Heat exchanger arrangement

Abstract

The invention relates to a heat exchanger arrangement (1) with defrosting function, comprising a heatable fan chamber (6) with an evaporator (3) and a vertical air inlet and outlet surface open in evaporator operation, characterized in that the air inlet and / or the air outlet surface can be separated from the air exchange with the environment of the heat exchanger arrangement (1) by an air curtain device (8) in defrost operation, wherein the air curtain device (8) is arranged in the fan chamber (6) and is formed from an air curtain fan (9), an air duct (10) and an inlet element (11) arranged between them, wherein the air duct (10) has an air outlet (12) which extends at least partially over the air inlet and / or the air outlet surface.

Description

[0001] The invention relates to a heat exchanger arrangement with defrosting function, which is used as an evaporator in refrigeration systems, such as in cold storage facilities.

[0002] Typical heat exchanger arrangements often feature finned heat exchangers. These are operated as evaporators and air coolers, cooling the air via surface cooling. The fin surface cools the air at temperatures ranging from +5 °C to -50 °C. Condensation or frost formation can occur during the cooling process if the average surface temperature is lower than the dew point temperature of the air being cooled. In this case, the water contained in the air being cooled precipitates on the fin surface and freezes at temperatures below freezing.

[0003] Frost formation on the fin surface is a progressive process that increasingly reduces the evaporator's performance and thus the overall efficiency of the heat exchanger assembly. With a heavy frost buildup, the lowest surface temperature occurs in the area of ​​the refrigerant-carrying pipes.

[0004] A detrimental change in the performance data of the refrigeration system occurs due to progressive frost buildup on the evaporator. Furthermore, there is an increase in the air-side pressure drop during the airflow through the iced-up heat exchanger, a decrease in the heat transfer coefficient, and a decrease in the air volume flow due to a narrowing of the flow cross-section caused by the frost deposits on the evaporator.

[0005] Various defrosting systems are known in the prior art to defrost the frost or ice that forms on the evaporator.

[0006] During forced-air defrosting, the refrigerant supply to the appliance is interrupted and the evaporator is defrosted using circulating air from the refrigerator compartment. This method is suitable for air inlet temperatures of 3 °C or higher, but requires excessively long defrosting times.

[0007] Another option is the electric defrosting of the evaporators. In this system, tubular heating elements are placed in contact tubes within the evaporator's finned structure, directly heating the evaporator. However, these systems suffer from relatively poor efficiency due to the contact tube arrangement within the finned area and the refrigerant / heat transfer fluid pipes. The contact tube temperatures of approximately 200 °C lead to the evaporation of meltwater and thus to the formation of steam plumes, which is an undesirable side effect of this system.

[0008] As an alternative to the aforementioned strategies, hot gas / cold gas defrosting is known in the prior art. In this process, the refrigerant for defrosting is extracted before the condenser and routed through the evaporator via an additional pipe system. The hot gas then transfers heat to the evaporator. This process is known as hot gas defrosting.

[0009] If the refrigerant for defrosting is taken from the vapor phase of the collector and routed through the evaporator via an additional pipe system, this is called cold gas defrosting.

[0010] A disadvantage of these systems is that multiple evaporators are necessary and a higher level of control and regulation is required.

[0011] Evaporators can be defrosted using heat transfer fluids as an alternative to refrigerant. This involves utilizing waste heat, for example in the form of warm brine, and implementing a heat transfer fluid circuit or defrosting via an additional pipe system within the evaporator.

[0012] During water defrosting, heated water is trickled onto the heat exchanger block via a defrosting nozzle. This requires a large defrosting tray and a corresponding supply of hot water.

[0013] Frost removal with compressed air is achieved through a distribution pipe with nozzle attachments for distributing the compressed air below the evaporator. The frost is blown off at an overpressure of 2 to 3 bar.

[0014] In the prior art, additional systems are also known which are installed on the defrosting systems at the heat exchanger arrangements in order to prevent heat loss from the evaporator into the cold room during defrosting.

[0015] The installation of louvers or baffles on the air inlet side of the heat exchanger assembly is a commonly used technique.

