1,720,968 research outputs found
Thermo-fluid dynamic and kinetic modeling of hydrothermal carbonization of olive pomace in a batch reactor
No full textHydrothermal carbonization (HTC) represents one of the emerging and most promising technologies for upgrading biomass. Among the residual biomass waste, olive pomace and olive mill wastewater may be seen as valuable energy sources, especially for the Mediterranean countries, given the key role of the olive oil industry in those regions. This paper deals with the thermo-fluid dynamic performance of the HTC process of olive pomace. Computational Fluid Dynamics (CFD) modeling is employed in this study to numerically simulate such a process in batch reactor with the aim of understanding the complex fluid dynamics, heat transfer and reaction kinetics phenomena occurring under hydrothermal conditions. A parametric analysis is performed to evaluate the temperature fields inside the reactor and the output mass yields as a function of the power input required by the process. Velocity flow fields and the spatial distribution of the mixture during the process are also investigated to understand the change in feed conversion at different regions within the tubular reactor under different reaction times. The numerical results are validated and compared with experimental measurements conducted previously on a similar batch reactor. The model predictions are found to be in line with the experimental findings, thus laying the foundations for further modeling improvements towards the design optimization and scale-up of HTC reactors
Technical assessment of phase change material thermal expansion for passive solar tracking in residential thermal energy storage applications
No full textPhase changing materials (PCMs) have been widely investigated for Latent Heat Thermal Energy Storage (LHTES) applications in the last decades, due to their inherently high volumetric storage density and thermal control features. Nonetheless, PCMs and their related LHTES systems still require significant scientific and technical advancements and more efficient market penetration strategies, to be able to play a key role in the massive transition towards renewable energy that is expected to take place in EU in the near future. Some of the most investigated PCMs for low to medium temperature LHTES belong to the alkanes/paraffins family, which is characterized by a relatively high volumetric expansion solid-to-liquid phase transition. This is generally considered a side effect, which should be accounted for to avoid damaging the containment structure. However, it could also represent an opportunity to add extra functionalities and increase the overall efficiency of LHTES systems. In this paper, we evaluate the feasibility of using the mechanical work generated by the volumetric expansion cycles in a paraffin-based LHTES device for photovoltaic (PV) solar tracking purposes, thus assuming a novel paradigm for the efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical approach. Accurate charge/discharge profiles of the TES are implemented, considering data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this analysis allow to estimate the tracking capability of the chosen PCM in terms of number/surface of actuated PV panels
Feasibility of passive solar tracking through the thermal expansion of a PCM medium in a residential TES application: a numerical analysis
No full textPhase Changing Materials (PCMs) are widely adopted and studied for Thermal Energy Storage (TES) applications, due to their inherent capability of storing and releasing high amounts of thermal energy in a narrow temperature range. At the same time, some of the materials commonly implemented in PCM-based TES devices (e.g. paraffin waxes or other organic materials) are known to experience a significant volumetric expansion (up to 20% or more) during their solid-to-liquid phase transition. Such expansion is generally considered a side effect, which should be accounted for to avoid damaging the PCM containment structure in the TES device. Recently, the thermally driven expansion of PCMs has been considered as a driving force for passive solar tracking, showing promising technical developments for dedicated solar tracking devices. In the present paper, we evaluate the feasibility of using the volumetric expansion cycles in a PCM-based TES device for PV solar tracking purposes, thus assuming an innovative and efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of the temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical implementation. Accurate charge and discharge profiles of the TES device are implemented, assuming data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this numerical analysis allow to perform a parametric study in terms of specific tracking capability of the chosen PCM (paraffin wax) vs. the installed PV modules surface
Experimental and Numerical Electro-Thermal Characterization of Lithium-Ion Cells for Vehicle Battery Pack Applications
