Method for determining the volume or mass flow rate of a fluid in a piping system

Abstract

Method for determining a volume or mass flow rate of a fluid in a piping system (100) which has at least one branch (10) with at least one piping section (12, 14, 16, 18) through which the fluid flows in a flow direction (80), wherein at least two temperature sensors (20, 22) for determining temperatures of the fluid in the at least one piping section (12, 14, 16, 18) are arranged at a spatial distance (30) from each other in the branch (10), wherein a fluid transit time is determined from a time difference (32) that lies between at least two temperature changes which are caused by a temperature disturbance introduced into the at least one string (10) upstream of the at least two temperature sensors (20, 22) and which are determined by the at least two temperature sensors (20, 22), and wherein the volume or mass flow rate is determined from the fluid transit time (34) over the spatial distance (30) of the at least two temperature sensors (20, 22), wherein the piping system (100) is designed as an arrangement of absorber tubes (44) of solar collectors (40), and wherein the temperature disturbance is introduced by changing a focus or by defocusing a solar collector (40).

Description

State of the art

[0001] The invention relates to methods for determining a volume or mass flow rate of a fluid in a piping system and to the use of such a method in a solar collector with line focusing.

[0002] Solar thermal power plants typically use line-focusing parabolic trough collectors or Fresnel collectors that focus direct solar radiation onto a heat exchanger. Inside the heat exchanger is a heat transfer fluid, usually liquid, which is pumped through the system and heats up in the process. Usually, four to six collectors are connected in series to form strings, and a large number of these strings, for example, 150 strings, are then connected in parallel to form a subfield. Due to the large number of parallel strings, a volumetric flow rate measurement is typically only available for each subfield, but not for every parallel string. However, for various applications, it is advantageous to know the distribution of the volumetric and / or mass flow rates of the heat transfer fluid across the individual strings.Examples include the hydraulic adjustment of the branch inlet valves during commissioning or the continuous monitoring of the collector performance. For other applications, not only the distribution is required, but also the absolute volume or mass flow rates, or a good approximation of the volume or mass flow rates of the individual branches. Due to the high cost of measuring devices in each branch, this is generally omitted.

[0003] To determine the volumetric flow rate in parallel pipes, such as those found in parabolic trough power plants, a separate volumetric flow meter would be required for each individual pipe. These meters can either be installed as stationary devices within the fluid flow or attached to the pipe's outer wall as portable devices. Common operating principles for these meters are based on time-of-flight measurements of acoustic signals, pressure differential measurements before and after an orifice, eddy frequency measurements after a disturbance object, or magnetic-inductive measurements in an electrically conductive medium. Other types of meters may be based on thermal measurement methods.

[0004] Such measuring devices are expensive. Furthermore, installing an additional measuring device increases the overall system's susceptibility to failure. Every additional component in a power plant or pipeline can fail, resulting in incomplete information about the plant's condition.

[0005] From DE 102 02210 A1, a flow sensor for detecting the flow of a fluid medium is known. The flow sensor comprises a heating element and two downstream temperature sensors. The heat packet transferred from the heating element to the flowing medium is registered by both temperature sensors. The magnitude of the temperature change and / or the time the heat packet takes to travel from the heating element to the temperature sensors can be used as a measure of the mass flow rate of the fluid.

[0006] US Patent 2013 / 0008225 A1 discloses a system for measuring the velocity of a fluid flowing through a flow channel. The system comprises a heating element designed to generate a thermal marker in the fluid by supplying it with a predetermined, time-varying power. The system also includes a sensor array that generates a measurement signal indicating the velocity of the fluid flowing through the channel.

[0007] From DE 19858388 A1, a method for measuring the flow velocity of a medium is known. In this method, a control device, for example by means of a heating device, imposes a temperature change on the medium, which propagates with the medium and its flow velocity to the temperature sensors. The control device measures the transit time of the temperature change from the heating device to a temperature sensor or from one temperature sensor to the next. From the transit time and the distance between the heating device and a temperature sensor or between the temperature sensors, the control device calculates the flow velocity of the medium and, from this velocity and the cross-sectional area of ​​the medium flow, finally calculates its volumetric flow rate. Disclosure of the invention

[0008] One object of the invention is to provide an improved method for determining the volume or mass flow rate of a fluid in a piping system.

[0009] Another object of the invention is to specify a use of such an improved method in a solar collector with line focusing.

