DE3029780A1 - Initiating crystallisation of supercooled melt - with initiator effective only in supercooled temp. region, useful in latent heat store - Google Patents

Abstract

Initiation of the crystallisation of supercooled melts of one or more chemical substances, e.g. salts, is effected by placing insert(s) in the melt or on the walls of the vessel which act as initiator(s) only in the supercooled temp. range. The inserts are crystals or mechanical inserts, e.g. wires, rods, tubes, spirals etc., the surface of which wholly or partly contains crystals with a structure isotypical or epitaxial w.r.t. the me.t and with a m.pt. above the max. temp. occurring when the crystals are melted. To initiate crystallisation, the crystals are cooled by external means, pref. by Peltier element(s) or batteries or by thermodynamic equipment. The insert can be pt. (of the vessel walls) of a cooling aggregate, heat pump, heat exchanger or adiabatic equipment using the cooling of expanding gases (CO2). The process is used in latent heat stores and allows the advantages of supercooling to be utilised.

Description

B e 5 c h r e 1 b u n g

The invention relates to methods and measures for triggering crystallization of melting chemical substances. This process is sometimes also called "retrieval" The technical purpose of such a call is to make it available and usable the energy content of such melts when changing phases. Are required here the terms known to those skilled in the art of latent heat and enthalpy, where the term enthalpy is only used with reservations.

It is known that molten crystals, especially hydrates, tend to hypothermia, i.e. that the chemical substance is also below the actual melting temperature or the transition temperature in the liquid state remains. It is also known that the crystals develop during melting - which in the ideal case takes place at constant temperature - absorbed heat for Use of energy storage (using enthalpy of fusion or latent Warmth).

A melt cannot easily go down to an arbitrarily low level Subcool temperature or be subcooled.

It mostly depends more or less on coincidences which Spontaneous crystallization occurs. However, it is known that when adhered to certain circumstances, which depend on the melting material and its composition, a certain temperature range of hypothermia be respected can. Within this range, crystallization can only be achieved through targeted measures, to which he invention belong to be initiated.

In general, however, hypothermia is undesirable.

Top Reasons To Avoid Hypothermia speak are well known from the literature. Only the stratification and the undefined temperature, which is often dependent on randomness, at which one supercooled melt crystallized out spontaneously.

Nevertheless, it has already been proposed to use molten salt for heating purposes to undercool, with the melting point above room temperature, the possible However, the subcooling temperature is below room temperature.

Such proposals, however, are only those of the person skilled in the art per se data that are already known and can be taken from the literature, e.g. that the melting point of 0 sodium acetate trihydrate is + 58 c and a melt 0 of this substance can be supercooled to below OC under favorable circumstances. The same applies to many other salts, especially hydrates, such as sodium thiosulphate, Glauber's salt and The technical and economic use of hypothermia is similar, however not given by - as e.g.

in DE - OS 24 48 739 - only gives tabular values.

What is decisive is a technical instruction on how to make practical use of the conditions known from basic research can.

The advantages of a technically mastered and technically controllable Hypothermia are undeniable. Is the melting temperature or the transition temperature at a temperature that makes the use of a heat pump economically viable power to domestic hot water in the household or hot water for central heating to deliver, e.g. Glauber's salt 32 OC or N-at-rium acetate tri-0 hydrate 58 C, and will, what is technically possible, hypothermia to at least room temperature or The basement temperature, i.e. around 200C or 120C, is used for storage such a storage tank does not require any thermal insulation, i.e. the stored energy can be stored without loss.

However, the problem with which the present invention is concerned is the aforementioned "retrieval".

These measures include primarily the "vaccination" with appropriate Crystals. This is understood to mean in a known way the addition or the presence of chemical substances in solid, crystalline form, with three groups of crystals, based on the crystal structure of the material, the following are used and differentiated: 1. identical or isomorphic, 2. isotypic, 3. epitaxial.

When a chemical substance, especially a salt hydrate such as e.g. typically Glauber's salt, to be used reversibly as an energy store, so it is customary the storage substance isotypic or epitaxial To add crystals which have a melting point which is above the melting point the substance lies, is even higher than the so-called "overload temperature" that occurs in practice - this is the highest temperature which occurs or occurs during "charging" can - so that these crystals are always present in the melt in the solid state are. The presence (presence) of such crystals causes - if it works - That supercooling does not occur, so that the melt as the temperature drops starts to crystallize when the typical melting or transition point is reached But the presence of such crystals also means that crystals are definite Structure are formed because many melts per se crystals of different Structure and not all of these structures can form the desired enthalpy of fusion or have other technically harmful properties.

