Thermal Energy storage system with enhanced transition array

Abstract

This invention describes the design and applications of a thermal storage system with desirable thermo physical and kinetic properties for various applications including architectural design, increasing thermal mass of building envelops and climate control.

Description

FIELD OF THE DISCLOSURE

This disclosure relates to a phase change thermal energy storage system for climate control environments, building structures, energy management and safe transport of temperature sensitive materials and application thereof.

BACKGROUND

The present invention relates to the field of thermal energy storage and use of materials that can capture and release energy upon phase transition.

Phase change materials (PCMs) or phase change energy receptors are materials that store/release heat during phase transition without a rise in their own temperature. These features make PCMs ideal to capture and store heat for many applications including architectural design, increasing thermal mass of building envelops, thermal underlayment, climate control and shipping enclosures for temperature sensitive products.

PCMs can be used to construct building materials due to their latent heat storage capacity. It is based on enthalpy conversion when PCMs absorb heat and transition from solid to liquid. They continue to absorb heat without a significant rise in their temperature until all material is converted to liquid phase. The absorbed energy is released to the environment as PCM solidifies and transition from liquid to solid due to a fall in the environment temperature. This process is very useful to keep a building temperature within a constant comfortable range. PCMs store more heat per unit volume than many conventional building materials such as masonry, wood or rock.

There are two main classes of PCMs, organic and inorganic with a wide range of melting temperatures. Organic PCMs include paraffin compounds and non-paraffin compounds such as fatty acids, fatty alcohols and fatty esters that melt and solidify congruently with little subcooling. Organic PCMs have low density per volume, low thermal conductivity and are generally flammable.

Inorganic phase change materials such as salt hydrates are known for their heat of high fusion and storage density but suffer from congruent melting and irreversible processes. Most have slow or poor nucleating properties which result in subcooling where they solidify at much lower temperature than their general melting point. There are different crystal forms that may be produced causing stratification on repeated melting and crystallization. Unfortunately the formation of lower hydrate forms lead to severe stratification and water phase separation causing solid salts to fall to the bottom of the enclosure. Such undesired process deprives the top layer from the useful phase change material originally introduced and induces subcooling at temperatures below its congealing crystallization temperature. Several remedies were suggested to solve this problem including mechanical stirring, use of gelling and thickening materials or addition of other salts and nucleating agents to make the mixture congruent. The admixing of nucleating agents such as strontium, potassium and barium salts have been proposed to stabilize the compositions. U.S. Pat. No. 4,613,444, U.S. Pat. No. 4,690,769 and U.S. Pat. No. 6,402,982.

The performance of PCMs is also dependent on their environmental exposure conditions such as enclosure, humidity and surrounding temperature. PCMs enclosures describing plastic films or sheets forming sealed pockets were used to contain the PCM material from drying or absorbing excessive moisture as described in U.S. Pat. No. 5,626,936. The sealed confinement prevents material from escaping the enclosure and leaking into walls or ceiling structures. It is a significant benefit to minimize potential corrosion or damage caused by leaked PCM compounds. Additional steps were proposed to stabilize the compositions by using thickening adsorbents such as diatomaceous earth as described in U.S. Pat. No. 7,641,812 and U.S. Pat. No. 8,741,169. Additional superabsorbents and hydrophobic sorbents as viscosity modifiers were also proposed in U.S. 2009/0191408 A1 and U.S. 2014/0339460 A1 including chemical crosslinking PCM compounds with isocynate polymers which affect its thermal storage capacity and conductivity in comparison with native PCM compounds.

Although, these steps are helpful in attenuating the problem, they suffer from alteration in thermal conductivity and slow rates of crystallization when temperature changes are small thus lack to produce a total solution. Mechanical stirring or agitation is limited in use and inconvenient in most phase change energy storage applications. Thickeners may increase the viscosity of phase change materials but may increase the flammability of organic PCMs forming flammable gels. Also, for salt hydrates thickening agents absorb and share the water molecules necessary to maintain the salt hydrate at a higher hydration level, a phenomenon requiring all water molecules to be available to solubilize the desired salt form. Viscosity modifiers and cross linkers are thermally inert materials and reduce the thermal storage loading of the PCM composition and it negatively affect thermal conductivity. Additional improvements are therefore desired. The present disclosure offers thermal energy storage compositions and construct with enhanced reversible phase change transition while maintaining the original thermal storage properties of organic and inorganic PCMs.

