130,513 research outputs found
Optimization of the mass ratio and melting temperature of PCMs integrated in Salt Gradient Solar Ponds
Get PDFPhase Change Materials (PCMs) are promising materials to increase the storage capacity of solar energy-based systems, such as Salt Gradient Solar Ponds (SGSPs), as they are characterized by a large latent heat during the solid-liquid phase change. This paper introduces an optimization study for PCM integration in SGSP, in terms of PCM mass ratio (14 %, 19 %, 28 % and 47 %) in the lower convective zone and PCM melting temperature (35 °C, 44 °C and 50 °C). Numerically, a 2D model is developed, consisting in the continuity equation as well on momentum, thermal energy and diffusion equations. In order to validate this numerical model, an experimental campaign of a parallelepiped SGSP with PCM capsules in the bottom is constructed. The latter is tested for two PCMs (RT35HC and RT44HC) and under different climatic conditions of March and June. Numerical and experimental have been compared in which the maximum average relative error does not exceed 4.62 %, which ensures a positive validation. The optimization returns that the final liquid fraction of PCM decreases both increasing the mass ratio and melting temperature. Higher mass ratios reduce the final temperature of the PCM (49.5 °C with 14 % and 42 °C with 47 % for RT35HC), and also with higher melting temperatures reduce the thermal energy stored, since the pond tends to work only as a sensible energy storage system
Experimental investigation and optical visualization of a salt gradient solar pond integrated with PCM
No full textThe thermal performance of a solar pond is affected by the amount of heat lost to the ground through the lower convective zone (LCZ) in which the heat is stored. Studies are focused on decreasing the heat losses, to maximize the energy stored and guarantee the stability of the thermohaline system over time. Phase change materials (PCMs) can help to achieve all these goals, since they work as thermal energy storage (TES), exploiting the latent heat absorbed during the solid-liquid phase change. This paper presents an experimental application of PCMs in the LCZ of a small solar pond. The paraffin wax was enclosed in aluminium cylinders which have been arranged on the bottom. The temperature of the solution in deep is monitored both with and without the PCM. The stability of the pond is analyzed through a laser shadowgraph technique, to visualize the effect of the thermal convection on the interfaces. Results show that the LCZ of the solar pond with PCM is around 3 °C colder than the reference case after a 6-h heating period. The shadowgraph analysis proves that the thermal convection in the reference case is stronger and damage the interface until break. The monitoring of the solar pond with PCM shows an improved stability
Technical analysis and economic evaluation of a complex shore-to-ship power supply system
No full textIn port areas, with the progressive increase in maritime traffic, the problem of pollution is crucial especially when the port is near to an urban area. The cold ironing allows a reduction of pollutants satisfying the power demand of ships while they are at berth, replacing on board diesel engines. In this paper, the methodology of analysis of the electrical loads required by ships concerns the typical week of each month over a one year period. The power is provided by a cogeneration plant powered by natural gas. It is flanked by a Compressed Air Energy Storage system since the energy demand is linked to the presence of ships in port and so very variable over time. The heat waste is recovered in a heating district network for overall optimization. At last, the economical aspect has been evaluated to prove the feasibility of the whole system. The results, for the case of the port of Ancona, show that a 1.5 MW and 2 MW cogenerator covers the 83.05% and 92.5% of the electrical need of ships respectively, and the 61% and 74% of the thermal need of buildings over the period analysed. The coverage of the CAES system is not influenced by the rated power
Optimal sizing of a photovoltaic/energy storage/cold ironing system: Life Cycle cost approach and environmental analysis
Get PDFTraditional cold ironing allows ships to shut down their auxiliary engines, during the berthing time, and to be powered by an on-shore power supply. Traditionally the energy demand is satisfied by electricity form the national grid. Alternatively, a local energy production increases the energetic self-sufficiency of the port areas and reduces the pressure on the national grid with continuous peaks of energy demand. This way the port area can be considered a microgrid, characterized by both energy producers and consumers. This paper presents an optimization model, implemented on MATLAB, to provide the best sizing for a combined photovoltaic/energy storage/cold ironing system. The ferry traffic of the port of Ancona (Italy) has been taken as case study. The proposed model returns the percentage of the energy demand covered, the interactions with the national grid, and the optimal size of the PV plant and the storage capacity basing on a Life Cycle Cost (LCC) approach. Results show that the optimal configurations are 2100 kW and 3600 kW with 5750 kWh (without and with storage system) considering lower initial and operational costs, and 3700 kW and 6400 kW with 17,350 kWh (without and with storage system) hypothesizing higher costs. All scenarios ensure an environmental saving, compared to traditional on-board diesel generators, with 87.4 % maximal CO2 reduction achieved
Indoor and Outdoor Performance of an Enhanced Photovoltaic Panel through Graphene/Fins/Phase Change Materials
Get PDFThe operative temperature of a photovoltaic cell influences the electric conversion yield. This can be enhanced by cooling the panel. Among the studied solutions, phase change materials (PCM) exploit latent heat and absorb a large amount of energy at a nearly constant temperature. PCMs suffer from a low thermal conductivity. Under these premises the paper presents a hybrid graphene/fins/PCM cooling system to maximize efficiency gains and thermal recovery. An indoor laboratory characterization, under a solar simulator, compares the proposed model with a reference one (an identical, simple PV module) under fixed environmental conditions. Outdoor tests investigate the performances of the two systems under natural conditions. Indoor results show that the front temperature of the proposed PCM integrated module is averagely 6 °C less, with a peak of 8 °C, than the reference case. This means an increase in the electric yield of about 3%. Outdoor investigations prove that, when the PCM is solid and during the melting phase, the proposed system is averagely 1.12 °C and 4.87 °C colder than the reference case, respectively. The thermal efficiency is 30% and 65%, respectively. Once the melting process is completed, the performance becomes worse, and the hybrid panel is almost 3 °C warmer than the simple panel
