formed such that the fluid streams through the inlet section along a first streaming direction. The tube is connected to the inlet section such that the fluid is streamable from the inlet section through the tube, wherein the tube comprises a transition section which is formed such that the fluid streaming through the tube is deflected from the first streaming direction to a second streaming direction. The first streaming direction differs to the second streaming direction, wherein the tube is formed such that the tube is deformable by deflecting the fluid from the first streaming direction to the second streaming direction within the transition section. The deformation sensor measures a deformation of the tube, wherein the measured deformation is indicative of the shear stress of the fluid.

According to a further aspect of the present invention a method for measuring a shear stress of a fluid presented. The method comprises the step of guiding the fluid through an inlet section of a (e.g. a so called shear stress sensor) device, wherein the inlet section is formed such that the fluid streams through the inlet section along a first streaming direction. Furthermore the fluid is guided through a tube which is connected to the inlet section, wherein the tube comprises a transition section which is formed such that the fluid streaming through the tube is deflected from the first streaming direction to a second streaming direction. The first streaming direction differs to the second streaming direction, wherein the tube is formed such that the tube is deformable by deflecting the fluid from the first streaming direction to the second streaming direction within the transition section. A deformation of the tube is measured by a deformation sensor, wherein the measured deformation is indicative of the shear stress of the fluid.

The device according to the present invention may be used for example in an injection molding system or an extrusion line for measuring the shear stress and with known volumetric flow rate e.g. the viscosity of a plastic material. For example, the inlet section of the device may be coupled to an outlet of an extruder of the receiving molding system. Hence, the shear stress and the calculated viscosity and hence the material characteristic of the plastic material delivered by the extruder may be determined. At an outlet section of the device, for example a molding press comprising a cavity for receiving the plastic material or the extrusion die is coupled.

However, the above described device for measuring the shear stress of the fluid may be used in the pharmaceutical industry, wherein pharmaceutical materials are used. Additionally, the above described device may be used in the field of food technology where fluids are used as well. In general it can be used in all industries where a fluid is pumped, e.g. also in the processing of metals. Moreover, the device according to the present invention may be used, amongst others, in the field of cosmetic industry, construction material industry, chemical industry, in particular, color (vanish) material industry and plastic processing industry.

The fluid which may be analysed by the device according to the present invention may be for example mustard, ketchup, pulps, salves, emulsions, ice cream, chocolate or glaze.

Additionally, the fluid which may be analysed by the device according to the present invention may be a solidifiable fluid (liquid), such as dough, sausage mush, liquid concrete, jelly, dissolver containing color or resin.

Furthermore, the fluid which may be analysed by the device according to the present invention may be liquefiable solid material, such as tar, bitumen, thermoplast material, glass or metal melt.

The shear stress of the fluid is a measure or parameter of its resistance to gradual deformation. The parameter "shear stress" gives information of specific material properties and conditions of the fluid to be analyzed. For example, on the basis of the parameter "shear stress", the viscosity of the fluid is measurable.

The inlet section is formed for receiving the fluid. The inlet section is formed such that the fluid streams along a predefined first streaming direction. The inlet section may be in an exemplary embodiment an integral part of the tube, for example. Furthermore, the inlet section may be formed in a cone shaped profile. The flow diameter of the cone shaped profile may reduce along the flow direction of the fluid such that the cone shaped profile forms a kind of nozzle.

The tube includes a fluid channel for guiding the fluid through the tube. The tube is connected to the inlet channel for receiving the fluid which streams through the inlet section. The tube comprises a transition section, such as a curve section, for deflecting the fluid from the first streaming direction to the second streaming direction. The transition section may be arranged directly downstream of the inlet section. Alternatively, a straight section of the tube which comprises the first streaming direction for the fluid may be arranged between the fluid inlet and the transition section.

