EP0131213B1 - Heat exchanger - Google Patents

Abstract

A tube-type heat exchanger has the tube ends substantially flush with the upper tube sheet and liquid is distributed to the tubes through distributor heads which are sealed and therefore provide gas cushions absorbing volume changes in the tubes.

Description

The invention relates to a thin-film heat exchanger which is suitable for the use of liquids contaminated by solids as a heat-emitting medium, such as e.g. for the use of river, groundwater or the like. As a heat source for heat pumps, which is clearly superior to the heat exchangers previously used for such purposes in terms of heat transfer coefficient and space requirements. Preferred embodiments of the heat exchanger according to the invention also permit continuous operation which is not interrupted by cleaning work, even with heat-emitting liquids heavily contaminated by solids.

The most important properties of the currently known and practically used heat exchangers to which liquids contaminated by solids are put are listed below together with the heat transfer coefficients they can achieve, with the same substance, namely boiling C C1 ₂ F, being used as an example of the heat-absorbing medium in each case for comparison purposes _{2 is} selected.

Horizontal tube evaporators with tubes through which the heat-emitting liquid and tubes are covered by the refrigerant achieve a maximum heat transfer coefficient of approx. 400W / m ² K. When using water as the heat-emitting medium, its heat content must not be exploited beyond cooling down to + 4 ° C, to prevent the pipes from bursting due to ice formation. The pipes can only be cleaned after the sealed distribution covers have been removed.

Evaporator tubes or plate evaporators placed in the heat-emitting medium (e.g. water) and flowed through by the refrigerant allow a lower cooling limit of approx. +1 ° C to be maintained, but have a much larger space requirement than tubular boiler evaporators and a somewhat poorer heat transfer coefficient of approx. 300 W / m ² K. Cleaning the outside of the pipes or plates is cumbersome because they are up to 1.5 m deep in the water-carrying channel and their distance is a maximum of 100 mm.

The best heat transfer coefficient of approx. 800 W / mZK and the lowest cooling limit of + 0.2 ° C have plate and tubular trickle coolers, i.e. Horizontal pipes or plates through which the refrigerant flows, on the outer surfaces of which the heat-emitting liquid flows downwards as a thin film.

This must therefore be trickled from rows of holes in the bottom of a distributor trough with narrow bores arranged above the pipes or plates, which naturally tend to clog when solid contaminants are present. The cleaning of the surfaces of the pipes or plates also requires labor and business interruption, since the side covers have to be removed for this.

The use of vertical heat exchange tubes, on the inner surfaces of which a film of a first liquid intended for heat exchange flows downwards, while the outside of the tubes is surrounded by a second medium which participates in the heat exchange, has already been proposed in a different context, but could be found in in practice, especially because a reliable formation and maintenance of a liquid film on the inner surface of the exchange tube with the means proposed there, if at all, only succeeded in accepting at least as much a risk of clogging as with tube and plate trickle coolers.

So z. B. the introduction of the liquid into the downwardly flared replacement tube via a weir as in DE-B-1164990 or by several tangentially arranged inlets as in CH-A-600279 no guarantee that the liquid flow neither at the point of introduction nor at tears off the wall of the conical extension, but forms the desired coherent thin film over the entire length of the inner tube wall.

The measure proposed in DD-A-46722 is to attach to the upper part of the heat exchange tube a hollow, rotationally symmetrical body protruding into it, expanded towards the bottom and open at the top and bottom by at least three mounting ribs, the surface of which is curved and the liquid is directed towards the inner wall of the tube should not guarantee film formation on the inner wall of the pipe in the intended form, because the width of the opening shown between the rotating body and the inner wall of the pipe would be much too large, quite apart from the fact that the shape of the rotating body also does not cause the liquid flow to be torn off smoothly allows its lower edge, so that at least a significant part of the liquid supplied does not reach the inner tube wall, but falls freely downwards. Even a significant narrowing of the annular gap would not result in a reliable and uniform film formation due to the unfavorable shape of the rotary body, but would bring with it the same risk of clogging as in known tube and plate trickle coolers.

