AU2002302186B2 - A hot water tank of a water heater with an inlet diffuser - Google Patents

Description

WO 02/101297 PCT/AU02/00719 A Hot Water Tank of a Water Heater with an Inlet Diffuser Field of the Invention This invention relates generally to storage tanks, more particularly, to hot water storage tanks as used for water heaters. It more specifically relates to a hot water storage tank fitted with an inlet diffuser in a water heater.

Background of the Invention In the vast majority of water heaters of the storage tank type purchased by the public for use in homes and elsewhere, the design is such that cold water delivered to the lower end of the water heater tank replaces hot water withdrawn from the upper end. Typical tank heating elements cannot reheat the water as fast as it is withdrawn. Thus continuous withdrawal of hot water will lead to cold water eventually filling the tank. Even before the tank is full of cold water, the incoming cold water mixes with the heated standing water in the tank thereby causing unwanted reduction of the outlet water temperature over time. This reduction is jointly the result of the currents generated by the inward flow of cold water, by the outward flow of hot water and by natural convection currents established within the tank.

The hot water volume delivered at the outlet, above a required acceptably high temperature, can be increased, at the stage of initial purchase, by paying for a larger size of tank and/or greater heating power and hence the rate of heat input. Without the need for that cost penalty, the present invention enables the temperature of hot water at the outlet to be maintained over a longer delivery time, for a given capacity of tank, by preventing the hitherto experienced intermixing of hot and cold water within the tank.

Approaches in the past to contain and control the mixing of hot and cold water in tanks have not become commonplace or generally known in the field. Some found by searching patent records include providing separate chambers within the tank for cold and hot water.

U.S. Pat. Nos. 2,833,273 and 3,244,166 employ separate mixing chambers within the tank at the inlet. U.S. Pat. No. 2,207,057 uses a small baffle over the inlet to control mixing, while U.S. Pat. No. 3,987,761 employs a baffle plate with large openings, U.S. Pat. No. 3,062,233 simply uses a small inverted inlet cover. U.S. Patents No. 787,909 U.S. Pat. No. 4,390,008 show the use of a vertically movable barrier. In U.S. Pat. No. 2,809,267, a braided tube is attached to the cold water inlet located adjacent the tank bottom to control the turbulent' introduction of cold water into the tank and in an attempt to maintain the stratification of hot water above cold water.

WO 02/101297 PCT/AU02/00719 2 In a substantially different construction employing physical division of the tank interior, U.S. Pat. No. 2,625,138 divides the tank into separate vertical layers by using numerous horizontal baffles. U.S. Pat. No. 2,311,469 shows a fuel burner in which several secondary combustion chambers stratify the water in the storage tank. U.S. Pat. No. 4,436,058 attempts to minimise convection tendencies by confining water in numerous capillary type conduits stretched between the tank bottom and the tank upper end. U.S. Pat. No. 1,689,935 attempts to obtain constant temperature of water by continuously varying the energy input to the tank by using feedback in a control system involving a thermostat.

While the above designs tried to reduce flow created by the usual high velocity of incoming cold water and tried to separate hot and cold water layers, none have taken note of the existence of possible convection currents and, thus, none limit the formation of these thermal currents in the tank and concurrently preserve the smooth horizontal dividing layer between hot and cold water within the tank. Further, these thermal convection currents appear to flow primarily along the smooth side surfaces of the tank. In pressurized tanks, the smooth inner surface of the curved upper end enhance these currents, the domed upper end being common in pressure tanks because of its structural strength. These closed loop currents greatly enhance the mixing of hot and cold water. U.S. Pat. Nos. 4,632,065 and 4,739,728 attempt to stop mixing caused by these convection currents.

Convection currents are generated by turbulence resulting from high velocity of inrushing cold water and by thermal imbalance created by the localised dumping of cold water into the tank. None of the above patents is concerned with reducing or minimising convection currents near the cold water inlet. Further, none of the above patents is concerned with reducing or minimising convection currents resulting from thermal imbalance created due to localised dumping of cold water.

