Patent Application
20180045446
This application claims priority under 35 U.S.C. §119 from German Patent Application No. DE 10 2016 214 797.8, filed Aug. 9, 2016, the entire disclosure of which is herein expressly incorporated by reference.
The invention generally relates to the field of refrigeration machines. In particular, the invention relates to the design of the components of an air-conditioning/refrigeration system, for example for a motor vehicle.
An air-conditioning system serves to maintain and to generate a pleasant indoor climate. The term air-conditioning system can be understood here to be a generic term for ventilation systems which set the temperature and air humidity and, if appropriate, the air quality to a setpoint value in a room and then keep it constant. Air-conditioning systems usually have a refrigeration machine which is operated by a compressor and has to be lubricated during operation by way of a lubricant. The lubricant usually at least partially enters the refrigerant conveyed by the compressor in the air-conditioning/refrigeration circuit.
In calculations of the fluid dynamics and thermodynamics of an air-conditioning/refrigeration circuit for the design of the components of an air-conditioning system, the refrigerant is generally represented as a pure material. However, in practice additives, for example oil, are added to the refrigerant as a lubricant for the compressor. The physical properties of the refrigerant-oil mixture differ to a certain extent significantly from those of the refrigerant as a pure material. If the real refrigerant-oil mixture is modeled as a pure material, i.e. the oil portion is ignored, during the design of the components of an air-conditioning/refrigeration system, the fluid dynamic and thermodynamic properties of the real refrigeration circuit can differ from those of the calculation.
For example, DE 10 2006 000 690 A1 discloses that the lubricant portion in the refrigerant has, to a certain extent, considerable effects on the functioning and the efficiency of a refrigeration system. It also discloses a device and a method in which the behavior of a lubricant portion in a refrigeration system can be determined with a largely small influence on the refrigeration system.
A calculation in which the refrigerant is represented as pure material and not as a refrigerant-oil mixture is, however, the preferred practice since numerous different effects, which are, to a certain extent, not completely captured or are difficult to capture, make physically correct representation of the influence of the oil in an oil model difficult. The influence of the oil which is not taken into account can adversely affect the refrigeration capacity which is necessary for an air-conditioning/refrigeration system which is to be designed. For example, if the influence of the oil is not taken into account, then the calculation results can be unrealistically good, with the result that the air-conditioning system is underdimensioned. A further problem is that measured values at a real air-conditioning/refrigeration system with a real refrigerant-oil mixture can only be transferred to a conditional degree to the calculations of the air-conditioning/refrigeration circuit with modeling of the refrigerant as a pure material. This impedes or prevents quantitative calibration of the calculation model on the basis of measured values on the test rig.
The use of computer-assisted design systems which simulate a system which is to be designed during the dimensioning and design of the components of an air-conditioning system is known, for example, from DE 10 2012 214 098 A1.
In order to precisely dimension and design the components of an air-conditioning/refrigeration circuit, an oil model which is as physically precise as possible is therefore necessary for the oil which is contained in the refrigerant-oil mixture. However, the model is very complex to produce and has to be newly produced for every oil.
An object of the present invention is to provide an improved method for designing an air-conditioning/refrigeration circuit, in particular for a motor vehicle, in which the abovementioned adverse effects of the oil portion in the refrigerant can preferably be avoided. An object of the present invention is, in particular, to improve the modeling of a component within a method for designing an air-conditioning/refrigeration circuit in such a way that the influence of the oil can be better taken into account.
These and other objects are achieved by the design method and test rig according to embodiments of the invention. Features and details which are described in relation to the design method according to the invention also apply of course in relation to a corresponding real test rig and to a computer-assisted system, and respectively vice versa, and therefore reference is and can always be made reciprocally with respect to the disclosure of the individual aspects.
With respect to the following statements it is to be noted that here the term “refrigerant” is used to refer to the pure refrigerant, i.e. without an oil portion. A real refrigerant, which contains oil, is correspondingly referred to here as a refrigerant-oil mixture.
