Method and apparatus for storing heat energy

Method and apparatus for storing of heat by use of the heat of fusion or crystallization of a liquid-solid storage medium. A conventional crystallization roller rotates with its circumference partially immersed in the melted storage medium. Heat receiving liquid circulated through the drum to a point of use receives heat from melted storage medium in contact with the drum, whereby such storage medium solidifies on the surface of the drum. The drum rotates the solidified storage medium past a fixed scraper which transfers the solid storage medium to a heat exchanger. Heat supplying liquid circulating through the heat exchanger imparts its heat to, and melts, the scraped-off storage medium which returns to the storage medium reservoir and brings with it the heat obtained from the heat supplying liquid.

FIELD OF THE INVENTION 
The present invention relates to a method and apparatus for storing heat 
energy by the employ of a crystallization cylinder for utilizing heat 
energy available at inopportune times or at unsuitable temperature levels 
(e.g. solar energy). 
BACKGROUND OF THE INVENTION 
For physical reasons, a substance can assume three different states of 
aggregation, in which its specific heat may be different. The storage of 
heat with the specific heat of a substance is most suitably accomplished 
in the solid and liquid states of aggregation. This method has already 
found technical application for instance in storage radiators with a stone 
filling and in water storage boilers. From the viewpoint of thermodynamics 
it appears more expedient to employ for storage purposes the heat energy 
required for a change of the state of aggregation, since this amount of 
heat is in many cases a multiple of the specific heat amount, and the heat 
exchange takes place at a constant temperature level. Of particular 
technical interest is the storage of heat by way of crystallization or 
fusion heat. The heat can be readily exchanged with a storage medium in 
the liquid or solid state. An obstacle for the technical employ of the 
fusion heat storage on a major scale is the crystallization delay which 
may cause the onset of crystallization to shift several degrees Celsius 
due to the lack of suitable nuclei or starting points. 
It is an object of the present invention to provide a method and apparatus 
as set forth in the introduction, permitting the storage of heat to be 
accomplished by way of crystallization or fusion heat. 
In order to attain this object by the said method, the invention provides 
that a heat-supplying primary carrier liquid is employed to convert a 
solid storage medium to the liquid state by supplying fusion heat thereto, 
and a secondary carrier liquid is employed for recovering heat on demand 
by causing said secondary liquid to flow in a desired amount through a per 
se known rotary crystallization drum immersed with a portion of its 
circumference in the liquid storage medium, so that said storage medium 
solidifies on the walls of said drum, whereupon the solidified storage 
medium is again carried into heat exchange relationship with the 
heat-supplying primary carrier liquid by the rotation of said drum. 
According to the invention the problem of crystallization delay is solved 
by generating the nuclei or starting points for the crystallization by a 
continuous mechanical action. This mechanical generation of the starting 
points is accomplished by the rotation of the drum in the liquid storage 
medium, said drum being comparable in the widest sense with a so-called 
flaking machine or crystallization drum. 
The method according to the invention offers the possibility to employ the 
fusion heat for storing heat energy on a commercial scale. The primary 
carrier liquid serves as supplier of heat for introducing heat into the 
system either continuously or at arbitrary intervals. The storage medium 
receives and stores the supplied heat. If there is then a demand of heat, 
the secondary carrier liquid is fed through the drum. The withdrawal of 
heat by the secondary carrier liquid causes the storage medium adjacent 
the walls of the crystallization drum to be cooled down. This results in 
the storage medium crystallizing on the crystallization drum and being 
subsequently carried in the solid state to an elevation above the level of 
the storage medium by the continuous rotation of the drum. The drum thus 
serves not only as a crystallization base, but also for conveying the 
solidified storage medium toward a location whereat it is to be brought 
into heat-exchange relationship with the heat-supplying primary carrier 
liquid. In most cases this location will be defined by a heat exchanger. 
At this point the cycle starts anew, since the primary carrier liquid 
reconverts the conveyed amount of the solidified storage medium to its 
liquid state in accordance with the available heat supply, the liquefied 
storage medium being returned to the body of the liquid storage medium. 
In order to attain the stated object by said apparatus, the invention 
provides that a heat-supplying primary carrier liquid is employed to 
convert a solid storage medium to the liquid state by supplying fusion 
heat thereto, and a secondary carrier liquid is employed for recovering 
heat on demand by causing said secondary liquid to flow in a desired 
amount through a per se known rotary crystallization drum immersed with a 
port of its circumference in the liquid storage medium, so that said 
storage medium solidifies on the walls of said drum, whereupon the 
solidified storage medium is again carried into heat exchange relationship 
with the primary carrier liquid by the rotation of said drum. 
For the proper functioning of the method and apparatus according to the 
invention it is not essential that the primary carrier liquid be identical 
to the secondary liquid. Suitable storage media are any substances having 
their phase conversion point from the solid to the liquid state within the 
range of the desired storage temperature. 
The heat exchanger may be, but does not have to be, located above the 
storage medium. Depending on the properties of the storage medium, the 
heat exchanger could for instance be immersed in the storage medium in the 
form of a coil heat exchanger. 
In the apparatus according to the invention, the secondary carrier medium 
is supplied to the interior of the drum through an inlet, and is then 
heated within the drum. The heated secondary carrier liquid may then be 
pumped off or exhausted through an outlet. The introduction and exhaustion 
of the secondary carrier liquid to the interior of the drum and from the 
drum, respectively, may be carried out continuously or intermittently. 
The drum is rotated during the heat exchange between the storage medium and 
the secondary carrier liquid. This enables a layer of solidified storage 
medium to form on the outer surface of the drum during its immersion in 
the liquefied storage medium. During rotation of the drum, this solidified 
layer is removed from the drum surface by means of a scraper assembly and 
conveyed to a portion of the reservoir space whereat the solidified 
storage medium may be reconverted to its liquid state by the available 
heat supply of the primary carrier liquid.

