13 results on '"Radomska, Ewelina"'
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2. Long-term modeling of the performance of a solar still with phase-change material
- Author
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Radomska, Ewelina and Mika, Łukasz
- Published
- 2023
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3. The Performance of Solar Still in Continental Climates: A Case Study in Poland.
- Author
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Radomska, Ewelina, Mika, Łukasz, Boruta, Piotr, and Bujok, Tomasz
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WATER shortages , *WATER masses , *WEATHER , *SUSTAINABLE development , *SOLAR radiation , *SOLAR stills , *SALINE water conversion - Abstract
AbstractThis paper addresses the global issue of water scarcity and the need for sustainable development by exploring eco-friendly desalination technology – solar still. Although solar still has lower productivity compared to conventional fossil-fueled desalination technologies, much research is being conducted to enhance its productivity. Most studies focus solely on optimizing water mass in solar still, neglecting other correlated factors. Hence, this paper presents mathematical modeling and experimental studies on the impact of water mass, initial temperature, and solar insolation on solar still performance in Polish weather conditions. The findings reveal that solar still productivity ranges from 215 mL/m2/day to 5079 mL/m2/day between June and October in Poland. It is observed that solar still productivity decreases with increasing water mass beyond the critical threshold of solar insolation on the glass cover plane, which is 2.676 kWh/m2/day. However, below that threshold, the effect of water mass on the solar still productivity strongly depends on its initial temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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4. Assessment of the Use of Carbon Capture and Storage Technology to Reduce CO 2 Emissions from a Natural Gas Combined Cycle Power Plant in a Polish Context.
- Author
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Garcés, Lucia F. Pérez, Sztekler, Karol, Azevedo, Leonardo, Boruta, Piotr, Bujok, Tomasz, Radomska, Ewelina, Mlonka-Mędrala, Agata, Mika, Łukasz, and Chmielniak, Tomasz
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CARBON emissions ,NATURAL gas ,GAS as fuel ,CARBON dioxide mitigation ,ELECTRIC power ,POWER plants ,CARBON sequestration ,GAS power plants - Abstract
This study investigates the crucial role of Carbon Capture and Storage (CCS) technology in mitigating CO
2 emissions from Poland's power systems, which is essential not only for meeting climate targets but also for maintaining energy security in the country. Acknowledging natural gas as a transitional fuel, the focus is on evaluating the decarbonization potential of the natural gas combined cycle (NGCC) power plant. The NGCC with and without an amine-based carbon capture unit was modeled using IPSEpro (SimTech, version 7.0). It was found that the annual CO2 emission from 435.68 MWe (net) NGCC can be reduced from 1,365,501 tons (357.8 kgCO2 /MWh) to 136,556 tons (42.9 kgCO2 /MWh). On the other hand, the CCS reduced the net electric power of the NGCC from 435.68 MW to 363.47 MW and the net energy efficiency from 55.60% to 46.39%. Nonetheless, these results demonstrate the potential of using the amine-based CO2 capture technology in NGCC systems. This is especially important in the context of the decarbonization of the Polish power system. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
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5. The Effect of Nozzle Configuration on Adsorption-Chiller Performance.
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Kalawa, Wojciech, Sztekler, Karol, Kozaczuk, Jakub, Mika, Łukasz, Radomska, Ewelina, Nowak, Wojciech, and Gołdasz, Andrzej
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SPRAY nozzles ,ENERGY consumption ,NOZZLES - Abstract
Broadly defined climate protection is a powerful incentive in the search for environmentally friendly refrigeration technologies. Adsorption chillers are considered to be one such technology; however, their main disadvantages include a low cooling capacity, a low energy efficiency ratio (EER), and cyclic operation. Thus, a great deal of effort is being put into improving adsorption-chiller performance. In this paper, the influence of the spray angle, the number of nozzles, and the water flow rate through the nozzles on adsorption-chiller performance was investigated. Adsorption-chiller performance was investigated mainly in terms of the cooling capacity (CC), the energy efficiency ratio (EER), and the specific cooling power (SCP). The results indicated that the chiller's cooling capacity increased from about 210 W to 316 W and that the EER increased from 0.110 to 0.167 when the spray angle of the nozzles was increased from 90° to 120°. It was also reported that increasing the flow rate of water through the nozzles did not improve the average cooling capacity or the other performance parameters but resulted in more stable operation of the chiller. Additionally, using six nozzles instead of three improved the average cooling capacity and EER tenfold. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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6. Simulation Analysis of Mechanical Fluidized Bed in Adsorption Chillers.
