EP2839129A1

EP2839129A1 - Method for regulating the temperature in a fluid-conducting circulation

Info

Publication number: EP2839129A1
Application number: EP13719722.4A
Authority: EP
Inventors: Andreas Welsch; Andreas Kugi; Alexander Michel
Original assignee: Hydac Cooling GmbH
Current assignee: Hydac Cooling GmbH
Priority date: 2012-04-21
Filing date: 2013-04-06
Publication date: 2015-02-25
Also published as: DE102012008043A1; WO2013156115A1

Abstract

The invention relates to a method for regulating the temperature of a fluid conducted in a circulation (I) for cooling or heating at least one device (14), wherein at least one heat exchanger (10) is provided in the circulation (I) to emit or absorb heat through the fluid that reaches the heat exchanger (10) at an intake temperature (T_Iin) and leaves at a discharge temperature (T_iout). The method is characterised in that the cooling or heating capacity to be applied to the device (14) is determined from the intake temperature (T_Iin) and the discharge temperature (T_iout) of the fluid at the heat exchanger (10) and/or from the volumetric flow (qi) of the fluid conducted in the circulation (I) and the emission or absorption of heat at the heat exchanger (10) is adjusted correspondingly.

Description

Method for controlling the temperature in a fluid-carrying circuit

The invention relates to a method for controlling the temperature of a circulating in a circuit for cooling or heating at least one device guided fluid, wherein in the circuit at least one heat exchanger is provided for discharging or receiving heat by the fluid, which reaches the heat exchanger with an inlet temperature and leaves with an outlet temperature.

Heat exchangers are widely used in almost all sectors of the manufacturing industry, see R.C. Shah and D.P. Sekulic, Fundamentals of Heat Exchanger Design, New Jersey: John Wiley & Sons, 2003. Liquid-liquid heat exchangers are frequently used, in which the volume flow on one side, such as a volume flow in another, second circuit, is specifically predefined via a valve can be. In many applications, in addition to the stationary accuracy of the outlet temperature to be set, high dynamics and at the same time a large working range of the regulated heat exchanger are required. Traditionally, linear concentrated parametric control strategies are used in the industry. However, the mathematical model of a heat exchanger has a non-linear, distributed-parametric due to the convective heat transfer between the cold and the hot water side

System behavior, which then leads to two fundamental problems when using linear control strategies: i) Because of the large Working range and the associated non-linear behavior, the linear control inherently reaches its limits, which manifests itself in the form of a low control quality up to an unstable control behavior, ii) Due to the widely varying applications and the associated high product diversity of the heat exchangers used, the controller parameters be redesigned for each system and workspace.

The object of the invention is to provide a controller structure which, in a large operating range without a separate adaptation of controller parameters, enables reliable regulation of the temperature of a fluid circulated in order to cool or heat at least one device.

This object is achieved by a method having the features of claim 1 in its entirety. An inventive method is characterized in that determined from the inlet and the outlet temperature of the fluid at the heat exchanger and / or the volume flow of circulating fluid to be applied to the device cooling or heating power and accordingly the delivery or absorption of heat at the heat exchanger is set.

In contrast to known methods, in which the outlet temperature is regulated at the outlet or outlet of the heat exchanger to the circuit, the cooling or heating power is controlled in the circuit according to the invention. For this purpose, the desired cooling or heating power in the circuit is calculated on the basis of the desired temperature for cooling or heating of the at least one device and this serves as a target value for the control according to the invention. This results in the advantage of a compensation of the different dynamic behavior of the controlled system for different volume flows of the heat exchanger for cooling or heating or flowing fluid. An essential advantage of the invention is that the inventive method or the corresponding control strategy, regardless of the design of the heat exchanger, such as a tube heat exchanger or plate heat exchanger, regardless of the operating mode as a cooling system or as a heating system, regardless of the flow as a DC or countercurrent heat exchanger and can be carried out regardless of the selected work area and thereby a control behavior is achieved, which shows a very good follow-up behavior at the same time high robustness against disturbances of the inlet temperatures and the unactuated flow rate.

