A Research Platform and Method for Fluid Heat Transfer and Automatic Control

Abstract

The present invention discloses a research platform and method for flow heat transfer and automatic control. In this platform, a cooling water tower is connected to a chiller; the cooling water tower is provided with two output ends for dividing the gas in the cooling water tower into two paths. One path passes through a first electromagnetic regulating valve to simulate the high-pressure low-temperature gas in a refrigerator with high-pressure normal-temperature gas, and the other path passes through a second electromagnetic regulating valve and an electric heater in sequence to simulate the high-pressure normal-temperature gas in a refrigerator with high-pressure heated gas. The high-pressure normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing through a pipe section. The mixed gas passes through a first long spiral pipe, a second long spiral pipe, a third long spiral pipe, and a fourth long spiral pipe connected in series. The gas coming out of the fourth long spiral pipe passes through a first switching valve and a second switching valve in sequence to reach a first superconducting device and a second superconducting device connected in series. The first superconducting device and the second superconducting device are used to absorb the heat in the gas to increase their own temperatures, and the temperature increase effect is used to simulate the cooling process of the superconducting device.

Description

Technical Field

[0001] The present invention relates to the fields of fluid heat transfer and automatic control, and particularly to an experimental platform and method for simulating the fluid heat transfer phenomenon and automatic control strategy during the cooling / rewarming process of superconducting equipment. Background Art

[0002] In recent years, large scientific projects newly built in the country (such as PAPS, HEPS, SHINE, CIADS, HIAF, CEPC, etc.) have all adopted large-scale helium cryogenic systems to provide cooling capacity for superconducting equipment. Limited by engineering site planning and vibration requirements, etc., the distance between the cold source and the actual cold-using equipment (superconducting cavity or superconducting magnet) is usually relatively far (on the order of hundreds of meters), and the cold-using equipment cannot withstand too much thermal stress, posing relatively high requirements for the cooling rate. The existing cooling methods usually mix high-pressure normal-temperature gas and high-pressure low-temperature gas in a refrigerator and then transport them through a low-temperature transmission pipeline to the cold-using equipment for cooling. During the cooling process, due to the long pipeline and large temperature range across which it spans, there are drastic changes in thermophysical properties, so its fluid heat transfer process has characteristics such as non-steady state, non-linearity, and large hysteresis. Usually, systems with hysteresis characteristics do not have an accurate mathematical model, and it is difficult to achieve ideal dynamic performance using traditional PID control systems. Therefore, it is very difficult for traditional control systems to achieve ideal control of systems with hysteresis characteristics (refer to Laslle J P. Stability Theory for Ordinary Differential Equations [J]. Journal of Differential Equations, 1968, 4(1): 57 - 65; Huang Lin, Qin Huashu. Theory of Complex Control Systems: Conception and Prospect [J]. Acta Automatica Sinica. 1993, 19(2): 129 - 137; Baumann W T. Feedback control of multi-input nonlinear systems by extended linearization [J]. IEEE Transactions on Automatic Control, 1988, 33(2): 193 - 197; Yang Dan. Modeling and Control of Hysteretic Nonlinear Systems [D]. University of South China, 2014). Currently, the usual practice for the cooling / rewarming process of cold-using equipment is to carry out slow cooling / rewarming in a manual control manner, which usually lasts for dozens of hours. It requires on-duty personnel to continuously manually adjust the temperature mixing valve to control the cooling rate, with low efficiency, no repeatability, and relatively relying on the cooling experience of on-duty personnel.

[0003] For the above reasons, there is an urgent need to develop a more intelligent automatic control system for the cooling / rewarming process of cold-using equipment. In addition, if experimental tests are directly carried out on a large-scale cryogenic system platform, it is necessary to operate a helium refrigerator and its auxiliary equipment, resulting in extremely high costs. Summary of the Invention

[0004] In order to overcome the deficiencies that in the existing large-scale cryogenic systems, it is difficult to precisely control the cooling process of cold-using equipment that is far from the cold source, and the existing manual control method is inefficient and non-repeatable, the present invention provides a flexible and economical small-scale flow heat transfer and automatic control research platform, which can simulate the unsteady flow heat transfer phenomenon of long-distance cold quantity transportation process. At the same time, in combination with modern control theory, an automatic heating technology based on the model predictive control algorithm (MPC, Model Predictive Control) is developed, and this technology can be easily extended to the cooling process.

