U.S. patent application number 13/343033 was filed with the patent office on 2012-07-12 for method for the commencement diagnosis of a heat storage material.
This patent application is currently assigned to ROBERT BOSCH GMBH. Invention is credited to Henrick Brandes, Lutz Rauchfuss.
Application Number | 20120174598 13/343033 |
Document ID | / |
Family ID | 45571330 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120174598 |
Kind Code |
A1 |
Brandes; Henrick ; et
al. |
July 12, 2012 |
METHOD FOR THE COMMENCEMENT DIAGNOSIS OF A HEAT STORAGE
MATERIAL
Abstract
The invention relates to a method and an apparatus for detecting
the point in time of commencement of crystallization of a heat
storage material (40), in particular a latent heat storage
material, which is supercooled by means of a Peltier element (32).
The profile (10) of the current I of the Peltier element (32) is
measured. The commencement of the crystallization process in the
heat storage material (40) is deduced when a discontinuity (20, 22)
which follows a continuous decrease (16) in the current and after
which the current (I) increases again (18) is detected in the
current profile (10).
Inventors: |
Brandes; Henrick;
(Ludwigsburg, DE) ; Rauchfuss; Lutz; (Mittweida,
DE) |
Assignee: |
ROBERT BOSCH GMBH
Stuttgart
DE
|
Family ID: |
45571330 |
Appl. No.: |
13/343033 |
Filed: |
January 4, 2012 |
Current U.S.
Class: |
62/3.2 |
Current CPC
Class: |
F28D 20/028 20130101;
Y02E 60/145 20130101; Y02E 60/14 20130101; F25B 2700/15 20130101;
F25B 21/02 20130101 |
Class at
Publication: |
62/3.2 |
International
Class: |
F25B 21/02 20060101
F25B021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2011 |
DE |
102011002424.7-52 |
Claims
1. A method of detecting a point in time of commencement of
crystallization of a supercoolable heat storage material (40),
which is supercooled by a Peltier element (32), characterized in
that a profile (10) of a current (I) of the Peltier element (32) is
measured and a commencement of the crystallization process in the
heat storage material (40) is deduced when a discontinuity (20, 22)
in the profile (10) is detected.
2. The method according to claim 1, characterized in that the heat
storage material (40) is a latent heat storage material.
3. The method according to claim 1, characterized in that the
discontinuity in the profile (10) is an increase in the current I
(18) following a continuous decrease (16) in the current I.
4. The method according to claim 1, characterized in that the
commencement of crystallization of the heat storage material (40)
occurs as a result of local supercooling from a metastable state in
a thermal equilibrium.
5. The method according to claim 4, characterized in that the heat
storage material (40) is a salt hydrate,
6. The method according to claim 1, characterized in that a
temperature difference between a hot side and a cold side of the
Peltier element (32) increases and the current I decreases (16)
during a period of time (12).
7. The method according to claim 1, characterized in that a
temperature increase in the heat storage material (40) occurs at
the commencement of crystallization (22).
8. The method according to claim 1, characterized in that the
discontinuity (20) in the current profile (10) is detected, with a
thermally produced delay, at a current sensor (30).
9. An apparatus for carrying out the method according to claim 1,
having a Peltier element (32) which locally supercools a heat
storage material (40), of a latent heat store (38), characterized
in that a power supply (44) to the Peltier element (32) has at
least one current sensor (30).
10. The method according to claim 9, characterized in that the heat
storage material (40) is a phase change material.
11. The method according to claim 9, characterized in that the
Peltier element (32) is a single-stage element.
12. The method according to claim 9, characterized in that the
Peltier element (32) is a multistage element.
13. An apparatus according to claim 9, characterized in that the at
least one current sensor (30) is located in the power supply (44)
to the Peltier element (32)
14. An apparatus according to claim 9, characterized in that the at
least one current sensor (30) is integrated into a control device
(42).
Description
BACKGROUND
[0001] There are various salt hydrates which can form super-cooled
melts and are therefore suitable for low-loss heat storage. To
start the release of heat from a heat storage material, a
crystallization nucleus is necessary. The provision of the
crystallization nucleus can be carried out in various ways. For
example, the crystallization nucleus can be provided in the form of
a cold finger, with this finger being continuously kept so cold in
a region in the heat storage material so that the heat storage
material never melts completely and a crystallization nucleus thus
remains continually.
