DE102019126214A1 - Device for transferring heat in a fluid circuit and method for operating the device - Google Patents

Abstract

The invention relates to a device (1, 1a, 1b, 1c) for transferring heat by sublimation of a working medium circulating in a fluid circuit. The device (1, 1a, 1b, 1c) is designed with a heat exchanger (2a, 2b, 2c) for absorbing heat through the subliming working medium and at least one expansion element (3-1). The device (1, 1a, 1b, 1c) also has a separator (4a, 4b) for separating solid particles of the working medium as well as an inlet (5) for flowing in liquid working medium and an outlet (7) for flowing out of gaseous working medium. The inlet (5) and the outlet (7) are each designed as a connection point to the fluid circuit. The invention also relates to a refrigerant circuit (11a, 11b) with at least one compressor (12), a circuit heat exchanger (13) for dissipating heat from the working medium circulating in the circuit and the device according to the invention (1, 1a, 1b, 1c). The invention also relates to a method for operating the device (1, 1a, 1b, 1c).

Description

The invention relates to a device for transferring heat, in particular for providing cold, by sublimating a working medium circulating in a closed fluid circuit. The device has a heat exchanger for absorbing heat through the subliming working medium and at least one expansion element. The invention also relates to a fluid circuit, in particular a refrigerant circuit, with the device for transferring heat by sublimation of the working medium and a method for operating the device.

The challenges in the technical use of sublimation as a phase transition of a working medium from the solid to the gaseous state of aggregation at pressures below the triple pressure, in particular for providing cold by means of a device integrated in a fluid circuit, are essentially aimed at the physical properties of the solid or the solid particles of the working medium circulating in the fluid circuit. For example, the solid particles harbor the risk of blocking within a pipe of a heat exchanger as a device for transferring heat or a connecting line arranged between components of the fluid circuit.
Incomplete sublimation of coarse, solid particles of the working medium can damage the compressor of the fluid circuit. In addition, the heat transfer coefficient in the process of sublimation of the working medium within the heat exchanger is lower than the heat transfer coefficient of the same working medium in the process of evaporation, so that the heat exchanger for transferring the same amount of heat has to be designed, for example, with a larger heat transfer surface and thus larger dimensions. As a heat exchanger acted upon by a subliming working medium, the sublimator consequently has a larger space requirement than an evaporator through which an evaporating working medium flows. Furthermore, with regard to the amount of heat to be transferred, also referred to as the cooling capacity of the fluid circuit, a sublimator cannot be scaled in a manner comparable to an evaporator, as is the case with the design of a tube bundle heat exchanger.

The provision of cold by sublimation of a working medium is known, for example, from the cooling of semiconductor technology or the deep freezing of foodstuffs, which are cooled in open fluid circuits by means of a wear process. The risk of blocking and incomplete sublimation of the working medium can be disregarded. In order to minimize or exclude the risk of blocking when providing cold through sublimation of a working medium, in addition to spraying a surface with the working medium where there is no risk of blocking, the flow cross-section of lines for the working medium or the length of the lines and thus the residence time of the solid particles within the line can be increased. Depending on the design of the lines and the mode of operation of the device, the sublimation as a process of the phase transition of the working medium can be completely completed.
When spraying the surface with the working medium, in which either a mixture of liquid and solid sublimates on the surface with a phase transition delay or the solid is sprayed onto the surface to be cooled in the form of a finely divided solid mist, the sprayed area is very limited as a heat transfer area. In addition, the flow cross-sections of the nozzles are small in order to be able to adapt the mass flow of the working medium to low heat outputs, which, however, causes high costs and increases the risk of the nozzles becoming blocked. Irregular distribution of the working medium to be sublimated leads to uneven cooling over the heat transfer surface. The control effort to maintain a continuous process is also very high.
Increasing the flow cross-section of the lines leads to a reduction in the flow rate of the working medium and thus to a higher risk of the fluid being carried over. The lower heat transfer coefficients are compensated for by increasing the heat transfer surface and consequently the entire heat exchanger, which increases the space requirement or the structural volume of the heat exchanger.
With the increase in the length of the lines and thus the dwell time of the solid particles of the working medium within the line, a large overheating area of the working medium in the form of the length of the overheating path within the heat exchanger must also be taken into account. The necessary overheating of the working medium, that is to say the temperature as a controlled variable, in particular to protect the compressor, is very difficult to adjust. Since the sublimation of the solid particles of the working medium takes a longer period of time, the working medium can be present as a mixture of gas and solid particles, while the gas phase of the working medium has temperatures well above the sublimation temperature. With the greater length of the lines, the overall efficiency of the refrigeration machine is reduced due to the thermodynamic influence and the space requirement or the structural volume of the heat exchanger is increased. The longer transport path for the solid particles causes higher pressure losses and also makes it more difficult to control the refrigeration machine.

It is also known from the prior art to mix the working medium to be sublimated with a secondary fluid in order to increase the heat transfer coefficient and improve the heat transfer and reduce the risk of blocking. A liquid separator is to be provided in order to prevent the carrier fluid from being carried over into the fluid circuit of the working medium.

In the DE 30 04 114 A1 describes a method for providing refrigeration at low temperatures with carbon dioxide as the refrigerant. In order to prevent the formation of agglomerations of solid carbon dioxide particles, the solid carbon dioxide particles are suspended in a non-freezing liquid and conveyed as a suspension through a heat exchanger operated as a sublimator. For the method with the device, which is very complex in terms of apparatus, in particular energetic and cost-intensive expenditures are necessary in order to provide the carrier liquid and to guide the suspension in the fluid circuit. The system is also very difficult to dimension.

