DE102008028731B4 - Heat exchanger for heating cryogenic hydrogen taken from cryogenic tanks - Google Patents

Abstract

Heat exchanger for heating cryogenic hydrogen taken from a cryogenic tank to supply a vehicle drive unit with its cooling liquid as heat transfer medium, which is guided around the heat exchanger essentially formed by a solid material block (1), while the cryogenic hydrogen in at least one in the solid material block (1) channel (2, 13) provided in the heat exchanger, characterized in that between the channel (s) (2) carrying the hydrogen and the heat transfer medium, at least one further channel (13) running essentially parallel to this channel (s) Is provided, which is only flowed through by cryogenic hydrogen to be heated when the heat transfer medium supplied to the heat exchanger has a higher temperature, while flow through this further channel (13) is blocked at lower temperatures of the supplied heat transfer medium.

Description

The invention relates to a heat exchanger for heating cryogenic hydrogen taken from a cryogenic tank to supply a vehicle drive unit with its cooling liquid as a heat transfer medium, which is guided around the heat exchanger essentially formed by a solid material block, while the cryogenic hydrogen in at least one in the solid material block of the heat exchanger provided channel is guided. In addition to the DE 10 2006 025 657 A1 and the WO 85/01101 A1 on the pamphlets US 3,749,155 A . EP 09 15 311 B1 . DE 27 04 551 C2 . DE 16 01 191 A and DE 100 30 627 A1 directed.

In the case of motor vehicles driven with hydrogen as an energy source, in which the hydrogen is stored in a cryogenic state in a so-called cryotank, the gaseous or even liquid hydrogen removed from this tank must be heated before it can be used, for example, by an internal combustion engine which acts as a drive unit for the Motor vehicle acts, can be supplied for combustion, cf. For example, the font just mentioned. Said heating can preferably take place in the heat exchange with the coolant of the liquid-cooled internal combustion engine, which is generally referred to here as the heat transfer medium. However, no conventional liquid-liquid heat exchanger can be used for this heat exchange, since the heat transfer medium in the heat exchanger would freeze due to the extremely low temperature (s) of the cryogenic hydrogen.

A heat exchanger which is simple in terms of its construction and nevertheless reliable for the general application described can be formed, for example, essentially by means of a so-called solid material block in the form of a cylinder, in which, for example, channels extending parallel to the longitudinal axis of the cylinder are provided, for example in the form of bores through which the initially cryogenic hydrogen to be heated is passed. Around the outer wall of this (e.g. cylindrical) solid material block, the heat transfer medium which supplies the required heat can, for example, be routed spirally in suitable lines or in so-called guide channels provided in the solid material block mentioned, as is shown, for example, in the document mentioned at the beginning.

In order to prevent the risk of freezing of the heat transfer medium mentioned above, it is already known, for example from the third-mentioned document at the outset, that a heat exchanger for a cryogenic fluid in those areas of the heat exchanger in which this fluid is still extremely cold has a lower heat transfer to enable between the fluid and the heat transfer medium than in other heat exchanger areas in which the fluid to be heated has already experienced a certain heating. The last-mentioned areas are, in particular, the so-called fluid outlet side, that is to say that section of the heat exchanger in which the hydrogen to be heated or which is already sufficiently heated then emerges from the heat exchanger. With this in mind is mentioned in the US 3,749,155 A a heat exchanger is shown in which a so-called mandrel is introduced into a circular-cylindrical channel with a constant diameter guiding the fluid to be heated through a suitable metal structure, said mandrel extending practically over the entire length of the channel and starting from the fluid inlet side of the channel has an increasing diameter towards the fluid outlet side of the channel. The annular gap between the channel wall and this mandrel thus narrows starting from a channel area which is further upstream and thus colder with respect to the flow direction of the fluid to a channel area which is further downstream and thus warmer. Since the free flow cross-section for the fluid has a larger area in a colder area of the channel than in a warmer channel area, the fluid flows in the colder area at a slower speed than in the warmer area. As a result, the heat transfer that can be achieved in the colder channel area is lower than in a warmer channel area lying downstream thereof, as a result of which the risk of freezing of the heat transfer medium in the vicinity of the colder channel area can be reduced.

At this point it should be briefly defined what is to be understood physically exactly by the term “lower heat transfer” used here for brevity. As is known, heat can be transferred by heat conduction, by heat radiation and by convection, specific physical relationships with specific influencing factors and coefficients being valid for each of these types of heat transfer. The foregoing is that different heat quantities or heat flows are or can be transmitted in different areas of a heat exchanger with otherwise the same boundary conditions. A lower heat transfer is therefore synonymous with the fact that a smaller amount of heat can be transferred under otherwise unchanged boundary conditions.

Although this is in the above US 3,749,155 A The principle shown to avoid icing of the heat exchanger has basically proven itself, but there are other advantageous designs for solving the problem described possible to demonstrate, the present invention has set itself the task.

