Numeric study of geothermal borehole heat exchanger enhancement via phase change material macro encapsulation

Funding text 1 This work was financially supported by the TESSe2b project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 680555 . This article reflects only the authors’ view and the European Commission is not responsible for any use that may be made of the information it contains. This publication was supported by the Polytechnic Institute of Setúbal, Portugal . Funding text 2 This work was financially supported by the TESSe2b project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 680555. This article reflects only the authors’ view and the European Commission is not responsible for any use that may be made of the information it contains. This publication was supported by the Polytechnic Institute of Setúbal, Portugal.This article addresses the theoretical effect of using geothermal boreholes enhanced with macro-encapsulated phase change materials (PCM) employed with a ground sourced heat pump (GSHP). The aim being the improvement of the heat pump performance through soil temperature stabilisation, taking advantage from the PCM inherent property of changing phase at a constant temperature, that can be matched with the temperature of the surrounding soil, contributing as well to increase the energy storage capacity underground. The numeric work studied different PCM thermal parameters with regards to their influence on the overall behaviour of the heat pump, with different operation modes (On/Off and Inverter) changing the solidus and liquidus temperatures and phase change enthalpy values. The CFD results showed that, while it underperformed having 0.15% difference in the best of cases (specifically the On/Off mode), it used in the best case scenario only 30% of the stored energy in the PCM. The application of macro-encapsulation did provide a stabilising effect to the soil and heap pump operation as it was originally intended to do, helping reduce energy expenditure by the system. Significant modifications are needed in order to improve, both concerning geometry and encapsulation techniques to overcome the PCM and other materials thermal limitations.publishersversionpublishe

WaveMIMO Methodology : Numerical Wave Generation of a Realistic Sea State

This paper presents a methodology that allows the numerical simulation of realistic sea waves, called WaveMIMO methodology, which is based on the imposition of transient discrete data as prescribed velocity on a finite volume computational model developed in Fluent software. These transient data are obtained by using the spectral wave model TOMAWAC, where the wave spectrum is converted into a series of free surface elevations treated and processed as wave propagation velocities in the horizontal (x) and vertical (z) directions. The processed discrete transient data of wave propagation velocity are imposed as boundary conditions of a wave channel in Fluent, allowing the numerical simulation of irregular waves with realistic characteristics. From a case study that reproduces the sea state occurring on March 31st, 2014, in Ingleses Beach, in the city of Florianópolis, state of Santa Catarina, Brazil, it was concluded that the WaveMIMO methodology can properly reproduce realistic conditions of a sea state. In sequence, the proposed methodology was employed to numerically simulate the incidence of irregular realistic waves over an oscillating water column (OWC) wave energy converter (WEC). From these results, the WaveMIMO methodology has proved to be a promising technique to numerically analyze the fluid-dynamic behavior of WECs subjected to irregular waves of realistic sea state on any coastal region where the device can be installed

Simulação numérica de um dispositivo de aproveitamento da energia das ondas do tipo coluna de água oscilante: comparação de dois códigos numéricos

Neste artigo apresentam-se os resultados da aplicação de dois códigos numéricos na simulação de um dispositivo de aproveitamento da energia das ondas do tipo coluna de água oscilante. Um dos códigos (FLUINCO) é baseado na técnica dos elementos finitos e o outro (FLUENT) na técnica dos volumes finitos. O objectivo do trabalho consiste na validação destes códigos para este tipo de escoamento, com o intuito de os aplicar de forma sistemática no projecto de sistemas de aproveitamento de energia das ondas. O caso simulado, que corresponde a um modelo simplificado testado experimentalmente, permitiu concluir da boa qualidade dos resultados obtidos, existindo uma boa correspondência entre os resultados experimentais e os obtidos pelos códigos numéricos.In this paper the results from the application of two numerical codes in the simulation of an oscillating water column wave energy device are presented. One of the codes (FLUINCO) is based on the finite elements technique and the other one (FLUENT) is based on the finite volume technique. The objective of the work is the validation of these codes for this type of flow, aiming the systematic application to wave energy system projects. The simulated case, corresponding to a simplified model tested experimentally, allows to conclude that numerical results have good quality, showing good correspondence among experimental and numerical results

Development of a Computational Model for Investigation of and Oscillating Water Column Device with a Savonius Turbine

This research was funded by the Brazilian National Council for Scientific and Technological Development-CNPq (Processes: 306012/2017-0, 307791/2019-0, 306024/2017-9, 131487/2020 and 440010/2019-5) and the Research Support Foundation of the State of Rio Grande do Sul-FAPERGS (Public Call FAPERGS 07/2021-Programa Pesquisador Gaucho-PqG).The present work aims to develop a computational model investigating turbulent flows in a problem that simulates an oscillating water column device (OWC) considering a Savonius turbine in the air duct region. Incompressible, two-dimensional, unsteady, and turbulent flows were considered for three different configurations: (1) free turbine inserted in a long and large channel for verification/validation of the model, (2) an enclosure domain that mimics an OWC device with a constant velocity at its inlet, and (3) the same domain as that in Case 2 with sinusoidal velocity imposed at the inlet. A dynamic rotational mesh in the turbine region was imposed. Time-averaged equations of the conservation of mass and balance of momentum with the k–ω Shear Stress Transport (SST) model for turbulence closure were solved with the finite volume method. The developed model led to promising results, predicting similar time–spatial-averaged power coefficients (CP ) as those obtained in the literature for different magnitudes of the tip speed ratio (0.75 ≤ λ ≤ 2.00). The simulation of the enclosure domain increased CP for all studied values of λ in comparison with a free turbine (Case 1). The imposition of sinusoidal velocity (Case 3) led to a similar performance as that obtained for constant velocity (Case 2).publishersversionpublishe

Numerical Wave Generation of a Realistic Sea State

This paper presents a methodology that allows the numerical simulation of realistic sea waves, called WaveMIMO methodology, which is based on the imposition of transient discrete data as prescribed velocity on a finite volume computational model developed in Fluent software. These transient data are obtained by using the spectral wave model TOMAWAC, where the wave spectrum is converted into a series of free surface elevations treated and processed as wave propagation velocities in the horizontal (x) and vertical (z) directions. The processed discrete transient data of wave propagation velocity are imposed as boundary conditions of a wave channel in Fluent, allowing the numerical simulation of irregular waves with realistic characteristics. From a case study that reproduces the sea state occurring on March 31st, 2014, in Ingleses Beach, in the city of Florianópolis, state of Santa Catarina, Brazil, it was concluded that the WaveMIMO methodology can properly reproduce realistic conditions of a sea state. In sequence, the proposed methodology was employed to numerically simulate the incidence of irregular realistic waves over an oscillating water column (OWC) wave energy converter (WEC). From these results, the WaveMIMO methodology has proved to be a promising technique to numerically analyze the fluid-dynamic behavior of WECs subjected to irregular waves of realistic sea state on any coastal region where the device can be installed.publishersversionpublishe

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved