U.S. patent application number 11/990721 was filed with the patent office on 2010-03-25 for fresnel solar collector arrangement.
Invention is credited to Johannes Gottlieb, Max Mertins, Martin Selig.
Application Number | 20100071683 11/990721 |
Document ID | / |
Family ID | 36778962 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071683 |
Kind Code |
A1 |
Selig; Martin ; et
al. |
March 25, 2010 |
Fresnel solar collector arrangement
Abstract
The invention relates to a Fresnel solar collector arrangement
consisting essentially of a receiver (1) and a mirror arrangement
associated with the receiver (1). The arrangement is
temperature-compensated by the use of materials with the same
temperature expansion coefficient for the receiver mast (2) and the
mirror supporting framework (4), and the adjustment of the primary
mirror (6, 6') in relation to the sun by a mechanical coupling of
the mirror is simplified by means of an electromotive connecting
rod.
Inventors: |
Selig; Martin; (Karlsruhe,
DE) ; Gottlieb; Johannes; (Karlsruhe, DE) ;
Mertins; Max; (Freiburg, DE) |
Correspondence
Address: |
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
36778962 |
Appl. No.: |
11/990721 |
Filed: |
August 18, 2006 |
PCT Filed: |
August 18, 2006 |
PCT NO: |
PCT/DE2006/001441 |
371 Date: |
May 22, 2008 |
Current U.S.
Class: |
126/605 ;
126/684 |
Current CPC
Class: |
F24S 50/20 20180501;
Y02E 10/47 20130101; F24S 30/425 20180501; F24S 2023/872 20180501;
F24S 23/80 20180501; F24S 2030/15 20180501; F24S 23/77 20180501;
F24S 2030/136 20180501 |
Class at
Publication: |
126/605 ;
126/684 |
International
Class: |
F24J 2/38 20060101
F24J002/38; F24J 2/10 20060101 F24J002/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2005 |
DE |
10 2005 039 404.3 |
Feb 9, 2006 |
EP |
06002605.1 |
Claims
1. Fresnel solar collector arrangement having at least one receiver
(1) mounted on a receiver supporting framework, elevated relative
to several primary mirrors (6, 6') that are disposed on a mirror
supporting framework (4) on both sides of the receiver (1) so as to
pivot, in such a manner that the solar radiation reflected by the
primary mirrors (6) is focused at least essentially onto the
receiver (1), and the primary mirrors (6) are, in each instance,
made to track the sun, wherein the mirror supporting framework (4)
that extends bilaterally outward from the receiver supporting
framework is mounted in a fixed location in the region of the
receiver supporting framework and/or in connection with the
receiver supporting framework and, for the remainder is mounted to
slide, i.e. in constraint-free manner, at least to a great
extent.
2. Fresnel solar collector arrangement according to claim 1,
wherein the receiver supporting framework and the mirror supporting
framework (4) are made from a material having at least largely
identical material expansion coefficients, preferably from steel
37, in each instance.
3. Fresnel solar collector arrangement according to claim 1,
wherein the receiver (1) comprises an absorber tube that is mounted
in an elevated manner by means of a row of receiver masts (2),
preferably disposed in an imaginary straight line, which
essentially form the receiver supporting framework, and that the
mirror supporting framework (4) comprises supporting rails (5) that
are spaced apart from one another and connected in a framework-like
manner by means of appropriate struts, if necessary, whereby these
supporting rails (5) extend outward at least essentially
orthogonally from an imaginary straight line of the receiver masts
(2) disposed in a row, and that these supporting rails (5) are
fixed in place in connection with the receiver masts (2), or in the
foundation region of the receiver masts (2), and otherwise are
mounted to slide.
4. Fresnel solar collector arrangement according to claim 1,
wherein the primary mirrors (6, 6') disposed on a common supporting
rail (5) along an imaginary line parallel or perpendicular to the
longitudinal expanse of the absorber tube of the receiver (1), are
combined to form a primary mirror group, whereby the primary
mirrors (6, 6') of the primary mirror group are mechanically
coupled by means of a common setting element and, as a result, are
made to track the sun together.
5. Fresnel solar collector arrangement according to claim 4,
wherein the primary mirrors (6) assigned to one or more supporting
rails (5) disposed in an imaginary extension relative to one
another are combined to form a primary mirror group.
