CN100430851C - Accurate mathematical control method for compact heat exchanger - Google Patents

Abstract

The present invention relates to an accurate numerical control method for a compact heat exchanger, which is widely used for the fields of chemical industry, aerospace, automobiles, etc. The present invention comprises the following procedures that an accurate mathematical model is established; an adjusting parameter is obtained; the accurate mathematical model of the heat exchanger is solved by a numerical method; an accurate mathematical controller is made of a single chip microcomputer or a PLC controller. The accurate mathematical controller comprises a microcomputer CPU, a multi-way analogic switch, an A/D converter, an RAM, an EPROM memory, a D/A converter, a set device and a power supply system. On the basis of feedforward control, the method leads the accurate mathematical model of the heat exchanger in a feedforward controller, combines a control method and hardware equipment into a whole to form the accurate mathematical controller of the compact heat exchanger, improves the control quality of the compact heat exchanger, realizes control with high accuracy and without a lag, and thereby, reaches the purposes that a process parameter level and the product quality are improved.

Description

Compact heat exchanger accurate mathematical control method

Technical field

The present invention relates to a kind of accurate mathematics controller that is widely used in the compact heat exchanger in fields such as chemical industry, space flight, automobile, belong to the energy and power engineering technology field.

Background technology

Compact heat exchanger is because numerous advantages such as compactness height, heat exchange property be good just are being widely used in fields such as chemical industry, space flight, automobile, and it is to guarantee process conditions and carry out temperature controlled major equipment.In actual moving process, because the variation of off-design operating mode usually takes place working condition, therefore, the control of heat interchanger is the key of good temperature control of quality and high product quality.At present, the control of heat interchanger mainly can be divided into two kinds, and the first is a controlled variable with the target fluid outlet temperature, is the FEEDBACK CONTROL of regulated quantity with the auxiliary fluid flow, under disturbance quantity was not very big situation, this control mode was widely used in compact heat exchanger; Another kind of control method is by increasing the by-pass governing method of target fluid bypass passageways, and this control mode is mainly used in the large-scale heat transmission equipment such as shell-and-tube, owing to increased bypass passageways, makes that the performance of heat interchanger can not be brought into play fully.Above-mentioned two kinds of control modes on control method, all belong to FEEDBACK CONTROL.Because the work characteristics of heat interchanger, making it all have very big volume lags behind and pure hysteresis, but FEEDBACK CONTROL only just can work after the target fluid technological parameter has changed, therefore, usually cause regulating action hysteresis, regulate shortcomings such as overlong time and overshoot be excessive, so, can not reach very high control of quality generally speaking.

In view of the above problems, start with from improving the control lag effect, feed forward control method also once was suggested, and what this method was used is the transport function that experimental method or theory method obtain.But, because the complicacy of heat transfer process in the heat interchanger, make parameter in the different operating points place transport function, even transport function integral body there are differences all, though therefore control rate makes moderate progress, be difficult to the control accuracy that reaches enough.

Summary of the invention

Purpose of the present invention is in order to overcome the weak point of existing control, provide a kind of on the basis of feedforward control, the mathematical models of heat interchanger is introduced feedforward controller, and integrated control method and hardware device are in the accurate mathematical control method of the compact heat exchanger of one, improve the control of quality of compact heat exchanger, realize its high precision, do not have the control that lags behind, thereby improve the level of technological parameter, the purpose of improving the quality of products.

Technical scheme of the present invention is: compact heat exchanger accurate mathematical control method may further comprise the steps:

1, set up precise math model, it comprises sets up energy-balance equation;

2, numerical solution solving heat exchange device mathematical models;

The method of its acquisition is in the porch of heat interchanger preposition temperature and flow probe to be set, disturbance situation by this detector perception suction parameter in time, and can obtain the situation of change of outlet parameter by mathematical models, when disturbance quantity is enough to change outlet parameter, obtain the numerical value of auxiliary fluid regulated quantity by the computing method of " indirect problem ", and in time regulate, like this, before changing, eliminates the target fluid outlet parameter its disturbance;

3, obtain to regulate parameter;

By a database that comprises the adjusting scale of all power condition changing situations,, obtain the numerical value of regulated quantity with the fastest speed by the method for feedforward controller Query Database;

4, make accurate mathematics controller with single-chip microcomputer or PLC controller.

The accurate mathematics controller that requires to make according to said method comprises:

1) finishes the micro computer CPU of functions such as all calculating, input and output, data query, data processing;

2) multiway analog switch and A/D converter;

3) provide CPU to calculate and the RAM storer of the storage space of deal with data;

4) eprom memory of application programs such as the master control program of inside solidification accurate mathematics controller, boot, data processor, Query Database or indirect problem algorithm program;

5) be used to provide auxiliary fluid topworks control valve or frequency converter signal, realize D/A converter the adjusting of auxiliary fluid flow;

6) be used to be provided with the occasionally setting apparatus of the form of thermal resistance output signal and range ability etc. of input sample primary element form and canonical parameter thermoelectricity;

7) power-supply system.

