GB1568696A

GB1568696A - Device for exchanging heat and/or mass between a liquid and a gas or vapour

Info

Publication number: GB1568696A
Application number: GB46328/76A
Authority: GB
Original assignee: HALMOS G
Current assignee: HALMOS G
Priority date: 1975-11-07
Filing date: 1976-11-08
Publication date: 1980-06-04
Also published as: DE2650565A1; NL7513102A; FR2330984A1; BE847958A

Description

(54) A DEVICE FOR EXCHANGING HEAT AND/OR MASS BETWEEN A LIQUID AND A GAS OR VAPOUR (71) I, GYORGY GUSZTAV BELA HAL MOS, of Generaal Winkelmanlaan 15, Bloemendaal, Netherlands, a national of the Netherlands, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a device for exchanging heat and/or mass between a liquid and a gas or vapour, the device com prising a number of vertical baffles, which are mutually parallel, and means provided at the upper sides of the baffles to cause a liquid flow along the baffles.

Such a device has been described in the German Specification No. 140,727. We have sought to improve a device of this type by stabilizing the contact surface between the flowing liquid on the one hand and the gas or vapour on the other hand, whereby the working reliability is increased, and a greater freedom of choice of the flow velocity of both the liquid and the gas or vapour is obtained, so that with aprede- termined surface area of the baffles, a greater exchange of heat and/or mass can be obtained.

Experiments have shown in this respect that, when increasing the gas or vapour velocity, the danger exists that droplets of the liquid that flow along the baffles downwardly, are loosened. It has proved to be of great importance that the flow conditions along the baffles should be such that on the one hand no droplets should be loosened as a result of local high velocities caused by turbulances, and on the other hand the transfer of heat and/or liquid between the liquid and the gas or vapour should be increased by a certain irregularity of the flow.

It is of importance that all portions of the baffles be wetted because a locally unwetted portion can attain a strongly deviating temperature, can grow in an area under the influence of the gas or vapour current and may at the limit of such an unwetted area cause the loosening of droplets.

The invention provides, in order to reduce the above indicated difficulties and to obtain the above improvements, respectively that the baffles should be covered with a layer of porous material.

Accordingly the present invention provides a device for exchanging heat and/or mass by direct contact between a liquid and a gas or vapour, the device comprising vertical baffles, each having an upper and a lower side, which baffles are mutually parallel with one another and means at the upper sides of the baffles to let a liquid flow along them, the baffles being covered with a layer of porous material. Preferably, the distance between the baffles measured in the main direction of the baffles is between 5 and 20 mm.

By a porous material is meant a material having interstices of small dimensions, which in any case are located at the surface. The liquid fills these interstices at least partly by reason of which a sufficient capillary bond between the baffle and the liquid flowing along it is obtained.

Examples are a fibre fleece or a foamed plastics material. Preferably, as foamed plastics material, one is chosen that has an open cell-structure, because in that instance the interstices at the surface also have a connection with interstices within the material. The material of the porous layer is preferably hydrophilic.

Further, it is advantageous if the baffles are as thin as is practically possible. The thickness of the baffles does not contribute to the working of the device, so that thin baffles in a device of the same dimensions enable a greater flow cross-sectional area to be obtained for the gas or vapour.

Also, it is important that the baffles be stable. If a vibration should occur in the baffles, this may easily cause the loosening of droplets.

According to a preferred embodiment of the invention it is provided that the baf ffes be wave- or zigzag-shaped in horizontal cross-section. By reason of this the mechanical strength of the baffles is considerably increased, so that the danger that they will vibrate is decreased and thinner baffles will therefore suffice. A further advantage is that, because the baffles are thin, the space between the baffles may be chosen to be relatively small, without decreasing strongly the cross-sectional area for the flow of gas or vapour. This enables economic solutions to be obtained, i.e. with the same gas velocities, which may be considerably higher than are nowadays usable, a stabile system is obtained, and no droplets are loosened from the liquid layer.

An additional reason is that baffles which are located near to each other prevent a sufficient turbulence to be created for the loosening of droplets. On the other hand, the undulating form of the flow channels between the baffles will create some irregularity of the flow that improves the transfers of heat and/or mass in the gas or vapour flow.

From the German Auslegeschrift No.

