GB2092282A

GB2092282A - A Liquid Flow Heater

Info

Publication number: GB2092282A
Application number: GB8202217A
Authority: GB
Original assignee: THERMALEC PRODUCTS Ltd
Current assignee: THERMALEC PRODUCTS Ltd
Priority date: 1981-01-29
Filing date: 1982-01-26
Publication date: 1982-08-11
Also published as: GB2092282B

Abstract

A liquid flow heater (1), e.g. for a swimming pool, comprises a container (2) with a longitudinal axis and having an inlet (4) for liquid to be heated and an outlet (5) for heated liquid. The container (2) contains at least one heating element of substantially flat, convoluted form, e.g. spiral form, which extends transversely of the longitudinal axis, the convolutions of the or each heating element being spaced apart to permit the flow of liquid between adjacent convolutions. The inlet (4), the outlet (5) and the container (2) are dimensioned and arranged to induce liquid to flow in a corkscrew manner through the container (2) about the said longitudinal axis (X), so that the liquid is induced to pass across, and between adjacent ones of, the convolutions of the or each heating element. <IMAGE>

Description

SPECIFICATION A Liquid Flow Heater This invention relates to a liquid flow heater and in particular, but not exclusively, relates to a flow heater for a swimming pool.

According to the invention a liquid flow heater comprises a container with a longitudinal axis and having inlet means for liquid to be heated and outlet means for heated liquid, and at least one heating element, of substantially flat, convoluted form, positioned in the container so as to extend transversely of said longitudinal axis, spaces, for the flow of liquid therethrough, being provided between adjacent convolutions of the or each heating element, the said inlet and outlet means and the container being dimensioned and arranged to induce liquid flowing into and out of the container via said inlet means and said outlet means, respectively, to flow in a corkscrew manner through the container about said longitudinal axis of the latter so that the liquid is induced to pass across, and between adjacent ones of, the convolutions of the or each heating element.

Advantageously, the said inlet and outlet means are arranged in the upper part of the container.

Conveniently the container is arranged with its longitudinal axis substantially horizontal and with the or each heating element having terminations passing through an upper part of the container.

Typically the upper part comprises a removable closure which supports the or each heating element. Suitably the container has an at least partly cylindrical inner surface, and a pair of spaced apart, flat, vertically disposed end walls.

Suitably the inlet means is arranged to supply at least a major proportion of the liquid to be heated to one longitudinal end of the container and the outlet means is arranged to extract at least a major portion of the heated liquid passing through the outlet means from the other longitudinal end of the container. Alternatively the inlet means may be arranged to supply at least a major portion of the liquid to be heated to an intermediate part of the container between its said longitudinal ends (or to both longitudinal ends of the container) and the outlet means may be arranged to extract a major portion of the heated liquid passing through the outlet means from both longitudinal ends of the container (or from an intermediate part of the container between its said longitudinal ends).Conveniently a first thermostat is positioned in the inlet means at a location where a major portion of liquid to be heated is adapted to be supplied to the container and a second thermostat is positioned in the outlet means at a location where a major portion of the heated liquid is adapted to be extracted from the container. in a preferred construction of flow heater the inlet means defines an inlet for directing liquid downwardly into the container and the outlet means defines an outlet for extracting heated liquid upwardly out of the container, the said inlet and outlet being disposed on opposite sides of a vertical plane incorporating the horizontal, longitudinal axis of the container and each having a cross-section which is nonconstant in the direction of the longitudinal axis.

Conveniently, in the aforementioned preferred construction of flow heater, the inlet means comprises a weir-like first baffle over which liquid to be heated is adapted to flow and a second baffle arranged to deflect liquid downwardly into the container after passing over the first baffle, the first and second baffles being spaced apart and defining the said inlet, which preferably extends from one to the other longitudinal end of the container. Typically the outlet means comprises a third baffle arranged to deflect heated liquid upwardly out of the container and a weir-like fourth baffle over which liquid deflected by the third baffle is arranged to pass, the third and fourth baffles being spaced apart and defining the said outlet, which preferably extends from one to the other longitudinal end of the container.The weir-like first and fourth baffles may be provided by side walls of the container and, when the container is provided with a removable closure, the second and third baffles may be fixed thereto. Conveniently the sum of the cross-sections of the said inlet and the said outlet is substantially constant in any plane perpendicular to the said longitudinal axis of the container. For example, if the first, second, third and fourth baffles are substantially planar, the second baffle may be arranged at an angle to the first baffle to define a wedge-shaped inlet, the second baffle being spaced furthest from the first baffle at the said one longitudinal end of the container, the third baffle may be arranged parallel to the second baffle and the fourth baffle may be arranged parallel to the first baffle to define a wedge-shaped outlet.It is not, however, essential for the baffles to be planar. Thus the first and fourth baffles may be planar and the second and third baffles may be non-planar, e.g. of Vshape.