Get PDFBatteries are the key elements for the massive electrification of the transport sector. With the rapidly growing popularity of electric vehicles, it is becoming increasingly important to characterize the behavior of battery packs through fast and accurate numerical models, in order to support experimental activities. A coupled electro-thermal simulation framework is required, as it is the only way to realistically represent the interactions between real world battery pack performances and the vehicle-level thermal management strategies. The purpose of this work is to pave the way for a comprehensive methodology for the development of a supporting modeling framework, to efficiently complement experiments in the optimal design and integration of battery packs. The full methodology consists of the following steps: i) an experimental analysis of the temperature and current dependence on various internal parameters of selected lithium-ion cells based on their electrochemical properties, ii) development and implementation of a battery cell electric model that takes into account the aforementioned dynamics and their dependencies; the electrical model is based on the Equivalent Circuit Model (ECM) and can be used to calculate the electrical output and losses of Li-ion cells as a function of state of charge and current; iii) development of a cell-level multi-domain computational framework for coupled electro-thermal simulations, based on state-of-the art CFD software tools; iv) validation and tuning of the multi-domain framework through ad-hoc designed experiments with controlled cell charge-discharge profiles and temperature measurement; v) extension of both the ECM and multi-domain approaches to full-scale battery packs, to be adopted for electric vehicle characterization under realistic driving conditions, with detailed battery thermal management. Results shown in the present paper cover steps i) to iv) and include a series of static and dynamic experimental tests with voltage response and temperature measurements performed on the selected Li-ion cells. It is shown that the proposed modeling tools can accurately predict the electro-thermal behavior of the cells under static and dynamic current conditions. Most of the average relative errors between predicted values and test values obtained do not exceed 10%
Energetic and exergetic performance evaluation of a solar cooling and heating system assisted with thermal storage
No full textFeasibility of passive solar tracking through the thermal expansion of a PCM medium in a residential TES application: a numerical analysis
No full textPhase Changing Materials (PCMs) are widely adopted and studied for Thermal Energy Storage (TES) applications, due to their inherent capability of storing and releasing high amounts of thermal energy in a narrow temperature range. At the same time, some of the materials commonly implemented in PCM-based TES devices (e.g. paraffin waxes or other organic materials) are known to experience a significant volumetric expansion (up to 20% or more) during their solid-to-liquid phase transition. Such expansion is generally considered a side effect, which should be accounted for to avoid damaging the PCM containment structure in the TES device. Recently, the thermally driven expansion of PCMs has been considered as a driving force for passive solar tracking, showing promising technical developments for dedicated solar tracking devices. In the present paper, we evaluate the feasibility of using the volumetric expansion cycles in a PCM-based TES device for PV solar tracking purposes, thus assuming an innovative and efficient integration between thermal and PV solar installations. To this aim, the temporal evolution of the temperature and density fields inside the PCM are modeled through a finite-difference/finite-volume numerical implementation. Accurate charge and discharge profiles of the TES device are implemented, assuming data from a previously investigated solar-assisted heating/cooling plant for a typical residential application in southern Italy. Outcomes from this numerical analysis allow to perform a parametric study in terms of specific tracking capability of the chosen PCM (paraffin wax) vs. the installed PV modules surface
Evaluating the potential of phase-change induced volumetric expansion in thermal energy storage media for passive solar tracking in high-temperature solar energy systems
Get PDFAs traditional fossil energy sources are continuously diminishing, the demand for optimising output from renewable energy sources is gaining particular importance. Among these, solar energy is certainly one of the most prominent technology and it is widely used in a variety of applications, either concerning electricity and heat production. Nonetheless, the global efficiency of solar systems still has to be largely improved, reducing at the same time generation costs, in order to make solar an even more relevant source of clean energy. In modern photovoltaic, concentrated photovoltaic as well as concentrated solar power plants, the net output can be increased through solar tracking solutions aiming at the optimal positioning of the solar panels/mirrors on a daily and seasonal basis. This typically requires electromechanical motors, which are designed to align the incident