WO2001021117A1

WO2001021117A1 - Heatingreservoir such as a hotwaterbottle etc. especially for heating beds

Info

Publication number: WO2001021117A1
Application number: PCT/NL1999/000581
Authority: WO
Inventors: Franciscus Gerhardus Maria Kokkeler; Martinus Johannus Petrus Janssen; Sander Vogelaar
Original assignee: E.Co Engineering & Consultancy B.V.
Priority date: 1999-09-20
Filing date: 1999-09-20
Publication date: 2001-03-29
Also published as: AU5884899A

Abstract

Heatingreservoir such as a hotwaterbottle for domestic use etc comprising a nondeformable envelope enclosing a heat storage medium whereas the envelope is completely closed and the heat storage medium is a substance with a heat transition from solid to liquid at a temperature equal to the main temperature at which the reservoir is used and heating element being arranged inside or against the outer wall of the envelope which heating elements being connectable to an external voltage source.

Description

Title:Heatingreservoir such as a hotwaterbottle etc. especially for heating beds

The present invention relates to a heatingreservoir such as a hotwaterbottle etc.for domestic use and for use in the health-and caresector,especially suitable for heating of beds and the like,comprising an envelope with a non-deformable shape enclosing a heatstoremedium. Heatreservoirs of the type to which the present invention relates are already used for a long time in the shape of hotwaterbottles for heating beds of especially tired,incapacitated or ill persons and small childeren.Such bottles are made of metal and normally have an elongated cilindrical shape with a filling opening which can be closed by a lid with a screw fitting. With these known bottles water is normally used as heatstoringmedium.This water first is heated in a kettle on open fire or electrically to a high temperature and is thereafter poured into the bottle via the filling opening.In order to store as much heat as possible the water is heated to the highest possible temperature i.e. 100 degrees C.

A disadvantage of such known bottles resides in the fact that the water has to be heated externally which causes a certain loss of heatFurthermore the heated water has to be poured into the bottle via the narrow filling opening which can easily lead to a spill of water. Thereafter the filling opening is closed by a screwcorck which may give rise to leakages.Due to all these necesary handlings the known bottles are not user-friendly.

In order to remedy the problems mentioned before at least partly there are also known reservoirs of the present type which are closed and whereby the enclosed heatstoremedium is heated by putting the reservoir in a specially constructed oven wich can be brought on a high temperature. A disadvantage of such reservoirs resides in the fact that always a special oven is required when using such reservoirs. This makes such reservoirs due to the costs of the special oven in practice only suitable for use in larger institutions and larger care-centres were great numbers of such reservoirs are used

A further disadvantage of such known bottles resides in the fact for storing a sufficient amount of heat in the bottle the water has to be heated to approximately 100 degrees C due to which a high

temperature will prevail at the outerside of the metal envelope. At direct contact therewith burning can easily occur.In order to avoid this the bottle is normally provided with a woollen cloth. A disadvantage of such a cloth resides in the fact that the fabrics of which such a cloth is made do attract bacteria and other disease causing substances.This makes regular changes of the cloth necessary.

DE 297 13 963 U discloses further a flexible reservoir which is completely closed and filled with a heat-storage-medium with a change of phase. A heating-element being arranged inside the reservoir which element is connectable to an external voltage-source. Similar reservoirs are disclosed in GB 2 160;GB 2 135 860;Gb 2 192 118 and GB 2291 321.Such flexible reservoirs can very well be used in situations in which a large contact area with the person to be heated is required-However in circumstances in which such a large contact area is not required or even prohibited use must be made of the herebefore mentioned coventional metal hotwaterbottle.. A further disadvantage of the flexible reservoir is that the wall thereof can easily come into direct contact with the heatingelement and thus be damaged.Due to this also the heating element will run the risk of being damaged sothat its construction has to take this into account. An object of the present invention is to provide a heating reservoir of the type as described before which in the first place avoids the mentioned disadvantages of the known reservoirs. A further object of the present invention is to provide a heating reservoir with a graet heat storing capacity at moderate temperature which can be made at an acceptable costprice. In order to achieve the envisaged objects the heatingreservoir is according to the invention charaterized in that the envelope is completely closed and the heat storage medium is a medium with a phasetransition from solid to liquid at a temperature equal to a main temperature of use of the reservoir, whereas one or more heatingelements are arranged inside or against the envelope,which can be connected via electrical conductors to an external voltage source and whereby the reservoir is further provided with means for compensating differences in thermalexpansion which occur during the phase-transition of the medium.In this way an reservoir is obtained which can be heated in a simple and efficient way to the desired temparature of use and which has a limited contact area with a body to be heated due to its non- deformable shape due to which also the risk of damaging the heating element is very small. A further embodiment of the reservoir is charaterised in that the heat-storage medium consists at least partly of one or more phase-transition substances or mixtures thereof with a phase transition from solid to liquid and vice versa equal to the main temperature of use of the reservoir.