This object is achieved for a heat exchanger according to the preamble of claim 1, characterized in that at least one further channel, which runs essentially parallel to this channel (s), is provided between the channel (s) carrying the hydrogen and the heat transfer medium only to be heated by cryogenic hydrogen to be heated if the heat transfer medium supplied to the heat exchanger is at a higher temperature, while flow through this further channel is blocked (or prevented) at lower temperatures of the supplied heat transfer medium. Advantageous training and further education are included in the subclaims.

It was recognized that the described risk of freezing the heat transfer medium or the coolant of the vehicle drive unit functioning as such can in practice only take place with a reasonable design of the heat exchanger if this coolant itself has a relatively low temperature. As is known, the coolant of an internal combustion engine (as a vehicle drive unit) can reach temperatures between the ambient temperature (namely when the internal combustion engine is shut down or started up for a short time after a long standstill) and approx. 115 ° C. While freezing of relatively hot coolant (e.g. 95 ° C) in heat exchange with cryogenic hydrogen can be practically ruled out with a suitable heat exchanger design, coolant with a temperature of e.g. 10 ° C in the same heat exchanger can definitely freeze. It is therefore proposed to provide different channels for the hydrogen to be heated in a heat exchanger according to the invention, at least one of these channels being relatively close to the heat transfer medium, while at least one further channel is further away from the heat transfer medium. Due to the longer heat conduction path in the solid material block of the heat exchanger, a lower “amount of cold” reaches the heat transfer medium from the last-mentioned channel than from the first-mentioned channel, which is closer to the heat transfer medium. If, as long as the heat transfer medium itself is relatively cold, only hydrogen to be heated is conducted in the channel further away from the heat transfer medium, while no hydrogen flows through a channel closer to the heat transfer medium, less heat is removed from the heat transfer medium than if the latter were closer Channel also flowed hydrogen. Freezing of the cold heat transfer medium can thus be effectively avoided by dividing the hydrogen according to the invention into different channels, from which a channel closer to the heat transfer medium is not flowed when the heat transfer medium is relatively cold.

A heat exchanger according to the invention can be formed by an essentially cylindrical solid material block, through which, in order to improve the heat transfer conditions, a plurality of channels which are always flowed through preferably run parallel to the cylinder axis. These are preferably arranged more centrally with respect to the cross-sectional area of the solid material block, while a plurality of further channels which conduct the hydrogen through the solid material block only at higher temperatures of the heat transfer medium can be arranged essentially in a ring around the first-mentioned channels. However, if in the latter channels, which only flow at higher temperatures, i.e. Even if there is no hydrogen flowing through it, hydrogen is desirably further hampered by the possible heat transfer from the more central, always-flowed channels to the heat transfer medium, since further heat transfers must first take place and the thermal conductivity of hydrogen is significantly lower than that of the solid material (of the solid material block of the heat exchanger). This effect just described can be achieved if, with a relatively cold heat transfer medium, it is possible for hydrogen to flow into the channels which are only flowed through at higher temperatures of the heat transfer medium, while only outflow of hydrogen from these channels is prevented by means of suitable valves or the like.

It is known that in connection with a desired removal of hydrogen from the cryotank, heat may have to be introduced into the cryotank in order to generate a certain overpressure therein, with the aid of which hydrogen is conveyed out of the cryotank. This heat input can take place with hydrogen heated in the said heat exchanger as the heat carrier. However, since such a heat transfer is not continuously necessary for the removal of hydrogen from the cryotank, a corresponding circuit which leads heated hydrogen into the cryotank or through a heat exchanger provided therein does not have to be operated continuously, but only as required. Using suitably switched lines, hydrogen removed from the cryotank can first be heated in a so-called primary heat exchanger and then passed through a heat exchanger provided in the cryotank in order to introduce a required amount of heat into the cryotank, after which the hydrogen heated in this cryotank heat exchanger a so-called. Secondary heat exchanger is passed before it to the vehicle drive unit Combustion is supplied. Alternatively, an independent circuit can be provided for an intended heat input into the cryogenic tank, as shown in the document mentioned at the outset, but for which a so-called secondary heat exchanger is also required.

It is now proposed in the present case that the secondary heat exchanger defined in the previous paragraph is formed by the channel or channels through which only the higher temperatures of the heat transfer medium flow. Since, in order to implement the present invention in a heat exchanger according to the invention, a division into two heat exchanger regions is required anyway, this division can advantageously be used to provide a primary heat exchanger and a secondary heat exchanger.

Particularly with regard to a uniform distribution of the heat transfer in individual quasi-disc-shaped areas of the solid material block, this block can actually be divided into individual discs in the sense of an advantageous further development, which are in one or more so-called gap plane (s) on which the cylinder longitudinal axis of the Solid material blocks is perpendicular, are slightly spaced apart. In each said slit plane, an approximately even distribution of the hydrogen to be heated can thus take place over the cross-sectional area having the channels carrying the hydrogen or at least the “central” cross-sectional area of the solid material block, of course by providing suitable ring seals or the like It must be borne in mind that there is no flow connection between the hydrogen channels which are always flowed through and those channels which surround them and which are only exposed to hydrogen flowing through at higher temperatures of the heat transfer medium.

