Flow velocity detection device and method

Abstract

A flow velocity detection device and method are provided that conserve hardware resources and improve the accuracy of flow velocity calculations. The flow rate detection device 100 includes a heating circuit 110, a temperature detection circuit 130, and a processor 120. The processor 120 executes the following steps: during a heating stage, controlling the heating circuit 110 to heat the fluid for a heating time; during a heat dissipation stage after the heating stage, controlling the heating circuit 110 to dissipate heat from the fluid for a heat dissipation time, thereby stopping heating of the fluid; determining whether the maximum temperature of the fluid during the heating stage and the heat dissipation stage satisfies a predetermined periodic recurrence condition; and, if the maximum temperature satisfies the predetermined periodic recurrence condition, calculating a temperature difference between the maximum temperature and an ambient temperature, and converting the heating time, heat dissipation time, and temperature difference into a flow rate of the fluid in the pipe based on a conversion curve diagram.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to the technical field of fluid detection, and more particularly to flow rate detection devices and methods. [Background technology]

[0002] Traditionally, thermal mass flow meters have been used in refrigeration cycles as flow rate alarm switches to roughly grasp fluid flow and prevent overheating due to under-cycling. However, current thermal mass flow meters often rely on multiple temperature sensors to detect temperature differences between upstream and downstream locations of different fluids to calculate flow rate and velocity. This method not only consumes hardware resources but also results in low accuracy in the calculation of flow rate and velocity. Therefore, how to conserve hardware resources while improving the accuracy of flow rate calculations has become an urgent issue for those skilled in the art. Summary of the Invention [Problem to be solved by the invention]

[0003] The main objective of the present disclosure is to provide a flow velocity detection device and method that can achieve the effects of saving hardware resources and improving the accuracy of flow velocity calculation.

[0004] In order to achieve the above object, the flow velocity detection device of the present disclosure comprises: a heating circuit provided on a probe rod of a thermal mass flow meter and configured to heat a fluid in a pipe, the probe rod being installed in the pipe; a temperature detection circuit disposed adjacent to the heating circuit and configured to detect a temperature of the fluid in the piping; a processor connected to the heating circuit and the temperature detection circuit; The processor: (a) controlling the heating circuit during a heating stage to heat the fluid for a heating time; (b) controlling the heating circuit to stop heating the fluid during a heat dissipation stage after the heating stage, so that the fluid dissipates heat for a heat dissipation time; a step (c) of determining whether the maximum temperature of the fluid detected by the temperature detection circuit during the heating step and the heat dissipation step satisfies a predetermined periodic recurrence condition; Step (d) of calculating a temperature difference between the maximum temperature and an ambient temperature when the maximum temperature satisfies the predetermined periodic recurrence condition, and converting the heating time, the heat dissipation time, and the temperature difference into a flow velocity of the fluid in the pipe based on a conversion curve diagram, wherein the conversion curve diagram includes a plurality of curves corresponding to a plurality of reference heating times and a plurality of reference heat dissipation times, respectively, and each curve shows a relationship between the temperature difference and the flow velocity at the corresponding reference heating time and the corresponding reference heat dissipation time, and the maximum temperature and the ambient temperature are detected by the temperature detection circuit at different times; If the maximum temperature does not satisfy the predetermined periodic recurrence condition, step (e) is executed to execute steps (a) to (c) again, with the heating time being lengthened and the heat dissipation time being shortened.

[0005] In order to achieve the above object, the flow velocity detection method of the present disclosure includes: (a) controlling, by a processor, during a heating stage, a heating circuit to heat the fluid in the piping for a heating time, the heating circuit being provided on a probe rod of a thermal mass flow meter, the probe rod being provided in the piping; (b) during a heat dissipation stage after the heating stage, controlling the heating circuit by the processor to stop heating the fluid so as to dissipate heat from the fluid for a heat dissipation time; (c) determining, by the processor, whether a maximum temperature of the fluid detected by a temperature detection circuit during the heating stage and the heat dissipation stage satisfies a predetermined periodic recurrence condition; If the maximum temperature satisfies the predetermined periodic recursion condition, the processor calculates a temperature difference between the maximum temperature and an ambient temperature, and converts the heating time, the heat dissipation time, and the temperature difference into a flow velocity of the fluid in the pipe based on a conversion curve diagram (d), wherein the conversion curve diagram includes a plurality of curves corresponding to a plurality of reference heating times and a plurality of reference heat dissipation times, respectively, and each curve shows a relationship between the temperature difference and the flow velocity at the corresponding reference heating time and the corresponding reference heat dissipation time, and the maximum temperature and the ambient temperature are detected by the temperature detection circuit at different times; and (e) a step in which, if the maximum temperature does not satisfy the predetermined periodic recurrence condition, the processor executes steps (a) to (c) again, with the heating time being lengthened and the heat dissipation time being shortened.

[0006] Compared to the related art, the present disclosure dynamically adjusts the heating and heat dissipation times of the fluid to obtain an appropriate maximum temperature of the fluid, and converts the temperature difference between the maximum temperature and the ambient temperature into the fluid flow rate using a preset conversion curve. This allows the present disclosure to use a single heating circuit to heat and dissipate the fluid, and to use the time difference to obtain the temperature difference of the fluid's thermal conductivity characteristics, thereby calculating the flow rate using the temperature difference. This method not only eliminates the need for multiple temperature detection circuits, but also significantly improves the accuracy of the flow rate calculation. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram of a flow velocity detection device according to some embodiments of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram of the placement of heating circuits and temperature detection circuits in some embodiments of the present disclosure. [Figure 3] 1 is a flowchart of a flow velocity detection method according to some embodiments of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram of a temperature curve of a fluid in some embodiments of the present disclosure. [Figure 5] 10 is a flowchart of several steps further involved in flow velocity detection in some embodiments of the present disclosure. [Figure 6] FIG. 2 is a schematic diagram of a first temperature curve according to some embodiments of the present disclosure. [Figure 7] FIG. 2 is a schematic diagram of a second temperature curve according to some embodiments of the present disclosure. [Figure 8] FIG. 2 is a schematic diagram of a third temperature curve according to some embodiments of the present disclosure. [Figure 9] FIG. 2 is a schematic diagram of a conversion curve diagram according to some embodiments of the present disclosure. [Figure 10] 5A-5C are schematic diagrams of temperature curves of fluids in accordance with some other embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1 is a block diagram of a flow detection device 100 according to some embodiments of the present disclosure. As shown in FIG. 1, the flow detection device 100 includes a heating circuit 110, a processor 120, and a temperature detection circuit 130. The processor 120 is connected to both the heating circuit 110 and the temperature detection circuit 130.