[0005] The technical solution of the present invention is as follows:

[0006] A flow heat transfer and automatic control research platform, characterized by comprising

[0007] An air compressor 001, which is connected to a cooling water tower 002 through a pipeline section for inputting air into the cooling water tower 002;

[0008] The cooling water tower 002 is connected to a water chiller 016; the cooling water tower 002 is provided with two output ends for dividing the gas in the cooling water tower 002 into two paths for output. One path passes through a first electromagnetic regulating valve 003 to simulate high-pressure low-temperature gas in a refrigerator with high-pressure normal-temperature gas, and the other path passes through a second electromagnetic regulating valve 004 and an electric heater 005 in sequence to simulate high-pressure normal-temperature gas in a refrigerator with high-pressure heated gas. The high-pressure normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing through a pipe section 006. The mixed gas passes through a series of a first long spiral pipe 007, a second long spiral pipe 008, a third long spiral pipe 009, and a fourth long spiral pipe 010. The gas coming out of the fourth long spiral pipe 010 passes through a first switching valve 011 and a second switching valve 012 in sequence to reach a series of a first superconducting device 013 and a second superconducting device 014. The first superconducting device 013 and the second superconducting device 014 are used to absorb the heat in the gas to increase their own temperatures, and the heating effect is used to simulate the cooling process of the superconducting device.

[0009] The gas coming out of the second superconducting device 014 enters the cooling water tower 002 through a third switching valve 015, is cooled and then discharged into the atmosphere.

[0010] The output ends of pipe section 006, the first long spiral pipe 007, the second long spiral pipe 008, and the third long spiral pipe 009 can be respectively connected to the switching valve 012 through a switching valve and reach the first superconducting device 013 and the second superconducting device 014 connected in series; the output end of the first switching valve 011 is sequentially connected through the fifth switching valve 018 and the sixth switching valve 019; the output end of the first superconducting device 013 is connected to the input end of the sixth switching valve 019 through a switching valve.

[0011] When the high-pressure normal-temperature gas and the high-pressure heated gas are mixed in pipe section 006 and the mixed temperature does not reach the target temperature, the mixed gas enters the cooling water tower 002 through the fourth switching valve 017 for cooling and then is discharged; when only studying the temperature rise of the pipe section along the way without studying the temperature rise process of the superconducting device, the mixed gas passes through the first long spiral pipe 007, and / or the second long spiral pipe 008, and / or the third long spiral pipe 009, and / or the fourth long spiral pipe 010, and then enters the cooling water tower 002 through the first switching valve 011, the fifth switching valve 018, and the sixth switching valve 019 for cooling and then is discharged; the first long spiral pipe 007, the second long spiral pipe 008, the third long spiral pipe 009, and the fourth long spiral pipe 010 are used to combine and simulate the temperature drop process of low-temperature transmission pipelines at different distances.

[0012] Furthermore, a pressure sensor P1 is provided on the pipeline connecting the air compressor 001 and the cooling water tower 002, and a pressure sensor P2 and a flowmeter F1 are provided between the first electromagnetic regulating valve 003 and the pipe section 006; a pressure sensor P3 and a flowmeter F2 are provided on the pipeline connecting the second electromagnetic regulating valve 004 and the electric heater 005; a pressure sensor P4 is provided on the pipeline connecting the pipe section 006 and the first long spiral pipe 007, and a flowmeter F3 is provided on the gas discharge pipeline of the chiller 016.

[0013] Furthermore, the flowmeter F1 is a vortex flowmeter, the flowmeter F2 is a vortex flowmeter, and the flowmeter F3 is a thermal flowmeter.

[0014] Furthermore, a temperature sensor T is provided on the pipe section 006 01 , a temperature sensor T is provided at the input end of the first long spiral pipe 007 02 , a temperature sensor T is provided at the input end of the second long spiral pipe 008 03 , a temperature sensor T is provided at the input end of the third long spiral pipe 009 04 , a temperature sensor T is provided at the input end of the fourth long spiral pipe 010 05 , a temperature sensor T is provided at the output end of the fourth long spiral pipe 010 06 , a temperature sensor T is provided at the output end of the first switching valve 011 07, a temperature sensor T is provided at the output end of the first electromagnetic regulating valve 003 08 , temperature sensors T are provided at the output ends of the second electromagnetic regulating valve 004 and the electric heater 005 09 .

