| 1. |
- Akbari, Keramatollah, 1961-
(författare)
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Simulation of Indoor Radon and Energy Recovery Ventilation Systems in Residential Buildings
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study aims to investigate the effects of ventilation rate, indoor air temperature, humidity and using a heat recovery ventilation system on indoor radon concentration and distribution.Methods employed include energy dynamic and computational fluid dynamics simulation, experimental measurement and analytical investigations. Experimental investigations primarily utilize a continuous radon meter and a detached house equipped with a recovery heat exchanger unit.The results of the dynamic simulation show that the heat recovery unit is cost-effective for the cold Swedish climate and an energy saving of about 30 kWh per floor area per year is possible, while it can be also used to lower radon level.The numerical results showed that ventilation rate and ventilation location have significant impacts on both radon content and distribution, whereas indoor air temperature only has a small effect on radon level and distribution and humidity has no impact on radon level but has a small impact on its distribution.
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| 2. |
- Gkoutzamanis, Vasilis, et al.
(författare)
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Thermal energy storage for gas turbine power augmentation
- 2019
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Ingår i: Journal of the Global Power and Propulsion Society. - : Global Power and Propulsion Society. - 2515-3080. ; 3, s. 592-608
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Tidskriftsartikel (refereegranskat)abstract
- This work is concerned with the investigation of thermal energy storage (TES) in relation to gas turbine inlet air cooling. The utilization of such techniques in simple gas turbine or combined cycle plants leads to improvement of flexibility and overall performance. Its scope is to review the various methods used to provide gas turbine power augmentation through inlet cooling and focus on the rising opportunities when these are combined with thermal energy storage. The results show that there is great potential in such systems due to their capability to provide intake conditioning of the gas turbine, decoupled from the ambient conditions. Moreover, latent heat TES have the strongest potential (compared to sensible heat TES) towards integrated inlet conditioning systems, making them a comparable solution to the more conventional cooling methods and uniquely suitable for energy production applications where stabilization of GT air inlet temperature is a requisite. Considering the system’s thermos-physical, environmental and economic characteristics, employing TES leads to more than 10% power augmentation.
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| 3. |
- Kavvalos, Mavroudis, et al.
(författare)
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A Modelling Approach of Variable Geometry for Low Pressure Ratio Fans
- 2019
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Ingår i: International Symposium on Air Breathing Engines, ISABE 2019, Canberra, Australia, 23 - 27 September 2019 Paper No. ISABE-2019-24382.
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Konferensbidrag (refereegranskat)abstract
- This paper presents the development and application of a modelling approach of variable geometry conceptsfor low pressure ratio fans; namely Variable Area Nozzle and Variable Pitch Fan. An enhanced approachfor Outlet Guide Vane pressure loss predictions and an aerothermodynamic analysis of variable pitchconcept are developed and integrated into a multi-disciplinary conceptual engine design framework. Astreamline curvature algorithm is deployed for the derivation of the off-design fan performance map,alleviating scaling issues from higher pressure ratio fan designs. Correction deltas are derived through thevariable pitch analysis for calculating the re-shaped off-design fan performance map. The aforementionedvariable geometry concepts are evaluated in terms of surge margin at engine and aircraft level for a lowpressure ratio aft-fan of a hybrid-electric configuration. Performance assessments carried out suggest thata +8° closing of fan blade cascades leads to a 33% surge margin improvement (with reference being thesurge margin without variable geometry) compared to a 25% improvement achieved by +20% opening thenozzle area at end of runway take-off conditions. Although weight and complexity implications of variablegeometry are not considered, the integrated modelling approach is shown to be able to assess and comparesuch novel engine technologies for low pressure ratio fans in terms of operability.
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| 4. |
- Kladovasilakis, Nikolaos, et al.
(författare)
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Rotor Blade Design of an Axial Turbine using Non-Ideal Gases with Low Real-Flow Effects
- 2017
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Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 142, s. 1127-1132
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to describe a design methodology for supersonic rotor blade geometry, depending on the working fluid, for a low enthalpy Organic Rankine Cycle (ORC) system. Thus, the working fluid is a non-ideal gas with low impact of real flow effects. An innovate algorithm was developed, in order to generate the two-dimensional geometry of the rotor blade, for various working media. A design method, based on the principle of vortex flow field, was used for the blading design and, for the design of supersonic blades, the method of characteristics was selected as the most optimum. The geometry was tested using a commercial simulation software that uses a pressure-based solving algorithm named SIMPLE (Semi-implicit Method for Pressure-Linked Equations). Key advantages of this procedure are both its simplicity and precision of the results.The above procedure was applied for three working fluids, indicatively isobutane (R-600a), tetrafluroethane (R134a) and a mixture of 15% isobutane – 85% isopentane. Considering the ratio of specific heat capacities as constant, which is a realistic assumption for the operating conditions of these systems, the algorithm produces three different blade geometries. Results comparison indicates that every working fluid, for the same operating conditions and for the same design options, has a significantly differentiated geometry of the two-dimensional blade. Finally, the calculated total to total isentropic efficiency, for these rotor blades, is almost 92%.
