Showing 16 results for Phase Change
Volume 7, Issue 4 (12-2023)
Abstract
Given the ever-increasing demand for energy and the limited nature of fossil fuel resources, improving energy efficiency and storage has become one of the most significant challenges facing humanity. Phase Change Materials (PCMs), substances capable of absorbing and releasing thermal energy at a constant temperature, have emerged as an innovative solution in the field of energy storage. With their high latent heat capacity, ability to maintain a stable temperature, and environmental friendliness, PCMs have great potential for applications in various industries. However, their low thermal conductivity, especially in organic PCMs, has hindered their widespread use. To address this challenge, researchers have been exploring various methods to enhance the thermal properties of PCMs. One of the most effective approaches involves incorporating high thermal conductivity nanoparticles into the PCM matrix. This research comprehensively reviews recent advancements in the preparation and applications of nanoparticle-enhanced phase change materials. It delves into various types of nanoparticles used, production methods for nanocomposites, the impact of nanoparticles on the thermal and mechanical properties of PCMs, the stabilization of nanocomposites with surfactants and surface modification, and also their potential applications in diverse industries. The results of this study indicate that the use of nanoparticles can significantly improve the thermal conductivity of PCMs, with carbon-based nanofillers showing the highest impact. Additionally, nanoparticles have led to a relative reduction in the phenomenon of supercooling in PCMs. Based on the results of numerous studies, nanoparticle-enhanced phase change materials hold great promise for improving the performance of energy storage systems, reducing energy consumption in various industries, and fostering the development of sustainable technologies. These nanocomposites can be employed in the construction, automotive, electronics, and textile industries to create more comfortable environments, enhance energy efficiency, and reduce greenhouse gas emissions. Continued research in this field is expected to lead to the development of even more efficient PCMs with a broader range of applications.
Volume 10, Issue 2 (9-2020)
Abstract
Aims: In the last century of Iranian architecture, the use of passive thermal comfort methods has been forgotten and replaced by active methods, in addition to environmental constraints and crises, this process have caused high costs and sometimes reduced access to electricity; As a result, it is essential to use elements and passive methods, especially in warm climates where more electricity is consumed. One of the most important elements of Iran's traditional architecture is wind tower which is still functional due to its simplicity of operation and use of wind energy. In recent years, the use of new building technologies, such as Phase Change Materials, has also led to the revival of passive methods and significant energy savings. Therefore, the present study has attempted to use this material in the wind tower to improve its performance in passive cooling.
Methods: This research was carried out in the form of modeling of airflow in the wind tower channel in Fluent Software and comparing the inlet and outlet temperature. In this regard, three models - fiberglass and two types of phase change with different melting constant temperatures as wall cover-were tested.
Findings: Testing of the models showed that the cover of the phase change material was much more effective than the fiberglass cover (at least between 4.5°C until 5.5°C) in reducing the outlet temperature of the wind tower.
Conclusion: This amount of cooling covers at least three months in warm season and some time of day in the warm and humid climate of Qeshm and will play a reliable role in reducing electricity consumption.
Mohamad Reza Ansari, Nima Samkhaniani,
Volume 15, Issue 2 (4-2015)
Abstract
In present study, volume of fluid method in OpenFOAM open source CFD package will be extended to consider phase change phenomena due to condensation process. Both phases (liquid – vapor) are incompressible and immiscible. Vapor phase is assumed in saturated temperature. Interface between two phases are tracked with color function volume of fluid (CF-VOF) method. ُSurface Tension is taken accounted by Continuous Surface Force (CSF) model and mass transfer occurs along interface is considered by Lee mass transfer model. Pressure-Velocity coupling will be solved with PISO algorithm in the collocated grid. This solver is validated with Stefan problem. In one dimensional Stefan problem, the desistance of interface motion from cold wall is compared by the analytical solution. Then condensate laminar liquid film flow over vertical plate is simulated in the presence of gravity. Numerical result shows calculated film thickness from numerical simulation is thinner than analytical solution. Also, it shows Nusselt number is a function of vapor specific heat which neglected in existing correlations, therefore analytical solution and experimental correlation should modified to consider this effect on the Nusselt Number.
Seyed Alireza Zolfaghari, Mehran Saadati Nasab, Elahe Norozi Jajarm,
Volume 15, Issue 5 (7-2015)
Abstract
Nowadays, using the double skin facades has attracted the attention of many engineers because of its significant effects on the buildings’ energy consumption. 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 Tehran climatic conditions. The results indicate that although using the ordinary double skin façades can decrease the building’s energy consumption up to 20% in cold months of the year; it can lead to increase the summer cooling load about 4.6%. 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 40% and 26%, respectively.