In a first variant of the invention, at least one heat exchanger can be flowed in by a fluid flow, in particular an air flow, supplied via a fan, the speed of the fan being regulated in accordance with the heat to be exchanged between the fluid and the fluid flow on the heat exchanger. According to the invention, a power-based control of the heat exchanger, which is arranged in the fluid flow generated by the fan and is impinged by the fluid flow, takes place with the speed of the fan as a manipulated variable.

In a second variant of the invention, at least one heat exchanger can be flowed through by a further fluid, wherein, according to the heat to be exchanged between the fluid and the further fluid at the heat exchanger, the further volume flow of the further fluid through the heat exchanger and / or the further inlet temperature of the further fluid at the heat exchanger is regulated. Preferably, the further fluid is passed in a further circuit and arranged the heat exchanger in the further circuit. According to the invention, a power-based regulation of the heat exchanger arranged between the two circuits takes place with the further volume flow of the further circuit as a manipulated variable. Typically, the warmer fluid is conducted in the first circuit and the colder fluid in the second circuit. The particular fluid may be a liquid, such as a water-glycol mixture. In the first circuit, for example, a machine tool to be cooled is arranged as the device, which is to be supplied with a constant coolant temperature. In this case, a plate heat exchanger located in the return should dissipate the power supplied by the process in order to ensure a constant tank temperature and thus flow temperature for the machine tool in the first cycle. The heat exchanger can be, for example, a plate heat exchanger with 40 plates. For regulation, the respective inlet and outlet temperatures of the two circuits on the heat exchanger are available. The first volume flow in the first circuit can also be measured. In most applications of the considered cooling system, however, no changes in the first volume flow occur in the first circuit, which is why in such cases, a volumetric flow sensor in the first circuit can be dispensed with.

Advantageously, the method according to the invention comprises the following method sequence: the reading of at least one inlet and at least one outlet temperature and / or at least one volume flow as sensor values, the determination of the cooling time currently discharged at the device. Heat output, the power to be exchanged at the heat exchanger and / or the disturbance from sensor values and substance parameters, the determination of at least one virtual manipulated variable according to a precontrol and / or a predetermined control law, the transformation of virtual manipulated variable into a real manipulated variable, and the transfer of the manipulated variable to one corresponding regulator.

From the power to be dissipated or dissipated at the heat exchanger and the desired outlet temperature in the first circuit, an error system stabilizable with a P controller can be used in the sense of an input-output circuit. Generate linearization. Consequently, a control law is determined which guarantees a stable error system, wherein a virtual control variable is selected. Recalculation from the virtual manipulated variable to the real manipulated variable is generally not analytically possible, which is why in most cases a numerical solution method must be used. The real manipulated variable is, for example, the further or second volume flow of the fluid passed through the further or second circuit, the fluid flowing through the heat exchanger, or the speed of the fan for generating a fluid flow, a cooling current or a heating current flowing to the heat exchanger.

In a preferred variant of the method according to the invention, the further or second volume flow from the heat transfer coefficient for the heat exchanger is determined during the transformation from virtual manipulated variable to real manipulated variable. Particularly preferably, an observer for the heat transfer coefficient is provided on the heat exchanger, in other words, the control includes an observer for the heat transfer coefficient at the heat exchanger. When selecting the second volumetric flow as a manipulated variable, the non-linear dependence of the heat transfer coefficient on the volumetric flow must not be neglected. Extensive experimental investigations have shown that it is precisely the consideration of this effect that is decisive for the model quality and thus the quality of the model-based control strategy, cf. A. Michel, W. Kemmetmüller and A. Kugi, "Modeling and Regulating a Plate Heat Exchanger" Workshop GMA-Fachausschuss 1 .40, 2010. In addition to a model-based control strategy, it is also possible to approximate the mathematical relationship between the heat transfer coefficient and the volume flow online, which means that complex experimental identifications can be omitted. In a first variant, the further or second volume flow is determined from the desired heat transfer coefficient by means of at least one semiempirical similarity relationship and the definition of the heat transfer coefficient. The heat transfer coefficient is the most important characteristic of a heat exchanger and is highly dependent on the chosen heat exchanger type. At most, for simple geometries, an analytical solution can be found, but this is no longer possible for complex geometries, as occur, for example, in the plate heat exchangers typically used. In order to describe the heat transfer comparatively easily, semiempirische similarity-theoretical approaches are used, as they come in the design phase of heat exchangers are used, see VDI Society Process Engineering and Chemical Engineering, VDI Heat Atlas, 9th edition, Berlin / Heidelberg: Springer, 2002. These approximations or semiempirical similarity-theoretical approaches set the Nusselt number in relation to the Prandtl number and Reynolds number. For the sake of simplicity, the heat transfer coefficient can be approximated by the global heat transfer coefficients calculated for the respective circuit via the temperature values of inlet and outlet temperature. Overall, a distributed parametric model results, from which a controller design model and a controller law can be derived.