[0010] The problems are solved by the features of the independent claims. Favorable embodiments and advantages of the invention become apparent from the further claims, the description, and the drawings.

[0011] The features listed individually in the patent claims can be combined in a technologically meaningful way and can be supplemented by explanatory facts from the description and by details from the figures, showing further embodiment variants of the invention.

[0012] According to one aspect of the invention, a method for determining the volume or mass flow rate of a fluid in a piping system is proposed, which has at least one branch with at least one pipe section through which the fluid flows in one direction. At least two temperature sensors for determining the temperature of the fluid in the at least one pipe section are arranged at a spatial distance from each other in the branch. A fluid transit time is determined from the time difference between at least two temperature changes caused by a temperature disturbance introduced into the at least one branch upstream of the at least two temperature sensors and determined by the at least two temperature sensors. The volume or mass flow rate is then determined from the fluid transit time as a function of the spatial distance between the at least two temperature sensors.

[0013] The piping system is designed as an arrangement of absorber tubes for solar collectors. This allows the proposed method to be advantageously applied to a solar thermal power plant. The distribution of the volumetric and / or mass flow rate of the heat transfer fluid to the individual strings of solar collectors in the power plant can thus be reliably determined. This facilitates, for example, the hydraulic adjustment of the string inlet valves during commissioning or the continuous monitoring of the collector performance.

[0014] For other applications, not only can this distribution be determined, but also the absolute volume or mass flows, or a good approximation of the volume or mass flows of the individual strands, can be determined.

[0015] The temperature disturbance is introduced by changing the focus or by defocusing a solar collector.

[0016] The solar collectors are typically able to adjust their focus to respond to changes in fluid flow within the solar radiation receiver and local fluctuations in irradiance. By changing the focus, and thus the coupled heat, the fluid temperature can also be actively influenced. This allows temperature changes at two or more temperature sensors to be measured. Based on their fixed spatial separation and a correction term between the temperature transit time and fluid transit time, conclusions can be drawn about the fluid transit time between these points. Therefore, given a known density and pipe cross-section, the mass flow rate can also be determined. The flow rate can be deduced from the transit time of the temperature signal and the correction function. Alternatively, existing temperature changes can be used instead of active excitation.

[0017] A device for carrying out the method comprises a piping system with at least one branch, wherein pipe sections through which fluid flows are arranged one after the other in the branch. At least two consecutive temperature sensors for determining the temperature of the fluid in pipe sections are arranged at a spatial distance from each other in the branch. The temperature sensors can be arranged in different consecutive pipe sections or in the same pipe section.

[0018] When determining relative flow distributions, the piping system has fluidically parallel connected strands, with each strand containing sequentially flowing pipe sections. At least two consecutive temperature sensors for determining the fluid temperature in pipe sections are arranged at a spatial distance from each other in each strand.

[0019] Temperature measurements in a section of the piping system are used in this method to determine information about the fluid transit time. This can be achieved by utilizing either existing or actively generated temperature changes, which can be measured at sequentially arranged temperature sensors with a time delay.

[0020] Temperature sensors are frequently used to control and monitor fluid flows in piping systems. The fluid temperature can usually be influenced externally at selected points. This allows temperature disturbances to be introduced into the piping system, and the resulting temperature changes downstream to be measured at two or more temperature sensors. Based on their fixed spatial separation and a correction term between the time difference of the measured temperature changes and the actual fluid transit time, conclusions can be drawn about the fluid transit time between these points. Therefore, given a known density and pipe cross-section, the mass flow rate can also be determined. The flow rate can be deduced from the transit time of the temperature signal using the correction term. Instead of active excitation, existing temperature changes can also be used.

[0021] Thermal inertia and heat transfer in the pipes between the measuring points can delay the arrival of the temperature signal compared to the actual fluid transit time. The time difference between the temperature signals and the fluid transit time can advantageously be determined using a correction term. The proposed method is advantageous for determining fluid transit times even with large measurement volumes, such as those found in solar thermal collectors and long pipelines.

[0022] The presented method also allows for the determination of absolute fluid transit times. Correction functions can be advantageously used for this purpose. These can be described using dimensionless parameters or derived, for example, from models or interpolable tables. If dimensionless parameters are used, the correction term can be determined; that is, the fluid transit time can be determined from the measured time offset of the temperature signals, independent of the boundary conditions of the piping system or the fluid.