The object of the present invention is therefore to provide a thin-film heat exchanger with upright pipes, which is free from the disadvantages of the known coolers, in particular results in extraordinarily high heat transfer coefficients, and furthermore permissible cooling limits which are still superior to the lowest known to date and which permit special embodiments which even when using heavily with solids such as sand, mud u. Like contaminated liquids as heat-emitting medium enables continuous operation not interrupted by cleaning and / or repair work. One of the advantages of the cooler according to the invention is, inter alia, the possibility of water to temperatures below 0 ° C, for example on - to run _^1/2 'C in the supercooled state, and thus better utilize its heat content than with known heat exchangers is possible.

This is essentially achieved in that in the upper part of the heat exchange tube or a plurality of heat exchange tubes a full or at least bottom full or at least bottom closed distributor head is attached, which widens downwards in such a way that between its sharp-edged lower edge and the inner wall of the tube narrow annular gap of maximum 1 mm, preferably 0.3-0.7 mm, remains free and that the supply of the heat-emitting liquid into the heat exchange tube takes place by means of preferably adjustable hydrostatic pressure from a flow container arranged above the heat exchange tube, in which the upper opening of the heat exchange tube is located. For this purpose, the upper end of the heat exchange tube, which is completely open above the distributor head, is accommodated in a flow tank, the height of which is large enough to be able to vary the level of the heat-giving liquid and thus the hydrostatic pressure on the annular gap and the flow rate within sufficiently wide limits.

The device according to the invention therefore differs from the device described in GB-A-1458592 not only in that the heat exchange tube is smooth and not fluted and in that the film flowing down on its inner wall gives off heat and does not heat up to the point of evaporation through the heat-emitting medium surrounding the tube and that the steam thus developed is therefore not sucked downwards out of the pipe, but above all by the fact that the upper end of the heat exchange pipe projects openly into the flow vessel below the level of the heat-emitting liquid. This would not be possible with the prior art given by GB-A-1458592, because then the liquid would be sucked out of the flow vessel up to the level of the upper edge of the heat exchange tube together with the steam developed inside it.

According to US-A-2753932, which, like GB-A-1458592, does not describe a cooler but an evaporator, the upper end of the heat exchange pipe is open, but it does not protrude into a flow vessel with variable height, but ends just above a distributor plate.

It can be seen that the ventilation of the heat exchange tube, which was previously considered indispensable, is not necessary. It is therefore possible to avoid the risk of contamination of the naturally large liquid surface by germs from the air, which previously used thin-film coolers for cooling milk and the like. The like is practically prevented.

Another significant difference compared to the two previous publications mentioned is that the distributor head according to the invention is axially displaceable in the heat exchange tube and is preferably provided with a pin protruding from the tube, by means of which it can be set in an upward and downward movement. Preferred embodiments of the invention relate to advantageous embodiments of the distributor head and devices which automatically start the movement of the distributor head when the annular gap becomes blocked and, if this measure does not remove the blockage in the case of particularly heavy soiling, temporarily remove the distributor head completely from the pipe. Further embodiments relate to a special management of the refrigerant circuit, which improves the heat transfer on the refrigerant side and the efficiency of the phase separation of the refrigerant, and measures to further improve the heat transfer on the refrigerant side by reducing the space available to the refrigerant in the evaporator.

The invention is explained schematically below with reference to the figures and, for example, in more detail.

A large number of heat exchange tubes are usually used for the practical application of the invention; However, since the invention can basically also be carried out with a single heat exchange tube and the structure and function of all tubes is the same even when using one or more tube bundles, for the sake of simplicity, reference is usually only made to one heat exchange tube below and the tube bundle is only mentioned where this is due to the interaction of others Apparatus parts with it or the tube sheets holding it together appear necessary.

