DE112018001417T5 - Evaporator of an air conditioning circuit, in particular for a motor vehicle - Google Patents

Abstract

An air conditioning evaporator (1) includes an exchanger body, an upper head (2) with an inlet for the liquid phase and an outlet for the gaseous phase and a lower head (3), the exchanger body being formed by a bundle of two rows of flat ones Heat exchange tubes (6) is formed, which are arranged in parallel and at a distance from one another, heat exchange elements (7) having a plurality of fins (11) being arranged between the flat tubes (6). The thickness (T) of the exchanger body is less than 38 mm and the distance (TP) between the heat exchange tubes is always 5.5 to 9 mm. The distance (FP) of the fins of the heat exchange elements to each other is 1.3 to 1.5 mm, and the heat exchange elements (7) extend on both sides of the exchanger body in the direction of the thickness (T) of the evaporator (1) slightly over the ends of the Heat exchange tubes (6).

Description

Technology field

The present invention relates to an evaporator of an air conditioning circuit, in particular for motor vehicles, for the heat exchange between a coolant circulating in a circuit with the evaporator and a cooled medium, usually air, which moves from the outside through an exchanger body. More particularly, the invention relates to an air conditioning evaporator that includes an exchanger body, an upper head with an inlet for the liquid phase and an outlet for the gaseous phase, and a lower head, the exchanger body being formed by a bundle of two rows of flat heat exchange tubes is formed, which are arranged in parallel and spaced from each other, heat exchange elements being arranged between these flat tubes.

State of the art

Evaporators of an air conditioning circuit for motor vehicles according to the prior art generally use the coolants R134a or R1234yf as the working medium, the operating pressure of which varies from approximately 3 bar to a maximum of 30 bar (in extreme situations).

The EU Directive 2006/40 / EC of 2017 prescribes the use of coolants with a global warming potential (GWP)> 150 (the reference value is GWP = 1, which corresponds to that of CO ₂ ) in new automotive air conditioning systems. The coolant R134a with a value of GWP = 1430 is therefore prohibited under this directive for use in new automotive air conditioning systems. The coolant R1234yf with a value of GWP = 4 corresponds to the legislation.

The existing head versions are therefore designed for low pressure media with a maximum pressure resistance of up to 30 bar (g) and are not suitable for use in high pressure exchangers.

The use of CO ₂ as a coolant is not new per se, since it started in the mid-19th century and reached its peak in the 1920s, and from then on it is gradually replaced by synthetic coolants (CFCs, CFCs, HFO etc.) and has been replaced by ammonia (R717) which operate at much lower pressures.

In particular with regard to the current ecological and safety requirements, attempts have been made to use the coolant R744 (CO ₂ ) again for the evaporators of a climate cycle, in particular for motor vehicles. In contrast to the synthetic coolants used recently, it is a natural product that also does not contribute to the formation of a hole in the ozone layer, has little influence on global warming and is also cheap, readily available, corrosion-resistant, non-toxic and in usual concentrations is not flammable. With a value of GWP = 1, it is the most suitable from the point of view of legislation. However, the pressure in the evaporator is significantly higher with CO ₂ than with previous coolants.

For heat exchangers that work with the coolant R744, designs are known which consist of a bundle of heat exchange tubes between which heat exchange elements are arranged, these heat exchange tubes between an upper head and a lower head, which in this branch of industry are often used as upper and lower tanks a coolant.

The dimensions of the evaporator are determined by the space that is used for heating or cooling and by the available space that is designed in the ventilation system of the motor vehicle. The height dimension of the evaporator is in turn determined by the space dimension in the ventilation system, and this dimension is specified directly by the manufacturer of the system. This measure varies with regard to the size of the system depending on the size of the motor vehicle and the required thermal efficiency. The length dimension of the evaporator, like its height, is specified by the space in the ventilation system, this dimension being specified by the manufacturer of this system.

