EP0537650B1 - Heat-exchanger with a higher performance and hygiene level - Google Patents

Abstract

Heat exchangers of high performance and high hygiene levels are produced from steel and galvanised. It has been found that a more stable and resistant structure is achieved by constructing the heat-transferring ribs by means not of plates, but of sheets 19 to 21, 23 to 25 arranged in a multiplicity of rows. The alternating use of sheets of different width permits different dividing spacings of the sheets to be achieved in the direction of passage of the air to be cooled, without the need arising for a corresponding number of gaps acting as balancing zones. Due to the elimination or substantial reduction of the number of gaps, the latter can be held so wide without essential impairment of the thermal performance that metal bridges are avoided in the case of galvanisation and the settling of foreign bodies which impair hygiene is suppressed during operation. <IMAGE>

Description

The invention relates to a heat exchanger made of steel of high performance and hygiene for spontaneous freezing, in particular of foodstuffs, with a number of tube coils, which are formed in an S-shaped manner within a common plane and are formed by tubes connected by means of tube bends and connected to collectors at both ends, the core tubes of which are specified Grip through arranged slats, which are provided with recesses provided in rows, the edge regions of which project laterally like a collar.

For the spontaneous freezing of food, for example, during ongoing production, hygienically perfect heat exchangers of high performance are required, which require correspondingly large heat-exchanging surfaces. It is customary to provide groups of meandering coils parallel to a block and to provide them with lamellae which improve the heat transfer through large areas provided. In order to achieve a structure that is also mechanically resistant to vigorous cleaning measures and chemically resistant to effective cleaning agents and thus meets the highest hygiene requirements, the pipe coils and the steel fins penetrated by them must be manufactured and stabilized with hot-dip galvanizing that connects and protects the pipes and fins.

Since the air passing through is guided cyclically and absorbs not inconsiderable amounts of moisture from the frozen goods, the fins assigned to the cooling coils are arranged on the inlet side in a relatively wide division and are only provided in narrower division in the sections following in the direction of air passage. This ensures that in the last section, by means of narrow division, considerable areas which promote heat transfer are to be accommodated, while on the inlet side, moisture is extracted from the incoming air without the frost crystals which settle on the fins due to the water which has separated out prematurely reducing the distance remaining between the fins are able to add and thus require an early defrost cycle.

In general, in the case of heat exchangers constructed from steel, a strip-shaped lamella extending over this is provided per tube coil, but strip-like lamellae have also been used which contain two or, in some cases also three, rows of holes and thus for two or at most three Pipe coils are applicable. Unpleasant is noticeable that lamella strips arranged one behind the other in the direction of passage of the air do not stand within common planes, even with a given equal division, but are statistically offset from one another by tolerances which are unavoidable during production. In order to avoid a constriction of a passage formed between two lamella strips by a subsequent lamella strip, it is therefore necessary to design the lamella strips with a reduced width in such a way that exchange zones remain between them, which, however, even with a small width, the sum of those for heat exchange due to their large number restrict available slat surfaces disadvantageously. Difficulties are also encountered with conventional heat exchangers, however, in the entry zone, where the separation distances are so large to take account of the start of frost to be chosen that these can no longer be adjusted by the collar-shaped approaches of the recesses; in general, lamellas, the spacing of which exceeds the maximum possible height of the collar-shaped lugs, are secured by inserting the lamellas by inserting wooden laths. After removal, however, undesirable and disadvantageously displacements can occur in the course of transport and further processing, for example hot-dip galvanizing.

From DE-A-21 54 487 a heat exchanger is known which consists of a plurality of coils which are connected by transverse ribs of the same size, arranged closely next to one another. The transverse ribs have slits in the edge regions and elongated openings in the central region with end regions for receiving the coils. These end regions are arranged in such a way that the coils of rows arranged one behind the other are arranged alternately offset from one another.

FR-A-962 473 describes a car cooler which has tubes arranged one above the other in three rows and having different distances within the row. The tubes are connected to each other by fins, the tubes with the larger distances being in contact with only a part of the fins, while the tubes are enclosed with a small distance from all the fins and are also offset from the rear tubes so that they have disadvantages mentioned above.

The invention is based on the object of further developing the type of fins of heat exchangers made of steel in such a way that the number of required exchange zones which reduce the heat transfer surfaces is reduced to a minimum and at the same time the distances of fins exceeding the possible collar height are reliably maintained will.