• Figur 1 eine zum Teil geschnittene Ansicht eines erfindungsgemässen Wärmeaustauschers mit dem zugehörigen Abscheider;
• Figur 2 eine Seitenansicht der Figur 1 von links;
• Figur 3 eine vergrösserte Aufsicht auf Figur 1;
• Figur 4 ein vergrösserter Ausschnitt des in Figur 1 mit dem Kreis IV umrandeten Teiles;
• Figur 5 eine Aufsicht auf Figur 4;
• Figur 6 eine Alternative der Figur 4, ein Schnitt längs der Linie IV-IV der Figur 5;
• Figur 7 eine Aufsicht auf Figur 6;
• Figur 8 eine Aufsicht auf den Kessel ohne Abscheider und Zubehör;
• Figur 9 ein Schnitt längs der Linie IX-IX in Figur 8;
• Figur 10 ein Prinzip einer Schaltung zur automatischen Betätigung der Verteilerköpfe.

In the pictures is:

• Figure 1 is a partially sectioned view of a heat exchanger according to the invention with the associated separator;
• Figure 2 is a side view of Figure 1 from the left;
• Figure 3 is an enlarged plan view of Figure 1;
• FIG. 4 shows an enlarged section of the part surrounded by the circle IV in FIG. 1;
• Figure 5 is a plan view of Figure 4;
• Figure 6 shows an alternative to Figure 4, a section along the line IV-IV of Figure 5;
• Figure 7 is a plan view of Figure 6;
• Figure 8 is a top view of the boiler without a separator and accessories;
• Figure 9 is a section along the line IX-IX in Figure 8;
• Figure 10 shows a principle of a circuit for automatic actuation of the distributor heads.

Referring first to FIGS. 1 and 2, the application of the invention for operating a heat pump is described below, for example.

The heat releasing medium, e.g. B. river, ground or resulting cooling water 15 passes through a - not shown - supply line in a flow vessel 37, which sits tightly on the upper tube plate 6, in which the heat exchange tubes 1st of the tube bundle tightly fitted, e.g. B. are rolled, in such a way that their appropriately somewhat expanded upper ends 4 protrude beyond the tube plate 6. In the same way, the lower tube ends 5 are rolled into the lower tube plate 7 in such a way that they protrude somewhat downwards. The two tube plates 6 and 7 close the boiler 2, in which the heat-absorbing medium 35 surrounding the tubes 1 is located, at the top and bottom. The heat-emitting liquid reaches the heat exchange tubes 1 from the supply vessel 37, which is at least partially open at the top, and is distributed through the distributor heads 3 with a cylindrical part 18 (see FIGS. 4, 5 and 6, FIG. 7) guided to the inner wall 13 of the tubes 1 via a narrow annular gap 14. The lowermost circumference 12 of each distributor head is designed in such a way that the liquid flowing down rips off smoothly at this point, flows out through the annular gap 14, is applied as a thin film to the inner tube wall 13 and as such flows down the inner tube wall. In order to ensure a smooth tearing off of the liquid at the lowest circumference 12, this is of sharp-edged design, as shown in the figures. Preferably, the underside of the distributor head 3 is also z. B. conically hollowed out so that there is already a sharply rising recess 124 from the lowest circumference 12. The radius of the lowest circumference 12 is preferably matched to the inner radius of the tube 1 such that the width of the annular gap 14 is approximately in the range from 0.1 to 1 mm, preferably 0.3 to 0.7 mm.

Precise compliance with these dimensional tolerances can be made easier in terms of production technology in accordance with a particular embodiment shown in FIGS. 6 and 7 in that the distributor head 3 is fitted in an extension tube 8 placed on the upper part of the heat exchange tube 1, the inside diameter 10 of which is the same at the location of the distributor head 3 that of the heat exchange tube 1. According to a preferred embodiment of the invention, the inside of the extension tube 8 is slightly conical, so that the width of the annular gap 14 can be adjusted within the limits in question by adjustable change in the height at which the distributor head 3 is located. An attachment possibility of the top tube 8 on the heat exchange tube 1 is shown in FIG. 6, for example.

