Heat exchanger with coil constituted by a tubular element with drop-shaped cross-section

Abstract

 The invention relates to a heat exchanger that is particularly suitable for use in boilers designed for heating and production of sanitary water, wherein the coil through which the water passes has a drop-shaped cross-section, and more particularly a cross-section in which the lower part is semi-circular, or preferably parabola-shaped with a rounded tip, and the upper part is substantially cusp-shaped, ie. has a cross-section that tapers towards the top, with slightly concave sides.
This solution produces the ideal balance between the amount of heat that can be transferred across the surface of the pipe which constitutes the coil and the volume of water that is circulated in it, and therefore improves the dynamics of the heat and water flows, at the same time aiding the flow of fumes and gases.

Description

[0001] This invention relates to a special profile for pipes intended for use in a heat exchanger for boilers for domestic use which are designed to produce hot water for heating and for supply to sanitary fittings.

[0002] In particular, the invention relates to a heat exchanger that is particularly suitable for use in boilers designed for heating and production of sanitary water, wherein the coil through which the water passes has a drop-shaped cross-section, and more particularly a cross-section in which the lower part is semi-circular, or preferably parabola-shaped with a rounded tip, and the upper part is substantially cusp-shaped, ie. has a cross-section that tapers towards the top, with slightly concave sides.

[0003] This solution produces the ideal balance between the amount of heat that can be transferred across the surface of the pipe which constitutes the coil and the volume of water that is circulated in it, and therefore improves the dynamics of the heat and water flows, at the same time aiding the flow of fumes and gases.

[0004] The heat exchangers employed in boilers for domestic use, especially wall-mounted boilers, generally include a coil attached to a plurality of fins to ensure better heat exchange.

[0005] The dimensions of boilers, especially wall-mounted boilers, are more or less standardised, and the space available to instal the heat exchanger is fairly limited (there is an increasing tendency to reduce size nowadays).

[0006] As a result, it is necessary to find a solution in which the coil is long enough, while still maintaining a large enough diameter for passage of the water, so that the water circulates well even if the pump has a low head; without compromising the hydrodynamics of the flow.

[0007] The pipes used to make the coil usually have round or oval cross-sections. Space being equal, a round shape limits the number of pipes used and therefore the possibility of achieving balanced heat distribution.

[0008] Round pipes have the advantage of requiring a pump with a low head to circulate the water; however, although the ratio between the circumference and area of the cross-section is minimal, the quantity of heat transferred to the fluid is also minimal, with the result that the risk of noise, generally due to resonance, is increased when the usual diameters are employed.

[0009] Pipes with an elliptical or oval cross-section have been used to increase the amount of heat that can be transferred during a given unit of time, and to improve the dynamics of the flow.

[0010] With this configuration, the ratio between circumference and cross-section increases, as does the amount of heat transferred.

[0011] Moreover, this configuration enables more pipes (usually six or seven) to be fitted into a heat exchanger with the same overall dimensions.

[0012] The drawback to this solution is that the heat exchanger is heavier, and above all is more expensive than those with a cylindrical coil.

[0013] The situation is even more complicated in the case of bi-thermal heat exchangers, in which the coil is formed by two coaxial pipes; the outer pipe serves for the primary water conveyed to the heating apparatus, while sanitary water flows through the inner pipe.

[0014] In the case of bi-thermal heat exchangers, considerable problems are encountered because, in view of the small cross-section of the pipes, pumps with a high head are required to circulate the water at the necessary speed.

[0015] Even greater problems are encountered in the case of heat exchangers with oval pipes.

[0016] In order to solve the financial problems posed by oval pipes, their number has to be reduced, but this leads to an excessive increase or decrease in loss of head, depending on whether the hydraulic circuit is in series or parallel. Both solutions generate incorrect fluid dynamics in the pipes.

[0017] The problem therefore arises of designing a heat exchanger whose characteristics enable a good balance to be achieved between the amount of heat transferred across the surface and its distribution on the exchanging parts, the flow rate of the water treated, and the head required to obtain this flow rate in a given unit of time.

[0018] The invention solves this problem by offering a heat exchanger with pipes having a substantially drop-shaped cross-section, and preferably a cross-section in which the lower part of the pipe has a semicircular, arc or elliptical shape, or preferably a parabola shape, while the upper part tapers towards the top and has concave sides.

[0019] This invention will now be described in detail, by reference to the annexed figures, in which:

• figure 1 shows a cross-sectional view of a pipe used to make a heat exchanger in accordance with the invention
• figure 2 shows a cross-sectional view of a possible configuration of a sanitary water pipe for use in a bi-thermal heat exchanger in accordance with the invention
• figure 3 shows a cross-sectional view of the pipe of a coil in a bi-thermal heat exchanger in accordance with the invention
• figure 4 shows a cross-sectional view of a heat exchanger in accordance with the invention, illustrating the heat-exchange fins
• figures 5, 6 and 7 show a further preferred version of (i) a pipe used to make a heat exchanger in accordance with the invention, (ii) a sanitary water pipe and (iii) the pipe of a coil in a bi-thermal heat exchanger in accordance with the invention, respectively.

[0020] The concept on which the invention is based is that the coil is made with a pipe having a cross-section such that the ratio between the length of the circumference and the area of the said cross-section is as suitable as possible, and produces the ideal loss of head necessary for the distribution of heat and pressure gradients in the heat exchanger compatibly with the ease of circulation of the water, and in particular a larger ratio than would be obtained with a circular cross-section.

[0021] The problem is solved by this invention, which uses a pipe with the cross-sectional configuration shown in the annexed figures to make the coil.