According to a further advantageous embodiment the heat-storage medium consists of a combination of one or more phase-transition substances and at leastone substance which is liquid in the area of the main temperature of use of the reservoir. Due to the combination of characteristic features as described before a heating reservoir is obtained which is very safe and which can be easely loaded with heat;simply by coupling the reservoir to an external voltage source e.g.the public electricity network.By using a medium which at least partly consists of a substance with a phase transition from solid to liquid it the cooling down trajectory of the reservoir a relative great amount of heat can be stored in the medium; which heat will be released during the said phase transition at constant temperature,which temperature when the phase transition is wellchoosen is equal to the main temperature of use of the reservoir. Generally the substance will be choosen such that the phase transition takes place at a temperature of about 60 degrees C.With such a temperature the reservoir can be put in the bed without any protecting cover and the risk of burning will be non- existent.

Although the heat storage medium may consist of one or more substances with a phase- transition it has been found that in connection with the heattransport in the medium and also in connection with the heattransfer from the medium to the wall of the reservoir it is advantageous to use a combination of one or more substances with a phase-transition and a substance which remains liquid in the temperature trajectory in which the reservoir is used.

Due to the fact that the heat storage medium during cooling and heating will undergo thermal volume changes which may cause large stresses in the envelope and eventually will damage the envelope in a further embodiment of the reservoir according to the invention measures are taken to compensate the effects of the said thermal volume changes. With an envelope having a mainly cilindrical shape such measure consist of giving the envelope an oval transvers section. In an other embodiment inside the envelope a hollow flexible element is provided which is connected to the innerwall and communicates via a small opening in the wall with the atmosphere. According to a further embodiment of the invention the heat storage medium consists mainly of wax,fat,stearine,salt,or mixtures thereof with a large phasetransitionheat and a phasetransitiontemperature from solid to liquid equal to the main temperature of use of the reservoir possibly in combination with a substance which remains liquid. Waxes,fats and stearines are substances with long chaines of carbon atoms whereby the phasetransitiontemperature depends on the choosen length of these chains of carbon atoms.These substances futher have a number of charateristics which make them especially suitable for use as heat storage medium in a closed reservoir. Some of these characteristics are;a large heat of phase transition;non agressive;low vapour pressure;non dangerous;non toxic; chemically stable;good cristal movability so that undercooling is low;small volume changes during phase transition;good heat conducting;cheap and abundantly available.

According to a further embodiment of the invention the heat storage medium consists of a substance such as parrafine of the type which when solidifying forms a porous mass whereas in the envelope also a certain amount of water is present which collects at the bottom of the reservoir which is in contact with an electrical heating element and whereby inside the reservoir a pressure prevails such that the boiling temperature of the water is at least approximately equal to the melting temperature of the parafine.Parafines of the type which when solidifying form a porous mass are known per se and are disclosed in the International patentapplication WO 94/12588.Using such parrafines in a reservoir of the present type causes the water to collect at the bottom of the reservoir with the solid porous mass of parafine on top of it.By presetting a certain pressure in the reservoir the boiling temperature of the water can be made equal to the melting temperature of the parrafine.In most cases the preset pressure will be an underpressure which lowers the boiling temperature of the water to a temperature which is acceptable for the reservoir. When now by means of the heating elements the water is brought to its boiling temperature it will evaporate and the vapour will penetrate into the porous parafine and will condens on the wall of the pores thereby giving up its heat to the parafine which thus will be heated. The condensate will under gravity run through the pores to the bottom to be heated and evaporated again. In this way a quick and efficient way for heating and melting the parrafine is obtained. In order to avoid a very violent boiling of the water in a further embodiment of the invention on the bottom of the reservoir a number of small balls of a chemically stable substance such as glass are provided.