In a second variant, the further or second volume flow from the desired heat transfer coefficient is determined by means of an approximation via a steady-state power balance. Here, the exchanged between the two sides or chambers of the heat exchanger heat flow and a simple relationship between the heat transfer coefficient and the second volume flow is taken into account, whereby a complex numerical calculation of the second volume flow can be omitted. In a simulation study, this is distributed Parametric model has been approximated using the finite-volume method by a concentrated-parametric system with 100 states. Furthermore, the dynamics of typical temperature sensors have been considered. The simulation study has led to the conclusion that the selected control strategy has a very high control quality, regardless of whether the second volume flow is determined as a manipulated variable via a numerical inversion or via a stationary power balance. Although the system is subject to strong disturbances in the supplied power of the process, in other words when cooling the device, such as a machine tool, the second inlet temperature and the first volume flow, the power dissipated in the first circuit in both cases follows very well their setpoint, so that the tank temperature in the first cycle and consequently the flow temperature for the device to be cooled, such as a machine tool, remains almost constant. On the other hand, through the use of the control concept with the approximation of the heat transfer coefficient by means of the stationary power balance, a costly experimental identification of the heat exchanger used can be dispensed with. Thus, the derived control strategy has a very high adaptability with high control quality. Furthermore, the numerical complexity of the control law is very low, which makes it easy to implement in common control devices. Further advantages and features of the invention will become apparent from the figures and the following description of the drawing. The above-mentioned and the further cited features can be inventively realized individually or in any combination with each other. The features shown in the figures are purely schematic and not to scale. It shows: 1 shows a fluid-carrying system with a rule known from the prior art rule;

FIGS. 2a-2e each show a fluid-carrying system with a regulation according to the invention;

Fig. 3 shows a controller structure for carrying out the inventive

Method of regulation; and FIG. 4 shows a flow chart of the method according to the invention for regulation.

1 shows a fluid-carrying system with a heat exchanger 10, which is arranged between a fluid-carrying first circuit I and a further fluid-carrying, second circuit II. In the first circuit I are further a first reservoir Ri for the respective fluid, a motor-pump unit 12 for conveying fluid in a first volume flow qi in the first circuit I as well as a trained as a machine tool device 14, by the in first circuit I guided fluid is cooled, arranged. The fluid in the first circuit I leaves the heat exchanger 10 with a first outlet temperature Tiout, reaches the device 14 with a flow temperature T flow U nd reaches the heat exchanger 10 with a first inlet temperature Tun. At a constant first volume flow

= const, the flow temperature Tvoriauf differs from the first outlet temperature Tiout present in the first reservoir Ri or on the corresponding outlet side of the heat exchanger 10 by a constant value. Due to the cooling power applied to the device 14, the fluid is heated or heated accordingly and I follow the first inlet temperature Tun compared to the flow temperature Tvoriauf or the first outlet temperature Tiout increased. In the second circuit II, the second volume flow qn for fluid conducted in the second circuit II is set or set via an electromagnetically actuated, prestressed valve 16. The guided in the second circuit II fluid reaches the heat exchanger 10 with a second inlet temperature Tiiin and leaves it with a second outlet temperature Tnout, wherein the second outlet temperature Tnout compared to the second inlet temperature Tiiin by heat transfer from the guided in the first circuit I warmer fluid to that in the second circuit II guided colder fluid is increased in the region of the heat exchanger 10. Corresponding to the first reservoir Ri in the first circuit I, a second reservoir Rn for the corresponding fluid is provided in the second circuit II.

