Potential Thermal Energy Storage Research Articles

Thermophysical Properties of Lithium Nitrate Trihydrate from (253 to 353) K

Lithium nitrate trihydrate is of interest as a thermal energy storage material, due to its large specific and volumetric enthalpy of fusion and its low melting temperature. Here, we report the thermophysical properties of solid and liquid lithium nitrate trihydrate at temperatures from (253 to 353) K and compare this compound to water and octadecane, two other potential thermal energy storage materials. Furthermore, we examine the lithium nitrate–water phase diagram and accurately determine the enthalpies of fusion and melting temperatures for lithium nitrate trihydrate, ΔHfus = (287 ± 7) J·g–1 and Tfus = 303.3 K, and the lithium nitrate trihydrate–lithium nitrate eutectic, ΔHfus = (264 ± 2) J·g–1 and Tfus = 301.4 K.

Poly(2‐alkyloyloxyethylacrylate) and poly(2‐alkyloyloxyethylacrylate‐co‐methylacrylate) comblike polymers as novel phase‐change materials for thermal energy storage

AbstractA series of poly(2‐alkyloyloxyethylacrylate) and poly(2‐alkyloyloxyethylacrylate‐co‐methylacrylate) polymers as novel polymeric phase‐change materials (PCMs) were synthesized starting from 2‐hydroxyethylacrylate and fatty acids. The chemical structure and crystalline morphology of the synthesized copolymers were characterized with Fourier transform infrared and 1H‐NMR spectroscopy and polarized optical microscopy, respectively, and their thermal energy storage properties and thermal stability were investigated with differential scanning calorimetry and thermogravimetric analysis, respectively. The thermal conductivities of the PCMs were also measured with a thermal property analyzer. Moreover, thermal cycling testing showed that the copolymers had good thermal reliability and chemical stability after they were subjected to 1000 heating/cooling cycles. The synthesized poly(2‐alkyloyloxyethylacrylate) polymers and poly(2‐alkyloyloxyethylacrylate‐co‐methylacrylate) copolymers as novel PCMs have considerable potential for thermal energy storage and temperature‐control applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and thermal performance of gypsum boards incorporated with microencapsulated phase change materials for thermal regulation

The application of phase change materials (PCMs) for solar thermal-energy storage has received considerable attention in recent years due to their high storage density. A series of microencapsulated PCMs (micro-PCMs) with good phase change behavior have been synthesized through in-situ polymerization and the applications of the obtained micro-PCMs in thermal regulation of gypsum boards are presented in this study. Scanning electron microscope images reveal that the micro-PCMs were dispersed homogeneously in the gypsum boards. Differential scanning calorimeter results show that all the gypsum boards with different weight percentages of the micro-PCMs possess good phase change behavior. The melting and freezing temperatures as well as the latent heat of the gypsum board with 50wt% or 60wt% micro-PCMs and 3wt% glass fibers are quite suitable for the potential thermal energy storage of building applications. Thermal cycling tests indicate that the gypsum board with micro-PCMs maintains excellent thermal reliability after 60 melting–freezing cycles. Furthermore, the gypsum boards with micro-PCMs show a good thermal-regulated property. The temperature of the board incorporated with 60wt% micro-PCMs can be kept in the rage of 22–27°C for about 1735s due to the phase change of the inside micro-PCMs. In addition, the thermal-regulated gypsum boards achieve good thermal stability, high thermal capacity and thermal conductivity, especially for the sample incorporated with 50wt% micro-PCMs. From the above results, it can be concluded that the gypsum boards incorporated with 50wt% micro-PCMs have a good potential for thermal energy storage purpose in buildings.

