NZ585205A

NZ585205A - Hot water tank with high conductivity material placed between heat transfer tube and tank wall

Info

Publication number: NZ585205A
Application number: NZ585205A
Authority: NZ
Inventors: Craig Holmes
Original assignee: Peter Sachs Ind Pty Ltd
Priority date: 2009-05-15
Filing date: 2010-05-07
Publication date: 2010-10-29
Also published as: AU2010201827A1

Abstract

Disclosed is a water heater with a tank wall of a material of a first thermal conductivity (typically a steel wall) a tube to carry a heat transfer fluid and a sheet of material with a higher thermal conductivity than the first material juxtaposed between the tank wall and the tube.

Description

585205 COMPLETE SPECIFICATION Where priority as provided by subsection (2) or subsection (3) of section 11 of the Patents Act 1953 is wanted in respect of one or more provisional specifications, please quote the number(s) below Patent Number Date Title of Invention: AN IMPROVED HOT WATER TANK We, Peter Sachs Industries Pty Ltd, an Australian company, of 212 Zillmere Road, Zillmere, Queensland, 4034, Australia hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 585205 2 Field of the Invention.

The present invention relates to a hot water tank with improved heat transfer characteristics.

Background Art.

Australian Patent No. 603510 discloses a water heater and a method of making a water heater wherein a tube adapted to carry a refrigerant fluid is wound around a water tank and is bonded to the wall of the water tank by a heat conductive bonding material. The tube is wound around the tank under tension so as to reduce the likelihood of the heat conductive bonding material breaking during the expansion and 10 contraction of the tube and tank during use. The tank is baked in an oven to enable the bonding material to set. The bonding material performs two roles; namely to bond the coil onto the tank and to secondly improve the heat transfer performance between tube and the tank.

One problem associated with this method is that it requires the use of 15 an expensive, specially formulated bonding material that requires baking in an oven or kiln at an elevated temperature of the order of 250°C for a time period of approximately two hours so as to enable the paste to harden. The need to use an oven to harden the paste also adds to the time and cost of manufacture.

International Patent Publication No. W003/038342 seeks to overcome 20 the issues with the above described configuration by providing a heat conductive material along the length of the tube between the tube and the tank wall. The heat conductive material provided according to this application is provided in the form of a paste which either does not need to be cured, or if curing is required, may be cured under ambient conditions, hence alleviating the need for curing at elevated 25 temperatures in an oven or kiln. The paste used according to this application is a heat conductive paste preferably located along the entire length of the interface between the tube and the tank wall so as to provide heat transfer therebetween.

The provision of a heat conductive paste which does not cure provides a solution to the problem of the tube and tank expanding and contracting under 30 different heat loads and possibly separating from one another, by maintaining the heat transfer pathway between the tube and tank through the flexible paste.

It would be an advance in the art to provide a hot water tank with 585205 3 improved heat transfer between the tube and the tank.

It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

Summary of the Invention.

The present invention is directed to an improved hot water tank, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

With the foregoing in view, the present invention in one form, resides broadly in an improved hot water tank including a tank for containing a volume of heat storage fluid, a tube secured about the external surface of the tank to carry heat exchange medium to facilitate a heat transfer to the heat storage fluid contained in the tank and a high thermal conductivity material juxtaposed between the tank and the tube.

According to alternative embodiment, the present invention resides in an improved hot water tank including a steel tank for containing a volume of heat storage fluid, a tube secured about the external surface of the tank to carry heat exchange medium to facilitate a heat transfer to the heat storage fluid contained in the tank and a sheet of metal with a higher thermal conductivity than steel juxtaposed between the tank and the tube.

In still a further alternative embodiment, the present invention resides in a water heater including a water tank having a wall formed from material having a first thermal conductivity; a tube adapted to carry a heat transfer fluid secured externally about said tank wall to facilitate a heat transfer to the water contained in the tank; and a sheet of metal with a second thermal conductivity higher than the first thermal conductivity juxtaposed between the tank and the tube.

The tank of the preferred embodiment will normally be manufactured of steel or similar metal in order to reduce costs. The tank will normally be cylindrical and hold a volume of water or similar fluid.