[0009] In this embodiment, the heating circuit 110 is provided on the probe rod of any type of thermal mass flow meter and is used to heat the fluid in the pipe in which the probe rod is provided. In other words, the probe rod of the thermal mass flow meter can be inserted into the pipe, and the heating circuit 110 on the probe rod can heat the fluid in the pipe. In some embodiments, the heating circuit 110 can be any type of electrical heating circuit (e.g., a resistance heating circuit, an induction heating circuit, an arc heating circuit, an electron beam heating circuit, an infrared heating circuit, a dielectric heating circuit, etc.).

[0010] In this embodiment, the temperature detection circuit 130 is provided adjacent to the heating circuit 110 and is used to detect the temperature of the fluid in the piping. In other words, the temperature detection circuit 130 is provided adjacent to the heating circuit 110 on the probe rod of the thermal mass flow meter. In some embodiments, the temperature detection circuit 130 detects a voltage corresponding to the fluid and converts it into the temperature of the fluid (a higher voltage converts to a higher temperature, and a lower voltage converts to a lower temperature). In some embodiments, the temperature detection circuit 130 can be any type of thermal sensing circuit (e.g., a thermistor-type thermal sensing circuit, etc.).

[0011] 2 is a schematic diagram of the positions of the heating circuit 110 and the temperature detection circuit 130 in some embodiments of the present disclosure. As shown in FIG. 2, a probe rod 200 of a thermal mass flow meter can be inserted into a pipe 300. A fluid in the pipe 300 flows along a certain flow direction FD1. In the embodiment of FIG. 2, the heating circuit 110 is disposed at a tip 210 of the probe rod 200, and the temperature detection circuit 130 is also disposed at the tip 210 of the probe rod 200 and adjacent to the position of the heating circuit 110.

[0012] 1, the processor 120 controls the heating circuit 110 and the temperature detection circuit 130 to perform the steps of the flow rate detection method described in the following paragraphs. In some embodiments, the processor 120 may comprise, but is not limited to, a central processing unit (CPU), a micro control unit (MCU), a programmable logic controller (PLC), a system on chip (SoC), or a field programmable gate array (FPGA).

[0013] In some embodiments, the flow detection device 100 further includes a memory 140 that stores a conversion curve diagram 141 that is used to convert the temperature difference to a flow velocity in the following paragraphs. This conversion curve diagram 141 is described in detail in the following paragraphs and will not be further described here.

[0014] FIG. 3 is a flowchart of a flow velocity detection method according to some embodiments of the present disclosure, which is applied to the flow velocity detection device 100 as shown in FIG.

[0015] As shown in FIG. 3, the flow rate detection method includes steps S310 to S350. First, in step S310, processor 120 controls heating circuit 110 to heat the fluid for a heating time (e.g., 1 second) during the heating phase. In some embodiments, processor 120 initially sets the heating time to the minimum value (e.g., 1 second) of a plurality of reference heating times, where the plurality of reference heating times are a plurality of preset time lengths (e.g., 1 second, 1.5 seconds, and 3 seconds). Note that temperature detection circuit 130 can continuously detect the temperature of the fluid in the piping during the heating phase.

[0016] In step S320, during the heat dissipation phase following the heating phase, the processor 120 controls the fluid heating circuit 110 to stop heating the fluid so that the fluid dissipates heat by free convection for the heat dissipation time. In some embodiments, the heat dissipation time is initially set by the processor 120 to the maximum value (e.g., 3 seconds) of multiple reference heat dissipation times, where the multiple reference heat dissipation times are multiple preset time lengths (e.g., 3 seconds, 2.5 seconds, and 3.1 seconds). Note that the temperature detection circuit 130 can continuously detect the temperature of the fluid in the piping even during the heat dissipation phase. In one embodiment, the heating phase is a phase in which the heating circuit 110 starts operating to heat the fluid, and corresponds to the heating time described above. The heat dissipation phase is a phase in which the heating circuit 110 stops operating to stop heating the fluid, and corresponds to the heat dissipation time described above. In one embodiment, the temperature detection circuit 130 continuously detects the temperature of the fluid in the piping regardless of switching between the heating phase and the heat dissipation phase.

[0017] In step S330, the processor 120 determines whether the maximum temperature of the fluid detected by the temperature detection circuit 130 during the heating phase and the heat dissipation phase satisfies a predetermined periodic recurrence condition. If the maximum temperature satisfies the predetermined periodic recurrence condition, the processor 120 executes step S340. Conversely, if the maximum temperature does not satisfy the predetermined periodic recurrence condition, the processor 120 executes step S350. Specifically, the processor 120 receives multiple fluid temperatures from the temperature detection circuit 130 during the heating phase and the heat dissipation phase and determines whether the maximum value of the multiple temperatures (i.e., the maximum temperature) satisfies the predetermined periodic recurrence condition. In some embodiments, the predetermined periodic recurrence condition is that the maximum fluid temperature exceeds a predetermined temperature threshold (in the principles of fluid mechanics and heat transfer, the temperature threshold represents a noticeable temperature difference achieved by substantial heating power and is noticeable in the subsequent heat dissipation phase). In other words, the processor 120 obtains the maximum temperature throughout the heating phase and the heat dissipation phase. Processor 120 begins executing step S340 as long as it determines that the maximum temperature of the fluid has exceeded the temperature threshold. Conversely, processor 120 begins executing step S350 as long as it determines that the heating and heat dissipation phases have ended but the maximum temperature of the fluid has not yet exceeded the temperature threshold.