- Author
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Kalawa, Wojciech, Sztekler, Karol, Mlonka-Mędrala, Agata, Radomska, Ewelina, Nowak, Wojciech, Mika, Łukasz, Bujok, Tomasz, and Boruta, Piotr
- Subjects
FLUIDIZED-bed combustion ,ADSORPTION (Chemistry) ,HEAT exchangers ,MASS transfer ,COOLING systems ,HEAT transfer - Abstract
Adsorption systems are alternatives to compressor cooling systems. Apart from many advantages, these systems are characterized by low COP and SCP parameters. One of the most promising options to improve the performance of adsorption chillers is the replacement of the stationary bed with a fluidized one. A fluidized bed significantly increases the heat and mass transfer within the bed, enables better contact between gas and solid phases, and results in the proper mixing of adsorbent particles. This paper presents the possibility of using fluidized beds in adsorption chillers. This paper shows the results of CFD numerical modelling of the operation of a fluidized bed for an adsorption chiller and simulations of the bed temperature profiles during the adsorption and desorption processes of sorbent in a fluidized bed. This article presents an analysis of CFD simulation results for the optimal angle of heat exchangers. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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7. Experimental and Theoretical Investigation of Single-Slope Passive Solar Still with Phase-Change Materials.
- Author
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Radomska, Ewelina, Mika, Łukasz, Sztekler, Karol, Kalawa, Wojciech, Lis, Łukasz, Pielichowska, Kinga, Szumera, Magdalena, and Rutkowski, Paweł
- Subjects
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SOLAR stills , *PHASE change materials , *PARAFFIN wax , *ORDINARY differential equations , *WATER temperature , *ANALYTICAL solutions - Abstract
Many attempts are made worldwide to create cheap, efficient, and eco-friendly water desalination systems. Passive solar stills (SS) are considered to be such. This paper presents the results of the experimental and theoretical investigation of the effects of using phase-change materials (PCM) on the performance of SS. The experiments were conducted for two paraffin waxes, as PCM and 1.0, 2.5, and 5.0 kg of PCM were used. The results of the experimental studies were used to validate a mathematical model, which was based on the energy balance ordinary differential equations. The equations were solved numerically since the approximate solutions obtained numerically are sufficient and relatively simple as compared to the exact analytical solutions. A theoretical analysis was then carried out and a novel and detailed dependence on the water evaporation rate as a function of water temperature and the difference between water and cover temperature was determined. It was also found that the productivity of the SS with PCM strongly depends on the operating conditions. For uniform initial temperatures of the SS, its productivity decreases with an increasing PCM-to-water mass ratio, and the maximum decrease is 10.8%. If the SS is not thermally insulated, the PCM can take the role of a thermal insulator and increase productivity by 1.1%, but there is an optimal PCM-to-water mass ratio. The greatest increase in productivity, by up to 47.1%, can be obtained when the PCM is heated outside the SS and inserted into the SS when the water temperature starts to decrease. In this case, the productivity increases with the increasing PCM-to-water mass ratio. These outcomes fill a knowledge gap caused by a lack of justification for why in some cases, the application of PCM fails to improve the productivity of SS. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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8. The Effects of Using Steam to Preheat the Beds of an Adsorption Chiller with Desalination Function.