6. Fresnel solar collector arrangement according to claim 5,
wherein the primary mirrors (6, 6') of the primary mirror group
are, in each instance, mounted to pivot on the supporting rail(s)
(5), whereby these primary mirrors (6) are rigidly connected with
one another by means of a connecting rod (10, 10'), preferably
driven by an electric motor, and can be pivoted together, relative
to the absorber tube of the receiver (1), by means of linear
movement of the connecting rod (10, 10') in the direction of the
longitudinal expanse of the connecting rod (10, 10'), in terms of
their respective angle of incidence.
7. Fresnel solar collector arrangement according to claim 6,
wherein the primary mirrors (6, 6') of a primary mirror group are
firmly connected with one another by means of a tracking shaft
(17), for the purpose of common pivoting, which shaft is
essentially disposed parallel to the longitudinal expanse of the
absorber tube, to rotate relative to the supporting rails (5).
8. Fresnel solar collector arrangement according to claim 7,
wherein the tracking shaft (17) is mounted in a roller bearing
block (15) that surrounds the shaft, whereby the shaft is held in
the roller bearing block (15) by means of a multiplicity,
preferably three, of barrel-shaped roller elements (16, 16', 16''),
in such a manner that axial rotation of the tracking shaft (17) is
made possible.
9. Fresnel solar collector arrangement according to claim 5,
wherein the connecting rod (10, 10') can be displaced by a motor in
the direction of its longitudinal expanse, by means of a linear
motor (11).
10. Fresnel solar collector arrangement according to claim 6,
wherein the linear motor (11) is preferably disposed in the region
of the receiver mast (2), and one or more connecting rods (10, 10')
are driven by the linear motor (11), whereby the primary mirrors
(6) disposed on the right of the receiver (1) are moved opposite
the primary mirrors (6') on the left of the receiver (1), for the
purpose of tracking, whereby this opposite movement is implemented
by means of a corresponding deflection mechanism provided on only
one side of the receiver (1).
11. Fresnel solar collector arrangement according to claim 1,
wherein a heat storage medium, preferably steam or thermal oil,
flows inside the absorber tube.
12. Fresnel solar collector arrangement according to claim 10,
wherein the receiver (1) additionally comprises a secondary
reflector assigned to the absorber tube, which essentially absorbs
the scattered radiation reflected by the primary mirrors (6, 6'),
and deflects it onto the absorber tube.
13. Fresnel solar collector arrangement according to claim 1,
wherein the dimensions and spacings of the primary mirrors (6, 6')
are dimensioned in such a way that mutual shadowing of the primary
mirrors (6, 6') is precluded, at least to a great extent.
Description
[0001] The invention relates to a Fresnel solar collector
arrangement.
[0002] This is understood to mean a line-focusing system in which
multiple mirror strips disposed parallel to a receiver are made to
track the position of the sun, and the solar radiation is guided
onto a fixed absorber tube in which a heat storage medium flows. In
addition, a secondary reflector assigned to the absorber tube
guides the radiation onto the focal line essentially formed by the
absorber tube. The absorber tube and the secondary reflector form
the receiver disposed in elevated manner above the mirror strips.
Such a Fresnel solar collector is currently in operation in
Australia, for example, in a field trial. The heat that is produced
can be utilized as process heat, or it can be converted into an
electric current, for example by means of a Stirling motor.
[0003] The advantage of Fresnel solar collectors as compared with
conventional parabolic trough collectors lies in their
significantly simplified structure. Parabolic trough collectors
consist of a reflector that has the shape of a parabolic cylinder.
Here also, the light is focused onto a line, the focal line. The
absorber tube of the parabolic trough collector, which absorbs the
concentrated radiation and passes it on to the medium flowing
through, is situated in this line. In this connection, the medium
is typically heated to values of approximately 400.degree. C. In
order to improve the efficiency, the absorber can be surrounded by
a glass tube. A vacuum prevails in the interstice between absorber
tube and glass tube, for insulation. The "solar steam" produced in
this way can also be utilized directly for process heat
applications, or for conventional steam power plants and
cogeneration power plants.
[0004] Alternatively, flat collectors and CPC collectors are known
as further types of collectors.
