Patent Application
20120241120
The invention relates to a latent heat store comprising a plurality of heat exchanger units which are arranged alongside one another and each comprise at least one phase change store according to the preamble of Claim 1.
At present, the use of so-called latent heat stores is increasingly being discussed and promoted. Latent heat stores are used for the temporary intermediate storage of heat, with a phase change of the widest variety of substances in the event of a change in temperature being utilized. In recent years, a preferred field for the application of such latent heat stores has primarily also become vehicles with internal combustion engines or fuel cells with or without reformation. In this case, the waste heat which arises during operation is preferably intermediately stored in an appropriate latent heat store, in order to provide heat energy for the start-up phase, primarily after a pause in operation where the engine is switched off, for preheating or heating up the widest variety of components, such as catalytic converters, engine components or the like.
In coming years, this will have to be taken into consideration increasingly owing to ever stricter emission regulations. In the case of internal combustion engines, the start-up phase specifically forms a relatively large number of undesired or harmful exhaust gas components, which form because vehicle components are not yet at operating temperature. Of considerable importance in this context are not only the catalytic converters, which to some extent are used diversely, but also components of the combustion chambers of the engine and moving parts of the engine.
A good heat exchange between the heat store masses, or the phase change material, and the heat exchanger fluid, in particular the heat exchanger liquid, is decisive for discharging and charging the heat stores.
By way of example, DE 41 33 360 C2 and DE 38 21 358 A1 have already disclosed latent heat stores with phase change material, wherein the heat exchanger fluid does not flow rectilinearly between the entrance and the exit of the latent heat store on the shortest path, but instead by detours, and therefore by an extended flow path through the store. As a result, an improved uptake and/or release of the heat between phase change store material and heat exchanger fluid should be achieved.
In addition, DE 90 05 049 has already disclosed a cylindrical latent heat store, in which the heat medium is supplied to the individual segments on one side of the cylinder and then the heat medium flows through the heat segments from this point transversely to the opposite side, and the heat medium is collectively discharged in an appropriate manner in a lateral collection channel.
In addition, DE 4 322 813 has already described the use of vacuum insulations and of getter elements, and DE 10 2004 023 347 A1 has already described the use of thin-layer electric heaters between two flat sides of two adjacent heat segments.
However, it has been found that such latent heat stores cannot realize optimum charging and therefore also discharging of heat, since regions of differing warmth or fewer warm regions arise. Accordingly, the storage size of the latent heat store or the power density, i.e. the amount of power per unit volume, of such latent heat stores is also not optimal.
In this respect, it is an object of the invention to propose a latent heat store of the type mentioned in the introduction, with which improved heat management, in particular in relation to the charging of heat and the discharging of heat, is realized, and/or with which an improved usability for mobile applications is realized.
Proceeding from a latent heat store of the type mentioned in the introduction, this object is achieved by the characterizing features of claims 1, 2, 4 or 7. Advantageous embodiments and developments of the inventions are possible by virtue of the measures mentioned in the dependent claims.
Accordingly, a latent heat store according to the invention is distinguished, by way of example, by the fact that at least one common intake for supplying the heat exchanger fluid to the heat exchanger units and for dividing said fluid into a plurality of separate partial flow sections and also at least one common drain for discharging the heat exchanger fluid from the heat exchanger units and for bringing all partial flow sections together are provided, such that the heat exchanger units arranged between the intake and the drain form a stack collectively exposed to the flow, and such that the heat exchanger units of the stack collectively exposed to the flow are connected in parallel to one another, wherein the inflow point of the heat exchanger unit is arranged in the central region of the heat exchanger unit and the outflow point of the heat exchanger unit is arranged in the radially outwardly arranged casing region of the heat exchanger unit, or wherein the inflow point of the heat exchanger unit is arranged in the radially outwardly arranged casing region of the heat exchanger unit and the outflow point of the heat exchanger unit is arranged in the central region of the heat exchanger unit, such that the heat exchanger fluid flows in the radial direction along the heat exchanger units substantially over the entire cross section thereof, wherein the length of all partial flow sections of the heat exchanger fluid from the intake to the drain is substantially of equal length.
According to the invention, the sums of all lengths of the individual flow paths between the entrance and the exit of the latent heat store are approximately the same in the case of parallel flow through the stack. In contrast to the latent heat store disclosed in DE 90 05 049, this applies according to the invention substantially to the entire cross section of each heat exchanger unit, since the fluid flows radially from the inside outward or radially from the outside inward. Accordingly, according to the invention the same pressure losses are realized in the entire inner region of the housing or along the surfaces of all heat exchanger units and therefore along all partial flow sections.
By contrast, according to DE 90 05 049, the fluid flows through the regions outside the direct, rectilinear connection line of the two inflow and outflow points each arranged on the outside at the edge of the cylinder and on opposing sides to a significantly smaller degree compared to the direct intermediate region along the straight, central connection line.