[0018] The heating stage and the heat dissipation stage will be described below with specific examples. Figure 4 is a schematic diagram of a temperature curve of a fluid in some embodiments of the present disclosure. As shown in Figure 4, during the heating stage t1, the processor 120 controls the heating circuit 110 to heat the fluid for a heating time tm1, and then during the heat dissipation stage t2, the processor 120 controls the fluid heating circuit 110 to stop heating the fluid so that the fluid dissipates heat for a heat dissipation time tm2.

[0019] From the temperature curve in FIG. 4, it can be seen that when the fluid is at ambient temperature T1, the temperature of the fluid rises from ambient temperature T1 to maximum temperature T2 after heating for a heating time tm1. Furthermore, by stopping the heating of the fluid, the fluid is allowed to dissipate heat, and after a heat dissipation time tm2 has elapsed, the temperature of the fluid drops to ambient temperature T1. Thus, processor 120 obtains maximum temperature T2 from the temperature curve and determines whether maximum temperature T2 is greater than a preset temperature threshold tT. At this time, it can be seen from FIG. 4 that maximum temperature T2 is not greater than the preset temperature threshold tT. Therefore, processor 120 begins executing step S350. Conversely, if maximum temperature T2 is greater than the preset temperature threshold tT, processor 120 begins executing step S340.

[0020] Returning to FIG. 3 , in step S340, processor 120 calculates the temperature difference between the maximum temperature and the ambient temperature and converts the heating time, heat dissipation time, and temperature difference into the flow velocity of the fluid in the pipe based on conversion curve diagram 141. In this embodiment, conversion curve diagram 141 includes multiple relationship curves corresponding to multiple reference heating times and multiple reference heat dissipation times, respectively, where each relationship curve indicates the relationship between the temperature difference and the flow velocity at the corresponding reference heating time and the corresponding reference heat dissipation time. In some embodiments, memory 140 further stores an ambient temperature, where the ambient temperature indicates the temperature of the environment outside the pipe. In some embodiments, processor 120 selects a relationship curve corresponding to the currently used heating time and heat dissipation time from conversion curve diagram 141, where the corresponding relationship curve corresponds to the same reference heating time and reference heat dissipation time, respectively, and indicates the relationship between the temperature difference and the flow velocity at the same reference heating time and reference heat dissipation time. Then, processor 120 obtains the flow velocity corresponding to the calculated temperature difference from the corresponding relationship curve as the flow velocity of the fluid in the pipe.

[0021] In some embodiments, if processor 120 cannot select a relationship curve corresponding to the currently used heating time and heat dissipation time from conversion curve diagram 141, processor 120 calculates multiple differences between the reference heating time and the heating time for each of the multiple relationship curves in conversion curve diagram 141 and selects two smallest differences from the multiple differences. Then, processor 120 selects two relationship curves from conversion curve diagram 141 that correspond to the two smallest differences, respectively, and obtains two flow rates corresponding to the temperature differences from the two corresponding relationship curves. Then, processor 120 calculates one flow rate by performing an interpolation operation on the two corresponding flow rates based on the reference heating time and the heating time for each of the two corresponding relationship curves, and sets this flow rate as the flow rate of the fluid in the pipe.

[0022] In some embodiments, memory 140 further stores multiple conversion curves 141 corresponding to multiple fluid types (e.g., water, silicone oil, etc.). In some embodiments, processor 120 controls temperature detection circuit 130 to detect the rate of temperature rise of a fluid with a zero flow rate during the heating phase and the rate of temperature decrease of a fluid with a zero flow rate during the heat dissipation phase. Processor 120 determines the possible types of fluid based on the rate of temperature rise and decrease. Then, processor 120 converts the heating time, heat dissipation time, and temperature difference into the flow rate of the fluid in the pipe based on the conversion curve corresponding to the selected fluid type.

[0023] The method for generating the conversion curve diagram is further described below. FIG. 5 is a flowchart of steps S510-S540 executed before step S310 of FIG. 2 in some embodiments of the present disclosure. As shown in FIG. 5, in step S510, the processor 120 controls the heating circuit 110 to heat the fluid for a first reference heating time and to dissipate heat from the fluid for a first reference heat dissipation time for each of the fluids at a plurality of reference flow rates, and then stops heating the fluid (at which time, dissipating heat to return to ambient temperature). In some embodiments, the first temperature curve diagram shows a plurality of temperature curves of the fluids at various reference flow rates when the fluids are heated for the first reference heating time and then dissipated for the first reference heat dissipation time by stopping the heating of the fluid. In some embodiments, the first temperature curve map is used to generate a relationship curve suitable for low flow rates (i.e., 0-50 cm / s) in the conversion curve map (this is because when the fluid is at low flow rates, the shortest reference heating time is sufficient for the fluid temperature to exceed the temperature threshold, while the longest reference heat release time is required for the fluid temperature to return to ambient temperature).

[0024] The first temperature curve diagram will be described below with reference to specific examples. FIG. 6 is a schematic diagram of a first temperature curve diagram according to some embodiments of the present disclosure. As shown in FIG. 6, the first temperature curve diagram includes multiple temperature curves C1 to C4. When the reference flow velocity is 600 cm / s, the processor 120 controls the heating circuit 110 to heat the fluid for a first reference heating time rt1 during the heating phase t1, and then controls the heating circuit 110 to stop heating the fluid during the heat dissipation phase t2, so that the fluid dissipates heat for a first reference heat dissipation time rt2. Here, the first reference heating time rt1 is 1 second, and the first reference heat dissipation time rt2 is 3 seconds. Meanwhile, for a fluid with a reference flow velocity of 600 cm / s, the temperature detection circuit 130 detects multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 and transmits them to the processor 120. The processor 120 can generate a temperature curve C1 based on these temperatures.

[0025] Similarly, when the reference flow velocity is 300 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a first reference heating time rt1 during the heating stage t1, and controls the heating circuit 110 to stop heating the fluid so that the fluid dissipates heat for a first reference heat dissipation time rt2 during the heat dissipation stage t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating stage t1 and the heat dissipation stage t2 for the fluid having a reference flow velocity of 300 cm / s, and the processor 120 can generate a temperature curve C2 based on these temperatures.