In the above-referenced patents, prevention of mixing of cold water in a more active manner involves presenting a physical obstruction to convection currents. US patent 5,137,053 prevents mixing in a more passive manner by foiling convection currents by use of a diffuser inlet dip tube that introduces water evenly across a horizontal cross section of the tank. However his proposals are not ideal with respect to production on such high capacity production lines as are common in the industry manufacturing domestic water heaters because his invention relies on inserting a plate of relatively large diameter with respect to the tank diameter horizontally inside the tank and aligning a hole in it with a dip tube that extends WO 02/101297 PCT/AU02/00719 3 from an opening in the upper end wall of the tank. This must be done before attaching one end wall to the tank, which makes for slower assembly.

As an explanatory general comment, those water heaters heated by gas most commonly have central flues extending vertically through the tank and are heated by a high input burner centrally below the lower wall of the tank. These heaters have internal convection current problems that go beyond subduing convection as being the only rationale for improving safe and effective operation. The present invention concentrates its attention away from this type, although its application to the type is not precluded. The present invention displays its greatest advantage applied to tanks that have an internal electrical resistance heating element protruding into the tank from an opening near the lower end of the vertical side wall of the tank.

The applicant does not concede that the prior art discussed above forms part of the common general knowledge in the art at the priority date of this application.

Summary of the Invention The present invention provides a storage tank of a water heater including: a side wall, a lower end and an upper end wall defining an internal storage space for the heated water; a cold water inlet for introducing cold water into the lower portion of the tank, the inlet being connected at an outer end to an inlet port in a wall of the tank; an outlet for withdrawing hot water from the upper end portion of the tank; and an inlet diffuser connected to said inlet are located at a region of discharge of cold water into the storage space in the lower portion of the tank; the diffuser including plural spaced distribution openings which are aligned to distribute cold water into the storage space in streams emitting from the diffuser in a downward direction.

Preferably the cold water is emitted into the storage space in streams radiating from the diffuser in a downward direction.

The spaced openings are substantially uniform and aligned to deliver a discrete layer of cold water within a lower portion of the storage space upon withdrawal of hot water from the tank outlet.

The inlet diffuser can include a tube extending with a substantially horizontal direction component from the cold water inlet.

The diffuser preferably spans, in the horizontal direction, less than one quarter of a diameter of the tank.

WO 02/101297 PCT/AU02/00719 4 Preferably the plural distribution openings perforate a portion of the surface of the diffuser, that portion being subtended by an angle between 450 and 900 on either side of a vertical axis passing through the centre of the tube.

The plural spaced distribution openings are each smaller across its transverse axis than the diffuser inlet but in total area of openings, much larger than the diffuser inlet.

The cold water can be distributed into the storage space as a layer spreading around a circumferential corner formed by ajoin between the lower end wall and the vertical wall.

The tank can include an inwardly domed lower end wall that extends upwardly a predetermined height into the tank and the distribution openings discharge into a lowest portion of the storage space below said height.

The inlet diffuser can be curved with a radius of curvature so that no part of it touches the lower end wall of the tank while at the same time all the spaced openings are proximate the lower end wall. Preferably the radius curvature is between 100 and 150 mm.

The inlet and inlet diffuser are interconnected and include shapes and dimensions to enable both to be inserted from outside the tank through the cold water inlet port.

Preferably the cold water inlet port is between 15 and 22 millimetres diameter.

Preferably the inlet port is located in the upper wall of the tank, the inlet cold water tube extending from an upper end, connected to the inlet port, to a region proximate the lower wall of the tank.

The diffuser can extend with horizontal and radial direction components from a lower end of the inlet.

The openings are preferably formed in such said diffuser by means of a lattice construction. The lattice construction can be formed from axial and transverse members.

With the axial members being located on the inside of said diffuser relative to said transverse members. The axial members can have a curved cross section.

