Papers by Keyword: Thermal Storage

Abstract: This paper investigates the application of polymer materials for low-temperature, pressure-less thermal storage in Czech district heating systems integrated with high-performance heat pumps. A dynamic simulation was conducted for a residential building of 180 occupants, equipped with a 32 kW heat pump, 10 kW photothermal panels, and 200 m³ of stratified water storage divided into preheating and high-temperature sections. Composite tanks for thermal storage can provide lower cost per cubic meter of storage, superior structural resilience under thermal cycling, and competitive environmental performance relative to polypropylene alternatives. The findings highlight composite storage as a technically and economically viable pathway for enhancing flexibility, efficiency, and decarbonization in Czech district heating networks.

Abstract: An evaporator-absorber geometry allows the absorption of incident solar radiation andconverts it into thermal energy useful for the evaporation of a working fluid. The evaporator-absorberworks with two fluids: a heat transfer fluid transmitting heat to a working fluid, which, circulatesalong the thermal circuit composed of an evaporator, a turbine, a condenser and a pump. The aim ofthis research work is to analyze the heat transfer through the evaporator-absorber and to extract themathematical equations model the heat exchange process between the component elements of theevaporator-absorber: a serpentine tube, a working fluid and a cylindrical tube. In this case, theworking fluid is water, and the heat transfer fluid is air, which is heated by the thermal energyconverted from solar energy. The mathematical equations describing the heat transfer are extractedby using the nodal method and discretized by the finite difference method. Afterwards, the presentwork estimates the outlet temperature of each element of the evaporator-absorber and studies thestorage capacity of the cylindrical tube. Then, the water temperature distribution on the geometry ofthe evaporator and the required quantity of water and the number of spires to have a high outlettemperature of the water vapor are determined. As a result, the mathematical modeling estimated thatthe outlet temperature of the serpentine tube is higher than the outlet temperature of the water.Additionally, the temperature of the storage tube maintains its increase throughout the day. Thequality of the heat transfer in the serpentine tube is improved by placing the tube in a vertical positionand by adopting a lower volume of water compared to the maximum volume, which is supported bythis tube.

Abstract: Implementation of high temperature solar reservoirs is associated with problems related to the physical properties of materials, especially with temperature resistance of the material at temperature changes, with high heat capacity, with high thermal conductivity and with material fire resistance. In the case of silicate materials, more specific materials with favourable physical properties are available, which can be used for the construction of high temperature containers. The basic prerequisite for designing such container is the knowledge of the physical properties of the heat storage core and the thermal insulation ability of container cladding layers.The paper deals with the problem of identification of material properties of silicates in the wide temperature range up to 800 °C, using the standard measurement methodology, improved by additional temperature recording at a defined distance from the thermal source during the dynamic thermal development of the linear thermal source, well-known as the hot wire method.

Abstract: This work presents a numerical study of the phase change process of PCM (Phase Change Materials) stored in spherical cavities. The numerical model is two-dimensional and it is composed by the equations of conservation of mass, momentum, energy and volumetric fraction, which are modeled using the enthalpy-porosity technique. The computational mesh is tetrahedral, with refinements on regions that have large thermic and fluid dynamic gradients. The numeric model was validated with result from literature. It was studied the melting process of PCM RT35, RT 55 and RT 82 in spherical cavity with constant wall temperature. Four diameters of spheres D were used (40, 60, 80 and 100 mm) and three temperature differences ΔT (10, 20 and 30 oC) between the wall temperature and the melting temperature of the PCM. Liquid fraction results from the 36 cases studied are presented. It was observed that the time required to reach a certain liquid fraction increases with the diameter and reduces with the increment of ΔT, being possible to predict the fusion time by knowing the characteristic length of the sphere. The largest percentage reduction of the fusion time was obtained with ΔT = 10 oC – 20 oC for all the D considered. The shortest fusion time was obtained with the largest ΔT combined with the smallest D. It is possible to see the dependence of the liquid fraction results in relation with the PCM properties and the its independence in relation its melting temperature, since all the PCM studied presented equal fusion time for the same ΔT and D.