The heat-emitting liquid flowing down the inside 13 of the tubes 1 as a film, after its heat has been released, passes to the tube 1 and via this to the heat-absorbing medium 35, in the example shown a boiling refrigerant 34 such as NH3 or Freon, and occurs at the lower end 5 of the tube Tube cooled, e.g. B. with a temperature of - '/ Z ° C from.

As a result of the reduction in cross-section through the annular gap 14, the heat-emitting liquid accumulates in the flow vessel 37 until a dynamic steady state is reached when the liquid level 45 is reached.

The tube bundle, which, as mentioned, can also consist of a single tube in the limit, is located in the outer boiler 2, which contains the boiling refrigerant 35. This is kept at the boil by the heat absorption from the tubes 1 and by the suction effect of the compressor (not shown) connected to the boiler 2 via the suction line 169 and the separator 160. As a result of the reduction in the average specific density of the refrigerant in the boiler 2 caused by the formation of vapor bubbles, its level rises above that of the vapor-free refrigerant in the sump 36 of the separator 160 and passes through the overflows 161, 162 into the separator 160, from which the vaporous refrigerant passes through the Connection 169 is sucked in by the compressor. After the refrigerant has been compressed and in the - not shown - the condenser has given off the heat absorbed in the boiler 2 at a higher temperature level and, if appropriate, has been partially relaxed, it is injected through the pipe 109 into the center pipe 159 of the separator 160 via a nozzle 184. The increase in speed caused by the nozzle 184 causes the refrigerant to be sucked in from the overflows 161, 162, as a result of which the circulation in the boiler 2 is increased and thus the heat transfer is improved, and the liquid-steam mixture is applied to the inlet side 99 of the tube with considerable energy 109 impact opposite wall 168 of the separator 160, whereby a substantial separation of liquid and vapor is already effected. The majority of the separated liquid flows into the sump 36 of the separator 160, from which it returns via line 171 to the lower part of the boiler 2. The vapor, which still contains residual liquid droplets, must travel the entire length of the separator 160 until it emerges from it through the suction connection 169 of the suction line of the compressor. The entrained liquid droplets have enough time to settle so that practically liquid-free steam is sucked in from the suction connection 169.

According to a further embodiment of the invention (cf. FIG. 8), part of the interior of the boiler 2 located between the heat exchange tubes 1 is filled by inert fillers 180 such as glass or metal balls or preferably upright rods or tubes closed at the top and bottom. This not only reduces the required amount of heat-absorbing liquid 35 and thus the investment requirement, especially when using expensive refrigerants, but also further improves the flow rate of the refrigerant and thus the heat transfer coefficient on the refrigerant side when using upright rods or tubes.

If the heat-emitting liquid is contaminated by solid particles, which, for. B. slightly before using groundwater or river water can come, there is a risk that dirt particles settling in the annular gap 14 lead to malfunctions due to constipation.

According to the invention, this danger can be countered by the fact that the distributor head 3 is designed to be axially displaceable in the tube 1 and is preferably provided with guide devices 20, 21, 22. These can e.g. (see Figs. 4, 5 and 6, 7) consist of a cylindrical part 18 which is freely adapted to the inner diameter of the tube 1 and from which some, appropriately evenly distributed over the circumference, e.g. Passages 23, 24, 25 arranged in a uniform triangular arrangement are removed for the passage of the heat-emitting liquid. In addition, the distributor head 3 is connected to the bolt 9, which can move it up and down in the tube 1 as soon as the rise in the liquid level 45 in the supply vessel 37 caused by the blockage exceeds a certain height. In the simplest case, this can be brought about by visual observation of the flow vessel 37 and movement of the bolt 9 connected to the distributor head 3 by hand. Preferably, however, the distributor head 3 is connected to a device, for example explained in more detail in FIG. 10, which automatically sets it in an upward and downward movement when a predetermined level 45 in the supply vessel 37 is exceeded, as determined by at least one level controller 126.