A core concept of the invention is a particular way of implementing the realization that an influence of the oil which is added to the refrigerant accounts for the fact that the thermal power which is transmitted to a component which is under consideration in the air-conditioning system is reduced or increased. Therefore, it is firstly proposed here to approximate an influence of the oil which is initially not captured in the calculation by correspondingly reducing the refrigerant mass flow which flows through a component under consideration. The reduction in the refrigerant mass flow which flows through the component is implemented according to the invention by way of a bypass which is attached parallel to the component. By use of this bypass, the portion of the refrigerant mass flow which is attributed to the influence of the oil is made to bypass the component during the calculation of the air-conditioning system and then fed again to the circuit. An influence of the oil which is not initially covered in the calculation can also be approximated by correspondingly increasing the refrigerant mass flow which flows through a component under consideration; an increase in a refrigerant mass flow which flows through the component can be represented computationally by defining a negative value for a portion of the mass flow which is directed through the bypass, with the result that the mass flow through the component is increased.
The quantity of the refrigerant which is conducted through the bypass is determined as a function of the fluid dynamic and thermodynamic conditions which prevail at the components of the air-conditioning system (in particular temperatures and pressures of the refrigerant) as well as the portion of oil in the refrigerant-oil mixture. In order to determine the quantity of the refrigerant which is conducted through the bypass it is proposed to take into account one or more of the following effects which are identified by the inventor and which can be attributed to the oil as a cause: mass flow defect, pre-evaporation, reduction in enthalpy, refrigerant solution. Of course, the invention is not restricted to these four effects and, when necessary, further effects can be taken into account in accordance with the principle proposed here.
It is to be noted here that in the design method according to the invention and the modeling according to the invention of one or more components of the air-conditioning/refrigeration circuit it is possible, if, for example, an oil portion of zero is to be explicitly considered (for example as a reference), to continue to use the method proposed here. That is, for example, the bypasses which are installed for each component can be maintained in a corresponding simulation model, i.e. for the case “without an oil portion” the simulation model does not have to be restructured.
The invention permits the influence of the oil to be approximately captured, and therefore the informative quality/accuracy to be improved to a relevant degree even in computer-assisted design systems, in particular in software applications which are available for this purpose, such as e.g. simulation programs for calculating the fluid dynamics and thermodynamics of a refrigeration process, or on a test rig for air-conditioning systems in which the influence of the oil is not taken into account. A reduction in the necessary additional expenditure for calibrating corresponding calculation components (evaporators, etc.) is also to be expected.
A first aspect of the invention therefore relates to a design method for an air-conditioning/refrigeration circuit having a refrigerant with an oil portion. At the design stage, only the presence of a pure refrigerant is assumed in a calculation of the air-conditioning/refrigeration circuit and the fluid-dynamic and thermodynamic influence of the oil portion for at least one circuit component of the air-conditioning/refrigeration circuit is approximated by reducing or increasing the refrigerant mass flow flowing through this circuit component. According to the invention, this mass flow reduction or mass flow increase is simulated by a bypass by which a bypass portion of the refrigerant mass flow is extracted from the circuit component at an extraction point upstream of the circuit component, e.g. a first valve, is made to bypass the circuit component and is then fed back to the circuit at a feed point, e.g. a second valve. A mass flow reduction is implemented computationally by defining a positive value for a portion of the mass flow which is conducted through the bypass. An increase in mass flow is correspondingly implemented by defining a negative value for a portion of the mass flow which is conducted through the bypass.
The bypass portion can be determined on the basis of the fluid dynamic and thermodynamic conditions at the components of the air-conditioning system, in particular at the extraction point, for example a first valve, at the feed point, e.g. a second valve and at the circuit component, and on the basis of the oil portion in the refrigerant-oil mixture.