For example, from the document US2006185386 an air conditioning evaporator thus operating with carbon dioxide refrigerant is known which contains a bundle of two rows of flat heat exchange tubes which are connected at their upper and lower ends to an upper and lower head of the evaporator, respectively. This document specifies an advantageous length of 200 to 350 mm and a height of 100 to 235 mm. Specifically, it describes an evaporator with a length of 307 mm, a height of 235 mm and a thickness of 38 mm.

The known solutions are unsatisfactory both in terms of their resistance to the high pressures required and in terms of their dimensions. The excessive thickness of the evaporator on the one hand increases the requirements for the installation space and thus the manufacturing effort and on the other hand leads to a more demanding assembly of the evaporator and an increase in unwanted water absorption.

The aim of the present invention is to design an evaporator of a climatic cycle, in particular for motor vehicles, which ensures the required thermal efficiency with the smallest possible thickness of the exchanger body.

Essence of the invention

The evaporator of an air conditioning circuit according to the invention has an exchanger body which is formed by a bundle of two rows of flat heat exchange tubes which are arranged in parallel and at a distance from one another, the upper and lower ends of the heat exchange tubes being connected to the upper and lower heads , while heat exchange elements with a plurality of fins are arranged between the flat tubes over the entire thickness of the exchanger body. The essence of the invention is that the thickness of the exchanger body, the spacing of the flat heat exchange tubes to one another and the geometries of the heat exchange elements optimize each other so that with an air throughput of 600 kg per hour, a relative humidity of 40% and an air temperature of 40 ° C a cooling capacity of at least 15 W per cm ² gross area of the exchanger body is achieved when CO _{2 is used} as a coolant.

The exchanger body refers to the core of the evaporator, which is active in terms of heat transfer and comprises two rows of flat heat exchange tubes and wave-shaped heat exchange elements which are arranged in the spaces between the heat exchange tubes. The heat exchange elements can, but do not have to protrude slightly beyond the heat exchange tubes on both sides of the exchanger body in the direction of the thickness of the evaporator. The heat exchange elements form a plurality of ribs, which are always formed between the shafts of the wave-shaped heat exchange element, the spacing between the ribs of the heat exchange elements advantageously being 1.3 to 1.5 mm. The gross area of the exchanger body here refers to the product of the length and height of the evaporator core in the imaginary envelope plane, which encloses the outer ends of the heat exchange areas which are accessible from the front. The gross area of the exchanger body is thus the plane in which the ends of the flat heat exchange tubes or the ends of the wave-shaped heat exchange elements lie when they extend beyond the heat exchange tubes.

The thickness of the exchanger body is advantageously less than 38 mm, and the distance between the heat exchange tubes is advantageously 5.5 to 9 mm. The thickness of the exchanger body is particularly advantageously 26 to 34 mm, e.g. 26 mm or 32 mm.

The thickness of the exchanger body may correspond to the distance from the outer end of the flat heat exchange tube of one row to the outer end of the flat heat exchange tube of the other row. In an advantageous embodiment, however, the heat exchange elements in the direction of the thickness of the evaporator on both sides of the exchanger body extend slightly beyond the heat exchange tubes, i.e. by 1 to 15%, advantageously by 1 to 4 mm of the thickness of the exchanger body. In this advantageous embodiment, the thickness of the exchanger body is greater by the amount of these two protrusions than the distance from the outer end of the flat heat exchange tube of one row to the outer end of the flat heat exchange tube of the other row. In this case, the thickness of the exchanger body is advantageously 28 to 34 mm.

The fins of the heat exchange elements are advantageously provided with fins for tilting the air flow, which are arranged parallel in the longitudinal direction of the exchanger body and in half of the heat exchange element lying between the flat heat exchange tubes, in the section of the thickness of the exchanger body which belongs to the first row of the flat heat exchange tubes those in half of the heat exchange element lying between the flat heat exchange tubes, in the section of the thickness of the exchanger body belonging to the second row of flat heat exchange tubes, are oriented so that the openings delimited by the fins in a row of tubes are opposite to those in FIG open the other row of pipes.