According to the invention, provision is preferably made of a central inflow or alternatively a central outflow of the heat medium in the center of the preferably substantially circular housing and/or the heat exchanger units or segments. In each heat exchanger unit, the heat fluid therefore preferably flows from the centrally or axially arranged inflow point from inside in the radial direction and primarily advantageously over the full extent or over the entire cross section or over the entire circumference of the heat exchanger units uniformly outward to the preferably substantially annular outflow point or to the lateral surface of the housing or of the heat store, where it is collected and collectively discharged. Alternatively, the heat fluid is guided from outside via the substantially annular inflow point or from the lateral surface of the housing/heat store in the radial direction and substantially over the full extent over the entire cross section or circular surface inward to the central or axially arranged outflow point.
This radially oriented flow of the fluid leads to a considerably better or to an optimum heat distribution with all-over uniformity over the cross section of the heat exchanger units. By contrast, in the prior art there are edge regions through which the fluid flows to a lesser extent on both sides of the connection line formed centrally and rectilinearly through the heat exchanger plates. In these edge regions, in the prior art the heat fluid on the one hand has to cover a path which is significantly greater, specifically by as much as the factor Pi/2 (i.e. about 1.7), than a rectilinear connection line directly through the center or a direct connection line which corresponds exactly to the diameter. On the other hand, in the prior art dead regions are formed for the heat fluid laterally alongside said connection line, in which dead regions said fluid has regions of return flow/vortices and/or only a very low flow or possibly even no flow at all. Therefore, existing latent heat stores cannot realize optimum charging and therefore also discharging of heat, since regions of differing warmth or fewer warm regions arise. Accordingly, the storage size of the latent heat store or the power density, i.e. the amount of power per unit volume, of existing latent heat stores is also considerably poorer than in the case of the invention.
By way of example, the heat exchanger units according to the invention have a short intake flow path in the region of the intake, but a correspondingly long drain flow path to the drain of the latent heat store. In the case of heat exchanger units in the region of the drain, the situation is accordingly the opposite, i.e. a long intake flow path but a correspondingly short drain flow path. According to the invention, however, the sum of the intake flow path to the heat exchanger unit and the path along the heat exchanger unit plus the drain flow path of said heat exchanger unit is virtually the same for all heat exchanger units of the stack and over the entire circumference of the heat exchanger units.
Alternatively or in combination therewith, the flow resistances of all partial flow sections of the heat exchanger fluid from the intake to the drain are substantially of the same magnitude. By way of example, the cross-sectional ratios and the length ratios of the individual partial flow sections are matched to one another in such a manner, e.g. by means of throttle and/or regulating elements, that the approximately identical flow resistances are established.
Given substantially identical cross-sectional ratios of the individual partial flow sections, it is preferable that flow resistances of approximately the same magnitude are realized by the length of all partial flow sections of the heat exchanger fluid from the intake to the drain being substantially of equal length.
Accordingly, it is an advantage of the invention that all heat exchanger units of the stack are exposed to approximately the same pressure losses on account of the features according to the invention, and thus approximately identical volumetric flow rates are established for the individual heat exchanger units. This in turn has the effect that approximately identical heat flows are supplied to and discharged from the heat exchanger units, which in turn leads to the same or more homogeneous charging and discharging of the phase change stores of the heat exchanger units for the entire stack, such that a virtually optimum heat distribution is achieved throughout the latent heat store. Accordingly, in contrast to the prior art, the latent heat store according to the invention can also make use of its maximum storage capacity.
For the case of application, this means that the highest or the maximum possible energy density/power density is achieved for the structural volume of the latent heat store used. Consequently, compared to the prior art, given an identical amount of useful heat the required structural volume of the latent heat store is reduced, which is a crucial advantage specifically for applications with very limited available space, e.g. in vehicle applications, etc.
With a latent heat store according to the invention, it is possible to provide more heat energy, e.g. to exhaust gas catalytic converters and/or components of the engine, etc., than is achieved with latent heat stores according to the prior art given the same structural volume after a preceding stoppage phase.
The latent heat stores disclosed in DE 41 33 360 C2 and DE 38 21 358 A1 have a serial connection of appropriate heat exchanger units, such that a higher temperature level and therefore greater amounts of heat energy are stored at the intake of the latent heat store than is possible in the drain region of the latent heat store in the case of cooled heat exchanger fluid. Accordingly, primarily the existing heat exchanger units cannot store an optimum or high amount of energy in the outflow region of the latent heat store, which leads to a relatively low energy efficiency for the entire stack or latent heat store.
It is preferable that all heat exchanger units have a substantially identical form. It is thereby possible for a stack to be formed from identical heat exchanger units, such that the production of the individual heat exchanger units is improved on account of the production of a relatively large number of identical heat exchanger units.
In a particular development of the invention, the housing has a substantially cylindrical form. In contrast to a cuboidal housing of the latent heat store, a cylindrical housing has improved stability and pressure properties and also flow properties.
It is also possible for numerous identical heat exchanger units to be stacked advantageously both in a cuboidal and in a cylindrical housing in the longitudinal direction of the housing or along the central mid-axis. This is a major advantage primarily in the case of virtually identical heat exchanger units, since these housings have no significant changes in cross section along the stack, primarily if the stacks are correspondingly oriented transversely in or perpendicular to the direction of the central mid-axis or longitudinal axis.
