Evaporator of an air conditioning circuit

Abstract

Evaporator (1) of an air conditioning circuit, in particular for motor vehicles, containing: - an exchanger body with a thickness (T) and a gross area determined by its length (L) and height (H), - an upper head (2) with a connecting piece (4) comprising an inlet for the liquid phase and an outlet for the gaseous phase, and - a lower head (3), wherein the connecting piece (4) has the basic shape of a block with at least two arms (41, 42) projecting upwards in extension of opposite walls, wherein the exchanger body is formed by a bundle of two rows of flat heat exchange tubes (6) arranged parallel and spaced from each other, wherein the upper and lower ends of the heat exchange tubes (6) are connected to the upper and lower heads (2, 3), respectively, while heat exchange elements (7) with several fins are arranged between the flat tubes (6) over the entire thickness of the exchanger body, wherein the thickness (T) of the exchanger body, the distances (TP) of the flat heat exchange tubes (6) to each other and the geometries of the heat exchange elements (7) are adapted so that at an air mass flow rate of 600 kg per hour, a relative humidity of 40% and an air temperature of 40 ºC a cooling capacity of at least 15 W per cm 2 Gross area of the exchanger body is achieved when CO2 is used as coolant, and wherein the thickness (T) of the exchanger body is between 26 mm and 38 mm and the distance (TP) between the heat exchange tubes (6) is always 5.5 mm to 9 mm.

Description

Technology field

[0001] The present invention relates to an evaporator of an air conditioning circuit, particularly for motor vehicles, for 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. The invention particularly relates to an evaporator of an air conditioning circuit comprising 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 is formed by a bundle of two rows of flat heat exchange tubes arranged parallel and spaced from one another, with heat exchange elements arranged between these flat tubes. State of the art

[0002] State-of-the-art evaporators in motor vehicle air conditioning systems generally use the refrigerants R134a or R1234yf as the working medium, with an operating pressure ranging from approximately 3 bar to a maximum of 30 bar (in extreme situations).

[0003] The 2017 EU Directive 2006 / 40 / EC requires the use of refrigerants with a global warming potential (GWP) > 150 (the reference value is GWP = 1, which corresponds to that of CO2) in new automotive air conditioning systems. The refrigerant R134a, with a GWP of 1430, is therefore prohibited for use in new automotive air conditioning systems under this directive. The refrigerant R1234yf, with a GWP of 4, complies with the legislation.

[0004] The existing head designs 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.

[0005] The use of CO2 as a refrigerant is not new in itself, having already begun in the mid-19th century and reaching its peak in the 1920s, from which point on it was gradually replaced in most applications by synthetic refrigerants (CFCs, HFCs, HFOs, etc.) and by ammonia (R717), which operate at much lower pressures.

[0006] Particularly in light of current environmental and safety requirements, attempts have been made to reuse the refrigerant R744 (CO2) for the evaporators of air conditioning systems, particularly in motor vehicles. Unlike the synthetic refrigerants recently used, it is a natural substance that does not contribute to the formation of a hole in the ozone layer, has little impact on global warming, and is also inexpensive, readily available, corrosion-resistant, non-toxic, and non-flammable in normal concentrations. With a GWP of 1, it is the most suitable from a regulatory perspective. However, the pressure in the evaporator with CO2 is significantly higher than with previous refrigerants.

[0007] For heat exchangers that work with the refrigerant R744, designs are known that consist of a bundle of heat exchange tubes between which heat exchange elements are arranged, these heat exchange tubes carrying a refrigerant between an upper head and a lower head, which in this industry are often referred to as upper and lower tanks.

[0008] The dimensions of the evaporator are determined by the space used for heating or cooling, as well as the available space in the vehicle's ventilation system. The height of the evaporator, in turn, is determined by the space in the ventilation system, and this dimension is specified directly by the system manufacturer. This dimension varies with the size of the system depending on the size of the vehicle and the required thermal efficiency. The length of the evaporator, like its height, is determined by the space in the ventilation system, and this dimension is specified by the system manufacturer.

[0009] For example, document US 2006 / 0 185 386 A1 discloses an evaporator for an air conditioning circuit operating in this manner with carbon dioxide refrigerant. The evaporator comprises a bundle of two rows of flat heat exchange tubes connected at their upper and lower ends to an upper and lower evaporator head, respectively. This document specifies a preferred 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.

[0010] The existing solutions are unsatisfactory both in terms of resistance to the required high pressures and in terms of dimensions. The excessive thickness of the evaporator increases the space requirements and thus the manufacturing effort, while also leading to more complex evaporator assembly and an increase in undesirable water absorption.

