Calcium Chloride Hexahydrate Research Articles

Electrochemical characteristics of uranium ions in calcium chloride hydrate melts

Redox reactions of tetravalent uranium ion in calcium chloride hexahydrate CaCl2·6H2O melt ([CaCl2] = 6.9 M) were studied electrochemically and spectrophotometrically. Cyclic voltammograms in CaCl2·6H2O melt containing UCl4 were measured with a pyro-graphite carbon working electrode. A cathodic peak corresponding to the reduction of U4+ to U3+ was observed, and it was found to be controlled by the diffusion of U4+ in the melt. Although the concentration of H+ in the melt was negligible, the redox reaction of U4+ was observed without the disturbance of hydrolysis. The formal potential of the U4+|U3+ couple was determined to be -0.483 ± 0.005 V vs. NHE. The diffusion coefficient of U4+ in CaCl2·6H2O melt was determined to be 1.5 × 10−7 cm2 s−1 at 300 K. The anodic peak in the voltammogram was attributable to the oxidation of U4+ to UO22+, which was identified by using a technique based on the combination of electrolysis and spectrophotometry. Influences of the water content on chemical status of uranium ions in CaCl2 hydrate melts were studied.

Thermal Energy Discharge Characteristics of a PCM Heat Exchanger with Calcium Chloride Hexahydrate

Calcium chloride hexahydrate (CaCl2•6H2O) is an important inorganic phase change material used for thermal energy storage or discharge at lower storage temperature. Thermal energy discharge characteristics of a new type of PCM heat exchanger were investigated after thermal energy storage, in which its main body is based on the traditional structure of a shell-and-tube heat exchanger, and is full of PCMs (CaCl2•6H2O) in the tubes. The cold air of 16-17°C with different velocities flowed through the PCM heat exchanger, the temperature distributions of all the test points were measured by means of the experimetal system. The experimental results showed that, since the latent heat of phase transition in the tubes was so large during the process of thermal energy discharge, the time intervals of air temperature that maintained beyond 20°C at the outlet of the PCM heat exchanger were respectively 594min and 717min when the mass velocities of the cold air were 0.132 kg/s and 0.096kg/s, which is one of the important characteristics in the structure of this type of PCM heat exchanger. It can be used in the situations of temperature control or maintenance at the certain temperature, such as greenhouses, air conditioning etc.

Removal of Phenols with Encapsulated Horseradish Peroxidase in Calcium Alginate

Horseradish peroxidase was encapsulated in calcium alginate for the purpose of phenol removal. Considering enzyme encapsulation efficiency, retention activity and enzyme leakage of the capsules, the best gelation condition was found to be 1 % w/v of sodium alginate solution and 5.5 % w/v of calcium chloride hexahydrate. Upon immobilization, pH profile of enzyme activity changes as it shows higher value at basic and acidic solution. Besides, for each phenol concentration there would be an enzyme concentration which going further than this value has no significant effect on phenol removal. Investigation into time course of phenol removal for both encapsulated and free enzyme showed that encapsulated enzyme had nearly similar efficiency in comparison with the same concentration of free enzyme; however the capsules were reusable up to four cycles without any changes in their efficiency. The ratio of hydrogen peroxide/phenol at which highest phenol removal obtained, found to be dependent on initial phenol concentration and in the solution of 2 and 8 mM phenol it were 1.15 and 0.94 respectively.

Phase change characteristic study of spherical PCMs in solar energy storage

This paper investigates the phase change behavior of 65 mol% capric acid and 35 mol% lauric acid, calcium chloride hexahydrate, n-octadecane, n-hexadecane, and n-eicosane inside spherical enclosures to identify a suitable heat storage material. Analytical models are developed for solidification and melting of sphere with conduction, natural convection, and heat generation. Both the models are validated with previous experimental studies. Good agreement was found between the analytical predictions and experimental study and the deviations were lesser than 20%. Heat flux release at the wall, cumulative energy release to the external fluid, are revealed for the best PCM. The influence of the size of encapsulation, initial temperature of the PCM, the external fluid temperature on solidified and molten mass fraction, and the total phase change time are also investigated.

