High-Temperature Geothermal Utilization in the Context of European Energy Policy—Implications and Limitations

Publisher's version (útgefin grein)The European Union (EU) has made climate change mitigation a high priority though a policy framework called "Clean Energy for all Europeans ". The concept of primary energy for energy resources plays a critical role in how different energy technologies appear in the context of this policy. This study shows how the calculation methodologies of primary energy content and primary energy factors pose a possible negative implication on the future development of geothermal energy when comparing against EU's key energy policy targets for 2030. Following the current definitions of primary energy, geothermal utilization becomes the most inefficient resource in terms of primary energy use, thus contradicting key targets of increased energy efficiency in buildings and in the overall energy use of member states. We use a case study of Hellisheidi, an existing geothermal power plant in Iceland, to demonstrate how the standard primary energy factor for geothermal in EU energy policy is highly overestimated for efficient geothermal power plants. Moreover, we combine life cycle assessment and the commonly utilized combined heat and power production allocation methods to extract the non-renewable primary energy factor for geothermal and show how it is only a minimal fraction of the total primary energy factor for geothermal. The findings of the study apply to other geothermal plants within the coverage of the European Union's energy policy, whether from high- or low-temperature geothermal resources. Geothermal has substantial potential to aid in achieving the key energy and climate targets. Still, with the current definition of the primary energy of geothermal resources, it may not reach the potential.This work is a part of the Primary Energy Efficiency (PEE) project that was funded by Nordic EnergyResearch, grant number 16X753.02, and co-financed by the National Energy Fund (Orkusjóður), grant number 12-2007, owned by the Government of Iceland. Also partially funded by the Landsvirkjun Energy Research fund,grant number FMV 04-2013.Peer Reviewe

Mesh Twisting Technique for Swirl Induced Laminar Flow Used to Determine a Desired Blade Shape

Publisher's version (útgefin grein)Swirling flow has been shown to increase heat transfer in heat exchangers. However, producing swirl while not presenting a severe pressure drop can be a challenge. In this paper, a desired shape of guidance blades for laminar swirl flow is determined by numerical simulation in OpenFOAM. Emphasis is on the mesh technique, where a predefined blade shape is formed by mesh twisting, or morphing. The validity of numerical simulations on a twisted mesh is shown by comparing it to the theoretical solution of laminar flow in a pipe without swirl and guidance blades. A sensitivity study shows that a cell size ratio of 0.025 of diameter is sufficient and affects the solution minimally. To determine the desired shape of guidance blades previously found optimal swirl decay and velocity profile for laminar swirling flow are utilized. Three blade shapes are explored: (I) with a twist angle that varies with axial location only; (II) having a deviation angle matching the theoretical deviation angle for laminar swirling flow; (III) same as II but with a hollow center. Simulations are performed for Re=100 and swirl number S=0.2. Case II is able to sustain swirl longest while maintaining a low pressure drop and is therefore a desired swirler shape profile as predicted theoretically.Peer Reviewe

Experimental and numerical modelling comparison of thermal performance of expanded polystyrene and corrugated plastic packaging for fresh fish

Experiments were carried out to compare the thermal performance of wholesale fresh fish boxes made of corrugated plastic (CP) and expanded polystyrene (EPS). Free standing boxes containing whole, fresh fillets were exposed to dynamic thermal loads. The chilling effect of frozen ice packs was studied by including them in some of the boxes. The frozen ice packs proved efficient for protecting fresh fish fillets against temperature abuse. Further-more, the results show that the insulating performance of EPS is significantly better than were recorded inside the thermally abused boxes without ice packs, initially at 1.9 to 2.1 °C and stored for 6.1 h at a mean ambient temperature of 19.4 °C. The fish temperature distributions during thermal abuse were studied with a numerical model for both pack-aging types, applying effective thermal properties of the sandwich-structured CP box. The purpose of the model was to cost effectively improve the packaging design. A satisfactory agreement between numerical results and experimental results was obtained

Structural Analysis of Casings in High Temperature Geothermal Wells in Iceland

ABSTRACT Large temperature changes are a central design concern in a diverse range of structures. Large and quick wellbore temperature changes in high temperature geothermal wells, e.g. during discharge and quenching of wells, produce large thermal stresses in the production casing which can cause casing failures. The wellbore temperature change during discharge causes the wellhead to rise due to thermal expansion of the casings, since the wells are constructed of several concentric steel casings which are fully cemented to the top. The structural integrity of such casings is essential for the utilization of high temperature geothermal wells. The casings in connection to the wellhead form a structural system which involves nonlinear interaction of the contacting surfaces. Therefore, the structural system is analyzed numerically with the use of the nonlinear finite element method (FEM). Three FEM models are presented here with the purpose of evaluating the structural integrity of high temperature geothermal well casings. A load history is used in the analysis, consisting of transient wellbore temperature and pressure changes

A probabilistic geologic model of the Krafla geothermal system constrained by gravimetric data

