GB2132741A - Liquid heating apparatus - Google Patents

Abstract

An electrical water heater of the type where the water is heated immediately before use as it passes through a container of small volume has two heating elements 11, 12, a first element 11 being brazed to the container 10 at a point adjacent a thermal cut-out device 28, the remaining element 12 being brazed to the first element at a position 32 spaced from where said first element 11 is brazed to the container 10. <IMAGE>

Description

SPECIFICATION Liquid heating apparatus This invention relates to improvements in fluid heating equipment. It is especially concerned with improvements in electrical water heaters of the "instantaneous" type, ie heaters where the water is heated immediately before use as it passes through a container of small volume.

Instantaneous water heaters have recently come into general use for hot showers, hand washers and other domestic applications where relatively small flow rates are required.

Instantaneous water heaters need to be both safe and efficient. High wattage heaters up to 7 KW have been employed to heat water as it passes through a small container, so that if for any reason the power remains connected to the heating element when the water cannot leave the container, as for example in closed outlet heaters, there is a risk that the container could rupture under the high pressure which can rapidly develop. A thermal cut-out or other temperature related safety device is normally installed at the hottest part of the container to ensure that this cannot happen, but the presence of these cutouts or other devices can lead to other problems associated with the operation of the heater, particularly where the element has a relatively high heat input.

Although cut-outs of rapid response can be provided, the heat stored in the element at the instant of cut-out may be sufficient to cause the temperature of the relatively small volume of water to rise significantly after the operation of the cut-out. If a cut-out respon sive to a lower temperature is installed to overcome this problem, the water heater may be prone to what is known as "nuisance tripping" ie the thermal put-out is triggered during normal use, or by a slight drop in the inlet water pressure.

Consumer demand has resulted in the requirement for even higher wattages in heaters of this type, eg 9 KW or more, and it is an object of the present invention to provide a safe and effective instantaneous water heater, particularly suitable for such higher wattage application.

According to the invention, we provide an instantaneous electrical liquid heater comprising a container through which liquid can flow, at least two continuous electrical resistance heating elements sheathed with thermally conductive material extending into said container, a thermal cut-out device mounted on a region of the exterior of said container and responsive to disconnect the electrical supply to the elements at a predetermined temperature setting, a portion of the sheath of a first of said elements being in thermal contact with the interior of said container in said region, the second element and any further elements being spaced from said region, and the sheaths of said second and any further elements being in thermal contact with the sheath of said first element at a predetermined spacing from said region.

The thermal contact referred to above is typically provided by brazing material of suitable heat-transmitting properties. The elements may be connected in parallel. Each element may have five U bends, the second or fourth U bend of one element being in thermal contact with the region referred to above.

Typically the container is right cylindrical in shape, and in use is arranged with its axis vertical. The elements typically enter all from one end, normally the upper end of the cylinder, that end being the one on which the thermal cut-out is mounted. Each element typically has two terminals on the container end, and where two elements are used it is preferably for the terminals of one element to be located in a position intermediate or between the position of the terminals for the other element(s). The upper cylinder end may be slightly domed, and the thermal cut-out may be mounted on a flat portion of the dome.

The heated liquid outlet from the container preferably extends into the container to a position adjacent the end of the container where the thermal cut-out is mounted. In use this is normally the uppermost part of the container. The liquid inlet is typically arranged to direct the inlet liquid entering the container specifically towards the region where one of the elements is in thermal contact with the region referred to above.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: Figure 1 is a side elevation in section of a liquid heater according to the invention, and Figure 2 is an end elevation in section of the heater of Fig. 1 seen in the direction of arrow II.

The heater comprises a copper container 10 in the shape of a right cylinder. As installed, the axis of the cylinder is aligned vertically. A pair of heating elements 11, 1 2 having thermally conducting sheaths enter container 10 through the upper end 27 of container 10.

Elements 11, 1 2 are shown simply as lines in the schematic drawings, but typically they are about 8mm in diameter. Each element 11, 1 2 is continuous within container 10 and externally of container 10 has a pair of terminals which in use are connected to.a power supply, the terminals for element 11 being identified in the drawings as 13, 14 and those for element 12 as 15, 16.