[0023] To increase accuracy, the proposed method assumes that the temperature sensors used have a comparable thermal inertia and therefore a comparable response behavior.

[0024] The temperature change measured at the respective temperature sensors is therefore not affected by the inertia of the temperature sensors, or the inertia is considered identical and can therefore be neglected. Another possibility is to correct for thermal inertia when determining the fluid transit time, provided sufficient data on the response behavior of the temperature sensors is available.

[0025] Advantageously, the method involves at least introducing a temperature disturbance into the fluid in a pipe section arranged upstream of the at least two temperature sensors; determining a time difference between the temperature changes caused by the temperature disturbance and those determined by the at least two successive temperature sensors; determining a fluid transit time from the spatial distance between the two successive temperature sensors based on the time difference; and determining the volume or mass flow rate from the fluid transit time.

[0026] The proposed method thus makes it possible to measure temperature changes at two or more temperature sensors and, based on their known, in particular fixed, spatial separation and a correction term between the temperature transit time and fluid transit time, to make statements about the fluid transit time between these points and, consequently, with known density and pipe cross-section, also about the mass flow rate. The flow rate can be deduced from the transit time of the temperature signal using the correction term. Instead of active excitation, existing temperature changes can also be used.

[0027] In an advantageous embodiment of the method, a correction function can be considered to determine the fluid transit time. This correction function includes at least parameters relating to the fluid's material properties, and / or material properties of the at least one pipe section, and / or geometric data of the at least one pipe section, and / or process variables. The correction function can be used, in particular, to determine absolute fluid transit times and thus also the volume or mass flow rate.

[0028] According to an advantageous embodiment of the procedure, the correction function can have dimensionless key figures that are derived from the information.

[0029] Advantageously, a large number of simulations with modified parameters regarding fluids, pipe sections, and process variables can first be performed to investigate the effect on the time lag of temperature changes. From this, dimensionless parameters can then be determined, making it possible to apply the method conveniently independently of changed parameter configurations. For example, the following dimensionless parameters can be defined: A dimensionless runtime difference π1=ΔtΔTcp,R2ρRλF as a sought-after key figure; a density ratio π2 = ρ F / ρ R ; a thermal conductivity ratio π3 = λ F / λ R ; a dimensionless pipe length π4 = l / d i : a dimensionless pipe inner diameter π5 = d i / d a ; a Prandtl number π6=Pr=ηF∗cp,FλF for momentum transport and / or heat transport; a heat capacity ratio π7 = c p,F / c p,R .

[0030] Here, Δt represents the correction between the time difference of the temperature changes determined by the at least two temperature sensors and the transit time of the fluid, ΔT the temperature changes determined by the at least two temperature sensors, ρ R the density of the pipeline section, λ F the thermal conductivity of the fluid, ρ F the density of the fluid, λ R the thermal conductivity of the pipe section, d i the inner diameter of the pipe section, d a the outer diameter of the pipe section, η F the dynamic viscosity of the fluid, c p,F the specific heat capacity of the fluid, c p,R represents the specific heat capacity of the pipeline section.

[0031] The dimensionless parameters can advantageously be determined once for all parameter variations of the simulations performed. The parameter π1 contains the desired time difference Δt = t F - t T The relationship between fluid transit time and the time difference of the temperature signals is explored. To determine this difference, a function is sought that expresses π1 as a function of the other π-numbers (π1 = f(π2,..., π7)). One possible equation represents a linear regression: π1=6.1526∗1015∗π2+−1.0924∗1017∗π3+4.8093∗108∗π4 +−3.1719∗1014∗π5+3.0565∗1013∗π6+−4.6620∗1013∗π7

[0032] This correction function allows us to adjust π1 and thus the fluid transit time t. F , the volume flow rate V̇, where A is the cross-sectional area, for example in the case of round cross-sections A=π4∗di2, and ultimately the mass flow rate ṁ can be determined. Here, V̇ and ṁ represent the time derivatives of the fluid volume and the mass of the fluid volume, respectively. tF=tT+π1∗λFΔT∗cp,R2∗ρR V˙=A∗ltF m˙=V˙∗ρF

[0033] The method can therefore be used for common fluids and material properties from the field of process engineering.