[0011] The generic DE 10 2005 062 423 A1 describes an evaporator in a CO2 refrigerant circuit in which the longitudinal dimensions of the evaporator and the diameter of the refrigerant lines are optimized. A refrigerant inlet and outlet are arranged in a connecting piece and mounted below a base plate of a head of the evaporator.

[0012] DE 10 2007 009 535 A1 discusses the arrangement of fins on an evaporator.

[0013] DE 10 2004 056 557 A1 describes an evaporator in a CO2 refrigerant circuit with optimized longitudinal dimensions and optimized spacing of the refrigerant lines.

[0014] The aim of the present invention is to design an evaporator of an air conditioning circuit, in particular for motor vehicles, which ensures the required thermal efficiency with the smallest possible thickness of the exchanger body. Essence of the invention

[0015] The evaporator of an air conditioning circuit according to the invention has the features of claim 1. The thickness of the exchanger body is less than 38 mm, and the distance between the heat exchange tubes is 5.5 to 9 mm. The essence of the invention is that the thickness of the exchanger body, the distances between the flat heat exchange tubes and the geometries of the heat exchange elements are mutually optimized, so that at an air 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 Gross area of the exchanger body is achieved when CO2 is used as coolant.

[0016] 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 undulating heat exchange elements arranged in the spaces between the heat exchange tubes. The heat exchange elements may, 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 several fins, which are always formed between the corrugations of the undulating heat exchange element, with the spacing of the fins 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 shell plane that encloses the outer ends of the heat exchange surfaces accessible from the front.The gross area of the exchanger body is therefore the plane in which the ends of the flat heat exchange tubes or the ends of the wave-shaped heat exchange elements lie if they extend beyond the heat exchange tubes.

[0017] The thickness of the exchanger body is particularly advantageously 26 to 34 mm, e.g. 26 mm or 32 mm.

[0018] The thickness of the exchanger body can correspond to the distance from the outer end of the flat heat exchange tube in one row to the outer end of the flat heat exchange tube in the other row. However, in an advantageous embodiment, the heat exchange elements extend slightly beyond the heat exchange tubes in the direction of the thickness of the evaporator on both sides of the exchanger body, 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 projections than the distance from the outer end of the flat heat exchange tube in one row to the outer end of the flat heat exchange tube in the other row. The thickness of the exchanger body in this case is advantageously 28 to 34 mm.

[0019] The fins of the heat exchange elements are advantageously provided with fins for tilting the air flow, which are arranged in parallel in the length direction of the exchanger body and are oriented oppositely in the half of the heat exchange element located between the flat heat exchange tubes, in the section of the thickness of the exchanger body belonging to the first row of flat heat exchange tubes, to those in the half of the heat exchange element located 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, so that the openings delimited by the fins in one row of tubes open oppositely to those in the other row of tubes. List of figures in the drawings

[0020] The invention will now be explained in more detail with reference to specific embodiments illustrated in the drawings, in which: Fig. 1 is an overall view of the evaporator according to the invention, Fig. 2 a detailed view of a part of the assembled evaporator according to the invention at the junction of the inlet and outlet, Fig. 3a a wavy heat exchange element in a front view of the evaporator, Fig. 3b a section of the design of the wave-shaped heat exchange element along the thickness of the evaporator, Fig. 4 a flat heat exchange tube in cross section, Fig. 5 a section of the arrangement of the heat exchange tubes in the evaporator and Fig. 6 a graphical representation of the optimization of the thickness of the exchanger body and the distances between the flat heat exchange tubes according to the invention. Embodiment of the invention

[0021] 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. Fig. 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 indicated directions 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 Fig. 1 from 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.

[0022] A refrigerant flows through the evaporator 1, entering the evaporator 1 as a liquid phase essentially in liquid form (but may contain refrigerant that is already in a gaseous state) and exiting it as a gas phase (also known as vapor phase).

[0023] The evaporator 1 consists of two heads 2, 3, which are opposite each other and connected by two rows of flat heat exchange tubes 6, between which heat exchange elements 7 are arranged, which serve to exchange heat with another medium, air, which flows transversely through the evaporator 1 in the direction of its thickness T. In the embodiment shown, each heat exchange tube 6 has nine channels 14, which ensure the flow of coolant in the evaporator 1.

[0024] In Fig. 1, the heat exchange elements 7 are shown only on the left side in order to better see the heat exchange tubes 6 leading between the two heads 2, 3 of the evaporator.