[0015] Furthermore, it further includes a measurement and control module for controlling the opening degrees of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004

[0016] Furthermore, the measurement and control module is used to receive the signals of the temperature, pressure, and flow sensors of the flow heat transfer and automatic control research platform collected, and send them to the upper computer terminal, and receive the control signals of the upper computer to control the opening degrees of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004

[0017] A flow heat transfer and automatic control method based on the flow heat transfer and automatic control research platform, the steps of which include

[0018] 1) Obtain the initial wall temperature of the pipeline along the way of the flow heat transfer and automatic control research platform as the measured value T 0，01 mea ~T 0，07 mea , use the interpolation method to obtain the wall temperature distribution of the pipeline along the way, and take the temperature T 0，07 mea at the end of the pipeline as the target measurement point; the source inlet temperature is T 01 , the temperature to be reached at the target measurement point is T end , the heating rate is T speed , and the set time interval is h

[0019] 2) Calculate the target temperature T speed after the jth time interval of the target measurement point according to the time interval h and the heating rate T target pre ;

[0020] 3) According to the temperature difference between T 01 and T target pre , solve the unsteady flow heat transfer equation by iterative method to find the inlet flow rate m g that meets the requirements; then according to the inlet temperature T 01 , inlet flow rate m g , calculate the isenthalpic mixing process to obtain the mass flow rate output after passing through the first electromagnetic regulating valve 003 and the mass flow rate Subsequently, based on the calculated mass flow rate and the relationship diagram between the valve opening and the mass flow rate, the openings of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004 can be deduced inversely, thus realizing the automatic control process within the first time interval; after measuring the temperature actual value T of the target measuring point at the end of the j-th time interval target mea , take T target mea +T speed as the target temperature of the target measuring point after the (j + 1)-th time interval, and calculate the automatic control process of the openings of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004 within the (j + 1)-th time interval; iterate until the temperature difference between the target measuring point and T end is less than the set value;

[0021] Among them, the unsteady flow heat transfer equation includes a pressure drop equation and a heat transfer equation. The pressure drop equation is dP is the pressure drop in a one-dimensional pipe, K i is the i-th resistance factor, is the resistance coefficient of the i-th pipe elbow, f ri is the frictional resistance coefficient along the i-th pipe, L i is the length of the i-th pipe, D is the pipe diameter; the heat transfer equation includes: Q i =(T i，out -T i，in )·C p ·m g , Q i =h i ·(T wi，inner -(T i，out +T i，in ) / 2)·πD inner L i , where, q i_out is the external heat leakage heat flux density of the i-th pipe, Q i is the heat flux passing through the wall of the i-th pipe per unit time, λ i is the thermal conductivity of the wall material of the i-th pipe, T i，in is the inlet temperature of the i-th pipe, T i，out is the outlet temperature of the i-th pipe, Tw i，inner is the inner surface temperature of the i-th pipe, Tw i，outer is the outer surface temperature of the i-th pipe, h i is the convective heat transfer coefficient of the flow inside the i-th pipe, D outer is the outer diameter of the pipe, D inner is the inner diameter of the pipe, C p is the specific heat capacity at constant pressure of the fluid, mg is the mass flow rate of the fluid.

[0022] Furthermore, the convective heat transfer coefficient h i = Nu·(λ / D); where λ is the thermal conductivity of the fluid and Nu is the Nusselt number.

[0023] Furthermore, the outer wall temperature at the τ+1 moment is obtained using the forward difference scheme where step_t represents the time step, C ps and ρ s are the heat capacity and density of the pipeline metal material, V i represents the volume of the i-th pipeline, is the outer wall temperature of the i-th pipeline at the τ moment.

[0024] Furthermore, according to the energy conservation equation and the mass conservation equation calculate the isenthalpic mixing process to obtain the mass flow rate after the first electromagnetic regulating valve 003 as well as the mass flow rates after the second electromagnetic regulating valve 004 and the electric heater 005 H1 is the enthalpy value after the first electromagnetic regulating valve 003, which can be obtained by querying the temperature T 08 , pressure P2 and the physical property table of air. H2 is the enthalpy value after the second electromagnetic regulating valve 004 and the electric heater 005, which can be obtained by querying the temperature T 09 , pressure P3 and the physical property table of air.

[0025] Compared with the prior art, the flow heat transfer and automatic control multi-functional experimental platform provided by the present invention has the following advantages:

[0026] First, the platform of the present invention uses the model predictive control algorithm MPC, which is different from the traditional PID control method that cannot solve the problem that it is difficult to achieve ideal control for a hysteretic system. It can realize time-domain rolling optimization, online solve the one-dimensional discrete equation of unsteady flow in the pipe and obtain the valve opening, and then realize the automatic heating process.

[0027] Second, the platform of the present invention is provided with long spiral pipes 007-010 with a length of about one hundred meters and temperature sensors T 01 ~T 09 , which can study the unsteady, non-linear, and large hysteretic flow heat transfer phenomena under normal temperature or heating conditions, and can greatly reduce the experimental cost. Brief Description of the Drawings

[0028] Figure 1 is a schematic diagram of the platform process of the present invention.