If several repetitions of this measure do not remedy the situation and therefore the liquid level 45 continues to rise to the switching point of the second level controller 76, the movement of the distributor head 3 is changed in such a way that it is lifted completely out of the pipe 1, according to a further embodiment of the invention that even the coarsest mechanical impurities can flow through the pipe, which clears the blockage.

A preferred embodiment of this embodiment of the invention is shown in FIG. 10.

The two level regulators 126 and 76 are arranged in such a way that they do not respond as long as the liquid level 45 does not rise above the level that occurs during operation without clogging. Then all electrical lines of the control system are de-energized and all contacts are in idle status. The contacts of the two microswitches 63 and 128 are closed, the two contacts 136 and 137 of the relay 135 are open and the four-way solenoid valve 70 is in the “off” position. In this position, the upper part of the pneumatic cylinder 46 is connected to the compressed air source 74 via line 142, solenoid valve 70 and line 53 and the part below the piston 47 is connected to the free atmosphere via line 141.

1st stage

However, as soon as the level controller 126 strikes its contact 125, the circuit is closed: power source 140 → contact 125 → microswitch 63 -4128 → relay 135, the latter closing the two contacts 136 and 137. For the time being, the closing of the contact 137 does nothing more than ensure that nothing further happens later. This ensures that the circuit remains closed even when the microswitch 63 is opened. By closing the contact 136, on the other hand, the coil 69 of the four-way solenoid valve 70 is excited and this is brought into the “on” position. In this position, the part of the cylinder 46 located above the piston 47 is connected to the compressed air source 74 via line 141, solenoid valve 70 and line 53. The compressed air flowing into the cylinder 46 below the piston 47 presses it together with the piston rod 50, 51 and thus also the distributor head 3, so that soon after the start of this process the upper control cam 55 contacts the scanning wheel 62 which is expediently attached. As a result, the contact of the microswitch 63 is opened, but then nothing else happens because the current flow to the solenoid valve 70 is maintained by the contact 137, which has already been closed. Only when the movement of the piston rod 50 has progressed so far that the lower control cam 132 actuates the sensing roller 131 does the contact 128 open, which finally interrupts the current supply to the coil 69, as a result of which the solenoid valve 70 returns to the “off” position returns. As a result, the compressed air is again directed from above onto the piston 47, which presses it and thus the distributor head 3 down again.

2nd stage

If the blockage has not been cleared by this point in time so that the liquid level 45 has sunk low enough to switch off the level regulator 126, this game is repeated either until the blockage is cleared or until the liquid level 45 has risen so far, that the upper level controller 76 also responds. Its contact 79 is connected directly to the junction of the power source 140 and the coil 69 and is therefore not limited to the above-described up-down mechanism, but switches the solenoid valve 70 to the "on" position, so that the compressed air is the way 74 → 53 → 141 is released. Since the automatic of the first stage is bridged and therefore ineffective, the upward movement is no longer reversed but continues until the distributor head 3 is lifted completely out of the pipe and thus the entire pipe cross section is released, the liquid in large gushes through the The pipe is flowing, all dirt particles are entrained and the liquid level 45 drops rapidly and both level controls are out of operation again.

For the practically most preferred embodiments of the invention with a plurality of heat exchange tubes 1, it is of course not necessary to use a separate movement device for each distributor head 3, as in the simplified exemplary embodiment described. Rather, a single such system is sufficient for all pipes. In the ge in the embodiment This embodiment means that only one lower level controller 126 and one upper controller 76 and only one pneumatic cylinder 46 with piston 47, piston rod 50 and control cams 55 and 132 need be present, the piston rod 50 with a holder plate 49 of which all the bolts 9 of the various distributor heads 3 are fastened (see FIGS. 1, 6 and 7).