[0016] Louvered dampers offer the advantages of low heat loss and rapid defrosting, while simultaneously preventing icing of the cold room ceiling at the air inlet. The system is also very robust, even with high humidity levels in the cold room. A disadvantage is the requirement for damper drive motors integrated into a control system. Furthermore, additional trace heating at the louvered damper is often necessary for smooth system operation, and therefore the additional use of ShutUps is recommended.

[0017] So-called ShutUps are used to thermally separate the heat exchanger assemblies from the cooling room during the defrosting process.

[0018] Shut-ups offer the advantages of low heat loss and rapid defrosting, as well as preventing icing on the cold room ceiling at the air outlet. However, shut-ups also lead to increased air-side pressure loss and a risk of contamination and icing.

[0019] Intake hoods offer low heat loss and enable rapid defrosting, while simultaneously preventing icing on the cold room ceiling at the air inlet. However, a disadvantage is ice formation on the hood itself when there is high humidity in the cold room or when defrosting at high temperatures. In such cases, the additional use of a ShutUp unit is usually necessary.

[0020] ShutUps are increasingly used as additional components for the defrosting process on evaporators due to their comparatively low purchase costs. These are textile tubes that are erected by the airflow generated by the fan during the refrigeration process and then collapse to block the airflow path when the airflow decreases.

[0021] However, if the defrost control is faulty or the customer deviates from the manufacturer's recommendations, frost and ice can form inside the ShutUp unit due to stagnant steam. This can prevent the textile hose from fully extending during the cooling process due to its stiffness, leading to a significant increase in air-side pressure loss at the fan. Consequently, the fan's operating point shifts. Exceeding the characteristic curve specified by the fan manufacturer can drastically shorten the service life of the ball bearings and cause bearing damage. This ultimately results in system shutdown. During the defrosting process, the frost-covered textile hose does not completely seal the fan opening and therefore can no longer fully prevent heat from entering the cold storage compartment.

[0022] The object of the invention is to provide a heat exchanger arrangement with a defrost function that enables efficient defrosting of the evaporator fin surface and prevents increased heat input into the cooling compartment during the defrosting process. Furthermore, it aims to reduce or at least significantly decrease any additional air-side pressure loss.

[0023] The problem of the invention is solved by an object according to claim 1. Further developments of the invention are specified in the dependent claims.

[0024] The object of the invention is achieved in particular by a heat exchanger arrangement with a defrost function, which has a heatable fan chamber with an evaporator and a vertical air inlet and outlet surface that is open during evaporator operation. During defrost operation of the heat exchanger arrangement, the air inlet and / or outlet surface is separated or sealed off from the air exchange with the surroundings of the heat exchanger arrangement by an air curtain device. The air curtain device is arranged in the fan chamber and consists of an air curtain fan, an air duct, and an inlet element arranged between them. The air duct has an air outlet that extends at least partially over the air inlet and / or air outlet surface of the fan chamber.

[0025] Evaporator operation of the heat exchanger arrangement refers to the cooling operation of the refrigeration system, in which the evaporator cools the air flowing past it.

[0026] A defrost cycle is defined as the heating of the evaporator to melt ice or frost. According to the invention, warm air from the fan chamber is prevented from entering the cooling compartment via the air inlet and / or outlet by the air curtain generated by the air curtain device.

[0027] Preferably, in the direction of airflow during evaporator operation, at least one fan is arranged downstream of the air outlet surface, and the air curtain device is arranged upstream of the air outlet surface in the fan chamber. The fan of the heat exchanger assembly draws the airflow to be cooled through the evaporator.

[0028] Alternatively, the airflow to be cooled can be forced through the evaporator.

[0029] The air curtain device is advantageously arranged at the top of the air inlet and / or outlet surface, with the air outlet directed downwards, thus generating an air curtain in the form of a flowing air film. The air curtain flows downwards as a two-dimensional film, preferably parallel to the air inlet and / or outlet surface of the fan chamber, and largely prevents convection currents of the warm air through the air curtain into the cooling chamber. The warm air is entrained by the air curtain and circulated within the fan chamber.