Solid−Liquid Metastable Equilibria in the Quaternary System (NaCl + LiCl + CaCl2 + H2O) at 288.15 K

The solubility and the physicochemical properties (densities, viscosities, refractive indices, conductivities, and pH) of the liquid-solid metastable system (NaCl + LiCl + CaCl 2 + H 2 O) at 288.15 K have been studied using the isothermal evaporation method. On the basis of the experimental data, the dry-salt phase diagram, water phase diagram, and the diagram of physicochemical properties versus composition in the system were plotted. The dry-salt phase diagram of the system includes two three-salt cosaturated points of (CaCl 2 ·6H 2 O + NaCl + CaCl 2 ·LiCl·5H 2 ·O) and (LiCl-H 2 O + NaCl + Cad; LiCl·5H 2 O), five metastable solubility isotherm curves, and four crystallization regions corresponding to sodium chloride (NaCL), lithium chloride monohydrate (LiCl·H 2 O), calcium chloride hexahydrate (CaCl 2 .6H 2 O), and the double salt LiCl.CaCl 2 .5H 2 O. No solid solution was found. It was found that the physicochemical properties in the metastable equilibrium solution change regularly with increasing CaCl 2 concentration.

Phase change behaviour of some latent heat storage media based on calcium chloride hexahydrate

Phase change behaviour of pure and some chemically modified calcium chloride hexahydrate materials suggested in the literature as suitable heat storage media was studied in storage systems with a low degree of mixing in order to evaluate their long-term reversibility. The influence of gravitation on the phase change properties of the pure system was elaborated by determining local salt concentrations in the liquid phase and changes in the volume of the system during repeated melting and crystallization, whereby the amounts of the different phases being present could be assessed. It was found that thermo gravitational effects are of minor importance in generating salt concentration gradients in the liquid phase when compared to the concentration gradients resulting from the sedimentation of the formed tetrahydrate and the hexahydrate during the phase change reactions. Due to these effects it was not possible to prevent irreversible tetrahydrate formation and deterioration in heat storage capability by adding a surplus of water to the hexahydrate materials, if seeds for the tetrahydrate were present during repeated melting and crystallization. Upon addition of SrCl 2 · 6H 2O a solid solution of the two hexahydrates is formed and as a result the formation of the tetrahydrate is suppressed. Due to irreversible formation of SrCl 2 · 2H 2O a state of true congruent melting seems, however, not possible to reach. Phase segregation effects also in this case lead to irreversible calcium chloride tetrahydrate formation if seeds for the latter are added during repeated melting and crystallization. If Ca(OH) 2 is also added, the tetrahydrate formation can be further suppressed. But, even in this case, irreversible tetrahydrate formation can not be prevented if the composition of the liquid phase corresponds to the hexahydrate. On addition of 5 wt% KCl or 5 wt% KCl + 2 wt% SrCl 2 · 6H 2O or 5 wt% KCl + 0.4 wt% NaCl, repeated melting and crystallization in the presence of seeds of the tetrahydrate can, however, be carried out without irreversible formation of the latter occurs. In the heat storage system CaCl 2 · 6H 2O + 5 wt% KCl, formation of tetrahydrate is observed but its rate of dissolution is found considerably faster than in the pure hexahydrate system. It was concluded that with those modified calcium chloride hexahydrate systems reversible phase change cycling can be performed and therefore there is for example no the need for thickener agents to be added to avoid irreversible tetrahydrate formation successively reducing heat storage capability of systems in those cases.