Contrary to the common belief that hypothermia is avoided but the thought - but no more than the thought - is also a conscious one or intentional hypothermia - as I said - known. It is now evident that in such a case, the above-mentioned crystals commonly used do not can be used without further ado, because these are supposed to prevent hypothermia avoid.

However, if one wants to take advantage of hypothermia, this means that the melt only at the desired time of the start of crystallization Seed crystal (or more) can, may or must be added Takes If you add isotypic or epitaxial crystals, then such a melt is usually Can only be used once, because repeated hypothermia due to the presence of this Crystals is prevented.

If you want to go through the melt-crystallization cycle practically as often as you like Use as latent heat storage, so initially only the supercooled one is advisable Inoculate melt with identical crystals. This measure is technically unsatisfactory.

Surprisingly, it is possible according to the invention, despite the presence isotypic or epitaxial crystals lead to supercooling of the melt achieve and take advantage of their advantages.

The present invention is based on the fact that for education of a crystal - e.g. an ion crystal such as NaCl - energy is released when the Crystal by approaching the components - e.g. the ions from "infinite" distance - is formed. The formation of the crystals, especially the spontaneous formation of the The deeper the first or the first crystal or crystals, the sooner it becomes possible is the temperature, i.e. the smaller the mobility, i.e. the statistical kinetic Power of the components is.

In the case of hypothermia there is the phenomenon that the disordered Movement of the components is still too great for the components to "come together" to enable.

Crystal formation can now be forced in various ways. One of these possibilities is that a supercooled melt as the temperature drops crystallized "sometime". The quotation marks next to the word "sometime" indicate indicates that the beginning of crystallization is completely indefinite and of not reconstructable factors, states and conditions depends.

Another option is inoculation through crystals, being too it should be noted that the uncontrolled spontaneous crystallization actually also eie Is inoculation, namely with some crystal structure of the material of the vessel, in which the melt is located or the materials which are in the melt are located, for example heat exchangers. Even substances that are classified as "impurities" are in most cases crystalline, if only possibly in the molecular domain.

It is state of the art to add crystals to the melt, which should avoid any hypothermia with its known alleged disadvantages.

Between these two extreme possibilities lies a third, which The subject of the invention is.

To explain the idea on which the main claim is based must be pointed out to the systematics of the crystal structure, which in the professional world is by no means uniform.

For example, 7 systems are set up (this means, for example, tetragonal or hexagonal, etc.). Continue to be e.g. Trigonal-bipyramidal class or rhombic-biphenoid class). In addition there is the derivation of 230 room groups. If you now consider that almost all (if not all) of the more than one million known chemical substances are crystalline, although organic substances may only be in the microscopic range, it is not possible to cover all chemical-technical possibilities within the scope of this description to represent.

Therefore, only one example characterizing the invention can be used here to be named.

Depending on the water content, sodium acetate has a melting point between around 500C and 70C. The melt can be supercooled according to the state the technology in a known manner up to at least OOC. It is understandable that by Adding crystals to the "retrieval" can be done at a certain temperature. The technique used to date to avoid hypothermia uses crystals used to avoid this hypothermia.

In the other extreme case, the melt remains down to a low temperature get and crystallize only when in the whole melting system, to which too the vessel, heat exchanger and incidental impurities belong to a seed crystal structure is present, which triggers the first crystal formation and thus the "chain reaction" initiates the entire crystallization of the melt. The most ideal seed crystal is the identical crystal of the melt, of course. But there are also crystals the still in a certain range below the melting temperature do not induce crystal formation, e.g. by means of state-of-the-art measures such as OS and the like.

In the case of sodium acetate, for example, mica can be found in the supercooled melt be present without crystal formation occurring at room temperature. Will however, if the 0 crystalline mica is cooled down to about 0 C, then crystallization occurs and the whole melt gives off its heat content at 500 to 700C. The process is reversible, which means that the crystallized mass is melted again can and in spite of the presence of mica undercooled in the manner mentioned.

This method according to the invention works particularly effectively, if the melt by known processes that are not the subject of the invention, is brought into a quasi-stable state, which allows a strong hypothermia.

Appropriately, one uses for the triggering solid substance, which is of course not soluble in the melt, crystals that are the same system how to belong to the melt.

Both sodium acetate and mica belong to the monoclinic system at.

Because of the very large. Variety of chemical compounds and the Crystal room groups can only be given this example, but still be pointed out that as practical latent heat storage materials Sodium thiosulphate and Glauber's salt are also currently in the foreground of interest stand, but the invention is not limited to these materials.