SUMMARY OF THE INVENTION

This invention represents a significant improvement and solution to slow crystallization rates and phase transition of thermal storage materials. The primary objective is to produce highly responsive, thin, light weight storage panels with high thermal mass and efficient thermal charging and discharging of energy for use in building spaces, walls, ceilings, floor boards, underlayment flooring, strategic heat storage walls (fireplaces and kitchen areas), positively impact low thermal mass and light weight buildings as well as the exterior thermal envelope including siding boards and stone veneer. Such applications can reduce costs of heating and air conditioning while enhancing occupant comfort with a cooling effect and reduction in temperature swings.

For this purpose, for example the inventive heat storage compositions can be used advantageously as latent heat energy panels. They may be encased in walls, ceilings, doors, warehouses, storage structures and barns. In addition, the disclosed system can be used to prevent excessive heating from various sources or from people and equipment in buildings and vessels. For example it can be integrated into window coverings or encased into office modules, furniture, automobile liners and in the walls of transport vehicles, caravans, trailers or vessels.

In some embodiments, for example, the thin three dimensional (3-D) media matrix with high absorption affinity and tremendous active surface network acting as nucleating sites enables a reversible phase change transition and rapid melting and crystallization rate. The media's high absorption capacity allows the immobilization of organic and inorganic phase change materials and cofactors for enhancing thermal conductivity and rapid response to changes in the environment temperature. Additionally, the media matrix retains water molecules in intimate contact with the phase change material molecules to maintain effective solubility, segregation and formation of lower hydrated salt forms. The disclosure describes the embodiment of large solvating and nucleation active site dispersed onto and within the media network. The encapsulated energy storage array employs neat, high energy storage PCMs in a self-contained, leak proof, flexible and efficient matrix capable of storing and discharging energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of one design of a fiber network made from fibers selected from cellulosic ingredients, bamboo fibers, polypropylene, melt blown synthetic polymers and the like.

FIG. 1B shows the networking for two or more fiber formation scheme patterns.

FIG. 1C shows the integration of a high absorbing capacity support component integrated between layers of fine fibers.

FIG. 2 is a schematic view illustrating one media matrix loaded with phase change energy composition and crystal cores and is encapsulated in a sealed flexible barrier film forming thermal energy storage Cell.

FIG. 3 is a schematic of a cross section of various temperature transition phase change materials. A dual PCM energy storage 1 and 2 is used to store and release energy at different temperatures during melting and crystallization phases.

FIG. 4 shows a cross section of the energy storage system configured as a flow through cell where hot or cold energy input is processed in various applications.

DETAILED DESCRIPTION

This disclosure is generally described to illustrate a construct, compositions and method to produce thermal energy storage system using Phase Change Materials for many applications where thermal energy and temperature management is necessary. Various embodiments are presented; some embodiments describe amplified crystallization and efficient molecular hydration by using an inert 3-D fiber network media as the support matrix for the PCM and crystal core stabilizing cofactors. The media matrix and method presented herein offer total composition containment to prevent leakage and phase separation or segregation on repeated melting and crystallization while enhancing thermal stability. The embedded PCM compositions represent an array of thermal storage islands in one platform. These pseudo conjugated PCM islands increase thermal conductivity resulting in high heat of fusion turnover and specific heat per unit volume and weight. This decreases the necessary time needed for nucleation to occur in a recrystallization cycle and the subsequent stored energy release.

Another advantage of the invention is the high loading of phase change material receptor in the large area network of the holding media matrix where neat liquid PCM is directly loaded forming an array of crystallization islands within the media layer. Furthermore, the high density and higher stability of pure PCM compositions (without thickening agents, polymerization and molecular modification) provide high thermal storage per unit volume and reduces volume changes during the melting and solidification cycles at reduced cost.