Solid–liquid metastable equilibria in the quaternary system (NaCl–KCl–CaCl 2–H 2O) at 288.15 K

The solubilities and the physicochemical properties (densities, viscosities, refractive indices, conductivities, and pH) in the liquid–solid metastable system (NaCl–KCl–CaCl 2–H 2O) at 288.15 K have been studied using the isothermal evaporation method. Based on the experimental data, the dry-salt phase diagram, water-phase diagram and the diagram of physicochemical properties vs. composition in the system were plotted. The dry-salt phase diagram of the system includes one three-salt co-saturated point, three metastable solubility isotherm curves, and three crystallization regions corresponding to sodium chloride, potassium chloride and calcium chloride hexahydrate. Neither solid solution nor double salts were found. Based on the extended Harvie–Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β (0), β (1), C ϕ for NaCl, KCl and CaCl 2, the mixed ion-interaction parameters θ Na,K, θ Na,Ca, θ K,Ca, Ψ Na,K,Cl, Ψ Na,Ca,Cl, Ψ K,Ca,Cl, the Debye–Hückel parameter A ϕ and the standard chemical potentials of the minerals in the quaternary system at 288.15 K were obtained. In addition, the average equilibrium constants of metastable equilibrium solids at the same temperature were obtained using a method derived from the activity product constant for the metastable system. Using the standard chemical potentials of the minerals and the average equilibrium constants of solids at equilibrium, the solubility predictions for the quaternary system are presented. A comparison between the calculated and experimental results shows that the predicted solubilities obtained with the extended HW model using the average equilibrium constants agree well with experimental data.

Thermal cycle testing of calcium chloride hexahydrate as a possible PCM for latent heat storage

In order to study the changes in latent heat of fusion and melting temperature of calcium chloride hexahydrate (CaCl 2·6H 2O) inorganic salt as a latent heat storage material, a thousand accelerated thermal cycle tests have been conducted. The effect of thermal cycling and the reliability in terms of the changing of the melting temperature using a differential scanning calorimeter (DSC) is determined. It has been noticed that the CaCl 2·6H 2O melts between a stable range of temperature and has shown small variations in the latent heat of fusion during the thermal cycling process. Thus, it can be a promising phase change material (PCM) for heating and cooling applications for various building/storage systems.

Thermal Energy Storage Behavior of CaCl2.6H2O during Melting and Solidification

In this study, experiments are conducted to investigate melting and solidification characteristics of calcium chloride hexahydrate (CaCl2.6H2O) as a phase change material (PCM). In the present study, some parameters that affect the melting and the solidification time of PCM used to store low temperature energy have been observed experimentally. These parameters are inlet temperature and mass flow rate of water used as a heat transfer fluid (m = 2.51, 3.75, and 4.95 kg min−1), fin numbers inside the PCM. For this purpose, PCM has been stored constantly between the coaxial pipes and water adjusted to 45°C for the melting process and to 5°C for the solidification process, and was circulated by a pump through the inner pipe at the experimental setup. During the experiments, when the water mass flow rate is increased to 49 and 97% with respect to the starting mass flow rate (m = 2.51 kg min−1), a rate of 5 and 15% decrease at the melting time is obtained, respectively. As a result, it has been observed that the effect of the fins placed inside the PCM to the melting and solidification time is much more than the effects obtained by the flow rate and the swirling generators.

Heat Storage Performance of a PCM Heat Exchanger with Calcium Chloride Hexahydrate

Calcium chloride hexahydrate (CaCl2·6H2O) is an important inorganic phase change material used for heat storage at lower storage temperature. Heat storage in a PCM heat exchanger is an effective means of energy conservation or recovery in many engineering applications. A study was made on heat storage performance of a PCM heat exchanger with staggered tube bank in which there are full of calcium chloride hexahydrate solution. The experimental measurements of its heat storage and discharging performances during the heating/cooling cycle were carried out at a given rate of air flow. The analyses and discussion of its experimental results were also made. Its prospect in the industrial applications as heat energy storage was forecasted.

Elastic Ceramic-Polymer Scaffold with Interconnected Pore Structure: Preparation and In Vitro Reactivity

A series of ceramic-polymer scaffolds were studied for bone tissue engineering applications. These applications require bone reactivity as well as suitable scaffold properties and structure. Bioactive glass (BAG) and sol-gel derived silicas were chosen for ceramic components of the scaffolds, and crosslinked poly(ε-caprolactone/D,L-lactide) copolymers with monomer ratios 90/10 and 70/30 were used as polymer matrices. Scaffolds were prepared by photo-curing crosslinkable oligomers in the presence of the ceramic component and porosity producing salt. Scaffolds with 60-80 vol-% continuous phase macroporosity were obtained by using calcium chloride hexahydrate (CaCl2⋅6H2O), and were further tested in simulated body fluid (SBF). The ceramics remained highly reactive during scaffold preparation resulting in in vitro calcium phosphate formation.