This object is achieved in that the lamellae are designed as wide boards with more than six rows of recesses and each of the rows has at least 15 recesses, each of which is penetrated by a single or multi-pipe coil and that the spacing of the boards in the direction transverse to Level of coils are gradually reduced. Here, it was recognized as expedient to have slats provided in a narrow division extend at least over the entire width range provided for this division. On the other hand, however, it is also possible to provide lamellae of different widths which are periodically arranged alternately to form a plurality of width regions of different division.

Figur 1

anhand einer ausschnittsweisen Darstellung eine mit Lamellen auszustattende Rohrschlange,

Figur 2

im abgebrochenen Querschnitt eine Durchbrechung einer Lamelle,

Figur 3

eine platinenartig ausgebildete Lamelle,

Figur 4

perspektivisch-schematisch einen Wärmetauscher,

Figur 5

perspektivisch-schematisch einen weiteren Wärmetauscher,

Figur 6

in gleicher Darstellung zum Vergleiche einen Wärmetauscher herkömmlicher Lamellenanordnung, und

Figur 7

einen die Anordnung der Lamellen deutlicher darstellenden vergrößerten Ausschnitt der Fig. 6.

The features of the innovation are explained in detail on the basis of the following description of an exemplary embodiment in conjunction with the drawings which illustrate the same. They show:

Figure 1

on the basis of a partial representation, a pipe coil to be equipped with fins,

Figure 2

in the broken cross-section an opening in a lamella,

Figure 3

a plate-like slat,

Figure 4

perspective-schematic of a heat exchanger,

Figure 5

another heat exchanger in perspective and schematic,

Figure 6

in the same representation for comparison, a heat exchanger conventional lamella arrangement, and

Figure 7

6 shows an enlarged section of FIG. 6 which shows the arrangement of the slats more clearly.

In Fig. 1, a single-pipe coil 1 is shown schematically, broken off and interrupted in the central area. It is made of hairpin-shaped tubes, the straight legs of which are referred to as core tubes 2, the free ends of two core tubes being connected by welded-on tube bends 3, so that a continuous, meandering tube is formed, the core tubes of which take up the heat transfer fins 4 capital. A section of a lamella 4 is enlarged, cut and shown broken off on both sides in Fig. 2. To reach through the core tubes, recesses 5 are provided, the edge areas of which are folded into a collar-like shape by punching, pressing and the like to form lugs 6, which are able to determine their mutual distance and thus their division when lamellae are strung together. The slightly conical taper of the extension 6 towards its free end makes it easier, on the one hand, to push the lamella 5 onto the core tubes 2 with the slightly funnel-shaped opening 5 ahead. At the same time, however, this taper of the extension 6, with a corresponding press fit of its free end, may also allow assembly at intervals which exceed the possible maximum length of the heel 6, once the positions of the slats have been reliably maintained without securing wooden strips or the like to secure the distance would be needed. The slight additional annular enlargement in the area of the recess 5 results in a secure hold when applied to the free end of the extension 6 of the preceding lamella 4 without the risk of this free end being split up by cracks formed in it during the shaping, and in any case will be The hot-dip galvanizing offers the coating metal solid, extensive attachment areas.

In the case of large heat exchangers, strip-shaped fins are usually used which each have only one row of recesses 5 and which, for example, extend over a coil of pipes. Since, when lining up fins 4 on core tubes 2, their lugs 6 determine the spacing of the fins and thus their division, these distances can only be maintained within wide tolerances, fins arranged one behind the other in the direction of passage of the air are usually not within a common plane , but they are more or less staggered behind each other. In this way, however, the free passage space for the air is divided and split, and narrow gaps are formed between the mutually facing ends in the air flow of successive lamellae, which on the one hand hold entrained dirt, e.g. also blown away particles of the frozen food, and on the other hand during galvanizing Unwanted zinc bridges give starting points and thus additionally narrow the gaps locally in such a way that water which has set out can ripen the passage channels prematurely. One has therefore designed the strips of the coils, which are designed as strips, so narrow that a space serving as an exchange zone remains between them, which expediently amounts to a multiple of the division distance, and which ensures a flow around and a redistribution of the air passing through the fins. This means that the areas that determine the heat transfer are unpleasantly restricted.