[0005] In this connection, the efficiency of the Fresnel solar
collector essentially depends on how well the reflected solar
radiation is focused onto the absorber tube. For this purpose, it
is practical to make the primary mirrors assigned to the absorber
tube track the sun. Only in this way can acceptable efficiencies be
achieved for the system. This usually takes place by means of an
electric motor assigned to each primary mirror. In turn, the
electric motors are usually provided with a timing device, so that
tracking is more a question of controlling than of regulating.
[0006] A significant problem with Fresnel solar collectors is that
such arrangements achieve their best efficiencies in regions with
the highest incoming solar radiation, for example in desert
regions, where extreme temperature variations from degrees below
zero to degrees above zero of far in excess of 40.degree. C. are at
least not unusual. The materials and supporting structures used are
exposed to considerable stresses, in this connection, whereby
thermal deformations of the material are practically unavoidable
and therefore can lead to angular deviations within the entire
system, which can be manifested in the double-digit percentage
range in the efficiency of the entire system. Even a small angle
deviation in the supporting structure of the mirror arrangement can
lead to having a large part of the radiation reflected by the
primary mirrors not focused onto the absorber tube but rather
reflected past the absorber tube. Furthermore, individual control,
i.e. individual regulation and coordination of the various electric
motors for tracking, i.e. controlling the panning movement of the
mirrors is accompanied by considerable regulation and control
effort, making the system somewhat susceptible to
malfunctioning.
[0007] Proceeding from this prior art, the invention is based on
the task of configuring the system more robustly, overall, and of
improving its efficiency as much as possible.
[0008] This task is accomplished by means of a Fresnel solar
collector arrangement according to the main claim. Advantageous
embodiments can be seen in dependent claims 2 through 11.
[0009] Because, according to the main claim, the mirror supporting
framework is mounted in a fixed position in the region of the
receiver supporting framework and/or in connection with the
receiver supporting framework, and furthermore is mounted in
sliding manner, i.e. free from constraint, it is assured, in the
case of unavoidable thermal expansion of the supporting framework
as a result of the effects of heat, that the mirror supporting
framework balances out these corresponding changes.
[0010] This succeeds even better if the receiver supporting
framework and the mirror supporting framework are essentially made
from the same material and are essentially mounted in fixed manner
at the same location. If thermal expansions or contractions of the
material occur, one can at least approximately assume that the
alternating expansions of the supporting frameworks take place to
the same extent. For example, the receiver mast is then expanded,
as the result of the effect of heat, in approximately the same way
as the mounting rails of the primary mirrors disposed as the mirror
framework. Because the receiver framework and the mirror supporting
framework are at least essentially disposed orthogonal relative to
one another and are made from the same material, and therefore have
the same expansion coefficient, it is assured that the angle
relationships do not change relative to one another or, at most,
change only slightly. However, this is possible only if both the
receiver framework and the mirror supporting framework are mounted
in constraint-free manner, i.e. only one of at least two required
supports is fixed in place. This surprisingly simple solution
eliminates complicated re-adjustments for material expansions or
contractions, or making a largely hopeless attempt to use materials
that are more or less temperature-independent. The use of such
materials is usually ruled out for cost reasons alone.
[0011] In a concrete embodiment, the receiver of the Fresnel solar
collector arrangement can be mounted as an absorber tube on a row
of receiver masts, whereby the mirror supporting framework can also
be mounted in a fixed location at the same point, if necessary
using the same concrete pedestal. In this connection, receiver mast
and mirror supporting framework are advantageously made from steel
37, in each instance, and therefore exhibit largely the same
expansion coefficient.
[0012] In an advantageous further development, some of the primary
mirrors mounted on the mirror supporting framework are combined to
form a primary mirror group, which in turn are mechanically coupled
by means of a common mechanical setting element, for tracking
purposes, and thus are made to track the sun. Because of the use of
a common setting element, complicated coordination, complicated
control and regulation of the electric motors used is eliminated,
at least within the primary mirror group in question. Instead, the
entire primary mirror group can be adjusted by means of a common
setting element, whereby the relative angle relationship between
the primary mirrors is maintained at all times. Again, this is
based on the actually trivial recognition of the law governing
radiation, that the relative angle adjustments of the primary
mirrors required in the course of tracking the sun, where these
mirrors are disposed one behind the other, in an imaginary
orthogonal line relative to the absorber tube, which is disposed at
a distance and elevated, are the same relative to one another.
