Patent Application
20220252349
The present invention relates to a heat exchanger and to a thermal circuit having at least one such heat exchanger.
In heat pump applications and heat exchangers having merely a single passage there is a problem in unfavourable outside conditions that the same freeze up easily. This situation can be solved by increasing the pressure at the inlet of the refrigerant tubes (after any expansion device). Higher pressure equates to a higher saturation temperature which is the mechanism which helps delay frost formation. Simply increasing the inlet pressure is not easily accomplished as the desirable outlet pressure is a fixed value and any changes, which increase the refrigerant pressure drop, without improving the heat transfer coefficient have a negative impact on capacity. Since the outlet is a fixed value and the increase in pressure at the inlet needs to occur after any expansion apparatus (including the distributor) the increase in pressure must come from something in the core block itself to minimize performance loss. Adding pressure drop within the exit manifold through a device commonly referred to as a “gas collector” reduces performance by about 3-4% per degree of saturation temperature loss which comes with the pressure loss. Accomplishing the slightly higher refrigerant pressure drop within the core tubes themselves allows the possibility of the potential loss to be recovered. This can be achieved for example through a meander-like or multi-loop flow through the heat exchanger.
From EP 1 710 525 A1 a generic heat exchanger for a motor vehicle having two flat tubes and altogether three collectors is known, wherein a flow takes place from a first collector via a first flat tube into a return distributor and from the latter via a second flat tube into the second collector. At their longitudinal ends, the flat tubes are twisted by 90°. In the direction of an air through-flow, the individual flat tubes or in each case a pair of flat tubes are arranged one after the other, which causes an increased air pressure drop during the flow.
From EP 1 762 808 A1 a further generic heat exchanger is known, having a first collector via which fluid can be conducted in first flat tubes to an opposite return distributor and from there back via second flat tubes into a second collector. There, the two collectors are arranged one after the other in the direction of an air flow. The individual flat tubes are bent, wherein two flat tubes each are incorporated in a common opening in the return distributor. However, a heat transfer cannot be configured optimally. In addition, the individual flat tubes are arranged, seen in the direction of an air flow, one after the other at least in regions, as a result of which an air pressure drop when flowing through the heat exchanger is increased.
From CN 103 644 685 A a further heat exchanger having two inflow collectors and two outflow collectors is known. However, this creates a comparatively expensive and complex construction. In addition, no mixing of a refrigerant takes place here since the known solution shows merely two heat exchanger circuits in a common heat exchanger area.
From US 2018/0340746 A a heat exchanger having a first distributor and a second distributor is known, which are arranged on the same side of the heat exchanger and comprises a multiplicity of flat heat exchanger tubes. Accordingly, the heat exchanger tubes run substantially U-shaped. A mixing of a refrigerant does not take place there.
From CN 109 595 951 A a heat transfer with two inlet collectors and two outlet collectors is likewise known, wherein between an inlet collector and an outlet collector flat tubes are arranged in each case and all flat tubes run in a plane at least in regions. In addition, no mixing of a refrigerant takes place here since the known solution shows merely two heat exchanger circuits in a common heat exchanger area.
From US 2019/0049194 A a heat exchanger likewise having two inlet collectors and two outlet collectors is known, wherein between an inlet collector and an outlet collector flat tubes are arranged in each case. There, the flat tubes are tapered at a longitudinal end, i.e. they have an inlet or outlet merely on a part surface on an end face, in order to be thereby inserted into the respective associated inlet collector or outlet collector. In the middle region of a heat exchanger block, these expand and are consequently arranged in flow direction of the air parallel to one another. However, basically two circuits that are separated from one another are also present here.
Generally there is the problem with heat exchangers known from the prior art of not having a solution to having a single fluid circuit with high pressure drop that allows for re-distribution or inter-mixing of the refrigerant within the heat exchanger circuit while also not greatly increasing the air pressure drop of the heat exchanger.
The preferred embodiment of the present disclosure therefore deals with the problem of presenting an improved or at least an alternative embodiment for a heat exchanger of the generic type which overcomes in particular the disadvantages known from the prior art.
The present invention is based on the general idea of increasing an internal fluid pressure drop in a heat exchanger, in particular in a heat exchanger operated by means of refrigerant, without at the same time increasing a pressure drop of an air flow and thereby achieve a pressure drop within the heat exchanger with the heat exchanger output remaining the same or under certain conditions even increasing. The heat exchanger according to the invention possesses first flat tubes which with a first longitudinal end are received in associated first openings of a first collector and with an opposite second longitudinal end in associated second openings of a second collector. Additionally provided are second flat tubes which with a first longitudinal end are received in associated third openings of a third collector and with an opposite second longitudinal end in associated fourth openings of a second collector. In the second collector the second and fourth openings have the same geometry and are arranged spaced apart from one another at the same time, so that each flat tube with a respective longitudinal end is received in a single opening that is separate from other openings.
