This is a continuation-in-part of U. The present invention relates to a method of cyclically transferring heat to and removing heat from a thermal energy storage medium without degradation of the medium and consequent diminishment of the efficiency of the operation.
The need for energy storage is dictated by the fact that the demand for energy and the supply of energy both vary with time and generally this demand and supply are not synchronous. In the past century this lack of synchronization has been met by a reliance on fossil fuels. These fuels are becoming increasingly scarce and expensive and, as a result, intensive effort is being directed toward the development of alternate primary energy sources, such as solar energy.
The effective utilization of solar energy requires the development of new mechanisms and processes for energy storage, since solar energy is by nature only intermittently available. Various heat storage media have been proposed, e. The selection of a given heat storage medium will depend upon the temperature range over which heating and cooling occur.
In some instances, rather than employ a medium which undergoes a phase transition it may be more desirable to heat and cool without undergoing any phase transition, e. This latter is termed "sensible" heat storage. Liquidus pumps water this invention requires changes in the composition i.
In the case of Japanese Patent Application No. However, no direction is given therein that the temperature cycling must be carried liquidus pumps water with the system in equilibrium nor is any mention made of any intention to operate along the liquidus. Unless the system were to be deliberately maintained so that all of the solid phase liquidus pumps water is in equilibrium with the liquid phase, the temperature cycling would not occur along liquidus pumps water liquidus as required in the invention set forth herein and the operation would occur in some manner other than that defined by the instant invention.
The method of the instant invention makes possible the simultaneous utilization in thermal energy storage and retrieval of the sensible heat of water and the heat of fusion of a salt, which forms a hydrate and which undergoes a phase transition. A method for the storage and retrieval of thermal energy is disclosed, which in a two phase, two component system is able to utilize both the sensible heat of water always one of the components and the heat of fusion of the second component a salt which forms a hydrate.
The system to be employed must be graphically definable in a phase diagram including a liquidus, the range of composition of the system being selected liquidus pumps water as to lie within the liquidus pumps water range of the liquidus during the heating and cooling cycle. During operation, stirring is carried on to induce inter-particle motion to hydrate particles present in the system sufficient to maintain the system in liquidus pumps water and thereby insure that the temperature cycling occurs along the liquidus.
The subject matter of the instant invention for which protection is sought is presented as claims at the conclusion of the written description of the invention set forth herein. The description sets forth the manner and process of making and using the invention and the accompanying drawing forms part of the description for schematically illustrating the best mode. The view shown in FIG. Understanding of this invention will be facilitated by defining certain terms of art utilized herein:.
A graphic representation at constant pressure of the relationship between phases in equilibrium with each other in a system defined in terms of temperature and composition. The locus of temperature-composition points representing the maximum solubility saturation of a solid phase in a liquid phase. In a binary system, it is a line.
Liquidus pumps water temperatures above the liquidus, the system is completely liquid, and a point on the liquidus represents equilibrium between liquid and, in general, one crystalline phase. Any portion of the material universe which can be isolated completely and arbitrarily from the rest for consideration of the changes which may occur within it under varying conditions. An exemplary phase diagram to illustrate the practice of the method of this invention is shown in FIG.
This is part of the Na 2 SO 4 - water phase diagram. The line ABC represents the liquidus and this line defines for the Na 2 SO 4 -water system the temperature-composition operative limits for the application of this invention thereto.
The liquidus pumps water phases are set forth on the diagram. Changes in temperature along the liquidus as by adding or removing heat from the system, when the system is in equilibrium, will change the composition of the liquid phase in the fixed relationship shown. The steeper the gradient of the liquidus, the greater the temperature differential that liquidus pumps water be employed in the process.
A compilation of phase diagrams from which appropriate systems may be selected is "Solubilities of Inorganic and Metal Organic Compounds"--A. Some of the phase diagrams from liquidus pumps water compilation are set forth in the report "Thermochemistry of Salt Hydrates"--N. Both sources of phase diagrams and information on salt hydrates are incorporated by reference. By changing the particular salt hydrate employed some particular liquidus pumps water temperature liquidus pumps water and level may be selected for operation to match a storage system having a particular temperature interval requirement.
Examples of temperature intervals for particular applications are as follows:. As noted above, a match for the particular temperature interval selected for operation must be available along the liquidus pumps water of the two component system water plus a hydrate-forming salt selected, preferably with the high point of the selected temperature interval falling close to the upper end of the liquidus line e. Thus, considering the phase diagram in FIG.
Thereafter, if the system is properly stirred during temperature cycling to maintain equilibrium, as heat is withdrawn from the system, the temperature of the system falls and the composition of the liquid phase becomes automatically adjusted along the liquidus as solid phase forms. In this way the lower end i. As heat is put back into the system the sequence described above occurs in reverse the solid phase redissolves and cycling in this manner can be carried on indefinitely.
Such isolated solid phase would no longer be in equilibrium with the liquid phase and operation could no longer take place on the liquidus. The method of this invention in the storing of thermal energy combines utilization of the sensible heat of water with the latent heat of fusion of the particular salt which forms a hydrate constituting the second component of the system. The heat of fusion of the hydrate is substantial.
In this temperature range the ratio of total heat evolved to the sensible heat evolved from the water alone is calculated as 1. Thus, in the practice of this invention a greatly augmented thermal storage density for water can be obtained, because of the approximate doubling of the effective heat capacity thereof e.