Abstract: The present work numerically investigates for a latent heat thermal storage (LHTS) unit, the effect of key design parameters such as the inlet temperature of the heat transfer fluid (HTF), initial and melting temperatures of the PCM, thermophysical parameters such as specific heat, thermal conductivity etc., on its performance. A numerical model has been developed considering the discharging mode of operation and solved employing finite difference technique. The parametric study reveals that the effect of HTF inlet temperature on the unit's thermal response is more compared to initial temperature of the PCM and the influence of thermal conductivity of the PCM is very strong compared to specific heat capacity of the solid PCM

Abstract: High-temperature behaviour of refractory composites needs proper experimental and theoretical analysis, coming from classical thermodynamics. The dependence of usual thermal characteristics, as the thermal conductivity and thermal capacity, on temperature, cannot be neglected in any computational simulation, thus the experimental identification of their effective values is required. Whereas valid technical standards related to the hot-wire measurement technique enables us only certain approximate evaluation of thermal diffusivity, the very similar experimental configuration, supplied by the more advanced physical, mathematical and computational analysis, offers a possibility of reliable simultaneous identification of more characteristics. The crucial application is to the selection of appropriate silicate materials for the design of high-temperature storage of solar energy where both high thermal conductivity and thermal capacity are required. The first results refer to certain magnesite-based products as the good choice.

Abstract: In this paper, a series of magnetic Stearic acid (Sa)/Fe₃O₄/TiO₂ nanocomposites were synthesized as a functional phase change materials through a two step methods; sol gel method followed by dispersion technique. Fe₃O₄/TiO₂ nanocomposites were first synthesized by varying the molar ratio of Fe₃O₄:TiO₂ from 1:1 to 1:5 followed by dispersing the synthesized Fe₃O₄/TiO₂ nanocomposites in stearic acid (Sa). The structural properties were confirmed by X-ray diffractometer (XRD), while their chemical compositions were determined from energy dispersive X-ray (EDX). The molecular interaction were detected by Fourier transform infrared spectroscopy (FT-IR). Thermal storage capability such as latent heat and specific heat were detected by differential scanning calorimetry (DSC) while high thermal reliability of their phase change performance were detected by thermogravimetric analysis (TGA) experiment. The result shows that the incorporation of nanocomposites Fe₃O₄/TiO₂ enhance the latent heat as well as heat capacity of phase change materials.

Abstract: This chapter shows the most recent and innovative contributions and research trends arounbd the wide issue of energy efficiency in buildings by means of passive techniques, such as new effective materials for building envelope optimization. In particular, cool materials will be dealt with by considering their capability to keep a surface cooler than other solutions when exposed to solar radiation. Then multifunctional materials such as thermal and acoustic insulation panels will be analyzed. Finbally, natural and biobased solutions for energy saving will be investigated. Each one of these topics will be studied by elaborating a first general assessment of each technique and then by analyzing the most recent contributions and research trends in order to provide a wide perspective of the question that is going to be addressed in this chapter.

Abstract: Today the use of fatty acids as heat storage substance is growing. The use of several types of fatty acids such as oleic acid, palmitic acid, and stearic acid as heat storage materials has been studied. But, ricinoleic acid from castor oil has not been studied yet. This study was conducted to ascertain the characteristics of ricinoleic acid as a heat storage material.Methyl ricinoleic was obtained through transesterification of castor oil by methanol with sodium methoxide catalyst. Methyl ricinoleic was then hydrolyzed using sodium hydroxide in ethanol to produce ricinoleic acid. Ricinoleic acid was identified by FTIR (Fourier Transform Infrared Spectrophotometer) test standard ASTM E 1252-07 and its chemical composition was determined by Gas Chromatography-Mass Spectrometry (GC-MS). The identification of the type, amount, and environment of hydrogen in the compound was determined by Nuclear Magnetic Resonance (NMR). The analysis on characteristics, that is, transition and melting temperatures of material was performed by DSC (Differential Scanning Calorimetry) test standard ASTM D 3419-08.Based on the results of FTIR, GC-MS, ¹H-NMR, dan ¹³C-NMR tests, the spectra that were obtained indicated that the test substances were methyl and ricinoleic acid 70.349%. And, the results of DSC tests indicated that the characteristics of ricinoleic acid absorbed and released latent heat at the temperature from 8.58°C and absorbed sensible heat at the temperature from-7.17°C to 8.58°C.

Abstract: This chapter starts with a background about concentrating solar power systems and thermal energy storage systems and then a detailed literature review about concentrated solar power systems and supercritical Brayton carbon dioxide cycles. Next, a mathematical model was developed and presented which generates and optimizes a heliostat field effectively. This model was developed to demonstrate the optimization of a heliostat field using differential evolution, which is an evolutionary algorithm. The current model illustrates how to employ the developed model and its advantages. The optimization process calculates the optical performance parameters at every step of the optimization considering all the heliostats; thus yields accurate results as discussed in this chapter. On the other hand, complete mathematical model of supercritical CO₂ Brayton cycles when integrated with solar thermal power tower system was presented and discussed.