[0034] In an advantageous embodiment of the method, a dimensionless time difference can be determined from the dimensionless parameters using linear regression. With such a correction function, the fluid transit time and the volume or mass flow rate can be reliably determined.

[0035] In an advantageous embodiment of the method, the mass flow rate can be determined from the fluid transit time using the fluid density and the cross-sectional area of ​​at least one pipe section. The fluid transit time can thus be conveniently converted into the mass flow rate.

[0036] In an advantageous embodiment of the method, thermal inertia in the response behavior of the at least two temperature sensors can be taken into account to determine the fluid transit time. This allows the fluid transit time to be determined with even greater accuracy.

[0037] In an advantageous embodiment of the method, the time difference can be determined from the temperature measured by at least two temperature sensors using linearized temperature gradients. Advantageously, the temperature measured at the temperature sensors can be linearized around the maximum temperature gradient, and then the intersection point with the undisturbed temperature can be determined for each temperature signal. In this way, the time difference between the at least two temperature signals can be advantageously determined.

[0038] According to an advantageous embodiment of the method, relative volume or mass flows between fluidically parallel connected strands of the piping system, each with one or more pipe sections, can be determined by determining time differences in the various strands between the temperature change caused by the respective temperature disturbance in the respective strand and relating them to each other.

[0039] This method enables the measurement of relative volume flow distributions in parallel pipelines. To achieve this, temperature changes can be generated in a sufficient number of parallel pipe flows, or existing temperature changes can be utilized, and the time interval between the temperature signals can be determined. By comparing the measured values, a relative deviation can be identified. For certain applications, knowing the relative deviations may be sufficient.

[0040] In an advantageous embodiment of the method, the temperature disturbance can be introduced periodically over a predetermined time interval. This allows the fluid transit time and, consequently, the volume or mass flow rate to be determined with even greater accuracy. Furthermore, the periodic pattern allows for the unambiguous identification of the temperature disturbance.

[0041] According to another aspect of the invention, the use of such a method for determining a volume or mass flow rate of a fluid in a piping system in a solar collector with line focusing is proposed.

[0042] Temperature sensors are typically installed on each solar collector for control and monitoring. Furthermore, the solar collectors are able to adjust their focus to respond to changes in fluid flow within the receiver and local fluctuations in irradiance. By changing the focus, and thus the heat input, the fluid temperature can also be actively influenced.

[0043] In the case of a solar thermal power plant, one of the solar collectors can be used directly to generate measurable temperature changes. The focus of the solar collector can be adjusted, which, with a constant volume or mass flow rate and irradiance, results in a defined temperature jump that can be measured at downstream temperature sensors after a time delay. The focus can also be changed periodically to generate a longer and therefore clearly identifiable temperature signal. The measurement process can thus be actively initiated using the solar collector itself, eliminating the need for additional components that could influence the flow.

[0044] The spacing of the temperature sensors in a solar thermal power plant is often determined by the collector length, which can lead to distances between the temperature sensors on the order of 100 m to 200 m.

[0045] According to a further aspect of the invention, a computer program product for determining the volume or mass flow rate of a fluid in a piping system is proposed, which has at least one branch with at least one pipe section through which the fluid flows in one direction. At least two temperature sensors for determining the temperature of the fluid in the at least one pipe section are arranged at a spatial distance from each other in the branch.

[0046] The computer program product comprises at least one computer-readable storage medium containing program instructions that are executable on a computer system and cause the computer system to execute a method in which a fluid transit time is determined from a time difference that lies between at least two temperature changes caused by a temperature disturbance introduced into the at least one string upstream of the at least two temperature sensors and which are determined by the at least two temperature sensors, and the volume or mass flow rate is determined from the fluid transit time over the spatial distance between two successive of the at least two temperature sensors.

[0047] The piping system is designed as an arrangement of absorber tubes for solar collectors. This allows the proposed method to be advantageously applied to a solar thermal power plant. The distribution of the volumetric and / or mass flow rate of the heat transfer fluid to the individual strings of solar collectors in the power plant can thus be reliably determined. This facilitates, for example, the hydraulic adjustment of the string inlet valves during commissioning or the continuous monitoring of the collector performance.

[0048] For other applications, not only can this distribution be determined, but also the absolute volume or mass flows, or a good approximation of the volume or mass flows of the individual strands, can be determined.

[0049] The temperature disturbance is introduced by changing the focus or by defocusing a solar collector.