[0025] Each head 2, 3 of the evaporator according to the invention comprises an assembly of distribution plates 21, 31, intermediate plates 22, 32, and cover plates 23, 33, inserted into a U-shaped profile 20 or an inverted U-shaped profile 30 and interconnected by an internal arrangement of the plates that determines the desired direction(s) of the medium flow through the head and distributes the medium to the active part of the evaporator, toward the bundle of heat exchange tubes. With regard to the energy transfer of the air, this distribution head is essentially an inactive part. These parts are interconnected by brazing.

[0026] The head 2, 3 of the evaporator also serves to distribute the refrigerant in the liquid state (and possibly already partly in the gaseous state), which, via the inlet connected to one of the two heads 2 or 3, gradually reaches the individual heat exchange tubes 6 leading between the two heads 2, 3 and finally (now in the form of a gaseous vapor phase) to the outlet.

[0027] Fig. Figure 2 illustrates a section of the evaporator 1 according to the invention with the attached connecting piece 4, which itself includes the coolant inlet and the coolant outlet. Bushings 5 for connecting pipes for introducing the liquid phase and discharging the gas phase are mounted in the connecting piece 4. The connecting piece 4 has the basic shape of a block with at least two arms 41, 42 that project upward as an extension of its two opposite walls.

[0028] The evaporator 1 comprises an exchanger body, which forms the active part in terms of heat exchange, and two heads 2, 3. The active part consists of heat exchange tubes 6 and wave-shaped heat exchange elements 7. The flat heat exchange tube 6 always has several channels 14 for the coolant flow and is made by extrusion from an aluminum alloy. The wave-shaped heat exchange element 7 is attached to the wider surface of the flat heat exchange tube 6 by brazing. The air flow flowing through the active part of the evaporator is cooled by the wave-shaped heat exchange element 7, which absorbs the heat and transfers it to the heat exchange tube 6.

[0029] The overall shape of the wave-shaped heat exchange element 7 is in Fig. 2. A section of the wavy heat exchange element 7 in a front view of the evaporator is shown in Fig. 3a. The fins 11 of the wavy heat exchange element 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. Fig. The components shown in Figure 3a are not drawn to scale for reasons of clarity. The slats 12 are best seen in Fig. 3b, which shows the section of the heat exchange element 7 according to Fig. 3a in a plan view. This shape influences the performance parameters of the exchanger body. The performance depends on the size and opening of the fins 12 and on the number of corrugations 13 that form the ribs. This shape also allows the removal of moisture that has condensed in parts of the wave-shaped heat exchange element 7. The quality of the soldered connection between the wave-shaped heat exchange element 7 and the heat exchange tube 6 is influenced by the shape of the corrugations 13 of the wave-shaped heat exchange element 7. The design of the heat exchange tube 6 is shown in Fig. 4 and the arrangement of the heat exchange element 7 in the spaces between the tubes 6 in Fig. 5 shown.

[0030] When optimizing the exchanger body geometry, the inventors were surprised to discover that a small thickness T of the exchanger body, less than 38 mm, and ideally between 26 and 32 mm, can be used to achieve the required cooling capacity. At all these thicknesses, the basic parameters for effective cooling of the other medium by the exchanger body are met.

[0031] The distance between two adjacent heat exchange tubes, like the thickness T of the evaporator body, also influences the pressure loss. The optimal distance between two adjacent tubes 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 is shown in Fig. 6. The distance between two adjacent heat exchange tubes 6 is one of the main factors determining the pressure loss during an air flow through the active part of the evaporator 1.

[0032] Area A in Fig. Figure 6 represents the range in which the distance between two adjacent tubes is 5.59 to 8.94 mm and the thickness T of the evaporator body is also between 26 and 38 mm. This range represents the range of optimal efficiency, expressed by a cooling capacity of at least 15 W per cm 2 Gross surface area of the exchanger body using CO2 as coolant and an air flow of 600 kg per hour, a relative humidity of 40% and an air temperature of 40°C. The entrapment of water between the heat exchange surfaces 9, 7, 11, 12, 13 is satisfactorily low in area A.

[0033] Area B in Fig. 6 represents the area of an oversized exchanger body. A thickness of more than 38 mm already does not lead to any increase in efficiency. The entrapment of water between the heat exchange surfaces 9, 7, 11, 12, and 13 is bordering on an unsatisfactory condition.

[0034] Area C in Fig. 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 small.

