FR2473166A1 - Solar fluid heat exchanger - has glass plate with parallel tubes in two passes with inlet and outlet on same sides - Google Patents

Abstract

The heat exchanger is enclosed under a glass case with a sloping ridge roof. The heat exchanger has a header (8) at each end with parallel tubes in the plate (3). The tubes are divided into two banks separated by a centre line (7). The water is admitted through an inlet connection (6a). Water circulates to the opposite end (4) through the bottom half of the tubes, and back through the top half to the outlet connection (6b) at the same end as the inlet.

Description

 The present invention relates to heat exchangers composed of extruded tubular plates of elongated shape.

 The technical sector of the invention is that of the construction of heat exchangers which can be used for example as solar collectors, as heat absorbers for the fermentation of plants, as convectors, as heated mulches etc., that is to say in relatively low temperature applications.

 Tubular or cellular plates of transparent or opaque plastic are known, in particular polycarbonate plates which are extruded in great lengths. These tubular plates are composed of two parallel plates connected to one another by partitions perpendicular to the plates which delimit therewith. parallel channels.

 These tubular plates have already been used to construct insulating panels thanks to the air trapped in the channels. These plates have also been used as exchangers in which a coolant is circulated by equipping the two ends of a plate with collectors, into which the channels open. Patent application FR 79 09816 describes such exchangers and their applications, in particular as solar collectors placed under a greenhouse cover, as heating tables or as vertical radiators. In these applications, each end of a plate is equipped with a manifold which has a circular section and which comprises two parallel lips, one of which is tangent to the circular section.

 Since these tubular plates are extruded and can be supplied in coils of very long length, the inventors have sought solutions allowing the construction of elementary exchangers of very long length, avoiding that air bubbles do not remain trapped in the channels. and do not risk slowing the circulation of the liquid in certain channels and reducing as much as possible the equipment of each exchanger in fittings which increase the cost of the exchangers since the price of the fittings is relatively high compared to the price of the tubular plates which constitute a inexpensive material.

 An object of the present invention is to provide exchangers composed of tubular plates of elongated shape, the length of which is clearly greater than the width, for example of plates whose length is at least equal to ten times the width and can be of the order of fifty times to a hundred times the width.

In the case of a greenhouse cover for example, the length L of the greenhouse is generally between 40 and 60 m, while the width 1 of the slopes is of the order of 3 m to 6 m
An objective of the invention is to provide solar collectors which can be placed under the cover of the greenhouse parallel to the longitudinal axis and which have a length L of the order of 50 m for a width of the order of 0 , 50 m, therefore a length equal to a hundred times the width.

Compared to sensors arranged along the line of greatest slope of the roof slopes, as were the sensors used previously, the length of the collectors and the number of rac
L cords in the L1 ratio, that is to say in a ratio of the order of 10 which constitutes a very significant saving in manifolds and fittings which are accessories whose manufacturing and mounting price is high relative at the price of tube sheets.

 The same cost reduction is found in many applications where it is necessary to equip with absorbent or radiant panels rectangular surfaces of elongated shape, the length of which is clearly greater than the width, for example in the case of solar collectors arranged on railings. balcony or on horizontal building strips, in the case of very long convectors or in the case of heating panels placed on the ground between rows of plants, to form heating tables or heated mulch.

 A heat exchanger according to the invention is of the known type comprising, on the one hand, an extruded tubular plate, composed of two thin plates connected to each other by partitions which delimit parallel channels and, on the other hand, two collectors which are located along the two edges of the plate perpendicular to the channels and which have a circular cross section extended by two lips, one of which is tangent to the circular section.

 The objectives of the present invention are achieved by means of exchangers in which the tubular plate has the form of an elongated strip whose length is parallel to said channels and in that one of the two collectors is divided into at least two sections successive comprising one an inlet pipe and the other an outlet pipe of a heat transfer liquid which traverses said exchanger along a hairpin path.