[0050] The computer program can advantageously calculate the time-dependent correction function between the temperature transit time and the fluid transit time in a model. Alternatively, a lookup table can be used for the correction function. It is also possible to calculate the correction value as a function, for example, using a dimensionless functional relationship.

[0051] The computer program product comprises software code segments that can be directly loaded into the memory of a digital computer and that execute the procedure when the software code segments are run by the computer.

[0052] The computer program product can consist of a computer program or, in addition to the computer program, comprise at least one additional component. This additional component can be implemented as hardware and / or software.

[0053] An example of the at least one additional component designed as hardware is a storage medium that is readable by the digital computer and / or on which the software code sections are stored.

[0054] An example of the at least one additional component that is trained as software is a cloud application program which is trained to distribute the software code sections to different processing units, in particular different computers, of a cloud computing system, wherein each of the processing units is trained to execute one or more software code sections.

[0055] In particular, the software code snippets can be used to perform the procedure as described above if the software code snippets are executed by the processing units of the cloud computing system.

[0056] According to another aspect of the invention, a data processing system for executing a data processing program is proposed, which includes computer-readable program instructions for executing a method for determining a volume or mass flow rate of a fluid in a piping system. drawing

[0057] Further advantages become apparent from the following description of the drawings. The drawings illustrate exemplary embodiments of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0058] They show, for example: Fig. 1 a schematic representation of a piping system with fluidically parallel connected strands of piping sections, each with two temperature sensors; Fig. 2 a schematic side view of a solar collector with line focusing for use in a method according to an embodiment of the invention; Fig. 3 exemplary temperature profiles in one section of a piping system after the introduction of a temperature disturbance; Fig. 4. Determining the time difference between the temperature changes caused by a temperature disturbance in two pipeline sections; Fig. 5 a schematic representation of a piping system with a multitude of fluidically parallel connected strands of piping sections; Fig. 6 a mass flow ratio of the parallel flow through the strands of pipeline sections according to Fig. 5; Fig. 7 a flow diagram of a method for determining a volume or mass flow rate of a fluid in a piping system according to an embodiment of the invention; and Fig. 8 a data processing system for carrying out a method according to an embodiment of the invention. Embodiments of the invention

[0059] In the figures, similar or equivalent components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0060] Before the invention is described in detail, it should be noted that it is not limited to the respective components of the device or the respective process steps, as these components and processes may vary. The terms used here are intended solely to describe particular embodiments and are not used restrictively. Furthermore, where the singular or indefinite articles are used in the description or in the claims, this also refers to the plural of these elements, unless the overall context clearly indicates otherwise.

[0061] The directional terminology used below, including terms like "left," "right," "above," "below," "in front," "behind," "after," and the like, serves only to improve the understanding of the figures and is in no way intended to limit their generality. The components and elements depicted, their interpretation, and their use may vary according to the considerations of a person skilled in the art and be adapted to the specific applications.

[0062] Fig. Figure 1 shows a schematic representation of a piping system 100 with fluidically parallel connected strands 10 of successive piping sections 12, 14, 16, wherein in each strand 10 two temperature sensors 20, 22 are arranged, for example, in the piping sections 14, 16.

[0063] The piping system 100 has, by way of example, three fluidically parallel strands 10 of piping sections 12, 14, 16 through which the fluid flows one after the other in the direction of flow 80. In each strand 10, at least two temperature sensors 20, 22 for determining the temperature of the fluid in piping sections 12, 14, 16 are arranged at a fixed spatial and known distance 30 from each other.

[0064] The piping system 100 can, for example, represent part of a field of solar collectors 40 with line focusing ( Fig. 2, Fig. 5).

[0065] Each strand 10 carries a fluid flow in a direction 80. The temperature sensors 20, 22 are arranged at a spatial distance 30 from each other in the successive pipe sections 14, 16 to determine the temperatures of the fluid.

[0066] A temperature disturbance of the fluid introduced into a strand 10 upstream of the two temperature sensors 20, 22, for example in the pipe section 12, can be transported further in the strand 10 as a temperature change of the fluid in the flow direction 80 and determined by the two temperature sensors 20, 22, i.e. first by temperature sensor 20 and with a corresponding time offset by temperature sensor 22.