It is to be observed that in the mentioned patentapplication a reservoir with a completely closed envelope is shown however this reservoir is not provided with means for supplying heat to the parrafine. This makes this reservoir less suitable for domestic use and for use in the health- and caresector,because of the disadvantages as mentioned before in connection with the conventional hot water bottle.This known reservoir also is not provided with any means for compensating the volume changes of the heat storage mediom which occur during heating and cooling. It has become apparent that also salts and mixtures of salts can very well satisfy the conditions as required in this connection such as mentioned herebefore in connection with waxes and stearine; a difference hereby is that such salts in general have a somewhat lesser chemical stability. An example of a salt which is very suitable for use as a heat storage medium in this type of reservoirs is sodiumacetate. A further embodiment of the reservoir according to the invention is characterised in that the electrical conductors for the supply of energy to the heating element are connected to an adaptor with pins which is connected to the outside of the envelope, which adaptor cooperates with an external basic station provided with one or more connectors in which the pins of the adaptor can be taken up whereas the basic station is provided with means for coupling with a voltage source.In this way the reservoir can easily be located on the basic station in order to be loaded with heat. All handlings in connection with the heating of a kettle with water;the filling of a bottle;the closing of the bottle by means of screwed on lid thereupon followed by covering the bottle with a protective cloth is now replaced by simply placing the reservoir in the basic station. According to a further embodiment a switch can be taken up in the electrical conductors in the vincinety of the adaptor or in the basic station for switching on the energy supply to the heating elements which switch after a certain .possibly preset, time will automatically switch of.In this way the reservoir can be placed in the basic station without immediately starting the heat loading operation;only shortly before the moment the reservoir will be used the loading of heat will be started. In the elctrical conductors a thermostatic switch can be included which possibly can be combined with the on/of switch which thermostatic switch will interrupt the energy supply as soon as a certain predetermined temperature has been reached. This last mentioned temperature will in practice be the same as the phase transition temperature of the medium or be slightly higher. The heating reservoir according to the invention as described before can be constructed in many different ways. Special charateristics hereof are further described in the accompanying claims and will be further elucidated in the following description of the figures in wich by way of example a couple of possible embodiments of heating reservoirs are shown. The following figures show: Fig, 1 schematically and not to scale a sectional view of an embodiment of a heating reservoir according to the invention comprising a heat storage medium mainly consisting of a porously sollidifying wax.

Fig.2,3 and 4 show schematically and not to scale different embodiments of heating reservoirs according to the invention. Fig.5 shows the cooling down curves of a heating reservoir comprising water as a heat storage mediom and a heating reservoir comprising sodiumacetate as a heat storage medium respectively.

Fig.1 shows a heating reservoir having a metall inner envelope 1 comprising a small amount of water2 and a relatively great amount of a porously solidifying parrafine 3 and a small amount of air 4.The presure in the inner envelope is choosen such that the boiling point of the water is approximately equal to or preferably somewhat higher than the melting point of the parrafine 3. A number of small glass grains 6 are provided on the bottom 5 whereas against the outerwall of the bottom 5 one or more heating elemente are mounted. The inner envelope 1 is surrounded by an outer envelope 8 for example made of a plastics material.The envelope 8 continues under the bottom 5 and there has a shape 9 which fits on a basic station 10. An adaptor 11 is located in the shape 9 which is provided with pins which can cooperate with bushings of a connector 12 forming part of the basic station 10. The basic station is provided with electrical conductors (not shown)which can be connected to an external voltage source e.g. the public electricity network. The adaptor 11 is connected to the heating elements 7. The basic station is further provided with a push-switch 13 via which energy supply to the connector,the adaptor and the heating elements is switched on at the desired moment.the switch is preferably of a type which switches off after a certain time.Instead of being provided on the basic station the switch may be taken up in the part 9 of the outer envelope.Possibly thermostatic safety devices may be incorporated in the electrical conductors running to the heating elements.

The heating up of the reservoir operates as follows. Under influence of gravity the water 2 will collect on the bottom 5 with on top thereof the porous mass of solidified parrafine3. After activation of the switch 13 electrical current will be supplied to the heating element 7 due to which the bottom 5 is heated. The water will also be heated to its boiling point after which the water evaporates.The vapour rises up and penetrates in the pores of the parrafine and will condens there while giving up its heat of condensation. The condensate runs back to the bottom 5 where it is again evaporated. This goes on untill the parrafine is completely melted.In this way an efficient and quick heating of the parrafine is achieved.

Although in the figure the heating element 7 is placed against the outer wall of the bottom 5 it will be evident that this heating element can also be placed inside the envelope.A very violent boiling of the water is avoided by means of the glass grains 6.

While in the embodiment as described here before porously solidifying parrafine is used as the heat storage medium it is also possible to use different storage media such as fats,waxes and salts provided that when solidifying they form a porous structure into which the water vapour can penetrate.

