DE102011050200A1 - Heat accumulator for receiving medium such as coolant of coolant circuit, has heater which is immersed in receiving space to surround receiving space and is designed as heat radiator so that heat is dissipated mainly by heat radiation - Google Patents

Abstract

The heat accumulator has a receiving space for medium, which is provided with a heater (14) for heating the medium to a storage temperature. The heater is immersed in the receiving space to surround the receiving space and is designed as a heat radiator so that heat is dissipated mainly by heat radiation. The heater is surrounded by a cladding tube at a distance, such that heat radiation from the heater is transferred to the jacket tube through annular space.

Description

The invention relates to a heat accumulator for receiving a medium according to the preamble of patent claim 1.

In modern internal combustion engines and also in alternative drive concepts, such as hybrid drives and electric drives, there is a problem in that only very little or virtually no heat loss arises, which can be used in particular for conditioning the vehicle interior in winter. In addition, there is still the requirement for internal combustion engines and hybrid drives to bring the engine as soon as possible to operating temperature during a cold start, so that on the one hand the wear and on the other hand the pollutant emissions and fuel consumption is minimized. This problem occurs especially in short-haul traffic, where modern machines can not reach the optimum operating temperature. In short-haul traffic and also in normal operation does not generate enough power loss to bring the coolant circuit of the vehicle to operating temperature. In modern engines, therefore, the lack of power loss is compensated by targeted supply of heat energy. Known here are so-called "Zuheizer", as described by the applicant, for example in the EP 0 350 528 B1 are described.

In the DE 42 35 883 A1 and the EP 0 214 517 A2 In each case, a coolant circuit for an internal combustion engine is described in which a latent heat accumulator is charged via the cooling water. This is - similar to a thermos - so well insulated that it can hold the stored heat energy for a long time, for example, over a period of several days. These latent heat accumulators consist of a material, for example a salt, which is liquid at the normal operating temperature of the engine and solidifies in the region of the phase change temperature, for example a temperature of 60-90 ° C. (Phase Change Material (PCM)). By cooling this melt, the liberated phase transformation or crystallization enthalpy can be used to heat up another medium, for example the cooling water, by heat exchange. When the engine is cold-starting, the cooling water is in heat exchange with the latent heat storage, so that the liquid material is cooled and finally crystallized, using the heat released to heat the cooling water, so that it can be brought to operating temperature. When the coolant circuit is heated, the latent heat accumulator is then charged again so that it is ready for the next cold start.

Such solutions contribute to the reduction of pollutant emissions and wear during cold start, but especially in short-haul traffic, the power loss of the engine is not sufficient to charge the latent heat storage and to exceed the phase change temperature. Another disadvantage of such latent heat storage is that the conversion of the liquid phase into the crystalline phase takes a relatively long time, so that the above-described heating of the cooling water may take several minutes due to the low heat transfer rate. When using paraffins as PCM, this heat transfer rate can be improved, but the thermal conductivity of this material is relatively low, so further measures to improve the heat transfer rate must be provided. Thus, the thermal diffusivity can be improved, for example, by a matrix of highly thermally conductive material, for example a graphite composite material in the PCM - however, such latent heat accumulators are very expensive due to their complex construction.

In the EP 0 791 497 A2 In general, a coolant circuit is described in which an unspecified heat accumulator can be charged via an electric heater, this heater is provided with a connection for an external power source, such as charging the heat accumulator and heating the coolant circuit before the start of the drive is possible.

In the DE 10 2008 015 283 B3 is a coolant circuit disclosed in the cold start of the vehicle, first a "small" coolant circuit is heated and then switched to a large coolant circuit. This heating can take place via a heater which can be activated when the drive is switched off.

The DE 103 44 018 A1 describes a coolant circuit in which the entire coolant is conveyed when switching off the drive in a so-called hot water tank, from which the coolant is returned when starting the drive in the coolant circuit.