By way of example, this is a central difference in relation to the stack and to the passage of flow through the latent heat store according to DE 41 33 360 C2, wherein the stacks are not stacked transversely to the mid-axis, but rather in the direction of the mid-axis, such that they have to have the widest variety of cross-sectional areas in the case of the cylindrical housing disclosed. Accordingly, in this case it is not possible to produce and stack any identical heat exchanger units, as is advantageously effected however according to the present invention.
It is preferable that the heat exchanger units are produced substantially from high-grade steel, with the provision of a high-grade steel with relatively good thermal conductivity being advantageous. Accordingly, a high chemical resistance and also an advantageous thermal conductivity function of the heat exchanger units are achieved.
In the case of a latent heat store according to the preamble of Claim 1 and/or as an advantageous variant of inventive features mentioned above, the object of the invention can also be achieved in that the heat exchanger units have at least one spacer for fixing a spacing for the heat exchanger fluid to flow through between the heat exchanger units. It is thereby possible for separately producible and/or mountable spacers and/or fixings for producing a spacing between the heat exchanger units to be dispensed with. This leads to a particularly advantageous production of the latent heat store according to the invention. The spacers according to the invention for the heat exchanger units have the effect that a defined through-flow of the heat exchanger fluid in the intermediate region between two heat exchanger units is ensured. This leads to advantageous flow conditions and pressure losses within the latent heat store or the stack according to the invention, which in turn ensures advantageous heat management in terms of the charging and discharging of the latent heat store.
It is preferable that the phase change stores comprise at least the spacers and that the phase change stores are in the form of spacers. This means that the phase change stores are dimensioned in such a way that they realize a predefined or defined spacing between two heat exchanger units, and at the same time form open flow cross sections for the heat exchanger fluid between the heat exchanger units. Primarily in the case of identical heat exchanger units, it is also ensured in this respect that identical flow conditions and therefore pressure losses are ensured between the individual heat exchanger units, which leads to an advantageous flow through the entire stack or latent heat store.
In an advantageous embodiment of the invention, the spacers are in the form of a bend of a heat exchanger unit. By way of example, the heat exchanger units can be produced from deformed/reformed metal sheets, in which case by way of example two advantageously shaped metal sheets are connected to one another in such a way that a storage volume for the phase change material is generated. For heat exchanger units which are correspondingly produced from sheet material or else heat exchanger units which are produced from metal in another way, it is possible to provide advantageous bends, which at the same time are in the form of spacers according to the invention. This leads to a particularly cost-effective method for producing the individual heat exchanger units and therefore the entire latent heat store.
By way of example, the bends may fulfill not only spacing functions, but also further functions, e.g. centering, i.e. alignment in relation to the central mid-axis and/or to the housing, and/or also a fixing function in terms of twisting, adjustment of the heat exchanger units both in the transverse direction and in the longitudinal direction and/or in the radial direction of the latent heat store according to the invention. On account of the numerous functions which can be realized by spacers and/or bends, the latent heat store according to the invention is realized with an advantageous design and such that it can be manufactured cost-effectively.
Alternatively or in combination therewith, it is also possible for example for adjacent heat exchanger units to be welded or spot-welded to one another or fixed cohesively to one another and/or spaced apart, in order inter alia to suppress a relative movement therebetween, such that as far as possible there is no change concerning the flow paths or pressure losses between the heat exchanger units and/or between heat exchanger units and the housing even in the long term. The heat exchanger units, which preferably consist essentially of sheet metal, or the phase change stores can therefore have inter alia depressions or recesses such as grooves, etc., and/or protrusions or elevations or the like, in order to ensure an advantageous fluid flow and/or spacing and/or fixing/holding between two adjacent heat exchanger units and/or in relation to the housing of the latent heat store.
A latent heat store according to the preamble of Claim 1 and/or according to one of the above-mentioned embodiments can advantageously be distinguished by the fact that the heat exchanger units have at least one anti-twist device for preventing radial twisting of heat exchanger units. It has been found that this is advantageous specifically when radially symmetrical housing forms or heat exchanger units are used. In this case, anti-twist means primarily make advantageous, stable flow conditions possible between the heat exchanger units or in the latent heat store according to the invention. These clearly defined flow conditions in and around the stack or within the latent heat store, which as far as possible are stable even over relatively long periods of time, in particular throughout the service life of the latent heat store, are of significant importance, for avoiding disadvantageous effects concerning the maximum realizable energy density or storage capacity.
It is preferable that the spacers of the heat exchanger units are in the form of an anti-twist device. A corresponding multiple function reduces the outlay on design and therefore production.
The housing advantageously has at least one thermal insulation unit as a sheathing. It has been found that primarily a vacuum insulation unit is particularly advantageous, since a distinctly high or advantageous thermal insulation action is achieved with a relatively small insulation volume. This is particularly advantageous primarily for vehicle applications, since in this case there is generally relatively little space available.
A particularly advantageous embodiment, which achieves the object according to the invention, of a latent heat store according to the preamble of Claim 1 having a vacuum insulation unit as a thermal insulation unit and/or according to one of the above-mentioned variant embodiments is distinguished by the fact that the vacuum insulation unit comprises at least one getter unit with a getter material. An advantageous getter material ensures a particularly advantageous vacuum in the vacuum insulation unit. In this respect, the gas molecules enter into a direct chemical bond with the atoms of the getter material at the surface of the getter material, or the gas molecules in the vacuum are detained by sorption. As a result, gases or molecules which remain are appropriately bound in the vacuum, such that the vacuum of the vacuum insulation unit can be improved or can be retained even over a relatively long time.