The container may include at least one deformable insert, e.g. a hollow insert of plastics material, which is deformable to take up any expansion in the liquid contained in the container when the contained liquid freezes. In this manner damage to the container is prevented. When the container is provided with said second and third baffles, the insert(s) may be attached thereto.

Preferably the or each insert is dimensioned to provide the inside of the container with an at least partly cylindrical shape.

Conveniently the or each heating element is of generally spiral form. Typically the two outermost convolutions or coils are each connected to a respective heating element termination, the outermost pair of coils spiralling inwards together and being integrally connected together adjacent the centre of the heating element. At least the lowermost part of the outermost convolution or coil of each heating element closely follows the contour of, and is spaced a relatively small distance from, the inner surface of the container. Suitably adjacent coils or convolutions of the or each heating element are spaced at least 0.5 cm apart, e.g. 0.65 cm apart.By providing the or each heating element with a generally spiral form there will be relative movement between adjacent convolutions of the heating element on expansion and contraction of the heating element causing any scale deposited across adjacent convolutions of the heating element to be dislodged. If, as is preferred, more than one heating element is provided which heating elements are spaced from each other in the longitudinal direction of the container, it is desirable to arrange for the convolutions of adjacent spirally wound heating elements to be wound in opposite directions so that any scale trapped between adjacent heating elements will be subjected to relative movement between the adjacent heating elements on expansion or contraction of the latter.

Suitably the said inlet means and the said outlet means are arranged to ensure that a body of liquid is trapped in the container during a period of non-use, following a period of use, of the flow heater, the level of trapped liquid being sufficient to immerse completely the or each heating element.

The invention will now be described, by way of example, with referrence to the accompanying drawings, in which: Figure 1 is a side sectional view through a flow heater according to the invention, Figure 2 is an end view of the flow heater shown in Figure 1, Figure 3 is a plan of the flow heater shown in Figures 1 and 2 with its lid removed, and Figure 4 is a view, on an enlarged scale, of a heating element of the flow heater shown in Figures 1 to 3.

Figures 1 to 3 show a flow heater, generally designated by the reference numeral 1, comprising a container in the form of an opentopped vessel 2 provided with an uppermost plate-like closure 3 and having inlet means, generally designated 4, for liquid to be heated, and outlet means, generally designated 5, for heated liquid, disposed on opposite sides of a vertical plane Y.

The vessel 2 has a pair of spaced apart, substantially vertical end walls 6 and 7 which are joined by a substantially U-shaped wall section defining side walls 8 and 9 of the vessel. Upper parts 8a and 9a of the side walls are substantially vertical and terminate beneath, so as to be spaced from, the lower surface of the closure 3. The lower part of the U-shaped wall section has a smooth contour, preferably being part-cylindrical about a horizontal, longitudinal axis X (shown in chain lines in Figures 2 and 3) of the vessel 2 which is contained in the plane Y. Around the upper edge of the vessel 2 there is provided an endless flange 10 to which the closure 3 is removably fixed, e.g. by bolts (not shown), in a liquid-tight manner. Closable drainage valves 30, which are normally kept closed, are provided at the bottom of the vessel 2.

The closure 3 has a pair of substantially vertically disposed baffles 11, 1 2 fixed to its underside, each baffle 11(12) being positioned adjacent, but spaced from and at an angle relative to, one of the associated upper wall parts 8a (9a).