[0026] Similarly, when the reference flow velocity is 100 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a first reference heating time rt1 during the heating phase t1, and controls the heating circuit 110 to stop heating the fluid so that the fluid dissipates heat for a first reference heat dissipation time rt2 during the heat dissipation phase t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 for the fluid having a reference flow velocity of 100 cm / s, and the processor 120 can generate a temperature curve C3 based on these temperatures.

[0027] Similarly, when the reference flow velocity is 10 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a first reference heating time rt1 during the heating phase t1, and controls the heating circuit 110 to stop heating the fluid so that the fluid dissipates heat for a first reference heat dissipation time rt2 during the heat dissipation phase t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 for the fluid with a reference flow velocity of 10 cm / s, and the processor 120 can generate a temperature curve C4 based on these temperatures.

[0028] The processor 120 then obtains the maximum temperatures T2 to T5 of the temperature curves C1 to C4 and calculates multiple temperature differences between the maximum temperatures T2 to T5 and the ambient temperature T1. Finally, the processor 120 generates one of the relationship curves in the conversion curve diagram 141 using these temperature differences and the reference flow rates. In some embodiments, the processor 120 uses any regression algorithm (e.g., a polynomial regression algorithm) to generate a regression curve from these temperature differences and the reference flow rates, which can be one of the relationship curves in the conversion curve diagram 141 (e.g., the relationship curve RC1 in FIG. 9 described in the following paragraph). It can be seen from the maximum temperatures T2 to T5 that the faster the flow rate, the slower the temperature rise rate and the faster the temperature drop rate (because heat is more easily carried away by the fluid). Conversely, the slower the flow rate, the faster the temperature rise rate and the slower the temperature drop rate. Although four temperature curves C1 to C4 are used as an example here, in reality, more temperature curves are generated for more reference flow rates in order to obtain the relationship between the temperature difference and flow rate when the first reference heating time rt1 and the first reference heat dissipation time rt2 are used.

[0029] 5 , in step S520, the processor 120 controls the heating circuit 110 to heat the fluid for a second reference heating time for each of the fluids at a plurality of reference flow rates, and controls the heating circuit 110 to allow the fluid to dissipate heat for a second reference heat dissipation time, and stops heating the fluid (at which time the fluid dissipates heat to return to ambient temperature) to generate a second temperature curve diagram. In this embodiment, the second reference heating time is longer than the first reference heating time, and the second reference heat dissipation time is shorter than the first reference heat dissipation time. In some embodiments, the second temperature curve diagram shows multiple temperature curves for the fluids at various reference flow rates when the fluids are heated for the second reference heating time and allowed to dissipate heat for the second reference heat dissipation time. In some embodiments, a second temperature curve is used to generate a relationship curve suitable for medium flow rates (i.e., 50-400 cm / s) in the conversion curve (this is because when the fluid is at medium flow rates, a longer reference heating time is required for the fluid temperature to exceed the temperature threshold, while a shorter reference heat release time is required for the fluid temperature to return to ambient temperature).

[0030] The second temperature curve diagram will be described below with reference to specific examples. FIG. 7 is a schematic diagram of a second temperature curve diagram according to some embodiments of the present disclosure. As shown in FIG. 7, the second temperature curve diagram includes multiple temperature curves C1 to C4. When the reference flow velocity is 600 cm / s, the processor 120 controls the heating circuit 110 to heat the fluid for a second reference heating time rt1' during the heating phase t1, and then controls the heating circuit 110 to stop heating the fluid for a second reference heat dissipation time rt2' during the heat dissipation phase t2. Here, the second reference heating time rt1' is 1.5 seconds, and the second reference heat dissipation time rt2' is 2.5 seconds. Meanwhile, for a fluid with a reference flow velocity of 600 cm / s, the temperature detection circuit 130 detects multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 and transmits them to the processor 120. The processor 120 can generate a temperature curve C1 based on these temperatures.

[0031] Similarly, when the reference flow velocity is 300 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a second reference heating time rt1' during the heating stage t1, and controls the heating circuit 110 to stop heating the fluid for a second reference heat dissipation time rt2' during the heat dissipation stage t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating stage t1 and the heat dissipation stage t2 for the fluid having a reference flow velocity of 300 cm / s, and generates a temperature curve C2 based on these temperatures.

[0032] Similarly, when the reference flow velocity is 100 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a second reference heating time rt1' during the heating stage t1, and controls the heating circuit 110 to stop heating the fluid for a second reference heat dissipation time rt2' during the heat dissipation stage t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating stage t1 and the heat dissipation stage t2 for the fluid with a reference flow velocity of 100 cm / s, and the processor 120 can generate a temperature curve C3 based on these temperatures.

[0033] Similarly, when the reference flow velocity is 10 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a second reference heating time rt1' during the heating stage t1, and controls the heating circuit 110 to stop heating the fluid for a second reference heat dissipation time rt2' during the heat dissipation stage t2. Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating stage t1 and the heat dissipation stage t2 for the fluid having a reference flow velocity of 10 cm / s, and the processor 120 can generate a temperature curve C4 based on these temperatures.

[0034] Then, the processor 120 acquires the maximum temperatures T2 to T5 of the temperature curves C1 to C4, respectively, and can calculate multiple temperature differences between the maximum temperatures T2 to T5 and the ambient temperature T1. Finally, the processor 120 generates another relationship curve in the conversion curve diagram 141 using these temperature differences and the above-mentioned reference flow rates. In some embodiments, the processor 120 can use any regression algorithm to generate a regression curve from these temperature differences and the above-mentioned reference flow rates, and use this as another relationship curve in the conversion curve diagram 141 (e.g., relationship curve RC2 in FIG. 9 described in the following paragraph). Note that although four temperature curves C1 to C4 are used as an example here, in practice, more temperature curves are generated for more reference flow rates to obtain the relationship between the temperature difference and the flow rate when the second reference heating time rt1′ and the second reference heat dissipation time rt2′ are used.