[0029] Figure 2 This is a schematic diagram of the heating process of a superconducting device based on the MPC control method for this platform.

[0030] Figure 3 It is a block diagram of the specific implementation steps of flow heat transfer and automatic control based on MPC.

[0031] Figure 4 It is a schematic diagram of the one-dimensional discrete form of unsteady flow in a pipe.

[0032] Figure 5 It is a graph showing the relationship between the ideal equal percentage valve opening and the flow rate.

[0033] Among them, 001 - air compressor, 002 - cooling water tower, 003 - first electromagnetic regulating valve, 004 - second electromagnetic regulating valve, 005 - electric heater, 006 - pipe section, 007 - first long spiral pipe, 008 - second long spiral pipe, 009 - third long spiral pipe, 010 - fourth long spiral pipe, 011 - first on-off valve, 012 - second on-off valve, 013 - first superconducting device, 014 - second superconducting device, 015 - third on-off valve, 016 - chiller, 017 - fourth on-off valve, 018 - fifth on-off valve, 019 - sixth on-off valve. Specific implementation method

[0034] The present invention will be further described in detail below with reference to the accompanying drawings.

[0035] The flow schematic diagram of the flow heat transfer and automatic control research platform of the present invention is as Figure 1 shown. In Figure 1 , the mainstream flowing working medium: air; pressure source: mobile screw air compressor (1.3 MPa); heating method: electric heater; cooling method: chiller + water / air shell-and-tube heat exchanger (cooling water tower); heat insulation method: aluminosilicate wool; pipeline: DN25 304 stainless steel electro-polished pipe, which is of long spiral type and is wrapped with heat insulation material on the outside; pipeline connection method: welding and flange; temperature measurement method: PT100 thermal resistance; pressure measurement method: pressure sensor and differential pressure sensor; flow measurement method: vortex flowmeter * 2 + mass flowmeter * 1; measurement and control method: PC host computer + PLC, controlling electromagnetic CV regulating valve.

[0036] Figure 1The specific process is introduced as follows: The air compressor 001 and the cooling water tower 002 are connected by a section of intake pipe. The gas coming out of the cooling water tower 002 is split into two paths. One path passes through the first electromagnetic regulating valve 003 to simulate the high-pressure and low-temperature gas in the refrigerator with high-pressure and normal-temperature gas. The other path passes through the second electromagnetic regulating valve 004 and the electric heater 005. The maximum power of the electric heater is 14 kW, and the outlet temperature is maintained stable through the PID temperature control program of the heater itself. The temperature of the heated gas can reach up to 350 °C at most, and the high-pressure heated gas is used to simulate the high-pressure and normal-temperature gas in the refrigerator. The high-pressure and normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing in the pipe section 006. The mixed gas passes through four sections of 25 m long spiral pipes 007 - 010 with adiabatic layers outside, and the temperature rise process of the pipe section along the way is used to simulate the temperature drop process of the low-temperature transmission pipeline. The gas coming out of the fourth long spiral pipe 010 passes through the first switching valve 011 and the second switching valve 012 and reaches the first superconducting device 013 and the second superconducting device 014 connected in series. The superconducting device absorbs the heat in the gas and causes its own temperature to rise, and the temperature rise effect is used to simulate the temperature drop process of the superconducting device. The gas coming out of the second superconducting device 014 passes through the third switching valve 015 and enters the cooling water tower 002, where it is cooled by the constant-temperature cooling water (about 7 °C) from the chiller 016 and then discharged into the atmosphere. When the high-pressure and normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing in the pipe section 006 and the mixed temperature has not reached the target temperature, the mixed gas can pass through the fourth switching valve 017 and enter the cooling water tower 002, where it is cooled and then discharged; when only the temperature rise of the pipe section along the way is studied and not the temperature rise process of the superconducting device, the mixed gas can pass through the long spiral pipes 007 - 010, and then through the first switching valve 011, the fifth switching valve 018 and the sixth switching valve 019, and enter the cooling water tower 002, where it is cooled and then discharged. The long spiral pipes 007 - 010 can also be freely combined according to experimental requirements, and a switching valve is set at the rear end of each pipe section, and the temperature rise effect of different lengths of pipe sections can be studied. P1 - P4 are pressure sensors, F1 - F3 are flow meters, where F1 and F2 are vortex flow meters and F3 is a thermal flow meter, T 01 ~T 09 are temperature sensors.

