285 research outputs found
Carta de Ryszard Palacz a Alain Guy. Varsovia, 8 de septiembre de 1963
No full textCarta de Ryszard Palacz, historiador polaco de la filosofía, a Alain Guy expresándole que está muy contento porque ha ido a su patria a dar conferencias. También le comenta que ha recibido una carta de M. Markowski (discípulo del profesor Swiezawski) contándole que es un excelente conferenciante y la visita de Andrzej Kempfi. Le informa además, que está leyendo su libro sobre los filósofos españoles y que en la próxima carta le enviará una foto suya.Se conserva el sobre de la carta con 4 sellos
Distribution of phytoplankton functional types in high-nitrate low-chlorophyll waters in a new diagnostic ecological indicator model
No full textModeling and monitoring plankton functional types (PFTs) is challenged by insufficient amount of field measurements to ground-truth both plankton models and bio-optical algorithms. In this study, we combine remote sensing data and a dynamic plankton model to simulate an ecologically-sound spatial and temporal distribution of phyto-PFTs. We apply an innovative ecological indicator approach to modeling PFTs, and focus on resolving the question of diatom-coccolithophore co-existence in the subpolar high-nitrate and low-chlorophyll regions. We choose an artificial neural network as our modeling framework because it has the potential to interpret complex nonlinear interactions governing complex adaptive systems, of which marine ecosystems are a prime example. Using ecological indicators that fulfill the criteria of measurability, sensitivity and specificity, we demonstrate that our diagnostic model correctly interprets some basic ecological rules similar to ones emerging from dynamic models. Our time series highlight a dynamic phyto-PFT community composition in all high latitude areas, and indicate seasonal co-existence of diatoms and coccolithophores. This observation, though consistent with in situ and remote sensing measurements, was so far not captured by state-of-the-art dynamic models which struggle to resolve this "paradox of the plankton". We conclude that an ecological indicator approach is useful for ecological modeling of phytoplankton and potentially higher trophic levels. Finally, we speculate that it could serve as a powerful tool in advancing ecosystem-based management of marine resource
The comparative analysis of the R290 heat pump system working with standard expansion valve and two-phase ejector
No full textThe heat pump systems play a significant role in the global energy transition process of household heating sources towards zero-emission. One of the key technologies to improve the efficiency of heat pump systems utilizing natural working fluids is application of the two-phase ejector, which is able to recover part of the expansion losses. The comparative experimental analysis of a novel ejector-based air-source R290 heat pump was performed. The two-phase bypass ejector was installed in a R290 heat pump unit and a number of modifications were introduced to the baseline system. The adaptions included implementation of the internal heat exchanger, increasing the superheat at the compressor suction port, and a liquid separator for handling the two-phase flow at the ejector outlet. The performance evaluation of the system was based on COP and system heating capacity. The comparative analysis with the R290 heat pump utilizing standard expansion valve and two-phase ejector was carried out for typical operating conditions for its domestic application during heating seasons. The system working with an ejector as a throttling device allowed for up to 25% of COP improvement over the system utilizing an expansion valve. Additionally, the ejector implementation resulted in decreased pressure ratio of the compressor, which increased the system heating capacity by up to 10%
Experimental analysis of the air-to-water ejector-based R290 heat pump system for domestic application
No full textThe aim of this study was to analyze and compare the performance of an 8 kW ejector-based R290 heat pump system for hot water heating applications that operates with two different expansion devices: a throttling valve and a two-phase ejector. The vapor compression system was designed to compare the unit operating in direct expansion and ejector-based working modes under similar operating conditions. The test results were assessed for overall system performance measured by COP and heating capacity and for single-component operation. The ejector mode allowed operation at the same range of ambient temperatures as direct expansion mode with the potential to completely replace the expansion valve. The COP of ejector system was up to 2.6, which was 38% higher than direct expansion when working under similar conditions for an ambient temperature of -12.8 degrees C. Moreover, the COP in direct expansion mode decreased significantly along the decrease of ambient temperature, whereas for the ejector mode this decrease was considerably smaller
The experimental analysis of ejector‐based R290 heat pump system for domestic applications
No full textThe preliminary experimental study of a novel ejector‐based air‐source R290 heat pump was performed. The two‐phase bypass ejector was installed in a R290 heat pump unit and a number of modifications were introduced to the baseline system. The adaptions included implementation of the internal heat exchanger, increasing the superheat at the compressor suction port, and a liquid separator for handling the two‐phase flow at the ejector outlet. The performance evaluation of the system was based on COP and system heating capacity. Additionally, the comparative analysis with the R290 heat pump utilizing standard expansion valve for five typical operating points was carried out. The system working with an ejector as a throttling device allowed for up to 30% of COP improvement over the system utilizing an expansion valve. Additionally, the ejector implementation resulted in decreased pressure ratio of the compressor, which increased the system heating capacity by up to 12%
Numerical investigation of the expansion devices applied in modern vapour compression refrigeration unit considering specific entropy and entropy generation analyses