Figure list

• 1 eine Gesamtansicht der Verdampfung gemäß der Erfindung,
• 2 eine Detailansicht eines Teils des zusammengesetzten Verdampfers gemäß der Erfindung an der Verbindungsstelle des Ein- und Auslasses,
• 3a ein welliges Wärmeaustauschelement in einer Vorderansicht des Verdampfers,
• 3b einen Ausschnitt der Ausgestaltung des wellenförmigen Wärmeaustauschelements entlang der Dicke des Verdampfers,
• 4 ein flaches Wärmeaustauschrohr im Querschnitt,
• 5 einen Ausschnitt der Anordnung der Wärmeaustauschrohre im Verdampfer und
• 6 eine grafische Darstellung der Optimierung der Dicke des Tauscherkörpers und der Abstände der flachen Wärmeaustauschrohre zueinander gemäß der Erfindung.

The invention will now be explained in more detail with reference to special exemplary embodiments which are illustrated in the drawings. In it show:

• 1 an overall view of the evaporation according to the invention,
• 2nd 2 shows a detailed view of part of the assembled evaporator according to the invention at the connection point of the inlet and outlet,
• 3a a wavy heat exchange element in a front view of the evaporator,
• 3b a section of the configuration of the wave-shaped heat exchange element along the thickness of the evaporator,
• 4th a flat heat exchange tube in cross section,
• 5 a section of the arrangement of the heat exchange tubes in the evaporator and
• 6 a graphical representation of the optimization of the thickness of the exchanger body and the spacing of the flat heat exchange tubes to each other according to the invention.

Embodiment of the invention

Throughout this document, terms relating to the orientation of the evaporator, such as top, bottom, vertical, horizontal, etc., refer to its orientation as shown in the figures, see e.g. 1 . The evaporator 1 of the air conditioning circuit, in particular for a motor vehicle, is often arranged in exactly such an orientation, and the directions given thus correspond to the position of such an evaporator 1 during its use. The height H of the evaporator body is in the vertical direction, the length L of the evaporator body is in 1 left to right and the thickness T of the evaporator body is in a direction perpendicular to the vertical direction and the left to right direction.

A coolant flows through the evaporator 1 and enters the evaporator as a liquid phase, essentially in liquid form 1 on (but can contain coolant that is already in the gaseous state) and as a gas phase (also known as vapor phase).

The evaporator 1 consists of two heads 2nd , 3rd that face each other and through two rows of flat heat exchange tubes 6 are interconnected, between which heat exchange elements 7 are arranged, which serve the heat exchange with another medium, air, the evaporator 1 towards its thickness T flowed across. In the embodiment shown, each heat exchange tube has 6 nine channels 14 on the coolant flow in the evaporator 1 to ensure.

In 1 are the heat exchange elements 7 only shown on the left to the between the two heads 2nd , 3rd of the evaporator leading heat exchange tubes 6 to see better.

Every head 2nd , 3rd of the evaporator according to the invention comprises an assembly of distribution boards 21 , 31 , Intermediate plates 22 , 32 and cover plates 23 , 33 that are in a U-shaped profile 20th or an inverted U-shaped profile 30th used and connected to each other with such an internal arrangement of the plates, which determines the desired direction or directions of flow of the medium through the head and distributes the medium to the active part of the evaporator in the direction of the bundle of heat exchange tubes. With regard to the energy transmission of the air, this distributor head is essentially an inactive part. The parts mentioned are connected to each other by soldering.

The head 2nd , 3rd The evaporator is also used to distribute the coolant in the liquid state (and possibly already partially in the gaseous state), which is above that with one of the two heads 2nd or 3rd connected inlet gradually to the individual heat exchange tubes 6 that between the two heads 2nd , 3rd lead, and finally (now in the form of a gaseous vapor phase) to the outlet.

2nd illustrates a section of the evaporator according to the invention 1 with attached connector 4th , which itself includes the coolant inlet and the coolant outlet. In the connector 4th are sockets 5 attached for the connection of pipelines for the introduction of the liquid phase and the discharge of the gas phase. The connector 4th has the basic form of a block with at least two arms 41 , 42 that protrude upward from its two opposite walls.

