جستجوی مقالات مرتبط با کلیدواژه « Phase change materials » در نشریات گروه « مکانیک »

In recent years, generation of electricity through photovoltaic power plants has developed rapidly. The availability of sunlight and the appropriate return on investment are two important factors in the impressive growth of photovoltaic (PV) power plants. Unfortunately, increase in PV cell temperature is one the main defects of them and it has a significant negative effect on the electrical efficiency of PV panels. In this paper, using paraffin as phase change material (PCM) on the performance of photovoltaic cells has been investigated experimentally. The material has melting point of about 58˚C. Also, the effect of airflow at two different velocities of 2 and 4 km/h in presence of paraffin have been tested, too. To have a better management on performing the tests, a solar simulator was used, so that the solar irradiation and wind stream were supplied by means of a projector and an industrial blower, respectively. Results showed 13-16˚C decrease in PV temperature for the three modified cases, in comparison with the conventional one. Moreover, the effect of mentioned temperature reduction on both electrical efficiency and output power were also studied. Finally, the environmental effects of commissioning a 10-kW PV power plant were checked by using RETScreen software. Accordingly, the annual reduction of carbon dioxide (CO2) emission is estimated for all considered cases.

One of the most important goals of sustainable development is to preserve nature and improve it, and the manifestation of sustainable development in the built environment basin is called sustainable architecture. Green roof is one of the new approaches to architecture and urban planning and arises from the concepts of sustainable development, which can be used to increase the per capita green space, improve the quality of the environment. Today, due to the increasing need for energy and the limitation of fossil fuels as depleting and polluting sources of the environment, the need to use more renewable energy sources is felt. One of the increasing uses of energy is thermal energy. One of the methods of thermal energy storage is the use of phase change materials. This research has been prepared with the aim of thermal optimization of green roof using phase change materials. By selecting biodegradable materials as phase change materials used in the roof, the research was conducted in three models and three different uses, using Energy Plus software. According to the results, the green roof model optimized with phase change materials in all three different uses of the building has increased the temperature in the building in cold seasons and significantly increased the temperature in hot seasons, and achieved thermal comfort. Therefore, according to the results, using green roof separately causes more temperature balance.

Based on experimental evidence, the presence of thermocouples in solid phase change materials affects the results and changes the melting regime from unconstrained melting to constrained melting. In this study, a new method for direct measurement of liquid mass fraction of phase change materials during melting was proposed based on the image processing technique. In this method, images of the melting process are prepared in controlled conditions at successive times. By performing image processing techniques, the boundary of the solid core is determined and the enclosed surface area is calculated and divided by the initial surface of the solid phase. This method was applied to unconfined paraffin melting inside a horizontal cylinder. The problem was also numerically simulated by the multi-phase method (VOF) and the change in the total volume of paraffin (total volume of solid and liquid phases) due to the difference between solid and liquid density was taken into account. A good agreement between numerical and experimental results was observed. The shape and sizes of the solid core in the experimental images and the numerical results at different times match well.

Environmental concerns and the scarcity of fossil fuels have led to the rapid development of rechargeable battery technologies. It has been proven that the performance of lithium-ion batteries is susceptible to temperature, and temperature significantly affects the capacity and power of batteries. Therefore, it is necessary to build an efficient battery thermal management system to maintain the battery's operating temperature in a safe range. Utilizing PCM.s can be an exciting option in thermal management systems of lithium-ion batteries, and several studies have been conducted about them. The biggest challenge in PCM-based BTMS systems is to overcome the problems related to the poor thermal conductivity of PCMs. Many researchers in this field proposed different types of metal fins (pinned fins, circular fins, longitudinal fins, and triangular fins), metal foams (aluminum, copper, and nickel foam), metal meshes, and carbon-based nanomaterials to increase the thermal conductivity in PCM-based BTMS systems. Some proposed carbon-based composite nanomaterials are expanded graphite, carbon nanotubes, and carbon fiber. In this article, recent developments and new methods of thermal management and performance optimization of lithium-ion batteries have been reviewed.