[0030] The air curtain fan of the air curtain device is advantageously designed as an axial fan and is arranged to draw in heated air from the fan chamber. An alternative embodiment of the invention provides that the air curtain fan is arranged to draw in warm air from the environment or warm exhaust air from other processes.

[0031] An air inlet or outlet surface that is not equipped with the air curtain device is advantageously closed with a closing device, thereby reducing or preventing heat input from warm air from the defrosting process into the cold room.

[0032] The additional or alternative closure device is designed as a louvered flap or as a dust cover.

[0033] Preferably, an air straightener is arranged in the air duct upstream of the air outlet. The air straightener is a flow-guiding element and generates a uniform airflow, which forms the air curtain.

[0034] The air straightener is typically designed as a perforated or honeycomb sheet. The flow-guiding elements result in a uniform airflow, which is directed downwards in the subsequently forming air curtain.

[0035] Preferably, a trace heating element is arranged in the air duct. This prevents the flow guide elements from freezing during evaporator operation and / or introduces additional heat energy into the heat exchanger assembly for defrosting operation.

[0036] The fan is arranged on the heat exchanger assembly so that it can be folded out from the plane of the air inlet or outlet surface for ease of maintenance and repair.

[0037] The invention's concept thus consists of supplementing a defrosting system of a heat exchanger assembly with an air curtain device incorporating an additional axial fan as the air curtain fan. The air curtain fan is located within the fan chamber and draws in heated air during the defrosting process. Via an air duct and guide vanes, the air is distributed as an air curtain over the entire length of the air inlet or outlet surface, or at least the length of the nozzle plate. The resulting downward-directed air curtain in front of the main fan thus achieves thermal separation during defrosting and ensures continuous circulation of the heated air.

[0038] An additional system mounted on the intake side, which implements a partitioning of the intake side via a louvered flap or baffle hood or similar, also prevents heat losses via the intake side of the heat exchanger block into the cooling room.

[0039] To ensure even air distribution throughout the air duct, air equalizers in the form of perforated or honeycomb-patterned sheets are installed within the duct. This ensures that the air curtain is homogeneous across the entire duct surface.

[0040] During the defrosting process, the air inside the heat exchanger heats up significantly faster in the upper part of the fin stack than in the lower part. The air circulation and the resulting forced convection allow the entire heat exchanger block to heat up more quickly, resulting in more efficient defrosting and a comparatively shorter defrosting time. A trace heating element prevents the air duct from icing up.

[0041] The advantages of the invention lie in the fact that no shift in the fan's operating point occurs due to the avoidance of additional pressure losses. This leads to increased operational reliability of the system and ensures complete defrosting. The reduction in defrosting times through air circulation and consistently low heat losses result in increased efficiency of the system's refrigeration process. The accessibility and ease of maintenance provided by hinged fans further enhance the advantages of the inventive design of the heat exchanger arrangement. The air curtain also prevents icing of the fan and the main fan of the heat exchanger arrangement.

[0042] Further details, features, and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1: Perspective view of a heat exchanger assembly, air outlet side; Fig. 2: Perspective view of a heat exchanger assembly, air inlet side; Fig. 3: Fan chamber of the heat exchanger assembly without housing and evaporator; Fig. 4: Air outlet surface in oblique top view with air curtain device; Fig. 5: Air curtain device on the top of the air outlet surface; Fig. 6: Air curtain device in perspective view; Fig. 7: Air curtain device in side view; Fig. 8: Air curtain device in perspective view from below at an oblique angle with air outlet; Fig. 9: Air duct cross-section in perspective view; and Fig. 10: Air duct in cross-section.