solar radiation with the optical axis, thus enhancing the overall energy conversion efficiency but draining at the same time up to 1–2% of the theoretically achievable net power output. Furthermore, to increase energy dispatchability concentrated solar power plants usually incorporates thermal energy storage units, which can be of the sensible-heat or latent-heat storage type. The latter imply phase transition of the storage material which, in turn, can generate up to 20% volumetric expansion for a solid-to-liquid transition. Although generally assumed as an undesired side effect, such expansion can represent an opportunity to extract mechanical work and thus increase the overall efficiency of the solar system. The main objective of this study is to provide an initial quantitative assessment of the passive tracking potential related to the phase-change induced expansion of thermal storage media in concentrated solar power plants. To this aim, a solar-integrated waste-to-heat steam power plant, rated at 15 MWe, has been taken as a reference and a coupled finite-difference/finite-volume numerical model of the latent-heat thermal energy storage unit of the plant has been developed. The model takes input data from the power plant operating conditions and is able to retrieve time-resolved temperature and volumetric density changes of the thermal storage media. Results from the numerical model shows that passive solar tracking is achievable for a fraction of the heliostat field that ranges from 10% to 100%, depending on the season and operating pressure of the tracking system. In terms of electrical power savings, this is up to 2% of the net power output of the reference plant, thus representing a promising basis for further investigations on the applicability of the proposed novel integrated passive solar tracking concept
Identification of the Best Vehicle Segment for e-Taxis from a Life Cycle Assessment Perspective
No full textExperimental investigation on high-temperature hydrothermal carbonization of olive pomace in batch reactor
Get PDFBiomass hydrothermal carbonization (HTC) is the thermochemical conversion of cellulose, hemicellulose, lignin and lipids into organic, homogenized, carbon rich and energy dense solid fuel, called hydrochar. Process occurs under high - temperature and pressure conditions in the presence of subcritical water. The HTC process represents an effective alternative solution to the common treatments for wet biomass, i.e. composting and anaerobic digestion, over which HTC has several advantages. It is faster compared to the conventional treatments, and it is not affected by inhibiting or toxic substances. Moreover, the HTC process generates a solid product exploitable in different fields such as energy production, soil improvement or raw material for high added value applications. In this study, olive pomace is analyzed as raw material in HTC. A batch reactor (Vreactor: 5.0 L; Pdesign: 100 bar; Tdesign: 310 °C) was designed and constructed to investigate the HTC process in terms of mass yield, product composition and High Heating Value of the generated hydrochar. Experiments with temperature in the range of 260 °C to 305 °C (remaining in subcritical conditions) and reaction time from 60 to 180 minutes were carried out to investigate the mass yield of the produced hydrochar, the concentration of carbon in the produced solid and the High Heating Value (HHV). Depending on the test conditions, the obtained char showed a HHv up to 31.14 MJ/kg, with a definitive increase with respect to 22.4 MJ / kg of the initial olive pomace biomass. The effects of the HTC high temperature process on the olive mill waste water were also investigated in terms of residual Biological Oxygen Demand (BOD)5
A comparison of different approaches for assessing energy outputs of combined heat and power geothermal plants
Get PDFIn this paper, we assess using two alternative allocation schemes, namely exergy and primary energy saving (PES) to compare products generated in different combined heat and power (CHP) geothermal systems. In particular, the adequacy and feasibility of the schemes recommended for allocation are demonstrated by their application to three relevant and significantly different case studies of geothermal CHPs, i.e., (1) Chiusdino in Italy, (2) Altheim in Austria, and (3) Hellisheidi in Iceland. The results showed that, given the generally low temperature level of the cogenerated heat (80–100 °C, usually exploited in district heating), the use of exergy allocation largely marginalizes the importance of the heat byproduct, thus, becoming almost equivalent to electricity for the Chiusdino and Hellisheidi power plants. Therefore, the PES scheme is found to be the more appropriate allocation scheme. Additionally, the exergy scheme is mandatory for allocating power plants’ environmental impacts at a component level in CHP systems. The main drawback of the PES scheme is its country dependency due to the different fuels used, but reasonable and representative values can be achieved based on average EU heat and power generation efficiencies
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