The deflection of the fluid from the first streaming direction to the second streaming direction causes mechanical loads, such as shear stress, frictional forces, bending forces and/or torsion forces, which acts within the transition section onto the material of the tube. The mechanical loads caused by the deflection of the fluid cause a deformation of the tube, at least in the region of the transition section. Furthermore, by the pressure and the shear stress, respectively, of the fluid, the tube may be widened and hence increases its diameter or the transition section may be bended by the deflection, such that the angle between the first streaming direction and the second streaming direction changes, for example.

The above described deformation caused by the pressure and the shear stress, respectively, of the fluid is measurable by the deformation sensor(s). The measured deformation of the tube which is measured by the deformation sensor(s) is indicative of the shear stress of the fluid. The deformation sensor may also measure the deformation force which is indicative of a deformation of the tube. Hence, the device may comprise a stopper element which is arranged such that the tube is pressed against the stopper element if the fluid streams through the tube. Hence, the shear stress of the fluid generates the deformation and in particular the deformation force which acts against the stopper element. The deformation force (such as a compressive force acting against the stopper element), which is indicative to a deformation, is measured by the deformation sensor. For example, the deformation sensor is arranged between the stopper element and the tube.

Furthermore, the deformation sensor may measure the deformation by measuring a deformation of a change of an angle of a reference section of the tube. For example, the reference section may be an end section of the tube, wherein an angle between the end section and a defined reference line may be measured. The angle change which occurs if the fluid flows through the tube may be indicative of the deformation and hence of the shear stress of the fluid.

For example, the tube may comprise a helical run, wherein the deformation sensor measures the distance of two adjacent windings of the helical tube, wherein the distance between the adjacent windings is indicative of the deformation and hence of the shear stress of the fluid flowing through the tube.

For example, each kind of fluid comprises a predeterminable shear stress which is linked via the information about a measured volumetric flow rate e.g. to the viscosity of the fluid at predefined environmental conditions, which causes a definable deformation of the tube. Hence, by measuring the deformation of the tube, the shear stress is determined and for example the viscosity can be calculated in an accurate and precise manner.

For example, the deformation sensor measures specifically the deformation of the transition section. However, sections of the tube which are arranged upstream or downstream of the transition section may also deform if fluid streams through the tube and the transition section, respectively. Hence, the deformation sensor(s) may be arranged such that the deformation of the sections upstream or downstream of the transition sections may be measured too in order to determine an accurate shear stress and further the viscosity of the fluid.

According to a further exemplary embodiment, the deformation sensor(s) comprise(s) an optical sensor and/or a strain gauge sensor. The optical sensor, such as a camera, may measure a change of the diameter of the tube and/or of the orientation and/or the angle between the main flow directions hence the change in the bending(s) of the tube, in particular at the transition section. Similarly, a strain gauge sensor comprising a resistive wire strain arranged at the surface of the tube may be used for measuring the deformation. The deformation sensor may also form a sensor system comprising a plurality of optical sensors and strain gauge sensors. The sensor for measuring the deformation may be for example a sensor which is based on inductive, capacitive, resistive and/or piezo-resistive sensor technologies.

According to a further exemplary embodiment, the tube comprises a further transition section which is formed spaced apart from the transition section.

The further transition section is formed such that the fluid is deflected within the further transition section from the second streaming direction to a third streaming direction when flowing through the tube. The tube is formed such that the tube is further deformable by deflecting the fluid from the second streaming direction to the third streaming direction within the transition section, wherein the measured further deformation is further indicative of the shear stress of the fluid.

Hence, the measuring of the shear stress may be more precise if more than one measuring points and hence more than one transition sections of the tube are available. Hence, the tube may comprise for example an S-like run or path comprising at least two transition sections. In a further exemplary embodiment, the tube may comprise a meander-like shape comprising a plurality of transition sections. Furthermore, measuring errors caused due to disturbances within the channel of the tube may be detected.

According to a further exemplary embodiment the device further comprises an outlet section through which the fluid is guidable. The outlet section is formed such that the fluid streams from the tube through the outlet section. The outlet section may comprise a cone like shape comprising a flow diameter which increases along the flow direction of the fluid through the outlet section.