The evaporator 1 has an exchanger body, which forms the active part in terms of heat exchange, and two heads 2nd , 3rd on. The active part consists of heat exchange tubes 6 and wave-shaped heat exchange elements 7 . The flat heat exchange tube 6 always has multiple channels 14 for the coolant flow and is manufactured by extrusion from an aluminum alloy. On the wider surface of the flat heat exchange tube 6 is the wave-shaped heat exchange element 7 fixed by soldering. The air flow that flows through the active part of the evaporator is through the wave-shaped heat exchange element 7 cooled, which absorbs the heat and to the heat exchange tube 6 forwards.

The overall shape of the wave-shaped heat exchange element 7 is in 2nd to see. A section of the wavy heat exchange element 7 in a front view of the evaporator is in 3a shown. Ribs 11 of the wavy heat exchange element 7 are with slats 12th provided for tilting the air flow in the direction of length L of the exchanger body are arranged in parallel. In the 3a The components shown are not drawn to scale for reasons of clarity. The slats 12th are best in 3b to see the section of the heat exchange element 7 corresponding 3a in a top view. This shape affects the Performance parameters of the exchanger body. The performance depends on the size and opening of the slats 12th and the number of waves 13 that form the ribs. This shape also allows the removal of moisture in parts of the corrugated heat exchange element 7 is condensed. The quality of the solder joint between the wave-shaped heat exchange element 7 and the heat exchange tube 6 is determined by the shape of the waves 13 of the wave-shaped heat exchange element 7 influenced. The design of the heat exchange tube 6 is in 4th and the arrangement of the heat exchange element 7 in the spaces between the pipes 6 in 5 shown.

The inventors were surprised when performing an optimization of the geometry of the exchanger body to find that a small thickness T of the exchanger body, which is less than 38 mm, preferably 26 to 32 mm, can be used to achieve the required cooling capacity. With all these thicknesses, the basic parameters for effective cooling of the other medium by the exchanger body are met.

The distance between two adjacent heat exchange tubes is similar to the thickness T of the evaporator body also influences the pressure loss. The optimal distance between two neighboring pipes is 5.59 to 8.94 mm. The relationship between the thickness T of the evaporator body and the distance between two adjacent tubes 6 to each other is in 6 illustrated. The distance between two adjacent heat exchange tubes 6 to each other is one of the main factors affecting the pressure loss during an air flow through the active part of the evaporator 1 determine.

The area A in 6 represents the area in which the distance between two adjacent tubes to each other 5.59 to 8.94 mm and the thickness T of the evaporator body is also between 26 and 38 mm. This area represents the area with optimal efficiency, expressed by a cooling capacity of at least 15 W per cm ^{2 of} gross area of the exchanger body when using CO ₂ as coolant and an air flow of 600 kg per hour, a relative humidity of 40% and an air temperature of 40 ° C. The inclusion of water between the heat exchange surfaces 9 , 7 , 11 , 12th , 13 is satisfactorily low in area A.

The area B in 6 represents the area of an oversized exchanger body. The thickness of more than 38 mm already does not lead to an increase in efficiency. The trapping of water between the heat exchange surfaces 9 , 7 , 11 , 12th , 13 is on the borderline of an unsatisfactory condition.

The area C in 6 represents the area with insufficient efficiency, ie a cooling capacity of less than 15 W per cm ² gross area. The inclusion of water would be satisfactorily low.

The area D in 6 represents an area of sufficient efficiency, however, large amounts of water are trapped between the fins of the evaporator, which can be manifested by water spraying from the air conditioner.

The area E in 6 represents an area in which the evaporator can only achieve the required performance due to the influence of the pressure loss in the air at the expense of high fan performance. A high pressure drop generally increases the performance of the cooling device and at the same time the water accumulation in the wave-shaped heat exchange element 7 and the possible freezing of this water when the system is at a standstill and the ambient temperature drops below 0 ° C. A high pressure drop also increases the power consumption of the fan, the air through the evaporator 1 presses.