From the NL 9401324 A a fluid circuit is known in which carbon dioxide is expanded to a pressure below the triple pressure and, using the kinetic energy, is injected into a fluid reservoir by means of a motive nozzle. The resulting solid carbon dioxide particles sublime as they circulate in the carrier fluid and provide the required cold. The injection of carbon dioxide into the fluid reservoir to provide cold is very slow. The propellant nozzle is difficult to control and is usually set to a specific operating point. The demand-dependent cooling capacity must therefore be regulated using additional instruments. In addition, the motive nozzle must always be arranged above the evaporator, which affects the space required.

The object of the invention is to provide a device for transferring heat, in particular for providing cooling power, within a fluid circuit. The cold should be used at a temperature level or pressure level below the triple point. The device should be of a simple design and a modular design, compact, easy to design and scalable to different cooling capacities. With the modular design, the device should be able to be combined cost-effectively with available condensing units or standard components of fluid circuits. The device should be able to be operated efficiently with a minimal space requirement with a minimal risk of blocking by solid particles as well as a uniform distribution of the particles and thus a uniform heat transfer over the heat exchanger surface.

The object is achieved by the objects with the features of the independent patent claims. Further developments are given in the dependent claims.

The object is achieved by a device according to the invention for transferring heat by sublimation of a working medium circulating in a closed fluid circuit. The device is designed with a heat exchanger for absorbing heat through the subliming working medium and at least one expansion element for relaxing the working medium.

According to the conception of the invention, the device has a separator for separating solid particles of the working medium as well as an inlet for flowing in liquid working medium and an outlet for flowing out of gaseous working medium. The inlet and the outlet of the device are each designed as a connection point to the fluid circuit. The outlet is advantageously arranged on the separator.
The device represents a combined design of a heat exchanger for providing cooling power using the sublimation enthalpy of the working medium for a closed fluid circuit. The components for expansion, heat exchangers, in particular sublimation heat exchangers or sublimators, and separators, especially particle separators, are coordinated with one another and are used as viewed as a coherent sublimator unit. Carbon dioxide is preferably provided as the working medium.

According to a development of the invention, the heat exchanger for absorbing heat through the subliming working medium is designed with flow channels aligned parallel to one another. An expansion element, also referred to as the first expansion element, is assigned to each flow channel. The heat exchanger for absorbing heat through the subliming working medium can have a primary sublimator and a secondary sublimator. In particular, the primary sublimator is formed from the flow channels aligned parallel to one another, each with an expansion element. The primary sublimator and the secondary sublimator are each to be viewed as partial areas or sections of the heat exchanger.

According to an advantageous embodiment of the invention, the expansion element is arranged in each case at an inlet in the flow channel or within the flow channel, in particular in the area of the inlet of the flow channel.
The flow channels are preferably aligned in the horizontal direction or in the vertical direction. Especially with the horizontal alignment of the Flow channels, the flow channels are preferably each designed to open into the separator.

According to a preferred embodiment of the invention, a conveying device for conveying solid particles of the working medium separated from a gaseous fluid flow in the separator is provided between an outlet of the separator and the heat exchanger for absorbing heat through the subliming working medium.
The delivery device can be designed as an ejector or a gas-operated nozzle or a pump. Especially when the delivery device is designed as an ejector or gas-operated nozzle, the device is advantageously designed with an inlet for the inflow of gaseous working medium. In this case, an additional, second expansion element is arranged within a connecting line extending between the inlet and the conveying device. Depending on the design of the device, a conveying device can be dispensed with using the natural circulation.

Another advantage of the invention is that in addition to the heat exchanger for absorbing heat through the sublimating working medium as the first heat exchanger within the separator, a second heat exchanger for transferring heat from the liquid working medium flowing into the device through the inlet to solid separated from the gaseous fluid flow Particles of the working medium is formed. The second heat exchanger is arranged between the inlet for the inflow of liquid working medium and the at least one first expansion element.

The object is also achieved by a refrigerant circuit according to the invention with at least one compressor and a circuit heat exchanger for removing heat from a working medium circulating in the circuit. According to the concept, the refrigerant circuit is designed with an aforementioned device according to the invention for transferring heat by sublimation of the working medium. The inlet for flowing in the liquid working medium of the device is connected to an outlet of the circuit heat exchanger or a medium-pressure container and the outlet for flowing out of the gaseous working medium of the device is connected to an inlet of the at least one compressor.

According to a further development of the invention, the inlet for the inflow of gaseous working medium of the device is connected to an outlet of the compressor or an outlet of the medium-pressure container.

Conventionally, the expansion element and the heat exchanger operated as an evaporator / sublimator are designed separately from one another. A system-specific adaptation of both components is always required. With the device according to the invention, the system boundary between the sublimator unit and conventional refrigeration technology is changed in such a way that a system-specific adaptation of the expansion element and heat exchanger is no longer necessary, since both components are part of the sublimator unit. The adaptation or scaling of the entire sublimator unit with regard to the heat output to be transmitted, in particular the cooling output, is achieved through the targeted coordination of the components to be used in each case within the sublimator unit. The external interfaces to the conventional fluid circuit to be defined in an application concern, on the one hand, the outlet of the circuit heat exchanger or a collector and, on the other hand, the suction port of the compressor. Both interfaces can be defined relatively simply and uniformly with regard to the boundary conditions, which enables a modular design between commercially available condensing units or refrigeration systems made of standard components and the sublimator unit according to the invention - comparable to the modular construction typical in cold vapor refrigeration technology, consisting of a condensing unit and a heat exchanger operated as an evaporator with associated expansion device.
In addition, extended temperature ranges below the specific triple point can be used, depending on the choice of working medium. Working media are taken into account, the triple point pressure of which is advantageously above atmospheric pressure, which leads to different application temperatures. With the advantageous use of carbon dioxide as the working medium or refrigerant, refrigeration capacities can be provided at temperatures below -50 ° C. Against the background of environmentally-politically motivated restrictions on refrigerants commonly used up to now, in particular those with a high global warming potential, briefly referred to as GWP for "global warming potential", the device according to the invention enables cold generation at temperatures below -50 ° C.