In this research, the role of Phase Change Materials (PCM) in energy saving in lightweight prefabricated buildings is studied. For this purpose, a typical building in Kermanshah, Iran is simulated in DesignBuilder software. A split unit is used as air conditioning system. The annual energy consumption of the building in the reference state is 2577.27 kWh. The implementation of the InfiniteRPCM21C was investigated in all directions including each individual wall, ceiling, four walls simultaneously and the entire building envelope. The southern wall is the best option among the walls with 12.14% energy saving. From an economic point of view, this wall has the best performance as well by saving 2.08 kWh/kgPCM. Implementation on the entire envelope increases savings up to 37.2%. Although this is not an economical case, but it reduces the need for energy to almost zero in four months of the year. By examining the PCM in different layers of the wall, it was found that in all directions, the inner surface of the wall leads to the greatest energy savings. Also, taking account the PCM thickness in the range of 5 to 25 mm showed that the smaller the thickness, the greater the savings per unit mass of the PCM. Therefore, thicknesses more than 20 mm are not recommended. Finally, the effect of the PCM melting point in the range of 18 to 29 degrees Celsius was investigated and it was found that the maximum energy saving is obtained at the melting point of 21 degrees Celsius.

Heat sinks have always played a crucial role in cooling electrical equipment. In this research, in a new approach, paraffin is used as a phase change material according to the suitable phase change temperature range with multi-wall carbon tube nanoparticles homogeneously in a heat sink. AnasysFluent software with finite volume method and PISO algorithm was used to model and solve the governing equations. The melting process of the PCM is numerically investigated in a three-dimensional space by applying three heat fluxes of 10,000, 20,000, and 30,000 watts per square meter, using the enthalpy-porosity method. According to the obtained results during the phase-change process, the addition of nanoparticles with volumetric percentages of 4, 6, and 8% leads to better performance in reducing the phase-change temperature. After the completion of the phase change process, increasing the volume percentage of nanoparticles does not always have a positive effect, and among the proposed options, nanoparticles with a volume fraction of 4% showed the best performance.This improvement is due to the increased conductive heat transfer in the PCM, resulting from reduced viscosity. Overall, adding 8% nanoparticles increases the total melting time by 15% compared to the pure PCM.

Phase change materials are increasingly playing an important role as heat transfer fluids and energy storage sources. This is a new technology in the field of thermal energy storage using phase change materials. In this article, the properties of microcapsules of phase change materials are studied and some widely used materials as core and shell materials were presented. Also, some of the uses of these materials are briefly mentioned. In the following, the method of manufacturing microcapsules based on n-octadecane and silica shell and microcapsule of phase change material with melamine core and formaldehyde shell is discussed.

The air humidification-dehumidification method is a good option for decentralized freshwater production because of no need for high temperature operation. The main disadvantage of these systems is their dependence on direct sunlight. to solve this problem, using the sun's thermal energy storage during the day and using this energy during the night can be a very good option that can be achieved using phase change materials. In the present work, it is also possible to continue the desalination process after sunset, by equipping the solar collector with phase change material from two different types of paraffin wax. MATLAB software has been used to solve the equations governing the components of the desalination system. According to the results, the temperature of the output water from the solar collector plays a significant role in the amount of fresh water produced. The results also confirm that the use of phase change material leads to more than 9% increase in fresh water production. Another important result is that in the phase change materials the melting process speed is substantially higher than the freezing process speed.

Buildings represent the largest energy-consuming sector; thus, exploring methods to decrease energy consumption within them is of utmost importance. Two energy-generating solutions within buildings are rooftop photovoltaic (PV) systems and PV windows. Additionally, incorporating Phase Change Materials (PCM) into building walls presents an energy-saving solution. This research compares the reduction of energy consumption through PCM with electricity generation via rooftop PV systems and PV windows. Results indicate that reductions in electricity consumption for rooftop PV, PV windows, and PCM are 11.5%, 1.4%, and 2.1%, respectively. Furthermore, an economic analysis was conducted on the energy produced by the photovoltaic power plant for sale to Iran’s Ministry of Energy. Findings reveal that under the condition of selling electricity, the payback period for a rooftop PV system is 6.3 years.

In this study, management of the electronic board temperature using an aluminum heat sink with9 fins containing phase change material (PCM) was investigated, experimentally. The critical temperature of the electronic board was 85 ° C and according to this temperature, stearic acid was selected as PCM for temperature management of the system. Experiments were performed in the wide power range and in different volume fractions of PCM. Using PCM at 11% volume fractions at power of 4 W significantly increased 20 minutes the operating time of the electronic board. Increasing the volume fraction of PCM from 11% to 50% at the power of 6 W, increased PCM melting range by 878 seconds and increased the operating time by 14 minutes. Experiments with alternative power (10 minutes on and 80 minutes off) in several consecutive heating-cooling cycles and at high powers (10, 15 and 18 watts) showed that the sensitivity of heat sink performance to PCM volume percentage at high powers is more than in low powers.

In this experimental study the effect of using phase change materials (PCM) in the thermal storage tank on the performance of a solar dryer was investigated. The experiments were carried out for three levels of PCM 1.54, 2.45 and 3.6 kg and two levels of fluid flow rate of 0.2 and 0.4 l/min. The results showed that with increasing the fluid flow, the thermal efficiency of the collector from 62.4% to 20.2% for 0.4 l/min. The thermal energy for fluid flow of 0.2 and 0.4 lit/min obtained about 13.31 to 13.63 MJ and 14.45 to 14.92 MJ, respectively. The results also showed that the overall efficiency of the dryer increased with increasing PCM and it changes from 32.92% to 35.55% for the fluid flow rate of 0.2 l/min and 32.19% to 36.02% for 0.4 l/min. Considering the specific energy used for drying of the samples and drying efficiency the fluid flow with 0.2 l/min and PCM with 3.6 kg is a proper choice for drying of apple slices. The payback period was obtained about 20 months.

In this paper, the thermal analysis of the solar wall system equipped with photovoltaic cells and phase-change materials (PCM) has been numerically investigated. For the thermal modeling of the system, the energy balance for its various components, including photovoltaic cells, air channel, adsorbent plate, Phase-change material and room are written. The validation of the numerical results is consistent with the experimental data of previous studies. In parametric studies the effect of PCM thickness, inlet air flow rate, collector width and packing factor have been investigated on the increase of room temperature and average system energy efficiency in four consecutive days. Results show that the optimal PCM thickness is 0.05 m. Increasing the PCM thickness reduces the room temperature and the energy efficiency. Increasing the air flow rate decreases the photovoltaic cells temperature and increases electrical efficiency, thereby increasing energy efficiency. However, it reduces room temperature. Therefore, the optimum flow rate of air was obtained 0.04 kg/s. Increasing the collector width, despite increasing room temperature, reduces energy efficiency, so the optimum collector width was 0.7 m. The increase of the packing factor increases room temperature and reduces energy efficiency. Therefore, the optimum packing factor was 0.5.

A majority portion of energy resources in the world is supplied by fossil fuels. Excessive consumptions of fossil energy resources have instigated many environmental issues such as climate change. Burning fossil fuels release toxic and dangerous pollutants that will affect the environment and finally the human food chain. Overconsumption of nonrenewable fossil fuels concerns the global community to develop concepts such as sustainable renewable energies, energy storage, thermal energy and phase change materials within the framework of energy management. The idea of using phase change materials for storage of renewable thermal energy is growing.  Having variety types of phase - change materials with different characteristics has led to the possibility of using these materials in several industries such as textiles, medicine, smart clothes, civil and electronic industries. Additionally, storage and release of renewable energies are important factor in the development of energy management. Therefore, in this study, the role of phase change materials in smart clothing is investigated.

Energy consumption and energy saving are attracting many attentions recently from every politician, managers, researchers, engineers and even users. In order to this, there are many efforts to use the renewable energy resource.
So solar cells and all systems which are able to absorb, save and then release the heat energy, are examined and there are many improvements. Regarding the characteristics of saving energy, many materials are examined and
finally phase change materials (PCM) are considered. These materials are able to absorb and release the energy in low temperature too and could be an interesting option for saving energy. In this article, in spite of introducing
PCMs, we look on the possibility of using metals and alloys as saving energy materials. Metals with low melting temperature like Ga, In, Bi, Al and Si due to their good and acceptable thermal-physical properties, could show better performance.

Providing the human thermal comfort, because of its impact on productivity and health is very important. This can be more challenging under extreme cold conditions and when the human body cannot adapt itself to the environment by using the physiological thermoregulatory mechanisms. Under these conditions, using protective clothing is one of the effective ways to protect the human body against the thermal injuries. In this study, the performance of protective clothing with a Phase Change Material (PCM) layer has been analysed by simultaneous modeling of physical and physiological mechanisms of the human under extreme cold conditions. For this purpose, multi-layer protective clothing with a PCM layer has been considered and its thermal performance has been investigated for two different arrangements of the layers. The results show that the middle layer of protective clothing is the best position for implementing the PCM layer and the best melting temperature for the mentioned PCM is about 10˚C. Also, using the PCMs in protective clothing can increase the thermal tolerating time from 4000 seconds up to 6000 seconds under extreme cold conditions.