 Preferably, the ratio between the length and the width of the tube plate is greater than ten. The inlet and outlet pipes -of the heat transfer liquid are located inside a sector having an angular opening of the order of 1200, of which. one side is in line with the tubular plate and on the same side of the plate as the manifold to which they are connected.

 An exchanger according to the invention used as absorber of a solar collector comprises an opaque or black tubular plate and one of the collectors is divided into three successive sections and the two end sections are very short and both have an inlet duct of cold heat transfer liquid, while the intermediate section comprises a pipe for the start of hot heat transfer liquid, so that the cold liquid circulates at high speed in one direction in two narrow bands located along two longitudinal edges of the plate and returns in opposite direction towards the intermediate section by heating up.

 A device according to the invention for capturing the calories produced by the fermentation or slow combustion of a pile of plants comprises vertical partitions which are buried in the pile of plants and each partition comprises an easily removable structure, for example a structure in scaffolding tubes and exchangers which are: supported by said structure and one end of which, which emerges from the pile of plants, carries said collectors which are divided into two sections.

 The collectors of the same partition which are located outside the pile of plants are connected together in series.

 A device according to the invention for heating rows of plants in a greenhouse or in the open field comprises very long narrow exchangers according to the invention, which are placed on the ground along the rows of plants and the two inlet ducts and liquid outlet in the collector which is divided into two sections are connected, one on a general flow collector and the other on a general return collector, in which water circulates having a temperature between 150C and 500C .

 The invention results in inexpensive new exchangers which are particularly well suited to many uses requiring large capture or radiation surfaces and, more particularly, to applications in which the surfaces can be divided into strips of elongated shape or very elongated, such as solar collectors placed under a transparent greenhouse or building cover, or along balcony railings or on building strips of elongated form or even heated mulches or flattened and elongated conduits laid on the soil between rows of plants, or the heating tables used in some greenhouses.

 All these applications have in common the fact that the maximum temperatures are relatively low, of the order of 50 to 600 and that it is necessary to use large exchange surfaces to capture or emit enough calories. The exchangers according to the invention which are composed of extruded tubular plates and manifolds which can be made of plastics and a number of fluid inlet and outlet connections per unit of exchange surface which is very reduced are a relatively low manufacturing cost. They have the advantage that the heat transfer fluid inlets and outlets are located on the same side, which facilitates their installation.

The shape of the manifolds combined with the arrangement of the fluid inlet and outlet conduits in the collector which is divided into two or three sections makes it possible to obtain a uniform distribution of the liquid in the various channels of each exchanger element.

 The unit areas of the exchangers according to 1 invention are relatively large of the order of several tens of square meters and the thickness of the tubular plates is small, of the order of 5 to 10 mm, depending on the manufacturing. As a result, the speed of passage of the liquid in the channels is high, which has the effect of preventing air bubbles from risking blocking the circulation of the liquid in certain channels.

 In the application to the heating of greenhouses or rows of plants in the open field by means of narrow strips placed on the ground between the rows of plants, the exchangers according to the invention have the advantage, thanks to the pin-shaped path. , to standardize the average temperature over the entire length of the rows of plants.

 The following description refers to the appended drawings which represent, without any limiting character, examples of embodiment and applications of exchangers according to the invention.

 Figure 1 is a schematic overview of a greenhouse.

 FIG. 2 is a top view of an elementary exchanger used as a sensor in the greenhouse according to FIG. 1.

 Figures 3 and 4 are sections along III-III and IV-IV of Figure 2.

 Figures 5 and 6 are partial sections on a larger scale of the inlet and outlet manifold of the heat transfer liquid.

 FIG. 7 represents a solar collector absorber according to the invention.

 Figures 8 and 9 show a device for capturing the calories released by the fermentation or slow combustion of heaps of plants.

 FIG. 10 is a plan view of a device for heating rows of plants in a greenhouse or outside.