[0035] In step S530, the processor 120 controls the heating circuit 110 to heat the fluid for a third reference heating time and to dissipate heat from the fluid for a third reference heat dissipation time, respectively, to generate a third temperature curve diagram. In this embodiment, the third reference heating time is longer than the second reference heating time, and the third reference heat dissipation time is shorter than the second reference heat dissipation time and the first reference heat dissipation time. In some embodiments, the third temperature curve diagram shows multiple temperature curves for fluids at various reference flow rates when the fluid is heated for the third reference heating time and dissipated for the third reference heat dissipation time. In some embodiments, a third temperature curve is used to generate a relationship curve suitable for high flow rates (i.e., >400 cm / s) in the conversion curve (this is because when the fluid is at high flow rates, the highest reference heating time is required for the fluid temperature to exceed the temperature threshold, while the lowest reference heat release time is required for the fluid temperature to return to ambient temperature).

[0036] The third temperature curve diagram will be described below with reference to specific examples. FIG. 8 is a schematic diagram of a third temperature curve diagram according to some embodiments of the present disclosure. As shown in FIG. 8, the third temperature curve diagram includes a plurality of temperature curves C1 to C4. When the reference flow velocity is 600 cm / s, the processor 120 controls the heating circuit 110 to heat the fluid for a third reference heating time rt1" during the heating stage t1, and then controls the heating circuit 110 to stop heating the fluid so that the fluid dissipates heat for a third reference heat dissipation time rt2" during the heat dissipation stage t2. Here, the third reference heating time rt1" is 3 seconds, and the third reference heat dissipation time rt2" is 1 second. Meanwhile, for a fluid with a reference flow velocity of 600 cm / s, the temperature detection circuit 130 detects a plurality of temperatures of the fluid during the heating stage t1 and the heat dissipation stage t2 and transmits them to the processor 120. The processor 120 can generate a temperature curve C1 based on these temperatures.

[0037] Similarly, when the reference flow velocity is 300 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a third reference heating time rt1" during the heating phase t1, and then controls the heating circuit 110 to stop heating the fluid during the heat dissipation phase t2, causing the fluid to dissipate heat for a third reference heat dissipation time rt2". Meanwhile, the temperature detection circuit 130 also detects and transmits multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 for a fluid with a reference flow velocity of 300 cm / s to the processor 120, and the processor 120 can generate a temperature curve C2 based on these temperatures.

[0038] Similarly, when the reference flow velocity is 100 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a third reference heating time rt1" during the heating phase t1, and then controls the heating circuit 110 to stop heating the fluid during the heat dissipation phase t2, causing the fluid to dissipate heat for a third reference heat dissipation time rt2". Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 for a fluid with a reference flow velocity of 100 cm / s, and the processor 120 can generate a temperature curve C3 based on these temperatures.

[0039] Similarly, when the reference flow velocity is 10 cm / s, the processor 120 also controls the heating circuit 110 to heat the fluid for a third reference heating time rt1" during the heating phase t1, and then controls the heating circuit 110 to stop heating the fluid during the heat dissipation phase t2, causing the fluid to dissipate heat for a third reference heat dissipation time rt2". Meanwhile, the temperature detection circuit 130 also detects and transmits to the processor 120 multiple temperatures of the fluid during the heating phase t1 and the heat dissipation phase t2 for a fluid with a reference flow velocity of 10 cm / s, and the processor 120 can also generate a temperature curve C4 based on these temperatures.

[0040] Then, the processor 120 obtains the maximum temperatures T2 to T5 of the temperature curves C1 to C4, respectively, and can calculate multiple temperature differences between the maximum temperatures T2 to T5 and the ambient temperature T1. Finally, the processor 120 generates another relationship curve in the conversion curve diagram 141 using these temperature differences and the above-mentioned reference flow rates. In some embodiments, the processor 120 can use any regression algorithm to generate a regression curve from these temperature differences and the above-mentioned reference flow rates, and use this as another relationship curve in the conversion curve diagram 141 (for example, the relationship curve RC3 in FIG. 9 described in the following paragraph). Note that although four temperature curves C1 to C4 are used as an example here, in practice, more temperature curves are generated for more reference flow rates to obtain the relationship between the temperature difference and the flow rate when a third reference heating time rt1″ and a third reference heat dissipation time rt2″ are used.

[0041] In step S540, processor 120 generates conversion curve diagram 141 based on the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram. In some embodiments, the multiple curves in conversion curve diagram 141 include a first relationship curve, a second relationship curve, and a third relationship curve. In some embodiments, the first relationship curve, the second relationship curve, and the third relationship curve apply to a fluid at a low flow rate, a fluid at a medium flow rate, and a fluid at a high flow rate, respectively. In some embodiments, processor 120 converts the multiple temperature curves in the first temperature curve diagram into a first relationship curve in conversion curve diagram 141, where the first relationship curve indicates the relationship between the temperature difference of the fluid and the flow rate when the fluid is heated for a first reference heating time and the fluid is allowed to lose heat for a first reference heat loss time. In some embodiments, processor 120 converts the plurality of temperature curves in the second temperature curve diagram into a second relationship curve in conversion curve diagram 141, where the second relationship curve indicates the relationship between the temperature difference and the flow rate of the fluid when the fluid is heated for a second reference heating time and the fluid is allowed to dissipate heat for a second reference heat dissipation time. In some embodiments, processor 120 converts the plurality of temperature curves in the third temperature curve diagram into a third relationship curve in conversion curve diagram 141, where the third relationship curve indicates the relationship between the temperature difference and the flow rate of the fluid when the fluid is heated for a third reference heating time and the fluid is allowed to dissipate heat for a third reference heat dissipation time.

[0042] The conversion curve diagram will be described below with specific examples. FIG. 9 is a schematic diagram of a conversion curve diagram according to some embodiments of the present disclosure. As shown in FIG. 9, the conversion curve diagram includes a plurality of relationship curves RC1 to RC3. Continuing with the example of FIG. 6, the processor 120 obtains a plurality of temperature differences (i.e., a plurality of differences between the maximum temperatures T2 to T5 and the ambient temperature T1) and reference flow rates corresponding to each temperature difference from the first temperature curve diagram of FIG. 6, and generates a relationship curve RC1 using these temperature differences and the corresponding plurality of reference flow rates, where the relationship curve RC1 indicates the relationship between the temperature difference and the flow rate of the fluid when the fluid is heated for a first reference heating time rt1 and the fluid is allowed to dissipate heat for a first reference heat dissipation time rt2.