In heat exchangers made of steel, strip-shaped fins have also been used, which have two rows of recesses and, in exceptional cases, also three rows of recesses, so that accordingly two or three coils are encompassed. However, this only results in a gradual enlargement of the areas causing the heat transfer due to the elimination of some of the exchange zones to be kept clear between groups of strip lamellae.

According to the invention, however, plate-like fins made of sheet steel are used, which have at least as many rows 8 of recesses 5 as a section of the heat exchanger with the same fin division has coils, while within the rows 8 there are as many recesses 5, like the pipe coil in question has extensive core tubes. The circuit board 7 of FIG. 3 is shown broken off and shows only six of the rows 8, while only seven recesses 5 are shown within a row.

A heat exchanger designed according to the invention is shown schematically in perspective in FIG. 4, but in order to facilitate the overview, circuit boards are only shown in regions. The heat exchanger of the figure is made up of a number of successively arranged, three-pass coils 1, so that three connections 11 are connected to each of the collectors 9 and 10 effecting the supply and discharge of the refrigerant, and the core pipes 2, which are only partially and symbolically represented, are connected Elbows 3, 12 and 13 are connected to each other, which bridge different widths. The coils are held together by end plates 14 braced against them on both sides.

The fins of the heat exchanger are arranged along the entire length of the core tubes in a constant division, but, as already mentioned, only two groups of these fins are shown for reasons of simplification. In the direction of flow of the air, indicated by the arrow 15, three sections 16, 17 and 18 follow one another, within which different divisions of the arrangement of the boards are used. In section 16, which is at the front in the direction of arrow 15, a division of 18 mm is provided in the exemplary embodiment over four pipe coils, in the following section 17, a division of 9 mm is provided over seven pipe coils, while in the last section 18, a division of 18 mm is provided 7 mm is applied. The gradual narrowing of the passage of air in the direction of the arrow takes into account a relatively strong water excretion when cooling for the first time, and that which has passed through when cooling further Air then falls off.

In section 17 there are alternating plates 19 and 20 which only extend over the entire section 17 and both over the section 16 and over the section 17. It is thereby achieved that within the section 17 the division of 9 mm is determined by the collar-like projections 6 of the recesses 5 of the plates 19 and 20 receiving the core tubes 2, and since every second plate 20 additionally extends over the section 16, here twice the pitch. This separation distance of 18 mm could no longer be achieved by the collar-like projections 6, since these cannot be formed so cantilevered. If you wanted to provide separate boards, you would also have to use distance-keeping aids. According to the innovation, this is circumvented by the lamella division of 9 mm being secured by the collar-like projections 6 of the alternately provided boards 19 and 20, the boards 20 additionally extending over the section 16 and therefore maintaining the double division here. An additional stabilization is achieved by the slight press fit of the end regions of the conical projections 6.

The narrowest division and thus the essential heat transfer surfaces are provided in section 18. The boards 21 arranged here have twelve rows 8 of recesses 5 for core tubes 2 in the exemplary embodiment, and the collar-like projections 6 surrounding the recesses 5 extend over 7 mm and thus ensure the division of the slats which have been pushed on.

At the transition from section 16 to section 17, no special measures need to be taken, since the boards 20 are indeed extend in one piece and thus in alignment over both sections. Between sections 17 and 18, however, a gap 22 has been kept as an exchange zone between the facing ends of the plates 19 and 20 on the one hand and 21 on the other hand, in order to allow the air to flow from section 16 to section 17 without bottlenecks which impair the flow. Since the heat exchanger has only one such gap 22 between boards, it can be designed with a width which reliably prevents bridging during galvanizing or in use due to blown-in food residues or by freezing water which forms. By eliminating further exchange zones between sections, this not only makes it easier to slide the boards on during manufacture, but also makes optimal use of the space available for heat-transferring surfaces.

After the fins have been slid on, the heat exchanger is finished in a manner known per se: the second of the end plates 14 is pushed on and fastened, and the pipe bends 3, 12 and 13 are welded on to complete the three-pipe coils, that is to say they have three separate conduit paths. The pipe coils, collectors and fins or blanks generally made of steel in heat exchangers of this size, but especially these hygienic requirements, are then protected against corrosion, for example by galvanizing, with a suitable galvanizing, for example hot-dip galvanizing, also simultaneously further connection and definition of the individual components is achieved. An unwanted zinc bridge formation is practically excluded or reduced to a minimum by the width of the only one gap 22.