 Figure 1 shows a greenhouse or other similar shelter with a transparent cover. Figure 1 shows for example a greenhouse 1 composed of glazed frames, which has two vertical longitudinal walls and a roof composed of two inclined sides. The greenhouse has a length L which is generally of the order of 40 to 60 meters and the sides of the roof have a width 1 of the order of 4 to 6 meters for example. The dimensions which are given by way of illustration correspond to the order of magnitude of the current dimensions of greenhouses. The ratio 1 is therefore of the order of 10. Of course, the greenhouse could have other shapes, for example a curved shape.

 Under the transparent cover of the greenhouse are arranged transparent sensors 2 according to the invention. These sensors 2 are composed of several elementary sensors 2a, 2b ... 2n, which can be mounted in series or in parallel. Each element is composed of a transparent tubular plate 3 which has two transparent walls connected by partitions 3a which delimit channels 3b between them, for example a polycarbonate plate, which is connected at each of its ends on a tubular manifold 4, 5 which is perpendicular to the channels 3b of the plate. The partitions 3a and the channels 3b are arranged parallel to the longitudinal axis of the greenhouse and each elementary sensor extends over the entire length L of the greenhouse while the collectors 4 and 5 are arranged along the line of greatest slope of the roof. The collectors 4 and 5 conform to those which have been described in an earlier patent application FR 7909816. These are circular section tubes comprising two lips, one of which is tangent to the circular section, which delimit between them a longitudinal opening in which one of the edges of the tubular plate perpendicular to the channels is engaged. A liquid is circulated in the collectors which absorbs part of the solar energy. This liquid can be a filtering liquid, for example a colored liquid which completely absorbs certain frequency bands of the light spectrum, in particular the bands of the spectrum which are not useful for photosynthesis. It can also be an aqueous suspension, the concentration of which can be modulated as a function of the external light and / or the temperature inside the greenhouse. Greenhouses have already been built comprising such sensors associated with the cover, which were composed of tubular plates whose channels were arranged along the lines of greatest slope of the sections of the roof and whose collectors were arranged horizontally. This solution entailed for each roof section a length of collectors equal to 2L which is reduced to 21 by the arrangement according to Figure 1, L or in a ratio L1 of the order of 10, resulting in a very significant saving.

 But to be able to use the sensors according to this horizontal arrangement of the channels, it is necessary to solve the problem of the evacuation of the air bubbles in order to avoid that these do not prevent the circulation of the heat-transfer liquid in certain channels.

 Figures 2, 3 and 4 show a preferred embodiment of each elementary sensor. This comprises a tubular plate whose width is of the order of 0.50 m to 1 m.

 Experience shows that it becomes very difficult to obtain a uniform speed of the liquid in the various channels in parallel and therefore a good distribution of temperatures as soon as the width of the sensors exceeds 1 m and that, on the other hand, a very good distribution with a width of about 0.50 m. In order to reduce the number of channels connected in parallel, each elementary sensor is divided into two halves which are connected in series according to a hairpin circuit.

 This result is obtained by dividing one of the collectors, for example the collector 5, into two sections, which are for example two separate sections or else two sections of the same collector separated by a partition 9 and by equipping each of the two sections a connector, respectively 6a and 6b, which serve as an inlet and the other as an outlet for the elementary sensor. The second manifold 4 does not have a partition or fittings.

 There is shown in Figures 2 and 4, by arrows, the direction of circulation of the coolant which arrives for example by the connector 6a, then flows in the channels of one half of the plate 3, is taken up by the collector 4a and returns via the channels of the other half of the plate to the outlet connector 6b. In the collectors 4a and 4b, the liquid circulates along helical paths.

 There is shown in Figure 2 by a dotted line 7, the theoretical separation between the two hairpin circuits. Of course the ends of the two collectors 4a and 4b are closed by plugs 8. This pin arrangement has the advantage of halving the number of fittings for the same width of channels connected in parallel between two collectors.

 In order to facilitate the helical circulation of the liquid in the two sections of the manifold 5, it is important that the inlet and outlet fittings 6a and 6b are properly connected to the manifold 5.

 FIG. 5 represents, on a larger scale, one end of a tubular plate 3, the manifold 5 and an inlet or outlet connector 6.