[0037] The Siemens S7-1200 PLC is used as the measurement and control module to collect all temperature, pressure, and flow sensor signals. Then, the measurement and control data are transmitted to the upper computer terminal via Ethernet. The TIA Portal V15 is used as the upper computer configuration software. After configuration, the measurement and control interface can store the measurement data and the heating requirements (heating rate, target temperature, time interval, etc.) into a.dat file at a specified time interval. Then, an external calculation program is called at the specified time interval. The external calculation program can calculate based on the data in the.dat file and feedback the calculation results (the opening signals of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004) to the configuration software, and then feedback to the control components (the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004) to achieve the automatic control process.

[0038] The implementation of the external calculation program is based on the Model Predictive Control (MPC) algorithm for time-domain rolling calculation to obtain the open-loop control sequence by solving the open-loop problem online. The basic schematic diagram of this platform based on the MPC control method for the superconducting equipment heating process is as Figure 2 shown.

[0039] In Figure 2 , the horizontal axis is time, the vertical axis is temperature, the dotted line represents the measured value, and the solid line represents the predicted value. In the temperature time interval i~i+1, there are two temperature measurement signals (T i ) mea and (T i+1 ) mea , and two temperature prediction signals (T i ) pre and (T i+1 ) pre . At each sampling moment, according to the temperature point measurement information and the control input, a finite-time open-loop problem is solved online. Using the new measurement value and the corresponding deviation information as the initial condition for predicting the next moment of the system and re-solving, the control sequence can be obtained to act on the controlled object.

[0040] Now, an example of the heating process is given to specifically illustrate the specific implementation steps of this platform based on the MPC control method, as Figure 3 shown.

[0041] Known conditions: The initial wall temperature of the pipeline along the way is the measured value T 0，01 mea ~T 0，07 mea . The interpolation method is used to obtain the wall temperature distribution of the pipeline along the way. The source inlet temperature is T 01 , and the pipeline end temperature T 0，07 meaAs the target measurement point, the required temperature T end is 500K, and the target heating rate T speed is 50K / h. The specified time interval is 1h (one hour).

[0042] Calculated from the time interval and the heating rate, the target temperature T target pre after one time interval. Obviously, if we want the temperature of the target point to reach T target pre at the end of this time interval (1h), then we need to control two variables: the source inlet temperature and the flow rate. Among them, the source inlet temperature T 01 needs to be higher than T target pre . Directly assume that the inlet temperature T 01 in the first time period is 20K higher than T target pre (ignoring the heat leakage loss along the way). Then we only need to solve the unsteady flow heat transfer equation by iteration to find the inlet flow rate that meets the requirements. Then, according to the inlet temperature T 01 and the inlet flow rate m g , calculate the isenthalpic mixing process to obtain the mass flow rate after the first electromagnetic control valve 003 and the mass flow rate after the second electromagnetic control valve 004 and the electric heater 005. Then, based on the calculated mass flow rate and the relationship diagram between the valve opening and the flow rate, we can inversely deduce the opening degrees of the first electromagnetic control valve 003 and the second electromagnetic control valve 004, thus realizing the automatic control process within the first time interval. After one time interval, the measured value T target mea of the target point plus T speed can obtain the target point temperature after the second time interval. Collect the wall temperature measurement points of the pipeline along the way at this time, and re-call the calculation program for calculation to realize the automatic control process within the second time interval. Repeat the above process until the target point temperature reaches the required temperature T end (the iteration convergence condition is that the absolute difference between the calculated temperature of T target pre and T target pre is within 1K).

[0043] Figure 4 The temperature and pressure of the fluid in the pipeline follow the one-dimensional flow heat transfer law, and the schematic diagram of the discrete form is as shown in Figure 4 .

[0044] For the control volume, the three major conservation equations of mass, energy, and momentum can be listed, and they are discretely calculated using numerical methods. For any discrete element, it is considered that within a certain moment, its inlet temperature T i，inand the outlet temperature T i，out are both uniform, and the temperatures Tw of the inner and outer surfaces of the solid domain i，inner and Tw i，outer are both fixed values. The physical properties are calculated in real time by calling the physical property function with the qualitative temperature and pressure.

[0045] For the time term, the forward difference and explicit stepping method are used for calculation. The main unsteady flow and heat transfer equations are as follows:

[0046] (1) Pressure drop calculation:

[0047] After neglecting the gravity term, the pressure drop in the one-dimensional pipe can be expressed as:

[0048]

[0049] where the resistance factor K i can be composed of the elbow resistance coefficient and the frictional resistance coefficient f along the way ri as well as the pipe length L i and the pipe diameter D:

[0050]

[0051] (2) Heat transfer calculation:

[0052] Since the total pressure is relatively low in this example (there is a large pressure loss after passing through the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004, and the pressure at T 01 depends on the standby pressure), the overall flow velocity is basically less than 0.3 Ma, belonging to the category of low-speed flow. Therefore, the temperature increase caused by factors such as frictional dissipation and local resistance is ignored, and radiation heat transfer is also ignored. It is considered that the change in temperature mainly comes from the convective heat transferred from the solid wall.