FIG. 5 shows a heat exchanger in the representation corresponding to FIG. 4, in which gaps 22 in FIG. 4 could be completely dispensed with. The boards 23 extend over the full depth of the heat exchanger, the boards 24 are made shorter, and the boards 25 have an even smaller depth. Thus, on the input side, designated by the arrow 15 symbolizing the air flow, the widest division of the boards 23 is achieved, while in the following areas boards 23 and 24 alternately result in half the division, and in the outlet-side section the boards 23, 24 and 25 have the narrowest division and offer the largest share of heat transfer surfaces.

In Fig. 6, a similar heat exchanger is shown for comparison, which has a vertically extending fin 26 for two levels of coils in a manner known per se. The lamellae are set to different pitches in individual rows or one behind the other and separated by gaps 27 to form a number of compensation zones. Since, in this example of a conventional construction, nine groups of fins are arranged one behind the other, there are eight gaps which are kept narrow in order to reduce the reduction in the size of heat-transfer surfaces. As is shown in the enlarged section of FIG. 7, this gives rise to the risk of the formation of zinc bridges 28 during the galvanizing process, and in operation there is the risk of foreign bodies being carried in the air to be cooled, which is further increased by zinc bridges which have already been formed becomes.

The heat exchangers designed according to the invention are characterized by extensive use of space as well as by favorable distribution of the approach of the water separated out on cooling, so that dead times given by thawing and cleaning the heat exchanger only occur after longer operating phases and thus the percentage useful life of the heat exchanger is increased. The necessary cleaning processes can be carried out more easily and more completely than is the case with known heat exchangers by essentially smooth surfaces and avoidance of excess end faces as well as the mechanically stable and corrosion-resistant structure, so that the hygiene required for freezing or shock freezing of food is also improved . By eliminating the usual cross-sectional constrictions and, connected with them, niche and void-forming zinc bridges, the inventive design prevents the cleaning-resistant settling of organic residues and prevents the bacterial contamination that often occurs in such heat exchangers by removing nutrient media and improving cleaning options.

Claims (7)

1. Heat exchanger, which is made of steel, of high performance and hygiene for spontaneous freezing of foodstuffs, comprising a number of pipe windings (1), which are constructed in S-shape each time within a common plane, are formed by tubes connected together by tube bends (3), are connected at both ends to collectors and the core tubes (2) of which engage through plates (4) arranged in predetermined pitch and equipped with recesses (5), which are provided in rows and the edge regions of which project laterally in the manner of a collar, for the reception of the tube windings, characterised thereby that the plates (4) are constructed as wide platelets (7, 19, to 21, 23 to 25) with more than six rows (8) of recesses (5) and each of the rows (8) has at least 15 recesses (5), which are engaged through each time by a single or multiple tube winding (1) and that the pitch spacings of the platelets are reduced in steps in a direction transverse to the plane of the pipe windings.
2. Heat exchanger according to claim 1, characterised thereby that platelets (19, 20) of different widths are provided in periodic alternation in width regions (16 and 17).
3. Heat exchanger according to claims 1 and 2, characterised thereby that platelets (18) provided in tight pitch extend over the width region (section 18) provided for this pitch and that present between these and platelets (16, 17) of an adjacent width region are gaps (22) of a width which corresponds at least to the pitch width thereof.
4. Heat exchanger according to one of claims 1 to 3, characterised thereby that necks (6) pressed out from the recesses (5) of the platelets (7) slightly conically narrow towards their free ends.
5. Heat exchanger according to one of claims 1 to 4, characterised thereby that necks (6) pressed out from the recesses (5) of the platelet (7) have, at their end going over into the platelet (7), an annular enlargement matched to the outer diameter of the free end of the neck (6).
6. Heat exchanger according to claim 5, characterised thereby that the free ends of the necks (6) engage, in a manner securing spacing, into the recesses (5) or the annular enlargements of the platelets (7) respectively standing in front thereof.
7. Heat exchanger according to claim 1 to 6, characterised by a hot galvanising which coats and connects pipe windings and platelets.

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