Hence, the outlet section may function as a diffusor for providing a proper flow characteristic of the fluid exiting the tube.

According to a further exemplary embodiment the device further comprises a further outlet section through which the fluid is guidable, wherein the tube is decoupled from the outlet section and the further outlet section, such that an exit of the tube is coupleable selectively to the outlet section or the further outlet section due to a deformation of the tube caused by the shear stress of the fluid. For example, if a shear stress of a first type of fluid is lower, the deformation of the tube is small such that the exit of the tube is coupled to the outlet section. However, if a shear stress of a second type of fluid is higher than the first type, the deformation of the tube is larger such that the exit of the tube is coupled to the further outlet section. Hence, a mechanical control of a fluid guidance is generated. Furthermore, also three or more spaced apart outlet sections may be coupleable selectively to the exit of the tube due to a deformation of the tube caused by the shear stress of the fluid.

The deformation of the tube is dependent on the shape/path of the tube, the material of the tube, the wall thickness, the tube profile, etc., such that the deformation of the tube in all dimension caused by a fluid flowing through the tube may be predetermined. Furthermore, it may be assured, that the deformation of the tube comprises the same deformation (dependent on a certain fluid viscosity) for common environmental conditions (same shear stress of the fluid, temperature, (environmental) pressure).

According to a further exemplary embodiment the device further comprises a reference body which is coupled to the inlet section and to the outlet section.

A further deformation sensor for measuring a reference deformation of the reference body is provided, wherein the reference deformation is comparable with the measured deformation of the tube for determining a corrected deformation of the tube.

The deformation sensor measures the deformation of the tube and the further deformation sensor measures the deformation of the reference body. Hence, the measured deformation of the tube and the further deformation measured of the reference body will be compared and correlated such that the deformation of the tube is comparable to present environmental conditions, such as the environmental temperature and an environmental pressure. This means that the deformation of the reference body is indicative of the deformation caused by the environmental conditions (e.g. temperature, mechanical distortion external loads...). Thus, the corrected deformation of the tube caused by the fluid without the environmental conditions may be calculated. Hence, the deformation of the tube which is caused only by the fluid and not caused by the environmental conditions is determinable. Hence, -10 -a more precise definition of the shear stress and the viscosity of the fluid is achievable.

For example, a deformation map of the reference body and the tube may be established e.g. under laboratory conditions if no fluid is flowing through the tube. The map comprises deformation values for the reference body and the tube under predefined environmental conditions, such as under certain environmental temperatures and environmental pressures, for example.

Hence, under operation, fluid is flowing through the tube and causes a deformation of the tube, wherein the corrected deformation of the tube may be read out of the map.

The reference body may be made of a similar material as the tube, for example may be made of metal material, such that the reference body may have similar material characteristics. Furthermore, the reference body may comprise similar geometrical extensions with respect to the tube. However, the material between the reference body and the tube may differ as well because the deformation of the reference body is measured by the further deformation sensor. In a further exemplary embodiment, the referenced body may be an identical copy of the tube and may form a so-called blind copy of the tube.

The reference body may be coupled with its exit section to the outlet section or may be decoupled from the outlet section and the further outlet section, respectively. For example, if the tube is decoupled from the outlet section and the further outlet section, the reference body may also be decoupled from the respective outlet sections, such that a deformation of the reference body and hence a movement of the exit section of the reference body may be indicative of the deformation caused by the environmental conditions.

-11 -However, according to a further exemplary embodiment, the reference body forms a frame surrounding the tube. Hence, the frame may additionally stabilize the tube and forms a robust design of the device.

According to a further exemplary embodiment, the device further comprises a temperature sensor for measuring the temperature of the fluid and/or the temperature of a wall of the tube.

According to a further exemplary embodiment, the device further comprises a pressure sensor for measuring the pressure of the fluid within the tube.

According to a further exemplary embodiment, the device further comprises a flow rate sensor for measuring the flow rate of the fluid within the tube. For example, the viscosity of the fluid may be determined by using the parameter "flow rate" and the parameter "shear stress".