As the getter material, use is made for example of barium, aluminum, titanium, zirconium and/or magnesium and/or the alloys thereof. The getter material is preferably in the form of disks, pellets, rings or the like, and a plurality of such getter units are secured together, for example, by means of a securing element, for example by means of a metal sheet or the like which is to be formed appropriately.
It is preferable that the getter material is arranged on the side lying opposite an evacuation opening of the housing or of the insulation unit. Since the getter material acts like a pump, the vacuum can thereby be generated in an advantageous manner, in which case narrow points or the like which may be present between the two housings or the opposing sides of the latent heat store are not disadvantageous for the evacuation.
By heating the getter material, the latter can be regenerated or reactivated, such that substantially the original binding capacity or sorption capacity of the getter material is available again. This regeneration or reactivation can be effected very frequently.
The getter material is advantageously arranged in the region of the intake of the latent heat store within the vacuum insulation unit. By way of example, the heat exchanger fluid can thereby be advantageously provided for heating or regenerating the getter material. This regeneration of the getter material can be initiated or carried out, for example, after predefined time intervals and/or if required by means of advantageous sensors or the like.
A vacuum which is advantageous also in the long term in the vacuum insulation unit is of great advantage primarily for ensuring the high thermal insulation action. Accordingly, the amount of heat stored by the phase change material can also be advantageously provided after relatively long periods of time for appropriate applications, such as the heating of vehicle components or the like.
In principle, waste heat from the cooling water and/or from the exhaust system and/or from the brake system and/or from other vehicle components which produce waste heat can be used in vehicle applications for heat storage according to the invention. By way of example, in the case of fuel cell vehicles, too, it is possible to use appropriate amounts of waste heat from fuel cell components and/or from stationary heating systems or similar contributions for filling the latent heat store according to the invention.
For the latent heat store according to the invention, it is generally advantageous to provide a heat transfer oil or the like as the heat exchanger fluid, which is pumped through the latent heat store or pumped along the heat exchanger units, for example by means of an advantageous pump.
In addition, it is advantageous by way of example to provide as the phase change material a salt or the like which has a phase change at about 200° C., for example. This phase change material is stored in the phase change store or in appropriate chambers of the heat exchanger units, which, for example, are evacuated.
The latent heat store advantageously has an inner housing, in which the stack with the heat exchanger units is arranged, and an outer housing, with thermal insulation or a vacuum being provided between the inner housing and the outer housing.
It is preferable that (if possible all) components of the latent heat store according to the invention which come into contact with the vacuum are formed from high-grade steel, e.g. 1.4301 or the like. Compared to many other metals, high-grade steel has, for example, a lower outgassing rate.
It is preferable that the vacuum insulation unit at least in parts has a surface layer or a coating for reducing the emissions into the vacuum. By way of example, a relatively favorable material is provided for the vacuum insulation unit or the housing. Losses resulting from heat radiation can be reduced by up to about 50% for example by an advantageous low-emission coating or surface layer with an advantageous material, such as preferably copper and/or e.g. silver, aluminum, zinc, etc. In principle, it is advantageous to use low-emission materials for the vacuum insulation unit.
It is advantageous that (if possible all) components of the latent heat store according to the invention which come into contact with the vacuum are specially treated or formed. Firstly, the surfaces are formed with particular purity, in order to ensure as far as possible a low outgassing rate and/or also a short evacuation time.
In a particular development of the invention, the surface of the vacuum insulation unit or of (if possible all) components which come into contact with the vacuum is at least partially advantageously electropolished and/or blasted with glass beads or the like, for example. By way of example, an emittance of less than 3% can be achieved by the measures according to the invention.
Secondly, all surfaces which emit heat or come into contact with the vacuum should have the smallest possible emittance, in order to keep radiation losses as small as possible. To this end, such surfaces are preferably likewise electropolished and/or advantageously coated.
Advantageous, for example flexible, holding and/or fixing devices can be provided for fixing or arranging the inner housing or the stack within the outer housing. By way of example, (metal) strips or the like and/or spiral springs or spring elements can be used for holding both in the longitudinal and/or in the radial direction. Holding components having a relatively poor thermal conductivity (e.g. <10 W/mK) are particularly advantageous, such that thermal conduction between the stack or the inner housing and the outer housing is minimized as far as possible. This also applies in relation to advantageous intake lines and/or drain lines between the outer housing and the inner housing or the stack of the latent heat store.
As an alternative to or in combination with strips, springs or the like, the holding and/or fixing device can be in the form of a so-called supported vacuum insulation system. A supported vacuum insulation system advantageously comprises numerous insulating/supporting elements such as insulating fibers, e.g. made of glass fibers or the like, wherein the space in which these are arranged is evacuated and, in particular applications, may be sealed off by means of a sleeve or cladding layer, e.g. made of foil or the like. The inner housing and the outer housing of the latent heat store according to the invention substantially advantageously form the cladding layer, such that a separate or additional foil or the like can be dispensed with.