[0022] In figure 1 the pipe, shown as 1, has a substantially drop-shaped cross-section; the lower part 2 has a substantially semicircular, arc or elliptical shape, while upper part 3 has a cusp shape, or at any rate a cross-section which has two concave sides and tapers towards the top.

[0023] This makes the area of the cross-section smaller than that of a pipe having a circular cross-section with the same circumference, while maintaining a shape favourable to water circulation and enabling the advantages of both the round and oval configurations to be obtained where required.

[0024] In accordance with a preferred version of the invention (fig. 5), the lower part 2 of pipe 1 has a substantially parabola shape, while the upper part 3 has a cross-section with two concave sides 4.

[0025] The upper section 5, which connects concave sides 4, preferably has an arc-shaped cross-section.

[0026] As a result of the parabola shape of lower part 2, this configuration promotes the upward flow of fumes, thus preventing stagnation and ensuring a more efficient heat exchange.

[0027] In the case of the bi-thermal heat exchanger, there is a second pipe 2 inside pipe 1 which may have the shape shown in figure 2, or any other shape which leaves a cavity with a sufficient cross-section to allow easy circulation of primary water, even when used with a pump having a low head.

[0028] Inner pipe 6 will advantageously have the shape shown in figure 6, with a lower stem 7 connected to an upper bulb 8 of larger dimensions.

[0029] In particular, as shown in figure 7, pipe 6 can be contained precisely inside a round pipe, illustrated with a dotted line and indicated as number 9, which is used as the base for making outer pipe 1 of the heat exchanger, and is suitably shaped by known techniques to give the pipe the drop-shaped cross-section described above.

[0030] The upper side of bulb 8, indicated as 10, therefore has an arc-shaped contour with a radius equal to that of round pipe 9 from which outer pipe 1 of the heat exchanger is obtained.

[0031] If the configuration shown in figure 3 is observed, it will be seen that two cross-sections 12 and 12', which are not excessively flattened, are formed in the cavity between the two pipes, through which the primary water passes, while the sanitary water flows through the composite cross-section of pipe 6.

[0032] The fact that the two cross-sections through which the primary water flows are not excessively flattened reduces losses caused by friction. Although the illustrated cross-section of the inner pipe, through which the sanitary water passes, presents a somewhat flattened part, it also has another fairly rounded part. Two flows are substantially formed in that cross-section: the main water flow will tend to concentrate on the rounded part of the cross-section, while a slower secondary flow will be observed in the other part.

[0033] As the two flows are in contact with one another at the narrowest part, turbulence will be created due to the different speeds, thus improving the efficacy of the heat exchange.

[0034] The ratio between the cross-sections of pipes 6 and 1 can vary according to the various applications; however, it has been found that the best results are obtained with ratios of between 1:2,5 and 1:4.

[0035] Pipes of this shape can be obtained by deforming a cylindrical pipe, for example by rolling, profiling or other known system, or can be directly made with the required cross-sectional shape.

[0036] As a result of the cross-sectional shape of pipe 1, heat exchanger fins 13 will have the configuration shown in fig. 4.

[0037] Protuberances 14 or grooves 15, obtained by deforming the metal used to make fins 13, are present on the surface of the said fins, and create a degree of turbulence which aids the heat exchange.

[0038] The configuration of the pipes in the heat exchanger in accordance with the invention improves the heat exchange, thus allowing the size of the heat exchanger to be reduced with no loss of exchange power or efficiency, and enables primary water to circulate easily, even when a pump with a low head is used.

Claims

1. Heat exchanger for boilers designed for heating and production of sanitary water, characterised in that it includes pipes (1) for the passage of water having a cross-sectional shape in which, in order to ensure the efficacy of the heat exchange, the ratio between the length of the circumference and the area of the cross-section is greater than that of a circular cross-section having a circumference of the same length.

2. Heat exchanger for boilers designed for domestic use, as claimed in the preceding claim, characterised in that pipes (1) have a substantially drop-like shape.

3. Heat exchanger for boilers designed for domestic use, as claimed in claim 2, characterised in that the lower part (2) of pipe (1) has a parabola shape.

4. Heat exchanger for boilers designed for domestic use, as claimed in claim 3, characterised in that the upper part (3) of the pipe narrows towards the top and has a cross-sectional shape with concave sides (4).

5. Heat exchanger for boilers designed for domestic use, as claimed in claim 2, characterised in that the lower part (2) of pipe (1) has an arc-shaped cross-section, while the upper part (3) of the said pipe is substantially cusp-shaped.

6. Heat exchanger for boilers designed for domestic use, as claimed in claim 2, characterised in that the lower part (2) of pipe (1) has an elliptical cross-section while the upper part (3) of the said pipe is substantially cusp-shaped.

7. Bi-thermal heat exchanger for boilers designed for domestic use, of the type comprising a coil attached to a set of fins (13), characterised in that the said coil consists of an outer pipe (1) in accordance with any of claims 2 to 7, inside which a second pipe (6) for sanitary water is situated.

8. Bi-thermal heat exchanger for boilers designed for domestic use, as claimed in claim 7, characterised in that the said inner pipe (6) has an arrow-shaped cross-section.

9. Bi-thermal heat exchanger for boilers designed for domestic use, as claimed in claim 7, characterised in that the said inner pipe (6) has a cross-section that presents a lower stem (7) connected to an upper bulb (8) of larger dimensions.

10. Bi-thermal heat exchanger designed for boilers for domestic use, as claimed in each of claims 7 to 9, characterised in that the ratio between the cross-sections of inner pipe (6) and outer pipe (1) is between 1:2.5 and 1:4, and preferably approximately 1:3.

Drawing