Unes Pahamly, Seyed Mohammad Javad Hosseini Kahsari, Ali Akbar Ranjbar,
Volume 15, Issue 10 (1-2016)
Abstract
This paper presents a numerical study on melting behavior of phase change material (PCM) in a horizontal double pipe heat exchanger. The shell side is filled with RT50 as PCM and water is used as heat transfer fluid (HTF) which flows through inner tube. The aim of the study is to investigate the effect of eccentricity as a geometrical parameter on melting behavior of PCM through downward movement of the inner tube. In addition, effective flow parameters such as mass flow rate and HTF inlet temperature are investigated on thermal storage performance. Enthalpy porosity method is used to modeling the phase change process. At the beginning of melting process, conduction is dominant heat transfer mechanism and by time pass natural convection will be the main heat transfer mechanism. Results show that by increasing eccentricity, the dominant area for the natural convection expands and phase front penetration velocity increases which leads to considerable decrease in melting time. By increasing inlet temperature from 70˚C to 75˚C and 80˚C, total melting time decreases up to 16% and 27% respectively. Although By Increasing Reynolds number from 1000 to 1500 and 2000, total melting time only decreases to 1% and 3%, respectively. These results show that Stefan number influences melting time more pronounced than Reynolds number.
Habib Ramezannezhad Azarboni, Mansour Darvizeh, Aboalfazl Darvizeh, Reza Ansari,
Volume 15, Issue 11 (1-2016)
Abstract
When a dynamic load passes a control volume of material as a shock wave, passing this wave through the control volume could cause different phases such as elastic and plastic. From the microscopic view, during phase change, material flow would be taken in control volume which includes mass, heat, energy, and momentum transport. Phase change in material causes a material discontinuity in the control volume. During the phase change process, mass, heat, energy, momentum transport and etc will occur and the equations governing these phenomena are called transport equations. In this article, for the first time, the governing equations of elastoplastic behavior of beam under dynamic load are extracted by using mass, energy and momentum transport equations. Using transport equations with non-physical variables in integral form will cause in employing discontinuity conditions in governing equations and eliminates the discontinuity condition. These equations are also used in continuously modeling of beam elastoplastic behavior under dynamic loading and a continuous model is presented. Finite element method is used to solve the transport equation with non-physical variable. Finally, the time history of stress, strain and velocity wave propagation along beam are presented in elastic and elastoplastic phases
Seyed Alireza Zolfaghari, Mohammad Fathian, Mohsen Talebi,
Volume 15, Issue 11 (1-2016)
Abstract
Under the critical thermal conditions, the human body cannot adapt itself to the environment by using physiological thermoregulatory mechanisms. Under these conditions, using the protective clothing is one of the effective ways to protect the human body against the thermal injuries. Therefore, in the present study, the effect of using Phase Change Materials (PCMs) on the performance of firefighters’ protective clothing has been numerically investigated under the critical scorching conditions. The main contribution of this study is the simultaneous modeling of a PCM based protective clothing with physical and physiological mechanisms of the human body. For this purpose, a multi-layer protective clothing with a PCM layer has been considered and its thermal performance has been investigated under scorching conditions for three different arrangements of the layers. The results show that the middle layer of protective clothing is the best position for implementing the PCM. Also, and is the best melting temperature for the mentioned PCM is about 40˚C. Moreover, the results indicate that using the PCMs in protective clothing can increase the thermal tolerating time from 300 seconds (for non-PCM protective clothing) up to 900 seconds, under the scorching conditions.
Seyed Amirreza Hosseini, Ramin Kouhikamali,
Volume 16, Issue 5 (7-2016)
Abstract
Numerical simulation of boiling has always been a challenging problem in terms of the variety and effectiveness of two-phase models. Furthermore choosing an appropriate heat and mass transfer model increases the complexity of the solution. Problem of film boiling of saturated liquid is numerically simulated in this investigation by using of VOF (volume of fluid) model together with the geo-reconstruction of interface. Three phase change models of sharp interface model, Lee model and Tanasawa model are used at the same time on a single problem in order to calculate the rate of phase change and source terms. One-dimensional Stephan benchmark is solved for verification the numerical solver. The periodic Nusselt, flow pattern, bubble form and its detachment time have been studied in mentioned various phase change models. Also empirical coefficients used in both models of Lee and Tanasawa are presented. The results of Nusselt number obtained from simulation is compared with two empirical Nusselt correlations of Berenson and Klimenko. The results show good agreement with the Klimenko’s Nusselt. The results reveal although the Lee model is dependent on empirical coefficient, it is more accurate than the two other models for prediction of film boiling on flat plate.