A pair of deformable hollow inserts 13 and 14 of a plastics material may be fixed to the baffles 11 and 12, respectively, and/or to the underside of the closure 3. The inserts each have a substantially part-cylindrical surface which, together with the part-cylindrical lower part of the U-shaped wall section of the vessel 2, provide the flow heater 1 with a substantially cylindrical cavity 1 5 having a first end 1 6 adjacent the end wall 6 and a second end 1 7 adjacent the end wall 7. The inserts 13 and 14 also serve to prevent the flow heater 1 from being damaged if any liquid in the cavity 15 freezes. If freezing does occur, the increase of volume of the frozen liquid is taken up inside the cavity by the deformation of the inserts 1 3 and 14 instead of by the bursting of the vessel 2.

The inlet means 4 provides an inlet channel 18 communicating with the cavity 1 5 for liquid to be heated, and comprises a substantially horizontal inlet section of circular cross-section, formed in the flange 10, a substantially vertical intermediate section of rectangular cross-section defined between the upper wall part 8a, the flange 10 and the closure 3, and a substantially vertical outlet section of non-uniform, e.g. wedge-shaped, crosssection defined between the baffle 11 and the upper wall part 8a.The outlet means 5 provides an outlet channel 19 for liquid heated in the cavity 1 5 and comprises a substantially vertical inlet section of non-uniform cross-section, e.g. wedgeshaped cross-section (see Figure 3), defined between the baffle 12 and the upper wall part 9a, a substantially vertical intermediate section of rectangular cross-section defined between the upper wall part 9a, the flange 10 and the closure 3, and a substantially horizontal outlet section of circular cross-section formed in the outlet passage 1 9.

In the particular embodiment of flow heater described, the baffles 11 and 12 are arranged parallel to each other and are spaced similar distances from their associated upper wall parts 8a and 9a, respectively. Thus, the sum of the dimensions of the cross-sections of the outlet section of the inlet of the channel 1 8 and the inlet section of the outlet channel 1 9, taken in any plane perpendicular to the longitudinal axis X, is substantially constant.

The closure 3, in addition to having the baffles 11 and 12 and the inserts 13 and 14 fixed thereto, also carries a pair of vertically disposed thermostats 20 and 21 and three flat heating elements 22, 23 and 24. The thermostat 20 acts as a control thermostat and is positioned in the inlet channel 18 at the "wide" end of the wedgeshaped cross-section vertical outlet section. The control thermostat 20 is connected to the heating elements 22 to 24 and is designed to sense the temperature of incoming liquid to control its temperature within +1 OC of a desired, settable temperature. The thermostat 21 acts as a safety thermostat and is positioned in the outlet channel 19 at the "wide" end of the wedgeshaped cross-section vertical inlet section.The flat heating elements 22, 23 and 24 occupy vertical planes which are spaced from, and parallel to, each other and which extend transversely to the longitudinally axis X, e.g.

perpendicular to the longitudinal axis or perpendicular to the planes containing the baffles 11 and 1 2. Each heating element is typically sheathed with heavy duty nickel plated copper and is wound in a spiral form (see Figure 4) with adjacent convolutions preferably being spaced at least 0.5 cm, e.g. 0.65 cm, from each other. The lower part of the outermost convolution of each heating element closely follows, but is spaced a relatively small distance from, the curved lower parts of the side walls 8 and 9 of the vessel 2 so that in use little liquid is able to flow between the walls of the vessel and the heating elements without being heated by the latter.The two outermost convolutions of each heating element are bent upwardly to provide straight, verticallydisposed terminal portions 25 and 26 which are carried by the closure 3 and which are adapted in use to be connected to a 3-phase a.c. supply (not shown). These vertically-disposed terminal portions are thus positioned to minimise the accumulation of scale thereon. However, if scale does form on the heating elements, the latter can be easily cleaned by unfastening the closure 3 from the vessel 2 and removing as a single unit the closure and heating elements. When in position in the vessel 2, the heating elements are conveniently arranged so that adjacent elements have their spiral convolutions wound in opposite directions.Thus when the heating elements expand or contract there is both relative movement between adjacent convolutions of each heating element as the adjacent convolutions coil or uncoil and relative movement between adjacent convolutions of adjacent heating elements as the adjacent heating elements coil or uncoil in opposite directions. The relative movements between the convolutions of the heating elements assists in preventing or dislodging the accumulation of scale bridging between convolutions of each heating element or between adjacent heating elements.