In the case of the last three solutions mentioned, the coolant is brought into a kind of "hot water storage tank" and optionally heated there. When starting the internal combustion engine, the coolant absorbed in the heat accumulator is returned to the coolant circuit, so that it reaches its operating temperature relatively quickly. The problem, however, is that the temperature in the heat storage should correspond approximately to the designed operating temperature of about 95 ° C. A clear Exceeding this temperature is not possible because the glycol / water mixture used is decomposed thermally from about 160 ° C. In addition, the engine block is also designed for operating temperature, so overheated coolant can cause engine block tensions and damage.

Another problem of such conventional solutions is that the electric heater in the heat storage can lead to local overheating of the coolant and thus to the formation of vapor bubbles, which deteriorates the heat transfer.

In contrast, the invention has for its object to provide a heat storage, on the one hand enables an effective energy-optimized temperature of a medium to be stored, preferably of cooling water, thermal problems to be avoided.

This object is achieved by a heat accumulator having the features of patent claim 1.

Advantageous developments of the invention are the subject of the dependent claims.

According to the invention, the heat accumulator for receiving a heated or to be heated medium, for example a coolant of a coolant circuit, a preferably surrounded by an isolation receiving space for the medium and a heater for heating the medium to a storage temperature, wherein the heater dips into the receiving space or surrounds it and is designed as a radiator, so that their heat dissipation essentially by heat radiation, to a lesser extent by convection in the air, takes place.

The invention is directed against conventional heaters for heat storage, in which the heating either externally ( EP 0 791 497 A2 ) is arranged or is provided directly in the heat accumulator and transfers the heat predominantly by convection in the coolant or heat conduction.

This type of heat transfer has disadvantages when the heater is heated to very high temperatures, which is significantly above the storage temperature. In this case, it may come to the above-mentioned local overheating of the medium, which can be accompanied either with a decomposition of the medium with strong vapor bubble formation or with damage to the flow path of the medium.

A heat transfer by thermal radiation has the significant advantage that on the one hand, the heat can be transferred much faster than latent heat storage on the medium, the transmittable amount of energy in the heat radiation with increasing temperature of the heat radiator is significantly higher than in a heat transfer by conduction or convection.

It was found that when using a heat radiator, the heating temperature can be set very high, with local overheating and the deterioration of heat transfer due to vapor bubbles can be reliably avoided and, moreover, the efficiency is improved over the solutions described above.

In one embodiment of the invention, the heating is surrounded by a cladding tube, so that an annular space is formed between the outer circumference of the heater and the inner circumferential wall of the cladding tube, via which radiant heat from the heater can be transmitted to the cladding tube. This cladding tube is then in heat transfer contact with the medium at the area remote from the heater so that it is heated via the cladding tube, the heat transfer from the heater to the cladding tube essentially by radiant heat and from the cladding tube to the medium essentially by convection and heat conduction he follows.

To improve the heat transfer from the cladding tube to the medium heat exchange surfaces can be performed on the cladding tube.

The structure of the heat accumulator is particularly simple if the heater is designed as a tubular heater.

The cladding tube is preferably made of a metallic material which conducts heat well, for example of aluminum.

In one embodiment of the invention, the receiving space of the heat accumulator is surrounded by a cylinder jacket, which is provided with the insulation and on which an inlet and an outlet are formed.

In this case, the heater may be formed coaxially to the cylinder jacket, in which case the inlet and the outlet may be provided frontally. However, as explained above, the heater can also encompass the receiving space, wherein corresponding inlet and outlet can again be formed on the front side.

In one embodiment of the invention, the maximum temperature of the heater is significantly higher as the storage temperature. Thus, the temperature of the heater can be designed by more than a factor of 4 higher than the storage temperature.

In one embodiment of the invention, a circulating / mixing device is provided for reliably avoiding local overheating.

The diameter ratio between cladding tube and jacket tube is preferably greater than 1.2.

A preferred embodiment of the invention will be explained in more detail below with reference to schematic drawings. Show it:

1 a block diagram of a coolant circuit of an internal combustion engine;

2 a longitudinal section through a heat accumulator of the coolant circuit according to 1 ;

3 a radial section through the heat storage and

4 a diagram to illustrate the temperature profile in a recuperation.