Faramarz Talati, Mohammad Taghilou,
Volume 16, Issue 8 (10-2016)
Abstract
The use of phase-change material to enhance the capacity of energy storage/release is the subject of many new researches on management of the energy supply. Study of these systems is directly related to the solid-liquid phase-change problem, in which the evaluation of temperature distribution, position of phase-change front and liquid or solid fraction becomes a basic problem. Study of freezing and melting process with regard to natural convection in the liquid phase is the main purpose of the present paper. For this purpose, a rectangular finned container of phase-change material is intended. Fins are used to enhance the heat transfer rate. This fact necessitates the use of immersed boundary condition on the solid phase. Hence, the melting process considering the both effects of natural convection and movement of solid phase is studied. The freezing process is also studied taking into accounts the natural convection with no need to impose the immersed boundary condition. Lattice Boltzmann method is used as a numerical method and results are reported based on the dimensionless parameters. Based on the results, the effects of natural convection is negligible during freezing process, while imposing the effects of natural convection provides a significant change in the required time for complete melting of the phase change material.
Saeed Amirabdolahian, Hamid Jannesari,
Volume 17, Issue 5 (7-2017)
Abstract
Thermal energy storing technologies are a new approach in reducing energy costs, managing demand side, pick shaving and increasing portion of renewable energies in energy production. In spite of lots of advantages of thermal energy storage techniques, there are still major challenges in the path of Latent heat thermal storages (LHTS). One of the challenges is the low charge and discharge rate of heat transfer in LHTS. In the current study charging rate of a shell and tube LHTS is numerically studied by enthalpy-porosity numerical technique. Exact positioning of the heat transfer tubes and thermal fins has great impact on the natural convection flows. In this study effect of increasing heat transfer tubes (HTF), lower positioning of tubes in four tubes configuration, changing upper tubes distance and using interconnected axial fins has been studied and compared to each other. Moreover, velocity and temperature contours have been analyzed. Results demonstrated that increasing number of tubes could not solve the slowing rate of charging at the end of process and tubes need to be positioned lower in the tube. In addition, it was observed that heat transfer axial fins can decelerate convection flows and develop stationary areas inside the shell. Prediction results revealed by lowering tubes and closing them to the shell wall, introduced in this article, it is possible to decrease charging time of 0.95 of storage capacity to one fourth of similar time in a one tube LHTS.
Babak Kamkari, Mohammad Vahabi,
Volume 17, Issue 11 (1-2018)
Abstract
This paper presents an experimental and numerical investigation of phase change material melting in a rectangular enclosure. The aim of this research is the study of the effect of the tilt angle of the enclosure on the flow structures and the melting rate. In the experimental section, the visualization of the melting process is carried out by the photography of the phase change material through a transparent enclosure. Then, the image processing of the photographs is performed to calculate the instantaneous liquid fractions. The variation of the solid-liquid interface by tilting the enclosure clearly implies the evolution of the flow structures in the liquid phase. Numerical simulation is performed using the enthalpy-porosity approach for tilt angles of 90, 45 and 0o and wall temperatures of 55, 60 and 70 oC. The results show that by decreasing the tilt angle from 90o to 45o and 0o, the melting times are 52% and 37% less than that of the vertical enclosure. Melting time reduction in the inclined enclosure is due to the formation of the vertical flow structures and thermal plums in the liquid phase. By Increasing the Stefan number from 0.36 to 0.43 and 0.55 the thermal energy storage increase by 5.4% and 13.8%, respectively. Also, a correlation is developed to predict the thermal energy storage in the tilt enclosures using nonlinear regression.
Hazhir Ahmadkermaj, Reza Maddahian, Mehdi Maerefat,
Volume 18, Issue 2 (4-2018)
Abstract
Ice slurry is called a mixture of fine ice particles with a fluid carrier such as water. The phase change ability of this mixture attracts the strong attention in the areas of thermal storage and refrigerant cooling of the secondary cycle. In this research, flow of ice slurry in horizontal tubes during the phase change is numerically investigated using FLUENT software. The two-phase nature of ice slurry mixture is studied using the Euler-Euler two-phase model based on kinetic theory of granular flows. The effect of ice particles phase change on heat and mass transfer between phases are investigated, the obtained results show that the local heat transfer coefficient for the use of the icy slurry mixture is increased 12% compare to the pure water. It is also determined by examining heat and mass transfer rate along tube, that the heat transfer coefficient for the pipe lengths larger than 10-15 times pipe diameter, remains constant. The variation of mean mass transfer is maximum at distance of 10-15 times of pipe diameter. The maximum value is 2-5 times larger than mean mass transfer in the pipe outlet. At the 20% end of the pipe, the decreasing trend of mass transfer accelerates.