In use of the flow heater 1 , for heating the water contained in a swimming pool (not shown), the water to be heated is passed, e.g. with the aid of a pump (not shown), via pipework (not shown), through the flow heater 1 at a high flow velocity. Typically the pipework has a diameter of 5 cm and the water is passed through the pipework at speeds of up to 3 ms-l to enable the whole water content of the swimming pool to be passed through the flow heater every 4 hours.

Because of the wedge-shaped outlet section of the inlet channel 18, and the wedge-shaped inlet section of the outlet channel 19, the majority of the water supplied to the cavity 1 5 via the inlet channel 1 8 is supplied to the first end 16 of the cavity through the widest part of the wedgeshaped inlet section and the majority of the water extracted from the cavity 1 5 via the outlet channel 1 9 is extracted from the second end 1 7 of the cavity through the widest part of the wedgeshaped inlet section. Thus the wedge-shaped inlet and outlet sections ensure that water passing through the cavity 1 5 of the flow heater 1 is subjected to a gradual axial motion or flow from the first end 1 6 to the second end 1 7 of the cavity.

The water in its passage at high speed through the inlet channel 1 8 is deflected downwardly into the cavity 1 5 by the vertically disposed baffle 11 thereby ensuring that the incoming water to be heated is prevented from impinging directly on any of the heating elements 22 to 24. The downwardly flowing water is caused to flow around the curved lower parts of the side walls 8 and 9 thereby imparting a circular or rotary motion about the longitudinal axis X to the body of water contained in the cavity 1 5. The strong downward flow of water entering the cavity 1 5 scours the curved lower parts of the side walls 8 and 9 helping to dislodge any sediment or scale deposited thereon.Any scale or sediment removed by the scouring action of the incoming water is carried by the rotating body of water in the cavity 1 5 up the side wall 9 and passes through the wedge-shaped inlet section of the outlet channel 1 9. It will thus be appreciated that little or no scale accumulates at the bottom of the vessel, thereby obviating the need for any scale detectors in the vessel 2. Any scale which does form at the bottom of the vessel 2 can be flushed out by the opening of the drainage valves 30.

The combined effect of the axial and rotary motions of the body of water contained in the cavity 1 5 is for the water to follow a substantially corkscrew path about the axis X through the cavity 1 5 from its first end 1 6 to its second end 17. The magnitude of the rotary motion is large compared with that of the axial motion and incoming water will often complete several complete revolutions inside the cavity 1 5 before exiting from the latter.

Since the body of water at any one time in the cavity 1 5 has a large component of rotary motion, it is able to remain a comparatively long time in heat exchange relationship with each spiral form heating element, i.e. the rotary flow of water substantially follows the spiral path of each heating element. The force exerted by this component of rotary motion acts in a rotary direction-i.e. substantially along the spiral path of each heating element-the direction in which each heating element has its greatest strength.

Furthermore, because of the axial component of motion applied to the body of water, the water, in addition to flowing across the surface of each flat heating element, is also able to flow between adjacent convolutions of each heating element.

Each heating element is comparatively weak in the axial direction perpendicular to its plane.

However, it will be appreciated that only a small axial force is exerted by the flowing water in the cavity 1 5 because of the relatively small component of axial motion applied to the body of water in the cavity 1 5.

It will be appreciated by those skilled in the art that the flow heater 1 hereinbefore described is efficient, is of compact design and can be easily inspected for maintenance purposes. The compact design is possible because of the effectiveness of the liquid flow through the cavity 1 5 which permits both adjacent heating elements and adjacent convolutions of each heating element to be closely spaced apart. Thus, the vessel 2 can be made of a compact design having inherent strength. Furthermore the compact design of the flow heater ensures that the 'safety' thermostat 21 is quickly able to sense any abnormal rises in temperature caused, for example, by the heating elements being turned on either with no liquid flowing through the cavity 1 5 or with no liquid contained in the cavity 1 5.If such an abnormal temperature rise is detected, the thermostat 21 automatically switches off the heating eiements before any damage is caused to the flow heater, thereby obviating the need for temperature-detecting sensors to be attached to the heating elements. It will be appreciated that the design of the flow heater 1 is such that in normal use the cavity 1 5 will remain full of liquid, i.e. up to the level of the top of the upper wall parts 8a and 9a, there being a small air spaced left between the top of the liquid in the cavity 1 5 and the underside of the closure 3. In this case the heating elements will be immersed in the liquid and so, under normal circumstances, will not be switched on with the cavity 1 5 empty.