1 shows an extremely simplified block diagram of a coolant circuit 1 an internal combustion engine 2 , In this case, a water / glycol mixture is used as the coolant. That of the internal combustion engine 2 heated coolant can according to 1 be used to increase the vehicle interior temperature via an interior heating. This is what happens in the combustion engine 2 to its operating temperature of about 95 ° C heated coolant a heat exchanger 4 supplied to an air conditioner to heat the vehicle interior to be supplied air. The coolant slightly cooled after this heat exchange with the vehicle interior air becomes downstream of the heat exchanger 4 a cooler 6 fed and cooled there, for example, by wind and / or a fan. The cooler 6 Can during cold start of the engine by means of a bypass line 8th be bypassed, which has a bypass valve 10 can be opened or closed. When cold starting the engine is the radiator 6 by controlling the bypass line 8th bypassed, so that the coolant can be brought to operating temperature as quickly as possible.

In the illustrated embodiment, the bypass valve 10 As a 3-way valve, in principle, of course, another valve arrangement with valves upstream and / or downstream of the radiator 6 be used.

Downstream of the radiator 6 is a heat storage according to the invention 12 whose concrete structure is based on the 2 and 3 is explained. A special feature of this heat storage 12 is that as the storage medium, the coolant itself is used, this with charged heat storage 12 is heated to a temperature above the operating temperature. This heating can, for example, via an electric heater 14 respectively. This may be a tubular heater or the like, the storage medium - in the present case, the coolant - in the heat storage 12 heated. This is designed with a very good thermal insulation, which ensures that the stored heat is maintained even with a longer standstill of the vehicle.

To power the heating 14 For example, a generator 15 be provided, which has a much higher power output than conventional generators and in cooperation with unillustrated electrical energy storage provides the required electrical energy. Such a generator 15 does not have to be directly driven by the internal combustion engine, but can be coupled at the outlet of a transmission, so that, for example, when "sailing" with disengaged combustion engine, the generator 15 is driven via the wheels of the vehicle. Such a circuit also makes it possible, in a braking of the vehicle on the recuperation of braking energy generator 15 drive, so the heater 14 during the recuperation is supplied with energy. By interacting with a start-stop mode and the drive of the generator during the operating modes "braking" (recuperation) and "sailing" the energy emitted in conventional concepts only as heat loss to supply the electrical load, especially the heater 14 be used. The generator supports this 15 During braking, the actual brake system, so that the braking performance is improved.

The coolant circuit 1 also has a coolant pump 16 , about which the coolant in the coolant circuit 1 is pumped around.

After conventional internal combustion engines 2 are designed to a coolant temperature in the range of about 95 ° C, appropriate measures must be taken to the heat storage 12 decouple from the coolant circuit when the operating temperature is reached, so that no overheating of the coolant or better of the internal combustion engine 2 he follows.

For decoupling the heat accumulator 12 From the actual coolant circuit is a bypass line 18 provided, via a bypass valve assembly 20 can be opened or closed. With open bypass line 18 becomes the heat storage 12 from the via the coolant pump 16 bypassed circulated coolant and is thus thermally decoupled from the coolant circuit. About the heater 14 can then the coolant in the heat storage 12 be warmed to a storage temperature above the operating temperature. Due to the insulation of the heat accumulator 12 ensures that this storage temperature over a comparatively long period without control of the heater 14 can be held. When cold starting the internal combustion engine 2 will then be in the heat storage 12 stored, for example, heated to a temperature of about 130 ° C, coolant optionally by appropriate control of the bypass valve assembly 20 mixed with "cold" coolant and with the operating temperature of the internal combustion engine 2 fed so that it is heated very quickly. This mixing with "cold" coolant is advantageous to prevent stresses in the engine block. The mixing ratio of the coolant from the heat accumulator 12 and the "cold" coolant can via the bypass valve assembly 20 be set. A discharge of the heat accumulator 12 For example, can also be done if after phases of "sailing" a rapid warming of the engine 2 is required. After unloading the heat storage 12 this can be done by the control of the heating explained above 14 be charged very quickly to its storage temperature, in which case, of course, the bypass line 18 is turned on to the heat storage 12 thermally decouple from the coolant circuit.