[0043] Continuing with the example of Figure 7, the processor 120 obtains multiple temperature differences (i.e., multiple differences between the highest temperatures T2 to T5 and the ambient temperature T1) and the reference flow rates corresponding to each temperature difference from the second temperature curve diagram of Figure 7, and generates a relationship curve RC2 using these temperature differences and the corresponding multiple reference flow rates, where the relationship curve RC2 shows the relationship between the temperature difference and flow rate of the fluid when the fluid is heated for a second reference heating time rt1' and the fluid is allowed to dissipate heat for a second reference heat dissipation time rt2'. Continuing with the example of FIG. 8, the processor 120 obtains a plurality of temperature differences (i.e., a plurality of differences between the maximum temperatures T2 to T5 and the ambient temperature T1) and the reference flow rates corresponding to each temperature difference from the third temperature curve diagram of FIG. 8, and generates a relationship curve RC3 using these temperature differences and the corresponding plurality of reference flow rates, where the relationship curve RC3 indicates the relationship between the temperature difference and the flow rate of the fluid when the fluid is heated for a third reference heating time rt1" and the fluid is allowed to dissipate heat for a third reference heat dissipation time rt2". This allows the processor 120 to convert the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram into the conversion curve diagram of FIG. 9.

[0044] Although three reference heating times and three reference heat dissipation times are used as an example here, in practice, more temperature curves can be generated for more reference heating times and more reference heat dissipation times, allowing the processor 120 to convert each of the more temperature curves into more relationship curves.

[0045] Returning to FIG. 3 , in step S350, processor 120 again executes steps S310-S330, lengthening the heating time and shortening the heat dissipation time, until the detected maximum temperature of the fluid satisfies a predetermined periodic recursion condition. In other words, if the detected maximum temperature of the fluid is still below the temperature threshold even after the current heating and heat dissipation steps are completed, processor 120 first lengthens the heating time and shortens the heat dissipation time, and then continues executing the heating and heat dissipation steps. Processor 120 then continues to determine whether the detected maximum temperature of the fluid is greater than the temperature threshold. If the detected maximum temperature of the fluid is greater than the temperature threshold, processor 120 executes the flow rate conversion step. In some embodiments, processor 120 lengthens the heating time by a certain time increment (e.g., 0.1 seconds) and shortens the heat dissipation time by a certain time increment (e.g., 0.1 seconds) each time it executes step S350.

[0046] It should be noted that when the fluid flow rate is relatively high, the processor 120 needs to adopt a relatively long heating time and a relatively short heat dissipation time to ensure that the maximum temperature of the fluid is greater than the temperature threshold. In other words, when the fluid flow rate is relatively high, the processor 120 needs to perform more recursions to ensure that the maximum temperature of the fluid is greater than the temperature threshold. As an example, when the fluid flow rate is low, the heating time and the heat dissipation time need to be set to 1 second and 3 seconds, respectively. When the fluid flow rate is medium, the heating time and the heat dissipation time need to be set to 1.5 seconds and 2.5 seconds, respectively. When the fluid flow rate is high, the heating time and the heat dissipation time need to be set to 3 seconds and 1 second, respectively.

[0047] In addition, when the flow rate of the fluid is relatively high, the temperature of the fluid increases and decreases to a smaller extent. Therefore, if the heating time is too short, the resolution of the relationship between a relatively small temperature difference of the fluid (i.e., the difference between the maximum temperature and the ambient temperature) and a relatively high flow rate is significantly reduced (i.e., even a relatively small temperature difference affects a relatively large change in the flow rate). Therefore, in the present disclosure, a temperature threshold is preset and used to adjust the heating time and heat dissipation time, thereby avoiding the problem of a significant reduction in the resolution of the relationship between a relatively small temperature difference of the fluid and a relatively high flow rate.

[0048] From the conversion curve diagram in Figure 9, we can see that the portion of the relationship curve RC1 corresponding to medium and high flow velocities has low resolution, so it can be applied to low flow velocities. The portion of the relationship curve RC2 corresponding to high flow velocities has low resolution, so it can be applied to medium flow velocities. The portion of the relationship curve RC3 corresponding to high flow velocities has high resolution, so it can be applied to high flow velocities.

[0049] The flow rate conversion method will be further described below with reference to a specific example. FIG. 10 is a schematic diagram of a fluid temperature curve in some other embodiments of the present disclosure. As shown in FIGS. 4 and 10, continuing with the example of FIG. 4, in the embodiment of FIG. 4, after the heating stage and the heat dissipation stage are completed, the maximum fluid temperature T2 is equal to or less than the preset temperature threshold tT. Therefore, in the next cycle, the processor 120 lengthens the heating time tm1 by a certain time increment and shortens the heat dissipation time tm2 by a certain time increment. The processor 120 further detects and determines whether the maximum fluid temperature T2 has exceeded the preset temperature threshold tT during the heating stage and the heat dissipation stage of the next cycle. If it is determined that the maximum fluid temperature T2 is still equal to or less than the preset temperature threshold tT, the processor 120 further lengthens the heating time tm1 by a certain time increment and shortens the heat dissipation time tm2 by a certain time increment in the next cycle. This process is repeated until the maximum fluid temperature T2 exceeds the preset temperature threshold tT.

[0050] Assuming that the processor 120 lengthens the heating time tm1 by one or more time change amounts to obtain a heating time tm1' and shortens the heat dissipation time tm2 by one or more time change amounts to obtain a heat dissipation time tm2', the processor 120 can obtain the maximum temperature T2 from the temperature curve in Figure 10 and determine that the maximum temperature T2 is greater than the preset temperature threshold tT. Therefore, the processor 120 can calculate the temperature difference between the maximum temperature T2 and the ambient temperature T1.