Such an energy storage density in a relatively inexpensive system compares very favorably with the utilization of such heat of fusion materials as paraffins and waxes. By maintaining the system in equilibrium by stirring and operating along the liquidus with sequential melting and freezing, liquidus pumps water cycles liquidus pumps water completely reproducible without loss of salt from the system as would otherwise occur, if any portion thereof were to fail liquidus pumps water be available for re-dissolution in the liquid.
As a result even water-salt systems in which incongruently melting hydrates e. In systems in which operation is conducted over a sufficiently wide temperature range, extensive supercooling will cause thermal nucleation without creating problems in the system.
If the application is one in liquidus pumps water one wishes to avoid supercooling other provision must liquidus pumps water made for nucleation as is described hereinbelow.
An example of a thermostorage system in which the method of the instant liquidus pumps water may be practiced is liquidus pumps water forth in FIG. Having selected an appropriate system comprising water and a hydrate-forming salt, which system has a liquidus providing operation in the desired temperature range, a volume of water saturated with the salt is enclosed in cylinder liquidus pumps water disposed in air passage 12 and mounted on means 13 driven by motor 14 for slowly rotating cylinder 11 about its axis.
The rotation induces inter-particle motion of any hydrate crystals liquidus pumps water in the cycling operation. This device is described in greater liquidus pumps water in pending U. The aforementioned application is incorporated by reference. Air heated in the solar collectors 16, 17, 18, 19 is moved through ducts 21, 22 to conduit 12 by the driving force of fan As the heated air passes over cylinder 11, the content thereof is raised in temperature melting the hydrate therein.
In this manner liquidus pumps water energy from the solar collectors e. The air stream, after releasing its heat to the wall of cylinder 11 is returned to the solar collectors via duct 24 for reheating. When enough heat has been transferred to the saturated water in the cylinder 11 for the temperature thereof to reach the upper end of the preselected temperature range, sensors not shown actuate damper valves 26, 27 to the liquidus pumps water shown by dotted lines to place air passage 12 into flow communication with bypass conduit 28 and simultaneously close off the heating ducts 22, Thereafter, the thermal energy stored in cylinder 11 can be removed by continuing air circulation thereover and cooling the air by means of the expansion coils 29 for heat pump 31 whereby the heat received in air passage 12 is transferred to various rooms in the liquidus pumps water.
The slow rotation of cylinder 11 stirs the contents, promotes uniform internal temperatures liquidus pumps water maintains the inner surface thereof clean by separating the solidifying phase change material therefrom. This latter provides an efficient heat exchange surface during the cooling cycle.
The result of this stirring action is that the settling and caking of solid phase is obviated. Long term reliable nucleation liquidus pumps water is provided by hollow tube This tube is a receptacle for providing the permanent availability of solid crystalline material capable of initiating the formation of crystals in the contents of cylinder Tube 32 is closed at the distal end thereof and the interior of this tube is in flow communication with the interior of enclosure Usually, the nucleating material will be crystals of the salt hydrate formed by the second component and these crystals remain in contact with the liquid system.
When crystallization should occur, crystal growth will proceed along the length of tube 32 and enter enclosure 11 for the initiation of nucleation therein. The distal end of tube 32 penetrates insulated wall 33 into a region in liquidus pumps water the temperature is at a point below the maximum temperature of liquidus pumps water. When the composition water plus a salt which forms a hydrate in cylinder 11 has been cooled to the lower end of the preselected temperature range if heat is available at the solar collectorsthe damper valves 26, 27 are reset to shut off the bypass and the heating resumes.
The structure disclosed for conduct of the method of this invention is exemplary. Stationary tanks in which adequate internal stirring is possible may, of course, be employed. A heat exchanger can be employed disposed either inside or outside of the tank. The best mode to be selected depends upon the given application being considered.
Thus, the best mode for heating a residence would liquidus pumps water the arrangement as generally shown in FIG. The system to be employed must be graphically definable in a phase diagram including a liquidus, the compositional range of the system being selected so as to lie within the compositional range of the liquidus along which the system is to operate during both the heating and cooling cycles.
Phase Diagram A graphic representation at constant pressure of the relationship between phases in equilibrium with each other in a system defined in terms of liquidus pumps water and composition. Liquidus The liquidus pumps water of temperature-composition points representing the maximum solubility saturation of a solid phase in a liquid phase. System Any portion of liquidus pumps water material universe which can be isolated completely and arbitrarily from the rest for consideration of the changes which may occur liquidus pumps water it under varying conditions.
Examples of temperature intervals for particular applications are as follows: Heat Pump evaporator side. Heat Pump condenser side. The method for storing and releasing thermal energy comprising the steps of: The method recited in claim 1 where the hydrate-forming salt is Na 2 SO 4. The method recited in claim 1 wherein the hydrate-forming salt is Na 3 PO 4. Thermal energy storage and release utilizing combined sensible heat and latent heat of fusion.
Method for forming Liquidus pumps water salt crystals of reduced size by including a fluorine-containing surfactant. Method for forming Glauber's salt crystals liquidus pumps water reduced encapsulation by the addition of ethylene glycol monobutyl ether. Letter to the Editor, A.
Whillier-The Sun at Work, vol. Increasing the cycle stability of a sodium sulfate heat exchange medium by adding sulfuric acid. Method and apparatus for transferring energy in an absorption heating and cooling system. Review on phase change materials PCMs for cold thermal energy storage applications. Prevention of supercooling and stabilization of inorganic salt hydrates as latent heat storage materials. Compact storage of seat and coolness by phase change materials while preventing stratification.
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