Enhancement of solar thermal energy storage performance using sodium thiosulfate pentahydrate of a conventional solar water-heating system

The time variations of the water temperatures at the midpoint of the heat storage tank and at the outlet of the collector in a conventional open-loop passive solar water-heating system combined with sodium thiosulfate pentahydrate-phase change material (PCM) were experimentally investigated during November and then enhancement of solar thermal energy storage performance of the system by comparing with those of conventional system including no PCM was observed. It was observed that the water temperature at the midpoint of the storage tank decreased regularly by day until the phase-change temperature of PCM after the intensity of solar radiation decreased and then it was a constant value of 45 °C in a time period of approximately 10 h during the night until the sun shines because no hot water is used. Heat storage performances of the same solar water-heating system combined with the other salt hydrates-PCMs such as zinc nitrate hexahydrate, disodium hydrogen phosphate dodecahydrate, calcium chloride hexahydrate and sodium sulfate decahydrate (Glauber's salt) were examined theoretically by using meteorological data and thermophysical properties of PCMs with some assumptions. It was obtained that the storage time of hot water, the produced hot water mass and total heat accumulated in the solar water-heating system having the heat storage tank combined with PCM were approximately 2.59–3.45 times of that in the conventional solar water-heating system. It was also found that the hydrated salts of the highest solar thermal energy storage performance in PCMs used in theoretical investigation were disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate.

Semi-analytic solutions for freezing induced by evaporative cooling

Freezing in a one-dimensional region induced by evaporative cooling is investigated. Semi-analytic solutions in the limit of low mass transfer rates and Stefan numbers are presented. An nth order polynomial is used to express the vapor pressure function in terms of the evaporating fluid layer temperature. The freezing of a slab of calcium chloride hexahydrate subject to evaporative cooling of a thin layer of water into air is used to illustrate the utility of the model. Results show the existence of a transition region, depending upon the relative humidity and Biot number, where the fluid layer dry-out time competes with the freeze time of the slab.

Calcium chloride penetrates plant cuticles via aqueous pores.

Penetration of calcium chloride across astomatous cuticular membranes (CMs) isolated from leaves of Pyrus communis L. has been studied. Penetration was a first-order process when calcium chloride concentrations ranged from 2 gl(-1) to 10 gl(-1). Rate constants were increased 10-fold by adding wetting agents but they did not depend on temperature. The accelerators tributyl phosphate and diethyl sebacate had no effect on rates of penetration. Increasing humidity over the salt residue on the CMs from 50 to 90% increased rate constants by about 2-fold. Extracting cuticular waxes from pear leaf CMs increased rate constants by factors of 2 to 3, depending on humidity. Leaf CMs from Malus domestica Borkh., Populus aelha L., Stephanotis floribunda Brongn. and Schefflera actinophylla (Endl.) Harms were also permeable to CaCl2. Highest rate constants were observed with poplar CMs while Schefflera CMs exhibited the lowest permeability. By comparing these results with the well established transport properties of the lipophilic pathway it is concluded that calcium chloride hexahydrate penetrated cuticular membranes via aqueous pores.

Utilization of Solar Energy and Waste Heat

A heat pump and thermal energy storage unit were combined in an experimental setup to utilize solar energy and waste heat efficiently at low temperatures (10-50 C). The calcium chloride hexahydrate was used as the thermal energy storage medium and water was used as the working liquid between storage tank and collectors. The performance of the experimental setup at different heat source temperatures for space heating in a laboratory building in Trabzon, Turkey, were investigated both experimentally and theoretically. The fraction of the space heating load that was supplied by the solar-assisted system was determined as a function of collector area and storage volume from a developed numerical method and results were compared with experimental results.