Incidentally, this would also apply to the primary mirrors disposed
on an imaginary line parallel to the absorber tube.
[0013] In this connection, the embodiment of the collector
arrangement explained above, with mechanical coupling for the
common panning movement of the primary mirrors by means of a common
setting element, is also advantageous independent of the
constraint-free mounting of the mirror supporting framework.
[0014] This common panning movement is achieved as a result of
connecting the primary mirrors of a primary mirror group by means
of a tracking shaft. Due to the movement of the connecting rod when
aligning the primary mirrors, a rotation of the tracking shaft is
brought about, which is uniformly transferred to the entire primary
mirror group by means of the connection.
[0015] It is advantageous if the tracking shaft is mounted, at
regular intervals, in roller bearing blocks that surround the shaft
but that only support it using roller elements. These roller
elements permit axial rotation of the tracking shaft, and are
formed in barrel-like shape, in other words are essentially
cylindrical, whereby their mantle surfaces bulge out. This shape
makes it possible to dispose the tracking shaft not only along
planar surfaces but also, if required, to guide it along its path
over different heights. The shaft can be positioned at a slant on
the roller elements, so that simultaneous slanted positioning of
the roller bearing block can be eliminated.
[0016] In a concrete embodiment, mechanical coupling of the primary
mirrors combined to form a group can be implemented by means of a
common connecting rod, by way of which the primary mirrors mounted
on the mirror supporting framework so as to pivot are pivoted
relative to the absorber tube, as a function of the position of the
sun, i.e. the time of day or, to say it better, they are made to
track the sun.
[0017] In an advantageous embodiment, the connecting rod is driven
by an electric motor, using a linear motor, whereby the connecting
rod, which is disposed orthogonally relative to the longitudinal
expanse of the absorber tube, is moved inward or outward, as a
function of the sun's position, by means of the linear motor.
[0018] In an advantageous embodiment, water vapor or thermal oil
flows inside the absorber tube and is heated to a temperature of up
to approximately 400.degree. C. by the reflected radiation. The
thermal medium heated in this way can then be passed to further
use, in known manner, or can be used to produce electricity.
[0019] In order to further improve the efficiency of the
arrangement despite the improved angular accuracy of the
arrangement, a secondary reflector is additionally assigned to the
absorber tube, which reflector surrounds the absorber tube
essentially like a shield, and thus captures and deflects possible
scattered radiation from the primary mirrors, in such a way that
this scattered radiation is also focused onto the absorber
tube.
[0020] Thus the secondary reflector is also disposed so that the
absorber tube lies essentially in the focal line of the secondary
reflector.
[0021] In a further embodiment of the electric motor drive, the
linear motor is also disposed essentially centrally, i.e.
approximately in the region of the imaginary line formed by the
receiver masts disposed in a row. In this connection, when one and
the same linear motor is used for turning, one or more primary
mirror groups driven by one or more connecting rods, on the left of
the absorber tube, and one or more primary mirror groups driven by
one or more connecting rods, on the right of the absorber tube, can
be driven in such a way that a time-controlled panning movement of
the primary mirrors, i.e. a panning movement that tracks the sun,
takes place relative to the absorber tube.
[0022] The necessarily opposite movement of the primary mirrors on
the right of the absorber tube in comparison to the primary mirrors
on the left of the absorber tube is implemented by means of a
deflection mechanism for the linear movement of the connecting rod,
assigned to only one of the two sides.
[0023] In an advantageous embodiment, the linear motors can be
connected to a common control and/or regulation unit, since the
relative movements to be carried out by the connecting rods are
exactly identical over the entire length of the absorber tube, and
thus common regulation is possible for the entire system.
[0024] The invention will be explained in greater detail below,
using an exemplary embodiment only shown schematically in the
drawings.
[0025] The drawing shows:
[0026] FIG. 1: a Fresnel solar collector arrangement in
cross-section,
[0027] FIG. 2: a detail of the Fresnel solar collector arrangement
in a schematic diagram, and
[0028] FIG. 3: a control diagram for the Fresnel solar collector
arrangements shown in FIGS. 1 and 2.