The determination of the bypass portion is preferably based on at least one of the following effects: (a) portion of the refrigerant expelled by oil, here referred in abbreviated form as “mass flow defect”, (b) portion of changed quantity of refrigerant on the basis of hot or cold oil, referred to in abbreviated form as “pre-evaporization”, and (c) portion of the refrigerant dissolved in the oil, referred to here in abbreviated form as “refrigerant solution”. Each bypass portion which corresponds to a specific effect of the oil portion can be positive or negative. Overall, this results in an increase or decrease in the mass flow through the component under consideration. Even if the portions are explained below as a first, second and third portion, all the portions do not necessarily have to be taken into account. The words “first”, “second” and “third” do not define a sequence or valency but instead serve merely for the purpose of differentiation.
The effect referred to here as “mass flow defect” represents the fact that the oil in the real refrigerant-oil mixture expels a corresponding portion of the refrigerant, with the result that the overall mass flow of the refrigerant-oil mixture is reduced by the oil mass flow which can be described by means of the oil circulation rate (OCR). In order to represent the mass flow defect, the refrigerant mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component under consideration is reduced in the calculation approximately by a first portion Δ{dot over (m)}1 which corresponds to the oil mass flow. This first portion Δ{dot over (m)}1 is made to bypass the component with the bypass in order to obtain the mass flow.
The effect referred to here as “pre-evaporization” represents the fact that comparatively hot oil (oil at correspondingly high temperature) influences a portion of the refrigerant by feeding heat into the refrigerant, in such a way that this portion no longer contributes, or only contributes to a limited degree to the fluid dynamic and thermodynamic processes (in particular thermal transfer process) in the component under consideration—e.g. by partial pre-vaporization. For example, this effect can be observed when the refrigerant expands in an expansion valve upstream of an evaporator. However, it is to be noted that the idea that the refrigerant is reduced (pre-evaporized) by a portion of the refrigerant through the presence of “hot” oil applies independently of an expansion process and/or of the presence of a valve. Analogously, comparatively cold oil (oil at a comparatively low temperature level) can bring about corresponding effects from the conduction of heat away from the refrigerant. For example, this effect can be observed when the refrigerant is fed in a compression device (e.g. compressor). However, it is also to be noted here that the idea that the refrigerant changes by a portion of the refrigerant as a result of the presence of “cold” oil applies independently of a compression process and/or of the presence of a compressor. In order to form the “pre-evaporization”, the refrigerant mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component is increased in the calculation approximately by a second portion Δ{dot over (m)}2 which reduces or increases the effect of the pre-evaporization. This second portion Δ{dot over (m)}2 is also made to bypass the component with the bypass in order to obtain the mass flow.
For example, for “hot” oil the “pre-evaporization” effect can be taken into account at an expansion device, e.g. an expansion valve, and an evaporation device, e.g. an evaporator, as follows:
where:
{dot over (Q)}Oil is the quantity of heat of the oil which is output to the refrigerant;
ΔhRefrigerant is a difference between enthalpy values of the refrigerant;
cpOil is a specific thermal capacity;
T is a temperature; and
hRefrigerant is an enthalpy value of the refrigerant.
It is to be noted that the second portion Δ{dot over (m)}2 can also be defined negatively so that the bypass mass flow is therefore reduced by the corresponding portion, and the mass flow through the component is increased (even if the overall bypass mass flow continues to lead to a reduction in the mass flow through the component). The latter case would occur, for example, with a condensation device for which the term “pre-evaporization” would not apply but the treatment in terms of a formula is analogous.
The effect specified here “refrigerant solution” represents the fact that a portion of the refrigerant is dissolved in the oil and therefore no longer participates in the satisfactory processes such as, for example, evaporization. In order to represent the refrigerant solution, the mass flow ({dot over (m)}−Δ{dot over (m)}) of the refrigerant which flows through the component is reduced in the calculation approximately by a third portion Δ{dot over (m)}3. The third portion Δ{dot over (m)}3 corresponds to the refrigerant dissolved in the oil and is also made to bypass the component with the bypass in order to obtain the mass flow.
Δ{dot over (m)}3_:={dot over (m)}Oil*γRefrigerant solution; with γ=γ(T;p). Formula
where:
γ is a dimensionless factor; and
p is a pressure.