1,299,665 a device for transferring matter and/or heat between a liquid and a gas or vapour is also known, in which the liquid flows along waved sheets. The wave of the sheets extends at an angle of 45" with respect to the vertical and the corrugations of spaced sheets are mutually perpendicular to each other. Not only does this cause a considerably greater flow resistance than with the device according to the present invention and a less complete coverage of the corrugated sheets with liquid than with the present invention, but also such an irregular flow pattern is obtained that locally when the gas or vapour velocity is increased, droplets are loosened.

In an advantageous embodiment of the present invention, the baffles consist of a thin sheet which at both sides is covered with a thin layer of porous material. It has been shown that a metal sheet, for instance of aluminium, having a thickness of 005 mm, which at both sides has been covered with a thin layer of porous material each layer having a thickness of 02 mm, leads to very satisfactory results. Therewith, it has been shown that such a sheet allows a layer thickness of water streaming along it of about 2 mm with little formation - of droplets.

In practice it has been shown that as material for the fibre fleece or the foamed prastics,.polyvinylchloride is very suitable since it can easily be glued to metal sheets and experiments have shown that this par ticular material is very satisfactory in prac tice.

The baffles, especially if they are waved and supported at their upper and lower sides, are relatively stiff. If, however, the baffles have a considerable vertical dimension, it is desirable to support them at their vertical end-edges with respect to each other, and possibly also with respect to any mounting construction in which they may be present by means of bridge pieces. These bridge pieces may be streamlined in the gas or vapour flow direction and it has been shown that they do not cause loosening of the droplets or a detectable increase of the flow resistance of the gas or the vapour.

Feeding the liquid to the baffles in principle is possible in many ways. Thus, it is possible to attach the baffles to an upper and a lower sheet, the upper sheet being provided with perforations. Therewith, it has appeared that, if the baffles are located at a mutual distance apart of about 1 cm the liquid flows from the openings applied in the upper sheet along the baffles without giving rise to jets of liquid or falling droplets. It is also possible to locate the perforations in the upper sheet in such manner that the liquid directly trickles onto the baffles. A further possibility is to use an upper sheet having an open cell structure.

Means known per se can be used to control the liquid flow rate along the baffles, for instance, by adjusting the head of liquid above the sheet or by using members for the openings in the sheet, e.g. by means of a second sheet having correspondingly, located openings which second sheet can be shifted in such a way that the openings of the one and the other sheet will be in or out of register. Such constructions are known per se.

Reference is now made to the accompanying drawings, in which: Fig. 1 is a horizontal cross-section of an embodiment of the invention taken along the line I-I in Fig. 2; Fig. 2 is a cross-section along the waveline II-II in Fig. 1; Fig. 3A and 3B are plan views of a detail on a larger scale; Fig. 4 is a fragmentary cross-section of a baffle on a highly enlarged scale; Fig. 5 is a fragmentary plan of a detail; Fig. 6 is a cross-section through Fig. 5 along the line VI-VI; Fig. 7 is a cross-section on an enlarged scale of a further embodiment; and Fig. 8 shows a cross-section on a highly enlarged scale of a further embodiment.

The device shown in Fig. 1 comprises a rectilinear housing 1. At the left hand side of this housing a gas or vapour feed 2 is connected to the housing and at the righthand side there is an outlet 3. In the housing 1 a number of waved baffles 4 are present.

As more clearly appears from Fig. 2 the upper side of the housing is covered by a sheet 5 which is liquid permeable and is the bottom of a basin 6 having upstanding walls 7. The upper sides of the baffles 4 are connected to the sheet 5. At their lower sides, the baffles 4 are connected to a perforated bottom sheet 8. Below this sheet, a space 9 is provided under which the closed bottom 10 of the housing 1 has a liquid outlet 11.

The closed bottom 10 joins upstanding walls 12. The upper basin 6, together with the baffles 4 and the bottom 8 can be mounted into the housing 1 as a unit.