[0029] According to the illustration in FIG. 1, the Fresnel solar
collector arrangement consists of a receiver 1 mounted on a
receiver mast 2. For this purpose, the receiver mast 2 is mounted
in a fixed bearing 3 that simultaneously represents the center axis
of a mirror supporting framework 4 disposed with angle symmetry. In
this connection, the mirror supporting framework 4 essentially
consists of supporting rails 5 made from the same material as the
receiver mast 2, namely steel 37 in the case of the present
exemplary embodiment, and extend orthogonally outward, in each
instance, from the longitudinal axis of the receiver 1. In this
connection, the receiver 1 essentially consists of an absorber tube
in which a thermal medium that acts as a heat storing material
flows. This can be simple steam or a thermal oil. The absorber tube
is generally surrounded by a secondary reflector that captures any
stray radiation of the mirror arrangement and deflects it onto the
absorber tube. The primary mirrors 6, 6' are mounted to pivot on
both sides of the supporting structure, i.e. essentially with
mirror symmetry, on mirror paths relative to the receiver 1 set up
in elevated manner. In this connection, the mirror paths are
mounted on the mirror supporting framework 4 essentially in such a
way that the solar radiation acting on the Fresnel solar collector
arrangement is reflected and deflected in such a way that it is
focused onto the absorber tube in the region of the receiver 1.
Ideally, the absorber tube forms the focal line of the primary
mirrors 6, 6' mounted on the mirror supporting framework 4. In this
connection, several primary mirrors 6, 6' are to each receiver 1 at
a different distance, i.e. at an increasing orthogonal distance
from the central axis of the mirror supporting framework 4 defined
by the absorber tube.
[0030] Relative to the setup base, the mirror supporting framework
4 itself is, in turn, mounted with foot elements 7 connected only
by means of slide bearings to the supporting rails 5, which extend
in fixed manner, orthogonal relative to the longitudinal expanse of
the receiver 1. Thus, in concrete terms, the receiver mast 2 and
the supporting rails 5, which are disposed one behind the other in
the longitudinal expanse of the receiver 1, are fixed in place only
in the fixed bearing 3, and otherwise are mounted in
constraint-free manner, so as to slide. Since both the receiver
mast 2 and the supporting rails 5 are made from steel 37 and
therefore possess essentially identical expansion coefficients, any
thermal expansion of the two supporting frameworks is also
essentially the same. The longitudinal expansion of the receiver
mast 2 is thus essentially compensated in that any angle error in
the arrangement, with the possible consequence that the absorber
tube moves out of the focal line of the mirror arrangement, is
compensated by a similar expansion of the supporting rail 5.
[0031] The Fresnel solar collector arrangement according to FIG. 1
is thus essentially temperature-compensated in self-regulating
manner, in that any material expansions and contractions resulting
from the absolutely normal extreme temperature variations in the
regions of use of Fresnel solar collector arrangements are
reciprocally balanced out. As a result, the losses due to
scattering of the reflected radiation, which have a very negative
effect on the yield factor of the system, are avoided to a great
extent. Complicated techniques for compensating the changes in
length of the materials used, due to temperature, can therefore be
eliminated, to a great extent.
[0032] According to FIG. 2, the arrangement is advantageously
supplemented in that the primary mirrors 6, 6' assigned to the
individual supporting rails 5, are, in each instance, connected
with the supporting rail 5, in each instance, by means of a mirror
support 8, 8', so as to pivot. In this connection, it is known from
the prior art to assign a separate electric motor to each primary
mirror 6, 6' and to achieve tracking of the primary mirrors 6, 6'
according to the position of the sun relative to the receiver 1,
using this electric motor drive. According to FIG. 2, several
primary mirrors 6, 6' are combined to form a primary mirror group
that is characterized by being mechanically coupled with one
another by means of a common setting element, namely a connecting
rod 10, 10'. The connecting rod 10, 10' is driven in linearly
displaceable manner, by an electric motor, using a linear drive 11,
whereby the movement of the connecting rods 10, 10' on the left and
right of the receiver mast 2, and thus the movement of the receiver
1, go in opposite directions by means of a deflection mechanism not
illustrated further here. The connecting rods 10, 10' on the left
and right of the receiver 1 are thus either both moved inward or
both moved outward. This is understood to mean that one of the two
connecting rods 10 or 10' acts only indirectly on the primary
mirrors 6, 6', namely by way of a deflection mechanism that leads
to the aforementioned opposite movement. This, in turn, brings
about the result that the mirrors disposed on the right and left
are turned toward or away from the centrally disposed reflector or
absorber tube at precisely the same angle relationship. The
solution shown according to FIG. 2 therefore makes it possible to
create mechanical coupling by way of a simple connecting rod 10,
10', using a single electric motor, and thus to eliminate
complicated coordination of several individual electric motors, at
least along one supporting rail 5, i.e. within a primary mirror
group, and, instead, to allow precise tracking following the
position of the sun, using a single common linear drive, because of
the angle accuracy of the arrangement.