In particular applications, if the vacuum insulation system is in the form of a supported vacuum insulation system, it is advantageously possible to dispense with an additional holding and/or fixing device between the two housings. In this case, the insulating/supporting elements can perform the holding and/or fixing function. If corresponding (metallic) holding and/or fixing devices are dispensed with, it is possible to achieve a particularly advantageous insulation action.
In principle, it is advantageous to form both the holding and fixing components between the two housings and also the intake and drain lines in such a manner that no disadvantageous stresses occur on account of thermal expansion. By way of example, the intake and/or the drain lines have a bent form and/or have advantageous regions in order to be able to compensate for changes in length of the lines as far as possible with low stresses.
By virtue of the structure according to the invention and the advantageous geometry of the heat exchanger units with the phase change store material, flow advantageously passes through the latent heat store according to the invention, such that essentially no dead regions or regions through which flow passes poorly are generated within the store, as was readily the case to a considerable extent to date in the prior art.
Primarily where the latent heat store according to the invention is used for electric vehicles or else hybrid vehicles with an electric drive motor, it may be particularly advantageous for achieving the object of the invention to arrange at least one electric heating element for heating the phase change stores and/or heat exchanger units in particular within the heat exchanger housing.
Specifically in the case of electrically driven vehicles, there are large electric accumulators on board, but little or virtually no waste heat from the drive motor which can be used for the heat absorption for the latent heat store according to the invention. This invention provides that an electric energy supply or heat storage can be realized in an advantageous manner, for example the most homogeneous possible heating and therefore storage of the energy/heat introduced.
By way of example, at least two separate latent heat stores according to the invention are provided in a vehicle. A first latent heat store, which is supplied or charged with heat energy, e.g. waste heat from the brake system and/or from the electric drive motor, etc., and a second latent heat store, which is supplied or charged with electric energy, e.g. from the electric traction battery/accumulator, a photovoltaic unit arranged on the sleeve or outer skin of the vehicle and/or from a vehicle-external or stationary energy supply, e.g. from the “electric socket” or from an electric “filling station”. The vehicle-external charging variant of the invention in particular makes it possible for the latent heat store according to the invention to be supplied or charged with energy at the same time or additionally during the electric charging of the traction battery/accumulator, for example.
It is not only possible for a latent heat store according to the invention to be supplied or charged with a relatively large amount of energy very quickly. Rather, a considerably more advantageous energy storage in the vehicle or on board can be realized as a result in view of a comparison, relating to a weight and/or volume unit and also to the costs, with energy storage by means of a traction battery/accumulator. Latent heat stores according to the invention can advantageously provide the stored energy/heat inter alia for the air conditioning or heating of a passenger cabin or the like and/or for preheating vehicle components such as the battery/storage battery, catalytic converters, etc. If appropriate, in this latent heat store according to the invention the heat exchanger fluid is in the form of gas, preferably air. This has the effect that the stored heat/energy can be taken up directly from the gas/air by the heat exchanger units or the phase change material and conducted directly into the passenger cabin in an advantageous manner by means of ventilation ducts or the like, for example. As an alternative or in combination therewith, it is also possible to provide a primary and a secondary circuit with similar or else different heat exchanger fluids, i.e. liquid and gas/air.
A fan or the like is advantageously provided for gas/air to flow through the latent heat store according to the invention.
It is preferable that the heating element is arranged between two adjacent heat exchanger units. This achieves a particularly effective and efficient transfer of energy from the electric heating element to the heat exchanger units or to the phase change material.
In principle, the electric heating can be realized in the manner of an immersion heater or the like. In a particular development of the invention, the heating element is in the form of a heating foil. This heating foil is relatively thin and can advantageously be brought into direct contact with the heat exchanger units and thus be arranged very close to the phase change material. This additionally improves the heat absorption.
Specifically in the embodiment in which heat exchanger units have a flat or planar side, the use of a heating foil is particularly advantageous. Thus, said heating foil can be arranged or inserted between two planar sides/surfaces of the adjacent heat exchanger units. This is of major advantage when numerous heat exchanger units are used or stacked, particularly during production and also in relation to the utilization of space within the latent heat store according to the invention and also in relation to the most homogeneous possible heating and therefore storage of the energy/heat introduced.
In general, it is advantageous specifically also in the case of electrically driven vehicles to convert the brake energy into electric energy using an electric generator, i.e. to recuperate it, and to use this for heating the latent heat store according to the invention and/or for charging the traction battery/accumulator.
An exemplary embodiment of the invention is shown in the drawing and is explained in more detail hereinbelow with reference to the figures.
In detail:
Furthermore, both an intake 10 and a drain 11 for a heat exchanger fluid, such as a liquid or a gas, in particular a heat transfer oil, air or the like, are provided on the outside on the side of the outer or inner cover 6, 27. These are preferably used for the input and/or the output of the heat energy, which is intermediately stored in the latent heat store 1, in particular by means of the PCM material stored or incorporated in chambers 14 of the sheets 2. The chambers 14 or pockets are preferably evacuated and/or permanently closed.
Numerous sheets 2 are stacked as a stack 13 or arranged alongside one another in the longitudinal direction or along the mid-axis 12 in the interior of the inner housing 8. As will become clear primarily in
An alternative anti-twist means for two sheets 2 which lie against one another with the planar side is realized with the variant according to
In addition, further (partially bent) wings 31 or lugs 31 are provided in the central region of the sheets 2 and radially align or center the sheets 2 and generate one or more open flow cross-sectional openings with respect to the pipe 18.