• - Entspannen von durch einen Einlass zum Einströmen flüssigen Arbeitsmediums in die Vorrichtung eingeleiteten flüssigen Arbeitsmediums beim Durchströmen von mindestens einem Expansionsorgan auf ein Druckniveau unterhalb des Tripeldruckes des Arbeitsmediums und Erzeugen fester Partikel während des Einleitens des Arbeitsmediums in einen Wärmeübertrager zur Aufnahme von Wärme durch das sublimierende Arbeitsmedium,
• - Sublimieren fester Partikel des Arbeitsmediums beim Durchströmen des Wärmeübertragers unter Aufnahme von Wärme,
• - Einleiten des Arbeitsmediums in einen Abscheider und Separieren nicht sublimierter fester Partikel von einer gasförmigen Fluidströmung innerhalb des Abscheiders,
• - Ableiten des gasförmigen Arbeitsmediums durch einen Auslass und der festen Partikel aus dem Abscheider sowie
• - Fördern der festen Partikel des Arbeitsmediums, insbesondere mittels einer an einem weiteren Auslass des Abscheiders angeordneten Fördervorrichtung, zurück in den Wärmeübertrager.

The object is also achieved by a method according to the invention for operating an aforementioned device according to the invention for transferring heat by sublimation of a working medium circulating in a fluid circuit. The procedure consists of the following steps:

• - Relaxation of liquid working medium introduced into the device through an inlet for the inflow of liquid working medium when flowing through at least one Expansion device to a pressure level below the triple pressure of the working medium and generating solid particles while the working medium is being introduced into a heat exchanger to absorb heat through the subliming working medium,
• - Sublimation of solid particles of the working medium when flowing through the heat exchanger with absorption of heat,
• - Introducing the working medium into a separator and separating non-sublimated solid particles from a gaseous fluid flow within the separator,
• - Discharge of the gaseous working medium through an outlet and the solid particles from the separator as well
• - Conveying the solid particles of the working medium, in particular by means of a conveying device arranged at a further outlet of the separator, back into the heat exchanger.

According to a further development of the invention, the liquid working medium flowing into the device through the inlet for the inflow of the liquid working medium is subcooled before the expansion inside the separator. The heat is transferred from the liquid working medium to solid particles of the working medium, which sublime while absorbing the heat.

An advantageous embodiment of the invention consists in that the solid particles separated from the gaseous fluid flow in the separator are conveyed in a carrier liquid to the heat exchanger for absorbing heat through the subliming working medium. The heat exchanger and the separator are at least partially filled with the carrier liquid. In the separator, the non-sublimated solid particles and the carrier liquid are separated from the gaseous fluid flow.

The carrier liquid and the solid particles of the working medium preferably also serve to subcool the liquid refrigerant flowing into the device through the inlet. The carrier liquid separated in the separator is conveyed into the heat exchanger together with the solid particles of the working medium that have not sublimed even when the liquid refrigerant is undercooled.

According to a further preferred embodiment of the invention, the liquid working medium is expanded in the carrier liquid when it flows through the at least one expansion element of the heat exchanger to absorb heat through the subliming working medium. In the process, the working medium is then sublimed while absorbing heat within the carrier liquid and the carrier liquid is thus cooled.

• - einfache und kompakte Konstruktion aus einem Minimum an Komponenten sowie einfache Montage auch durch einen modularen Aufbau, dadurch zudem
• - gute Skalierbarkeit bezüglich der Kälteleistung, auch da die Komponenten als Bausätze verwendet werden können,
• - minimaler Platzbedarf mit einer minimalen Gefahr des Verblockens durch feste Partikel sowie
• - gleichmäßige Verteilung der festen Partikel und damit gleichmäßige Wärmeübertragung über der Wärmeübertragerfläche und effizienter Betrieb des Wärmeübertragers.

In summary, the device according to the invention also has further advantages:

• - simple and compact construction from a minimum of components as well as simple assembly also through a modular structure, thereby also
• - good scalability with regard to the cooling capacity, also because the components can be used as kits,
• - Minimal space requirements with a minimal risk of blocking by solid particles as well
• - even distribution of the solid particles and thus even heat transfer over the heat exchanger surface and efficient operation of the heat exchanger.

• 1: ein Druck-Temperatur-Diagramm mit Darstellung der einzelnen Phasen von Kohlendioxid,
• 2: eine erste Vorrichtung zum Übertragen von Wärme als trocken-betriebene Sublimatoreinheit mit einem ersten Wärmeübertrager mit in Strömungsrichtung des Arbeitsmediums vorgelagerten Expansionsorganen, einem Abscheider und einem zweiten Wärmeübertrager,
• 3a: eine Anordnung der Sublimatoreinheit aus 2 innerhalb eines Kältemittelkreislaufs mit einstufiger Verdichtung,
• 3b: eine Anordnung der Sublimatoreinheit aus 2 innerhalb eines Kältemittelkreislaufs mit zweistufiger Verdichtung mit Mitteldruckabscheidung,
• 4: eine zweite Vorrichtung zum Übertragen von Wärme, ähnlich der ersten Vorrichtung aus 2, als trocken-feucht-betriebene Sublimatoreinheit sowie
• 5: eine dritte Vorrichtung zum Übertragen von Wärme als feucht-betriebene Sublimatoreinheit mit einem ersten Wärmeübertrager mit zugeordneten Expansionsorganen, einem Abscheider und einem zweiten Wärmeübertrager.