[0035] Area D in Fig. 6 represents an area of sufficient efficiency, but large amounts of water are trapped between the fins of the evaporator, which may result in water spraying from the air conditioner.

[0036] Area E in Fig.6 represents a range where, due to the influence of the air pressure drop, the evaporator can only provide the required performance at the expense of a high fan power. A high pressure drop generally increases the performance of the cooling device and, at the same time, increases the accumulation of water in the wave-shaped heat exchange element 7 and the possible freezing of this water when the system is shut down and the ambient temperature drops below 0°C. A high pressure drop also increases the power consumption of the fan that forces air through the evaporator 1.

[0037] Another important parameter of the evaporator 1 is the distance between the fins 11 of the wave-shaped heat exchange element. This corresponds to the distance between two adjacent waves 13 of the wave-shaped heat exchange element and, in the described embodiments, is in the range of 1.3 to 1.5 mm.

[0038] According to one embodiment, the thickness of the exchanger body T is 26 mm, and the wave-shaped heat exchange elements 7, which in this case also have a width of 26 mm, do not extend beyond the ends of the heat exchange tubes 6 in the direction of the thickness of the exchanger body. The thickness 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 of one row of tubes to the outer end of the surface of the heat exchange tube 6 of the other row of tubes.

[0039] When using heat exchange elements 7 with a width of 32 mm in an otherwise identical evaporator, they would extend 3 mm beyond the ends of the heat exchange tubes 6 on both sides, and the total thickness of the exchanger body would also be T = 32 mm. The heat exchange in the evaporator increases from 74% to 82% compared to the embodiment without extension. This extension improves air cooling and limits the freezing of moisture that condenses in parts of the wave-shaped heat exchange elements 7 during operation of the exchanger body.

[0040] Although the above-described embodiment of the invention has been described only in connection with the evaporator of a cooling device, it is obvious to a person skilled in the art that an exchanger having the characteristics specified in the claims can also be used for other heat exchange applications.

Claims

[1] Evaporator (1) of an air conditioning circuit, in particular for motor vehicles, containing: - an exchanger body with a thickness (T) and a gross area determined by its length (L) and height (H), - an upper head (2) with a connecting piece (4) comprising an inlet for the liquid phase and an outlet for the gaseous phase, and - a lower head (3), wherein the connecting piece (4) has the basic shape of a block with at least two arms (41, 42) projecting upwards in extension of opposite walls, wherein the exchanger body is formed by a bundle of two rows of flat heat exchange tubes (6) arranged parallel and spaced from each other, wherein the upper and lower ends of the heat exchange tubes (6) are connected to the upper and lower heads (2, 3), respectively, while heat exchange elements (7) with several fins are arranged between the flat tubes (6) over the entire thickness of the exchanger body, wherein the thickness (T) of the exchanger body, the distances (TP) of the flat heat exchange tubes (6) to each other and the geometries of the heat exchange elements (7) are adapted so that at an air mass flow rate of 600 kg per hour, a relative humidity of 40% and an air temperature of 40 ºC a cooling capacity of at least 15 W per cm 2 Gross area of the exchanger body is achieved when CO2 is used as coolant, and wherein the thickness (T) of the exchanger body is between 26 mm and 38 mm and the distance (TP) between the heat exchange tubes (6) is always 5.5 mm to 9 mm. [2] Evaporator (1) according to claim 1, wherein the distance (FP) between the fins of the heat exchange elements (7) is 1.3 mm to 1.5 mm. [3] Evaporator (1) according to one of the preceding claims, wherein the heat exchange elements (7) on both sides of the exchanger body extend slightly, ie advantageously by 1 mm to 4 mm, beyond the ends of the heat exchange tubes (6) in the direction of the thickness of the evaporator (1). [4] Evaporator (1) according to one of the preceding claims, wherein the thickness (T) of the exchanger body is 26 mm to 34 mm, e.g. 26 mm or 32 mm. [5] Evaporator (1) according to claim 3, wherein the thickness (T) of the exchanger body is 28 mm to 34 mm. [6] Evaporator (1) 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 fins are arranged parallel in the direction of the length (L) of the exchanger body and are oriented oppositely in the half of the heat exchange element (7) located between the flat heat exchange tubes (6), in the section of the thickness of the exchanger body belonging to the first row of flat heat exchange tubes (6), to those in the half of the heat exchange element (7) located between the flat tubes (6), in the section of the thickness of the exchanger body belonging to the second row of flat heat exchange tubes (6), so that the openings delimited by the fins (12) in one row of tubes (6) open oppositely to those in the other row of tubes (6).

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