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  • Amiri, Shahnaz, et al. (författare)
  • Possibilities and consequences of deregulation of the European electricity market for connection of heat sparse areas to district heating systems
  • 2010
  • Ingår i: Applied Energy. - 0306-2619. ; 87:7, s. 2401-2410
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of the study is to analyse the conditions for connection of residential buildings in heat sparse areas to district heating systems in order to increase electricity production in municipal combined heat and power plants. The European electricity market has been assumed to be fully deregulated. The relation between connection of heat sparse areas, increased electricity and heat production as well as electricity prices, fuel prices and emissions rights is investigated. The results of the study show that there is potential to expand the district heating market to areas with lower heat concentrations in the cities of Gavle, Sandviken and Borlange in Sweden, with both economic and environmental benefits. The expansion provides a substantial heat demand of approximately 181 GWh/year, which results in an electricity power production of approximately 43 GWh/year. Since the detached and stand-alone houses in the studied heat sparse areas have been heated either by oil boiler or by direct electricity, connection to district heating also provides a substantial reduction in emissions of CO(2). The largest reductions in CO(2) emissions are found to be 211 ktonnes/year assuming coal-fired condensing power as marginal electricity production. Connection of heat sparse areas to district heating decrease the system costs and provide a profitability by approximately 22 million EURO/year for the studied municipalities if the price of electricity is at a European level, i.e. 110 EURO/MWh. Sensitivity analysis shows, among other things, that a strong relation exists between the price of electricity and the profitability of connecting heat sparse areas to district heating systems.
  • Cehlin, Mathias, et al. (författare)
  • Visualization of Isothermal Low-Reynolds Circular Air Jet Using Computed Tomography.
  • 2005
  • Ingår i: Proceedings of 6 th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics.
  • Konferensbidrag (refereegranskat)abstract
    • The intention of this paper was to demonstrate the principle and usefulness of computed tomography for concentration field measurements. Radial extinction coefficient profiles have been reconstructed using the LTD approach in the transition region of an isothermal jet of air at Reynolds number of 2 600. Reconstructed profiles were compared against velocity profiles at axial distances ranging from 2 to 20 nozzle diameters downstream. Results indicate that the width parameter of the reconstructed scalar distribution is around 23 % larger than the velocity distribution for distances between 10 and 20 nozzle diameters downstream. This finding is in good agreement with the results of other investigators. This technique has evidently yielded an accurate description of the scalar field of the round isothermal free jet. The quality of the reconstructions is very promising considering the relatively few measurement data, projection angles and low pixel resolution used in this study. Ccomputed tomography is superior for monitoring chemical concentrations over larger areas (whole room) when PMS and PLIF are unfeasible.
  • Chen, Huijuan, et al. (författare)
  • Comparing k-ε models on predictions of an impinging jet for ventilation of an office room
  • 2011
  • Ingår i: Roomvent 2011. - tapir academic press. - 9788251928120
  • Konferensbidrag (refereegranskat)abstract
    • The objective of this study is to compare the performance of different k-ε models, i.e. the Standard k-ε, the Renormalization Group (RNG) k-ε, and the Realizable k-ε, with a two-layer model for the prediction of the mean velocity field and the temperature pattern from a newly designed impinging jet supply device for ventilation of an office room. The numerical predictions are validated against the detailed experimental measurements. The experimental investigation was performed in a test room with the dimensions 4.2×3.6×2.5 m, as a mock-up of a single-person office. Detailed velocity and temperature field measurements including the comfort zone and the jet developing region along the floor were carried out. The in-house made single-sensor hot-wire probe and the thermocouple are measuring instruments used to investigate the mean velocity, turbulence intensity and temperature. The boundary conditions for Computational Fluid Dynamics (CFD) study are obtained from the same set-up measurement. The results mainly consist of the flow field presentation, i.e., the velocity and temperature profiles in the comfort zone and the jet developing region along the floor. The comparisons between the results from the three versions of the k-ε models and measurements show generally satisfactory agreement, and better consistency is observed at the free jet region and the wall jet region that farther from the impingement zone. Among the three tested turbulence models, RNG shows the best overall performance.
  • Ghahremanian, Shahriar, et al. (författare)
  • Investigation in the near-field of a row of interacting jets
  • 2015
  • Ingår i: Journal of Fluids Engineering - Trancactions of The ASME. - 0098-2202. ; 137:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Multiple interacting jets (confluent jets) are employed in many engineering applications, and the significant design factors must be investigated. Computational fluid dynamics (CFD) is used to numerically predict the flow field in the proximal region of a single row of round jets. The numerical results that are obtained when using the low Reynolds k — ε are validated with the experimental data that is acquired by particle image velocimetry (PIV). The low Reynolds k — ε underpredicts the streamwise velocity in the onset of the jets’ decay. The characteristic points are determined for various regions between two neighboring jets. The comparison of the merging point and the combined point computed from measurements and simulations shows good agreement in the different regions between the jets. In this study, a computational parametric study is also conducted to determine the main effects of three design factors and the interactions between them on the flow field development using response surface methodology. The influences of the inlet velocity, the spacing between the nozzles and the diameter of the nozzles on the locations of the characteristic points are presented in the form of correlations (regression equations). CFD is used to numerically predict the characteristic points for a set of required studies, for which the design values of the simulation cases are determined by the Box-Behnken method. The results indicate that the spacing between the nozzles has a major impact on the flow characteristics in the near-field region of multiple interacting jets. The response surface methodology shows that the inlet velocity has a marginal effect on the merging and combined points.