Synthesis, characterization and thermal properties of novel nanoencapsulated phase change materials for thermal energy storage

In this paper, nanocapsules containing n-octadecane with an average 50nm thick shell of poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), and a core/shell weight ratio of 80/20 were synthesized by the direct miniemulsion method, respectively. The average size of the capsules is 140nm and 119nm, respectively. The chemical structure of the sample was analyzed using Fourier Transformed Infrared Spectroscopy (FTIR). Crystallography of nanocapsules was investigated by X-ray diffractometer. The surface morphology was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The thermal properties and thermal stability of the sample were obtained from Differential Scanning Calorimeter (DSC) and Thermal Gravimetric Analysis (TGA). The temperatures and latent heats of melting and crystallizing of PEMA nanocapsule were determined as 32.7 and 29.8°C, 198.5 and −197.1kJ/kg, respectively. TGA analysis indicated that PEMA/octadecane nanocapsule had good thermal stability. The nanocapsules prepared in this work had a much higher encapsulation ratio (89.5%) and encapsulation efficiency (89.5%). Therefore, the findings of the work lead to the conclusion that the present work provides a novel method for fabricating nanoencapsulated phase change material, and it has a better potential for thermal energy storage.

Thermal energy storage by poly(styrene‐co‐p‐stearoylstyrene) copolymers produced by the modification of polystyrene

AbstractA series of poly(styrene‐co‐p‐stearoyl styrene) copolymers as novel polymeric solid–solid phase‐change materials (SSPCMs) were synthesized by the modification of polystyrene with stearoyl chloride. The chemical structure and crystalline morphology of the synthesized copolymers were determined with Fourier transform infrared spectroscopy and polarized optical microscopy, respectively. The thermal energy storage properties and thermal stability of the SSPCMs were investigated with differential scanning calorimetry and thermogravimetric analysis, respectively. In addition, the thermal conductivity of the SSPCMs was measured with a thermal property analyzer. Moreover, thermal cycling tests showed that the copolymers had good thermal reliability and chemical stability after being subjected to 5000 heating/cooling cycles. The synthesized poly(styrene‐co‐stearoyl styrene) copolymers as novel SSPCMs have considerable potential for thermal energy storage and temperature‐control applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and thermal energy storage properties of ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides as novel solid–liquid phase change materials

Ethylene dilauroyl, dimyristoyl, and dipalmitoyl amides were synthesized as novel solid–liquid phase change materials (PCMs) via condensation of ethylene diamine with the respective carboxyl chlorides (lauroyl chloride, myristoyl chloride, and palmytoyl chloride). The synthesized ethylene dilauroyl amide (EDLA), ethylene dimyristoyl amide (EDMA), and ethylene dipalmytoyl amide (EDPA) were characterized structurally by FT-IR and 1H NMR spectroscopy techniques. Latent heats of melting and freezing determined using DSC technique were found to be 127.83 and −118.30 J/g for EDLA, 129.95 and −132.40 J/g for EDMA, and 150.66 and −145.22 J/g for EDPA, respectively. Phase change temperatures of these PCMs were ranged between 38.5 and 52.5 °C. The synthesized PCMs were tested for durability by accelerated thermal cyclings including 1000 melting/freezing cycles. Besides the thermal endurance of the PCMs were determined by TG analysis. Based on the results it was concluded that EDLA, EDMA, and EDPA compounds synthesized as novel solid–liquid PCMs have considerable amount of thermal energy storage potential in terms of suitable phase change temperatures, high latent heats, thermal reliability, and thermal stability. Moreover, the other advantages of the synthesized PCMs over the fatty acids used are better odor, low corrosivity, and low sublimation rates.

Investigation on phase transitions of 1-decylammonium hydrochloride as the potential thermal energy storage material

1-Decylammonium hydrochloride was synthesized by the method of liquid phase synthesis. Chemical analysis, elemental analysis, and X-ray single crystal diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the compounds were measured with a precision automated adiabatic calorimeter over the temperature range from 78 to 380 K. Three solid–solid phase transitions have been observed at the peak temperatures of 307.52 ± 0.13, 325.02 ± 0.19, and 327.26 ± 0.07 K. The molar enthalpies and entropies of three phase transitions were determined based on the analysis of heat capacity curves. Experimental molar heat capacities were fitted to two polynomial equations of the heat capacities as a function of temperature by least square method. Smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K based on the fitted polynomials.