Furthermore the air space between the closure 3 and the top of the liquid in the cavity 1 5 is able to take up (together with the inserts 13 and 14 if provided) any expansion of the liquid caused by the latter freezing.

Other embodiments of a flow heater according to the invention are of course possible. For example it is possible for the liquid inlet channel 18 and the liquid outlet channel 19 to be formed in the closure 3, the channels being disposed substantially vertically, e.g. parallel to the thermostats 20 and 21. However, this construction is not preferred since the easy removal of the closure 3 is hindered. It is also possible for the heating elements to have a different form. For instance, instead of having a spiral form, the or each heating element may have some other flat, tortuous form, e.g. a zig-zag form, typically having a generally circular shape. Finally the baffles 11 and 12 may be of other than planar form, e.g. they may be of V-shape as shown in dotted lines in Figure 3. In this particular case the design of the outlet of the inlet channel 1 8 and the inlet of the outlet channel 19 would be such that the majority of incoming liquid would be supplied to a zone midway between the first and second ends of the cavity 1 5. The liquid contained in the cavity 1 5 would then spiral outwards in corkscrew paths to enable the majority of the outgoing liquid to be removed from the opposite first and second ends of the cavity.

Claims

1. A liquid flow heater comprising a container with a longitudinal axis and having inlet means for liquid to be heated and outlet means for heated liquid, and at least one heating element, of substantially flat, convoluted form positioned in the container so as to extend transversely of said longitudinal axis, spaces, for the flow of liquid therethrough, being provided between adjacent convolutions of the or each heating element, the said inlet and outlet means and the container being dimensioned and arranged to induce liquid flowing into and out of the container via said inlet means and said outlet means, respectively, to flow in a corkscrew manner through the container about said longitudinal axis of the latter so that the liquid is induced to pass across, and between adjacent ones of, the convolutions of the or each heating element.

2. A liquid flow heater according to claim 1, in which the said inlet and outlet means are arranged in the upper part of the container.

3. A liquid flow heater according to claim 1 or 2, in which the container is arranged with its longitudinal axis substantially horizontal and with the or each heating element having terminations passing through an upper part of the container.

4. A liquid flow heater according to claim 3 in which the said upper part of the container comprises a removable closure which supports the or each heating element.

5. A liquid flow heater according to any of the preceding claims, in which the container has an at least partly cylindrical inner surface, and a pair of spaced apart, flat, vertically disposed end walls.

6. A liquid flow heater according to any of the preceding claims, in which the said inlet means is arranged to supply at least a major proportion of the liquid to be heated to one longitudinal end of the container and the said outlet means is arranged to extract at least a major proportion of the heated liquid passing through the outlet means from the other longitudinal end of the container.

7. A liquid flow heater according to any of claims 1 to 5, in which the said inlet means is arranged to supply at least a major proportion of the liquid to be heated to an intermediate part of the container between its said longitudinal ends and the said outlet means is arranged to extract a major proportion of the heated liquid passing through the outlet means from both longitudinal ends of the container.

8. A liquid flow heater according to any of claims 1 to 5, in which the said inlet means is arranged to supply at least a major proportion of the liquid to be heated to both longitudinal ends of the container and the said outlet means is arranged to extract a major proportion of the heated liquid passing through the outlet means from an intermediate part of the container between its said longitudinal ends.

9. A liquid flow heater according to any of claims 6 to 8, comprising a first thermostat positioned in the inlet means at a location where a major proportion of liquid to be heated is adapted to be supplied to the container and a second thermostat positioned in the outlet means at a location where a major proportion of the heated liquid is adapted to be extracted from the container.

10. A liquid flow heater according to any of the preceding claims, in which the inlet means defines an inlet for directing liquid downwardly into the container and the outlet means defines an outlet for extracting heated liquid upwardly out of the container, the said inlet and outlet being disposed on opposite sides of a vertical plane incorporating the horizontal, longitudinal axis of the container and each having a cross-section which is non-constant in the direction of the longitudinal axis.