In addition, the chambers 14 have advantageous surface structures or so-called combs 17, which are in the form of spacers in relation to the spacing between two adjacent sheets 2 preferably in the direction of the longitudinal axis or mid-axis 12 (cf.
Alternatively, said ring or the outer circumference could also be in the form of an inflow point and the center hole or the center could be in the form of an outflow point according to the invention, wherein an advantageous radially oriented flow of the heat exchanger fluid is likewise realized over substantially the full extent of the cross section or over the circular surface of the sheets 2.
The preferably radially oriented combs 17 produce a gap 33 through which the heat exchanger fluid flows preferably in the radial direction approximately perpendicular to the longitudinal direction 12, such that the fluid can flow around the chambers 14 virtually over the entire area thereof and in the radial direction. This makes advantageous heat exchange possible between the fluid and the PCM material.
For vehicle applications, it has been found that a PCM material having a phase change approximately in the region of about 200° C. is particularly advantageous. To this end, use should also be made of a suitable heat exchanger fluid, in particular a heat transfer oil, which is suitable for this temperature range.
The fluid is supplied to the sheets 2 or the inflow points 34 thereof or to the stack 13 using a pipe 18, which is arranged approximately centrally in the longitudinal direction 12 and is spaced apart from a base 19 of the inner housing 8. An open end 20 of the pipe 18 advantageously has a so-called crown design, in order inter alia to compensate for possible assembly/component tolerances, i.e. to prevent a sufficient opening cross section for the fluid flowing out from being disadvantageously undershot even in the case of a slightly variable spacing between the end and the base 19 (even in the case of contact).
To compensate for or to reduce stresses which are caused by a change in length and can arise as a result of different temperatures of the sheets 2 or of the fluid, and to fix/hold the sheets 2 or the stack 13, an inner spring element 21 is provided. However, this spring 21 not only compensates for thermally induced changes in length of the stack 13, but also presses the sheets 2 against one another, such that for example the transfer of heat to contact surfaces, in particular the planar side (cf. above), is also improved. In addition, this prevents the sheets 2 from lying only loosely against one another and prevents the gaps 33 which are fixed between the chambers 14 with the aid of the combs 17 or the like from unintentionally being increased or widened, which could lead to a disadvantageous or undesired change in the flow conditions of the heat exchanger fluid in the inner housing 8. By way of example, the gaps 33 between the chambers 14 have a thickness of about 0.5 mm or a few millimeters.
Furthermore, to compensate for the thermally induced change in length, a sleeve 28 is arranged on the pipe 18, in order inter alia to prevent an upper pressure plate 29 from becoming caught during adjustment and also a disadvantageous flow of the heat exchanger fluid along the pipe 18. The pressure plate 29 advantageously distributes the locally introduced spring force of the spring 21 over the entire radius. So that this is effected as homogeneously as possible, the pressure plate 29 has a slightly conical profile of about 1° toward the center.
In the region between the inner and outer housings 3, 8, the intake 10 and the drain 11 have regions for compensating for thermally induced changes in length, e.g. in particular metal bellows 30 or the like provided in the bend region.
As already mentioned, the inner container/housing 8 is thermally insulated with respect to the outer housing 3 by means of a vacuum 9. To improve the vacuum 9, a getter material or getter pellets 25 is or are advantageously arranged on the inner and/or outer housing 3, 8 and/or on fixing/holding devices such as clamping or spring elements 22, 23, 24 and/or on the intakes/drains 10, 11. The getter pellets 25 are preferably arranged on the outer housing 3, in particular on the base 5, and/or on the intake 10 by means of a holder 26. As a result, when the getter material is charged the getter material or the getter pellets 25 can advantageously be regenerated by heating. In this case, the regeneration heat can be conveyed from outside through the wall or through the base 5 to the getter pellets 25 by means of a separate heat source and/or by means of the heat exchanger fluid.
In principle, the holder 26 should conceal the surface of the getter pellets 25 as little as possible, in order to make the advantageous accumulation of remaining atoms or molecules of the vacuum 9 possible.
The fixing/holding devices such as clamping or spring elements 22, 23, 24 hold and fix the inner container or housing 8 at a spacing from the outer housing 3. These elements should as far as possible be formed in such a manner that relatively poor thermal conduction by the latter is obtained. For this purpose, these can be produced inter alia in a relatively long and thin form or with a small cross section and also from appropriate material. By way of example, a high-grade steel having relatively poor thermal conduction properties can be used for this purpose.
According to the invention, an advantageous throughflow is realized, this being explained in more detail hereinbelow. The fluid flows through the intake 10 to the pipe 18 and enters into the inner space of the latent heat store 1 at the open end 20. Here, an annular contact surface of the lowermost sheet 2 together with the base 19 prevents unintentional “underwashing” of the lowermost sheet 2. On account of this, the fluid flows inter alia to the first/lowermost inflow point 34 between the lowermost and the second lowest sheet 2 in the radial direction past the chambers 14 thereof or the lowermost/first gap 33 to the outflow point 35 or to the circumference or outer edge of the sheets 2. Then, the fluid flows along further outflow points 35 of the other sheets 2 and along the casing of the housing 8 to the cover 27 and through the drain 11 out of the latent heat store 1.