- Author
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Sztekler, Karol, Kalawa, Wojciech, Mika, Lukasz, Lis, Lukasz, Radomska, Ewelina, and Nowak, Wojciech
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WASTE heat ,CHILLED water systems ,ADSORPTION (Chemistry) ,RENEWABLE energy sources ,SALINE water conversion ,DRINKING water ,HEAT exchangers - Abstract
Adsorption chillers are a promising alternative to traditional compressor-based devices. Adsorption chillers can be supplied with low- or medium-temperature waste heat or heat from renewable energy sources. In addition, they can be used for water desalination purposes. Thus, the adsorption chillers are unique devices that meet essential problems of the modern world: a need to limit the negative impact of humankind on the natural environment and growing problems with access to drinking water. However, adsorption chillers also have disadvantages, including ineffective operation and large size. Therefore, in this paper, the influence of steam utilization on the operation of an adsorption chiller with water desalination function was investigated experimentally, which has not been done before. The research was carried out on the adsorption chiller, working on a silica gel–water pair, installed in the AGH UST Center of Energy. The chiller was modified to preheat the sorbent with the use of steam. The results show that the use of steam instead of water for preheating the bed leads to higher temperatures in the heat exchanger and the bed. As a result, heat transfer from the heating medium to the bed is more intense, and a significant shortening of the desorption process is observed. In the case of using steam for preheating, the desorption time was about 30 s, while for water, it was 300 s. Thanks to this solution, it is possible to reduce the size of the device and increase its efficiency. The proposed solution opens a new course of research on adsorption chillers and broadens the horizon of their applications, as steam is a by-product of many industrial processes. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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9. Experimental Validation of the Thermal Processes Modeling in a Solar Still.
- Author
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Radomska, Ewelina, Mika, Lukasz, Sztekler, Karol, Kalawa, Wojciech, and Kant, Karunesh
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SOLAR stills , *SOLAR technology , *WATER masses , *MAXIMA & minima , *MATHEMATICAL models - Abstract
Passive solar distillation is cheap and energy-efficient technology but its main disadvantage is low productivity. Thus, there are many attempts to improve solar stills' productivity, and one of them is changing the mass of the water. This paper presents the results of validation of the thermal processes modeling in a solar still (SS). In order to validate the model, the experimental studies were conducted in a laboratory to ensure uniform climatic conditions. The studies were carried out for 10 kg, 15 kg, and 20 kg of water under three different solar irradiance conditions. The results show that 10 kg and 20 kg of water ensure the highest and the lowest daily productivity, respectively, independently of solar irradiance. When the water mass is 10 kg, the solar still's productivity is 800 mL/m2/day, 3732 mL/m2/day, and 9392 mL/m2/day for low, medium, and high solar irradiance, respectively. Additionally, it is found that reducing the water mass from 20 kg to 10 kg can improve solar still's productivity by a maximum value of 21.6%, which is obtained for low solar irradiance. The proposed mathematical model allows predicting the performance of the SS. The results of the theoretical calculations are in good agreement with the results of the experiments. The minimum and maximum deviation between the actual and theoretical productivity of the SS is 1.1% and 8.3%, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
10. A New Method of Regulating the Cooling Capacity of a Cooling System with CO 2.
- Author
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Bieniek, Artur, Kuchmacz, Jan, Sztekler, Karol, Mika, Lukasz, Radomska, Ewelina, and Chaer, Issa
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CARBON dioxide ,COOLING systems ,WORKING fluids ,HEAT exchangers ,COOLING loads (Mechanical engineering) ,HEAT pipes ,REFRIGERANTS - Abstract
New guidelines set by international organizations for refrigeration companies cause that natural working fluids such as carbon dioxide are increasingly used in new refrigeration systems. Carbon dioxide (R-744) is used in freezing, cooling, or air conditioning installations, in which the cooling load fluctuates hourly. To adapt the cooling capacity of the evaporator to the current cooling load of the cooled space, a number of control elements are used. The paper proposes a new method of regulating the cooling capacity for a one-stage refrigeration cycle with the R-744 refrigerant and an internal heat exchanger (IHX). The proposed method involves using an additional evaporator and combines the possibility of regulating the cooling capacity with the possibility of energy efficiency ratio (EER) improvement. The energy analysis of the proposed method of regulating the cooling capacity was performed and the results were compared with the control method. The control method was using the compressor hot gas bypass valve which allows the flow of hot vapor refrigerant to the suction side. The energy analysis was carried out for both subcritical and supercritical cycles using the energy equations. For each of the considered methods, the characteristics of the change in the EER as a function of the reduction of the cooling capacity in both supercritical and subcritical cycles were determined. It was found that when the cooling capacity decreased by 50%, the hot gas bypass regulating method was around 30% less efficient compared to the proposed additional evaporator regulating method. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