11. A liquid flow heater according to claim 10, in which the said inlet means comprises a weirlike first baffle over which liquid to be heated is adapted to flow and a second baffle arranged to deflect liquid downwardly into the container after passing over the first baffle, the first and second baffles being spaced apart and defining the said inlet.

12. A liquid flow heater according to claim 11, in which the said inlet extends from one to the other longitudinal end of the container.

13. A liquid flow heater according to any of claims 10 to 12, in which the said outlet means comprises a third baffle arranged to deflect heated liquid upwardly out of the container and a weir-like fourth baffle over which liquid deflected by the third baffle is arranged to pass, the third and fourth baffles being spaced apart and defining the said outlet.

14. A liquid flow heater according to claim 13, in which the said outlet extends from one to the other longitudinal end of the container.

1 5. A liquid flow heater according to claim 13 or 14, each when dependent directly or indirectly upon claim 11, in which the said weir-like first and fourth baffles are constituted by side walls of the container.

1 6. A liquid flow heater according to any of claims 1 3 to 15, each when dependent directly or indirectly upon claims 2 and 11, in which the second and third baffles are fixed to the said removable closure.

1 7. A liquid flow heater according to any of claims 10 to 1 6, in which the sum of the crosssections of the said inlet and the said outlet is substantially constant in any plane perpendicular to the said longitudinal axis of the container.

1 8. A liquid flow heater according to claim 17, in which the first, second third and fourth baffles are substantially planar, the second baffle being arranged at an angle to the first baffle to define a wedge-shaped inlet, the second baffle being spaced furthest from the first baffle at the said one longitudinal end of the container, the third baffle being arranged parallel to the second baffle and the fourth baffle being arranged parallel to the first baffle to define a wedge-shaped outlet.

1 9. A liquid flow heater according to any of the preceding claims, including at least one deformable insert, positioned in the container and which is deformable to take up any expansion in the liquid contained in the container when the contained liquid freezes.

20. A liquid flow heater according to claim 19, in which the or each deformable insert is a hollow insert of plastics material.

21. A liquid flow heater according to claim 19 or 20, in which the or each insert is dimensioned to provide the inside of the container with an at least partly cylindrical shape.

22. A liquid flow heater according to any of the preceding claims, in which the or each heating element is of generally spiral form.

23. A liquid flow heater according to claim 22, in which the two outermost convolutions or coils of the or each heating element are each connected to a respective heating element termination, the outermost pair of convolutions or coils spiralling inwards together and being integrally connected together adjacent the centre of the heating element.

24. A liquid flow heater according to claim 22 or 23, in which at least the lowermost part of the outermost convolution or coil of the or each heating element closely follows the contour of, and is spaced a relatively small distance from, the inner surface of the container.

25. A liquid flow heater according to any of claims 22 to 24, in which adjacent coils or convolutions of the or each heating element are spaced at least 0.5 cm apart.

26. A liquid flow heater according to any of claims 22 to 25, comprising at least two heating elements of generally spiral form spaced apart from each other in the longitudinal direction of the container, the convolutions of the heating elements of the or each adjacent pair of heating elements being wound in opposite directions.

27. A liquid flow heater comprising a container with a longitudinal axis and having inlet means for liquid to be heated and outlet means for heated liquid, and at least one heating element, of substantially flat, convoluted form, positioned in the container so as to extend transversely of said longitudinal axis, for the flow of liquid therethrough, being provided between adjacent convolutions of the or each heating element, the said inlet and outlet means and the container being dimensioned and arranged to induce liquid flowing into and out of the container via said inlet means and said outlet means, respectively, to flow through the container with rotary components of motion about, and longitudinal components of motion relative to, said longitudinal axis of the latter so that the liquid is induced to pass across, and between adjacent ones of, the convolutions of the or each heating element.

28. A liquid flow heater constructed and arranged substantially as herein described with reference to, and as illustrated in Figures 1 to 4 of the accompanying drawings.

29. A swimming pool fitted with a liquid flow heater according to any of the preceding claims.