Effectiveness of a thermal energy storage system using phase-change materials

Second law analysis is developed for a phase-change thermal energy storage system. The methodology starts with determining the number of entropy generation numbers ( N s ) for a cyclic operation consisting of heat storage and retrieval processes. During the cyclic operation, the phase-change material is maintained at its melting temperature. The entropy generation number is determined as a function of the Reynolds number of the operating fluid, specific heat transfer area, operating fluid inlet temperatures during the cyclic processes and the thermo-physical properties of both the storage materials and the heat transfer fluids. A case study is presented to demonstrate the applicability of the model developed. The storage material considered was either paraffin wax or calcium chloride hexahydrate (CaCl 2, 6H 2O), whereas the heat transfer fluid used was air or water.

Storing solar energy in calcium chloride

Using common chemistry concepts to determine the feasibility of storing solar energy in calcium chloride hexahydrate.

Phase change materials for energy storage nucleation to prevent supercooling

Abstract Phase change materials (PCMs) are useful for storing heat as the latent of fusion. Such storage has potential in heating and cooling buildings, waste heat recovery, off-peak power utilization, heat pump systems, and many other applications. Among the PCMs that have proven useful in heat storage applications are calcium chloride hexahydrate, CaCl2·6H2O, magnesium chloride hexahydrate, MgCl2·6H2O, and magnesium nitrate hexahydrate, Mg(NO3)2·6H2O. Many salt hydrate PCMs, including those listed above, have the disadvantage that during extraction of stored heat the material supercools before freezing. This reduces the utility of the material, and if too severe can completely prevent heat recovery. Many factors determine whether a particular additive will promote nucleation, for example, crystal structure, solubility, and hydrate stability. Candidate isomorphous and isotypic nucleating additives, with crystal structures that fit well with the PCM structure, were selected from tables of crystallographic data. Epitaxial nucleators, with less obvious lattice structure features that promote nucleation, were selected mostly by intuition. Effective nucleators were discovered by both methods. Based on laboratory test results, promising materials were developed into formalations based on CaCl2·6H2O, MgCl2·6H2O, Mg(NO3)2·6H2O, Mg(NO3)2·6H2OMgCl2·6H2O eutectic, and Mg(NO3)2·6H2ONH4NO3 eutectic salt hydrate PCMs. Subsequently, attempts were made to correlate crystal structure and hydrate stability with nucleating efficacy, and to speculate about active nucleating structures.

Observations sur le comportement a la fusion-solidification du chlorure de calcium hexahydrate

Calcium chloride hexahydrate is a potentially interesting material for heat storage by latent heat. However, it can exhibit pronounced supercooling and its non-congruent fusion leads to progressive degradation of the material with repeated fusion-solidification cycles. The behaviour of compounds containing calcium chloride hexahydrate has been studied using a specially constructed experimental apparatus in which a large number of fusion-solidification cycles (up to 50 cycles for some experiments) can be performed automatically without interruption and with continuous monitoring of the temperature of the sample. From observations made in experiments in which Ba(OH) 2 · 8H 2O and SrCl 2·6H 2O were added to the calcium chloride, a crystallization mechanism with heterogeneous nucleation can be inferred; nuclei effects were observed. Strontium chloride hexahydrate is an effective nucleating agent, by use of which almost total suppression of supercooling can be achieved. An unexpected observation was made when 1% by weight of Ba(OH) 2 · 8H 2O was added, for which no satisfactory explanation can be proposed for the time being. The temperature of fusion dropped by about 3°C over the first three cycles and remained stable thereafter. Compounds containing 3% by weight of SrCl 2 · 6H 2O exhibited very stable thermal behaviour over 50 fusion-solidification cycles. Performance tests involving a higher number of cycles need to be performed in order to assess the practical usage life of a heat storage material; however, the present work has shown that the addition of a small quantity of SrCl 2 · 6H 2O suppresses supercooling and prevents performance degradation of calcium chloride hexahydrate.

TG and DSC investigation of CaCl 2· 6H 2O PCM material

Samples of calcium chloride hexahydrate containing varying amounts of KCl in combination with SrCl 2, BaSO 4 and NaCl have been prepared and studied by thermogravimetric and differential scanning calorimetric methods. The additives improve the stability of the intermediate hydrate and change the stoichiometry of the dehydration process.