In one embodiment the sheet 5 is a perforated sheet and in Figs. 3A and 3B, the shape of a baffle has been shown on an enlarged scale, as well as two perforation patterns of the upper sheet 5. In Fig. 3A, oblong perforations 13 are located near to the baffle. In Fig. 3B circular perforations are applied in a regular pattern. Liquid which is poured into the basin 6 passes through the perforations in the sheet 5 and -thereafter flows along the lower side of the sheet 5 towards the nearest baffle and then downwardly over the baffle. Instead of using a perforated sheet, it is possible to make the upper sheet 5 from a fluid-permeable material, for instance a foamed plastics material having an open cell structure.

The perforations (not shown) in the sheet 8 need not be regularly distributed as are those in the sheet 5 and only need to comply with the requirement that they let pass sufficient liquid towards the space 9. The baffles 4 are connected to the sheets 5 and 8, e.g. by glueing. If the sheets 5 and 8 are comprised of a soft material, it is possible to press the baffles to some extent into the sheets, glueing being an additional connecting possibility.

In Fig. 4, a cross-section has been shown of a baffle that in practice has proved to be very suitable. On a central sheet 15 of rolled aluminium first the usual protective layers of a suitable paint or lacquer or the like is applied. To these layers at both sides a fibre fleece layer 15 of polyvinylchloride having a thickness of 0-2 mm is glued. Polyvinylchloride is a very suitable material to let a water film flow along it and a water film having a thickness of 2 mm flows without any difficulty, along the baffle and hardly without being loosened from the baffle. Glueing of polyvinylchloride can simply be done with commercially available glues.

In Fig. 5 on a larger scale than in Fig. 1 a horizontal cross-section has been shown through a part of two baffles 4, which as has been shown in the drawing have each been bent back at their front edge 17. A bridge-piece 18 having a streamlined cross section is provided with slits 19 in which the bent-back portions 17 have been housed.

It has appeared in practice that, for preventing vibrations, such bridge-pieces with the indicated thickness of the baffles have to be applied at a mutual vertical distance of about 15 cm with a flow velocity of the vapour or the gas of 7 to 8 meters per second and a mutual space between the baffles of 1 cm. These bridge-pieces appear to disturb the flow very little and do not give rise to loosening of droplets, whereas they further stabilize the baffles. The bridge-pieces 18 not only mutually support the baffles, but also secure them at their ends.

In Fig. 7 a cross-section through an upper sheet has been shown. A baffle 4 is angled at its upper side to form a horizontal upper sheet portion 20, which at its upper side has again been angled to form a flange 21, that has been glued to the next baffle 4.

The location of a perforation 13 according to the embodiment of Fig. 3A has also Fig.

7 been shown in cross-section. Oblong perforations having a width of 2 mm (Fig. 3A) or circular perforations having a diameter of 3 mm (Fig. 3B) can be used without having liquid falling as droplets from the sheet 5 downwardly, and contrary to this the liquid remains flowing along the baffles.

Fig. 8 finally shows a cross-section through a detail of another embodiment of the upper sheet and the baffles connected to it. The upper sheet consists in this case of strips 22 which in plan view have a waved shape corresponding to the space between the baffles 4 in Fig. 1.

The fibre fleece 16 at the side edges 23 of the strips 22 is somewhat compressed.

The strips 22 can be connected to the baffles in different ways, such as by glueing, hot pressing and so on. Evidently, at the outer sides of the strip packet, strips of a different shape have to be used, their shape corresponding to that of the walls of the housing 1 (Fig. 1).

The wave shape of the baffles 4 is not critical. It is even possible to use plain baffles or baffles which are zigzag-shaped in horizontal cross-section. On the one hand, a sufficient stiffness has to be obtained to make the baffles self-supporting in the sense that they need only be supported at their upper and lower sides and possibly at the front or back edges, but on the other hand the flow resistance has to be restricted.

With a wave period of 15 cm and a height of the wave of 5 cm (that is to say 10 cm from wave-top to wave-hollow) satisfactory results have been obtained with a mutual distance between the baffles of 1 cm.

The illustrated embodiment of the invention has the important advantage that, in a housing 1 of a predetermined volume, considerably larger quantities of liquid and vapour or gas can be brought in to an exchanging relation in comparison with known constructions. This is also due to the thinness of the baffles which by reason of the wave shape is admissible and to the flow pattern that allows relatively high velocities of the gas or the vapour without loosening droplets. The passage between two baffles perpendicular to the local flow direction is somewhat variable by reason of which, as has been shown on the one hand a reasonable transfer of heat and/or matter in the gas or vapour phase is possible, whereas on the other hand no turbulences of sufficient intensity occur to loosen droplets.