Further details, features and advantages of embodiments of the invention emerge from the following description of exemplary embodiments with reference to the associated drawings. Show it:

• 1 : a pressure-temperature diagram showing the individual phases of carbon dioxide,
• 2 : a first device for transferring heat as a dry-operated sublimator unit with a first heat exchanger with expansion elements upstream in the flow direction of the working medium, a separator and a second heat exchanger,
• 3a : an arrangement of the sublimator unit 2 within a refrigerant circuit with single-stage compression,
• 3b : an arrangement of the sublimator unit 2 within a refrigerant circuit with two-stage compression with medium pressure separation,
• 4th : a second device for transferring heat, similar to the first device from 2 , as a dry-damp operated sublimator unit as well as
• 5 : a third device for transferring heat as a wet-operated sublimator unit with a first heat exchanger with associated expansion elements, a separator and a second heat exchanger.

In 1 shows a pressure-temperature diagram with the schematic representation of the individual phases of carbon dioxide. The respective state of aggregation of the working medium is next to the Temperature T also depends on the pressure p prevailing in the system. All three phases solid (f), liquid (fl) and gaseous (g) are in thermodynamic equilibrium at the triple point.

Carbon dioxide, known for short as CO ₂ or with the refrigeration designation R744, is a natural refrigerant and is used in refrigerant circuits at evaporation temperatures, in particular in the range down to about -40 ° C. Carbon dioxide is advantageously non-flammable and nontoxic under normal conditions.

The triple pressure as the pressure level at the triple point of carbon dioxide is 5.18 bar and thus far above atmospheric pressure. The associated temperature at the triple point is about -56 ° C. This means that carbon dioxide is in the gaseous or solid state of aggregation at an atmospheric pressure of around 1 bar and by no means in liquid form. Carbon dioxide can only be liquid under increased pressure of at least 5.18 bar. At atmospheric pressure, carbon dioxide changes from the solid (f) state, also known as dry ice, to the gaseous (g) state while absorbing heat. The working medium sublimates. The line that characterizes the transition from the solid (f) to the gaseous (g) state in the phase diagram is also known as the sublimation line, while the line that characterizes the transition from the liquid (fl) to the gaseous (g) state is called the evaporation line.

The conventional cold vapor process generally runs in the two-phase region of the gaseous and liquid state of the refrigerant. In order to operate the process with carbon dioxide as the refrigerant at temperatures below -56 ° C, the pressure within the refrigerant circuit must be reduced to values below the triple point. Carbon dioxide is at least partially in the form of a solid or solid particles. The usable temperature level can be reduced to about -78 ° C or even below.

Compared to the conventional cold vapor process, the heat exchanger operated as an evaporator above the triple pressure on the evaporation line is operated as a sublimator when operated on the sublimation line and thus below the triple pressure. Since the carbon dioxide sublimes during the transition from the solid phase to the gaseous phase while absorbing heat, useful cooling is provided in this way.
The coexistence of the solid phase and the gaseous phase of the refrigerant can lead to the accumulation of solid particles of the refrigerant on the heat transfer surfaces of the sublimator and to the agglomeration of solid particles, which in turn constricts the flow cross-section or even blocks individual areas of the sublimator and thus a considerable pressure loss of the May result in refrigerant.

Out 2 goes a first device 1 , 1a for transferring heat as a dry-operated sublimator unit with a first heat exchanger 2a with upstream expansion elements in the direction of flow of the working medium 3-1 , 3-2 , a separator 4a for separating solid particles and a second heat exchanger 10a emerged.

During the operation of a fluid circuit, in particular a refrigerant circuit, liquid refrigerant, for example exiting from a condenser or gas cooler or collector and at a high pressure level, flows in the direction of flow 8th through a first inlet 5 into the device 1a a. When flowing through the first expansion organs 3-1 the refrigerant present in liquid form is expanded to a pressure level below the triple pressure and then in a primary sublimator 2-1a as a section of the first heat exchanger 2a initiated. When expanding, a first portion of the carbon dioxide is evaporated, which extracts the heat required for evaporation from the second portion. The second part of the refrigerant is converted into the solid state of aggregation. The solid particles of carbon dioxide are generated by the disintegration of the liquid-gas jet by shear forces in connection with the flash evaporation and a subsequent solidification of the liquid droplets.

If the refrigerant is liquefied during subcritical operation of the refrigerant circuit, as in certain ambient conditions with carbon dioxide below the critical point, the corresponding heat exchanger is referred to as a condenser. Part of the heat transfer takes place at a constant temperature. With supercritical operation or with supercritical heat dissipation in the heat exchanger, the temperature of the refrigerant, in particular of carbon dioxide, steadily decreases. In this case, the heat exchanger is also referred to as a gas cooler.

When flowing through the primary sublimator 2-1a the refrigerant is sublimed while absorbing heat, with one of the pressure inside the primary sublimator 2-1a corresponding sublimation temperature, the sublimation enthalpy of the refrigerant is used.
The primary sublimator 2-1a as a first component of the first heat exchanger 2a has at least two flow channels that can be acted upon by refrigerant parallel to one another. Each flow channel is in the direction of flow 8th of Refrigerant a first expansion element 3-1 upstream. The first expansion organ 3-1 is advantageously arranged in each case at the inlet of the flow channel. The first expansion organ 3-1 can for example be designed as a nozzle with a constant or adjustable flow cross-section or as a correspondingly adapted expansion valve. The expansion of the refrigerant and thus the transition to the solid state takes place in the form of an expansion cone within the flow channel.
With the arrangement of the first expansion organs 3-1 each directly at the inlet of a flow channel and thus the waiver of additional connecting lines with additional changes in the flow cross-section between the first expansion element 3-1 and the primary sublimator 2-1a on the one hand, the risk of blocking is minimized. On the other hand, the solid particles of the refrigerant already make a contribution to the transfer of heat directly after the expansion into the flow channel and thus at the inlet of the flow channel. Due to an agglomeration of the solid particles of the refrigerant, the heat transfer coefficient can be significantly reduced in the direction of flow. The agglomeration can be prevented or at least minimized by a correspondingly high flow speed of the working medium, since this reduces the dwell time of the solid particles in the flow channel and thus also the possible time for agglomeration.