Preparation, characterization and thermal properties of lauric acid/expanded perlite as novel form-stable composite phase change material

This paper mainly includes the preparation of a novel form-stable composite phase change material (PCM) by incorporation of lauric acid (LA) within the expanded perlite (EP), characterization of the composite by SEM and FT-IR techniques and determination of thermal properties and thermal reliability of the composite PCM using DSC analysis. The LA could be retained by 60 wt.% into EP without melted PCM seepage from the composite and therefore, this composite was described as form-stable composite PCM. SEM results showed that the LA confined into porous of EP. FT-IR analysis indicated that the composite formation of porous EP and LA was physical. The melting and freezing temperatures and latent heats of the composite were measured as 44.13 °C and 40.97 °C; 93.36 J/g and 94.87 J/g, respectively, by DSC analysis. Thermal cycling test showed that the form-stable composite PCM has good thermal reliability and chemical stability although it was subjected to 1000 melting/freezing cycling. Besides, thermal conductivity of the composite PCM was increased approximately as 86% by adding 10 wt.% expanded graphite (EG). As a result, this composite PCM could be considered to have good potential for thermal energy storage because of its good thermal energy storage properties, thermal and chemical reliability and thermal conductivity.

Clathrate Hydrate Formation from Cyclopentane-in-Water Emulsions

This paper reports the experimental examinations of hydrate-forming cyclopentane-in-water emulsions as potential thermal energy storage media for air-conditioning systems. It was demonstrated that an adequately compounded cyclopentane/water/surfactant mixture formed a stable emulsion with the aid of continuous agitation and, through its cooling to ∼2 °C, turned into a bulky mass of granular hydrate crystals. The behavior of the hydrate formation was investigated by varying the amount and composition of the surfactant (or surfactant mixture) in the sample cyclopentane/water/surfactant mixture from run to run in order to determine the appropriate preparation of the mixture for efficient hydrate formation. Also performed were measurements of the effective heat of dissociation for the granular hydrate products obtained in the above hydrate-forming experiments. The measurements showed that the effective heat of dissociation can be as high as ∼93% of the intrinsic heat of dissociation of cyclopentane hydrate crystals, thereby indicating a sufficient potential of the cyclopentane-in-water emulsions as thermal energy storage media.

Thermodynamic assessment of binary solid-state thermal storage materials

Polyalcohols are potential thermal energy storage materials that exhibit energetic solid-state phase transformations, and usually referred to as ‘Plastic Crystals’. The adjustment of solid-state phase transition temperatures is of significance to practical applications; phase diagram are useful for this purpose. We have established binary phase diagrams of 2-amino-2-methyl-1,3-propanediol (AMPL)–neopentylglycol (NPG), pentaerythritol (PE)–AMPL,tris(hydroxymethyl)aminomethane (TRIS)–NPG systems. In this work, we present results of our thermodynamic assessments of these organic binary systems. The CALPHAD approach using Thermo-Calc software was utilized for this purpose. It is interesting to note that two high temperature plastic phases co-exist in all three binaries considered here. Thermal energies are predominantly stored in these cubic γ or γ′ plastic phases in molecular librations (O–H⋯O bonds) and lattice vibrations. The calculated phase diagrams are in close agreement with the experimental phase diagrams.

Technology Potential of Thermal Energy Storage (TES) Systems in Federal Facilities

ABSTRACT Thermal energy storage (TES) reduces electric costs by shifting chilling activities to off-peak times. Water is chilled or ice is made during the night to either replace or augment operation of cooling equipment during the day. Off-peak demand and consumption rates produce significant dollar savings. TES requires favorable electric rate structures, available space to house the associated equipment, and either variation in buildings cooling loads or favorable climatic conditions. TES can be implemented anywhere cooling loads can be shifted to off-peak hours, with the best applications being office buildings, hospitals, and schools. Most TES projects are implemented in conjunction with an existing cooling system expansion, replacement of older cooling equipment, or new construction, thus reducing energy costs, consumption, and demand. A model was developed to estimate the potential application for TES in the federal sector utilizing weather data, cooling profiles for buildings of various size and g...

