Dynamic modelling of the solar radiation exposure effects on the thermal performance of a PCMs-integrated wall

The authors present a dynamic simulation of the thermal behavior of a multilayer plane wall, integrated with Phase Change Materials (PCMs), exposed to solar radiation in summer conditions, in a Mediterranean site. PCMs are a promising kind of heat storage materials that are particularly good in some climatic conditions: if properly placed, they can decrease heat flux through the walls, thus reducing cooling loads in buildings. Due to their strong non-linearity in thermal behavior, PCMs must be carefully modeled, possibly in transient conditions. The dynamic model consists of two main distinct parts. First, a solar radiation model is implemented, based on the daily evolution of the solar angles. This solution uses the results of a novel simple model for splitting the diffuse and the direct solar radiation starting from data on total radiation on a horizontal surface only. Then, solar radiation is used as a boundary condition for the dynamic modeling of a typical multilayer lightweight wall provided with one insulation layer integrated by PCMs. The calculated of solar effect and cooling loads are studied for three different melting temperatures of the PCMs

Thermodynamic transient simulation of a combined heat & power system

Abstract In this paper a numerical model aimed at studying dynamic behavior of CHP (Combined Heat and Power) plants is presented, paying particular attention to the components in which heat transfers take place. The analysis refers to a system powered by an internal combustion engine for a compression ignition type in cogeneration configuration, equipped with two heat extractors: the first one for coolant / water, the second one for exhaust gas / water. The numerical model has been implemented by using Matlab-Simulink software. After a description of the simplifying assumptions adopted for implementing the simulator, the model is exposed in detail with regards to each single element. Then simulation results are reported for two different operating conditions aiming to assess the effectiveness of the model in analyzing the dynamic behavior of CHP plants

Energy recovery from natural gas pressure reduction stations: Integration with low temperature heat sources

Energy recovery from Natural Gas (NG) distribution networks is a promising strategy in order to pursue energy sustainability in urban areas. The NG pressure reduction process, normally achieved by means of conventional throttling valves, can be upgraded by implementing turbo expander technology, which allows recovery of energy from the NG pressure drop. As commonly known, in this process the NG must be preheated in order to avoid methane-hydrate formation. The preheating temperature represents a key parameter of the process, on which depends the possibility of integrating low enthalpy heat sources into the system and of exploiting more efficient technologies and renewable energies as well. In this work, the possibility of integrating a pressure reduction station with low temperature heat sources is studied. In particular, a novel plant configuration consisting of a two-stage expansion system is presented and its energy performances are investigated by means of numerical dynamic simulations. The risk of formation of methane hydrate is assessed for different operating conditions and for transient behavior. Finally, the energy efficiency of PRSs with high and low temperature configuration is compared, showing how the two stage expansion can achieve higher energy performance and be effectively integrated with low enthalpy heat sources

Model for forecasting residential heat demand based on natural gas consumption and energy performance indicators

The forecasting of energy and natural gas consumption is a topic that spans different temporal and spatial scales and addresses scenarios that vary significantly in consistency and extension. Therefore, although forecasting models share common aims, the specific scale at which each model has been developed strongly impacts its features and the parameters that are to be considered or neglected. There are models designed to handle time scales, such as decades, years, and months, down to daily or hourly models of consumption. Similarly, there are patterns of forecasted consumption that range from continents or groups of nations down to the most limited targets of single individual users, passing through all intermediate levels. This paper describes a model that is able to provide a short-term profile of the hourly heat demand of end-users of a District Heating Network (DHN). The simulator uses the hourly natural gas consumptions of large groups of users and their correlation with the outside air temperature. Next, a procedure based on standards for estimating the energy performance of buildings is defined to scale results down to single-user consumption. The main objective of this work is to provide a simple and fast tool that can be used as a component of wider models of DHNs to improve the control strategies and the management of load variations. The novelty of this work lies in the development of a plain algebraic model for predicting hourly heat demand based only on average daily temperature and historical data of natural gas consumption. Whereas aggregated data of natural gas consumption for groups of end users are measured hourly or even more frequently, the thermal demand is typically evaluated over a significantly longer time horizon, such as a month or more. Therefore, the hourly profile of a single user's thermal demand is commonly unknown, and only long-term averaged values are available and predictable. With this model, used in conjunction with common weather forecasting services that reliably provide the average temperature of the following day, it is possible to predict the expected hourly heat demand one day in advance and day-by-day

Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries

Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management

Design and optimisation of impedance probes for void fraction measurements

The performance of impedance probes for measuring the conductance of gas\u2013liquid mixtures in horizontal pipes is here studied by means of the numerical solution of Laplace problem. In particular the work is aimed at optimising the probe geometry in order to improve the probe response both in terms of linearity and in terms of spatial resolution to step changes in phase distribution. Starting from basic shapes employed in literature (ring and half-ring electrodes), the adopted approach allowed new probe geometries (characterised by non-uniform electrode distance and/or electrode width) to be found. The analysis is performed with reference to annular, stratified and dispersed distributions and the results are compared with available theoretical models. Measurements have been carried out to verify the predicted sensor response and to ascertain the effect of the particle size on the probe response under dispersed flow conditions. The analysis demonstrates the behaviour of different probe arrangements with respect to different flow patterns and shows the possibility to obtain optimised geometries matching the desired features of linear response and of enhanced spatial resolutio

Preliminary CFD assessment of an experimental test facility operating with heavy liquid metals

open5The CFD analysis of a Venturi nozzle operating in LBE (key component of the CIRCE facility, owned by ENEA) is presented in this paper. CIRCE is a facility developed to investigate in details the fluid-dynamic behavior of ADS and/or LFR reactor plants. The initial CFD simulations have been developed hand in hand with the comparison with experimental data: the test results was used to confirm the reliability of the CFD model, which, in turn, was used to improve the interpretation of the experimental data. The Venturi nozzle is modeled with a 3D CFD code (STAR-CCM+). Later on, the CFD model has been used to assess the performance of the component in conditions different from the ones tested in CIRCE: the performance of the Venturi are presented, in terms of pressure drops, for various operating conditions. Finally, the CFD analysis has been focused on the evaluation of the effects of the injection of an inert gas in the flow of the liquid coolant on the performance of the Venturi nozzle.openLizzoli, Matteo; Borreani, Walter; Devia, Francesco; Lomonaco, Guglielmo; Tarantino, MarianoLizzoli, Matteo; Borreani, Walter; Devia, Francesco; Lomonaco, Guglielmo; Tarantino, Marian

Nuclear Hydrogen Production: Modeling and Preliminary Optimization of a Helical Tube Heat Exchanger

Hydrogen production is a topical issue in an energy scenario where decarbonization is a priority, especially with reference to the transport sector that has a great weight on global emissions. Starting from this consideration, GIF (Generation-IV International Forum) investigated the possibility to produce hydrogen by nuclear energy. The \u201cclassic\u201d strategy is based on the use of nuclear as energy source for the electrolysis; but on the medium-long term, a more sustainable and smart approach could be founded on the use of thermochemical processes (e.g., I-S) that require a direct coupling of a chemical plant to a nuclear reactor. In order to develop this strategy, it is mandatory to design and optimize all the key components involved in this complex plant. In this study, we developed the 3D-CAD and CFD models of the intermediate heat exchanger (IHX) installed in the Japanese HTTR nuclear power plant. This component is extremely important for both the safety of the two plants and the stability of the whole hydrogen production plant. Initially, our model (developed by AutoCAD 3D and implemented in Star CCM+) was validated on the basis of experimental data available in literature; then, an initial optimization of the IHX testing innovative materials, such as Alloy 617 and ODS\u2013MA754, and a different primary coolant (supercritical CO2) was performed