In contrast to the conventional design of a heat exchanger for evaporating refrigerants, the heat exchanger is 2a with regard to the power, in particular the cooling power, is not scaled by expanding the ratio of length to diameter of the hollow circular cylindrical flow channels, but by adapting the number of flow channels arranged parallel to one another.
In addition, in the case of a sublimator, also referred to as a sublimation heat exchanger, it cannot be ensured that the refrigerant is completely sublimated at the outlet of the heat exchanger and is therefore in the gaseous state. The non-sublimated and thus the solid particles that have not transitioned from the solid to the gaseous state become within the in the direction of flow 8th the primary sublimator 2-1a downstream separator 4a , for example a cyclone separator, also referred to as a particle separator, separated from the gaseous fluid flow.

The solid particles of the refrigerant accumulate on the bottom or in a lower area of the separator 4a and serve to subcool the through the first inlet 5 into the device 1a inflowing liquid refrigerant. The second heat exchanger, operated as a subcooler for the liquid refrigerant, is used 10a on the one hand with the liquid refrigerant and on the other hand with the one from the separator 4a removed solid particles of the refrigerant applied. The second heat exchanger 10a is consequently as an internal heat exchanger in the refrigerant circuit within the lower area of the separator 4a educated.
The internal heat exchanger is to be understood as a circuit-internal heat exchanger which serves to transfer heat between the refrigerant at high pressure and the refrigerant at low pressure or at sublimation pressure. On the one hand, the liquid refrigerant is cooled further after the condensation and, on the other hand, solid particles of the refrigerant are sublimed.
After leaving the second heat exchanger 10a On the one hand, the supercooled, liquid refrigerant becomes the first expansion organs 3-1 while, on the other hand, the solid particles of the refrigerant which are not sublimated even when the liquid refrigerant is supercooled from the separator 4a be derived.

The ones from the separator 4a The solid particles of the refrigerant are discharged by means of an at an outlet of the separator 4a arranged conveyor 9 into a secondary sublimator 2-2a as a second component of the first heat exchanger 2a promoted. When flowing through the secondary sublimator 2-2a the solid particles of the refrigerant become at one of the pressure inside the primary sublimator 2-1a corresponding temperature sublimed with absorption of heat. The non-sublimated and thus the solid particles that have not changed from the solid to the gaseous state become the in the direction of flow 8th of the secondary sublimator 2-2a downstream separator 4a fed back.
The conveyor 9 can for example be designed as an ejector or a gas-operated nozzle. In each case, gaseous refrigerant at a pressure level above the low pressure level, that is to say the sublimation pressure, is used as the driving medium in the direction of flow 8th through a second inlet 6th and a second expansion device 3-2 to the conveyor 9 directed. When flowing through the second expansion organ 3-2 the refrigerant is expanded to a pressure level above the low pressure or sublimation pressure in order to transport the fluid to the secondary sublimator 2-2a to ensure.

That from the separator 4a through an outlet 7th the device 1a in the direction of flow 8th Gaseous refrigerant flowing out is fed to a compressor of the refrigerant circuit at the low pressure level or suction pressure level.

The 3a and 3b each show an arrangement of the device designed as a sublimator unit 1 out 2 within a Refrigerant circuit 11a with single-stage compression or within a refrigerant circuit 11b with two-stage compression with medium pressure separation.

When operating the very compact and inexpensive first refrigerant circuit 11a to 3a the gaseous refrigerant is at low pressure level from the compressor 12th through the outlet 7th the device 1 from the device 1 sucked in and compressed to the high pressure level. After flowing out of the compressor 12th the refrigerant is passed through a circuit heat exchanger operated as a condenser or gas cooler 13th conducted and liquefied with the release of heat. The circuit heat exchanger 13th can be designed as a refrigerant air heat exchanger so that the heat is transferred from the refrigerant to air. The refrigerant, preferably liquid, which is present at the high pressure level then flows through the first inlet 5 the device 1 into the device 1 a and is especially when flowing through the first expansion organs 3-1 , according to the device 1a out 2 , relaxed. That when flowing out of the device 1 Gaseous refrigerant is used by the compressor 12th sucked in. The refrigerant circuit 11a is closed.
The device 1 is also via a connection line to the high pressure area of the refrigerant circuit 11a in the refrigerant circuit 11a involved. The connecting line opens into one between the compressor 12th , especially the outlet of the compressor 12th , and the circuit heat exchanger 13th running refrigerant line and extends to the second inlet 6th the device 1 . In this way, the gaseous refrigerant, which is compressed to a high pressure level, can be converted into a first partial mass flow to the circuit heat exchanger 13th and a second partial mass flow to the second inlet 6th the device 1 be divided. The conveyor device, not shown 9 the device 1 is operated with a gaseous refrigerant, also known as hot gas, compressed to a high pressure level, if necessary.