Local energy production scenarios for emissions reduction of pollutants in small-medium ports
No full textEnvironmental impact produced by ships in ports is a relevant problem, especially when they are located close to urban areas. This paper, taking Ancona (Italy) as a case study, analyzes the CO2 (and other chemical species) emissions produced by the auxiliary engines of ferry ships at berth. Three different configurations have been investigated, one grid-connected and two with local power plants. Cogenerative and photovoltaic scenarios have been considered varying the power size and the presence of a storage system. A computational model, based on maritime traffic and meteorological data over a one-year period, returns the percentages of the energy covered by the plant, the grid and the storage system. Environmental analysis shows that the grid-connected cold ironing scenario reduces the CO2 emissions by 34.5% compared to on-board diesel generators emissions. Cogeneration systems reduce CO2 emissions by 60–62%, while photovoltaic ones around 39%. All scenarios prove to be economically feasible
Effects of Double-Diffusive Convection on Calculation Time and Accuracy Results of a Salt Gradient Solar Pond: Numerical Investigation and Experimental Validation
Get PDFThe main aim of this study is to investigate numerically and experimentally the effects of double-diffusive convection on calculation time and accuracy results of a Salt Gradient Solar Pond (SGSP). To this end, two-numerical models are developed based on the Fortran programming language. The first one is based on energy balance neglecting the development of double-diffusive convection, while the second is two-dimensional and is based on Navier-Stokes, heat, and mass transfer equations considering the development of double-diffusive convection. The heat losses via the upper part, bottom, and vertical walls, as well as the internal heating of saltwater, are considered. In order to validate and compare both numerical models, a laboratory-scale SGSP is designed, built, and tested indoors for 82 h. Results indicate that the two numerical models developed can predict the SGSP thermal behavior with good accuracy. Furthermore, the average relative error between experimental and numerical results is around 9.39% for Upper Convective Zone (UCZ) and 2.92% for Lower Convective Zone (LCZ) based on the first model. This error reduces to about 5.98% for UCZ and 3.74% for LCZ by using the second model. Consequently, the neglect of double-diffusive convection in the SGSP modeling tends to overestimate the thermal energy stored in the storage zone by about 4.3%. Based on the calculation time analysis, results show that the second model returns a calculation time hundreds of times larger than the first one and, accordingly, an increase in computational cost
Cancer stem cell biomarkers predictive of radiotherapy response in rectal cancer: A systematic review
Get PDFBackground: Rectal cancer (RC) is one of the most commonly diagnosed and particularly challenging tumours to treat due to its location in the pelvis and close proximity to critical genitouri-nary organs. Radiotherapy (RT) is recognised as a key component of therapeutic strategy to treat RC, promoting the downsizing and downstaging of large RCs in neoadjuvant settings, although its therapeutic effect is limited due to radioresistance. Evidence from experimental and clinical studies indicates that the likelihood of achieving local tumour control by RT depends on the complete eradica-tion of cancer stem cells (CSC), a minority subset of tumour cells with stemness properties. Methods: A systematic literature review was conducted by querying two scientific databases (Pubmed and Scopus). The search was restricted to papers published from 2009 to 2021. Results: After assessing the quality and the risk of bias, a total of 11 studies were selected as they mainly focused on biomarkers predictive of RT-response in CSCs isolated from patients affected by RC. Specifically these studies showed that elevated levels of CD133, CD44, ALDH1, Lgr5 and G9a are associated with RT-resistance and poor prognosis. Conclusions: This review aimed to provide an overview of the current scenario of in vitro and in vivo studies evaluating the biomarkers predictive of RT-response in CSCs derived from RC patients
Effect of PCM melting temperature on solar ponds performance: Design and experimental investigation
No full textSalt gradient solar pond (SGSP) is a technology which uses a renewable source such as solar energy to store thermal energy in a saline solution. Traditional SGSPs work in the sensible zone, increasing its temperature as the solar radiation is absorbed. SGSPs suffer from a low stability and energy efficiency, mainly caused by the high temperatures reached. At high temperatures, higher heat losses correspond. PCMs are characterized by high latent heat and a solid-liquid phase change at a nearly constant temperature. A pond integrated with PCMs can store the same amount of energy at a lower temperature, improving thermal efficiency and stability. In this paper, a pond integrated with PCM (RT35 HC) and a traditional one were designed, built and tested to evaluate the different performance. According to results, over ten days, the average temperature in the pond with the RT35 HC is about 4 °C lower (corresponding to the 5.7 %). Then a second experimental analysis was conducted comparing two different melting temperatures (RT35 HC and RT44 HC). Results show that a higher melting temperature enables to smooth the high peaks of temperature. While a lower melting temperature guarantees a higher and more stable temperature at night, due to the release of latent heat, making the application useful in case of constant temperature demand at the outlet fluid. Results are widely discussed in the paper
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