References of "Leyer, Stephan 50003662"
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See detailEnergy performance comparison of ventilation-based heating versus water-based heating systems in an efficient residential building
Shirani, Arsalan UL; Merzkirch, Alexander; Leyer, Stephan UL et al

in Fluid Dynamics & Material Processing (in press)

The application of air-based heating systems as a possible approach to reduce the construction costs in highly efficient residential buildings is becoming popular. Air-based heating systems have been well ... [more ▼]

The application of air-based heating systems as a possible approach to reduce the construction costs in highly efficient residential buildings is becoming popular. Air-based heating systems have been well-known for their usage in passive houses during the past three decades. Available studies on such systems tend mostly to focus only on comparing exhaust air heat pump technology with conventional systems in efficient buildings. Moreover, most of the existing studies ignore the usual presence of the electrical heaters as backup. Besides, a comprehensive study and comparison between different air-based heating system concepts is still missing. In this study, four different air-based heating system concepts separated by the type of heat source of heat pump for heating and domestic hot water are defined. These systems are compared to four conventional heating system, including floor heating and direct electrical system employing dynamic annual simulations. According to simulation results, the systems with floor heating have shown the best system efficiencies and the lowest energy demand in comparison to the other systems. The main reason for this was the lower supply temperatures of the floor heating systems. Between the air heating systems, the system equipped with an outdoor air heat pump showed a better energy performance than an exhaust air system. The main reason for this could be attributed to the power limitation of exhaust air heat pump systems. [less ▲]

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See detailTheoretical Considerations about Energy Transition in Luxembourg
Arababadi, Ali; Leyer, Stephan UL; Hansen, Joachim UL et al

in Environmental Sciences Proceedings (2022)

The energy transition is a certain phenomenon in the future which as of yet has no agreed definition. It involves a shift in the dominant ‘rules of the game’—a transformation of established technologies ... [more ▼]

The energy transition is a certain phenomenon in the future which as of yet has no agreed definition. It involves a shift in the dominant ‘rules of the game’—a transformation of established technologies and societal practices and movement from one dynamic equilibrium to another, typically stretching over several generations. The study aims to explore some salient features of this transition that Luxembourg will face using a theoretical approach. The study was limited to the transportation sector, residential sector, and public dimension. it has been shown how the availability of different contextual factors in Luxembourg will raise the need for new pathways to move towards this transition. The alternative pathways have been argued, to [less ▲]

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See detailCharacterizing the theory of energy transition in Luxembourg— Part three— In the residential sector
Arababadi, Ali; Leyer, Stephan UL; Hansen, Joachim UL et al

in Energy Science and Engineering (2022)

Increasing consciousness to address future concerns is a challenging subject, noticed considerably by policymakers and investors. Investigation of energy use in residential buildings in terms of quantity ... [more ▼]

Increasing consciousness to address future concerns is a challenging subject, noticed considerably by policymakers and investors. Investigation of energy use in residential buildings in terms of quantity and sources of energy was the main focus of this study. Indeed, the paper was aimed to study the role of contextual factors on two points: the energy demand and the spreading of renewable technologies in the residential sector. It was theory- driven research to highlight some future concerns. The first theory was to reveal how the growth of single- family houses versus multi- family houses could affect the growth of energy consumption and the application of renewable technologies. The second theory was built to highlight that spreading energy measures to increase efficiency or introducing a new energy carrier should be embedded in the context of new construction activities or in a template of renovation projects. The third theory was to emphasize the priority of thinking about managing the changes in residential buildings because of the lasting impact of the decision about the type of building. Finally, the purpose of the ongoing transition was argued to highlight that the growth of renewable technologies has not been necessarily aligned with getting away from fossil fuels. [less ▲]

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See detailA correlation for pool entrainment phenomenon
Ouallal, Mohammed UL; Leyer, Stephan UL; Gupta, Sanjeev

in Nuclear Engineering and Design (2021)

The present work aims to study the phenomena of droplet entrainment from water pool in a confined atmosphere, which could be either a consequence of boiling or depressurization. Eventually, these droplets ... [more ▼]