When operating the second refrigerant circuit 11b to 3b the gaseous refrigerant is at low pressure level from the compressor 12th , in particular a first compressor stage 12-1 , through the outlet 7th the device 1 from the device 1 sucked in and compressed to a medium pressure level. The refrigerant, which has been compressed to the medium pressure level, is then extracted from a medium pressure tank 14th outflowing partial mass flow of gaseous refrigerant mixed and from a second compressor stage 12-2 sucked in and compressed to the high pressure level.
After flowing out of the compressor 12th , especially the second compressor stage 12-2 , the refrigerant is passed through the circuit heat exchanger operated as a condenser or gas cooler 13th conducted and liquefied with the release of heat.
The refrigerant present at the high pressure level, which is preferably liquid, is then used as it flows through a circuit expansion element 15th relaxes to the medium pressure level and flows as a two-phase mixture of liquid and steam into a medium pressure vessel 14th a. In the medium pressure tank 14th , also known as a medium pressure separator, the gaseous phase and the liquid phase of the refrigerant are separated from each other.

The refrigerant present in the liquid phase at the medium pressure level flows out of the medium pressure tank 14th out and through the first inlet 5 the device 1 into the device 1 a. That when flowing out of the device 1 Gaseous refrigerant is used by the compressor 12th sucked in. The refrigerant circuit 11b is closed. The refrigerant present in the gaseous phase at the medium pressure level, also known as flash gas, flows out of the medium pressure tank 14th and becomes with the one from the first compressor stage 12-1 outflowing partial mass flow of gaseous refrigerant mixed and from the second compressor stage 12-2 sucked in. The refrigerant can be used between the compressor stages 12-1 , 12-2 be intercooled. The flash gas can be injected in between in a continuous compression process, for example in screw compressors.
The device 1 is also via a connection line to the medium pressure area of the refrigerant circuit 11b in the refrigerant circuit 11b involved. The connecting line opens into one between the medium-pressure tank 14th and the compressor 12th , especially between the first compressor stage 12-1 and the second compressor stage 12-2 formed connection and extends to the second inlet 6th the device 1 . The gaseous refrigerant present at the medium pressure level can thus be converted into a first partial mass flow to the compressor 12th and a second partial mass flow to the second inlet 6th the device 1 be divided. The conveyor device, not shown 9 the device 1 is operated, if necessary, with a gaseous refrigerant at medium pressure level. Because the gaseous refrigerant present at medium pressure level has a lower temperature than that in the refrigerant circuit 11a to 3a as hot gas in the device 1 Having inflowing gaseous refrigerant, the refrigerant circuit can 11b to 3b with a higher energy efficiency than the refrigerant circuit 11a to 3a operate.

The first device designed as a dry-operated sublimator unit 1a out 2 points in the first heat exchanger 2a , especially in the secondary sublimator 2-2a , one reduced heat transfer coefficients compared to a heat exchanger with a direct evaporating working medium, especially a heat exchanger operated as an evaporator. In order to compensate for the associated lower heat transfer performance, the heat exchanger surface and the required installation space or space requirements must be increased.
In 4th is a second device 1 , 1b for transferring heat, similar to the first device 1 , 1a out 2 , as a dry-wet operated sublimator unit with a first heat exchanger 2 B with the in the direction of flow 8th expansion organs upstream of the working medium 3-1 , 3-2 , a separator 4b for separating solid particles and carrier liquid as well as a second heat exchanger 10b shown.

The main difference between the first device 1a according to 2 and the second device 1b lies in the operation of the second device 1b with a carrier liquid as a dry-wet operated sublimator unit instead of the operating mode of the first device 1a as a dry-operated sublimator unit. In particular, the secondary sublimator is included 2-2b as well as the separator 4b at least partially with the carrier liquid with the liquid level 16 filled. The separator 4b In addition to separating the non-sublimated solid particles and thus the solid particles that have not changed from the solid to the gaseous state, it also serves to separate the carrier liquid from the gaseous fluid flow.
The carrier liquid and the solid particles of the refrigerant are at the bottom or in a lower area of the separator 4b collected and used to subcool the through the first inlet 5 into the device 1b inflowing liquid refrigerant. The second heat exchanger operated as a subcooler for the liquid refrigerant 10b is consequently on the one hand with the liquid refrigerant and on the other hand with the one from the separator 4b removed mixture of carrier liquid and solid particles of the refrigerant applied.
After leaving the second heat exchanger 10b the supercooled, liquid refrigerant becomes the first expansion organs 3-1 directed. The one in the separator 4b The separated carrier liquid is transported together with the solid particles of the refrigerant, which are not sublimated even when the liquid refrigerant is undercooled, through the conveying device, which is designed, for example, as an ejector or gas-operated nozzle 9 in the secondary sublimator 2-2b returned.

The process of heat transfer in the secondary sublimator starts with the carrier liquid for the absorption of the solid particles 2-2b , especially the heat transfer to the wall of the secondary sublimator 2-2b , improved, which leads to the reduction of the heat exchanger surface and thus the size or the space requirement of the secondary sublimator 2-2b and consequently the first heat exchanger 2 B compared to the first heat exchanger 2a the first device 1a out 2 leads.

In 5 is a third device 1 , 1c for transferring heat as a wet-operated sublimator unit with a first heat exchanger 2c with associated expansion organs 3-1 , the separator 4b for separating solid particles and carrier liquid as well as the second heat exchanger 10b shown.