No full textEjector-based refrigeration cycles working with natural refrigerants have already gained industry attention. Replacing throttling valve with an ejector in vapour-compression cycles brings high improvement of the cycle efficiency due to the ejectors potential of recovering part of throttling losses. With the rapidly growing market for heat pumps, they are also being implemented in those cycles, but this requires redesigning the ejector geometry for new natural working fluids for different operating conditions and applications. Typical approach to perform the ejector shape optimization is to use the ejector mass entrainment ratio or overall efficiency as an objective function. However, an entropy generation analysis seems to be more efficient. For this reason, the aim of this work was to perform the numerical analysis of the entropy generation of two two-phase ejectors for R744 and R290 refrigerants in order to assess its potential as a tool for efficiency improvement in the shape optimization algorithms. The ejectorPL approach utilizing the HEM approach was complemented with the entropy generation model and implemented using an additional transport equation to the CFD software. The CFD models were validated based on experimental results obtained from ejectors working in R744 transcritical refrigeration system and R290 heat pump. Each ejector was simulated for set of operating conditions representing the system working in both supercritical and near critical point conditions. The CFD results of the mass flow rates for both devices were used for validation purposes. The results of the pressure and temperature were compared with experimental data. The entropy generation module allowed for the entropy generation analysis in terms of maximum values and their location showing critical areas of irreversibility characterizing different working fluids usage and ejector applications
Experimental analysis of the R290 variable geometry ejector with a spindle
No full textThe aim of this work was to experimentally analyze the variable geometry gas ejector with a spindle designed for operation with the natural working fluid propane (R290). The performance of the ejector was evaluated based on the mass entrainment ratio and critical temperature, being the most crucial parameters for optimizing the cooling capacity in ejector refrigeration systems, as well as the ejector efficiency using common literature notation. Additionally, local pressure drop measurements allowed for the determination of pressure profiles inside for different spindle positions used for capacity regulation. The experimentally defined ejector efficiency curves demonstrated the ability to control the ejector capacity by means of the spindle, irrespective of the unfavorable operating conditions. By decreasing the effective throat area using spindle, the ejector mass entertainment ratio increased by 35%. Spindle movement allowed for the decrease of the motive nozzle flow rate by up to 65%, while still maintaining the suction of the secondary flow of the ejector. Moreover, the behavior of a slight increase in suction nozzle flow with a decrease in motive nozzle flow has been observed for the initial movement of the spindle followed by a huge drop for further reduction of the effective throat area, confirming the previous conclusions shown in the literature
Experimental study of a R290 variable geometry ejector
No full textEjectors are classified as fluid-dynamics controlled devices where the "component-scale"performances are imposed by the local-scale fluid dynamic phenomena. For this reason, ejector performances (measured by the pressure-entrainment ratio coordinate of the critical point) are determined by the connection of operation conditions, working fluid and geometrical parameters. Given such a connection, variable geometry ejector represents a promising solution to increase the flexibility of ejector-based systems. The present study aims to extend knowledge on variable geometry systems, evaluating the local and global performances of the R290 ejector equipped with a spindle. The prototype ejector was installed at the R290 vapour compression test rig adapted and modified for the required experimental campaign. The test campaign considered global parameter measurements, such as the pressure and the temperature at inlets and outlet ports together with the mass flow rates at both inlet nozzles, and the local pressure drop measurements inside the ejector. In addition, the experimental data were gathered for different spindle positions starting from fully open position the spindle position limited by the mass flow rate inside the test rig with the step of 1.0 mm
Numerical modelling of the food freezing process in a quasi-hydrofluidisation system
No full textThe paper presents a study of food freezing using hydrofluidisation method, characterised by very high heat transfer coefficients exceeding 2500 W · m−2 K−1, which constitutes a novel and promising technology. A numerical analysis of a system with a stationary group of food products was performed. This study aimed to investigate the geometrical parameters governing the freezing process, i.e., the position of food products above the orifices (from 50 mm to 70 mm), their mutual position, the diameter of orifices (3 mm or 5 mm), and the spacing of the orifices in an array (from 8 mm to 12 mm). In this method, the freezing time was from 3 min for 10 mm spherical food sample in moderate refrigerating medium temperatures up to 12 min for 30 mm spherical sample. Moreover, the freezing times at different liquid temperatures were compared in the range of −20 °C to −5 °C. Reducing the temperature by 5 K may lead to shortening the process by up to 50%. The hydrofluidisation method was assessed versus the immersion freezing for spherical products of different sizes showing the reduction of the process time from about 35% to over 60%.Fil: Stebel, M. Silesian University Of Technology; PoloniaFil: Smolka, Jochen. Silesian University Of Technology; PoloniaFil: Palacz, M. Silesian University Of Technology; PoloniaFil: Piechnik, E. Silesian University Of Technology; PoloniaFil: Puchalski, Cecilia Mabel. Silesian University Of Technology; PoloniaFil: Knap, M,. Silesian University Of Technology; PoloniaFil: Felissia, Fernando Esteban. Silesian University Of Technology; PoloniaFil: Eikevik, Tm. Norges Teknisk-naturvitenskapelige Universitet; NoruegaFil: Tolstorebrov, I. Norges Teknisk-naturvitenskapelige Universitet; NoruegaFil: Peralta, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Zorrilla, Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
- …