The water heater of the present invention may be of the heat exchange or displacement type. 585205 For the purpose of the present description, the term "heat storage fluid" includes particularly water and any other fluid to capable of storing heat such as glycol for example.

For the purpose of the present description, the term "heat exchange 5 medium" includes any medium which is capable of transferring heat including water, refrigerant compositions and compounds and the like.

Preferably, the tube is wound around the tank with the high thermal conductivity material juxtaposed between the tank and the tube. Normally, the tube will be formed of copper or a copper-based alloy. The tube may be fastened, typically 10 mechanically, at one or more locations to the wall of the tank or to the high thermal conductivity material juxtaposed between the tank and the tube.

Preferably, the tube is mechanically fastened at first end adjacent either the upper or lower end of the tank, the tube then wound about the exterior of the tank under tension, and the tube mechanically fastened at a second end adjacent the other 15 of the upper or lower end of the tank. In this manner, the tension under which the tube is wrapped around the tank maintains a close abutment of the tube with the tank wall, even during expansion and contraction of the tube and tank or in use.

More than one tube may be wound around the tank and carry heat conductive material.

The tube used according to the present system is preferably flattened so that it is substantially D-shaped in cross-section. Normally, the flattened face of the tube is located towards the wall of the tank, and either in direct contact or adjacent to the high thermal conductivity material juxtaposed between the tank and the tube.

The present invention also includes a high thermal conductivity 25 material juxtaposed between the tank and the tube. According to a particularly preferred embodiment, the high thermal conductivity material is provided in the form of one or more sheet members, typically copper sheet members, copper being relatively available and having the requisite high thermal conductivity.

Preferably, the high thermal conductivity material is provided as one or 30 more sheet members which substantially cover the external surface of the cylindrical wall of the tank. In this manner, the heat from the material in the tube can be dispersed over a larger area, in contrast with a tube wrapped about the tank and in 585205 thermal contact with the tank only at the area of the tube. Thereby heat may be transmitted more effectively to the fluid in the tank.

The high thermal conductivity material may be secured to the tank wall or simply clamped there by the tension under which the tube is wound about the tank.

In an alternative configuration, the high thermal conductivity material may be provided as a strip which is located beneath the tube. Where provided in this form, the strip may be applied to the exterior of the tank contemporaneously with the placement of the tube.

According to a most preferred embodiment where the high thermal 10 conductivity material is provided as a strip, the strip, heat transfer paste (as described below) and tube may be wound about the tank at the same time and by a single unit.

Typically, the high thermal conductivity material is provided as a layer of material. Preferably, the layer of material, possibly a unitary sheet, will be wrapped about the tank under tension in order to maximise the thermal bond between 15 the layer and the tank notwithstanding the flexing of the materials caused by expansion and contraction in use.

Additional heat transfer material in the form of a paste or similar may be inserted or injected between the tube and the sheet. Preferably, heat transfer paste may be provided as a sealant between the sheet and the side of the tube in order to 20 provide additional heat transfer area. Heat transfer paste may bridge from the external surface of the sheet to a side portion of the tube.

Preferably, the paste does not need to be cured, or if curing is required, it may be cured under ambient conditions. A suitable heat transfer paste is "HTSP Silicone Heat Transfer Compound Plus", marketed in Australia by Electrolube. This 25 is a silicone oil-based heat transfer paste with a thermal conductivity of approximately 3.0 W/mK. Other suitable kinds of heat transfer paste, such as "Bostik 1128 Heat Transfer Sealer" marketed in Australia by Bostik, may also be used. There are several benefits associated with use of a heat transfer paste both between the tank and the sheet member and between the sheet member and the tube including improved heat 30 transfer performance of the system. Additionally, the need for a curing step is eliminated which results in a reduction in production time. 585205 6 The heat transfer paste may be applied to the exterior of the tank contemporaneously with the placement of the tube or it may be applied separately therefrom with the tube wound onto the tank at a later time.

Heat transfer paste may be applied between the tank and the high 5 thermal conductivity material juxtaposed between the tank and the tube, and/or between the tube and the high thermal conductivity material juxtaposed between the tank and the tube. This configuration may maximise the heat transfer area for the system.