During operation of the fluid circuit, in particular the refrigerant circuit, liquid refrigerant, for example exiting from a condenser or gas cooler or collector and at a high pressure level, flows in the direction of flow 8th through the first inlet 5 into the device 1c a. When flowing through the expansion organs 3-1 the refrigerant present in liquid form is expanded to a pressure level below the triple pressure and then used as a sublimator 2-1c trained first heat exchanger 2c initiated.
The sublimator 2-1c or first heat exchanger 2c has at least two flow channels that can be acted upon by refrigerant parallel to one another. In each flow channel there is an expansion element on the inlet side 3-1 provided, which is arranged within the carrier liquid acting on the flow channel. The expansion of the refrigerant and thus the transition of the refrigerant into the solid aggregate state takes place within the flow channels and within the carrier liquid. The liquefied refrigerant is expanded into the carrier liquid. The refrigerant is then in the form of a suspension of solid particles in the carrier liquid. The sublimator 2-1c as well as the separator 4b are at least partially with the carrier liquid with the liquid level 16 filled.
When flowing through the sublimator 2-1c the refrigerant is sublimated while absorbing heat within the carrier liquid, with one of the pressure inside the sublimator 2-1c corresponding sublimation temperature, the sublimation enthalpy of the refrigerant is used. The solid particles of the refrigerant can sublime completely within the carrier liquid. The carrier liquid is cooled down in the process. The resulting cold liquid with subliming solid particles of the refrigerant is either by means of a conveying device 17th or using the natural circulation through the first heat exchanger 2c directed. The carrier liquid has a low viscosity and a low freezing point and is advantageously non-toxic and non-flammable.

The carrier liquid as well as possibly non-sublimated and thus not converted from the solid to the gaseous state solid particles of the refrigerant are inside the in the direction of flow 8th the sublimator 2-1c downstream separator 4b separated from the gaseous fluid flow. The carrier liquid and the solid particles of the refrigerant are at the bottom or in a lower area of the separator 4b collected and used to subcool the through the first inlet 5 into the device 1c inflowing liquid refrigerant. The second heat exchanger operated as a subcooler for the liquid refrigerant 10b is consequently on the one hand with the liquid refrigerant and on the other hand with the one from the separator 4b removed mixture of carrier liquid and solid particles of the refrigerant applied.
After leaving the second heat exchanger 10b the supercooled, liquid refrigerant becomes the expansion organs 3-1 directed. In one located between the second heat exchanger 10b and the expansion organs 3-1 extending connecting line is a check valve 18th intended. The one in the separator 4b The separated carrier liquid is transported through the conveying device together with the solid particles of the refrigerant, which are not sublimed even when the liquid refrigerant is undercooled 17th in the sublimator 2-1c returned. The conveyor 17th can for example be designed as a pump, in particular a circulation pump.

That from the separator 4b through the outlet 7th the device 1c in the direction of flow 8th Gaseous refrigerant flowing out is fed to a compressor of the refrigerant circuit at the low pressure level or with the suction pressure

The process of heat transfer during the sublimation of the refrigerant is used as a sublimator with the carrier liquid for absorbing the solid particles 2-1c trained first heat exchanger 2c , in particular the heat transfer to the wall of the first heat exchanger 2c , improved, which leads to the reduction of the heat exchanger surface and thus the size or the space requirement of the first heat exchanger 2c compared to the first heat exchanger 2 B the second device 1b out 4th leads.
The main differences between the second device 1b according to 4th and the third device 1c lie in the design of the first heat exchanger 2c without secondary sublimator as well as the conveyors 9 , 17th for circulating the carrier liquid with the solid particles of the refrigerant from the separator 4b in the first heat exchanger 2 B , 2c . The third device 1c has a primary and secondary sublimator combined first heat exchanger 2c on.

With a preferably vertical alignment of the flow channels of the sublimator designed as heat exchanger tubes 2-1c the carrier liquid and the non-sublimated solid particles of the refrigerant can be circulated by the kinetic energy of the primary solid-gas mixture after expansion and by the weight of the carrier liquid. The conveyor 17th can be optionally provided as required.
With the injection of the refrigerant into the carrier liquid during the expansion, the flow channels of the first heat exchanger 2c Generates highly turbulent flow conditions and thus the heat transfer coefficient and consequently the process of heat transfer, at least locally, significantly increased. In addition, when the natural circulation principle is used, the injection of the refrigerant into the carrier liquid during expansion causes at least some of the drive to circulate the carrier liquid, so that the additional conveying device is triggered 17th can possibly be dispensed with.

As the third device designed as a sublimator unit 1c , similar to a conventional evaporator unit, with one inlet 5 for liquid refrigerant under high pressure, i.e. for example for refrigerants at high pressure level or medium pressure level, and an outlet 7th is designed for refrigerants at low pressure level or suction pressure level, the device 1c Can be used for any conventional system switching.

The devices designed as sublimator units 1 , 1a , 1b , 1c are very compact. Both the expansion and the sublimation of the refrigerant take place within several flow channels arranged parallel to one another, in particular heat exchanger tubes, which have a very low risk of blocking. The solid particles of the refrigerant are distributed more evenly and the covered heat transfer surface is larger than in the case of a heat exchanger operated on the principle of spraying a surface.
Taking into account the different characteristics in the heat transfer and flow dynamics, the separation of the sublimation of primary, fine solid particles on the one hand and agglomerated, coarse solid particles on the other hand is ensured, which increases the heat transfer surface required compared to a conventional once-through evaporator / sublimator.
The accumulation of non-sublimated solid particles of the refrigerant also fulfills the function of an integrated, latent cold store.