It is to be noted that the function γ=γ(T; p) can also be dependent on other components and not only on T and p.
A change in the material values of the refrigerant owing to an oil portion which is present in the real refrigerant-oil mixture is preferably allowed for in the calculation by virtue of the fact that the state variables and/or material values (e.g. temperature and/or enthalpy) are correspondingly changed at the outlet of the circuit component under consideration. The oil portion in the refrigerant-oil mixture changes the material values of the refrigerant, with the result that for example in the case of otherwise identical pressures and enthalpy values the presence of the oil means that the temperature of the refrigerant-oil mixture, for example at the outlet of a vaporization device, becomes higher than when there is only refrigerant. Correspondingly, the outlet temperature at the circuit component under consideration is changed or corrected in the calculation. For example analytical relationships, inter alia for correcting temperatures and enthalpies, can be established on the basis of material value correlations which represent the influence of the oil on the pure material for various thermodynamic states.
A refrigerant-side pressure loss which is directly dependent on the refrigerant mass flow through the component under consideration generally occurs in said component. In order to ensure that a refrigerant-side pressure loss is correctly represented by the component under consideration even in the case of a refrigerant mass flow which is corrected (reduced/increased) according to the invention, in the case of a correction (reduction/increase), caused by a mass flow bypass, of the refrigerant mass flow through the components a suitable correction of the refrigerant-side pressure loss can be performed. The correction can be implemented, for example, as a function of the oil portion. The correct representation of the pressure loss is important, for example, in a vaporization device, since the transmission of heat depends in some cases to a great extent on the pressure loss of the refrigerant across the vaporization device.
In one exemplary embodiment of the invention, the circuit component is a heat exchanger (such as, for example, primarily an evaporator, a condenser, internal heat exchangers, etc. but also lines or the like can function as heat exchangers). In particular, the component can be at least one from the group which is composed of: evaporization device (e.g. evaporator in the form of a heat exchanger for heating the refrigerant), compression device (e.g. compressor), expansion device (e.g. expansion valve), collecting device, precipitation device, condensation device or gas cooler including supercooling device (e.g. heat exchangers for cooling the refrigerant), lines and internal heat exchanger device.
As already mentioned above, the mass flow through the component can be increased computationally by defining a negative value for a portion Δ{dot over (m)} which is conducted through the bypass. This may possibly be expedient in the case of a condensation device as the component under consideration in order to represent the fact that the hot oil coming from the compression device has to be cooled in addition to the refrigerant. This could be approximated by a correspondingly increased refrigerant mass flow through the condensation device. For example, given the abovementioned partial effects, the mass flow defect would then continue to reduce the refrigerant mass flow through the component but the effect which was attributable to the “pre-evaporization” would be approximated by a negative sign as “additional condensation” and correspondingly increase the refrigerant mass flow through the component. It can also be apparent that a reduction in mass flow is also applicable to a condensation device.
A second aspect of the invention relates to a computer program having program code for carrying out a method according to the first aspect of the invention discussed above when the computer program is executed by a computer system.
A third aspect of the invention relates to a data carrier or a data stream with electronically readable control signals which can interact with a programmable computer system in such a way that the computer system carries out a method according to the first aspect of the invention discussed above.
A fourth aspect of the invention relates to a computer system for computer-assisted design of an air-conditioning/refrigeration circuit having at least one computing unit which is designed to carry out at least one of: (i) the execution of a computer program according to the second aspect of the invention, and (ii) the reading of the control signals of a data carrier or of a data stream according to the third aspect of the invention.
A fifth aspect of the invention relates to a test rig for generating measured values of an air-conditioning/refrigeration circuit, wherein the air-conditioning/refrigeration circuit is operated with a pure refrigerant, and the influence of an oil portion in a real refrigerant-oil mixture for at least one circuit component of the air-conditioning/refrigeration circuit is approximated by correcting (reducing/increasing) the refrigerant mass flow which flows through the circuit component in that a bypass by means of which a bypass portion of the refrigerant mass flow is extracted from the circuit at an extraction point, e.g. a first valve, upstream of the circuit component is provided on the circuit component, said bypass portion is made to bypass the circuit component and is then fed again to the circuit at a feed point, e.g. a second valve.