Another important parameter of the evaporator 1 is the distance between the ribs 11 of the wave-shaped heat exchange element to each other. This corresponds to the distance between two neighboring waves 13 of the wave-shaped heat exchange element and is in the described embodiments in the range of 1.3 to 1.5 mm.

According to one embodiment, the thickness of the exchanger body is T 26 mm, and the wave-shaped heat exchange elements 7 , which in this case also have a width of 26 mm, do not extend in the direction of the thickness of the exchanger body over the ends of the heat exchange tubes 6 out. The fat T of the exchanger body in this case corresponds to the distance from the outer end of the surface of the heat exchange tube 6 a series of tubes to the outer end of the surface of the heat exchange tube 6 the other row of pipes.

When using heat exchange elements 7 with a width of 32 mm in an otherwise identical evaporator, they would extend 3 mm on both sides over the ends of the heat exchange tubes 6 extend, and the total thickness of the exchanger body would also be T = 32 mm. The heat exchange in the evaporator increases compared to the embodiment without extension from 74% to 82%. This extension improves air cooling and limits the freezing of moisture in parts of the undulating heat exchange elements 7 condenses during the operation of the exchanger body.

Although the embodiment of the invention described above has only been described in connection with the evaporator of a cooling device, it is obvious to the person skilled in the art that an exchanger with the properties specified in the patent claims can also be used for other heat exchange applications.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• US 2006185386 [0009]

Claims (7)

Evaporator (1) of an air conditioning circuit, in particular for motor vehicles, which contains the following - an exchanger body with a thickness (T) and a gross area which is predetermined by its length (L) and its height (H), - an upper head (2) with an inlet for the liquid phase and an outlet for the gaseous phase and - a lower head (3), the exchanger body being formed by a bundle of two rows of flat heat exchange tubes (6) which are arranged in parallel and at a distance from one another, the upper and lower ends of the heat exchange tubes (6) being connected to the upper and lower heads (2, 3), respectively, while heat exchange elements (7) with a plurality of fins are arranged between the flat tubes (6) over the entire thickness of the exchanger body , characterized in that the thickness (T) of the exchanger body, the distances (TP) of the flat heat exchange tubes (6) from one another and the geometries of the heat exchange elements (7) optimize each other so that at an air mass flow rate of 600 kg per hour, a relative humidity of 40% and an air temperature of 40 ° C, a cooling capacity of at least 15 W per cm ^{2 of} gross area of the exchanger body is achieved when CO _{2 is used} as the coolant. Evaporator after Claim 1 , wherein the thickness (T) of the exchanger body is less than 38 mm and the distance (TP) of the heat exchange tubes (6) to each other is always 5.5 to 9 mm. Evaporator after Claim 2 , wherein the distance (FP) of the ribs of the heat exchange elements (7) to each other is 1.3 to 1.5 mm. Evaporator after Claim 1 , 2nd or 3rd , wherein the heat exchange elements (7) on both sides of the exchanger body in the direction of the thickness of the evaporator (1) extend slightly, ie advantageously by 1 to 4 mm beyond the ends of the heat exchange tubes (6). Evaporator according to one of the Claims 1 to 4th , wherein the thickness (T) of the exchanger body is 26 to 34 mm, for example 26 mm or 32 mm. Evaporator after Claim 4 , wherein the thickness (T) of the exchanger body is 28 to 34 mm. Evaporator according to one of the preceding claims, wherein the fins (11) of the heat exchange elements (7) are provided with fins (12) for tilting the air flow, which are arranged parallel in the direction of the length (L) of the exchanger body and in half of that between the flat ones Heat exchange tubes (6) lying heat exchange element (7), in the section of the thickness of the exchanger body, which belongs to the first row of the flat heat exchange tubes (6), to those in half of the heat exchange element (7) lying between the flat tubes (6), in the section the thickness of the exchanger body belonging to the second row of flat heat exchange tubes (6) are aligned so that the openings delimited by the fins (12) in one row of tubes (6) are opposite to those in the other row of tubes Open (6).

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