The embodiments of the present invention introduces cold water in a thin lanina made up of slow moving streamline flows spreading around the join region between the lower end wall and vertical wall of the heater tank, meaning unproductive convection currents are minimised. This means the hot water delivery performance of any tank using the invention can be maximised. The performance improvement in relatively small tanks, such as 15 US gallon or 50 litre capacity, is most noticeable. This improvement can be achieved with a low cost inlet diffuser, ideal for mass-produced water heaters, that can be assembled after all other WO 02/101297 PCT/AU02/00719 production steps have been completed. It can be added to already installed water heaters to improve their efficiency and hot water delivery.

The present invention also provides a vertical cylindrical storage tank has a side wall, a lower wall and an upper end wall enclosing an internal storage space for heated water. The tank comprises, among other usually employed features, a cold water inlet for introducing cold water into the lower portion of the tank and an outlet for withdrawing hot water from the upper end portion of the tank. It also includes, significantly, an inlet diffuser located in the cold water inlet and extending through an inlet port into the lower portion of the tank below the outlet and further extending into the storage space, the diffuser having plural spaced distribution openings, each smaller across its transverse axis than the diffuser inlet but in total area of openings, much larger than the diffuser inlet. The spaced openings are substantially uniform and aligned to deliver a discrete layer of cold water within the lowest portion of the storage space. This enables incoming cold water to be dispersed from the distribution openings uniformly in plural streamline flows into the storage space below the diffuser to minimise currents that cause mixing of hot and cold water in the tank so that a greater proportion of the tank's capacity is delivered at the outlet as hot water.

Optionally, the storage tank has the diffuser in the form of a tube extending inwardly from the vertical wall less than one quarter of the tank into the storage space, the plural distribution openings perforating a downwardly-facing portion of the surface of the diffuser in the storage space, that portion being subtended by an angle between 45 and 900 on either side of a vertical axis passing through the centre of the tube. Further, the perforations are aligned to distribute cold water into the storage space in streams emitting from the diffuser only in a downwardly radiating direction.

As a further option, the storage tank has an inwardly domed lower end wall and the inlet diffuser protrudes through the cold water inlet port opening in the vertical wall of the tank which is below a level which aligns with a maximum height that the inwardly domed wall extends into the tank.

Also optionally, the storage tank has the inlet diffuser upwardly curved so that no part of it touches the lower end wall of the tank.

Brief Description of the Drawings Here follows a full description of details of construction and operation of the invention with reference to the accompanying drawings including presently preferred examples of embodiments, in which: WO 02/101297 PCT/AU02/00719 6 Figure 1 is a cross-sectional through a water heater storage tank which can receive a first embodiment of the present invention; Figure 2 is a cross-sectional part detail elevation view of a first embodiment of the present invention showing the use of a straight perforated inlet diffuser extending into a water heater storage tank; Figure 3 is an enlarged side elevation view of the inlet diffuser of Figure 2; Figure 4 is a cross-sectional view of the diffuser of Figure 2 through the line IV- of Figure 3; Figure 5 is a further cross-sectional view of the diffuser of Figure 2 through the line I- V ofFigure 4; Figure 6 is a further view of the diffuser of Figure 2 in the direction X of Figure 3; Figure 7 is a cross-sectional part detail elevation view of a second embodiment of the present invention showing the use of an upwardly curved perforated inlet diffuser extending into a water heater storage tank; Figure 8 is an enlarged side elevation view of the inlet diffuser of Figure 7; Figure 9 is a further view of the diffuser of Figure 4 in the direction Z; Figures 10 and 11 are views of a pattern of inlet diffuser openings applicable to Figures 2 to 12 showing square or circular openings; Figures 12, 13 and 14 are a schematic perspective series of views of a tank according to the invention showing an interface of separation between incoming cold water and hot water already in the tank; and, Figures 15, 16 and 17 are a schematic perspective series of views of an already known tank without an inlet diffuser showing a simulation view of the interface of separation between incoming cold water and hot water already in the tank.