[0053] For a certain moment, it is considered that there is external heat leakage loaded on the outer wall of the pipe, and q i_out is the external heat leakage heat flux density, and at the same time, the heat transfer reaches a steady state. At this time, there is:

[0054]

[0055] Q i is the heat flux passing through the wall per unit time, and here λ i is the thermal conductivity of the local pipe wall solid material.

[0056] For the fluid, there is also:

[0057] Q i =(T i，out -T i，in )·C p ·m g (4)

[0058] Q i = h i ·(T wi，inner -(T i，out + T i，in ) / 2)·πD inner L i (5)

[0059] In the above, C p is the specific heat capacity at constant pressure of the fluid, and m g is the mass flow rate of the fluid. The two equations respectively represent the increase in the internal energy of the fluid in a certain micro-element section and the heat transferred from the outside. Among them, the convective heat transfer coefficient h i of the single-phase flow in the pipe can be expressed as:

[0060] h i = Nu·(λ / D) (6)

[0061] Here, λ is the thermal conductivity of the fluid, Nu is the Nusselt number, and D is the inner diameter of the pipe.

[0062] Since T i，in and T wi，outer are actually boundary conditions, there are 2 unknowns in the above equation, which are T wi，inner and T i，out . T i，out = T i+1，in . By constructing a numerical method, the temperature distribution of each micro-element section in the first time step can be solved sequentially.

[0063] For the time step, since the pipe wall is usually thin and has a large thermal conductivity, the unsteady factors in the radial direction are not considered, and the forward difference format is used to obtain the outer wall temperature at the next moment

[0064]

[0065] Here, step_t represents the time step. For example, within a specified time interval of 1 h, the iteration step can be selected as 10 seconds per step, then the number of iteration steps is 6 steps. C ps and ρ s are the specific heat capacity at constant pressure and density of the pipe metal material, D outer is the outer diameter of the pipe, D inner is the inner diameter of the pipe, and V i represents the volume of this section.

[0066] Using the above formulas (1) to (7), based on the Newton iteration method, the mass flow rate m g that can meet the heating requirement within a time interval can be solved. Then, according to the inlet temperature T 01 , the inlet flow rate m gThe mixing process is calculated. The mixing process is carried out by mixing two streams in pipe section 006 through the first electromagnetic regulating valve 003 in the first path, the second electromagnetic regulating valve 004 in the second path, and the electric heater 005. For the mixing process, we assume that the enthalpy value remains the same before and after mixing. The temperature T after the first electromagnetic regulating valve 003 08 , the pressure is P2, and according to the physical property table of air, the enthalpy value H1 can be obtained by querying two state parameters, temperature and pressure. The temperature T after the second electromagnetic regulating valve 004 and the electric heater 005 09 , the pressure is P3, and according to the physical property table of air, the enthalpy value H2 can be obtained by querying two state parameters, temperature and pressure. According to the isenthalpic process, the energy and mass conservation equations are listed:

[0067]

[0068]

[0069] The mass flow rate after the first electromagnetic regulating valve 003 can be derived and the mass flow rate after the second electromagnetic regulating valve 004 and the electric heater 005 If both the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004, the two temperature-mixing valves, are ideal valves with equal percentage characteristics, the relationship between the valve opening and the mass flow rate is as shown in Figure 5 (Note: The relationship between the valve opening and the flow rate can be obtained from the valve manufacturer when selecting the valve). According to the calculated mass flow rates and and the relationship diagram between the valve opening and the flow rate, the openings of the first electromagnetic regulating valve 003 and the second electromagnetic regulating valve 004 can be deduced inversely, and the automatic control process within the first time interval can be achieved. After one time interval, the measured value T of the target point target mea plus T speed The target point temperature after the second time interval can be obtained. Collect the wall temperature measurement points of the pipeline along the way at this time, and re-call the calculation program for calculation to achieve the automatic control process within the second time interval. Repeat the above process until the target point temperature reaches the required temperature T end (The iteration convergence criterion is that the absolute difference between the calculated temperature of T target pre and T target pre is within 1K).