The ox axis perpendicular to the plate 3 represents the normal position of the axis of the fitting 6. With respect to this normal position, the axis of the fitting 6 can vary on either side of the ox axis, but must stay inside an angular sector a whose total opening is 1200.

 FIG. 5 represents an extreme position of the connector 6. The positions of the connector 6 inside the angle a favor the helical movement of the liquid inside the manifold 5 and thereby a uniform circulation of the liquid in the various tubular plate channels 3.

 FIG. 6 represents a variant in which the manifold 5 is placed above the tubular plate 3. This partition is shown in this hatched shape 9. This partition is a plate cut out in the shape of a spiral that follows the shape of the manifold 5 and which enters a channel of the tubular plate 3. The relative position of the connector 6 with respect to the manifold and to the plate 3 is unchanged. The connector 6 is located inside a sector having an angular opening a of the order of 1200, one of the sides oy of which is in the extension of the plate 3 and it is located on the same side of the plate 3 than the collector.

 The elementary exchangers according to FIGS. 2 to 6 can be grouped in parallel or in series and be placed, for example vertically, to serve as convectors or sensors for the fermentation calories of a vegetable compost. They can also be placed horizontally to serve as heating mats or heating tables in greenhouses.

 Exchangers made up of opaque or black tubular plates can be used as solar collectors placed vertically or inclined.

 According to the uses, the collectors 4a and 4b are arranged above or below the plane of the tube plate which they equip.

 An advantage of the very long exchangers according to the invention lies in the fact that the unit surface area of each elementary exchanger is much larger, therefore the calorific power received or emitted is also greater, and to obtain the same temperature difference between l 'entry and exit of the exchanger, Liteau must be circulated much faster, which promotes heat exchange. In the application to greenhouses in which an aqueous suspension is circulated in transparent sensors, the high speed of circulation has the advantage of maintaining the homogeneity of the suspension.

 FIG. 7 represents a front view of a flat solar collector element according to the invention. It is composed of a tubular plate 3 of great length which is extruded in an opaque or black plastic, for example a length of several tens of meters, and a width of the order of one meter. This sensor is placed vertical or inclined and, in the case where it is inclined, the arrow P represents the slope line. The plate 3 is equipped, at each of its ends, with a collector 4, 5 of the same type as the collectors shown in FIGS. 2 to 6, The collector 5 is composed of three sections 5a, 5b, 5c, which are, either three separate collectors aligned, or three sections of the same tube separated by partitions 9a and 9b. The two extreme sections 5a and 5c are very short, their width being to twist from 3 to 5 cm and they are each equipped with an orifice 10a, 10b for entering the cold liquid. The orifices 10a, 10b are placed relative to the collector according to the arrangement described in FIGS. 5 or 6. The central section Sb is equipped with a liquid outlet orifice 11 which is disposed at the upper end of the section 5b.

 We have drawn in FIG. 7, in dotted lines, two theoretical lines 7a and 7b which extend the partitions 9a and 9b and which divide the plate 3 into three strips 3a, 3b and 3c which correspond to the three sections 5a, 5b and 5c. The cold liquid enters the sections 5a and 5c via the connections 10a and 10b and it travels, at high speed, the two narrow strips 3a and 3c. The liquid enters tangentially into the collector 4, follows a helical path and returns by heating through the channels of the central strip 3b towards the section 5b then it exits through the connector 11.

This arrangement has the advantage that cold liquid circulates along the longitudinal edges of the sensor, which limits heat loss by conduction.

 FIGS. 8 and 9 represent an application of exchangers according to the invention as sensors for the calories released by a heap of plant materials undergoing slow oxidation or fermentation, for example a heap of shrubbery or household waste constituting a compost in progress of fermentation, or a bunch of manure. The contours of the compost heap 12 which has, for example, a length L of the order of 10 m, a width 1 of the order of 6 m and a height h which varies between 3 meters at the initial stage, have been shown in dotted lines of fermentation and 2.20 m at the final stage. We recall that such a heap, whose useful volume is of the order of 130 m3, has a calorific power of approximately 11.4 KW and releases approximately 10 therms per hour and the temperature inside the pile is in the range of 50 "C to 65" C.