[0002] DE 103 03 498 A1 relates to an apparatus and a method for
cooling the heat material of a latent heat store. The apparatus
comprises a Peltier element which is controlled by a temperature
sensor. When a first predetermined temperature is exceeded, the
Peltier element cools the heat material in its environment. If a
second predetermined temperature is exceeded, the further supply of
heat is interrupted. Parts of the latent heat storage material are
locally maintained at a lower temperature level.
[0003] Further methods for inducing a regenerable, super-saturated
aqueous solution to crystallize by means of local supercooling or
thermal separation are known. Here too, Peltier elements are used
in order to generate local super-cooling in the latent heat storage
material.
[0004] At present, only methods which allow commencement of the
crystallization process to be concluded directly from a temperature
measurement are known. The use of a temperature sensor is
indispensible for measuring the temperature.
SUMMARY
[0005] It is an object of the present invention to be able to
determine the commencement of crystallization and thus the
commencement of the release of heat from a latent heat storage
material without use of a temperature sensor.
[0006] It is proposed according to the invention that the power
supply of a single-stage or multistage Peltier element used for
cooling be provided with at least one current sensor and the
profile of the current be measured, analyzed and evaluated. When
Peltier elements made of, for example, bismuth telluride
Bi.sub.2Te.sub.3 are supplied with a constant operating voltage,
heat flow and current decrease with increasing temperature
difference between the hot side and the cold side of the Peltier
element.
[0007] At the commencement of crystallization of a latent heat
storage material, which is generally a phase change material (PCM),
by means of local supercooling from a thermal equilibrium state, a
high heat flow and a high current initially flow because of the
small temperature difference between the hot side and the cold
side. Subsequently, the temperature difference between the hot side
and the cold side of the Peltier element increases. The heat flow
and the current decrease. At the commencement of crystallization
and the commencement of the release of heat in the heat storage
material, the temperature in the heat storage material increases
very quickly. The temperature difference between the hot side and
the cold side of the Peltier element consequently drops again and a
discontinuity occurs in the power uptake of the Peltier element.
The discontinuity marks, with negligible delay, the commencement of
crystallization and can be utilized for diagnosis of a successful
start of the crystallization process.
[0008] If other thermoelectrically active materials, for example
BiSb, PbTE, SIGE, CoSb.sub.3-based skutterudites and similar
materials, are used for generating a temperature difference, the
current can follow different profiles. In the extreme case, the
current could initially increase and would drop again on
commencement of the crystallization process.
[0009] A common feature when heat begins to be released by the heat
storage material is the discontinuity in the current profile, which
can be detected, taking into account a thermal delay, at the
current sensor of the Peltier element.
[0010] The method proposed according to the invention or the
Peltier element which has been modified according to the invention
can be used as diagnosis unit for a latent heat store both in
stationary operation, for example in the case of solar heat stores,
and also in the mobile sector, for example in comfort heaters,
stores for shortening the warming-up time in vehicles. Apart from
the abovementioned salt hydrates as heat storage materials, it is
in principle also possible to use all liquids which can be
supercooled as heat storage materials, accordingly also high-purity
water.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention is described in more detail below with the aid
of the drawing. In the drawing:
[0012] FIG. 1 shows a profile of the current in a Peltier element
at the commencement of the release of heat by a heat store by means
of local supercooling, and
[0013] FIG. 2 schematically shows the components of an arrangement
for measuring the profile of the current as per FIG. 1 in a Peltier
element.
DETAILED DESCRIPTION
[0014] FIG. 1 shows the profile of the current at the commencement
of crystallization of a heat storage material, in particular a
phase change material of a latent heat storage material, for
example a salt hydrate.
[0015] The method proposed according to the invention is a
commencement diagnosis for a phase change material (PCM) by
evaluation of the current gradient.
[0016] It can be seen from the depiction in FIG. 1 that a high heat
flow and a relatively high current flow at the commencement of
crystallization of a heat storage material, in particular a phase
change material (PCM), due to local supercooling by means of a
Peltier element from a thermal equilibrium state because of the
small temperature difference between hot side and cold side. The
current profile 10 decreases continuously during a first period of
time 12. During this first period of time 12, the temperature
difference between the hot side and the cold side of the Peltier
element employed for local supercooling increases. The heat flow
established during the first period of time 12 and the current
decrease continuously, cf. reference numeral 16. It is a property
of Peltier elements which are made, for example, of bismuth
telluride Bi.sub.2Te.sub.3 and are operated at a constant operating
voltage that heat flow and current I decrease with increasing
temperature difference between hot side and cold side. This can
clearly be seen in the current decrease 16 in the graph of FIG.