According to a further exemplary embodiment, the device further comprises a temperature control unit for controlling the temperature of an environment surrounding the tube and/or for directly controlling the temperature of the tube. Hence, if the shear stress of the fluid is too high or too low, the temperature control unit may be controlled accordingly such that the tube and hence the fluid flowing through the tube changes its temperature. Hence, by increasing the temperature, this shear stress and hence the viscosity of the fluid will be reduced and by reducing the temperature, the shear stress and hence the viscosity of the fluid will be increased. The temperature control unit may be connected to a monitoring unit as described below and may be controlled by a control unit and in particular to a flow control unit as described below.

-12 -According to a further exemplary embodiment, the device further comprises a monitoring unit for monitoring the determined shear stress of the fluid, wherein the monitoring unit comprises a comparator unit which compares an actual value of the determined shear stress with a nominal value of the shear stress of the fluid. Hence, if the actual value mismatches with the nominal value, the monitoring unit may give an alarm, for example. Alternatively, the monitoring unit may be connected to a control unit, wherein the control unit may control environmental parameters, such as the temperature surrounding the device, or control the flow rate of the fluid flowing through the tube until the actual value matches with the nominal value. However, in order to provide a more accurate determination of the shear stress of the fluid, the measured temperature and/or the measured pressure may be considered. The pressure level within the tube may be calculated out of the signals by the deformation sensor(s), if it is positioned accordingly.

Additionally, the flow control unit is adapted for controlling a flow rate of the fluid flowing through the tube. Hence, the flow control unit may be coupled for example to an actuator, such as a mass flow valve or an extruder, in order to control the mass flow through of the fluid through the device. The flow control unit may comprise a transducer which converts the measured signals (e.g. deformation signals from the deformation sensors and/or temperature signals from the temperature sensors) in a control signal for controlling the actuator.

Hence, a desired output mass/volume flow of the fluid is adjustable.

The device may further comprise a fluid pump which is connected to the control unit such that the control unit may control the fluid, in order to control the fluid flow flowing through the tube. As described above, the control unit may be coupled to the monitoring unit, wherein the control unit may control the fluid pump under consideration of the actual value of the flow rate and the nominal value of the flow rate of the fluid.

-13 -Hence, by the device according to the present invention, it is not necessary to use pressure holes or other perforations within the tube such that the tube is not weakened and the fluid flow through the tube is not disturbed. The shear stress of the fluid is directly derivable from the deformation of the tube and with known volumetric flow rate the viscosity can be calculated. Additionally, the device according to the present invention is robust and hence the lifespan of the device is increased.

A further benefit of the present device is that the shear stress of the fluid is determinable in the main stream of the fluid making further bypass fluid streams for measuring reasons obsolete. In combination with the deformation sensor the information of the volumetric flow rate is determinable and therefore the viscosity on the basis of the measured shear stress and volumetric flow rate is determinable.

Furthermore, if the tube comprises a plurality of transition sections, the respective deformation of the transition sections may be compared, wherein a variety of the deformation between the respective transition sections may be indicative of a pressure loss or increase of the fluid along the fluid path.

Furthermore, the device according to the present invention may be applied for different flow rates of the fluid and for varying counter pressures which may occur at the outlet section of the device.

Furthermore, the device according to the present invention may be designed with only one transition section, such that the flow path of the fluid through the device may be reduced dramatically. Hence, the device according to the present invention only needs a very small installation space.

-14 -It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to apparatus type claims whereas other embodiments have been described with reference to method type claims.

S However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters, in particular between features of the apparatus type claims and features of the method type claims is considered as to be disclosed with this application.

Brief Description of the Drawings

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of the embodiment but to which the invention is not limited.