A second flow path branches off at the open end 20 in such a manner that this partial flow flows back/up along the pipe 18 and then, at the next inflow point(s) 34, through the next or second gap 33 between two adjacent sheets 2 or chambers 14 and in the radial direction to the outer circumference or to the next outflow point(s) 35 of the next sheets 2 and then in turn along further outflow points 35 of the other sheets 2 and along the casing of the housing 8 to the cover 27 or drain 11. The same applies to the third, fourth, fifth, etc. gap 33 of the stack 13.
It is essential in relation to the flow according to the invention of the individual partial flows that the sum or length of the individual partial flows connected/realized in parallel from the open end 20 to the drain 11 is approximately the same, even in relation to the comprehensive radial flow of the fluid from the center or the inflow point 34 to the outflow point 35 or to the circumference of the sheets 2. This brings about identical pressure conditions or hydraulic or pneumatic resistances and therefore identical flow velocities or volumetric flow rates along the sheet 2 or the chambers 14 and also in the inner housing 8. This prevents dead spaces, through which flow passes only poorly or to a small extent. The system additionally regulates itself in an advantageous manner.
The text which follows mentions various components of the latent heat store 1 if appropriate with further properties or advantages.
The slide bushing or sleeve 28 is intended to prevent tilting of the pressure plate upon thermal expansion and “slide” on the oil guiding pipe 18. For this reason, the bushing material is preferably brass. Brass and high-grade steel have good sliding properties. Furthermore, the tolerances between the slide bushing 28 and the oil guiding pipe 18 are selected to be as small as possible, in order to have the smallest possible gap between the components, which permits no or only a very small bypass leakage. Likewise, the height or the gap length should be maximized for the installation, in order for it to be possible to provide the narrowest and longest possible gap.
In the installed state, the spring 21 inside should apply a defined contact pressure of the pressure plate 29 to the PCM stack 13. In the case of a vehicle, this contact pressure should be at least as great as the maximum lateral acceleration which occurs. In one application, a spring force of about 220-250 N is selected. This should be ensured for all thermal states. This means that, for example at about −40° C., the PCM stack height is reduced by about 5 mm as compared with about 20° C. At an operating temperature of about 250° C., the height increases by about 5 mm, for example, as compared with 20° C. The material of the spring 21 should be suitable for temperatures of >about 350° C., since the spring preload has to be retained after the heat-treatment process for evacuation.
At the lower side or the open end 20, the oil guiding pipe 18 has a “crown design”. The design is chosen such that the “tips” of the crown cannot act as a cutting edge in the case of direct contact with the base 19. The crown is intended to prevent blockage of the oil flow, should the pipe 18 be incorrectly installed until contact or should the pipe 18 be present on the base 19 on account of thermal distortion. Furthermore, it serves for additional centering of the PCM stack 13 and conveys the fluid or heat transfer oil to the base 19 of the store 1.
The pressure plate 29 serves as an “end cover” of the PCM stack 13. This end cover 29, together with the slide bushing 28, is intended to prevent a bypass leakage, in that the plate 29 conducts the oil flow in any case through the uppermost level of the PCM sheet. Furthermore, the pressure plate 29 has the task of distributing the spring force, which is introduced locally at the spring seat, as homogeneously as possible over the entire radius. Therefore, the pressure plate 29 tapers conically toward the center at about 1°. If appropriate, the material thickness of the pressure plate 29 may be reduced by introducing beads and/or ribs etc. for stiffening and distributing forces. Lugs of the plate 29 which are bent upward additionally serve as centering for the spring 21.
Casing of the housing 8: the special feature here is that the outer surface of the inner casing should be electropolished, for example. This reduces impurities, which would be very harmful during evacuation, and reduces the emittance of the surface and improves the outgassing rate. A reduction in the emittance leads to a reduction in the radiation losses. In addition, the outer surface should be completely free of dirt and grease.
The PCM sheets 2 are preferably welded together from two high-grade steel sheet halves. One side of the metal sheet has deep-drawn pockets or chambers 14 into which the liquid PCM is filled. A metal sheet which likewise has deep-drawn pockets or chambers 14 or preferably finally a flat, punched metal sheet is welded thereto.
An electrically heatable heating foil or the like (not shown inter alia in
In order for it to be possible to set the oil gap in each level, so-called “spacer combs” 17 are integrally formed in each pocket 14. The individual pockets 14 are welded in a holding-down device, for example by means of a laser. In order for it to be possible to ensure a redundancy, each pocket 14 is preferably provided with two circumferential weld seams.
In order to fix and align the sheets 2 in the inner casing, wings 16 which serve as spacers are fitted on the outside. This spacing is needed since the oil rises on the casing. The wings 16 also serve as spring elements, since instances of radial thermal expansion can occur as a result of differences in temperature in the sheet 2 itself. This thermal expansion is compensated for by the resilient wings 16 in an advantageous manner. In addition, the wings 16 serve as a torsional barrier, since the wings 16 engage into one another in the mounted operating state. Alternatively, a torsional barrier can also be ensured by spot-welding the individual sheets 2.