[0067] If active temperature disturbances are to be generated, a suitable device must be present upstream of the temperature sensors 20, 22. The first pipe section 12 within these pipe strings 10 offers the possibility of actively generating temperature disturbances in the fluid, for example, by focusing and / or defocusing a solar collector whose solar radiation receiver is the pipe section 12. Temperature disturbances can also be generated, for example, by mixing in cold fluid or by random disturbances, such as partial cloud cover of part of the string 10. The two temperature sensors 20, 22 are arranged downstream in the two subsequent pipe sections 14, 16, and are spaced a known distance 30 apart.

[0068] The temperature disturbance can be introduced as a one-off event or periodically over a predetermined time interval.

[0069] According to the proposed method, a fluid transit time 34 can be determined from a time difference 32, which corresponds to the difference between the time at which the first temperature sensor 20 determines the corresponding temperature change and the time at which the subsequent temperature sensor 22, located at a distance 30 from it, determines the temperature change. The volume or mass flow rate can be determined via the spatial distance 30 between the two temperature sensors 20, 22.

[0070] Fig. Figure 2 shows a schematic side view of a solar collector 40 with line focusing. The solar collector 40 has a reflector 46, for example parabolic, in the focus of which an absorber tube 44 is arranged. The reflector 46 collects the incident solar radiation 42 and focuses it onto the absorber tube 44.

[0071] The reflector 46 is arranged on a structure 48, which is pivotable about an axis of rotation 50 on a foundation 54. The structure 48 with reflector 46 can be pivoted over an angular range 52 and thus track the sun. Typically, a plurality of solar collectors 40 are arranged in a string 10. Fig. 1. Fluid-connected in series, with a typical length of several hundred meters. Several rows of series-connected solar collectors 40 correspond to the several strings 10 in Fig. 1 connected in parallel via fluid.

[0072] The piping system 100 can accordingly be formed as an arrangement of absorber tubes 44 of a large number of such solar collectors 40.

[0073] The temperature disturbance for the application of the proposed method can be introduced in a simple way by changing the focus or by defocusing a solar collector 40 or by introducing fluid with a different temperature.

[0074] When using the solar collector 40 to introduce temperature disturbances, the focus of the solar collector is briefly changed by deflecting the reflector 46 over a certain angular range 52.

[0075] This leads to a temperature change of the fluid flowing through the absorber tube 44 during the focus change. This temperature change can be measured at the temperature sensors 20, 22 of the individual solar collectors with a time delay. The time delay of the temperature signals can be measured using suitable methods.

[0076] Fig. Figure 3 shows exemplary temperature profiles 58, 60, 62, 64 in a strand 10 of a piping system 100 after the introduction of a temperature disturbance.

[0077] The temperature curves 58, 60, 62, and 64 were generated by simulating a string 10 of several absorber tubes 44 of a solar collector 40. The focusing of a first solar collector 40 was briefly reduced, leading to a decrease in the fluid temperature in the absorber tube 44. This decrease can then be observed, with a time delay, in all series-connected absorber tubes 44 of the string 10.

[0078] In Fig. Figure 3 shows the temperature of an absorber tube 44 as a function of time 31. The temperature curves 58, 60, 62, and 64 are shown for four fluidically connected absorber tubes 44 in series. The introduced temperature disturbance is visible in the temperature curve 58 of the first absorber tube 44. The reduction in temperature in the affected absorber tube 44 is then also visible in the other temperature curves 60, 62, and 64 as a brief drop in temperature with a corresponding time delay 59, 61, and 63.

[0079] In Fig. Figure 4 shows the determination of a time difference 32 between the temperature changes caused by a temperature disturbance in two absorber tubes 44 connected in series. Two temperature profiles 58, 60, which were determined with two temperature sensors 20, 22 in fluidically series-connected absorber tubes 44, are shown. The profile of the in Fig. The temperature curves shown in Figure 4, 58, 60, were created by simulating a string 10 of absorber tubes 44 of a solar collector 40.

[0080] The time interval between the temperature signals, the time difference 32, can be determined by a suitable method. For example, the time difference 32 can be determined from the temperature determined by means of at least two temperature sensors 20, 22 via linearized temperature gradients.

[0081] The temperature measured at the temperature sensors 20, 22 is linearized around the maximum temperature gradient (diagonal dashed lines in the figure) and then the intersection point with the undisturbed temperature, i.e. the constant temperature profile over time, is determined for each temperature signal 58, 60.