It is also not necessary to operate the device for moving the distributor heads 3 pneumatically. Any other type of drive, e.g. B. by an in principle the same way controlled electric motor is also applicable.

Claims (10)

1. Heat exchanger with at least one heat exchange pipe (1) which is arranged in a tank (2) containing a second heat-exchanging medium and is tightly secured in an upper (6) and a lower pipe plate (7), with a distributor head (3) for a first heat-exchange fluid arranged in its upper region and closed fully or at least at the bottom, the distributor head widening conically downward such that between its lowest sharp-edged circumference (12) and the inner wall (13) of the pipe (1) an annular gap (14) remains free, and the upper parts of the pipes extending into an advance vessel (37), characterized in that the open upper end (4) of the heat exchange pipe (1) or of an extension pipe (8) placed thereon is situated beneath the level (45) of the first heat-exchange fluid (15) in the advance vessel (37), which is high enough to be able to vary the height of the level of the first heat-exchange fluid (15) and consequently the hydrostatic pressure on the annular gap (14), and that the distributor head (3) is arranged in the heat exchange pipe (1), or respectively in the extension pipe (8) placed thereon, so as to be axially displaceable and preferably also removable therefrom.

2. Heat exchanger according to Claim 1, characterized in that the sharp-edged underside of the distributor head (3) has a recess (124) which rises from the lowest circumference (12) at an angle of at least 30°, preferably 45 to 60°.

3. Heat exchanger according to Claims 1 and 2, characterized in that the annular gap (14) has a width of 0,1 to 1,0 mm, preferably from 0,3 to 0,7 mm.

4. Heat exchanger according to Claim 1 to 3, characterized in that the distributor head (3), which is preferably provided with guide arrangements (20, 21, 22) is connected with a pin (9) projecting out of the pipe, through which it can be moved in an upward and downward movement.

5. Heat exchanger according to Claim 4, characterized by a holder plate (49), which is provided with a drive, by which plate the pins (9) projecting out of the pipes (1) are connected and are movable.

6. Heat exchanger according to Claims 4 or 5, characterized in that in the advance vessel (37), which is arranged above the upper pipe plate (6), at least one level regulator (126) is arranged, which closes a stop contact (125) when a predetermined height of the fluid level (45) in the advance vessel (37) is exceeded, through which stop contact a device (46, 47; 141, 142) is engaged, by which the pin (9) is set into upward and downward movement.

7. Heat exchanger according to Claim 6, characterized by a second level regulator (76), responding to a higher fluid level than the first level regulator (126), the stop contact (79) of which disengages the part (142) of the device (46, 47; 141, 142) which causes the downward movement of the pin (9) and thereby brings about the complete withdrawal of the distributor heats (3) out of the pipes (1).

8. Heat exchanger according to Claims 4 to 7, characterized in that the pin (9) is connected via a Cardan joint (51) with the device (46, 47; 141,142) which causes its movement.

9. Heat exchanger according to Claims 1 to 8, characterized by a separator for a refrigeration agent circuit, which is constructed as a horizontal cylinder (160) into which above the level (34) of the fluid sump (36) preferably rising overflow pipes (161, 162) open out from the tank (2) holding the refrigeration agent (35), and on the upper side of which close to a cylinder base (99) a suction connecting piece (169) is mounted, which is connected with the suction side of the compressor, whilst centrally through the cylinder base (99) an injection pipe (109), ending in a nozzle (184) is guided for the refrigeration agent, which is compressed by the compressor and then condensed and if required partially expanded, into the interior of the separator (160) and that the nozzle (184) injects into a pipe (159) which is arranged centrally and concentrically in the cylinder (160) and into which the overflow pipes (161,162) open out.

10. Heat exchanger according to Claims 1 to 9, characterized by inert filling bodies (180) mounted in the interior of the tank (2) between the heat exchange pipes or respectively pipe bundles (1), which bodies are preferably formed from upright bars and/or pipes which are closed on both sides.

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