Most of energy sources have some disadvantages such as environmental problems and being expensive, so using solar energy for greenhouse heating in cold seasons is a very important issue. Solar energy is a periodic source, so using of energy storage systems is inevitable. In this paper, phase change materials was used in heating system of a solar greenhouse built in Dezful and its influence on temperature gradient of bed soil is experimentally investigated. A model greenhouse with a ground area of 3 m2 was coupled with a heating system consisting of a water tank contained 18 kg paraffin wax (latent heat 190 kj/kg and melting point 55ºC) as phase change material. During the daytime, temperature of the paraffin wax reaches to melting point, with energy of solar radiation absorbed by tow collectors, and daily available energy stored as thermal energy (sensible heat and latent heat). This stored energy is released during the night to heat bed soil of greenhouse. Temperature gradient of soil were evaluated to figure out thermal performance of this energy storage system. Results of this study indicates that about 10 ºC increase in minimum nighttime temperature and average temperature of soil in different depths was achieved.

Regarding the variability nature of the solar ray in a day, application of a thermal storage system seems necessary to accompany the solar system. Latent heat energy storage in a solar water heater can occur in a phase-change material. These materials are generally encapsulated in a container and positioned in the water container. Shape, material type, and size of the encapsulating container have direct eect on the eciency of the storage system. In this paper, eort has been made to investigate experimentally the encapsulation diameter eect on the storage system eciency. Industrial paran with 5- 7% fat was used as a phase-change material. They were encapsulated in aluminum tubes of 6, 10, and 12 mm diameter. The thicknesses of the capsules in all diameters are 1mm. For each tube size, a set of tests was carried out. For each test, 88 capsules with 280 mm height containing the paran were used. As a result, for capsules with 6, 10, and 12mm diameter, 281.6gr, 1126.4gr, and 1760gr of paran were used, respectively. The results show that the rate of energy storage using aluminum tubes of 6, 10, and 12 mm with phase-change material in comparison to when using no phase-change material, improved energy storage eciency by 4.4, 15.3, and 11.2%, respectively. With regard to the fact that by reduction of capsule diameter, the rate of surface area to the volume increases; hence, heat transferring surface area increases. Therefore, it is expected that by reducing the capsule diameter, density of energy storage will increase. Consequently, by reducing the capsule diameter, total paran mass will decrease. Hence, by considering these two factors, maximum rate of energy storage occurs when the capsule diameter is 10mm.

Nowadays, using the double skin facades has attracted the attention of many engineers because of its significant effects on the buildings’ energy consumption, beside of maximum absorption of solar renewable energy. The previous researches have shown that the double skin facades have an appropriate thermal performance in the cold season. However, using double skin façade may lead to increase the building’s energy demand in the warm season. Therefore, in the recent years, the idea of using double skin facades with phase change materials (PCM) has been proposed in order to decrease the summer energy consumption of buildings. In this study, a thermal performance analysis has been performed by considering a high-rise building with the phase change material double skin façade in Tabriz and Bandarabas climatic conditions. The results indicate that using the ordinary double skin façades in Tabriz climatic conditions can decrease the building’s energy consumption up to 20% in cold months of the year; but it can lead to increase the summer cooling load about 14%. However, by using double skin façades with the phase change material glazing, the building’s energy consumption in cold and warm seasons may decrease about 12.5% and 7%, respectively. Also, the double skin façades with the phase change material glazing shows a good performance in Bandarabas climatic conditions with cooling and heating load energy saving about 5.7 and 12.6%, respectively.

Energy consumption tendency in buildings and to find out the methods to manage and optimize it as audit or energy management methods are considered nowadays. Energy audit in every building is influenced by academic studies, experience and acquainting with new technologies of energy conservation. Renewable energies can play an important role in this way. Phase change materials (PCMs) are new substances with high heat of fusion. They absorb energy as latent heat until transformation in their phase. When the absorbed heat is needed, heat is extracted and material change to the primary condition. PCMs are very effective because they can be used in a variety of temperatures in cooling and heating. During the summer season, the benefits are a decrease in overall energy consumption and a time shift in peak load to off-peak hours that can decrease energy consumption cost. So, in this paper the role of PCMs in energy consumption management is considered.