Each element 11, 1 2 has five U bends in its run before leaving container 10. Element 11 has U bends at 17, 18, 19, 20 and 21 and is shown in dashed line in Fig. 1 in the second half ot its run as from the direction viewed it is directly behind the first half of its run. The first two bends 17, 1 8 are in the same plane, the third bend 1 9 is in a plane at right angles to the said plane, and bends 20 and 21 are in the same plane as bends 17, 18. Element 12 has U bends at 22, 23, 24, 25 and 26, in coincident planes to those of- element 11, and is represented in the same manner as element 11 in Fig. 1.Whereas in Fig. 2 a number of the bends of elements 11, 1 2 are shown side-by-side for clarity, bend 1 8 is directly behind bend 17; bend 20 is directly behind bend 21; bend 23 is directly behind bend 22; bend 25 is directly behind bend 26.

Terminals 13, 1 4 of element 11 are located in a position intermediate between terminals 15, 16 of element 12 on the upper end 27 of container 10. Also located on the upper end 27 of container 10. Also located on the upper end 27 of container 10 is a thermal cut-out device 28, of known type, responsive to the temperature of a region of the container upper end 27. The sheath of element 11 at the tip of bend 20 is brazed to the region of the upper end 27 immediately adjacent the cutout device 28.Bend 25 of element 1 2 which is close to bend 20 of element 11 at this point is spaced from the container upper end 27, but the sheath of element 11 is brazed to the sheath of element 1 2 at a position, indicated by numeral 32, between bends 24 and 25 on element 1 2. Elements 11 and 12 are in fact in relatively close proximity at the position of braze 32, contrary to the representation in Fig. 2 which is only schematic. The precise position for braze 32 is determined by the conductivity of the sheath material, the rating of the heater elements 11, 1 2 and the sensitivity of the cut-out device 28. The upper end 27 of container 10 is slightly domed, the region where cut-out device 28 is mounted being a flat on the dome.

A heated water outlet is provided by a tube 29 which passes through the base of container 10 to an open end in the upper region of the container 10 adjacent the cut-out device 28. Cold water is directed into the heater, towards the region where element 11 is brazed to the upper end 27 of container 10, by means of inlet tube 30. Inlet tube 30 has a deflector at its end inside container 10 which directs water under pressure in the direction of arrow 31.

Elements 11, 1 2 have approximately equal power ratings eg 4.5 KW each, giving a total power input of 9 KW. The heater is fitted with a flow switch (not shown) in the inlet water supply, and a user valve on the outlet for heated water.

If for any reason the pressure switch fails to cut off electricity to elements 11, 1 2 when water ceases to flow through the heater, the temperature of water inside container 10 will rise very rapidly. The temperature of the region of the upper end 27 of container 10 will also rise rapidly since it is directly connected to the sheath of element 11 and trigger the thermal cut-out device 28. Even if element 11 has failed, the cut-out device 28 will be triggered by the heat conducted from element 1 2 via braze 32 and the sheath of element 11 to the region of the upper end 27 of container 10. Similar protection is provided by cut-out device 28 shouid the container run dry.

The invention thus provides an instantaneous heater of relatively high power rating which responds rapidly and effectively to either outlet blockage or failure of the conventional switch.

Claims (10)

1. An instantaneous electrical liquid heater comprising a container through which liquid can flow, at least two continuous electrical resistance heating elements sheathed with thermally conductive material extending into said container, a thermal cut-out device mounted on a region of the exterior of said container and responsive to disconnect the electrical supply to the elements at a predetermined temperature setting, a portion of the sheath of the first of said elements being in thermal contact with the interior of said container in said region, the second element and any further elements being spaced from said region, and the sheaths of said second and any further elements being in thermal contact with the sheath of said first element at a predetermined spacing from said region.

2. A heater as claimed in Claim 1 wherein the thermal contact is provided by brazing material of suitable heat-transmitting properties.

3. A heater as claimed in Claim 1 or Claim 2 wherein the elements are connected in parallel.

4. A heater as claimed in any preceding claim wherein the first element has five U bends, and the second or fourth U bend is in thermal contact with said region of the container.

5. A heater as claimed in any preceding claim wherein the container is right cylindrical in shape, and in use is arranged so that its axis is vertical.

6. A heater as claimed in Claim 5 wherein the elements all enter from the upper end of the cylinder, the thermal cut-out being mounted on the same end.

7. A heater as claimed in Claim 5 or Claim 6 wherein each element has two terminals on the container end, and the terminals of one element are located in a position intermediate or between the position of the terminals for the other element or elements.

8. A heater as claimed in any of Claims 5-7 wheren the element having the inner most terminals is brazed directly to the container.

9. A heater as claimed in any of Claims 5-8 wherein the upper cylinder end is domed, and the thermal cut-out is mounted on a flat portion provided on said dome.

10. An instantaneous electrical water heater as hereinbefore described with reference to and as shown in the accompanying drawings.