Effect of the present invention is:

The present invention adopts the method (indirect problem algorithm perhaps simply feedovers) of data base querying, and the fastest regulated quantity given way can be provided, and therefore, can guarantee control rate to greatest extent; Adopt mathematical models, can guarantee control accuracy,, when the heat exchanger performance parameter is accurate, can realizes high precision, not have the control dynamic transition process that lags behind, even can eliminate transient process in conjunction with the advantage of control rate; Heat interchanger control system in the past adopts a whole set of computer system often, and not only investment is big, and complex structure, and the wiring debugging cycle is long; And make things convenient for controller architecture compactness, the application that this method is made; The present invention is on the basis of feedforward control, the mathematical models of heat interchanger is introduced feedforward controller, and it is integrated into accurate mathematics controller, realizes the compact heat exchanger high precision, does not have the control that lags behind, and obtains obvious effects.

Description of drawings

Fig. 1 is a compact heat exchanger accurate mathematics controller structured flowchart.

Embodiment

Compact heat exchanger accurate mathematical control method may further comprise the steps:

1, setting up precise math model, be directed to the compact heat exchanger of any known structure and duty parameter, can set up its mathematical models, is example with the plate type finned heat exchanger, and its mathematical model comprises:

The fluid energy balance equation

${\left(\mathrm{\ρ}{C}_p\right)}_i\frac{\∂T_i}{\∂\mathrm{\τ}}+{\left({\mathrm{GC}}_p\right)}_i\frac{{\mathrm{dT}}_i}{\mathrm{dz}}={(1-\mathrm{\ξ\δ})}_i{\mathrm{\α}}_i(T_{b,i}+T_{b,i+1}-2T_i)+2{\mathrm{\ξ}}_i{\mathrm{\α}}_i{\∫}_{x=0}^{b_i}(T_{p,i}\left(x\right)-T_i)---\left(1\right)$

The dividing plate energy-balance equation

$-{\left(\mathrm{\&xi;\&delta;}\right)}_i\mathrm{\&lambda;}\frac{{\&PartialD;T}_{p,i}}{\&PartialD;x}{|}_{x=b_i}+{\left(\mathrm{\&xi;\&delta;}\right)}_{+1i}\mathrm{\&lambda;}\frac{{\&PartialD;T}_{p,i+1}}{\&PartialD;x}{|}_{x=0}\stackrel{\&OverBar;}{+}{\mathrm{\&delta;}}_i\mathrm{\&lambda;}\frac{{\&PartialD;}^2{T}_{b,i}}{{\&PartialD;\mathrm{<figure-callout\; id="2"\; label="z"\; filenames="C20031010930300081.png"\; state="\{\{state\}\}">z</figure-callout>}}^2}+{(1-\mathrm{\&xi;\&delta;})}_i{\mathrm{\&alpha;}}_i[T_i-T_{b,i+1}]---\left(2\right)$

$+{(1-\mathrm{\&xi;\&delta;})}_{i+1}{\mathrm{\&alpha;}}_{i+1}[T_{i+1}-T_{b,i+1}]=\left({\mathrm{\&rho;}}_b{C}_p\right)\frac{{\&PartialD;T}_{p,i}(p,i+1)}{\&PartialD;\mathrm{\&tau;}}$

The fin energy-balance equation

${\left(\mathrm{\&xi;\&delta;}\right)}_i\mathrm{\&lambda;}\frac{{\&PartialD;}^2{T}_{p,i}(x,z)}{{\&PartialD;x}^2}+{\left(\mathrm{\&xi;\&delta;}\right)}_i\mathrm{\&lambda;}\frac{{\&PartialD;}^2{T}_{p,i}(x,z)}{{\&PartialD;z}^2}-2{\mathrm{\&xi;}}_i{\mathrm{\&alpha;}}_i(T_{p,i}(x,z)-T_i)=\left({\mathrm{\&rho;}}_p{C}_p\right)\frac{\&PartialD;T_{p,i}(x,z)}{\&PartialD;\mathrm{\&tau;}}---\left(3\right)$

Using numerical solution can be in the hope of the heat interchanger output parameter under any initial conditions.

2, numerical solution solving heat exchange device mathematical models;

After the control of heat interchanger is meant that target fluid or auxiliary fluid suction parameter (temperature or flow) change, guarantees that the target fluid outlet parameter is constant or turn back to the setting process parameters range by regulating action.Therefore, Guan Jian problem is to regulate the acquisition of parameter.If directly obtain this parameter, and regulating action can be provided in time, control of quality will be improved widely so.Therefore, this method is that preposition (temperature and flow) detector is set in the porch of heat interchanger, disturbance situation by this detector perception suction parameter in time, and can obtain the situation of change of outlet parameter by mathematical models, when disturbance quantity is enough to change outlet parameter, obtain the numerical value of auxiliary fluid regulated quantity by the computing method of " indirect problem ", and send regulating action in time, like this, just the effect of disturbance can be eliminated before the target fluid outlet parameter changes.