[0033] In this connection, according to the schematic diagram in
FIG. 3, this can be a control unit and/or a regulation unit.
According to the illustration in FIG. 3, a common regulator 12 is
assigned to the linear motors 11, 11', 11'', to which one or more
connecting rods 10, 10' or supporting rails 5 are assigned, in each
instance. In the simplest case, this regulator 12 can be controlled
in time-controlled manner, in the sense of a control, according to
a predefined program that associates every time of day with a
certain position of the sun and thus with an angle position of the
primary mirrors 6. For this purpose, the regulator 12 is
data-connected to a time detection device 14. Alternatively,
however, the regulator 12 can also be connected to a true actual
value/reference value comparator 13, whereby the actual value and
target value either compare the real position of the sun to the
target value default or, on the other hand, the efficiency of the
system is directly fed back to the regulating variable, for example
by evaluating the radiation intensity achieved or the current yield
of electricity as the actual value, in order to determine any
regulatory deviation. The angle positioning of the primary mirrors
6, 6' can then be re-adjusted using the setting element. Thus,
understood correctly, the connecting rod 10, 10' more or less
represents the setting element for the regulation or tracking of
the primary mirror arrangement, whereby the electric motor 11, 11',
11'' is also part of this setting element. The triggering or
regulation of the linear motors 11, 11', 11'' is implemented by
means of a common regulator 12.
[0034] FIGS. 4 and 5 show a roller bearing block 15 in which a
tracking shaft 17 is guided. The tracking shaft 17 connects the
primary mirrors 6, 6' of a primary mirror group and ensures
parallel rotation of all the mirrors of this group as a result of
tracking initiated by the movement of a connecting rod 10, 10'. The
roller bearing block 15 surrounds the tracking shaft 17, whereby
the shaft is mounted on roller elements 16, 16', 16'' in the roller
bearing block 15. These roller elements 16, 16', 16'' are
essentially cylindrical, but have concave mantle surfaces on which
the tracking shaft 17 is supported. As a result of this barrel-like
shaping, it is possible to position the tracking shaft 17 at a
slant as shown in FIG. 5, whereby the roller bearing block 15
remains in its perpendicular position. This allows laying the
tracking shaft 17 along slanted surfaces, for example on hills or
on uneven terrain. In this connection, one must, of course, ensure
that the receiver 1 is not covered up relative to the primary
mirrors 6, 6' in question.
[0035] Thus a Fresnel solar collector arrangement is described
above, which is temperature-compensated, to a great extent, in that
materials having the same thermal expansion coefficients are used
for the supporting rails 5 of the mirror supporting framework 4 and
the receiver masts 2 and that furthermore, the receiver mast and
the mirror supporting framework 4 are mounted in constraint-free
manner. Beyond that, tracking of the primary mirrors 6, 6' to
follow the position of the sun is significantly simplified by means
of mechanical coupling of the primary mirrors 6, 6'.
LIST OF REFERENCE SYMBOLS
[0036] 1 Receiver [0037] 2 Receiver mast [0038] 3 Fixed bearing
[0039] 4 Mirror supporting framework [0040] 5 Supporting rail
[0041] 6, 6' Primary mirror [0042] 7 Foot elements [0043] 10, 10'
Connecting rod [0044] 11 Linear motor [0045] 12 Regulator [0046] 13
Actual value/target value comparator [0047] 14 Time detection
device [0048] 15 Roller bearing block [0049] 16, 16', 16'' Roller
elements [0050] 17 Tracking shaft
* * * * *