The second and fourth openings of the second collector alternate such that the first and second tubes alternate at the same time. According to the invention, only the first flat tubes or both flat tubes have an angled or bent end region in order to be received by the first collector or by the first and third collectors. By way of the so-called U-flow of a fluid within the heat exchanger, an increased pressure drop compared with a heat exchanger that merely has to be flowed through once can thus be achieved, wherein through the flat tubes that are spaced apart from one another using heat exchange fins used to exchange heat with the passing air, at the same time substantially lie in one plane so an easily passable air flow can be ensured, as a result of which a high heat exchanger output and at the same time a low pressure drop of the air flowing through the heat exchanger can be brought about. The second collector, for example a return distributor, receives the first and second flat tubes alternating with a standard distance between the individual flat tubes, while the first and third collector, for example an inlet distributor and an outlet distributor, merely have half the openings which additionally are arranged with twice the standard distance from one another. The inflow and the return flow into or out of the heat exchanger are thus located on a side while on the opposite side merely the second collector, i.e. the return distributor, is arranged. Basically, the same can be arranged at the top or bottom. With the heat exchanger according to an embodiment of the invention a high heat exchanger output with low air pressure drop of the air flowing through the heat exchanger and at the same time increased pressure drop for example of a refrigerant in the heat exchanger is thus possible through the U-flow. By way of this, the heat exchanger output can thus be at least maintained preferentially even increased and at the same time a frost risk lowered. In addition, an even distribution of the fluid in the heat exchanger can be achieved with the heat exchanger according to the invention since the individual flat tubes are preferentially arranged alternating and at the same time a mixing of the fluid flowing in the heat exchanger, for example a refrigerant, takes place in the second collector, i.e. the return distributor. Through the alternating arrangement of the individual flat tubes a defrosting capacity can also be increased and thereby a defrosting cycle shortened and the overall energy efficiency of the heat exchanger increased.
The angled, bent or folded region is angled, bent or folded such that the first collector or the first and third collector can be positioned in the direction of airflow, outside or adjacent to the plane of the coil, as a result of which an arrangement of the first and third collector for example next to one another is possible. Altogether, a heat exchanger block can be created with such an arrangement which over a large part of its height only has one plane and is therefore a comparatively flat construction.
In an advantageous further development of the solution according to the invention, the first flat tubes are formed not straight and the second flat tubes are formed angled, bent or folded. In particular a second embodiment offers the major advantage that the individual flat tubes can be formed identically which lowers the production costs and have to be installed in the heat exchanger according to the invention merely turned by 180°. In this case, the first collector and the third collector are situated one behind the other seen in the flow direction of the air.
Practically, a height H1 of the angled, bent or folded region of the first flat tubes maximally amounts to half of a height H of the first flat tubes, preferentially even maximally 20% of the total height H of the first flat tubes. The lower the height H1 of the bent or angled region of the flat tubes is, the greater is a parallel arrangement of the first and second flat tubes in a common plane, as a result of which a heat exchanger of a comparatively flat construction can be achieved.
Practically, the first collector, the second collector and/or the third collector have a circular cross section. Through the circular design, a flow-optimized shape in particular without corners and edges can be created. The circular cross section is also a pressure optimized shape in particular having resistance to high internal pressure.
In a further advantageous embodiment of the solution according to the invention, at least one of the collectors and/or the first and/or second flat tubes and/or the heat transfer fins between the tubes is/are formed from aluminium. Aluminium has a comparatively high heat conduction coefficient, as a result of which a high heat transfer rate is achievable. In addition, aluminium is light which is advantageous in particular when the heat exchanger according to the invention is employed in an on-road or over the road application.
In a further advantageous embodiment of the solution according to the invention, the first collector is arranged closer to the second collector than the third collector, or vice versa. Because of this, a slightly offset arrangement in terms of a height of the first and second collector can be achieved, as a result of which altogether a flatter design of the heat exchanger can be achieved.
Furthermore, the present invention is based on the general idea of equipping a thermal circuit, for example a coolant circuit or a refrigerant circuit of an air conditioning or refrigeration system, especially for a refrigerated trailer of a motor vehicle, with at least one such heat exchanger according to the preceding paragraphs. By way of this, the risk of freezing can be significantly reduced but a heat exchanger output maintained at least at the same level.
Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the associated figure description by way of the drawings.
It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.
Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference numbers relate to same or similar or functionally same components.
In the drawings,
According to
According to the invention, either only the first flat tubes 3 now have an angled, bent or folded end region 14 (see
With the embodiment of the heat exchanger 1 selected according to the invention, a higher pressure drop can be achieved through the U-shaped deflection of a fluid flow, for example of a refrigerant, within the heat exchanger 1 from the first collector 6 via the first flat tubes 3, the second collector 9, the second flat tubes 10 and the third collector 13, which reduces the risk of a freezing of the fluid flowing in the heat exchanger 1. Through the alternating arrangement of the flat tubes 3, 10 a defrosting performance can be increased and thereby a defrosting cycle shortened and an overall energy efficiency of the heat exchanger 1 increased. By both flat tubes 3, 10 opening into the second collector 9, a mixing of the fluid flowing in the heat exchanger 1, for example of the refrigerant, and thus an evening-out of the temperature in the heat exchanger 1 can be achieved. Because of the circumstance that the flat tubes 3, 10 are at least predominantly arranged in one plane (see
Practically, a height L1 of the angled, bent or folded region 14 can maximally to half of a total height L of the first flat tubes 3 or of both flat tubes 3, 10, wherein preferably a height L1 of the bent or angled region 14 of the first flat tubes 3 or of both flat tubes 3, 10 maximally amounts to 20% of the total height L of the first flat tubes 3 or of both flat tubes 3, 10. By way of this, a comparatively large region L-L1 can be created, in which the two flat tubes 3, 10 are arranged stacked above one another and parallel to one another, because of this bring about merely a low air pressure drop. The minimizing of the length “L1” simply maximizes the available heat transfer area. Leading to increased performance and efficiency.
According to the embodiment of
The heat exchanger 1 according to the invention can be incorporated in particular in a thermal circuit 20, for example in a coolant circuit or a refrigerant circuit of an air conditioning or refrigeration system of a refrigerated trailer of a motor vehicle 2, where it brings significant advantages because of its high heat exchanger output and its reduced risk of frost. The heat exchanger 1 according to the invention can also be employed in heat pump applications, for example as evaporator or as condenser, wherein in an evaporator function the first collector 6 represents an inlet distributor and the second collector 13 an outlet distributor. In the condenser mode, this is reversed.
While the above description constitutes the preferred embodiments of the present invention, the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.