Also the bypass valve assembly 20 is exemplified as a 3-way valve, of course, can also be another valve arrangement, for example with valves at the entrance and at the output of the heat accumulator 12 be used. The valve arrangements 10 and 20 are preferably designed as electrically adjustable by the engine control valves.

In principle, it is also possible, the heat storage 12 to charge to temperatures above 130 ° C. This results in an increased pressure. For heat exchange with the coolant in the coolant circuit then suitable precautions would have to be made to the coolant when emptying the heat accumulator 12 to relax. As explained above, in such a variant suitable means must be provided for decoupling the pressure-operated heat accumulator, which is elevated in relation to the coolant circuit, and for releasing the coolant received in the accumulator at elevated pressure, so that a pressure equalization with the coolant takes place in the actual coolant circuit. In the simplest case, the pressure build-up in the heat accumulator takes place due to the temperature increase of the coolant in the heat accumulator 12 , In principle, however, a pump could be provided to pressurize the coolant received in the heat accumulator with a pressure. In thermodynamic connection of the heat accumulator with the actual coolant circuit then the pressurized pressure medium must be relaxed via suitable throttles or the like.

When loading the heat storage 12 over the heater 14 It may cause local overheating or uneven heating of the storage medium in the heat storage 12 come. To avoid this, can in accordance with 1 a circulation pump 22 be provided, which in a circulation line 24 is arranged, via the coolant at an outlet 26 the heat storage 12 deducted and to an entrance 28 can be promoted back, so that a uniform heating of the heat storage 12 absorbed coolant (storage medium) is ensured and the formation of vapor bubbles can be avoided by thermal overheating. Instead of the circulation can also be ensured that to avoid local overheating the coolant in the heat storage 12 is mixed, for example, a kind of stirrer or by suitable flow guidance. Of course, the heating 14 be executed without such a circulation device.

According to the invention, the heater 14 additionally with an external connection, over which the heating 14 For example, in a garage or the like can be controlled overnight to the heat storage 12 recharge, so that it is ready for use even during prolonged engine standstill.

2 shows a longitudinal section through a heat storage 12 , as in a coolant circuit according to 1 is usable. The heat storage 12 has an outer jacket, which in the illustrated embodiment as a cylinder jacket 30 is made of a metallic material. Other materials, such as plastic are possible. The cylinder jacket 30 is frontally over front flanges 32 . 34 closed off, leaving a recording room 36 is formed, in which the coolant through the entrance 28 can be fed and over the exit 26 is removable. In the illustrated embodiment are input and output 28 . 26 formed by axially parallel connecting pieces, the in 2 overhead end flange 34 push through.

The cylinder jacket 30 and the two end flanges 32 . 34 are from an isolation 37 surrounded, for example, designed so that in the recording room 36 absorbed coolant can be kept at a predetermined storage temperature of, for example, 130 ° C at least overnight without significant drop in temperature. The container is further designed so that the coolant in the heat storage 12 can be maintained with a slight overpressure of, for example, 1.5 bar, so that the usable heat energy is further increased.

The actual heating 14 is designed in the illustrated embodiment as a tubular heater, of course, other heating elements can be provided. The tubular heater can be performed for example in resistance wire technology, wherein a heating wire 38 isolated in magnesium oxide 41 embedded and this magnesium oxide bed in a jacket tube 39 is included. The electrical contacting of the tubular heater via a power supply 40 , which also in the illustrated embodiment axially through the end flange 34 extends through. A ground connection 42 is also on the front flange 34 executed.

The tubular heater with its jacket tube 39 is in a cladding tube 44 picked up, extending between the two end flanges 32 . 34 extends and with these - for example, by soldering, welding - is connected. Between the outer circumference of the jacket tube 39 and the inner peripheral wall of the cladding tube 44 becomes an annulus 46 limited, either with air or with another gas, such as N ₂ , CO ₂ , is filled. In principle, this annulus could 46 also be evacuated. The cladding tube is made of aluminum, for example.