In one particular embodiment of the design method according to the first aspect of the invention, measured values at an air-conditioning/refrigeration circuit of the test rig according to the fifth aspect of the invention are used to calibrate the calculations in the design method.
Further advantages, features and details of the invention can be found in the following description in which an exemplary embodiment of the invention is described in detail with reference to the drawings. In this context, the features which are mentioned in the claims and in the description can each be essential to the invention individually per se or in any desired combination. Likewise, the features which are mentioned above and the features which are explained further below can each be used per se or in a plurality of combinations as desired. Functionally similar or identical parts or components are to a certain extent provided with the same reference symbols. The terms “on the left”, “on the right”, “at the top” and “at the bottom” which are used in the description of the exemplary embodiments relate to the drawings in an orientation with a normally readable designation of the figures or normally readable reference symbols. The exemplary embodiment which is shown and described is not to be considered as conclusive but instead has an exemplary character for explaining the invention. The detailed description serves to inform the person skilled in the art, and therefore known circuits, structures and methods are not shown or explained in detail in order to avoid making the present description more difficult to understand.
Liquid refrigerant at a device 110 for collecting and/or filtering the refrigerant is fed to an expansion device 120 and relaxes. The refrigerant then evaporates in an evaporation device 130. The evaporation device 130 is a heat exchanger, at which, for example, heat is extracted from air fed to the latter by evaporation of the refrigerant, and therefore the air is cooled and then fed, for example, to the passenger compartment. The heated refrigerant then passes further via a device 140 for filtering and/or drying the refrigerant to a compression device 150, for example a mechanical compressor. The refrigerant is then conducted from the compression device 150 into a condensation device 160 in order to liquefy the usually gaseous refrigerant again. The condensation device 160 is usually a heat exchanger which is designed to extract heat from the refrigerant so that the latter condenses again.
It is to be noted that the air-conditioning/refrigeration circuit 100 in
In the lower part of
It is to be noted that the approximation device 170 approximates only the influence of oil in the expansion and evaporation device 120/130. In order to approximate the influence of oil in the entire air-conditioning/refrigeration circuit 100 an approximation device would have to be respectively introduced for each component of the air-conditioning/refrigeration circuit 100.
The objective is to approximately represent the influence of the oil portion in a refrigerant in practice without the need for a separate oil model, in order thereby to design the air-conditioning/refrigeration circuit 100 correctly, i.e. be able to dimension its components correctly.
For this purpose, the approximation device 170, which is explained in more detail in
As explained above, by defining a negative value for a portion Δ{dot over (m)} of the mass flown {dot over (m)} which is conducted through the bypass 220 (see
For this purpose, a branching device 212, for example a first three-way valve 172 in
The approximation device 200 (170 in
Therefore, it is proposed here to approximate a power-reducing or power-increasing effect owing to the oil portion, which is initially not captured in a calculation with a pure refrigerant, by correspondingly reducing or increasing the coolant mass flow {dot over (m)} flowing through the components of the air-conditioning/refrigeration circuit. The reduction Δ{dot over (m)} or increase−Δ{dot over (m)} of the refrigerant mass flow flowing through the component 210 is converted in
The bypass device 220 can be an additional component in a calculation model of a computer system with a computer-assisted design of an air-conditioning/refrigeration circuit or a real bypass on a test rig P of an air-conditioning/refrigeration circuit. Measured values of such a test rig P can then be used to calibrate the calculation model. During the calculation of the air-conditioning/refrigeration system, the ineffective portion Δ{dot over (m)} of the refrigerant/mass flow {dot over (m)} can be made to bypass the component 210 and then be fed again to the air-conditioning/refrigeration circuit by way of the bypass device 220. That is to say in the component 210, the part {dot over (m)}−Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} acts in the component 210.