Fig. 1 shows a schematic view of a device for measuring a shear stress of the fluid according to an exemplary embodiment of the present invention, Fig. 2 shows a schematic view of the tube of the device according to an exemplary embodiment of the present invention, Fig. 3 shows a schematic view of an extrusion system which comprises the device according to an exemplary embodiment of the present invention, -15 -Fig. 4 shows a schematic view of the tube of the device which is coupleable to two different outlet sections according to an exemplary embodiment of the present invention, and Fig. 5 shows a schematic view of the tube of the device according to the exemplary embodiment shown in Fig. 4.

Detailed Descriition of Exemilarv Embodiments The illustrations in the drawings are schematic. It is noted that in different figures similar or identical elements are provided with the same reference signs.

Fig. 1 shows a device 100 for measuring a shear stress of a fluid according to an exemplary embodiment of the present invention. The device 100 comprises an inlet section 101, a tube 103 and a deformation sensor 106. Fluid which shear rate is to be measured is guidable through the inlet section 101, wherein the inlet section 101 is formed such that the fluid streams through the inlet section 101 along a first streaming direction 102. The tube 103 is connected to the inlet section 101 such that the fluid is streamable from the inlet section 101 through the tube 103, wherein the tube 103 comprises a transition section 104 which is formed such that the fluid streaming through the tube 103 is deflected from the first streaming direction 102 to a second streaming direction 105. The first streaming direction 102 differs to the second streaming direction 105, wherein the tube 103 is formed such that the tube 103 is deformable by deflecting the fluid from the first streaming direction 102 to the second streaming direction 105 within the transition section 104. The deformation sensor 106 measures a deformation of the tube 103, wherein the measured deformation is indicative of the shear stress of the fluid.

-16 -The device 100, also called shear stress sensor or rheometer device, may be used for example in an extrusion system for measuring the shear stress of a plastic material (see an exemplary embodiment in Fig. 3).

The inlet section 101 is formed for receiving the fluid. The inlet section 101 is formed such that the fluid streams along a predefined first streaming direction 102. The inlet section 101 comprises a cone shaped profile, wherein the flow diameter of the cone shaped profile reduces along the first flow direction 102 of the fluid such that the cone shaped profile forms a kind of nozzle.

The tube 103 includes a fluid channel for guiding the fluid through the tube.

The tube 103 is connected to the inlet channel 101 for receiving the fluid which streams through the inlet section 101. The tube 103 comprises a transition section 104, such as a curve section, for deflecting the fluid from the first streaming direction 102 to the second streaming direction 105. A straight section of the tube 103 which comprises the first streaming direction 102 for the fluid may be arranged between the fluid inlet 101 and the transition section 104.

The deflection of the fluid from the first streaming direction 102 to the second streaming direction 105 causes mechanical loads, such as shear stress, frictional forces, bending forces and/or torsion forces, which acts within the transition section 104 onto the material of the tube 103. The mechanical loads caused by the deflection of the viscous fluid cause a deformation of the tube 103, at least in the region of the transition section 104. In particular, by the pressure of the fluid, the tube 103 may be widened and hence increases its diameter or the transition section 104 may be bended by the mechanical loads, such that the angle between the first streaming direction 102 and the second streaming direction 105 changes, for example.

-17 -The deformation caused by the deflection of the fluid is measurable by the deformation sensor (system) comprising deformation sensors 106, 106' and/or 106". The measured deformation of the tube which is measured by the deformation sensor 106 is indicative of the shear stress of the fluid. Hence, by measuring the deformation of the tube 103, the shear stress is determined in an accurate and precise manner.

For example, the deformation sensor 106" is located in the transition section 107' and measures specifically the deformation of the transition section 107".

However, sections of the tube which are arranged upstream or downstream of the respective transition sections 104, 107, 107" do also deform if fluid streams through the tube 103 and the transition sections 104, 107, 107", respectively. Hence, the deformation sensors 106, 106' are arranged such that the deformations of the sections upstream or downstream of the transition sections 104, 107, 107" are measured in order to determine an accurate shear stress of the fluid. However, in other exemplary embodiments also more than three sensors 106, 106', 106" may be applied.