3, obtain to regulate parameter;

By a database that comprises the adjusting scale of all power condition changing situations,, obtain the numerical value of regulated quantity with the fastest speed by the method for feedforward controller Query Database.At present, finding the solution of compact heat exchanger mathematical model mainly contains two kinds of methods, i.e. numerical method and analytical method.In the two, numerical method is acknowledged as method the most accurately, and it can find the solution the heat interchanger diffusion model that does not add any simplification and hypothesis, and analytic solution are only under certain simplified condition, and just can find the solution under the simple situation of heat exchanger structure.Therefore, the art of this patent is utilized numerical solution solving heat exchange device mathematical models, has considered that fluid heat conduction, fin and dividing plate laterally reach vertical heat conduction and whole internal divergence effects, can obtain the result of clock like precision.But, need the long period by numerical methods of solving " indirect problem ", can not guarantee the speed controlled, therefore, for any heat interchanger, be the adjusting scale that comprises all power condition changing situations by one of prior acquisition, be stored in chip internal, inquire about at any time for control system with the form of database.Like this, can obtain the numerical value of regulated quantity with the fastest speed.The capacity of database can decide according to the actual condition change conditions.

In addition, adopt ε-NTU method or log-mean temperature difference method also to can be used as the core feedforward arithmetic of the simple compact heat exchanger accurate mathematics controller of structure, because it calculates simple, can directly use indirect problem algorithm, and needn't adopt " database ", but be not so good as " database " method on the precision.

4, make accurate mathematics controller with single-chip microcomputer or PLC controller.

The accurate mathematics controller that requirement is finished according to said method, by shown in Figure 1, it comprises:

1) finishes the micro computer CPU8 of functions such as all calculating, input and output, data query, data processing, adopt single-chip microcomputer (98 or 51 series) or programmable logic controller (PLC) cpu chip;

2) multiway analog switch 6 and A/D converter 7 are selected general-purpose device for use according to required precision and speed, constitute analog input channel, realize the touring detection of heat exchanging device suction parameter (temperature and flow) under the CPU commander, and are converted to data volume for the CPU processing;

3) provide CPU to calculate and the RAM storer 11 of the storage space of deal with data, the employing general-purpose chip when storer desired volume hour, also can adopt the CPU on-chip memory, thereby save this element;

4) eprom memory 12 of application programs such as the master control program of inside solidification accurate mathematics controller, boot, data processor, Query Database or indirect problem algorithm program adopts general-purpose chip;

5) be used to provide auxiliary fluid topworks (control valve or frequency converter etc.) signal, realization is to the D/A converter 9 of the adjusting of auxiliary fluid flow, select general-purpose chip for use according to required precision and speed, current signal of outputting standard (4-20mA or 0-10mA) or voltage signal (0-10V or other optional scope);

6) be used to be provided with the setting apparatus 13 of the form of input sample primary element form and canonical parameter (for example thermoelectricity thermal resistance occasionally, and thermopair kind etc.), output signal and range ability etc.;

7) power-supply system 10, provide all required power supply signals of accurate mathematics controller.

1 is that target fluid, 2 is that auxiliary fluid, 3 is that heat exchanger body, 4,5 is heat exchanger entrance and outlet among the figure.

Claims (2)

1, a kind of compact heat exchanger accurate mathematical control method is characterized in that it may further comprise the steps:

1) sets up precise math model;

2) with numerical solution solving heat exchange device mathematical models;

The method of its acquisition is in the porch of heat interchanger preposition temperature and flow probe to be set, disturbance situation by this detector perception suction parameter in time, and can obtain the situation of change of outlet parameter by mathematical models, when disturbance quantity is enough to change outlet parameter, obtain the numerical value of auxiliary fluid regulated quantity by the computing method of " indirect problem ", and in time regulate, before changing, eliminates the target fluid outlet parameter its disturbance;

3) obtain to regulate parameter;

By a database that comprises the adjusting scale of all power condition changing situations,, obtain the numerical value of regulated quantity with the fastest speed by the method for feedforward controller Query Database;

4) adopt single-chip microcomputer or PLC controller to make accurate mathematics controller.

2. compact heat exchanger accurate mathematical control method according to claim 1 is characterized in that described compact heat exchanger accurate mathematics controller comprises:

1) finishes the micro computer CPU of functions such as all calculating, input and output, data query, data processing;

2) multiway analog switch and A/D converter;

3) provide CPU to calculate and the RAM storer of the storage space of deal with data;

4) eprom memory of application programs such as the master control program of inside solidification accurate mathematics controller, boot, data processor, Query Database or indirect problem algorithm program;

5) be used to provide auxiliary fluid topworks control valve or frequency converter signal, realize D/A converter the adjusting of auxiliary fluid flow;

6) be used to be provided with input sample primary element form and canonical parameter the thermoelectricity occasionally form of thermal resistance output signal and the setting apparatus of range ability;

7) power-supply system.

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