Provided downstream of the component 210 in
The part Δ{dot over (m)} of the refrigerant which is fed through the bypass 220 is determined as a function of the fluid dynamic and thermodynamic conditions, in particular temperatures and pressures of the refrigerant which are present at the component 210 and optionally at further locations of the air-conditioning/refrigeration circuit 100 in
The component 220 can be a heat exchanger like the evaporation device 130 or the condensation device 160 in
The invention advantageously permits the influence of the oil to be approximately captured, and therefore the informative quality/accuracy to be sufficiently improved, for example in computer-assisted design systems, particularly in software applications which are available for this such as e.g. simulation programs for calculating the fluid dynamics and thermodynamics of a refrigeration process, or on a test rig for air-conditioning systems in which the influence of the oil is not taken into account. A reduction in the additional expenditure which is necessary for the calibration of corresponding calculation components (such as e.g. the evaporation device 130, etc.) is also to be expected.
The design method serves, for example, to design the air-conditioning/refrigeration circuit 100 in
In the design in step S1, only a pure refrigerant, i.e. without an oil portion, is assumed in the calculation of the air-conditioning/refrigeration circuit 100.
In a step S2, the fluid dynamic and thermodynamic influence of the oil portion is approximated for at least one circuit component such as the evaporation device 130 in
Then, in a step S3 the air-conditioning/refrigeration circuit 100 is calculated taking into account the reduction/increase in the refrigerant flowing through the component. The influence of the oil is thus approximated in the calculation by the bypass 174. The bypass 174 therefore constitutes a workaround as a replacement for an oil model in the calculation. In this context, in step S3 the calculation is carried out in such a way that by means of the bypass 174 the bypass portion Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} is extracted from the circuit 100 at the branch 172 upstream of the circuit component 130, made to bypass the circuit component 130 and then fed again to the circuit 100 at the junction 176 downstream of the component 130. The step S3 is also carried out for each component at which the influence of the oil is to be approximated.
The bypass portion Δ{dot over (m)} is determined in the example in
Further, in a step S4, a change in the material values of the refrigerant owing to the oil portion in the calculation is taken into account in that the outlet temperature and/or enthalpy at the circuit component 130 is correspondingly corrected or changed in the calculation.
The method can optionally have a step S5 in which the model on which the calculation is based is corrected on the basis of measurement data of a real test rig P.
The method, which is described above, can also particularly advantageously be used on a real test rig P for testing an air-conditioning/refrigeration circuit 100 and measuring on the air-conditioning/refrigeration circuit 100. The test rig P is then essentially constructed as shown in
On the test rig, the air-conditioning/refrigeration circuit 100 is operated with a pure refrigerant. The influence of an oil portion in a real refrigerant-oil mixture is approximated for at least one circuit component 130 of the air-conditioning/refrigerant circuit 100 by correction of the refrigerant mass flow flowing through the circuit component 130. For this purpose, a bypass portion Δ{dot over (m)} of the refrigerant mass flow {dot over (m)} at the valve 172 upstream of the circuit component 130 is extracted from the air-conditioning/refrigeration circuit 100 at the circuit component with the bypass 174, is made to bypass the circuit component 130 and is then fed again to the air-conditioning/refrigeration circuit 100. Measured values can particularly advantageously be used at the air-conditioning/refrigeration circuit 100 of the test rig P to calibrate the calculations in the design method.
It is to be noted that the design method described here can also be embodied in a computer program. The computer program then has program code for carrying out the design method described here when the computer program is executed by a computer system. The computer program can also be embodied on a data carrier or in a data stream, wherein the data carrier or the data stream has electronically readable control signals which can interact with a programmable computer system in such a way that the computer system carries out the design method described here. Correspondingly, the design method can be embodied in a computer system for computer-assisted design of an air-conditioning/refrigeration circuit with at least one computing unit, wherein the at least one computing unit is designed to execute the specified computer program and/or to read the control signals of the specified data carrier or of a specified data stream.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 214 797.8 | Aug 2016 | DE | national |