The deformation sensors 106, 106', 106" measure a change of the diameter of the tube 103 and/or of the orientation and hence the bending of the tube 103, in particular at the transition sections 104, 107, 107', 107". Similarly, a strain gauge sensor comprising a resistive wire strain arranged at the surface of the tube 103 may be used for measuring the deformation. The deformation sensors 106, 106', 106" may also form a sensor system comprising a plurality of optical sensors and strain gauge sensors.

As shown in Fig. 1 and as described above, the tube 103 comprises further transition section 107, 107', 107" which are formed spaced apart from each other and from the transition section 104. The further transition section 107, -18 - 107', 107" are formed such that the fluid is deflected within the further transition sections 107, 107', 107" from the second streaming 105 or another streaming direction to a third streaming direction 108 when flowing through the tube 103. Hence, the tube 103 may comprise as shown in Fig. 3 an S-like run or path comprising at least four transition sections 104, 107, 107', 107".

Furthermore, measuring errors caused due to disturbances within the channel of the tube 103 may be detected.

The device 100 further comprises an outlet section 109 through which the fluid is guidable. The outlet section 109 is formed such that the fluid streams from the tube 103 through the outlet section 109. The outlet section 109 comprises a cone like shape comprising a flow diameter which increases along the flow direction of the fluid through the outlet section 109.

Furthermore, a reference body 110 is shown which is coupled to the inlet section 101 and to the outlet section 109. A further deformation sensor 111 for measuring a reference deformation/temperature of the reference body 110 is provided, wherein the reference deformation is comparable with the measured deformation of the tube 103 for determining a deformation which is free of environmental influences of the tube.

The deformation sensor 106, 106', 106" measures the deformation of the tube 103 and the further deformation sensor 111 measures the deformation of the reference body 110. Hence, the measured deformation of the tube 103 and the further deformation measured of the reference body 110 will be compared and correlated such that the deformation of the tube 103 is comparable to present environmental conditions, such as the environmental temperature, an environmental pressure, humidity and mechanical loads from outside the shear stress sensor. This means that the deformation of the reference body 110 is indicative of the deformation caused by the environmental conditions.

-19 -Thus, the corrected deformation of the tube 103 caused by the fluid without the environmental conditions may be calculated. Hence, the deformation of the tube 103 which is caused only by the fluid and not caused by the environmental conditions is determinable.

The reference body 110 shown in Fig. 1 forms a frame surrounding the tube 103. Hence, the frame may additionally stabilize the tube 103 and forms a robust design of the device.

Fig. 2 shows a sectional view of the tube 103 of the device 100 as shown in Fig. 1. The device 100 further comprises a control unit 200 which is connected e.g. to the deformation sensors 106, 106', 106" for receiving the sensor data.

Furthermore, the control unit 200 may control a flow rate of the fluid flowing through the tube 103. Hence, the control unit 200 may be coupled for example to a mass or volume flow valve in order to control the mass or volume flow through of the fluid through the device 100. Hence, the control unit 200 may be coupled to the control unit of the injection moulding machine or the extruder in order to change the screw speed to different values in order to change the output of the machinery. Hence, a desired output mass flow of the fluid is adjustable.

Fig. 3 shows an extrusion system which comprises the device 100 shown in Fig. 1 and Fig. 2. The inlet section 101 of the device 100 is coupled to an outlet of an extruder 301. Hence, the shear stress and hence,knowing the volumetric flow rate, the calculated viscosity and hence the material characteristic of the plastic material delivered by the extruder 301 is determined by the device 100. A nozzle section 302 is connected to an extrusion die at an outlet section 109 of the device 100.

-20 -The device further comprises temperature sensors 303, 303', 303" for measuring the temperature values Ti, T2, T3 of the fluid within the tube 103.