The 3-D media member is an inert media matrix of large surface area and high absorption affinity towards aqueous and non-aqueous compositions and is used to contain PCMs of varying temperatures ranging from subzero to 150° C. FIG. 1A illustrates one fiber network 1 made from fibers selected from cellulosic ingredients, bamboo fibers, polypropylene, melt blown synthetic polymers and the like. Alternatively, FIG. 1B shows the networking for two or more fibers 2, 3 and formation scheme while FIG. 1C shows the integration of a high absorbing capacity component 4 or an air blown fibrous composition sandwiched between layers of fine fibers 1 and 3 used as the holding matrix for the phase change material. FIG. 2 illustrates one media matrix 4 loaded with phase change energy composition and crystal cores 5, and the layers 1-5 are encapsulated in a sealed flexible barrier film 6, 7 forming thermal energy storage Cell. The cell configuration may be replicated over various lengths and widths as energy storage panels. Selected temperatures of phase change materials are generally designed to create a cooling effect of a few degrees Celsius as heat storage medium. In some embodiments and as mere examples, the preferred transition temperatures include 4, 6, 10, 15, 18, 21, 23, 25, 27, 28, 29, 32, 35, 37, 49° C.

A simplified representation of the invention comprises a absorbent support or continuous three dimensional fibrous media member impregnated with additive crystal core nucleating sites and PCM selected from inorganic salts and crystalline hydrates, molten salts, inorganic eutectic mixtures, fatty acids/esters, alcohols, organic eutectics, aliphatic hydrocarbons and combinations thereof. Various compositions may be loaded into the media's matrix separately or as mixtures of the phase change material. Alternatively, PCM additives may be added with the phase change material and within the support media matrix. The addition of nucleating agents serves as crystal core and anchoring sites for crystal growth while distributed within the media microstructures as well as within the fibrous matrix construct. In addition, the large media's surface area and PCM distribution ensures high nucleation array to avoid subcooling while the high rate of crystal growth speeds the recovery of heat from the PCM. Furthermore, the uniform density and high volumetric thermal density minimizes volume variation during phase change solidification

Thermal conductivity is a measure of a materials ability to conduct heat. It is generally measure by heat flow meters, the greater the thermal conductivity indicate a more efficient heat transfer and phase change transition. The present disclosure uses thermal conductor materials including fine fibers, flakes, layers, and particles in the media matrix. The thin layer and 3-D media structure maintains the PCM and thermal conductors in close contact during the molten state when thermal conductivity is at higher value. This additional feature of the invention facilitates an efficient heat transfer and rapid crystallization rate.

In another embodiment, the generally low thermal conductivity of phase change material may be improved by the media matrix comprising highly conductive sites or particles selected from aluminum, iron, copper, silica, carbon black, carbon fibers, carbon nanotubes, metal oxides and grapheme/oxides. Additionally, the integration of these materials within the media matrix structure plays a dual purpose as active a thermal conductor and crystal core for enhanced crystallization and efficient phase transition rate.

It should be recognized that the various embodiments and illustration are merely described for illustrative fulfillment of the various objectives of the present invention. In another embodiment and of further advantage of the use of the media's role to contain PCMs and cofactors, it plays a major role to contain organic PCM molecules (fatty acids/esters and alcohols) entrapped within the media's open structure. For example, methyl palmitate crystallizes faster within the media's network and microstructures than in bulk volume. Conjugated methyl palmitate crystal islands make energy recovery more efficient and enhance phase change transition turnover rate. In addition, the ability of the media to retain water molecules in close proximity helps prevent inorganic PCM degradations associated with water molecule loss during heating cycles. This is especially important for crystalline hydrates and eutectic mixtures where water loss drops the PCM to lower hydration states and induced phase separation. This high hydration proximity prevents PCM salting out and promotes rapid charging and discharging of energy during both solid and liquid phases.

In another embodiment, dual energy storage panels are produced to represent the use of PCMs of different melting temperatures. FIG. 3 illustrates the employment of this invention to produce thermal energy storage systems responsive to seasonal climate conditions. The brief illustration shows the potential use of two or more phase change materials 5 and 8 of different melting temperature serially produced as in FIG. 2 and placed in parallel to generate proactive energy storage systems that are responsive to seasonal conditions.

For example, a PCM that melts at 23° C. for cooler days of the year while using a 29° C. PCM for the warmer days delivering comfort while saving energy.

The diversity of the storage system provided in this invention allows its use in various configurations to produce an array of thermal cells for inline use utilizing a flow through cell design application as in FIG. 4. including but not limited to HVAC ductwork, suspended floor platforms and use in active mode PCM activation and recycling. This also demonstrates the wide applicability of the flexible and easily formed energy storage panels to various shapes from planar, sheets, cylindrical and rectangular shapes depending on the application.

The examples described herein are non-limiting and represent some embodiments as further illustrations of the disclosure.

