Guest editorial for the special issue on progress in energy storage systems

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Determining thermal properties of heat storage materials using the twin bath method

The thermal properties of paraffin, high density polyethylene, zinc nitrate tetrahydrate, ethylene glycol, and brick are determined using the twin bath method. The heat storage capacities of the materials with and without the effect of container are measured. The heating and cooling curve for zinc nitrate tetrahydrate is obtained to detect its supercooling tendency.90K120430Acknowledgements--The authors thank the State Planning Organization of Turkey for providing financial support under the project 90K120430, TOBITAK for their contribution in DSC measurements and the Computer Center of (~ukurova University for their assistance in preparing the software used in the data logger system

Calculation of excess heat capacities for liquid mixtures

Experimental data of excess heat capacities for 29 binary liquid mixtures of various types have been correlated by the nrtl and uniquac models. For nine of these mixtures data at several isotherms is included. The parameters of the models, six for the nrtl and four for the uniquac, have been estimated by a minimization technique using Simplex and Fletcher techniques simultaneously. The partial molar excess heat capacities at infinite dilution are also calculated. Agreement between experimental and calculated values is satisfactory except for associating and highly non-ideal mixtures. The uniquac model performs better than the nrtl model. © 1992

Excess enthalpy surfaces for n-heptane + carboxylic acid, amylamine and n-octanol mixtures by the nrtl model

The temperature and composition dependences of the excess enthalpy, hE, have been calculated using the nrtl model for mixtures of n-heptane with the hydrogen-bonded liquids of acetic acid, propionic acid, amylamine and n-octanol. Reduced and partial molar excess enthalpies were also calculated. The temperature-dependent parameters of the nrtl model, estimated directly from hE data for more than one isotherm, were used in the calculations. The overall deviations of all the experimental data points fall in the range 0.5-6.5% which shows highly satisfactory correlation of hE data with the model. The temperature range for the mixtures is 285.15-330.15 K. The surfaces of excess enthalpy functions facilitate better understanding of the thermodynamic properties of the hydrogen-bonded mixtures. The nrtl model is a reliable thermodynamic model for studying the hydrogen-bonded mixtures in a qualitative and quantitative manner. © 1995

Polystyrene-based caprylic acid microencapsulation for thermal energy storage

In this study, caprylic (octanoic) acid microcapsules were synthesized with polystyrene shell material using the emulsion polymerization method. The influence of the type and concentration of the crosslinking agent on the phase-change properties of the microcapsules was examined. The structure and properties of the microcapsules have been characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). A second main contribution of this work is to investigate whether we could synthesize microcapsules with the same thermal properties during serial production. The effects of serial production on microencapsulated caprylic acid (microPCMs) have been investigated by thermal methods. The results show that reproducibility is an important parameter in the microencapsulation process. It was determined that when the synthesis amount is increased, we obtained lower efficiency in the microencapsulation of caprylic acid. © 2016 Elsevier B.V.111M614We would like to thank The Scientific & Technical Research Council of Turkey ( TUBITAK ) (The Project Code: TUBITAK 111M614 ) for financial support for this study. We would also like to thank Mr. Süleyman Konuklu for his technical help for this study. Finally, we would like to extend special thanks to the editor, Dr. Carl M. Lampert, and the anonymous reviewers for their constructive suggestions

Thermal analysis of heat storage materials

An improved method for testing the thermal performance of encapsulated heat storage materials in large nonstirred samples is presented. The method consists of measuring and comparing the energy loads of two identical thermostatted baths. Water, silicone oil or polyethylene glycol may be used as the working liquids in the baths, depending on the operating temperature. One of the baths operates with the sample of the encapsulated heat storage materials and the second operates with the working liquid alone under similar experimental conditions. Temperatures of the working liquids and the sample can be measured, and compared in the range 0-200° C. Differential measurements of this type provide valuable information on the thermal behaviour of the sample without the need to take into account the heat loss effects which are mainly difficult to determine. The test measurements for paraffin and high density polyethylene are discussed. © 1993.90K120430TThe authors thank the State Planning Organization of Turkey for providing financial support under the project 90K120430T, UBITAK for their contributionso n DSC measurementsa, nd the Computer Centre of Cukurova University for their assistancein preparingt he softwareu sed in the data logger system

Correlation of heats of mixing data by the NRTL and UNIQUAC models. Part 2. Predictions of the calorimetric properties

Using heats of mixing data only, the temperature dependent parameters of the local composition models NRTL and UNIQUAC have been estimated and presented in the first part of this series. Here, these parameters are employed to predict the calorimetric properties: these are the heats of mixing hE, partial molar heats of mixing at infinite dilution ?Hi, and excess heat capacities CpE. Limiting activity coefficients are also estimated at different isotherms. All the predictions have been compared with experimental values. The NRTL and UNIQUAC models satisfactorily represent heats of mixing data at different isotherms for highly non-ideal and partially miscible systems. However, predictions in the region of high dilution are not always satisfactory, especially for associating mixtures. The values of CpE obtained from the differentiation of equations for hE are poor. Also, the predicted values of ?i? show large deviations from the experimental values. © 1992.90K120430The authors extend their thanks to State Planning Organization for providing financial support under project No. 90K120430,a nd to the ComputerC entre of the Universityo f (;ukurovaf or providingt he computation facilities

Correlation of heats of mixing data by the NRTL and UNIQUAC models. Part 1. Estimation of the model parameters

Using data for heats of mixing hE, temperature dependent parameters of the NRTL and UNIQUAC models have been estimated for 57 systems of binary mixtures. In order to test the models thoroughly, systems of various types, including associating and partially miscible systems, that have data for hE at more than one different isotherm are considered. Temperature dependences of the models are assumed as non-linear. This form of dependence is found to be more suitable for associating systems and for prediction of excess heat capacity CEp from differentiation of a correlation for hE. No fixed values are assumed for the parameters of the models. The physical meanings and non-uniqueness of the parameters are discussed. © 1992.90K120430aThe authorsw ish to thank the State Planning Organization,f or providing financial support under project No. 90K120430a, nd also the Compute

Energetic and exergetic efficiency of latent heat storage system for greenhouse heating

In this research, solar energy has been stored using the paraffin with the latent heat technique for heating the plastic greenhouse of 180 m2. Energy and exergy analyses were applied for evaluation of the system efficiency. An average values of the rates of heat and thermal exergy stored into the HSU were 1 740 W and 60 W for the charging periods. It was determined that the average values of the net energy and exergy efficiencies of the system were 41.9 % and 3.3 %, respectively. © 1998 Elsevier Science Ltd. All rights reserved

Microencapsulation of coco fatty acid mixture for thermal energy storage with phase change material

Thermal energy storage systems provide several alternatives for efficient energy use and energy conservation. Microcapsules of natural coco, fatty acid mixture were prepared to be used as phase change materials for thermal energy storage. The coacervation technique was used for the microencapsulation process. Several alternatives for the capsule wall material were tried. The microcapsules were characterized according to their geometric profiles, phase transition temperatures, mean particle sizes, chemical stabilities, and their thermal cycling. The diameters of microcapsules prepared in this study were about 1 mm. Coco fatty acid mixtures have kept their geometrical profiles even after 50 thermal cycles for melting and freezing operations in temperature range from 22 to 34°C. It was found that gelatin + gum Arabic mixture was the best wall material for microencapsulating coco, fatty acid mixtures. Copyright © 2005 John Wiley & Sons, Ltd