Furthermore, a temperature controlling unit comprises e.g. the heating units 304 to 308 which are arranged along the sensor system for controlling the temperature of the fluid flowing through the tube 103. The heating units 304 to 308 may comprise a respective further temperature sensor T and a heating device or temperature control device TC for adjusting the temperature of the fluid. Furthermore, an environmental temperature TA surrounding the tube 103 may be measured for improving the calculation of the corrected deformation of the tube 103.

Moreover, the fluid pressure pv and the temperature Tmv of the fluid exiting the extruder 301 may be measured. For example, the control unit 200 may control the extruder 301 such that by varying the rotational speed n of the extruder 301 a mass or volume flow is adjustable. In order to control the mass or volume flow of the fluid through the extruder 301 more accurate, the temperature Tex and pEX of the fluid at the inlet of the extruder 301 is measurable.

The device 100 and the extruder system, respectively, further comprise pressure sensors for measuring a pressure pn, pv of the fluid upstream and downstream of the device 100. Further temperature measures Tmn and Tmv may be taken upstream and downstream of the device 100.

Fig. 4 shows the tube 103, 103' of the device 100 which is coupleable to two different outlet sections 109, 401 according to an exemplary embodiment of the present invention.

Fluid is guidable from the tube 103, 103' either through the outlet section 109 or through the further outlet section 401. Accordingly, the tube 103, 103' is -21 -structurally decoupled from the outlet section 109 and the further outlet section 401, such that an exit section 402 of the tube 103, 103' is coupleable selectively to the outlet section 109 or the further outlet section 401 due to a deformation of the tube 103, 103 caused by the shear stress of the fluid.

In Fig. 4, one tube 103, 103' is shown in two operating states. A second type of fluid flows in one operating state (in a first shear stress load) through the tube 103 and another first type of fluid flows in another operating state (in a second shear stress load) through the tube 103'.

For example, if a shear stress of a first type of fluid is lower, the deformation of the tube 103' is small such that the exit 402' of the tube 103' is coupled to the further outlet section 401. The lower the viscosity of a fluid, the lower the deformation of the tube 103, 103' and hence the lower the stretching of the tube 103, 103'.

However, if a shear stress and a viscosity of a second type of fluid is higher than the first type of fluid, the deformation of the tube 103 (and hence the stretching of the tube 103) is larger such that the exit 402 of the tube 103 is coupled to the outlet section 109. Hence, a mechanical control of a fluid guidance is generated. Furthermore, also three or more spaced apart outlet sections may be coupleable selectively to the exit 402 of the tube 103, 103' due to a deformation of the tube 103, 103' caused by the shear stress of the respective fluid types.

Fig. 5 shows a more detailed view of the tube 103, 103' of the device 100 shown in Fig. 4. If the fluid has a higher shear stress, the fluid tries to form a flow path through the tube 103, 103' with lower resistance. Hence, the fluid flowing through tube 103 causes a deformation of the transition section 104 such that the tube 103 is more stretched and straighter, so that it is easier for -22 -the fluid to flow through the straightened tube 103. The tube 103' is in an operating state, wherein no fluid or a fluid comprising a reduced shear stress flows through the tube 103'.

The deformation caused by the fluid e.g. at the transition section is measured by the deformation sensor 106.

It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

-23 -List of reference signs: device 101 inlet section 102 first streaming direction 103 tube 104 transition section second streaming direction 106 deformation sensor 107 further transition section 108 third streaming direction 109 outlet section reference body 111 further deformation sensor control unit 301 extruder 302 nozzle 303 temperature sensor 304-308 heating units 401 further outlet section 402 exit section