In the case of the regulator structure known from the prior art, the first outlet temperature Tiout in the first circuit I is regulated by means of a linear regulator designed as a PID controller and detected as a measured variable. The second volume flow qn in the second circuit II, which is adjusted as a function of the fluid pressure in the second circuit II by the corresponding position of the valve 16, serves as the manipulated variable.

FIGS. 2a-2e for illustrating the solution according to the invention differ from FIG. 1 in that at least the inlet temperature Tun and the outlet temperature Tiout of the fluid flowing through the heat exchanger 10 and the first volume flow qi of the fluid in the first circuit I are shown as measured variables first circuit I are detected.

In the exemplary embodiment of FIG. 2 a, the inlet temperatures Tiin, Tiiin and the outlet temperatures Tiout, Tnout in both circuits I, II as well as the first volume flow qi in the first circuit I are detected as measured variables. Furthermore, the first outlet temperature Tiout required for cooling the device 14 as a constant variable or the corresponding flow temperature Tvoriauf regulated, wherein in the controller structure according to the invention, a non-linear regulator is used. The manipulated variable is still the second volume flow qn in the second circuit II, which is adjusted in dependence on the fluid pressure via the valve 16.

In the embodiment of FIG. 2b, the second volume flow qn is additionally detected in the second circuit II.

In the embodiment of FIG. 2c, a further motor-pump unit 1 3 is provided instead of a valve for adjusting the fluid flow and the fluid pressure in the further or second circuit II. The further motor-pump unit 13 delivers according to the desired second volume flow qn fluid from the second reservoir Rn to the heat exchanger 10 and after passage of the heat exchanger 10 again back to the second Reservoir Rn. FIG. 2 c shows that the power of the pump of the motor-pump unit 12 arranged in the first circuit I can be adjusted as required. Alternatively or additionally, the power of the pump of the further motor-pump unit 13 arranged in the further or second circuit II can be configured to be adjustable.

The embodiment of Fig. 2d is compared to the arrangement of Fig. 2b modified such that the first circuit I and the second circuit II are interchanged. This illustrates that both circuits I, II can be designed both as a cooling or heating circuit and as a tempering circuit for the heat exchanger 10.

In the embodiment of FIG. 2e, the heat exchanger 10 is not tempered by a fluid flowing through it, but by a fluid flowing against it. A motor 15 drives a fan 1 7 which has a fluid flow, here an air flow, for the removal of waste heat emitted by the heat exchanger 10 or for the supply of heat to the heat exchanger. shear 10 produced. By the engine 1 5, the speed of the fan 1 7 and according to the temperature, more precisely the cooling or heating, the heat exchanger 10 is given, increased or decreased. The heat exchanger 10, the fan 1 7 and the motor 1 5 can be arranged in a common structural unit 19, in particular in a common housing.

3 shows that the first outflow temperature Tiout is first transferred as a setpoint quantity to a device 18, which receives, for example, the first inlet temperature Tun and the first volume flow qi as further input variables and the desired, in the first circuit I or through the fan 1 7 dissipated power ΔΡι, soii calculated and passes to a regulator device 20.

In the regulator device 20, the power to be dissipated via the heat exchanger 10 is calculated as a virtual manipulated variable ui and further calculated in a conversion device 22 from the inlet and outlet temperatures Tiin-Tnout and the first volume flow qi as sensor values of the second volume flow qn as a real manipulated variable. About the setting of the second volume flow qn via the valve 16 or the further motor-pump unit 1 3, the heat exchanger 10 is used to cool the corresponding fluid and are, influenced by the influence or. Disturbance variables, the inlet and outlet temperatures Tiin-Tnout and the first volume flow qi, the actual first outlet temperature Tiout off. The actual first outlet temperature Tiout is interrogated via the device 18 and taking into account the first inlet temperature Tun and the first volume flow qi the dissipated power at the heat exchanger 10 APi, is calculated and given back to the regulator device 20. 4, the sequence of the method according to the invention is shown. In a first step S1, the inlet and outlet temperatures TimTiout and the first volume flow qi are read in as sensor values. If one of the variables is known, its measurement can be dispensed with; for example, the first volume flow qi is often constant. In a subsequent second step S2 is from the sensor values and material parameters, the currently transmitted, ie discharged or supplied, power ΔΡι, the power transferred to the heat exchanger 10 ΔΡι, soii and / or determines the disturbance. In a third step S3, a virtual manipulated variable ui is determined in accordance with a precontrol and / or a predetermined control law. In a subsequent fourth step S4, the heat transfer coefficient U to be set for the heat exchanger 10 is determined from the virtual manipulated variable ui. In the fifth step S5, the second volume flow qn is determined from the desired heat transfer coefficient U, wherein in a first alternative S5a the determination is made by means of a semiempirical similarity relationship and the definition of the heat transfer coefficient U and in a second alternative S5b the determination by means of approximation via a stationary current account. In a subsequent sixth step S6, the desired second volume flow qn is transferred to a volume flow controller. As the first result Ea, in the method according to the invention, a power control, as shown in dashed lines in FIGS. 3 and 4, is achieved. Furthermore, the second result Eb is calculated back to the second volume flow qn as a real manipulated variable via a stationary power balance from the heat transfer coefficient U for the heat exchanger 10, as shown in FIGS. 3 and 4 in each case with a dotted border.