For further explanation, reference is made to the attached schematic diagram, in which a heat exchanger according to the invention for heating cryogenic hydrogen removed from a vehicle cryogenic tank for supplying a vehicle drive unit is shown in a half section. This heat exchanger is through a circular cylindrical solid material block 1 with the longitudinal axis running horizontally here 6 formed in which several parallel to the longitudinal axis 6 and these relatively obvious channels 2 and further from the central longitudinal axis 6 spaced channels 13 which the channels 2 are provided in a quasi ring-shaped manner, which can all lead to cryogenic hydrogen to be heated from an inlet side to an outlet side of the heat exchanger. The canals 2 and the channels 13 is a separate so-called distribution room on both the entry and exit sides 4E (Entry for the channels 2 ) respectively. 14E (Entry for the channels 13 ) such as 4A (Exit for the channels 2 respectively. 14A (Exit for the channels 13 ) assigned, with all distribution rooms 4E . 4A . 14E . 14A on the respective end faces of the solid material block 1 provided and by a suitably guided boundary wall 5 of the heat exchanger are limited. Hydrogen can enter the distribution spaces through suitably provided openings in the boundary wall 4E respectively. 14E initiated or from the distribution rooms 4A respectively. 14A be diverted.

During the distribution rooms mentioned 4E . 14E respectively. 4A . 14A for the hydrogen to be heated essentially on the two faces of the circular cylindrical solid material block 1 (or the entire heat exchanger) are provided, are guide channels 9 for guiding the coolant of a vehicle drive unit, which coolant acts as a heat transfer medium and which uses the heat to heat the hydrogen in the heat exchanger, on the outer surface of the circular cylindrical solid material block 1 intended. These lead channels 9 are around the outer wall of the solid material block 1 For example, led around in a spiral. A feed connector for these channels 9 or the heat transfer medium contained therein is with the reference number 10a marked, while a discharge nozzle the reference number 10b wearing.

To prevent the heat transfer medium from possibly in the guide channels 9 freezes, when this heat transfer medium itself is relatively cold, only those closer to the longitudinal axis 6 lying channels 2 of cryogenic hydrogen flows through it, while the quasi-ring surrounding it and therefore closer to the heat transfer medium or to its guide channels 9 lying channels 13 then the cryogenic hydrogen will not flow through it. However, the heat transfer medium has a sufficiently high temperature so that it freezes in the guide channels 9 can be excluded with certainty, so also with respect to the central longitudinal axis or cylinder axis 6 channels further out and therefore closer to the heat transfer medium 13 flowed through with hydrogen. In the former case, there is naturally a significantly lower heat transfer between the cryogenic hydrogen and the heat transfer medium than in the second case, so that in the first case the heat transfer medium does not freeze despite its relatively low temperature, with sufficient heating for the supply to the vehicle drive unit still taking place can. A suitably provided valve or the like, which is controlled by an electronic control unit at low temperatures of the heat transfer medium and then has an outflow of hydrogen from the channels, is not shown in the figures 13 and thus also prevents it from flowing through. In particular, such a valve can be located at a drain opening of the distribution space already mentioned 14A be provided, it being pointed out that a large number of details can deviate from the above explanations without departing from the content of the claims.

Claims (4)

Heat exchanger for heating cryogenic hydrogen taken from a cryogenic tank to supply a vehicle drive unit with its cooling liquid as a heat transfer medium, which is guided around the heat exchanger essentially formed by a solid material block (1), while the cryogenic hydrogen in at least one in the solid material block (1) channel (2, 13) provided in the heat exchanger, characterized in that between the channel (s) (2) carrying the hydrogen and the heat transfer medium, at least one further channel (13) running essentially parallel to this channel (s) Is provided, which is only flowed through by cryogenic hydrogen to be heated when the heat transfer medium supplied to the heat exchanger has a higher temperature, while flow through this further channel (13) is blocked at lower temperatures of the supplied heat transfer medium. Heat exchanger after Claim 1 with an essentially cylindrical solid material block (1), characterized in that a plurality of channels (2) which are always flowed through run parallel to the cylinder axis (6) and are surrounded by a plurality of channels (13) which are arranged essentially in a ring and flowed through only at higher temperatures of the heat transfer medium, in which, however, there is always hydrogen. Heat exchanger after Claim 1 or 2 with a secondary heat exchanger, which is integrated into a heating circuit, via which heat can be supplied to the cryogenic hydrogen in the cryogenic tank by means of hydrogen heated in the heat exchange with the heat transfer medium, characterized in that the secondary heat exchanger is heated by the one or only at higher temperatures the channel or channels (13) through which the heat transfer medium flows is formed. Heat exchanger according to one of the preceding claims, characterized in that the solid material block (1) is subdivided into at least two individual disks, which are arranged in one or more so-called gap plane (s) on which the cylinder axis (6) of the solid material block (1) is perpendicular, are slightly spaced apart.

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