1.
[0017] After the period of time 12 has elapsed, crystallization
commences in the heat storage material, in particular the phase
change material used therein, at a crystallization point in time
t.sub.K, cf. reference numeral 22 in FIG. 1. With commencement of
crystallization and thus the release of heat by the heat storage
material, the temperature within the heat storage material, in
particular the phase change material, increases rapidly. The
temperature difference between the hot side and the cold side of
the Peltier element therefore decreases again and the local minimum
20 shown in FIG. 1, i.e. a discontinuity in the power uptake by the
Peltier element, occurs. This discontinuity, which is encircled in
FIG. 1, represents a local minimum 20 which detects the
commencement of crystallization in the heat storage material, i.e.
in the phase change material of the latent heat storage material,
and can be utilized for diagnosis of the successful commencement of
crystallization. The use of a temperature sensor is therefore no
longer necessary.
[0018] The commencement of crystallization 22 at the point in time
t.sub.K' and the associated commencement of release of heat by the
heat storage material, in particular the phase change material,
leads to a temperature increase 18 in the heat storage material
which progresses rapidly and leads, cf. the graph in FIG. 1, to the
increase 18 in current which follows the achievement of the local
minimum 20, i.e. said discontinuity in the current curve 10.
[0019] If other thermoelectrically active materials are used for
generating a temperature difference, different profiles 10 of the
current I can occur. In the extreme case, an increasing current
would firstly be observed and this would decrease again on
commencement of the crystallization process.
[0020] In the method proposed according to the invention, the
characteristic of a heat storage material 40, in particular a phase
change material, that the commencement of the liberation of heat by
this material is associated with a discontinuity in the current
profile of a Peltier element 32 which locally supercools the heat
storage material 40, where this discontinuity can be detected,
taking into account a thermal delay, at at least one current sensor
30 arranged in the power supply to the single-stage or multistage
Peltier element 32, is exploited.
[0021] As heat storage material 40 (phase change material), it is
in principle possible to use paraffins, carbonates and also
fluorides. The heat storage materials used all have to meet the
requirement that they are a supercoolable heat storage material.
The supercoolability of the heat storage material used is the key
requirement for usability of the material.
[0022] FIG. 2 shows a schematic arrangement of a latent heat store
38 having a heat storage material 40, in particular a phase change
material (PCM), a Peltier element 32 which generates local
supercooling and in whose power supply at least one current sensor
is installed.
[0023] FIG. 2 schematically shows the components of an arrangement
for detecting a discontinuity in the current profile of a Peltier
element.
[0024] It can be seen from the greatly simplified depiction in FIG.
2 that a Peltier element 32 is arranged between the latent heat
store 38 and a heat dissipation device 34--here indicated roughly
by finning. At least one current sensor 30 is located in a control
line 44 which extends from a control device 42 to the single-stage
or multistage Peltier element 32. The current profile established
in the Peltier element 32, in particular the discontinuity depicted
in FIG. 1, cf. position 14 in FIG. 1, can be measured by means of
this at least one current sensor 30. The heat storage material 40,
which is a supercoolable heat storage material, is present in the
latent heat store 38, where the salt hydrate can in principle be
any supercoolable liquid, i.e. including high-purity water,
paraffins, carbonates, fluorides and the like. As shown in FIG. 2,
it is possible for heat to be both introduced into and removed from
the heat storage material 40, which is a phase change material,
present in the latent heat store 38 by means of a heat exchanger
36. An entry side of the heat exchanger 36 indicated schematically
in FIG. 2 is denoted by position 46, and an exit of the heat
exchanger 36 is indicated by position 48.
[0025] A discontinuity 14 established in the current profile 10 as
per FIG. 1 can be detected by means of the arrangement depicted in
FIG. 2 since at least one current sensor 30 is arranged in the
control line 44 which extends from the control device 42 to the
single-stage or multistage Peltier element 32. This current sensor
makes it possible to detect the current profile 10 in the Peltier
element 32, so that a discontinuity in the profile of the current
can be measured, analyzed and evaluated.
[0026] The Peltier element 32 is, for example, a Peltier element
which is made of bismuth telluride Bi.sub.2Te.sub.3 and is operated
at constant operating voltage.
* * * * *