The present work aims to study the phenomena of droplet entrainment from water pool in a confined atmosphere, which could be either a consequence of boiling or depressurization. Eventually, these droplets are entrained by the streaming gas (superficial gas velocity) or settling down due to gravity. The number of correlations developed so far quantify the entrainment based on empirical, semi-empirical and theoretical approaches, but they have been generally limited to a specific flow-regime in the water pool, thermal hydraulic conditions or even to a specific geometry. In this context, the present work aims to develop an empirical correlation to cover the flow regimes from bubbly to churn turbulent, and could be applied to a wide range of geometries. The present correlation shows an increase until a maximum entrainment of about 2.10-4, corresponding to superficial gas velocity of 0.05 m/s for bubbly flow regime, and then a slight decrease to 2⋅10􀀀 5, for the transition regime corresponding superficial gas velocity of 0.1 m/s, and a sharp increase in the churn turbulent flow regime as the gas velocity goes up to 5 m/s. The experimental database used to develop the present empirical correlation covers a broader range of boundary conditions, namely pressure [1 bar–15 bar], water pool thermal condition [subcooled – boiling], vessel diameter [0.19 m- 3.2 m], pool diameter [0.1 m–1.4 m], superficial gas velocity up to 5.0 m/s Therefore, the proposed empirical correlation aims to constitute an important tool to transfer the experimental results to reactor application. [less ▲]

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See detailA three-dimensional model for the heat and mass transfer in air-gap membrane distillation
Cramer, Kerstin UL; Niceno, Bojan; Prasser, Horst Michael et al

in Desalination and Water Treatment (2021)

Membrane distillation (MD) is a process to desalinate sea water. Pilot plants are operated aiming at increasing the modules’ efficiency for large-scale applications. In air-gap membrane distillation (AGMD ... [more ▼]

Membrane distillation (MD) is a process to desalinate sea water. Pilot plants are operated aiming at increasing the modules’ efficiency for large-scale applications. In air-gap membrane distillation (AGMD) the state-of-the-art modeling of mass and heat transfer is one-dimensional, combining evaporation and diffusion through the membrane and the condenser channel in one correlation. In this work, a numerical model is developed which computes AGMD modules in three dimen- sions. For evaporation and condensation, energy conservation equations at the interfaces are solved. Simulation results are compared to experimental data and a good agreement is found. The model is then employed to compare numerically two air-gap MD module configurations and evaluate their performance at different feed inlet temperatures, velocities and air-gap thicknesses. In the upside configuration, the hot feed flows above the membrane, while in the downside configura- tion it flows below the air-gap and membrane. In the latter, the feed solution is not in contact with the membrane but separated by the air-gap which is expected to improve the fouling resistance of the membrane. The three-dimensional computational fluid dynamic computation allows the visu- alization of the velocity profile in the air-gap due to buoyancy in the downside configuration [less ▲]

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See detailCharacterizing the Theory of Spreading Electric Vehicles in Luxembourg
Arababadi; Leyer, Stephan UL; Leyer, Stephan UL et al

in Sustainability (2021)

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See detailLiterature survey of droplet entrainment from water pools
Ouallal, Mohammed UL; Leyer, Stephan UL; Gupta, Sanjeev

in Nuclear Engineering and Design (2021)

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See detailThree‑Dimensional Membrane Imaging with X‑ray Ptychography: Determination of Membrane Transport Properties for Membrane Distillation
Cramer, Kerstin UL; Prasianakis, Nikolaos; Niceno, Bojan et al

in Transport in Porous Medi (2021)

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See detailExperimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems
Shirani, Arsalan UL; Merzkirch, Alexander UL; Roesler, Jennifer et al

in Journal of Building Engineering (2021)

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat ... [more ▼]