 Inside the compost heap 12 are placed vertical partitions 13 = parallel to each other, which include heat exchangers according to the invention. The spacing between partitions 13 is for example 0.65 m.

 Figure 9 is. an elevation view along IX-IX of a partition 13. This comprises a light frame 14, for example a frame made of tubes, of the scaffolding tube type, which comprise easily removable assembly means. For clarity of the drawing, the framework 14 is shown in hatching in FIG. 9. This framework comprises for example at each end a stake 14a, 14b planted in the ground and horizontal spacers 14c. We see that one of the ends 14a of the partitions 13 emerges from the compost pile 12. The partitions 13 have for example a total height of the order of 1.50 m and a total length of twist of 5.50 m, of so that outside the end 14a, they are entirely buried in the compost pile.

 Each partition comprises several elementary exchangers according to the invention, for example two exchangers 15a and 15b in the case of the figure. Each exchanger comprises a tubular plate having for example a length of 5.50 m and a height of 0.50 m which is arranged vertically and supported by the framework 14. The two exchangers 15a and 15b are of the type described with reference to the Figure 2 and there is shown by arrows the direction of circulation of the heat transfer liquid which traverses a hairpin circuit in each exchanger-eur. The two exchangers 15a and 15b equipping each partition are connected in series by a strap 16 between a flow collector 17 placed at ground level and a return collector 18. It can be seen in FIG. 8 that the exchangers equipping two neighboring partitions are connected in parallel between the collectors 17 and 18. Of course, the connections on the collectors 17 and 18 can be made according to different arrangements in series, in parallel or in parallel series.

 A heat capture installation according to FIGS. 8 and 9 has the advantage of comprising very light and inexpensive equipment, hence very low investment costs. In addition, the heat exchangers and the metal structures that support them are very easy to assemble and disassemble. During the heaping of the crushed plants, the partitions are built one by one and each time the space is filled between two partitions before the next partition is constructed, which makes it possible to use handling machines of the mechanical loader type to make the bunch of plants. When the fermentation is complete and you want to evacuate the compost, the partitions are dismantled one by one starting from a longitudinal end of the heap, which greatly facilitates mechanical handling.

 The exchangers according to the invention which are composed of plastic plates and collectors are very suitable for this application because they resist corrosion by humic acids well and the temperatures are at a level at which the plastics have good behavior.

 FIG. 10 represents an application of the exchangers according to the invention used as heating mulches or as heating ducts for a greenhouse placed on the ground. The markers 19 represent plants, for example salads, planted in rows, or in the open field. either inside a greenhouse. Along the rows of plants, exchangers 20a, ...... are placed on the ground, according to the invention, of great length.

Each exchanger is composed of a single long and narrow tubular plate having for example a length of several tens of meters and a width which can be between 0.10 and 0.50m depending on the spacing between rows of plants and the degree of heating. research. One can for example use narrow bands posed beside the plants to heat the soil and the roots in the immediate vicinity of the plants. The direction of circulation of the heating liquid which is for example water at a temperature between 15 and 500C has been represented by arrows. The water circulates in each elementary exchanger in a taller and return hairpin path and the different exchangers are connected in parallel between a general flow manifold 21 and a return general collector 22 which are placed side by side, on the same side as the collectors 23a, 23b .., 23n, which are divided into two sections by partitions 24a, 24b ... 24n.

 In this application, the exchangers according to 1 invention advantageously replace flexible sheaths placed on the ground which are used for heating greenhouses or to form heated mulches intended to prevent freezing of plants grown outside.

 In this application, the exchangers according to 1 invention have the very important advantage that the average temperature of the water between the flow circuit and the return circuit in the various cross sections of the exchanger is substantially constant, which makes it possible to obtain very uniform heating of a greenhouse or a crop, thus avoiding the risk of freezing at the least heated points or overheating at other points.