Detailed Description Figure 1 shows a water heater 20, with a steel storage tank 22 having an upright, vertical axis and a nominal capacity in this example of 50 litres. The internal hot water storage space 24 of the tank 22 is defined by a cylindrical side wall 26, a lower inwardly concave wall 28 and an upper outwardly concave wall 30. The walls are welded together leaktightly at their joints.

WO 02/101297 PCT/AU02/00719 7 The tank 22 has a cold water inlet port 32; also and a conventional hot water outlet port 34, generally adjacent the upper end. Both the inlet port 32 and the outlet 34 are radially spaced from the tank cylindrical axis. The outlet 34 has a hot water dip tube 36 extending from the opening into the highest available point in the hot water storage space 22. The inlet port 32 is located adjacent to the tank lower wall 28.

An electric heating element 38 is provided generally toward the lower portion of the hot water storage space 24 to heat the water within the tank. The heating element 38 passes through an opening made in the side wall 26 and is sickle shaped see Figure 12 to facilitate its insertion given its large surface area. This configuration is preferred because it maximises the wetted area of the element inside the tank 22. This reduces the power density, because it reduces the rate of scale build-up over time from certain water supplies. Figure 1 shows the electric heating element 38 not fully inserted in the tank 22.

The side wall 26 also has an opening toward its upper end through which a conventional temperature-pressure relief valve is inserted (neither the opening or valve are illustrated). The tank 22 includes a lining of a smooth vitreous enamel and an anode extending into the tank 22 enhances the corrosion protection the enamel provides.

Figure 2 shows a lower comer detail of the water heater 20 shown in Figure 1 with a diffuser 44 in place. In operation, cold water, replacing the hot water withdrawn, is introduced into the tank 22 by way of the inlet port 32, thence through a very short length of straight, plain bored water inlet tube 42 connected at its inward end to a straight inlet diffuser 44. The inlet tube 42 and diffuser 44 are located inwardly from the cold water inlet port 32 and extend a short distance into the lower portion of the tank.

Figure 3 shows enlarged the straight diffuser 44 comprising plural spaced distribution openings 48 each relatively smaller across its transverse axis than the diffuser inlet and, in total area of openings, larger than the diffuser inlet Figure 4 shows the cross-section of the diffuser 44 is not circular, rather it has a flat on its lower surface 45, which is to ensure its correct alignment with respect to the tank axis by mating with a correspondingly shaped opening at the tank inlet port. It also shows that the openings 48 are arranged around the lower surface of the diffuser over a downwardly-facing are subtended by an angle of 83'on either side of the vertical axis of symmetry passing through the centre of the inlet.

As is seen from figures 3 and 4 the openings 48 are formed by a lattice arrangement formed from circumferential members 47 and axial members 49. The axial members 49 have WO 02/101297 PCT/AU02/00719 8 a rounded cross section as is visible in figure 4 while the circumferential members 47 are generally rectangular in cross section. The axial members 49 are located within the diffuser 44.

Figure 5 shows further detail of the arrangement of distribution openings 48.

Figure 6 shows the innermost end 51 of the inlet diffuser 44 is circular.

Figure 7 shows a lower comer detail of the water heater 20 shown in Figure 1 -with a diffuser 46 in place. In operation, cold water, replacing the hot water withdrawn, is introduced into the tank 22 by way of the inlet port 32, thence through a very short length of straight, plain bored water inlet tube 42 connected at its inward end to an upwardly curved inlet diffuser 46. The inlet tube 42 and diffuser 46 are located inwardly from the cold water inlet port 32 and extend a short distance into the lower portion of the tank.