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat pumps as an energy efficient heating technology to cover the heating and venting demand of the building is becoming conventional. The exhaust air heat pumps are attracting considerable interest due to their normally reasonable price and small footprint. This heat pump type is often installed as part of an air based heating system together with electrical heaters. These electrical heaters are installed to cover the residual heating demand and/or to insure thermal comfort. The technology of exhaust air heat pumps has been investigated in several studies. Available studies on exhaust air heat pumps have tended mostly to focus on comparison between different technologies utilized in efficient buildings. Almost all of the existing studies have ignored the actual application of this technology in air based heating systems together with electrical heaters. In this sense, there is still a need for discussion on the influence of different buildings’ standards and control strategies on the heating system performance. The present paper aims to call into question the energy efficiency of exhaust air heat pumps under different boundary conditions. In this study, the results of a long time field monitoring are utilized in order to model the dynamic behavior of an exhaust air heat pump in MATLAB/Simulink. The impact of different boundary conditions on the heat pump’s efficiency is studied and additionally compared to previous studies. The developed model is used for annual simulations of air based hybrid heating systems in three different building standards. Finally, the influence of control strategy on the system performance is investigated. It is shown that under certain boundary conditions and control strategy, the studied system could provide an efficient heating system with acceptable user comfort. Nevertheless, applying conventional heating control methods or installing the system in buildings with high heating energy demand could lead to high electrical energy consumption and/or undesirable thermal comfort. [less ▲]

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See detailField monitoring data on a residential exhaust air heat pump system (air-to-air heat pump)
Shirani, Arsalan UL; Merzkirch, Alexander; Roesler, Jennifer et al

in Data in Brief (2021)

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains ... [more ▼]

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains measurement results of a field monitoring on a residential exhaust air heat pump system (air-to-air heat pump) in Germany. This data could be used to investigate the dynamic behaviour and performance of the exhaust air heat pump systems. The data set contains air temperature and humidity of all four sides of the heat pump unit. Moreover, the electrical consumption of the unit and the dynamic pressure difference on the exhaust side (as indication of the air volume rate) could be also found in the data set. [less ▲]

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See detailPrevention of Electrostatic Charge Generation in Filtration of Low-Conductivity Oils by Surface Modification of Modern Filter Media
Staudt, Johannes; Duchowski, Johan; Leyer, Stephan UL

in Tribology Transactions (2020)

The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two ... [more ▼]

The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two materials participating in the event. In contrast to the previously proposed mechanisms that focused predominantly on fluid and material conductivities, new evidence strongly suggests that the relative placement of the substrates in the triboelectric series must be taken into account. The positions occupied in the triboelectric series account for the donor/acceptor tendencies exhibited by the materials when brought close together in close proximity ( 10 nm). Nevertheless, this behavior is only an outward manifestation of the deeper underlying characteristics that include material surface energies and, looking even deeper, the associated electron work functions of the interacting materials. Herein we provide several examples of the enhanced understanding of the electrostatic charging/discharging (ESC/ESD) phenomena as they occur in the course of filtration of hydraulic and lubricating fluids through modern filter elements constructed of synthetic glass fiber and polymer materials. [less ▲]

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See detailModelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II
Manthey, René; Viereckl, Frances; Moonesi Shabestary, Amirhosein et al

in Energies (2019)

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven ... [more ▼]

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modeling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modeling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities. [less ▲]

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See detailModelling of Passive Heat Removal Systems: A Review with Reference to the Framatome KERENA BWR Reactor: Part I
Moonesi Shabestary, Amirhossein; Viereckl, Frances; Zhang, Yu et al

in Energies (2019)

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventionsand are solely driven ... [more ▼]

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventionsand are solely driven by thermal gradients and gravitational force. This brings up new needs forperformance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modelling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I deals with numerical and experimental methods for modelling of condensation inside the emergency condensers and on the containment cooling condenser while part II deals with boiling and two-phase flow instabilities. [less ▲]

Detailed reference viewed: 78 (8 UL)
See detailPANAS- Project: Heat Transfer Model Development for Passive Safety Systems,
Leyer, Stephan UL; Hampel; Schuster, C et al

in NURETH-18 (2019, August 18)

Detailed reference viewed: 77 (6 UL)
See detailLuxCube the First CubeSat Student Satellite in Luxembourg
Rabbadan Santana, E; Weiss, T; Djordjevic, A et al

Poster (2019, June 15)

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See detailEvaluation of Stratified Condensation Models for a slightly inclined tube unsing ATHELT Code
Zhang, Yu; Moonesi Shabestary, Amir Hossein; Bieberle, Andre et al

in NURETH-18 (2019)

Detailed reference viewed: 98 (12 UL)
See detailInvestigation of Thermal Coupling in Condensation Process at COSMEA Facility with ATHLET Code
Zhang, Yu; Leyer, Stephan UL; Hampel, U

in Reactor engineering (2018, October)

Detailed reference viewed: 75 (16 UL)