 In all the application examples which have just been described, exchangers according to the invention are used which are in the form of narrow strips the length of which is at least equal to ten times the width and can reach up to a hundred times the width and in which the liquid circulates in a pin-shaped path, which has the effect of multiplying by two the ratio between the length of the exchanger and the width of each circuit. it follows that the liquid must circulate at high speed in the channels of the tubular plates which constitute these exchangers and, therefore, the air bubbles are entrained by the current of the liquid and do not risk obstructing certain channels.

 The arrangement in narrow strips and in a hairpin circuit also has the advantage of reducing the proportion of collectors and fittings per unit of exchange surface, hence an investment saving which is all the more appreciable than the exchangers. according to the invention are mainly intended for low temperature applications where large exchange areas must be used and where it is therefore essential to produce inexpensive installations.

The narrow strip exchangers according to the invention are particularly well suited to many applications in which one must use exchangers of very elongated shape or ~ in which exchangers of substantially rectangular shape can be replaced by exchangers of elongated shape. We will cite as possible applications, without this list having any limiting character
- transparent exchangers which are placed under the cover of a greenhouse or a glazed roof to serve as solar energy collectors and / or screens with adjustable shade and possibly as heating radiators;
- the absorbers of solar collectors placed on elongated surfaces, for example applied on the railings of balconies or on certain strips of buildings. In this case, opaque and preferably black tubular plates are used;
- convectors used for heating certain elongated buildings;
- mulches used to heat greenhouses or crops in the open field;
- the heating tables used in greenhouses; - - the sensors of the calories released by fermentation or by the slow combustion of plants (biomass) etc ...

 Of course, without departing from the scope of the invention, the various constituent elements of the exchangers which have just been described by way of example may be replaced by equivalent elements fulfilling the same functions.

Claims (7)

R E V E N D I C A T I O N S 1 - Heat exchanger comprising an extruded tubular plate composed of -  of two thin plates connected together by partitions which delimit  try parallel channels and two collectors which are located along  of the two edges of said plate perpendicular to the channels and which have  a circular cross-section extended by two lips, one of which  is tangent to said circular section, characterized in that said  tubular plate in the form of an elongated strip the length of which is pa  parallel to said channels and in that one of the two collectors is divided  in at least two successive sections comprising one, an inlet duct  and the other, an outlet pipe for a heat transfer liquid which  runs said exchanger along a hairpin path. 2 - Exchanger according to claim 1, characterized in that the ratio in  the length and the width of said strip is greater than ten. 3 - exchanger according to any one of claims 1 and 2, characterized  in that said inlet and outlet conduits are located inside  a sector with an angular opening of the order of 120, one of which  east side in the extension of said plate and they are located on the same  side of the plate that the manifold to which they connect:  4 - Exchanger according to any one of claims 1 to.3 used as  absorber of a solar collector, characterized in that said plate tu-  bular is opaque or black and in that one of the collectors is divided  in three successive sections and the two extreme sections are very  short and both have a heat transfer fluid inlet pipe  cold, while the intermediate section includes a  hot heat transfer liquid, so that the cold liquid circulates  the high speed in one direction in two narrow bands located the  along two longitudinal edges of the plate and back in reverse  towards the intermediate section by heating up. 5 - Device for capturing the calories produced by fermentation or  slow combustion of a pile of plants, characterized in that it comprises  vertical partitions which are buried in the pile of plants and  each partition has an easily removable structure, for example  a structure in scaffolding tubes and exchangers according to which one  conch of claims 1 to 3 which are supported by said structure  and one end of which, which emerges from the pile of plants, carries the said  collectors which are divided into two sections. 6 - Device according to claim 5, earctérisé in that the collec  teurs-- of the same partition located outside the pile of plants are connected  between them in series. 7 - Device for heating rows of plants in a greenhouse or in  full field, characterized in that it comprises narrow exchangers and  of great length according to any one of claims 1 to 3,  which are laid on the ground along the rows of plants and the two  liquid inlet and outlet pipes in the collector which is  divided into two sections are connected one on a general collector  go and the other on a general return collector in which circulates  water with a temperature between 150C and 500C.