Example 1

This example illustrates the 3-D media matrix and fiber network capable of absorbing aqueous and non-aqueous materials. The continuous media and/or its components is modified with crystal modifiers selected from Al, Cu, Fe, FeO, CuO, Cu₂O, ZnO, SrO, Al₂O₃, Fe₂O₃, SiO₂, BaO, NaCl, KCl, LiCl, StCl, Na₂CO₃, MgCl₂, ZnCl₂, FeCl₃, BaCl₂, MgSO₄, CuSO₄, BaSO₄, CaCO₃, Na₂SO₄, Na₂B₄O₇, Sr₃(PO₄)₂, CaB₄O₇, Na₅P₃O₁₀, BaS₂O₃, BaCO₃, SrCO₃, carbon fibers, carbon black, Magnesium stearate, bentonite, ethylene oxide, propylene oxide, or mixtures thereof in amounts of less than 30 percent by weight. The thermal storage PCM used with the media matrix is selected from inorganic salts and crystalline hydrates for example and not limited to calcium chloride hexahydrate, sodium carbonate dodecahydrate, eutectic mixtures, fatty acids/esters, alcohols, organic eutectics, aliphatic hydrocarbons and combinations thereof.

Compositions are loaded into the media's components or admixed with the phase change material and contained by the media matrix.

Example 2

This example illustrates the preparation of a salt hydrate PCM composition and loading of the media support. A feed stock calcium chloride is dissolved in an aqueous solvent at moderate temperatures (under 40° C.) to allow a much higher concentration to be achieved. The concentrated brine solution is stripped in purification steps such as filtration or settled particle separation while at elevated temperatures. The concentrated brine solution is cooled to less than 20° C. to crystalize calcium chloride hexahydrate crystals. The resulting crystals are separated and placed in a closed temperature controlled dissolution vessel. The temperature is set to 35-37° C. for the crystals to melt and the temperature is maintained at this level while stirring. The vessel is kept close to prevent water loss. Association of alkali metals made up of Group 1 and group 2 are added to the melted crystals at a total percent weight not to exceed 10%. In one embodiment of a formula, calcium chloride hexahydrate is paired with two alkali metal salts of group 1 for a total percent weight of less than 7 and two alkali metal salts of group 2 for a combined percent weight of less than 3 percent weight. While stirring, the molten complex is modified with one or combinations of CuO, Cu₂O, ZnO, TiO₂, SiO₂, BaO, carbon black or graphene in an amount of less than 4 percent by weight. The Composition is loaded into the media member and allowed to be absorbed by the media matrix. The loaded media member is sealed between film layers with vapor barrier quality film preferably with aluminum film component to produce the thermal energy storage panel to store and release heat.

Example 3

A saturated solution of calcium chloride is prepared in an aqueous solvent at 40 C while stirring. The concentrated brine solution is purified to produce the mother liquor. The concentrated brine solution is cooled to less than 20° C. to crystalize calcium chloride hexahydrate crystals. The resulting crystals are separated and placed in a closed temperature controlled dissolution vessel and heated to 35-37° C. An alkali metal salt from group 1 was added to the mix while stirring in amounts of less than 5 percent weight. A 2 percent weight magnesium chloride and 2 percent weight strontium chloride are added to the calcium chloride mixture. Barium sulfate and Titanium oxide are added while stirring in less than 1 percent weight. The formula is added to the media matrix and allowed to be absorbed and distributed in the support media. The loaded media matrix is then placed in a sealed moisture barrier film preferably with aluminum film component to produce the thermal energy storage panel to store and release heat.

Example 4

This example illustrates the use of media matrix to hold and disperse within its micro structures a non-aqueous PCM composition. The organic PCM is selected from fatty acids/ester, methyl laurate, methyl palmitate, methyl stearate, fatty alcohols or aliphatic carbon. The material is gently melted at a heat setting slightly above melting temperature. In a preferred embodiment, a fire retardant additive, calcium carbonate or sodium triphosphate is added while mixing. The composition is loaded into the media matrix and allowed to be absorbed and distributed to produce the phase change thermal energy storage panel. The loaded media matrix is sealed between sheets of barrier film.

