1,721,026 research outputs found
Hypothesis of thermal and mechanical energy storage with unconventional methods
No full textThere is not a real “storage market” and the range of technical solutions for electrical storage appears to be underdeveloped. The use of electrochemical batteries seems to be the easiest and cheapest way, but some problems related to disposal, average life span and storage capacity, still put a brake on their diffusion. The micro CAES-TES (Compressed Air Energy Storage – Thermal Energy Storage) systems with small renewable energy plants for cogeneration and trigeneration represent an important development perspective thank to the reuse of the heat generated at the stage of air compression (for heating) and air expansion (for cooling). This improves the complexity of the entire system because of the heat exchange and thermal storage units must match the capacities and performances of the air compression/expansion units. The paper presents a new mathematical model for micro CAES-TES systems, implemented in Matlab software environment. The novelty is the use of air compressed energy storage in small and residential applications, a trigeneration due to reuse of heat from air compression and expansion stage, only renewable energy used. By keeping the initial investment low, the analysis is extended to the optimal system configuration and identifies key parameters that have a dominant influence on improving system efficiency and provides useful guidance for CAES-TES system design. The results show that, for an air storage volume of 4 m3, the optimal configuration is with a compression ratio of 15 splitted in two stages, charging time 5 h, mechanical storage efficiency 48%, compression air flow rate 3.73 kg/hour. The proposed system has a possible future development overall if combined with new possible scenarios of direct use of compressed air in the residential sector
Multi-fidelity surrogate-based optimization of transonic and supersonic axial turbine profiles
No full textAutomated Fluid-dynamic Shape Optimization plays a key role in the design of turbomachinery and typically combines Computational Fluid Dynamics (CFD) solvers, parametrization techniques and numerical optimization methods, generally categorized as either direct or surrogate-based (SBO) ones. Here, a particular focus is given to SBO exploiting surrogate models constructed from low-fidelity models, often referred to as variable or multi-fidelity optimization. This study presents a multi-fidelity SBO approach for the optimization of a supersonic turbine cascade operating with an organic fluid and of the transonic LS89 high-pressure turbine vane. A cokriging method is used to simultaneously take into account quantities of interest (QoI) coming from models of different fidelities providing a global surrogate model. A classic Bayesian global optimization method permits to iteratively select promising designs. It relies on the maximization of the so-called Expected Improvement criterion. A geometrical parametrization technique based on B-splines is considered to describe the profile geometry. The total pressure loss coefficient is minimized while the mass flow rate is constrained. For both the application cases, the optimization study reveals a speed-up of 3 to 5 times in the convergence process with respect to classic optimization frameworks based on a single fidelity, while providing similar improvements in terms of fitness functions
Novel Framework for the Robust Optimization of the Heat Flux Distribution for an Electro-Thermal Ice Protection System and Airfoil Performance Analysis
No full textA new device hypothesis for water extraction from air and basic air condition system in developing countries
Full text linkThis work proposes a new device for air treatment with dehumidification and water recovery/storage, with possible mitigation of indoor environmental conditions. The system is based on Peltier cells coupled with a horizontal earth‐to‐air heat exchanger, it is proposed as an easy‐to-implement alternative to the heat pumps and air handling units currently used on the market, in terms of cost, ease of installation, and maintenance. The process provides the water collection from the cooling of warm‐humid air through a process that leads to condensation and water vapor separation. The airflow generated by a fan splits into two dual flows that lap the two surfaces of the Peltier cells, one flow laps the cold surfaces undergoing sensible, latent cooling with dehumidification; the other flow laps the hot surfaces and heats up. The airflow undergoes thermal pre‐treatment through the underground horizontal geothermal pipe that precedes the Peltier cells. In the water storage tank, which also works as a mixing chamber, the two air streams are mixed to regulate the outlet temperature. The system can be stand‐alone if equipped with a photovoltaic panel and a micro wind turbine, able to be used in places where electricity is absent. The system, with different configurations, is modeled in the African city Kigali, in Rwanda
Walls comparative evaluation for the thermal performance improvement of low-rise residential buildings in warm Mediterranean climate