[0070] During the heating / cooling process of superconducting equipment, due to the long pipeline and large temperature range it spans, the thermal physical properties change violently, so its flow and heat transfer process has characteristics such as non-steady state, non-linearity, and large hysteresis. Usually, a system with hysteresis characteristics does not have an accurate mathematical model, and it is difficult to achieve ideal dynamic performance using traditional PID control methods. Therefore, it is difficult for traditional control systems to achieve ideal control of systems with hysteresis characteristics. Thus, this invention introduces the model predictive control algorithm MPC, uses the one-dimensional discrete equation of unsteady flow in the pipe as the prediction model, online solves the one-dimensional discrete equation of unsteady flow in the pipe within the rolling time domain to obtain the valve opening, and then realizes the automatic heating process.

[0071] In summary, the above are only some implementation schemes of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles related to flow heat transfer and automatic control shall be included in the protection scope of the present invention.

Claims

1. A method for flow heat transfer and automatic control of a flow heat transfer and automatic control research platform, the steps of which include: 1) Obtain the initial pipeline wall temperature distribution of the flow heat transfer and automatic control research platform, and take the temperature at the pipeline end as the target measurement point; set the temperature at the pipeline source inlet and the temperature to be reached at the target measurement point as T end , and the heating rate as T speed , and set the time interval as h; 2) Calculate the target temperature at the target measurement point after the j-th time interval as T based on the time interval h and the heating rate T speed target pre ;​ 3) According to the temperature difference between the inlet temperature and T target pre , by iteratively solving the unsteady flow heat transfer equation, the required inlet flow rate m g is obtained; then, according to the inlet temperature and the inlet flow rate m g , the isenthalpic mixing process is calculated to obtain the mass flow rate output after passing through the first electromagnetic regulating valve (003) and the mass flow rate output after passing through the second electromagnetic regulating valve (004) and the electric heater (005); then, according to the calculated mass flow rate and the relationship diagram between the valve opening and the mass flow rate, the opening degrees of the first electromagnetic regulating valve (003) and the second electromagnetic regulating valve (004) are determined, and the automatic control process within the first time interval can be realized; after measuring the actual temperature value T target mea of the target measurement point after the j-th time interval, T target mea + T speed is used as the target temperature of the target measurement point after the (j + 1)-th time interval, and the automatic control process of the opening degrees of the first electromagnetic regulating valve (003) and the second electromagnetic regulating valve (004) within the (j + 1)-th time interval is calculated; the iteration loop is performed until the temperature difference between the target measurement point and T end is less than the set value; Among them, the flow heat transfer and automatic control research platform includes an air compressor (001), which is connected to a cooling water tower (002) through a section of pipeline and is used to input air into the cooling water tower (002); The cooling water tower (002) is connected to a chiller (016); the cooling water tower (002) is provided with two output ends, which are used to divide the gas in the cooling water tower (002) into two paths for output. One path passes through a first electromagnetic regulating valve (003) to simulate high-pressure low-temperature gas in a refrigerator with high-pressure normal-temperature gas, and the other path passes through a second electromagnetic regulating valve (004) and an electric heater (005) in sequence to simulate high-pressure normal-temperature gas in a refrigerator with high-pressure heated gas. The high-pressure normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing through a pipe section (006). The mixed gas passes through a series of a first long spiral pipe (007), a second long spiral pipe (008), a third long spiral pipe (009) and a fourth long spiral pipe (010). The gas coming out of the fourth long spiral pipe (010) passes through a first switching valve (011) and a second switching valve (012) in sequence to reach a series of a first superconducting device (013) and a second superconducting device (014). The first superconducting device (013) and the second superconducting device (014) are used to absorb the heat in the gas to increase their own temperature, and the temperature increase effect is used to simulate the cooling process of the superconducting device; The gas coming out of the second superconducting device (014) passes through a third switching valve (015) and enters the cooling water tower (002) to be cooled and then discharged into the atmosphere; The output ends of the pipe section (006), the output end of the first long spiral pipe (007), the output end of the second long spiral pipe (008), and the output end of the third long spiral pipe (009) are respectively connected to the second switching valve (012) through a switching valve to reach a series of a first superconducting device (013) and a second superconducting device (014); the output end of the first switching valve (011) is connected to the fifth switching valve (018) and the sixth switching valve (019) in sequence; the output end of the first superconducting device (013) is connected to the input end of the sixth switching valve (019) through a switching valve; Among them, when the high-pressure normal-temperature gas and the high-pressure heated gas are subjected to temperature mixing in the pipe section (006) and the mixing temperature does not reach the target temperature, the mixed gas passes through a fourth switching valve (017) and enters the cooling water tower (002) to be cooled and then discharged; when only studying the temperature rise of the pipeline along the way and not studying the temperature rise process of the superconducting device, the mixed gas passes through the first long spiral pipe (007), and / or the second long spiral pipe (008), and / or the third long spiral pipe (009), and / or the fourth long spiral pipe (010), and then passes through the first switching valve (011), the fifth switching valve (018) and the sixth switching valve (019) and enters the cooling water tower (002) to be cooled and then discharged; among them, the first long spiral pipe (007), the second long spiral pipe (008), the third long spiral pipe (009) and the fourth long spiral pipe (010) are used to combinatorially simulate the cooling process of low-temperature transmission pipelines at different distances; The unsteady flow heat transfer equations include the pressure drop equation and the heat transfer equation. The pressure drop equation is dP is the pressure drop in a one-dimensional pipe, K i is the i-th resistance factor, z bendsi is the i-th pipe elbow resistance coefficient, f ri is the i-th pipe frictional resistance coefficient along the way, L i is the length of the i-th pipe, D is the pipe diameter; the heat transfer equation includes: Among them, q i_out is the external heat leakage heat flux density of the i-th pipe, Q i is the heat flux passing through the wall of the i-th pipe per unit time, λ i is the thermal conductivity of the wall material of the i-th pipe, T i,in is the inlet temperature of the i-th pipe, T i,out is the outlet temperature of the i-th pipe, Tw i,inner is the inner surface temperature of the i-th pipe, Tw i,outer The outer surface temperature of the i-th pipe, h i is the convective heat transfer coefficient of the flow inside the i-th pipe, D outer is the outer diameter of the pipe, D inner is the inner diameter of the pipe, C p is the specific heat capacity at constant pressure of the fluid, m g is the mass flow rate of the fluid.