Figure 8 shows enlarged the diffuser 46 with curved longitudinal axis comprising plural spaced distribution openings 48 each relatively smaller across its transverse axis than the diffuser inlet 50 and, in total area of openings, larger than the diffuser inlet Figure 9 shows the appearance of the inside of the outermost end of the inlet diffuser 46 in which square distribution openings 48 are visible; as are axial members 49 and circumferential members 47.

The constructional features of the diffuser 46 are the same as that of diffuser 44 except that a curved longitudinal axis is provided. The like parts have been like numbered.

Figure 10 shows a pattern in which the distribution openings are arranged. There are nine rows of equi-spaced square cold water distribution openings 48. Each individual hole measures 1.7 mm 2 giving a total outlet area through which cold water enters the tank of 1.7 x 1.7 x 9 x 23, or 600 mm 2 approximately. The size of the inlet diffuser entry 50, that is, the inlet diffuser portion immediately upstream of the perforated region, is 18mm diameter approximately, which has a cross-sectional area of 255 mm 2 Therefore each hole of the perforated portion is relatively smaller across its transverse axis than the diffuser inlet, however, in total area of openings, larger than the diffuser inlet by a factor of 600/255 or 2.35.

The openings are substantially uniformly spaced over a total area measuring 80 mm in the axial direction by 30 mm in a circumferential or transverse direction to that axis. The size, distribution and direction of installation of the diffuser outlet openings spreads the incoming cold water as a discrete layer within the lowest portion of the storage space. The spaced WO 02/101297 PCT/AU02/00719 9 openings 48 deliver all incoming cold water as a discrete layer within the lowest portion of the storage space in the tank.

Figure 11 shows an alternative pattern made up of an array of 12 rows and 23 columns of circular distribution openings each of 1.7 mm diameter.

Figures 12, 13 and 14 show as a dark surface the interface between entering cold water and already stored water in a simulated tank of 50 litre capacity and 356 mm nominal diameter of an electrically heated water heater embodying to the invention. The tank contains a sickle-shaped heating element 38 extending circumferentially and horizontally into the stored water space 24. Each simulation represents a snapshot at a time, over a matter of seconds, between first admission of cold water as shown in Figure 12 to the final representation as shown in Figure 14 at a rate of inflow of 10 litres per minute. The behaviour evident of the cold/hot interface hugging the corner crevice has a material benefit in minimising the intermixing effect between the layers.

The spaced openings deliver all incoming cold waler as a discrete layer within the lowest portion of the storage space 24 in the tank. Incoming cold water disperses from the distribution openings 48 in plural streamline flows into the storage space 24 below the diffuser 44. Use of the curved inlet diffuser 46 leads to an essentially identical flow and intermixing pattern. This minimises convection currents that cause an excessive mixing of hot and cold water in the tank. Consequently, the diffusers 44 and 46 maximise the proportion of the capacity available at the outlet as hot water during a continuous draw-off. This effect ensures a significant improvement in the hot water delivery performance of a water heater having a storage tank. By contrast, refer now to the following series of illustrations, which show a corresponding series applied to a prior art heater.

Figures 15, 16 and 17 show as a dark surface the interface between entering cold water and already stored hot water in a simulated tank of 50 litre capacity and 356 mm internal diameter of an electrically heated water heater with no inlet diffuser as in the prior art. Each simulation represents a snapshot at a time, over a matter of 10 seconds, between first admission of cold water in Figure 8a to the final representation in Figure 8c, at a rate of inflow of 10 litres per minute. Comparison with the corresponding Figure 15 series shows that the absence of an inlet diffuser in the prior art tank leads to a rapid vertical eruption 52 of the cold interface between the layers. The eruption 52 enlarges substantially as indicated by the successively larger dark area visible against the tank wall 26 in Figures 15, 16 and 17 Furthermore, this leads to a transverse imbalance of hot and cold water, which further leads to WO 02/101297 PCT/AU02/00719 circulatory convection currents in the tank. This indicates why the hot water delivery performance of a water heater embodying the invention is improved.