[0043] In Figure 1Figure 1 shows a perspective view of a heat exchanger assembly 1 looking towards the air outlet side. The air outlet side has an air outlet surface in at least one section. The heat exchanger assembly 1 is formed by a housing 5, which encloses the fan chamber 6. The evaporator 3 is arranged in the fan chamber 6. The side housing elements have been omitted for clarity. The fan chamber 6 is bounded at the bottom by a drain 7 for the condensate. The illustrated embodiment shows a closing device 4 on the air inlet surface opposite the air outlet surface, which can be closed by means of the closing device during defrosting operation of the heat exchanger assembly. The air outlet surface of the heat exchanger assembly 1 is essentially covered by two fans 2, which draw the air to be cooled through the heat exchanger assembly 1.During evaporator operation, air enters the heat exchanger assembly 1 via the air inlet surface, flows through the evaporator 3 in the fan chamber 6, and is cooled in the process. The cooled air is drawn in by the fan 2 and exits the heat exchanger assembly 1 via the air outlet surface.

[0044] In Figure 2 is the in Figure 1 The described heat exchanger arrangement 1 is shown from the other side, the air inlet side, wherein the air inlet side is shown in the illustration according to Figure 2 The air inlet side has an air inlet surface in at least one section. Therefore, the heat exchanger assembly 1 is in defrost mode.

[0045] Figure 3Figure 1 shows a heat exchanger arrangement 1 in which some components have been omitted for clarity. The air curtain devices 8 are arranged above the fans 2 and thus outside the air outlet area, which is limited to the intake area of ​​the fans. Therefore, no components of the heat exchanger arrangement 1 are located directly in the flow path of the cooling air, and the air curtain device 8 does not create increased flow resistance for the air during evaporator operation. This is a particular advantage of the illustrated embodiment.

[0046] The air inlet area with the closing device 4 and the lower boundary of the heat exchanger arrangement 1 with the drain device 7 for the condensate during defrosting operation of the heat exchanger arrangement 1 complete the illustration in Figure 3 .

[0047] Figure 4Figure 1 shows a top-down view of the air outlet surface, which is limited or closed by the air curtain of the air curtain device 8 during defrosting operation. The fan 2 is located on the outside of the air outlet surface; during evaporator operation, this axial fan draws in the cooled air from the fan chamber 6 (not shown) and conveys it into the cooling compartment.

[0048] In Figure 5The air curtain device 8, with its components air curtain fan 9, inlet element 11, and air duct 10, is shown in its arrangement within the heat exchanger assembly 1 at the top of the air outlet surface. The closing device 4, which delimits the fan chamber 6, and the fan 2 are partially shown. The air curtain device 8 is arranged within the fan chamber 6 and is covered by the housing 5 (not shown). The air curtain fan 9 is angled slightly downwards over the inlet element 11 and thus draws in warm air from the direction of the air inlet surface during defrosting operation. This allows a warm air vortex to form when the closing device 4 is closed during defrosting operation.

[0049] To better illustrate the construction of the air curtain device 8, it is shown in the Figures 6 to 10 Shown in isolation and in enlarged detail.

[0050] Figure 6Figure 8 shows the air curtain device with the air curtain fan 9, which draws in warm air and conveys it via an inlet element 11 into an air duct 10. The air duct 10 is arranged horizontally, whereas the air curtain fan 9 is directed downwards at an angle of approximately 15°.

[0051] Figure 7 Figure 1 shows a side view of the air curtain device 8. The inlet element 11 is connected on one side to the air curtain fan 9, an axial fan, and on the other side to the air duct 10. The air curtain fan 9 is angled downwards from the horizontal and directed into the interior of the fan chamber. The warm air from the defrosting process is drawn in by the air curtain fan 9 and conveyed through the inlet element 11 into the air duct 10. The inlet element 11 tapers its cross-section from the connection of the air curtain fan 9 towards the inlet into the air duct 10.

[0052] Figure 8Figure 1 shows the air curtain device 8 in a perspective view from below, obliquely, in which the air outlet 12 is depicted in the air duct 10. The air outlet 12 extends downwards along the length of the air duct 10 along the air outlet surface. The air of the forming air curtain flows downwards through the air outlet 12 along the air outlet surface of the heat exchanger arrangement 1.