List of reference symbols

1, 1a, 1b, 1c

contraption

2a, 2b, 2c

first heat exchanger

2-1a, 2-1c

(primary) sublimator

2-2a, 2-2b

secondary sublimator

3-1

(first) expansion device

3-2

second expansion device

4a, 4b

Separator

5

(first) admission

6th

second inlet

7th

Outlet

8th

Direction of flow

9

Conveyor

10a, 10b

second heat exchanger

11a, 11b

Refrigerant circulation

12th

compressor

12-1

first compressor stage

12-2

second compressor stage

13th

Circuit heat exchanger

14th

Medium pressure tank

15th

Circulatory expansion organ

16

Fluid level

17th

Conveyor

18th

check valve

f

firmly

fl

liquid

G

gaseous

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 3004114 A1 [0005]
• NL 9401324 A [0006]

Claims (17)

Device (1, 1a, 1b, 1c) for transferring heat through sublimation of a working medium circulating in a fluid circuit with a heat exchanger (2a, 2b, 2c) for absorbing heat through the subliming working medium and at least one expansion element (3-1), characterized in that the device (1, 1a, 1b, 1c) has a separator (4a, 4b) for separating solid particles of the working medium as well as an inlet (5) for inflowing liquid working medium and an outlet (7) for outflowing gaseous working medium, wherein the inlet (5) and the outlet (7) are each designed as a connection point to the fluid circuit. Device (1, 1a, 1b, 1c) according to Claim 1 , characterized in that the heat exchanger (2a, 2b, 2c) is designed with flow channels aligned parallel to one another and an expansion element (3-1) is assigned to each flow channel. Device (1, 1a, 1b) according to Claim 1 or 2 , characterized in that the heat exchanger (2a, 2b) has a primary sublimator (2-1a) and a secondary sublimator (2-2a, 2-2b), the primary sublimator (2-1a) having flow channels aligned parallel to one another each formed with an expansion element (3-1). Device (1, 1a, 1b, 1c) according to Claim 2 or 3 , characterized in that the expansion element (3-1) is arranged in each case at an inlet into the flow channel or within the flow channel. Device (1, 1a, 1b, 1c) according to one of the Claims 2 to 4th , characterized in that the flow channels are arranged aligned in the horizontal direction or in the vertical direction. Device (1, 1a, 1b) according to one of the Claims 2 to 5 , characterized in that the flow channels are each designed to open into the separator (4a, 4b). Device (1, 1a, 1b, 1c) according to one of the Claims 1 to 6th , characterized in that between an outlet of the separator (4a, 4b) and the heat exchanger (2a, 2b, 2c) a conveying device (9, 17) for conveying solid particles of the separated in the separator (4a, 4b) from a gaseous fluid flow Working medium is arranged. Device (1, 1a, 1b, 1c) after a Claim 7 , characterized in that the conveying device (9, 17) is designed as an ejector or a gas-operated nozzle or a pump. Device (1, 1a, 1b) after a Claim 8 , characterized in that an inlet (6) is designed for the inflow of gaseous working medium and that an expansion element (3-2) is arranged in a connecting line extending between the inlet (6) and the conveying device (9). Device (1, 1a, 1b) according to one of the Claims 1 to 9 , characterized in that inside the separator (4a, 4b) a heat exchanger (10a, 10b) for transferring heat from the liquid working medium flowing through the inlet (5) into the device (1, 1a, 1b, 1c) to a gaseous working medium Fluid flow separated solid particles of the working medium is formed, wherein the heat exchanger (10a, 10b) is arranged between the inlet (5) and the at least one expansion element (3-1). Device (1, 1a, 1b, 1c) according to one of the Claims 1 to 10 , characterized in that the working medium is carbon dioxide. Refrigerant circuit (11a, 11b) with at least one compressor (12) and a circuit heat exchanger (13) for removing heat from a working medium circulating in the circuit, characterized in that a device (1, 1a, 1b, 1c) for transferring heat by sublimation of the working medium according to one of the Claims 1 to 10 is formed, with an inlet (5) for the inflow of the liquid working medium of the device (1, 1a, 1b, 1c) with an outlet of the circuit heat exchanger (13) or a medium-pressure container (14) and an outlet (7) for the outflow of the gaseous working medium of the device (1, 1a, 1b, 1c) are connected to an inlet of the at least one compressor (12). Refrigerant circuit (11a, 11b) after Claim 12 , characterized in that an inlet (6) for the inflow of gaseous working medium of the device (1, 1a, 1b) is connected to an outlet of the compressor (12) or an outlet of the medium-pressure container (14). Method for operating a device (1, 1a, 1b, 1c) for transferring heat by sublimation of a working medium circulating in a fluid circuit according to one of the Claims 1 to 10 , having the following steps: - Relaxation of liquid working medium introduced through an inlet (5) into the (device 1, 1a, 1b, 1c) when flowing through at least one expansion element (3-1) to a pressure level below the triple pressure and generating solid particles during the introduction of the working medium into a heat exchanger (2a, 2b, 2c) for the absorption of heat by the subliming working medium, - sublimation of solid particles of the working medium when flowing through the heat exchanger (2a, 2b, 2c) with absorption of heat, - introduction of the working medium into a separator (4a, 4b) and separating non-sublimated solid particles from a gaseous fluid flow, - diverting the gaseous working medium through an outlet (7) and the solid particles from the separator (4a, 4b) and - conveying the solid particles of the working medium into the heat exchanger (2a, 2b, 2c). Procedure according to Claim 14 , characterized in that the liquid working medium flowing into the device (1, 1a, 1b, 1c) through the inlet (5) is subcooled before the expansion inside the separator (4a, 4b), the heat being transferred from the liquid working medium to solid particles of the working medium is transferred, which sublimate. Procedure according to Claim 14 or 15th , characterized in that the solid particles separated from the gaseous fluid flow in the separator (4b) are conveyed in a carrier liquid to the heat exchanger (2b, 2c), the heat exchanger (2b, 2c) and the separator (4b) at least partially with the carrier liquid are filled and the non-sublimated solid particles and the carrier liquid are separated from the gaseous fluid flow in the separator (4b). Method according to one of the Claims 14 to 16 , characterized in that the liquid working medium is expanded in a carrier liquid as it flows through the at least one expansion element (3-1), the working medium then subliming while absorbing heat within the carrier liquid and cooling the carrier liquid.

Images