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| 5. |
- Papagianni, Andromachi, et al.
(författare)
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Conceptual Design of a Hybrid Gas Turbine - Solid Oxide Fuel Cell System for Civil Aviation
- 2019
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Konferensbidrag (refereegranskat)abstract
- A conceptual design of a hybrid Gas Turbine - Solid Oxide Fuel Cell (SOFC) system is presented for civil aviation applications. The system operates using hydrogen as fuel, for the aircraft’s propulsion, while at the same time produces electrical energy in the fuel cell. Hydrogen is produced during flight by reformation of methane. The motivation of the study is to investigate hydrogen’s use for aviation purposes, so the hybrid system’s operation characteristics need to be examined. A configuration is designed, where a SOFC and the burner is modeled as one and simulated, in a modern multidisciplinary programming environment, in order to analyze the thermodynamic characteristics of the hybrid system. The fuel cell sets into motion when the aircraft reaches top of climb. During operation, liquefied natural gas is converted to hydrogen in the fuel cell and part of it is used to produce electrical energy while the rest for combustion. To determine the efficiency of the system, its performance was simulated using two scenarios, one for longhaul flights and one for short-haul flights. Comparing the results, for long-haul flights, the hybrid system presents a reduction in fuel consumption and an increase in thermal efficiency. For flights of a short range, the existing conditions in the fuel cell inlet were found to be prohibitive for it’s operation and the use of the hybrid system ineffective. For the system’s efficiency, the larger the pressure in the SOFC’s inlet the better. However, SOFC’s pressure limits restrict the pressure range and the cell’s use only during flight. Concluding, according to the study’s results, the hybrid system can operate in flight conditions, making the use of hydrogen in civil aviation possible. As a result, a 12% and 35% benefit is achieved, in fuel saving and thermal efficiency respectively.
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| 6. |
- Skvaril, Jan, 1982-
(författare)
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Near-Infrared Spectroscopy and Extractive Probe Sampling for Biomass and Combustion Characterization
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass is characterized by highly variable properties. It can be converted to more valuable energy forms and products through a variety of conversion processes. This thesis focuses on addressing several important issues related to combustion and pulping.Experimental investigations were carried out on a biomass-fired industrial fluidized-bed boiler. The observed combustion asymmetry was explained by an imbalance in the fuel feed. Increased levels of carbon monoxide were detected close to boiler walls which contribute significantly to the risk of wall corrosion.Moreover, extensive literature analysis showed that near-infrared spectroscopy (NIRS) has a great potential to provide property information for heterogeneous feedstocks or products, and to directly monitor processes producing/processing biofuels in real-time. The developed NIRS-based models were able to predict characteristics such as heating value, ash content and glass content. A study focusing on the influence of different spectra acquisition parameters on lignin quantification was carried out. Spectral data acquired on moving woodchips were found to increase the representativeness of the spectral measurements leading to improvements in model performance.The present thesis demonstrates the potential of developing NIRS-based soft-sensors for characterization of biomass properties. The on-line installation of such sensors in an industrial setting can enable feed-forward process control, diagnostics and optimization.
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| 7. |
- Xu, Tianhao, et al.
(författare)
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Design Aspects of a Latent Heat Storage Unit for Heat Production Shifting at a Cogeneration Plant
- 2019
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Ingår i: SWC2019 Proceedings.
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Konferensbidrag (refereegranskat)abstract
- In the present study, a latent heat thermal energy storage (LHTES) unit with two different configurations (a shell-and-tube design using spiral coils as tubes and an encapsulation design using commercial capsules) are investigated and compared over their thermal performance for providing heat storage and recovery. The designed latent heat storage unit is to be implemented at an existing cogeneration plant for heat production shifting purposes. The design procedure involves several aspects of theoretical investigations: the determination of suitable melting point of the employed phase-change material (PCM); the selection of heat exchanger configuration; and the prediction of the units’ transient charging/discharging thermal behavior under operating conditions set by the cogeneration plant. Numerical approaches are used in this study to estimate the heat transfer conditions in PCMs as well as the transient charging/discharging thermal power of the entire unit. The accumulative stored/released energy throughout a charging process of three hours and a discharging process of one hour is also calculated. With the cylindrical containment tank in the same geometry, the spiral coil design exhibits a 52%-higher total heat storage capacity than the encapsulation design, and the simulation results show that it can store a higher amount of heat by 20% after first three hours of charging. For discharging, however, the encapsulation design exhibits a higher completion rate of 96% than the spiral coil design (53%) after first hour of discharging. Besides, the heat recovery capacity with the encapsulation design is 26% higher. The spiral coil design therefore shows advantage in the charging mode in terms of higher storage capacity while the encapsulation design outperforms when discharging due to is higher discharge rate within the given discharge operating duration of one hour.
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