As the heat transfer paste is typically non-curing, the paste may cause 10 undesirable mess after application. In cases such as these where heat transfer paste is used ,once the heat transfer paste has been applied and the tube wound about the tank, a film or similar coating may be applied to the tank and tube in order to avoid or limit mess during handling. The film will typically be applied as a plastic sheet wrapped about the tank.

Brief Description of the Drawings.

Various embodiments of the invention will be described with reference to the following drawings, in which: Figure 1 is a sectional schematic view of a tube wound about a steel water tank according to a reference configuration.

Figure 2 is a photograph of the configuration illustrated in Figure 1.

Figure 3 is a sectional schematic view of a tube wound about a steel water tank according to a first preferred embodiment of the present invention.

Figure 4 is a photograph of the configuration illustrated in Figure 3.

Figure 5 is a sectional schematic view of a tube wound about a steel 25 water tank according to a second preferred embodiment of the present invention.

Figure 6 is a photograph of the configuration illustrated in Figure 5.

Detailed Description of the Preferred Embodiment.

According to a preferred embodiment of the present invention, an improved water tank with increased heating efficiency is provided. 30 The water tank 10 illustrated in the embodiments illustrated in Figures 3 and 4, and 5 and 6 each has a wall 11 formed from steel or stainless steel. Each tank 10 also has a tube 12 adapted to carry a heat transfer fluid, secured externally about the tank wall 11 to facilitate a heat transfer to the water contained in the tank 10 with sheets 13 of a high thermal conductivity metal such as copper juxtaposed between the tank 10 and the tube 12.

A layer of heat transfer paste 14 is located between the tank wall 11 and the copper sheets 13.

The embodiment of the invention illustrated in Figures 3 and 4 has a tube 12 wound directly onto copper sheet members 13 interposed between the tube 12 and the tank wall 11.

The embodiment of the invention illustrated in Figures 5 and 6 has a tube 12 wound onto copper sheet members 13 interposed between the tube 12 and the tank wall 11, with heat transfer paste 14 juxtaposed between the tube 12 and the copper sheets 13 as well as between the tank wall 11 and the copper sheets 13. Also illustrated in Figure 6 is the layer of plastic coating 15 applied to the exterior of the arrangement in order to avoid mess.

As the performance of water heaters varies with water temperature, the air temperature and with humidity levels, tests in comparison to a reference model are performed under identical conditions.

The reference tank is illustrated in Figures 1 and 2. The reference tank includes a wall 11 formed from steel. This tank also has a tube 12 adapted to carry a heat transfer fluid secured externally about the tank wall 11 to facilitate a heat transfer to the water contained in the tank 10 with a layer of heat transfer paste 14 juxtaposed between the tube 12 and the tank wall 11. The layer of plastic coating 15 which is normally applied over the configuration illustrated has been removed from the upper two portions of the tube 12.

In the testing, the test tanks were also manufactured of steel in order to collect comparable results.

The results of the tests comparing the embodiment illustrated in Figures 3 and 4 with the reference tank and comparing the embodiment illustrated in Figures 5 and 6 with the reference tank are outlined below, in Tests 1 and 2 respectively.

Test 1 - Reference tank versus Tank illustrated in Figures 3 and 4 (New Tank 1) 585205 1. Time to heat to a predetermined temperature; • Reference Tank 265 min • New Tank 1 260 Min 2. Power Used to heat to a predetermined temperature; • Reference Tank 4045 kWh • New Tank 1 3935 kWh Summary of Test 1. New Tank 1 - 2% less time than standard tank. 10 2. New Tank 1 - 2.5% less power than standard tank.

Test 2 - Reference tank versus Tank illustrated in Figures 5 and 6 (New Tank 2) 1. Time to heat to a predetermined temperature; • Reference Tank 300 min 15 • New Tank 2 270 min 2. Power used to heat to a predetermined temperature; • Reference Tank 4560 kWh • New Tank 2 4200 kWh Summary of Test 1. New Tank 2 - 11% less time than standard tank. 2. New Tank 2 - 7% less power than standard tank.