2. The method according to claim 1, characterized in that Convective heat transfer coefficient h i = Nu·(λ / D); where λ is the thermal conductivity of the fluid and Nu is the Nusselt number.

3. The method according to claim 1, characterized in that Obtain the outer wall temperature at time τ+1 using the forward difference scheme where step_t represents the time step, C ps and ρ s are the heat capacity and density of the pipeline metal material, V i represents the volume of the i-th pipeline, and is the outer wall temperature of the i-th pipeline at time τ.

4. The method according to claim 1, characterized in that According to the energy conservation equation m g1 H1 + m g2 H2 = m g H3 and the mass conservation equation Calculate the isenthalpic mixing process to obtain the mass flow rate Mass flow rate H1 is the enthalpy value after the first electromagnetic regulating valve (003), and H2 is the enthalpy value of the second electromagnetic regulating valve (004) and the electric heater (005).

5. The method according to claim 1, characterized in that A pressure sensor P1 is provided on the connecting pipeline between the air compressor (001) and the cooling water tower (002). A pressure sensor P2 and a flowmeter F1 are provided between the first electromagnetic regulating valve (003) and the pipe section (006); a pressure sensor P3 and a flowmeter F2 are provided on the connecting pipeline between the second electromagnetic regulating valve (004) and the electric heater (005); a pressure sensor P4 is provided on the connecting pipeline between the pipe section (006) and the first long spiral pipe (007), and a flowmeter F3 is provided on the gas discharge pipeline of the water chiller (016).

6. The method according to claim 5, characterized in that The flowmeter F1 is a vortex flowmeter, the flowmeter F2 is a vortex flowmeter, and the flowmeter F3 is a thermal flowmeter.

7. The method according to claim 5 or 6, characterized in that A temperature sensor T is provided on the pipe section (006). 01 A temperature sensor T is provided at the input end of the first long spiral pipe (007). 02 A temperature sensor T is provided at the input end of the second long spiral pipe (008). 03 A temperature sensor T is provided at the input end of the third long spiral pipe (009). 04 A temperature sensor T is provided at the input end of the fourth long spiral pipe (010). 05 A temperature sensor T is provided at the output end of the fourth long spiral pipe (010). 06 A temperature sensor T is provided at the output end of the first switching valve (011). 07 A temperature sensor T is provided at the output end of the first electromagnetic regulating valve (003). 08 A temperature sensor T is provided at the output ends of the second electromagnetic regulating valve (004) and the electric heater (005). 09 .

8. The method according to claim 7, characterized in that It further includes a measurement and control module for controlling the opening degrees of the first electromagnetic regulating valve (003) and the second electromagnetic regulating valve (004).

9. The method according to claim 8, characterized in that The measurement and control module is configured to receive the signals from the temperature, pressure, and flow sensors of the flow and heat transfer and automatic control research platform, send them to the upper computer terminal, and receive the control signals from the upper computer to control the opening degrees of the first electromagnetic regulating valve (003) and the second electromagnetic regulating valve (004).

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