3 shows a radial section along the line AA in 2 , You can clearly see the heating wire 38 that is in the magnesia or alumina 41 embedded, with this compressed bed and the heating wire (resistance wire) 38 in the jacket tube 39 are fixed in position. The diameter of the jacket pipe 39 is significantly lower than that of the cladding tube 44 , Experience has shown that the air space between jacket and cladding tubes is between 5mm and 30mm. The resulting annulus 46 is - as mentioned above - filled with air or another gas or evacuated. To improve the heat exchange with the in the receiving space 36 absorbed coolant can on the outer circumference of the cladding tube 44 for enlarging the heat exchange surface provided ribs 48 be educated. In the illustrated embodiment, these ribs 48 for example, as projecting in the radial direction and in the longitudinal direction of the heat accumulator 12 extending webs executed. The wall thickness and the material of the cladding tube are designed so that an optimal heat transfer and good heat transfer to the cladding tube 44 surrounding coolant is ensured. As in 2 indicated, the running with a comparatively large axial length heating via radial support webs 50 on the inner peripheral wall of the cladding tube 44 be supported, so the geometry of the annular gap 46 is maintained even under mechanical loads.

As explained at the beginning, the heating has to be 14 not necessarily be constantly powered by the electrical system. It is sufficient, for example, when recuperation, the converted braking energy in addition to the power supply of other consumers to operate the heater 14 is used. Assuming, for example, that a 1600 kg car drives at a speed of 50 km / h or "sails" and is decelerated while the speed is reduced to 0 within five seconds and the braking distance is about 35 m, this is calculated a braking energy of about 150 kJ - the braking power is about 30 kW.

This considerable amount of energy is enough to heat storage 12 to charge, ie to heat the coolant contained therein to the intended temperature in the range of 120-130 ° C. Assuming, for example, the engine mass with about 30 kg and assumes a starting temperature of -20 ° C (winter), it must be supplied to heat the engine to a temperature of + 50 ° C, an energy in the amount of about 2100 kJ. Assuming that this warm-up time during cold start may be about 60 seconds, this corresponds to a power of 35 kW. That is, the comparatively high power of 35 kW must be transferred to the engine mass in a relatively short time of 60 seconds - by the use of preheated or even superheated coolant at a temperature in the range of 100-120 ° C from the heat storage according to the invention is a Such rapid heating of the cooling water quite possible by the cold cooling water of the coolant circuit with the heat storage 12 existing heated coolant is mixed or replaced by this. One problem is that the braking energy released during braking can be used only during the very short braking process, so that the memory must be charged in this time - the discharge can, as explained above, take place over a much longer period.

4 shows the temperature curves at the heater 14 and the coolant as a function of time during a braking operation. The top line showing a pronounced peak shows the temperature profile of the heater. you recognizes that during the braking process, the heater 14 over the generator 15 is supplied with energy and thus the heating temperature in a very short time, for example, within 10 seconds of an initial temperature (temperature of the nearly discharged heat storage 12 ) is heated to 600 ° C. After this time, the braking process is completed. The cladding tube 44 is then predominantly by heat radiation through the annulus 46 heated and then in turn gives its heat by heat conduction and convection (and also a small amount of heat radiation) to the in the receiving space 36 absorbed coolant. At the beginning of this heat transfer lies within the annulus 46 a very high heat radiation, which decays continuously over time, but also in the range of 300-400 ° C due to the infrared radiation present there is sufficient to the cladding 44 to warm up.

As in 4 indicated by the flat curve, the coolant is in the receiving space 36 via convection and heat conduction via the cladding tube 44 heated to the storage temperature in the range of 120-130 ° C, wherein the recuperation of the braking energy of one or more braking energy introduced sufficient to charge the entire contents of the heat accumulator to its storage temperature. After the decay of the heating temperature to this storage temperature (120-130 ° C) is thus the heat storage 12 charged, so that an additional heating and control of the heater is only necessary to compensate for the heat losses. As mentioned, the heating can 14 be performed with an external connection to operate the heater at a longer shutdown of the engine, for example in the garage to charge the heat storage before a cold start. By virtue of the described thermodynamically optimized process management, braking energy can be used, for example, effectively in electrical energy for charging the heat accumulator 12 be implemented, the heat transfer to that in the heat storage 12 absorbed coolant is carried out with sufficient speed, but it is ensured that no local overheating occurs with damage to the coolant or with the emergence of vapor bubbles.