Therefore in summary, New Tank 1 (embodiment illustrated in Figures 3 and 4) is slightly better performing than the reference tank by approximately 2% in 25 terms of both time to reach a reference temperature, and in power consumed to do so. New Tank 2 (the embodiment illustrated in Figures 5 and 6), however, shows significantly increased performance over the reference tank by approximately 11% in terms of time to reach a reference temperature and approximately 7% in power consumed to do so.

In the present specification and claims (if any), the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers. 585205 9 Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an 5 embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be 10 understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Received by B8QME25 Aug 2010

Claims

1. An improved water heater including a water tank having a wall formed from material having a first thermal conductivity; a tube adapted to carry a heat transfer fluid secured externally about said tank wall to facilitate a heat transfer to the water contained in the tank; and a sheet of metal with a second thermal conductivity higher than the first thermal conductivity juxtaposed between the tank and the tube.

2. An improved water heater including a steel tank for containing a volume of heat storage fluid, a tube secured about the external surface of the tank to carry heat exchange medium to facilitate a heat transfer to the heat storage fluid contained in the tank and a sheet of metal with a high thermal conductivity greater than steel juxtaposed between the tank and the tube.

3. An improved water heater as claimed in claim 1 or claim 2 of either the storage or instantaneous type.

4. An improved water heater as claimed in any one of the preceding claims wherein the tube is wound around the tank with the high thermal conductivity material juxtaposed between the tank and the tube.

5. An improved water heater as claimed in any one of the preceding claims wherein the tube is formed of copper or a copper-based alloy.

6. An improved water heater as claimed in any one of the preceding claims wherein the tube is fastened at one or more locations to the wall of the tank or to the high thermal conductivity material juxtaposed between the tank and the tube.

7. An improved water heater as claimed in any one of the preceding claims wherein the tube is mechanically fastened at a first end adjacent either an upper or lower end of the tank, the tube then wound about the exterior of the tank under tension, and the tube mechanically fastened at a second end adjacent the other of the upper or lower end of the tank.

8. An improved water heater as claimed in any one of the preceding claims wherein the tube used is flattened so that it is substantially D-shaped in cross-section. Received by B8QME25 Aug 2010 11

9. An improved water heater as claimed in any one of the preceding claims wherein the high thermal conductivity material is secured to the tank wall or clamped there by the tension under which the tube is wound about the tank.

10. An improved water heater as claimed in any one of the preceding claims 5 wherein the high thermal conductivity material is provided as one or more sheet members which substantially cover the external surface of a cylindrical wall of the tank.

11. An improved water heater as claimed in any one of claims 1 to 9 wherein the high thermal conductivity material is provided as at least one strip which is 10 located beneath the tube.

12. An improved water heater as claimed in claim 11 wherein the at least one strip is applied to the exterior of the tank contemporaneously with the placement of the tube.

13. An improved water heater as claimed in claim 11 wherein the at least one 15 strip, heat transfer paste and tube are wound about the tank at the same time and by a single unit.

14. An improved water heater as claimed in any one of the preceding claims wherein additional heat transfer material in the form of a paste or similar is be inserted or injected between the tube and the sheet. 20

15. An improved water heater as claimed in claim 14 wherein the heat transfer paste is applied to the exterior of the tank contemporaneously with the placement of the tube

16. An improved water heater as claimed in claim 14 wherein the heat transfer paste is applied to the exterior of the tank separately from the tube with the 25 tube wound onto the tank over the heat transfer paste at a later time.

17. An improved water heater as claimed in any one of claims 14 to 16 wherein the heat transfer paste is applied between the tank and the high thermal conductivity material juxtaposed between the tank and the tube.

18. An improved water heater as claimed in any one of claims 14 to 17 wherein 30 the heat transfer paste is applied between the tube and the high thermal conductivity material juxtaposed between the tank and the tube.

19. An improved water heater as claimed in any one of claims 14 to 18 wherein once the heat transfer paste has been applied and the tube wound about the Received by B8QME25 Aug 2010 12 tank, a film or similar coating is applied to the tank and tube in order to avoid or limit mess during handling.