Volume 18, Issue 119 (12-2021)
Abstract
In this research, a combined photovoltaic / thermal solar dryer containing phase change materials (PCM) was designed and fabricated for drying mint leaves. The performance of this dryer was evaluated under the climatic conditions of Mashhad city with a longitude of 59.62
and a latitude of 36.26
. The components of this dryer mainly include: photovoltaic panel, solar collector, blowers, phase change material chamber containing paraffin wax and drying chamber. Solar dryer and natural drying in shade as two different drying types were used to perform experiments on mint leaves. The initial moisture content of the mint leaves was 80% which reduced to 12%. The required drying time for the combined solar drying and natural drying was 290 minutes and 1560 minutes, respectively. Eight thin layer drying models available in the literature were fitted to the experimental data in which the Two-term model and the Wang and Singh model were the best fit models for natural and combined solar drying respectively. These models have the highest correlation (highest coefficient of determination and least root mean square error and Chi-square) with the experimental moisture ratio among the other models.
M. Iranmanesh, M.s. Barghi Jahromi,
Volume 19, Issue 11 (11-2019)
Abstract
One of the most important applications of solar energy is its utilization in solar dryers to maintain agricultural products for long-term storage. These dryers work based on passing warm air through fresh materials by natural or forced convection. So, they have a direct dependence on the intensity of the sun's irradiance to their collector, which it disrupts the drying process in the absence of a thermal energy source in the hours when the sun is not available. In order to solve this problem, the phase change material (PCM) as thermal energy storage is used. The materials that have the capacity to absorb the thermal energy (charge phase) and, they release the absorbed energy (discharge phase) when the intensity of the solar radiation is low or during the night and cause the uniformity of the outlet temperature solar collector, and inside the drying chamber. As well as they provide the necessary thermal energy for hours when the sun is not available and increase the duration of use of the dryer. In the present research, the experimental studies have been carried out through designing and construction of an indirect cabin type solar dryer equipped with a heat pipe evacuated tube collector and using PCM material as energy storage in the expansion tank. In the present research, the experimental studies have been carried out through designing and construction of an indirect cabin type solar dryer equipped with a heat pipe evacuated tube collector and use of PCM material as energy storage in the expansion tank. The effect of various parameters such as inlet and outlet temperatures of the collector, temperature, and humidity of the drying chamber and ambient, the intensity of the solar irradiance on the drying process is investigated, with and without PCM and at two different speed of forced convection through the drying chamber. The results show that the effectiveness of forced convection on the drying process is more than the effect of PCM.
Mohammad Saleh Barghi Jahromi, Vali Kalantar, Mehran Abdolrezaie,
Volume 20, Issue 7 (6-2020)
Abstract
In the current study, natural solar ventilation has been investigated aiming at reducing the consumption of fossil and thus, reducing greenhouse gas emissions in a hot and dry climate in which the behavior of various fluid variables (temperature, velocity, and flow rate) is considered in different conditions. Since solar radiation is not uniform throughout the day, passive solar ventilation is unstable. In this regard, the natural displacement flow in a solar ventilator with copper thermal absorber, double-glazed glass compartment to prevent thermal energy loss, as well as phase change materials for the storage of thermal energy has been investigated, experimentally. In the case of no phase change material, due to the creation of a suitable temperature difference, the panel has made the chimney effect possible for natural ventilation in some hours of the day, but in the early hours of the night, the temperature of the panel will be the same as the ambient temperature, and the chimney effect will not be available for proper ventilation. In a panel equipped with phase change materials, the system has acceptably been able to play an important role in reducing the temperature drop in the hours of the day with no solar radiation leading to a reliable air flow rate. In fact, the main purpose of using phase change materials in passive solar ventilation is the same effect, the use of excess energy in cases of energy shortages.
Mohammad Mazidi Sharfabadi, Nuha Majeed Karam, Reza Kurd,
Volume 24, Issue 1 (12-2023)
Abstract
In this article, the effect of using phase change materials to improve heat transfer in power distribution transformers has been investigated experimentally. To enhance the cooling of the transformer, a new method has been proposed, which involves adding paraffin inside aluminium containers that are sealed to the transformer oil. The test setup includes an electric transformer filled with transformer oil, two electrical heaters, a power regulator, a thermal camera, oil insulation measuring device, and temperature sensors placed at various locations. The experimental results demonstrated that the addition of phase change materials to the electronic transformer oil led to a decrease in the temperature of the transformer, particularly in summer weather conditions. Additionally, the mean temperature of the transformer oil was reduced from 46.7 to 42.5 degrees Celsius by adding 8 kg of paraffin. However, it was observed that when the temperature increases suddenly and rapidly within an hour, these materials are ineffective in dissipating the heat and reducing the temperature of the transformers. Additionally, the research examines the impact of continuous and high-temperature increases on the oil electrical insulation. The results revealed that using phase change materials increased the voltage that the oil could withstand as an electrical insulator from 56.8 kV to 61 kV.