Example 5

This example describes one application of the use thermal storage loaded media matrix with enhanced thermal conductivity. A low melting temperature PCM methyl Laurate is melted at a few degrees above its melting point. A crystal promoter and thermal conductor may be selected from Al, Cu, Fe, FeO, CuO, Cu₂O, ZnO, Fe₂O₃, SiO₂, CaCO₃, Na₂SO₄, Na₂B₄O₇, CaB₄O₇, Na₅P₃O₁₀, carbon fibers, carbon black, Magnesium stearate or bentonite in less than 10 percent weight. The melted methyl laurate composition is then used to impregnate the 3-D media matrix and the composition is allowed to be absorbed and contained to produce a fully loaded media member which is then sealed between film layers.

Claims

1. A thermal energy storage system comprising a three dimensional holding media and contained within it phase change materials or energy receptors and crystallization cofactors for enhanced thermal response comprising: a). A porous absorbent or reticulated network surface of about 1 mm to a bout 1000 mm thickness and of large surface area and void volume capacity to permanently hold and maintain thermal energy compositions or receptors.b). a thermal energy material or receptor composition to store and release energy upon its phase transition in repetitive cycles and to be fully contained by the media matrix member.c). an anchor site network and stabilizing cofactors of the phase change material distributed in and/or onto the holding media components to serve as crystal core growth site and stabilizer of the thermal storage composition.

2. The support and holding matrix of claim 1 comprises a structure of cellulosic material, natural or synthetic fibers, reticulated vitreous carbon, melt blown fibers and the likes randomly or uniformly integrated and networked to form a three dimensional absorbing or reticulated pad structure with affinity to aqueous and non-aqueous compositions.

3. The energy storage receptor and phase change material comprises of inorganic salts and crystalline hydrates, molten salts, inorganic eutectic mixtures, fatty acids/esters, fatty alcohols, fatty salts, organic eutectic mixture or aliphatic hydrocarbons.

4. The composition of claim 1 where the anchoring site and crystal landing sites may be of cellulosic nature, woven or nonwoven fibers, carbon fibers, polypropylene, graphene oxide, polyethylene, polyester and melt blown fibers in mono and multi filaments or combinations thereof, weaved or integrated in a panel open geometry to contain phase change energy storage receptors, enhance thermal conductivity and/or reduce subcooling effect during solidification cycle.

5. The composition of claims 1 and 4 including impregnating media matrix modifying surfactants and crystal stabilizers selected from ionic compounds, salts, fatty acid and ester salts, magnesium stearate, metal oxides, silicon dioxide or fine silica, aluminum, iron, copper, carbon fiber, carbon nanotubes, carbon black, to increase active crystal site, thermal conductivity and absorption capacity for rapid reversible crystallization.

6. The composition of claims 4 and 5, wherein the additive and nucleating agent is selected from H2O, FeO, CuO, Cu2O, ZnO, SrO, Al2O3, Fe2O3, SiO2, BaO, NaCl, KCl, LiCl, StCl, Na2CO3, CaCl2, MgCl2, ZnCl2, FeCl3, BaCl2, MgSO4, CuSO4, BaSO4, CaCO3, Na2SO4, Na2B4O7, Sr3(PO4)2, CaB4O7, Na5P3O10, BaS2O3, BaCO3, BaCl2, Sr(OH)2, SrCO3, K2PO4, Magnesium stearate, palmitic acid, stearic acid, bentonite, ethylene oxide, propylene oxide, or mixtures thereof.

7. The composition of claim 6, wherein additional thermal conductors and crystal core seeding are distributed within and onto the large network area of the media matrix in amounts ranging from 0.01 to about 10 percent by weight.

8. The energy storage compositions and the media matrix of claim 1-7 further comprising an array of cells serially or in parallel and of one or more PCM composition and transition temperature.

9. The configuration and compositions of claims 1-8 encapsulated in a film barrier forming a sealed enclosure comprising of one or more materials with vapor barrier and radiant film quality.

10. The compositions of claim 1-9 may be configured to produce thermal energy storage system for efficient charging and discharging of energy and use in building structures, walls, ceilings, floor boards, underlayment flooring, strategic heat storage walls (fireplaces and kitchen areas), overcome low thermal mass of light weight buildings, exterior thermal envelope, siding boards and stone veneer.

11. The compositions and construct of claim 1-9 for body cooling applications and as thermal guard panels in automobile liners, shipping vessels and storing temperature sensitive products.

12. The compositions and construct of claim 1-9 where thermal energy storage panels may be assembled as liners or flow through thermal energy store or batteries for charging and discharging thermal energy in large stationary operations as well as portable thermal store applications.