[0053] Figure 9Figure 1 shows the structure of the air duct 10 of the air curtain device 8. The air duct 10 consists of a cover plate 14, which is angled downwards on both sides and encloses the side plates 15 on both sides at their upper edges. The side plates 15 are angled inwards in their lower region and thus also form the underside of the air duct 10. The air outlet 12, designed as a slit, is located in the underside of the air duct 10, through which the warm air flows downwards as an air curtain during defrosting operation. Above the air outlet 12, the air straightener 13, in the form of a honeycomb plate, is arranged within the air duct 10. Both side plates 15 are held together by a spacer 16, which locks the air straightener 13 at the top, limiting its movement. Due to the angled side plates 15 in their lower region, the cross-section of the air duct 10 has a trapezoidal shape.In the upper section of the air duct 10, warm air flows, which is drawn from the fan chamber 6 by the air curtain fan 9 and conveyed into the air duct 10 via the inlet element 11. Before the air can exit the air duct 10 downwards to the air outlet 12, it flows through the air straightener 13. The flow through the downward-facing flow paths of the air straightener 13 straightens the airflow. In the configuration of the air straightener 13 as a honeycomb sheet, the air flows through cylindrical structures arranged in a honeycomb pattern, which impose a flow direction on the air that is maintained even after the air exits via the air outlet 12, thus forming the air curtain.

[0054] In Figure 10The air duct 10 is shown in cross-section with the components cover plate 14, side plates 15 and spacer 16. The air outlet 12 is guided by the air conveyed into the air duct 10 from its top to its bottom over the air straightener 13, and a corresponding straight downward flow is imposed on this air. Reference symbol list

[0055] 1 Heat exchanger assembly 2 Fan 3 Evaporator 4 Shut-off device 5 Housing 6 Fan chamber 7 Drainage device 8 Air curtain device 9 Air curtain fan 10 Air duct 11 Inlet element 12 Air outlet 13 Air straightener 14 Cover plate 15 Side plate 16 Spacer

Claims

1. Heat exchanger arrangement (1) with defrosting function, comprising a heatable fan chamber (6) with an evaporator (3) and a vertical air inlet and air outlet surface which is open in evaporator operation, characterized in that the air inlet and / or air outlet surface can be separated from the air exchange with the surroundings of the heat exchanger arrangement (1) by an air curtain device (8) during defrosting operation, wherein the air curtain device (8) is arranged in the fan chamber (6) and is formed from an air curtain fan (9), an air duct (10) and an inlet element (11) arranged therebetween, wherein the air duct (10) has an air outlet (12) which extends at least partially over the air inlet and / or air outlet surface.

2. Heat exchanger arrangement (1) according to claim 1, characterized in thatin the direction of air flow in evaporator operation, at least one fan (2) is arranged after the air outlet surface and the air curtain device (8) is arranged in front of the air outlet surface.

3. Heat exchanger arrangement (1) according to claim 1 or 2, characterized in that the air curtain device (8) is arranged at the top of the air inlet and / or air outlet surface and the air outlet (12) is directed downwards.

4. Heat exchanger arrangement (1) according to one of claims 1 to 3, characterized in that the air curtain fan (9) of the air curtain device (8) is designed as an axial fan and is arranged to suck in heated air from the fan chamber (6).

5. Heat exchanger arrangement (1) according to one of claims 1 to 4, characterized in that the air inlet or air outlet surface is designed to be closable with a closure device (4).

6. Heat exchanger arrangement (1) according to claim 5, characterized in thatthe closure device (4) is designed as a louvre flap or as a storage hood.

7. Heat exchanger arrangement (1) according to one of claims 1 to 6, characterized in that an air rectifier (13) is arranged in the air duct (10) in front of the air outlet (12).

8. Heat exchanger arrangement (1) according to claim 7, characterized in that the air rectifier (13) is designed as a perforated or honeycomb sheet.

9. Heat exchanger arrangement (1) according to one of claims 1 to 8, characterized in that a trace heater is arranged in the air duct (10).

10. Heat exchanger arrangement (1) according to one of claims 2 to 9, characterized in that the fan (2) is arranged so as to be foldable out of the plane of the air inlet or air outlet surface.

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