Melting and solidification of PCMs inside a spherical capsule: A critical review

To date, numerous phase change materials (PCM) have been developed for application in latent heat storage systems. There are many issues in the process from the development of PCM to using them in storage systems, which should be resolved. The problem of heat transfer in PCMs during the phase change process is the most important one. Latent heat storage containers usually have simple geometrical forms such as a sphere, cylinder, cylindrical annulus, rectangular enclosure, etc. A large number of papers were published on melting and solidification processes in PCMs. Therefore, there is a pressing necessity for generalizing the art of the state in this field and establish how accumulated knowledge meets practical requirements. The present review considers the current state in investigations of heat transfer in a spherical shell. Heat transfer in PCMs during constrained melting (solid PCM fixed inside the vessel), unconstrained (unfixed) melting and solidification, and phase change in finned shells are analyzed. It is shown that currently, there is no satisfactory description of the constrained melting process. For unconstrained melting and solidification, some correlations are suggested, describing these processes. The applicability range of the proposed correlations, as well as their accuracy were investigated and established. To intensify the process of phase change inside the spherical container, the use of orthogonal fins is appropriate option compared to the employ of circumferential fins

Empirical investigation to explore potential gains from the amalgamation of Phase Changing Materials (PCMs) and wood shavings

The reduction of gained heat, heat peak shifting and the mitigation of air temperature fluctuations are some desirable properties that are sought after in any thermal insulation system. It cannot be overstated that these factors, in addition to others, govern the performance of such systems thus their effect on indoor ambient conditions. The effect of such systems extends also to Heating, Ventilation and Air-conditioning (HVAC) systems that are set up to operate optimally in certain conditions. Where literature shows that PCMs and natural materials such as wood-shavings can provide efficient passive insulation for buildings, it is evident that such approaches utilise methods that are of a degree of intricacy which requires specialist knowledge and complex techniques, such as micro-encapsulation for instance. With technical and economic aspects in mind, an amalgam of PCM and wood-shavings has been created for the purpose of being utilised as a feasible thermal insulation. The amalgamation was performed in the simplest of methods, through submerging the wood shavings in PCM. An experimental procedure was devised to test the thermal performance of the amalgam and compare this to the performance of the same un-amalgamated materials. Comparative analysis revealed that no significant thermal gains would be expected from such amalgamation. However, significant reduction in the total weight of the insulation system would be achieved that, in this case, shown to be up to 20.94%. Thus, further reducing possible strains on structural elements due to the application of insulation on buildings. This can be especially beneficial in vernacular architectural approaches where considerably large amounts and thicknesses of insulations are used. In addition, cost reduction could be attained as wood shavings are significantly cheaper compared to the cost of PCMs

High-temperature phase change materials for thermal energy storage

The development of energy saving technologies is very actual issue of present day. One of perspective directions in developing these technologies is the thermal energy storage in various industry branches. The review considers the modern state of art in investigations and developments of high-temperature phase change materials perspective for storage thermal and a solar energy in the range of temperatures from 120 to 1000 °C. The considerable quantity of mixes and compositions on the basis of fluorides, chlorides, hydroxides, nitrates, carbonates, vanadates, molybdates and other salts, and also metal alloys is given. Thermophysical properties of potential heat storage salt compositions and metal alloys are presented. Compatibility of heat storage materials (HSM) and constructional materials have found its reflection in the present work. Data on long-term characteristics of some HSMs in the course of repeated cycles of fusion and solidification are analyzed. Article considers also other problems which should be solved for creation of commercial high-temperature heat storage devices with use of phase change materials.Heat storage materials (HSMs) Phase change materials (PCMs) Latent heat storage Thermal energy storage (TES) Salt mixes and compositions Metal alloys Thermophysical properties Corrosion

Enhancing thermal conductivity of paraffin wax 53–57 °C using expanded graphite

The latent heat thermal storage using Phase Change Materials (PCMs) is one of the essential aspects to be addressed for rapid expansion of utilisation of Renewable Energy sources and waste heat. The major disadvantage of PCMs, deployed in such thermal storage systems, is their low thermal conductivity and, in some cases, low latent heat.Paraffin wax/expanded graphite (PW/EG) composite PCMs with the EG mass fraction of 2%, 4%, and 6% were prepared by absorption of molten organic material into the EG structure. FireCarb TEG-315 and FireCarb TEG-160 were used as EG of A- and B-type, respectively, and PW 53–57 °C was deployed as the PCM in this study. Polarizing optical microscope, scanning electron microscopes and Fourier transform infrared spectroscopy were used to characterize the structure of composite PCMs. Thermal properties of pure Paraffin and produced composite materials were determined using a differential scanning calorimeter and thermal conductivity analyser.One of originalities of this work is that the statistical method of assessment of heterogeneity in composite PCMs was proposed for the first time with the use of Matlab software. This method was deployed for the quantitative assessment of uniformity of the EG distribution in composite PCMs structure.The novelty of obtained results is in detection of intermolecular interaction between B-type EG and PW. This interaction further enhances thermo-physical properties of the PW/EG composites. In contrast to pure PW and PW/A-type EG composite PCMs, in which the solid-solid transition and solid-liquid phase change are observed, PW/B-type EG compositions exhibit only the solid-liquid phase change. The heat storage capacity in both types of compositions was found to be almost identical. Despite of prolonged sample's ultrasonic treatment, the structure of PCM compositions was found to be far from being homogeneous. However, the thermal conductivity of compositions with 6 wt % of EG was determined to be 0.977 W/m°C for the PCM with A-type EG and 1.263 W/m°C for the PCM with B-type EG in comparison with the value of 0.258 W/m°C for pure PW. These values of the thermal conductivity correspond to the enhancement ratios of 3.79 and 4.9, respectively. If uniformity in the EG distribution in PW can be improved, then the thermal conductivity of composite PCMs would also considerably increase.Findings of this work are being used for designing a cost efficient solar thermal storage system with the reduced charging/discharging times as a part of an international project funded by EC

Wind power engineering in the world and perspectives of its development in Turkey

The development of a world wind power for the last decade is reviewed. Leading positions are taken by Germany, Spain and USA. The rates of growth of this branch of power engineering exceed 39% annually. It seems that the wind power is esteemed in these countries as the most perspective branch of electric power industry. The great success achieved by Germany and Spain in last years in developing wind power industry served as an example for all countries that have wind energy potentials. Information describing growth of powers, single wind power turbines, dynamics of increments of power of WPT on separate countries are submitted. During the last 10 years, the cost of WPT construction decreased more than twice, and it seems that specific investment costs reached a stable point for about 10 years. Furthermore, it can be concluded from wind farm investment costs that the cost of a WPT is about 1.3 times the cost of wind turbine. The information on the sizes of large WPT are adduced.Renewable energy Wind energy Wind turbines Electricity production Economy of wind power Energy Policy Wind farms Turkey