The wings 31 on the inside like the outer wings 16 likewise serve for the support, thermal compensation and/or centering of the oil guiding pipe 18. Furthermore, the three inner wings 31 form so-called “oil riser pockets”. In these pockets, the oil can flow back/rise coaxially along the oil guiding pipe 18 and flow into the respective level.
Cover 27 on the inside: the special feature here is that the outer surface should likewise be electropolished, for example. This reduces impurities, which would be very harmful during evacuation, and reduces the emittance of the surface and improves the outgassing rate. A reduction in the emittance leads to a reduction in the radiation losses. In addition, the polished surface has to be completely free of grease and clean.
Base 19 on the inside: here, too, the outer surface should be electropolished. This reduces impurities, which would be very harmful during evacuation, and reduces the emittance of the surface and improves the outgassing rate. A reduction in the emittance leads to a reduction in the radiation losses.
Furthermore, the inner base 19 should be designed in such a way that the lowermost PCM sheet 2 has a circumferential linear seating. This prevents a bypass leakage of the oil. In addition, the polished surface should be completely free of grease and clean, which inter alia improves the outgassing rate. The geometry is advantageously such that the base has a sufficient rigidity, in order to withstand the vacuum 9 and other influences.
Casing, cover 6 and base 5 of the outer housing 3: the inner surface of the casing or housing 3 should likewise be electropolished, for example. This reduces impurities, which would be very harmful during evacuation, and reduces the emittance of the surface. A reduction in the emittance leads to a reduction in the radiation losses. In addition, the polished surface should be completely free of grease and clean, which inter alia improves the outgassing rate. Beads in the casing on the outside stabilize the casing under negative pressure inside. It is therefore possible to use a thinner starting material.
The metal bellows 30 of the intake 10 and/or drain 11 has the task of compensating for the thermal expansion of the inner container 8. To this end, about ten billows which can compensate for thermal stresses are integrated in each bend. Furthermore, the metal bellows 30 should have the smallest possible wall thickness together with the longest possible overall length. Heat losses as a result of heat conduction are therefore reduced.
The holders 23, 24 have the function of fixing the vacuum gap of the inner container 8 in relation to the outer container 3. In addition, the holders 23, 24 are preferably optimized in terms of their thermal conductivity, i.e. they are as long as possible with the smallest possible cross section. Depending on the installed position of the store 1, the holders 23, 24 are to be arranged in such a way that the legs 31 of the holder 23, 24 are oriented parallel to the direction of greatest acceleration. In an application for vehicles, the axis of greatest acceleration is the Z axis of the vehicle (pitch holes). On account of the increased strength, the legs 31 of the holders 23, 24 are to be placed under tensile load; this tensile loading is spring-loaded inter alia by the spring 22 on the outside. The holders 23, 24 as well as all (metallic) elements which come into contact with the vacuum are preferably to be treated appropriately, i.e. electropolished, clean, free of grease, etc.
The spring 22 on the outside should place the lower holder 24 under tensile preload in order to minimize oscillation of the inner container 8.
Furthermore, the spring 22 is preferably in the form of a spiral spring, since spiral springs have the advantage of an extremely long wire length and thus have small heat losses as a result of thermal conductivity. The material of the spring should be designed for common applications for temperatures >about 350° C., since the spring preload has to be retained after the heat-treatment process for evacuation. The spring 22 as well as all (metallic) elements which come into contact with the vacuum is preferably to be treated appropriately, i.e. electropolished, clean, free of grease, etc.
Getter pellets 25: Getters “capture” free molecules which have not been pumped out or have passed into the vacuum space 9 as a result of microleakages and/or as a result of so-called “virtual leakages”, and bind them to the surface thereof. Following activation or regeneration (heating to >about 200° C.), the molecules bound to the surface diffuse into the interior of the getter, where they are chemically bonded. The surface then has “free” points again in order to be able to bind foreign molecules anew. Getters therefore make a large contribution to lengthening the life of the vacuum. Furthermore, they can shorten the evacuation time, since they likewise have a pump effect.
The getter holder 26 is to be designed preferably in such a way that it can accommodate the getter pellets 25 in an advantageous manner. At the same time, however, very little of the surface of the getter pellets 25 should be concealed by the holder 26. Furthermore, the getter holder 26 should conduct the externally applied activation temperature as well as possible to and around the getter 25, such that the getter is activated over the entire surface. The getter holder 26 as well as all (metallic) elements which come into contact with the vacuum is preferably to be treated appropriately, i.e. electropolished, clean, free of grease, etc.
The pinch pipe 7 or the connection 7 serves as a connection for a vacuum pump. The store is evacuated via the latter. The pinch pipe 7 is preferably soldered or welded onto the cover 6. The pipe 7 is made of copper, for example, since copper can be deformed and pinched off in an advantageous manner. Once the vacuum pressure has been reached, the pipe 7 is pinched, for example by means of pliers or the like, cut off and at the same time tightly welded. The pinch pipe 7 is to be designed to be as large as possible (e.g. >about 20 mm), since this represents the bottleneck upon evacuation.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE 102011012028.9 | Feb 2011 | DE | national |