  • Ghahremanian, Shahriar, 1974-, et al. (författare)
  • Numerical and experimental verification of initial, transitional and turbulent regions of free turbulent round jet
  • 2011
  • Ingår i: 20th AIAA Computational Fluid Dynamics Conference 2011.
  • Konferensbidrag (refereegranskat)abstract
    • Three-dimensional simulation of the whole domain (initial, transition and fully developed regions) of round jet is essential in order to predict and to study the flow behavior of multiple jets (e.g. confluent jets). According to authors knowledge, numerical prediction of round jet with RANS models that has been presented by other researchers, are only in two-dimensional (axisymmetric) and mostly for the fully developed region. The inlet boundary conditions,  inlet velocity profile, turbulent kinetic energy and its dissipation rate at the diffuser exit has been governed from an earlier verified numerical simulation. In the present paper, results of three-dimensional modeling of isothermal, free, turbulent round jet with two two-equation (Low Re  and SST ), a transition three-equation ( ) and a transition four-equation (SST) eddy-viscosity turbulence models with resolved inlet profiles are compared and validated with hot-wire anemometry. This study shows that numerical simulation of round jet with SST  gives good agreement with measured mean longitudinal velocities, while transition models could only predict the initial region of round jet.
  • Jahedi, Mohammad, 1984-, et al. (författare)
  • Experimental study of quenching process on a rotating hollow cylinder by one row of impinging jets
  • 2017
  • Ingår i: 9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 12-15 June, 2017, Iguazu Falls, Brazil.
  • Konferensbidrag (refereegranskat)abstract
    • Quenching cooling rate of rotary hollow cylinder by one row of water impinging jets has been experimentallystudied. Water jets (d = 8 mm) with sub-cooling 55 to 85°C and Reynolds number 8,006 to 36,738 impinged over rotaryhot hollow cylinder (rotation speed 10 to 70 rpm) with initial temperature 250 to 600°C. Impingement impact angle of row of jets varied between 0 to 135° and jet-to-jet spacing in row patten was 2 to 8d. The results revealed more uniformityon cooling rate of quenching in smaller jet-to-jet spacing (2 and 4d) where wetting front regions are located closer toneighbor jet’s region. By increasing spacing, footprint of annular transition region was highlighted in quenching coolingrate contour. A distinct quenching characteristic was obtained for impingement impact angle of 0° compare to otherangles. With initial temperature above the Leidenfrost temperature, low cooling rate was achieved in film and transitionboiling compare to a steep increase of cooling rate at start of quenching with higher maximum heat transfer for experimentswith initial temperatures less than Leidenfrost temperature. The effect of other parameters on quenching coolingrate was highlighted in film and transition boiling while no significant differences were observed in nucleate boiling.
  • Karimipanah, Taghi, 1953-, et al. (författare)
  • The air distribution as an indicator for energy consumption and performance of ventilation systems
  • 2008
  • Ingår i: Journal of the Human-Environment System. - 1345-1324. ; 11:2, s. 77-84
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper deals with the energy consumption and the evaluation of the performance of air supply systems for a ventilated room involving high- and low-level supplies. The energy performance assessment is based on the airflow rate, which is related to the fan power consumption by achieving the same environmental quality performance for each case. Four different ventilation systems are considered: wall displacement ventilation, confluent jets ventilation, impinging jet ventilation and a high level mixing ventilation system. The ventilation performance of these systems will be examined by means of achieving the same Air Distribution Index (ADI) for different cases.The widely used high-level supplies require much more fan power than those for low-level supplies for achieving the same value of ADI. In addition, the supply velocity, hence the supply dynamic pressure, for a high-level supply is much larger than for low-level supplies. This further increases the power consumption for high-level supply systems.The paper considers these factors and attempts to provide some guidelines on the difference in the energy consumption associated with high and low level air supply systems. This will be useful information for designers and to the authors' knowledge there is a lack of information available in the literature on this area of room air distribution.The energy performance of the above-mentioned ventilation systems has been evaluated on the basis of the fan power consumed which is related to the airflow rate required to provide equivalent indoor environment. The Air Distribution Index (ADI) is used to evaluate the indoor environment produced in the room by the ventilation strategy being used. The results reveal that mixing ventilation requires the highest fan power and the confluent jets ventilation needs the lowest fan power in order to achieve nearly the same value of ADI.
  • La Fleur, Lina, et al. (författare)
  • Energy use and perceived indoor environment in a Swedish multifamily building before and after major renovation
  • 2018
  • Ingår i: Sustainability. - MDPI AG. - 2071-1050. ; 10:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Improved energy efficiency in the building sector is a central goal in the European Union and renovation of buildings can significantly improve both energy efficiency and indoor environment. This paper studies the perception of indoor environment, modelled indoor climate and heat demand in a building before and after major renovation. The building was constructed in 1961 and renovated in 2014. Insulation of the façade and attic and new windows reduced average U-value from 0.54 to 0.29 W/m2·K. A supply and exhaust ventilation system with heat recovery replaced the old exhaust ventilation. Heat demand was reduced by 44% and maximum supplied heating power was reduced by 38.5%. An on-site questionnaire indicates that perceived thermal comfort improved after the renovation, and the predicted percentage dissatisfied is reduced from 23% to 14% during the heating season. Overall experience with indoor environment is improved. A sensitivity analysis indicates that there is a compromise between thermal comfort and energy use in relation to window solar heat gain, internal heat generation and indoor temperature set point. Higher heat gains, although reducing energy use, can cause problems with high indoor temperatures, and higher indoor temperature might increase thermal comfort during heating season but significantly increases energy use. © 2018 by the authors.
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