[0082] Fig. Figure 5 shows a schematic representation of a piping system 100 with, for example, twenty-one fluidically parallel connected strands 10, each consisting of four pipe sections 12, 14, 16, 18. Within each strand 10, four pipe sections 12, 14, 16, 18 are fluidically connected in series. Strand numbers 72 from 0 to 20 identify the individual strands 10.

[0083] The temperature disturbance can, for example, be introduced in pipe section 12, and a time difference in the three other pipe sections 14, 16, 18 can be determined using temperature sensors. The temperature sensors are located in Fig. 5 not shown.

[0084] In Fig. 6 are mass flow ratios 70 of the parallel flow strands 10 of pipeline sections 12, 14, 16, 18 according to Fig. 5 shown.

[0085] Relative volume or mass flows between fluidically parallel connected strands 10 of the piping system 100, each with one or more piping sections 12, 14, 16, 18, can be determined by measuring time differences 32 in the various strands 10. Fig. 4) between the temperature change caused by the respective temperature disturbance in the respective strand 10 and compare them to each other.

[0086] In this way, relative flow distributions can be advantageously determined by relating the time interval of individual temperature signals to the other time differences of the temperature signals. The operational state of a solar power plant, for example, can be advantageously assessed from these relative flow distributions.

[0087] The in Fig. Figure 6 shows the result of a simulation, which displays the relative mass flow ratios 70 for twenty parallel strands 10, identified by strand number 72. The mass flow ratios 70 are determined in the simulation using the inventive method over time differences 59, 61, 63 of temperature profiles from four successive absorber tubes 44, corresponding to the pipe sections 12, 14, 16, 18 ( Fig. 5) were determined. The actual values ​​74 of the mass flow ratio from the simulation are shown for comparison. It can be seen that the relative comparison of the time differences 59, 61, 63 shows good agreement with the simulation data 74.

[0088] In Fig. Figure 7 shows a flowchart of the procedure.

[0089] First, the temperature disturbance is introduced into the fluid in a pipe section 12, 14, 16 arranged upstream of the at least two temperature sensors 20, 22 ( Fig. 1) introduced. Then the time difference 32 between the temperature changes caused by the temperature disturbance and those determined by the at least two successive temperature sensors 20, 22 is determined.

[0090] To determine the fluid transit time 34, a correction function 26 can advantageously be taken into account, which includes at least parameter 36 of material properties of the fluid, and / or material properties of the at least one pipe section 12, 14, 16 and / or parameter 38 of geometric data of the at least one pipe section 12, 14, 16 and / or process variables.

[0091] The actual fluid transit time 34 can be determined from the time difference 32 using the correction function 26. The mass flow rate can then be determined from this fluid transit time 34.

[0092] The correction function can advantageously include dimensionless key figures derived from the information.

[0093] For example, a dimensionless time difference 32 can be determined from the dimensionless parameters using linear regression.

[0094] The mass flow rate can be determined from the fluid transit time 34 via a density of the fluid and a cross-section of the at least one pipe section 12, 14, 16.

[0095] Advantageously, to determine the fluid transit time 34, a thermal inertia in the response behavior of the at least two temperature sensors 20, 22 can be taken into account.

[0096] Fig. Figure 8 shows a schematic representation of a data processing device 200, for example a computer 210, for carrying out a method for determining the volume or mass flow rate of a fluid in a piping system. The data processing device 200 includes a data storage device 214, an associated processor 212, and an interface 216 for receiving and outputting data. Furthermore, the data processing device 200 has an interface to external devices 218, such as a network or an external storage system. A computer program 220, which implements the method, is stored on the data storage device 214. Corresponding program modules 222 represent the method steps, as described, for example, in Fig. 7 are shown. Reference sign 10 strand 12 Pipeline section 14 Pipeline section 16 Pipeline section 18 Pipeline section 20 Temperature sensor 22 Temperature sensor 26 Correction function 30 distance 31 Time 32 time difference 34 Fluid runtime 36 Material properties Fluid / Pipe section 38 geometry data 40 solar collector 42 Solar radiation 44 Absorber tube 46 Reflector 48 Structure 50 axis of rotation 52 angle range 54 Foundation 58 Temperature profile of collector 1 59 Time difference collector 1-2 60 Temperature profile collector 2 61 Time difference collector 2-3 62 Temperature profile of collector 3 63 Time difference collector 3-4 64 Temperature profile collector 4 70 mass flow ratio 72 strand number 74 Mass flow ratio actual data 80 Flow direction 100 piping systems 200 data processing systems 210 computers 212 processor 214 Data storage 216 Interface for receiving and outputting data 218 external facilities 220 computer programs 222 Program module