Technology Potential of Thermal Energy Storage (TES) Systems in Federal Facilities

Thermal energy storage (TES) reduces electric costs by shifting chilling activities to off-peak times. Water is chilled or ice is made during the night to either replace or augment operation of cooling equipment during the day. Off-peak demand and consumption rates produce significant dollar savings. TES requires favorable electric rate structures, available space to house the associated equipment, and either variation in buildings cooling loads or favorable climatic conditions. TES can be implemented anywhere cooling loads can be shifted to off-peak housrs with the best applications being office buildings, hospitals, and schools. Most TES projects are implemented inconjunction with an existing cooling system expansion, replacement of older cooling equipment, or new construction, thus reducing energy costs, consumption, and demand.

Technology Potential of Thermal Energy Storage (TES) Systems in Federal Facilities

Technology Potential of Thermal Energy Storage (TES) Systems in Federal Facilities

Solid-Solid Phase Transition in Trimethylolpropane (TRMP)

An orientationally disordered crystalline (ODIC) plastic phase (γ) was observed in Trimethylolpropane (TRMP) during heating by high resolution thermal and X-ray diffraction analyses. TRMP is a potential thermal energy storage material. The enthalpies of solid-solid (α → γ at 327.8 K) and fusion (γ → liquid at 332.7 K) transitions are 16.36 kJ/mol and 0.9 kJ/mol, respectively. Supercooling was observed during solidification of melts, and this supercooled γ phase began to transform to a metastable crystalline phase, designated as α′, after 20 minutes at room temperature. The lattice parameters of the monoclinic α phase, obtained from this study, are:

Study of solid–solid phase change of ( n-C nH 2n+1 NH 3) 2MCl 4 for thermal energy storage

A series of bis( n-alkylammonium) tetrachlorometallates (II) ( n-C n H 2 n+1 NH 3) 2MCl 4 (C n M, where n=10, 12, 16 and M=Cu, Zn, Hg, Mn, Co, Ni) were synthesized and elementary analysis carried out. Their solid–solid phase transitions were studied using DSC and IR. Transition temperatures of C n Mn, C n Co, C n Zn and C n Cu lie between 28 and 86 kJ mol −1. They are potential thermal-energy storage materials. C n Ni, C n Cd, C n Hg are unsuitable for thermal storage use, because C n Ni has poor thermal stability; moreover, C n Cd and C n Hg in the low temperature has lower latent heat for these application.

Molecular association of normal alkanoic acids with their thallium(I) salts: a new homologous series of fatty acid metal soaps

A new homologous series of thallium(I) hydrogen dialkanoates, fatty acid thallium soaps, from the dipropane up to the ditetradecane is reported for the first time. This association with 1:1 stoichiometry is the only one exhibited by the thallium derivatives. They have been prepared by solidification of molten mixtures with equimolar proportions of acid and corresponding neutral salt, through crystallization from an anhydrous ethanolic solution of the mixture has also been successful in getting pure compounds with largest chain lengths. Vibrational spectroscopies clearly characterize these crystalline compounds as very strong hydrogen bonding systems. Assignations of active modes in proton and carbon nuclear magnetic resonance spectrometry (NMR) (in ethanol) and infrared (IR) and Raman spectra (in solid state) are reported. According to X-ray diffraction (XRD) they have monomolecular lamellar structures with the acyl chains arranged up and down to the cation/H-bond network in a methyl-to-methyl fashion, and vertically oriented to the basal plane. The acyl chains present all-trans conformation and alternating configuration (perpendicular orthorhombic subcell), like the beta'-phases of other kinds of lipids. Lamellar thickness is reported for the six room-temperature crystalline members. The molecular compounds present polymorphism, one crystal/crystal transition at temperatures close to the peritectical melting. Phase transition thermodynamics are also given and discussed with respect to their acid and salt parents. Their incongruent melting involves nearly 90% of the total enthalpic increments of both constituents' melting processes, making these compounds potential thermal energy storage materials.

The Effect of Real Time Pricing (RTP) on Thermal Energy Storage (TES) Systems

With the onset of deregulation of electrical utilities it is interesting to speculate on what the future will bring and how it will effect existing and potential new thermal energy storage projects. Let us be realisatic, there is no reason to implement TES if there is not a rate structure that allows us to reduce energy cost. TES systems save money by reducing demand cost and utilizing lower energy charges during off peak periods. Certain electric utility companies in anticipation of what may be coming have developed an experimental rate structure that charges energy in relation to what it actually costs the utility on an hourly basis. Many factors influence the cost of electricity during the day so that the cost per kWh can vary considerably on an hourly basis.