[0051] 9, for example, if the heating time tm1' is 1.5 seconds, the heat dissipation time tm2' is 2.5 seconds, the second reference heating time is 1.5 seconds, and the second reference heat dissipation time is 2.5 seconds, the processor 120 can determine that the heating time tm1' and the heat dissipation time tm2' are equal to the second reference heating time and the second reference heat dissipation time, respectively. This allows the processor 120 to obtain a relationship curve RC2 corresponding to the second reference heating time and the second reference heat dissipation time from the conversion curve diagram. The processor 120 can then obtain the flow velocity corresponding to the temperature difference as the flow velocity of the fluid in the pipe from the relationship curve RC2.

[0052] As another example, assuming that the heating time tm1' is 1.3 seconds, the heat dissipation time tm2' is 2.7 seconds, the first reference heating time is 1 second, the first reference heat dissipation time is 3 seconds, the second reference heating time is 1.5 seconds, the second reference heat dissipation time is 2.5 seconds, the third reference heating time is 3 seconds, and the third reference heat dissipation time is 1 second, the processor 120 determines that none of the first reference heating time, the second reference heating time, and the third reference heat dissipation time is equal to the heating time tm1'. The processor 120 also determines that none of the first reference heat dissipation time, the second reference heat dissipation time, and the third reference heat dissipation time is equal to the heat dissipation time tm2'.

[0053] Based on this, processor 120 calculates three differences between the first, second, and third reference heating times and the heating times (i.e., 0.3, 0.2, and 1.7, respectively), and selects the two smallest differences (i.e., 0.3 and 0.2) from the three differences. Then, processor 120 selects two relationship curves (i.e., relationship curves RC1 and RC2) corresponding to the two smallest differences (i.e., 0.3 and 0.2) from the conversion curve diagram, and obtains two flow velocities corresponding to the above temperature differences from the two corresponding relationship curves. Finally, processor 120 performs an interpolation operation on the two corresponding flow velocities based on the respective reference heating times and heating times of the two corresponding relationship curves to calculate one flow velocity, and sets this flow velocity as the flow velocity of the fluid in the pipe.

[0054] As described above, the flow rate detection device and method disclosed herein dynamically adjusts the heating time and heat dissipation time of the fluid to obtain an appropriate temperature difference, and then directly converts the temperature difference into the fluid flow rate using a conversion curve diagram. This allows the flow rate detection device and method disclosed herein to obtain the fluid flow rate from the fluid temperature difference using only a single heating circuit. This not only significantly saves hardware resources (i.e., eliminates the need for multiple temperature detection circuits), but also avoids the problem of low flow rate calculation accuracy in conventional detection methods. Furthermore, the flow rate detection device and method disclosed herein also pre-sets a temperature threshold and uses the temperature threshold to adjust the heating time and heat dissipation time, thereby avoiding the problem of significantly reduced resolution in the relationship between a relatively low fluid temperature difference and a relatively high fluid flow rate.

[0055] The above description is merely a specific example of the present application and does not limit the scope of the claims of the present application, so that all equivalent modifications utilizing the contents of the present application are equally included in the scope of the present application. [Explanation of symbols]

[0056] 100: Flow velocity detector 110:Heating circuit 120: Processor 130: Temperature detection circuit 140: Memory 141: Conversion curve diagram 200: Probe rod 210: Tip 300: Piping FD1:Flow direction S310~S350, S510~S540: Step t1: Heating stage t2: Heat dissipation stage tT: temperature threshold T2~T5: Maximum temperature T1: Ambient temperature tm1, tm1': heating time tm2, tm2': heat dissipation time C1~C4: Temperature curve rt1, rt1', rt1": Reference heating time rt2, rt2', rt2": Reference heat dissipation time RC1~RC3: Relationship curve

Claims

1. a heating circuit provided on a probe rod of a thermal mass flow meter and configured to heat a fluid in a pipe, the probe rod being installed in the pipe; a temperature detection circuit disposed adjacent to the heating circuit and configured to detect a temperature of the fluid in the piping; a processor connected to the heating circuit and the temperature detection circuit; The processor: (a) controlling the heating circuit during a heating stage to heat the fluid for a heating time; (b) controlling the heating circuit to stop heating the fluid during a heat dissipation stage after the heating stage, so that the fluid dissipates heat for a heat dissipation time; (c) determining whether the maximum temperature of the fluid detected by the temperature detection circuit during the heating step and the heat dissipation step satisfies a predetermined periodic recurrence condition; Step (d) of calculating a temperature difference between the maximum temperature and an ambient temperature when the maximum temperature satisfies the predetermined periodic recurrence condition, and converting the heating time, the heat dissipation time, and the temperature difference into a flow velocity of the fluid in the pipe based on a conversion curve diagram, wherein the conversion curve diagram includes a plurality of curves corresponding to a plurality of reference heating times and a plurality of reference heat dissipation times, respectively, and each curve shows a relationship between the temperature difference and the flow velocity at the corresponding reference heating time and the corresponding reference heat dissipation time, and the maximum temperature and the ambient temperature are detected by the temperature detection circuit at different times; and (e) performing steps (a) to (c) again, if the maximum temperature does not satisfy the predetermined periodic recurrence condition, so that the heating time is lengthened and the heat dissipation time is shortened.

2. The plurality of curves includes a first relationship curve, a second relationship curve, and a third relationship curve, and the processor further: controlling the heating circuit to heat the fluid for a first reference heating time and to dissipate heat for a first reference heat dissipation time for each of a plurality of reference flow rates of the fluid to generate a first temperature curve; controlling the heating circuit to heat the fluid for a second reference heating time and release heat for a second reference heat release time for each of the fluids at the plurality of reference flow rates to generate a second temperature curve, the second reference heating time being longer than the first reference heating time and the second reference heat release time being shorter than the first reference heat release time; controlling the heating circuit to heat the fluid for a third reference heating time and release heat for a third reference heat release time for each of the fluids at the plurality of reference flow rates to generate a third temperature curve diagram, the third reference heating time being longer than the second reference heating time and the third reference heat release time being shorter than the second reference heat release time and the first reference heat release time; 2. The flow velocity detection device of claim 1, wherein the device is configured to perform the steps of: generating the conversion curve diagram based on the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram, wherein the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram are used to generate the first relationship curve, the second relationship curve, and the third relationship curve, respectively, and the first relationship curve, the second relationship curve, and the third relationship curve are applied to the fluid at a low flow velocity, the fluid at a medium flow velocity, and the fluid at a high flow velocity, respectively.