Fig.2 shows a heating reservoir in the form of a bottle comprising an envelope of plastics material formed by a cilindrical part 21 and an upper- and bottom surface 22 and 23. The cilindrical part 21 in transverse section can have a circular or oval shape. Within the envelope two heating elements 25 and 26 are present on which are mounted at a certain distance from each other aluminium plates 27 in order to ensure a good heat distribution also in transverse direction. The heating of the heat storage medium will by means of convection occur in a direction perpendicular to the plates. The heating elements run through the bottom 23 of the reservoir and are connected to an adaptor 28 mounted on the said bottom.At the top he heating element is coupled by means of a positioning part 29 to the upper surface 22.

The adaptor 28 is located in the part 30 of the housing which forms an elongated part of tje cilindrical envelope 21. The top surface of this part 30 is provided with an opening 31 trough which the pins 32 of the adaptor 28 can be reached. A small plate 33 is movable against spring force on the pins 32 which plate 33 closes the opening 31 in the situation in which the reservoir is uncoupled from the basic station.In the part 30 of the housing there are also located in a manner not shown a thermostatic switch and safety fuses.

A heat storage medium 40 is comprised in the cilindrical envelope of the reservoir which medium has a phase transition from solid to liquid and vice versa at a temperature which lies in the cooling down trajectory of the reservoir. Sodiumacetate is choosen as the heat storage medium however under circumstances also other salts or mixtures of salt or fat, waxes and stearine can be used.

A possibility is also to combine this heat storage medium having a phase transition with a medium which remains liquid such as water or to use solely a medium which remains liquid. This is shown schematically in the embodiment of a reservoir according to Fig.3.Here the reservoir 21 is filled with a mixture of water 50 and pieces 51 of a waxlike substance showing a phase transition. The pieces 51 may therein be provided with a thin coating of a plastics material. Above the mixture an air cushion 4 is provided such as in the embodiment of Fig.1 The heating element in this embodiment may have a simple construction or possibly be arranged on the outer wall of the envelope such as shown in Fig.1.

The choice of the heat storage medium with phase transition is mainly determined by the following considerations: high phase transition heat — a melting/solidifying temperature in the cooling down trajectory of the reservoir

— a low vapour pressure at the working temperature

— chemically stable

— non-corrosive - non-dangerous and non-toxic

— great cristal movability and consequently in the case of salts no undercooling

— small volume changes during phase transition

— good heat conducting

— non-expensive and abundantly available - good recyclable

The choosen salt sodiunacetate with a melting point of 58 degrees C fulfills these criteria very well,but also other salts, waxes.fats and stearine as mentioned before fulfill these requirements very well. In Fig.5 a grafic comparison is represented between the cooling down curve of a coventional hot water bottle filled with water and a reservoir according to the invention filled with sodiumacetate. On the vertical axis the temperature isrepresented and on the horizintal axis the time is placed. The cooling down curve of water is indicated reference sign A and the cooling down curve of sodiumacetate is indicated by B.From this it is clear that the water-reservoir is cooled down to 40 degrees C in 3 hours whereas the sodiumacetate-reservoir is cooled down to 40 degrees C in 7 hours.It is to be noted that the reservoir with the phase trasition medium gives its heat up for the greater part during phase transition. The temperature at which this occurs can be choosen as desired by choosing a suitable heat storage medium or a suitable mixture of heat transition substances. The lower part of part 30 of the reservoir is constructed and formed in such a way that this can cooperate with a basic station 42 which is provided with one or more connectors with connector- bushings in which the pins of the adaptor 28 fitFor the user it is in this way possible to simply place the reservoir in the basic station and to switch on the energy supply to the heating element by means of switch 37. All the conventionally necessary handlings such as heating of water in a kettle and pouring water in the reservoir are no longer required.Now it is sufficient to place the reservoir in the basic station and the reservoir will be loaded with heat in a short time after which it is ready for use. With a thermostat a maximum temperature which is equal to or slightly higher than the phase transition temperature can be preset. With such a temperature the reservoir can be placed in bed without any protective covering without running the risk of burnings. Such a reservoir which can be used without covering it with a cloth does not attract dirt or disease causing substances which improves the hygienic conditions. The reservoir according to the invention has a lot of user-friendly aspects such as ease of use, safe because no danger of fire and leakages,ambient friendly due to its high efficiency of heating. In order to compensate volume changes of the storage medium the cilindrical part 21 of the reservoir has an oval transverse section. the advantage of such a shape resides in the fact that on expansion of the medium the shape is deformed in the direction of a circular shape due to which the volume is expanded and the expanded medium can be accomodated.lt is also possible to compensate for the volume changes of the storage medium by arranging within the envelope a hollow flexible element which extends centrally in the longitudinal direction of the reservoir and is connected to the inner- wall of the top surface. A reservoir provided with such an element is shown schematically in Fig.4