The device according to the invention can be used for many purposes. Without limiting the application possibilities of the invention the following application fields can be mentioned: cooling towers, condensers, air-conditioning, heat collection from partly expanded steam, process industries, etc.

The small heat resistance between the gas or the vapour and the liquid allows the further possibility to transfer heat from a liquid or a gas, that may be wetted, via firstly a liquid-liquid heat-exchanger, followed by a device according to the invention, with which in many cases it is possible to obtain a cheaper and more effective system than a liquid-gas heat-exchanger with, if necessary, a moistening apparatus.

WHAT I CLAIM IS: 1. A device for exchanging heat and/or mass by direct contact between a liquid and a gas or vapour, the device comprising vertical baffles, each having an upper and a lower side, which baffles are mutually parallel with one another and means at the upper sides of the baffles to let a liquid flow along them, the baffles being covered with a layer of porous material.

A device according to Claim 1, in which the layer comprises a fibre fleece.

3. A device according to Claim 1, in which the layer comprises a foamed plastics material.

4. A device according to Claim 3, in which the foamed plastics material has an open cell structure.

5. A device according to any of the preceding claims, in which the baffles are wave-shaped or zigzag-shaped in horizontal cross-section.

6. A device according to any of the preceding claims, in which the baffles each comprise a thin sheet, covered on both sides with a thin layer of porous material.

7. A device according to Claim 6, in which the sheet is of metal.

8. A device according to Claim 7, in which the thickness of the baffles is less than 0.5 mm.

9. A device according to any of the preceding claims, in which the baffles contain a metal sheet having a thickness of less than 0 1 mm.

10. A device according to any of the preceding claims, in which the baffles are solely supported at their upper and lower sides.

11. A device according to Claim 10, in which the baffles along their upper and lower sides have been fixed respectively to an upper and a lower liquid permeable sheet and the vertical end-edges of the baffles are provided with bridge-pieces connecting those edges.

12. A device according to any of the preceding claims, in which the baffles at their upper sides are connected to a sheet, which is provided with through openings therein.

13. A device according to Claim 12, in which the sheet comprises metal strips.

14. A device according to any of the preceding claims, in which the distance between the baffles, measured in the main direction of the baffles, is between 5 and 20 mm.

15. A device according to any of the preceding claims, in which the total height of the waves from wave-top to wave-hollow, or of a zigzag line, is smaller than the length of the wave or the zigzag pattern.

16. A device according to any of the preceding claims, in which the porous layer is comprised of polyvinylchloride.

17. A device substantially as herein described and as shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. vapour or gas can be brought in to an exchanging relation in comparison with known constructions. This is also due to the thinness of the baffles which by reason of the wave shape is admissible and to the flow pattern that allows relatively high velocities of the gas or the vapour without loosening droplets. The passage between two baffles perpendicular to the local flow direction is somewhat variable by reason of which, as has been shown on the one hand a reasonable transfer of heat and/or matter in the gas or vapour phase is possible, whereas on the other hand no turbulences of sufficient intensity occur to loosen droplets. The device according to the invention can be used for many purposes. Without limiting the application possibilities of the invention the following application fields can be mentioned: cooling towers, condensers, air-conditioning, heat collection from partly expanded steam, process industries, etc. The small heat resistance between the gas or the vapour and the liquid allows the further possibility to transfer heat from a liquid or a gas, that may be wetted, via firstly a liquid-liquid heat-exchanger, followed by a device according to the invention, with which in many cases it is possible to obtain a cheaper and more effective system than a liquid-gas heat-exchanger with, if necessary, a moistening apparatus. WHAT I CLAIM IS:

1. A device for exchanging heat and/or mass by direct contact between a liquid and a gas or vapour, the device comprising vertical baffles, each having an upper and a lower side, which baffles are mutually parallel with one another and means at the upper sides of the baffles to let a liquid flow along them, the baffles being covered with a layer of porous material.

A device according to Claim 1, in which the layer comprises a fibre fleece.

7. A device according to Claim 6, in which the sheet is of metal.

13. A device according to Claim 12, in which the sheet comprises metal strips.