No full textBuildings built in warm climates are affected by severe overheating problems in summer, which negatively affects people's comfort and health. For these reasons, many users are forced to install cooling systems, leading to an increase in costs, consumption and a meaning impact on the environment. This study gives a valid method to monitor the overheating problems in buildings located in Mediterranean climates, without the use of cooling systems, but just with an accurate design of the envelope. The main challenge is to demonstrate that the hourly monitoring of the internal operative temperature (TOP), in accordance with the UNI EN ISO 52016, is able of defining univocally the performances of the building, taking into consideration the characteristics of the envelope. The optimization of this parameter permits to reach high level of internal comfort in a building, ensuring the designer to identify the best choice of building materials that compose the envelope. The TOP trends, for a whole year, are tested on a single-residential building model located in a warm Mediterranean climate, considering different configurations of the external walls. The results put in evidence that the best solutions are characterized by the presence of the double layer of tuff, with a very massive layer in the internal side and resistive layer outside. At the end, this study demonstrates that once optimized the envelope, it is easier to reach good values of internal operative temperature with the only use of a mechanical ventilation system
Energy-sustainable hospitals: Integration of a novel compound parabolic concentrator system with two storage tanks for domestic hot water production at high and low temperatures
No full textHospital buildings are known to be energy-intensive, since they are operated all year round at high costs, contain sophisticated medical equipment, and follow strict cleaning practices and environmental regulations. Domestic hot water consumption accounts for most of the energy consumption in hospital buildings. The objective of this research work is to study the energy performance of a novel compound parabolic concentrator system connected to two heat exchangers arranged in series, in turn, connected to two storage tanks that supply domestic hot water to two different hospital users. The first user requires high temperatures for laboratories, cleaning, sterilization of operating room instruments, and so on, while the second user requires lower temperatures mostly represented by health services. To guarantee the supply of the thermal energy needs, an external integration system was connected to each storage tank. A calculation scheme was created in a transient simulation environment that provides dynamically all temperatures at the output of the various system components and all thermal exchanges through each component. Starting from a reference configuration, a parametric simulation was carried out by varying the size of the plant components. The research aim was to
evaluate the influence of the component sizes on the plant’s transient behaviour by means of a qualitativequantitative determination of the monthly and yearly system energy exchanges and some performance indicators, such as the solar fraction, solar efficiency and fuel consumption on a monthly and yearly basis. The outcomes of this research demonstrated that the choice of the storage tank volumes and the secondary circuit flow rate allows designers to allocate the solar energy produced between the two users, while the collector area and the primary circuit flow rate allow designers to fix the fraction of overall thermal demand to be satisfied and the efficiency of solar energy conversion into thermal energy to the fluid. Finally, similarly to the f-chart method, some empirical correlations are proposed to rapidly verify the system performance without using any transient simulation tool
Optimization under uncertainty of horizontal ground heat exchangers
No full textIn this work, we propose to extend an efficient strategy for robust optimization when a large number of uncertainties
is considered, in order to include multi-criteria decision making tools. This strategy is based on ANOVA analysis for
reducing the stochastic dimension and a massive use of metamodels for predicting the sensitivity indexes in the design
variables plan. This approach is applied to the optimization under uncertainty of horizontal ground heat exchangers,
used in Ground Source Heat Pumps (GSHPs) for heating and cooling of buildings. System efficiency is maximized
taking into account several uncertain parameters, such as the heat conductivity of the ground around the tubes, the velocity inside the tubes and the depth of installation
Hourly forecasting of the photovoltaic electricity at any latitude using a network of artificial neural networks
Full text linkNowadays, special attention is paid to the importance of using photovoltaic (PV) systems to tackle the problem of climate change and the energy crisis. Artificial intelligence is currently used in different science fields for its great potential and accuracy in forecasting problems. In this work, a network of artificial neural networks (ANNs) was trained and validated to forecast the hourly worldwide electrical power produced by various PV modules, with different electrical characteristics. Each ANN describes the worldwide performance of each PV module on the optimal inclination angle. The training data consists of the hourly air temperature, horizontal total solar radiation as input data and electrical power produced as output. The power is obtained from the hourly simulation of PV modules with an electrical circuit model in 24 localities at very different latitudes. The validation and generalization of the network were obtained by considering the six PV modules in further 24 localities and by considering two further PV modules in all 48 localities considered. The excellent results in terms of accuracy metrics confirmed that the network of ANNs is a reliable, simple and accurate tool that can be used to predict the hourly performance of any PV module in any location worldwide
Structural Uncertainty Estimation of Turbulence Models in Organic Rankine Cycle Applications
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