Other water heater constructions are feasible options within the scope of the present invention. For example, the storage tank can be one comprising an inlet port located in the upper wall of the tank (not illustrated) and the inlet cold water tube extending from the port to a region within a matter of centimetres from the lower wall of the tank. In this case the diffuser would extend with a horizontal direction component from the lower end of the inlet tube. The diffuser may be curved or straight in this instance, as before. Also, the radius of curvature of a connection between the tube and the diffuser may be large enough to facilitate its entry into the upper end of the tank, again, through a 20 mm or similar diameter hole.

The diffuser enables incoming cold water to be dispersed from the distribution openings uniformly in plural streamline flows into the storage space below the diffuser to minimise currents that cause mixing of hot and cold water in the tank so that a greater proportion of the tank's capacity can delivered continuously at the outlet as usefully hot water.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.

Claims (15)

1. 2. A storage tank as claimed in claim 1, wherein the spaced openings are substantially uniform and aligned to deliver a discrete layer of cold water within a lower portion of the storage space upon withdrawal of hot water from the tank outlet.
2. 3. A storage tank as claimed in claim 1 or 2, in which the inlet diffuser includes a tube extending with a substantially horizontal direction component from the cold water inlet.
3. 4. A storage tank as claimed in claim 3, wherein said diffuser spans, in the horizontal direction, less than one quarter of a diameter of the tank. A storage tank as claimed in any one of claims 1 to 4, in which the plural distribution openings perforate a portion of the surface of the diffuser, that portion being subtended by an angle between 450 and 90' on either side of a vertical axis passing through the centre of the tube.
4. 6. A storage tank as claimed in any one of claims 1 to 5, wherein said plural spaced distribution openings are each smaller across its transverse axis than the diffuser inlet but in total area of openings, much larger than the diffuser inlet.
5. 7. A storage tank as claimed in claims 5 or 6, in which the cold water is distributed into the storage space as a layer spreading around a circumferential comer formed by ajoin between the lower end wall and the vertical wall.
6. 8. A storage tank as claimed in any one of claims 1 to 7, in which the tank comprises an inwardly domed lower end wall that extends upwardly a predetermined height into the tank WO 02/101297 PCT/AU02/00719 12 and the distribution openings discharge into a lowest portion of the storage space below said height.
7. 9. A storage tank as claimed in any one of claims 1 to 8, in which the inlet diffuser is curved with a radius of curvature so that no part of it touches the lower end wall of the tank while at the same time all the spaced openings are proximate the lower end wall. A storage tank as claimed in claim 9, wherein said radius curvature is between 100 and 150 nnmm.
8. 11. A storage tank as claimed in anyone of claims 1 to 10, in which the inlet and inlet diffuser are interconnected and comprise shapes and dimensions to enable both to be inserted from outside the tank through the cold water inlet port.
9. 12. A storage tank as claimed in any of claims 1 to 11, in which the cold water inlet port is between 15 and 22 millimetres diameter.
10. 13. A storage tank as claimed in any one of claims 1 to 12, including an inlet port located in the upper wall of the tank, the inlet cold water tube extending from an upper end, connected to the inlet port, to a region proximate the lower wall of the tank.
11. 14. A storage tank as claimed in any one of claims 1 to 13, wherein the diffuser extends with horizontal and radial direction components from a lower end of the inlet. A storage as claimed in any one of claims 1 to 14, wherein said openings are formed in such said diffuser by means of a lattice construction.
12. 16. A storage tank as claimed in claim 15, wherein said lattice construction is formed from axial and transverse members.
13. 17. A storage tank as claimed in claim 16, wherein said axial members are located on the inside of said diffuser relative to said transverse members.
14. 18. A storage tank as claimed in claim 16 or 17, wherein said axial members have a curved cross section to engage the flow of water passing out of said diffuser.
15. 19. A storage tank as claimed in any one of claims 1 to 18, wherein said cold water is emitted into the storage space in streams radiating from the diffuser, which streams travel also in a downward direction.