DETAILED DESCRIPTION 
The shown apparatus according to the invention comprises a closed reservoir 
1 provided with an outer insulation layer 2. Supply and return ducts 3, 4 
for a primary carrier liquid extend through the reservoir wall to 
communicate with a heat exchanger 5 provided with a grid. The primary 
carrier liquid conveys the heat to be stored into the reservoir, wherein 
this heat is employed to convert a solidified storage medium 6 on the heat 
exchanger grid to the liquid state. The storage medium is thus liquefied 
by heat exchange and stores the supplied heat in the form of fusion heat. 
During liquefication, the storage medium drops off the grid into the lower 
portion of the reservoir 1 wherein it is collected in the form of a liquid 
body 13. 
Located within the reservoir is a crystallization drum 11 supported in the 
present case for rotation about a horizontal axis, so that a portion of 
its circumference is immersed in the liquid storage medium body 13. In an 
advanced embodiment of the invention, the mounting of the drum may not be 
stationary, but rather vertically adjustable with respect to the level of 
the liquid body 13. 
An inlet 7 for a secondary carrier liquid extends through one stub axle of 
the crystallization drum, said inlet having a closed end 12 and a 
plurality of exit openings interiorly of the drum. An outlet duct 8 for 
the secondary carrier liquid extends through the other stub axle of the 
drum. The outlet duct 8 has a depending open end portion serving to 
withdraw the secondary from the interior of the drum as by means of a pump 
for conveying it to the heat consumer. 
The secondary carrier liquid contained in the drum is heated at the drum 
wall by the heat surrendered by the storage medium. This causes the 
storage medium immediately adjacent the outer surface of the drum to cool 
so as to adhere to the drum in the form of a solidified crystal layer 9. 
The thickness of the crystal layer may be varied by varying the immersion 
depth and/or rotational speed of the drum. Rotation of the drum causes the 
crystallized layer 9 to be conveyed upwards in the direction of arrow P to 
a location above the liquid body. During rotation of the drum, the 
solidified layer adhering thereto is detached therefrom by means of a 
scraper arrangement 10 in the form of a downwardly inclined doctor blade 
in tangential contact with the drum, and returned to the grid of the heat 
exchanger 5. The so formed crystal flakes are collected on the heat 
exchanger grid in preparation for storing the heat supplied by the primary 
carrier liquid by liquefication, thus completing the cycle. In the 
embodiment of the invention shown, the heat exchanger 5 is located above 
the level of the liquid storage medium, so that the grid is at a higher 
elevation than the axis of rotation of the crystallization drum. The 
scraper arrangement forms a guide surface inclined downwards from the 
surface portion of the crystallization drum carrying the solidified 
storage medium towards the end of the grid adjacent the drum. It is also 
possible, however, to arrange the heat exchanger in a different manner. 
Depending on the properties of the storage medium, it could also be 
designed as a coil heat exchanger immersed in the storage medium. In this 
case the scraper arrangement would have to be modified so as to enable it 
to perform its function as a conveying means between the crystallization 
drum and the heat exchanger.