11. Experimental Study of Three-Bed Adsorption Chiller with Desalination Function.
- Author
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Sztekler, Karol, Kalawa, Wojciech, Nowak, Wojciech, Mika, Lukasz, Gradziel, Slawomir, Krzywanski, Jaroslaw, and Radomska, Ewelina
- Subjects
SALINE water conversion ,WASTE heat ,HEAT pipes ,SILICA gel ,ADSORPTION (Chemistry) ,ENERGY consumption ,WATER temperature ,POLLUTION - Abstract
Energy efficiency is one of the most important topics nowadays. It is strictly related to energy demand, energy policy, environmental pollution, and economic issues. Energy efficiency can be increased and operating costs reduced by using waste heat from other processes. One of the possibilities is to use sorption chillers to produce chilled water and desalinated water. Low-temperature waste heat is not easy to utilize because of the low energy potential. Using adsorption chillers in low-temperature conditions allows utilizing waste heat and producing useful products in many regions of the world. The paper presents the results of an experimental study carried out on a three-bed adsorption chiller with desalination function, using silica gel and water as a working pair. The laboratory test stand included one evaporator, one condenser, and three separate tanks for water, desalinated water, and brine, respectively. The test stands scheme and description were presented. All results were obtained during several test hours with stable temperature conditions in the range of 57–85 °C for the heating water. It is found that the Coefficient of Performance (COP) increased from 0.20 to 0.58 when the heating water temperature increased from 57 to 85 °C. A similar finding is reported for Specific Cooling Power (SCP), which increased from 27 to 160 W/kg as the heating water temperature increased from 57 to 85 °C. It can be concluded that the heating water temperature strongly impacts the performance of the adsorption chiller. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
12. The Impact of Heat Exchangers' Constructions on the Melting and Solidification Time of Phase Change Materials.
- Author
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Radomska, Ewelina, Mika, Lukasz, Sztekler, Karol, and Lis, Lukasz
- Subjects
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HEAT exchangers , *HEAT storage , *HEAT pipes , *ENERGY storage , *PHASE change materials , *HEAT transfer fluids , *HEAT transfer - Abstract
An application of latent heat thermal energy storage systems with phase change materials seems to be unavoidable in the present world. The latent heat thermal energy storage systems allow for storing excessive heat during low demand and then releasing it during peak demand. However, a phase change material is only one of the components of a latent heat thermal energy storage system. The second part of the latent heat thermal energy storage is a heat exchanger that allows heat transfer between a heat transfer fluid and a phase change material. Thus, the main aim of this review paper is to present and systematize knowledge about the heat exchangers used in the latent heat thermal energy storage systems. Furthermore, the operating parameters influencing the phase change time of phase change materials in the heat exchangers, and the possibilities of accelerating the phase change are discussed. Based on the literature reviewed, it is found that the phase change time of phase change materials in the heat exchangers can be reduced by changing the geometrical parameters of heat exchangers or by using fins, metal foams, heat pipes, and multiple phase change materials. To decrease the phase change material's phase change time in the tubular heat exchangers it is recommended to increase the number of tubes keeping the phase change material's mass constant. In the case of tanks filled with spherical phase change material's capsules, the capsules' diameter should be reduced to shorten the phase change time. However, it is found that some changes in the constructions of heat exchangers reduce the melting time of the phase change materials, but they increase the solidification time. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
13. The Impact of Additives on the Main Properties of Phase Change Materials.
- Author
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Radomska, Ewelina, Mika, Lukasz, and Sztekler, Karol
- Abstract
The main drawback of phase change materials (PCMs) is their low thermal conductivity, which limits the possibilities of a wide range of implementations. Therefore, the researchers, as found in the literature, proposed several methods to improve the thermal conductivity of PCMs, including inserting high thermal conductivity materials in nano-, micro-, and macro-scales, as well as encapsulation of PCMs. However, these inserts impact the other properties of PCMs like latent heat, melting temperature, thermal stability, and cycling stability. Hence, this paper aims to review the available in the open literature research on the main properties of enhanced PCMs that undergo solid–liquid transition. It is found that inserting high thermal conductivity materials and encapsulation results in improved thermal conductivity of PCMs, but it decreases their latent heat. Moreover, the insertions can act as nucleating agents, and the supercooling degree can be reduced. Some of the thermal conductivity enhancers (TCEs) may prevent PCMs from leakage. However, some test results are inconsistent and some seem to be questionable. Therefore, this review indicates these discrepancies and gaps in knowledge and points out possible directions for further research. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
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