Extensive calculations by the inventors show that for heating an engine block with a mass of about 30 kg, a heat accumulator with a capacity of about 8 kg is sufficient - i. the heat accumulator can be made extremely compact and requires only a small space within the engine compartment, the assembly depending on the requirements profile standing, lying or can be done in any other orientation. Comparative calculations also showed that the energy output of the heat accumulator according to the invention with coolant as a storage medium is only slightly lower than the energy output in a latent heat storage when, as in a cold start, the difference between charging temperature and discharge temperature is relatively large. It should be taken into account in favor of the heat accumulator according to the invention that this energy release can be done in a much shorter time and the device complexity is less than latent heat storage.

Disclosed is a heat storage for receiving a medium to be tempered, for example, a coolant of a coolant circuit, wherein a heater of the heat accumulator is designed as a radiator.

LIST OF REFERENCE NUMBERS

1

Coolant circuit

2

internal combustion engine

4

heat exchangers

6

cooler

8th

bypass line

10

bypass valve

12

heat storage

14

heater

15

generator

16

Coolant pump

18

bypass line

20

Bypass valve assembly

22

circulating pump

24

circulation line

26

output

28

entrance

30

cylinder surface

32

end flange

34

end flange

36

accommodation space

37

isolation

38

heating wire

39

casing pipe

40

power supply

41

magnesia

42

ground connection

44

cladding tube

46

annulus

48

Rib / heat exchanger surface

50

supporting web

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0350528 B1 [0002]
• DE 4235883 A1 [0003]
• EP 0214517 A2 [0003]
• EP 0791497 A2 [0005, 0014]
• DE 102008015283 B3 [0006]
• DE 10344018 A1 [0007]

Claims (11)

Heat accumulator for receiving a medium, for example a coolant of a coolant circuit, having a receiving space ( 36 ) for the medium and with a heater ( 14 ) for heating the medium to a storage temperature, characterized in that the heating ( 14 ) in the reception room ( 36 ) dips or surrounds it and is designed as a heat radiator, so that their heat dissipation occurs essentially by heat radiation. Heat storage according to claim 1, wherein the heating ( 14 ) of a cladding tube ( 44 ) is surrounded at a distance, so that an annular space ( 46 ), via the heat radiation from the heater ( 14 ) on the cladding tube ( 44 ) is transferable. Heat accumulator according to claim 1 or 2, wherein the cladding tube ( 44 ) with heat exchange surfaces ( 48 ) is designed for heat transfer to the surrounding medium. Heat accumulator according to one of the preceding claims, wherein the heating ( 14 ) is a tubular heater. Heat accumulator according to one of the claims 2 to 4, wherein the cladding tube ( 44 ) is formed metallic. Heat accumulator according to one of the preceding claims, wherein the receiving space ( 36 ) of a cylinder jacket ( 30 ) surrounded by an isolation ( 37 ) and to which an inlet and an outlet are assigned. Heat storage according to claim 6, wherein the heating ( 14 ) coaxial with the cylinder jacket ( 30 ) is executed, wherein input and output are frontally executed. Heat accumulator according to one of the preceding claims, wherein the temperature of the heating ( 14 ) is 4 times higher than the storage tank temperature. Heat accumulator according to one of the preceding claims, with a circulating device for circulating / mixing the medium in the receiving space ( 36 ). Heat accumulator according to one of the preceding claims, wherein the diameter ratio of cladding tube ( 44 ) and heating ( 12 ) is greater than 1.2. Heat storage according to one of the preceding claims, wherein the receiving space ( 36 ) thermally by means of an insulation ( 37 ) is isolated.

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