For the technical implementation of the invention it should be said: For "charging" the storage, i.e. the melting of the crystals, can be any heat source be used, preferably in the melt heat exchanger in known Form. Solar collectors, for example, can be used as a heat source or the waste heat from any technical or industrial process, such as Waste heat from power plants. Also the outflowing service water in the household or in the Industry can be used, taking the necessary temperature increase for melting of the crystal memory by additional electrical heating or by using a Heat pump is achieved.

When charging, of course, the temperature must be above the melting temperature, but it must not be the melting temperature of the invention Reach the trigger crystal located in the melt, as this is always in the solid State must remain.

The application of the release crystals according to the invention can be done in many ways Species are made. It is only important that the crystal cools down can be made externally up to the temperature which initiates the "retrieval" can, i.e. the storage container does not need to be opened. E.g. a Peltier element or a Peltier battery through the wall of the Container are guided, with the trigger crystal at the inner so-called soldering point is attached. But any other form of cooling is also possible, as in the Claims presented.

The meaning of the invention will be explained using an example. Sodium thiosulphate, which has a melting point, more precisely: transition point, of about 48.5 ° C, with appropriate preparation, which is considered to be the state of the art here is assumed to be cooled down as a melt until well below OOC. Will the melt energy Applied by solar panels, the stored latent heat can be used Any room or basement temperature without insulation and without loss of energy be kept for a long time. Now the trip crystal according to the invention, which is inside the melt, through the measures already mentioned from the outside, i.e. cooled down without opening the reservoir, crystallization is initiated and the memory emits all of the latent heat at a temperature of approx. 480C which can be used to heat domestic water. Expressed in extreme terms, this means that the solar energy obtained in summer is available in winter. Since according to the Invention of the memory does not need to be opened, there is also no possible Pollution and no change in the water content of the melt. It will i.e. F-actuators, which could unfavorably change the properties of the storage, avoided.

Claims (13)

Procedure and measures for triggering the crystallization of supercooled Melting Claims 1. Processes and measures for triggering crystallization of melts, also called retrieval in the following, the melts from a or can consist of several chemical substances, e.g. salts, in the following generally called crystalline substance, even if several substances are involved, which are in a temperature range below their melting or transition temperature meta- or quasi-stable, so-called supercooled, and in which the melt is located involved ions can arrange molecules etc. into solid crystals and thereby give off or give off an energy which is essentially theoretical corresponds to the enthalpy of fusion, that in the melt or at the edge of the melt, i.e. the vessel wall, one or more components is or are attached, which (s) as initiator (s) for the formation of crystallization only below the actual melting or transition temperature, i.e. in the subcooling range of crystalline substance is or are effective. 2. The method according to claim 1, d a d u r c h g e -k e n n z e i c h n e t that the components are crystals or mechanical components such as wires; Rods, tubes, spirals, etc., which on their surface wholly or partially have crystals contain, which have a crystal structure that is one opposite to the melt have isotypic or epitaxial structure and their melting temperature above the highest temperature occurring during the melting of the crystals. 3. The method according to claims 1 and 2, d a -d u r c h g e k e n It should be noted that the crystals are not in the sense of crystal chemistry and physics are specifically isotypic or have an epitaxial effect, but with sufficient cooling trigger crystallization (retrieval). 4. The method according to the preceding claims, d a -d u r c h g e k e It should be noted that the crystals are only below those typical for the melt Melting or transition temperature exert their inoculation effect, so that the melt supercooled in a range below the typical melting or transition temperature without crystallization (retrieval) from the crystals present. is triggered. 5. The method according to the preceding claims, d a -d u r c h g e k e It should be noted that to initiate crystallization the crystals through external measures are cooled. 6. The method according to the preceding claims, d a -d u r c h g e k e n n z e i n e t that the cooling by one (s) or more Peltier element (s) or Peltier battery (s). 7. The method according to the preceding claims, d a -d u r c h g e k e n n z e i c h n e t that the cooling via a thermodynamically operated device he follows. 8. The method according to claim 7 and the preceding claims, d a D u r c h g e k e n n n n e i c h n e t that the component is part of a cooling unit (Refrigerator, freezer, etc.) is. 9. The method according to claim 7 and preceding claims, d a d u It is noted that the component is part of a heat pump. ok Method according to claim 7 and the preceding claims, d a d u r c h e k e n n n z e i c h n e t that the component is part of an adiabatically acting Device taking advantage of the cooling of expanding gases is. 11. The method according to claims 7 and 1O and the preceding claims, it is noted that the expanding gas is carbon dioxide is. 12. The method according to claim 1 and the following claims, d a d It is indicated that the structural elements are parts of the vessel wall. 13. The method according to claim 1 and the following claims, d a d It is indicated that the components are parts of heat exchangers are.