Ionic Conductivity in Ordered and Disordered Phases of Plastic Crystals

Pentaglycerine (PG) and tris‐hydroxy‐aminomethane (Tris) are potential thermal energy storage materials which undergo energetic solid‐state phase transformations. The low temperature α‐phase structure of PG is body‐centered tetragonal and that of Tris is orthorhombic. The high‐temperature phase structure of both compounds is face‐centered cubic. Polymorphic changes in the structure occur at 89°C for PG and 135°C for Tris. These compounds are dielectrics at low temperature with conductivities on the order of 10−8 Ω−1 cm−1 (at 21°C) and 10−9 Ω−1 cm−1 (at 25°C), for PG and Tris, respectively. Heating samples from room temperature leads to an initial decrease in α‐phase conductivities followed by an increase for both of these compounds as a result of proton hopping. Continuous increases in the conductivity were observed at the transition temperature, with discontinuity evident in the case of PG. The conductivity variations in the α‐ and γ‐phases have been found to be thermally activated. The activation energies are nearly equal suggesting similar conduction mechanisms and charge carriers. From the relaxation time data, an equation has been obtained for the charge carrier self‐diffusion coefficient for the γ‐phase of PG, just above the transition temperature; . The conductivity in the γ‐phases are independent of the frequency in the range of 10 to 103 Hz. The temperature and frequency effects on the conductivities, relaxation times, and diffusional parameters of PG and Tris are presented.

AC Conductivities of Neopentylglycol and 2‐Amino‐2‐Methyl‐1,3‐Propanediol

Neopentylglycol (NPG) and 2‐amino‐2‐methyl‐1,3‐propanediol (AMPL) are potential thermal energy storage materials which undergo energetic solid‐state phase transformations. Both NPG and AMPL have monoclinic low temperature α‐phase and cubic high temperature γ‐phase structures. These polymorphic changes in structure occur at 41 and 80°C, for NPG and AMPL, respectively. Below the α→γ transition, these compounds are dielectric materials with conductivities on the order of 10−8 S/m (at 22°C) and 10−9 S/m (at 25°C),. for NPG and AMPL, respectively. The lack of appreciable conductivity in the low temperature phase is consistent with charge transport via low temperature structural reorientation. There is a significant increase in the conductivity through the α→γ phase transition with a maximum of 10−6 S/m (at 82.05°C) for NPG and 10−5 S/m (at 133.25°C) for AMPL in the high temperature phase. The conductivities in both the α‐ and γ‐phases have been found to be thermally activated. The temperature dependent conductivity follows the Arrhenius equation with the activation energy of the α→γ transition being larger in the case of NPG. Remarkably, the activation energies of the high temperature γ‐phases are nearly equivalent, suggestive of similar conduction mechanisms and charge carriers. The charge carrier diffusion coefficients, D(t) are in the range of for NPG, and between for AMPL. The ac conductivity in the α‐phase exhibits behavior representative of a double well potential energy profile where the low and high frequency conductivities are constant with a Debye‐like transition at intermediate frequencies. The γ‐phase ac conductivity is frequency independent as is the case in simple hopping conductivity processes. AC impedance spectroscopic measurements on NPG and AMPL have been made and frequency and temperature effects on the conductivities, relaxation times, and diffusional parameters of NPG and AMPL are presented.

Performance of a solarium: An analytical study

In this communication, a combination of phase change component material (PCCM) and water wall as a link wall in a solarium have been proposed and analysed for load levelling in the living space of the solarium. The choice of the aforesaid combination as a link wall has been made because of relatively high heat transfer coefficient of water and greater thermal energy storage potential of the combination. The relatively greater thermal storage potential of the proposed combination reduces the temperature swings in the living space and provides, thereby a comfortable living environment. Analytical expression for living space temperature as a function of climatic and system parameters as well as various heat transfer coefficients have been derived. Numerical calculations have been carried out for a typical day of North America (Boulder) for zero ventilation rate. It is concluded that the proposed combination as a link wall gives best thermal load levelling.