3. The conversion curve diagram includes a plurality of relationship curves, and in step (d), the processor a step of selecting the relationship curve corresponding to the heating time and the heat dissipation time from the conversion curve diagram, the corresponding relationship curve corresponding to the reference heating time and the reference heat dissipation time that are the same as the heating time and the heat dissipation time, respectively, and showing the relationship between the temperature difference and the flow rate at the same reference heating time and the same reference heat dissipation time; and obtaining, from the corresponding relationship curve, a flow velocity corresponding to the temperature difference as the flow velocity of the fluid in the pipe.

4. In the step (d), the processor When the relationship curves corresponding to the heating time and the heat dissipation time cannot be selected from the conversion curve diagram, calculating a plurality of differences between the reference heating time and the heating time of each of the plurality of relationship curves in the conversion curve diagram, and selecting two smallest differences from the plurality of differences; selecting two relationship curves corresponding to the two minimum differences from the conversion curve diagram, and obtaining two flow rates corresponding to the temperature differences from the two corresponding relationship curves; 4. The flow velocity detection device according to claim 3, further comprising: a step of calculating the flow velocity of the fluid in the pipe by performing an interpolation operation on the two corresponding flow velocities based on the reference heating time and the heating time of each of the two corresponding relationship curves.

5. 2. The flow velocity detection device of claim 1, wherein the predetermined periodic recurrence condition is that the maximum temperature of the fluid is greater than a temperature threshold.

6. (a) controlling, by a processor, during a heating stage, a heating circuit to heat a fluid in a pipe for a heating time, the heating circuit being provided on a probe rod of a thermal mass flow meter, the probe rod being provided in the pipe; (b) during a heat dissipation stage after the heating stage, controlling the heating circuit by the processor to stop heating the fluid so as to dissipate heat from the fluid for a heat dissipation time; (c) determining, by the processor, whether a maximum temperature of the fluid detected by a temperature detection circuit during the heating stage and the heat dissipation stage satisfies a predetermined periodic recurrence condition; If the maximum temperature satisfies the predetermined periodic recursion condition, the processor calculates a temperature difference between the maximum temperature and an ambient temperature, and converts the heating time, the heat dissipation time, and the temperature difference into a flow velocity of the fluid in the pipe based on a conversion curve diagram (d), wherein the conversion curve diagram includes a plurality of curves corresponding to a plurality of reference heating times and a plurality of reference heat dissipation times, respectively, and each curve shows a relationship between the temperature difference and the flow velocity at the corresponding reference heating time and the corresponding reference heat dissipation time, and the maximum temperature and the ambient temperature are detected by the temperature detection circuit at different times; and (e) if the maximum temperature does not satisfy the predetermined periodic recurrence condition, the processor performs steps (a) to (c) again, with the heating time being increased and the heat dissipation time being decreased.

7. the plurality of curves include a first relationship curve, a second relationship curve, and a third relationship curve; controlling, by the processor, the heating circuit to heat the fluid for a first reference heating time and to dissipate heat for a first reference heat dissipation time for each of the fluid at a plurality of reference flow rates to generate a first temperature curve; controlling, by the processor, the heating circuit to heat the fluid for a second reference heating time and to release heat for a second reference heat release time for each of the fluids at the plurality of reference flow rates to generate a second temperature curve, the second reference heating time being longer than the first reference heating time and the second reference heat release time being shorter than the first reference heat release time; controlling, by the processor, the heating circuit to heat the fluid for a third reference heating time and to release heat for a third reference heat release time for each of the fluids at the plurality of reference flow rates to generate a third temperature curve diagram, wherein the third reference heating time is longer than the second reference heating time and the third reference heat release time is shorter than the second reference heat release time and the first reference heat release time; 7. The flow velocity detection method of claim 6, further comprising: generating, by the processor, the conversion curve diagram based on the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram, wherein the first temperature curve diagram, the second temperature curve diagram, and the third temperature curve diagram are used to generate the first relationship curve, the second relationship curve, and the third relationship curve, respectively, and the first relationship curve, the second relationship curve, and the third relationship curve are applied to the fluid at a low flow velocity, the fluid at a medium flow velocity, and the fluid at a high flow velocity, respectively.

8. The conversion curve diagram includes a plurality of relationship curves, and step (d) a step of selecting, by the processor, the relationship curve corresponding to the heating time and the heat dissipation time from the conversion curve diagram, wherein the corresponding relationship curve corresponds to the reference heating time and the reference heat dissipation time that are the same as the heating time and the reference heat dissipation time, respectively, and shows the relationship between the temperature difference and the flow rate at the same reference heating time and the reference heat dissipation time; and obtaining, by the processor, a flow velocity corresponding to the temperature difference from the corresponding relationship curve as the flow velocity of the fluid in the pipe.

9. The step (d) When the relationship curves corresponding to the heating time and the heat dissipation time cannot be selected from the conversion curve diagram, the processor calculates a plurality of differences between the reference heating time and the heating time for each of the plurality of relationship curves in the conversion curve diagram, and selects two smallest differences from the plurality of differences; selecting, by the processor, two relationship curves corresponding to the two minimum differences from the conversion curve diagram, and obtaining two flow rates corresponding to the temperature differences from the two corresponding relationship curves; The flow velocity detection method according to claim 8, further comprising: a step in which the processor calculates the flow velocity of the fluid in the pipe by performing an interpolation operation on the two corresponding flow velocities based on the reference heating time and the heating time of each of the two corresponding relationship curves.

10. The method of claim 6 , wherein the predetermined periodic recurrence condition is that the maximum temperature of the fluid is greater than a temperature threshold.

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