Claims

[1] Method for determining a volume or mass flow rate of a fluid in a piping system (100) which has at least one branch (10) with at least one pipe section (12, 14, 16, 18) through which the fluid flows in a flow direction (80), wherein at least two temperature sensors (20, 22) for determining temperatures of the fluid in the at least one pipe section (12, 14, 16, 18) are arranged at a spatial distance (30) from each other in the branch (10), wherein a fluid transit time is determined from a time difference (32) that lies between at least two temperature changes which are caused by a temperature disturbance introduced into the at least one string (10) upstream of the at least two temperature sensors (20, 22) and which are determined by the at least two temperature sensors (20, 22), and wherein the volume or mass flow rate is determined from the fluid transit time (34) over the spatial distance (30) of the at least two temperature sensors (20, 22), wherein the piping system (100) is designed as an arrangement of absorber tubes (44) of solar collectors (40), and wherein the temperature disturbance is introduced by changing a focus or by defocusing a solar collector (40). [2] Method according to claim 1, wherein a correction function (26) is taken into account to determine the fluid transit time (34), which includes at least parameters of material properties (36) of the fluid and / or material properties of the at least one pipe section (12, 14, 16, 18) and / or geometry data (38) of the at least one pipe section (12, 14, 16, 18) and / or process variables. [3] Method according to claim 2, wherein the correction function (26) has dimensionless characteristic values ​​which are derived from the information. [4] Method according to claim 3, wherein a dimensionless time difference (32) is determined by means of a linear regression from the dimensionless parameters. [5] Method according to one of the preceding claims, wherein the mass flow rate is determined from the fluid transit time (34) via a density of the fluid and a cross-section of the at least one pipe section (12, 14, 16, 18). [6] Method according to one of the preceding claims, wherein to determine the fluid transit time (34) a thermal inertia in the response behavior of the at least two temperature sensors (20, 22) is taken into account. [7] Method according to one of the preceding claims, wherein the time difference (32) is determined from the temperature determined by means of the at least two temperature sensors (20, 22) via linearized temperature gradients. [8] Method according to one of the preceding claims, wherein relative volume or mass flows between fluidically parallel connected strands (10) of the piping system (100) with one or more piping sections (12, 14, 16, 18) are determined by determining time differences (32) between the temperature change caused by the respective temperature disturbance in the respective strand (10) and relating them to each other. [9] Method according to any of the preceding claims, wherein the temperature disturbance is introduced periodically over a predetermined time interval. [10] Use of a method for determining a volume or mass flow rate of a fluid in a piping system (100) according to one of the preceding claims in a solar collector (40) with line focusing. [11] Computer program product for determining a volume or mass flow rate of a fluid in a piping system (100) which has at least one string (10) with at least one piping section (12, 14, 16, 18) through which the fluid flows in a flow direction (80), wherein at least two temperature sensors (20, 22) for determining temperatures of the fluid in the at least one piping section (12, 14, 16, 18) are arranged at a spatial distance (30) from each other in the string (10), wherein the computer program product comprises at least one computer-readable storage medium which includes program instructions that are executable on a computer system (200) and cause the computer system (200) to execute a method according to at least one of claims 1 to 9, wherein a fluid transit time is determined from a time difference (32) that lies between at least two temperature changes which are caused by a temperature disturbance introduced into the at least one string (10) upstream of the at least two temperature sensors (20, 22) and which are determined by the at least two temperature sensors (20, 22), and wherein the volume or mass flow rate is determined from the fluid transit time (34) over the spatial distance (30) of the at least two temperature sensors (20, 22), wherein the piping system (100) is designed as an arrangement of absorber tubes (44) of solar collectors (40), and wherein the temperature disturbance is introduced by changing a focus or by defocusing a solar collector (40). [12] Data processing system (200) for executing a data processing program comprising computer-readable program instructions for executing a method for determining a volume or mass flow rate of a fluid in a piping system (100) according to at least one of claims 1 to 9.

Images