Claims

P a n t a n s p r e c h e

Method for controlling the temperature of a fluid circulated in a circuit (I) for cooling or heating at least one device (14),

wherein in the circuit (I) at least one heat exchanger (10) is provided for the release or absorption of heat by the fluid, which reaches the heat exchanger (10) with an inlet temperature (Tiin) and leaves with an outlet temperature (Tiout), characterized in that the cooling or heating power to be applied to the device (14) is determined from the inlet (Tim) and the outlet temperature (Tiout) of the fluid at the heat exchanger (10) and / or the volume flow (qi) of the fluid circulated in the circuit (I) and, correspondingly, the release or absorption of heat at the heat exchanger (10) is adjusted.

A method according to claim 1, characterized in that at least one heat exchanger (10) from a via a fan (1 7) supplied fluid flow, in particular an air flow, can be flowed, and that according to the heat exchanger (1 0) between the fluid and the fluid flow heat to be exchanged, the speed of the fan (1 7) is regulated.

A method according to claim 1 or 2, characterized in that at least one heat exchanger (10) can be flowed through by a further fluid, and that according to the heat to be exchanged between the fluid and the further fluid on the heat exchanger (10) the further volume flow (qn) of the further fluid through the heat exchanger (10) and / or the further inlet temperature (Tiiin) of the further fluid at the heat exchanger (10) is controlled. A method according to claim 3, characterized in that the wei ^¬ tere fluid is guided in a further circuit (II), and that the heat exchanger in the further circuit (II) is arranged.

A method according to claim 3 or 4, characterized in that the applied to the device (14) cooling or heating power alternatively or additionally to the inlet (Tim) and outlet temperature (Tiout) of the circulating (I) fluid through the further inlet temperature ( TiMn) and the further outlet temperature (TW) of the further fluid at the heat exchanger (10) is determined.

Method according to one of the preceding claims, comprising the following procedure:

Determining at least one inlet and at least one outlet temperature (Thn-Tiiout) and / or at least one volume flow (qi, qn),

Determination of the cooling or heating power (ΔΡι) currently discharged at the device (14), the heat to be exchanged at the heat exchanger (10) and / or the disturbance from sensor values and material parameters,

Determining at least one virtual manipulated variable (ui) according to a precontrol and / or a predetermined control law, preferably transformation of virtual manipulated variable (ui) into a real manipulated variable, and

Transfer of the manipulated variable to a corresponding controller.

Method according to claims 3 and 6, characterized in that in the transformation from virtual manipulated variable (ui) to real manipulated variable, the further volume flow (qn) of the further fluid from the heat transfer coefficient (U) for the heat exchanger (10) is determined.

8. The method according to any one of the preceding claims, characterized in that an observer for the heat transfer coefficient (U) on the heat exchanger (10) is provided.

9. The method according to claim 7 or 8, characterized in that the further volume flow (qii) from the desired heat transfer coefficient (U) by means of at least one semiempirischen similarity relationship and the definition of the heat transfer coefficient (U) is determined.

10. The method according to claim 7 or 8, characterized in that the further volume flow (qn) from the desired heat transfer coefficient (U) is determined by means of an approximation of a steady-state power balance.