This Fig.4 shows a different embodiment of the heating reservoir according to the invention with has a shape similar to the one shown in Fig.2 and differs therefrom in that the topsurface 22 is provided with a handlle-bar.A hollow flexible element 40 is connected to the innerwall of the topcover 22.The internal volume of the element 40 communicates via a small opening 41 with the ambient. Apart from a somwhat different embodiment of the heating element 43 the construction further is similar to that of the reservoir shown in Fig.2.The outer envelope21 preferably is made a plastics material,Which under circumsyances may consist partly or wholly of a plastics material that undergoes a change of colour when the temperature changes. Due to this it is possible to see wether the reservoir is loaded with heat or not.

From the foregoing it will be clear that the invention provides a heating reservoir which has several advantages over the conventional reservoirs and can very well be used as reservoir for heating beds.The reservoir can also very well be constructed in the shape of a flat box which can be used for heating of feet for example in rolling chairs.

Claims

Claims:

1. Heatingreservoir such as a hotwaterbottle and the likefor domestic use and for use in the health- and caresector especially suitable for heating beds and the like comprising an envelope with a non-deformable shape enclosing a heatstorage medium, characterised in that the envelope is completely closed and the heat storage medium is a medium with a phase transition from solid to liquid at a temperature equal to a main temperature of use of the reservoir, whereas one or more heating elements are arranged inside or against the envelope, which can be connected via elctrical conductors to an external voltage source and whereby the reservoir is further provided with means for compensating differences in thermal volume expansion of the medium during its phase transition.

2. Heatingreservoir according to claim l,charaterised in that,the envelope has a mainly cilindrical shape with an oval transverse section.

3. Heatingreservoir according to claim 1 or 2 characterised in that a hollow flexible element is arranged inside envelope which element is connected to the innerwall of the envelope and communicates via a small opening in the wall with the atmosphere.

4. Heatingreservoir according to claim l,2,or3 charactrised in that,the heat storage medium consists of a substance such as parrafine of a type which upon solidifying forms a porous mass,and that the envelope also comprises an amount of water which collects at the bottom of the reservoir which is in contact with an electrical heating element, whereas in the reservoir such a pressure prevails that the boiling point of the water is approximately equal to the melting temperature of the heat storage medium.

5. Heatingreservoir according to one or more of the preceding claims,charaterised in that, the electrical conductors for the current supply to the heating elements are connected to an adaptor WO 01/21117

12 with pins mounted on the outer wall of the envelope, which adaptor can cooperate with an external basic station provided with one or more connectors in which the pins of the adaptor can be taken up whereas the basic station is provided with means for coupling it to a voltage source.

6. Reservoir according to claim 5 characterised in that,a switch is taken up in the electrical conductors close to the adaptorbnor inthe basic station fot switching on the energy supply to the heating elements which switches automatically off after a certain possibly adjustable time.

7. Reservoir according to one or more of the preceeding claims which has the form of a bottle with an elongate cilindrical shape,characterised in that the completely closed envelope at one end is provided with a first elongation forming part of the cilindrical envelope and that in siad elongation at least the adaptor and possibly the switch are located wheras said elongation is provided with a closing top surface with an opening through which the connector can pass, whereas on the pins of the adaptor a plate can move against the force of a spring which plate when the reservoir is removed from the basic station will close the said opening.

8. Reservoir according to claim 7,characterised in that,between the two end faces of the cilindrical envelope one or more rod-like heating elments are provided which at mutually equal distances are provided with heat conducting plates which.plates extend transversely to to rod- like elements.

9. Reservoir according to claim 8 characterised in that, the mutual distance between the heat conducting plates is approximitely 2 cm.

10. Reservoir according to one or more of the preceeding claims,characterised in that the envelope of the reservoir at least partly made of a plastics material which at different temparatures has a different colour sothat on the basis of the colour of the envelope it can be seen wether the reservoir is loaded with heat or not.

11. Adaptor especially suitable for use in a reservoir according to claim 7, which adaptor is provided with pins enclosed by an envelope prodided with an entry-openind which extends tansversely to the pins for the insertion of a cooperating connector,characterised in that, on the adaptoφins a plate is movably arranged against springforce which plate when the connector is not inserted will close the entry-opening.