Claims

-24 -CLAIMS: 1. Device (100) for measuring a shear stress of a fluid, the device (100) comprising an inlet section (101) through which the fluid is guidable, wherein the inlet section (101) is formed such that the fluid streams through the inlet section (101) along a first streaming direction (102), a tube (103) which is connected to the inlet section (101) such that the fluid is streamable from the inlet section (101) through the tube (103), wherein the tube (103) comprises a transition section (104) which is formed such that the fluid streaming through the tube (103) is deflectable from the first streaming direction (102) to a second streaming direction (105), wherein the first streaming direction (102) differs to the second streaming direction (105), wherein the tube (103) is formed such that the tube (103) is deformable by deflecting the fluid from the first streaming direction (102) to the second streaming direction (105) within the transition section (104), and a deformation sensor (106) for measuring a deformation of the tube (103), wherein the measured deformation is indicative of the shear stress of the fluid.
2. Device (100) according to claim 1, wherein the deformation sensor (106) measures the deformation of the transition section (104).
3. Device (100) according to claim 1 or 2, wherein the deformation sensor (106) comprises an optical sensor, a range sensor and/or a strain gauge sensor and/or a piezo element.
4. Device (100) according to one of the claims 1 to 3, -25 -wherein the tube (103) comprises at least one further transition section (107) which is formed spaced apart from the transition section (104), wherein the further transition section (107) is formed such that the fluid is deflected within the further transition section (107) from the second streaming direction (105) to a third streaming direction (108) when flowing through the tube (103), wherein the tube (103) is formed such that the tube (103) is further deformable by deflecting the fluid from the second streaming direction (105) to the third streaming direction (108) within the transition section (104), wherein the measured further deformation is further indicative of the shear stress of the fluid.
5. Device (100) according to one of the claims 1 to 4, further comprising an outlet section (109) through which the fluid is guidable, wherein the outlet section (109) is formed such that the fluid streams from the tube (103) through the outlet section (109).
6. Device (100) according to claim 5, further comprising a further outlet section through which the fluid is guidable, wherein the tube (103) is decoupled from the outlet section (109) and the further outlet section (401), such that an exit (402) of the tube (103) is coupleable selectively to the outlet section (109) or the further outlet section (401) due to a deformation of the tube (103) caused by the shear stress of the fluid.
7. Device (100) according to claim 5 or 6,further comprising a reference body (110) which is coupled to the inlet section (101) , and a further deformation sensor (111) for measuring a reference deformation of the reference body (110), -26 -wherein the reference deformation is comparable with the measured deformation of the tube (103) for determining a corrected deformation of the tube (103).
8. Device (100) according to claim 7, wherein the reference body (110) forms a frame surrounding the tube (103).
9. Device (100) according to one of the claims 1 to 8, further comprising a temperature sensor (303) for measuring the temperature of a wall of the tube (103).
10. Device (100) according to one of the claims 1 to 9, further comprising a pressure sensor for measuring the pressure of the fluid within the tube (103).
11. Device (100) according to one of the claims 1 to 10, further comprising a flow rate sensor for measuring the flow rate of the fluid within the tube (103).
12. Device (100) according to one of the claims 1 to 11, further comprising a temperature control unit for controlling the temperature of an environment surrounding the tube (103) and/or for directly controlling the temperature of the tube (103).
13. Device (100) according to one of the claims 1 to 12, further comprising a monitoring unit for monitoring the determined shear stress of the fluid, wherein the monitoring unit comprises a comparator unit which compares an actual value of the determined shear stress with a nominal value of the shear stress of the fluid.

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14. Device (100) according to one of the claims 1 to 13, further comprising a flow control unit (200) for controlling a flow rate of the fluid through the tube (103).
15. Method for measuring a shear stress of a fluid, the method comprising guiding the fluid through an inlet section (101) of a device (100), wherein the inlet section (101) is formed such that the fluid streams through the inlet section (101) along a first streaming direction (102), streaming the fluid through a tube (103) which is connected to the inlet section (101), wherein the tube (103) comprises a transition section (104) which is formed such that the fluid streaming through the tube (103) is deflected from the first streaming direction (102) to a second streaming direction (105), wherein the first streaming direction (102) differs to the second streaming direction (105), wherein the tube (103) is formed such that the tube (103) is deformable by deflecting the fluid from the first streaming direction (102) to the second streaming direction (105) within the transition section (104), and measuring a deformation of the tube (103) by a deformation sensor (106), wherein the measured deformation is indicative of the shear stress of the fluid.