Publisher's version (útgefin grein).The quantitative connections between subsurface geologic structure and measured geophysical data allow 3D geologic models to be tested against measurements and geophysical anomalies to be interpreted in terms of geologic structure. Using a Bayesian framework, geophysical inversions are constrained by prior information in the form of a reference geologic model and probability density functions (pdfs) describing petrophysical properties of the different lithologic units. However, it is challenging to select the probabilistic weights and the structure of the prior model in such a way that the inversion process retains relevant geologic insights from the prior while also exploring the full range of plausible subsurface models. In this study, we investigate how the uncertainty of the prior (expressed using probabilistic constraints on commonality and shape) controls the inferred lithologic and mass density structure obtained by probabilistic inversion of gravimetric data measured at the Krafla geothermal system. We combine a reference prior geologic model with statistics for rock properties (grain density and porosity) in a Bayesian inference framework implemented in the GeoModeller software package. Posterior probability distributions for the inferred lithologic structure, mass density distribution, and uncertainty quantification metrics depend on the assumed geologic constraints and measurement error. As the uncertainty of the reference prior geologic model increases, the posterior lithologic structure deviates from the reference prior model in areas where it may be most likely to be inconsistent with the observed gravity data and may need to be revised. In Krafla, the strength of the gravity field reflects variations in the thickness of hyaloclastite and the depth to high-density basement intrusions. Moreover, the posterior results suggest that a WNW–ESE-oriented gravity low that transects the caldera may be associated with a zone of low hyaloclastite density. This study underscores the importance of reliable prior constraints on lithologic structure and rock properties during Bayesian geophysical inversion.Icelandic Centre for Research. This study was funded by Technical Development Fund of the Research Center of Iceland (RANNÍS—Grant Number 175193-0612 Data Fusion for Geothermal Reservoir Characterization).Peer Reviewe

Viðhorf stjórnenda til tækifæra og áskorana í sérleyfisrekstri á Íslandi

Sérleyfi er vinsæl leið til að herja á nýja markaði. Það er ódýrt fyrir sérleyfisveitendur og gefur sérleyfisþegum aðgang að innviðum sem annars hefðu líkast til fallið utan handar. Íslendingar eru ekki ókunnugir alþjóðlegum vörumerkjum og eiga það gjarnan til að mynda langar raðir þegar nýr aðili kemur inn á markað. Þessi rannsókn leitast til að varpa ljósi á viðhorf stjórnenda til slíkra vörumerkja á Íslandi frá sjónarhorni tveggja megináherslna: almenns rekstrargrundvallar og vörumerkisins. Til þess framkvæmdu rannsakendur fimm djúpviðtöl við stjórnendur sérleyfisvörumerkja úr fimm mismunandi iðnaðargreinum sem valdir voru með markmiðsúrtaki. Fjórir þeirra höfðu áður starfað í sérleyfi við að minnsta kosti eitt annað vörumerki og gátu því veitt djúpa og góða innsýn. Við úrvinnslu gagna var notast við þemagreiningu. Niðurstöður gáfu til kynna að gríðarleg tækifæri felast í sérleyfisrekstri á Íslandi, en þó ekki án áskoranna. Stjórnendur verða að átta sig á því að sérleyfi er ekki ávísun á árangur og að þeim fylgir alltaf fórnarkostnaður. Til að hámarka velgengni þarf að bera styrkleika saman við veikleika og vinna náið með sérleyfisveitanda til að finna rétta jafnvægið

Empirical relationships between bone density and ultimate strength: A literature review

Introduction Ultimate strength-density relationships for bone have been reported with widely varying results. Reliable bone strength predictions are crucial for many applications that aim to assess bone failure. Bone density and bone morphology have been proposed to explain most of the variance in measured bone strength. If this holds true, it could lead to the derivation of a single ultimate strength-density-morphology relationship for all anatomical sites. Methods All relevant literature was reviewed. Ultimate strength-density relationships derived from mechanical testing of human bone tissue were included. The reported relationships were translated to ultimate strength-apparent density relationships and normalized with respect to strain rate. Results were grouped based on bone tissue type (cancellous or cortical), anatomical site, and loading mode (tension vs. compression). When possible, the relationships were compared to existing ultimate strength-density-morphology relationships. Results Relationships that considered bone density and morphology covered the full spectrum of eight-fold inter-study difference in reported compressive ultimate strength-density relationships for trabecular bone. This was true for studies that tested specimens in different loading direction and tissue from different anatomical sites. Sparse data was found for ultimate strength-density relationships in tension and for cortical bone properties transverse to the main loading axis of the bone. Conclusions Ultimate strength-density-morphology relationships could explain measured strength across anatomical sites and loading directions. We recommend testing of bone specimens in other directions than along the main trabecular alignment and to include bone morphology in studies that investigate bone material properties. The lack of tensile strength data did not allow for drawing conclusions on ultimate strength-density-morphology relationships. Further studies are needed. Ideally, these studies would investigate both tensile and compressive strength-density relationships, including morphology, to close this gap and lead to more accurate evaluation of bone failure.ISSN:1751-6161ISSN:1878-018