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Małgorzata Sikora and Tadeusz Bohdal

Abstract

Investigations of refrigerant condensation in pipe minichannels are very challenging and complicated issue. Due to the multitude of influences very important is mathematical and computer modeling. Its allows for performing calculations for many different refrigerants under different flow conditions. A large number of experimental results published in the literature allows for experimental verification of correctness of the models. In this work is presented a mathematical model for calculation of flow resistance during condensation of refrigerants in the pipe minichannel. The model was developed in environment based on conservation equations. The results of calculations were verified by authors own experimental investigations results.

Open access

Tadeusz Bohdal, Henryk Charun and Małgorzata Sikora

Pressure drop during condensation of refrigerants in pipe minichannels

The present paper describes results of experimental investigations of pressure drop during the condensation of R134a, R404a and R407C refrigerants in pipe minichannels with internal diameter 0.31-3.30 mm. The results concern investigations of the mean and local pressure drop in single minichannels. The results of experimental investigations were compared with the calculations according to the correlations proposed by other authors. A pressure drop during the condensation of refrigerants is described in a satisfactory manner with Friedel and Garimella correlations. On the basis of the experimental investigations, the authors proposed their own correlation for calculation of local pressure drop during condensation in single minichannels.

Open access

Tadeusz Bohdal, Henryk Charun and Małgorzata Sikora

Abstract

Analysis of the state of-the-art in research of refrigerant condensation in miniature heat exchangers, so-called multiports, was made. Results of refrigerant R407C condensation in a mini condenser made in the form of two bundles of tubular minichannels from stainless steel with an inside diameter 0.64 mm and length 100 mm have been presented. Two exchangers consisted of four minichannels and 8 minichannels have been investigated. The values of average heat transfer coefficient and frictional pressure drops throughout the condensation process were designated. The impact of the vapor quality of refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A comparative analysis of test results for various refrigerants in both mini heat exchangers were made.

Open access

Izabela Drzewowska, Małgorzata Sobera and Aleksandra Sikora

Abstract

Aim of the study: The aim of this study was to verify whether the 5-month training exercises using specific balance exercises of the authorial program improves body balance control in children with Down syndrome (DS).

Materials and methods: The purpose of this study was the verification if the 5-months posture control exercises training by original program relays to posture control in Down syndrome (DS) children and youth. The subjects were 8 DS persons: 4 males and 4 females, aged 13-24. Two 20-seconds consecutive trails of natural bipedal standing position on 2 force platforms AccuSway (AMTI), one under each foot, were performed during research. On the basis of COP (centre of pressure) time series the following indices were computed: range, variability, velocity and area of COP shifts. There were 2 sessions of the research: one just before and the second just after 5-month lasting specific posture control training based on the original exercise program.

Results: The results revealed decreasing of the COP velocity of right lower limb and the COP range in anterior-posterior direction of both lower limbs after the training, comparing to the values from the first research session.

Conclusions: It is concluded that the specific posture control training by the presenting of the original exercises program influenced the posture control improving it and the program can be used in therapy of DS children and youth.

Open access

Małgorzata Dobrowolska, Mariola Paruzel-Czachura, Marta Stasiła-Sieradzka and Jagoda Sikora

Abstract

The paper presents the sociodemographic data obtained as a result of an empirical study carried out on a group of n=2118 workers employed under what is referred to as flexible forms of employment, within a more extensive research project entitled “Occupational problems of individuals working under flexible forms of employment - the psychological perspective”. The inspiration to focus on this particular part of the research was provided by a trend observed in the international literature, analysing the profile of an average flexible worker in highly developed countries. An analysis of the study sample of flexible workers shows that the group included rather young people, with a similar share of women and men, living in big cities, and with a rather short length of service; they were well-educated, married people with children, with a small number of previous employers, and mostly working in the private sector. The Polish study sample matches the descriptions of the average flexible European worker.

Open access

Małgorzata A. Jaworska, Elżbieta S. Sikora and Jan Ogonowski

The aim of this work was preparation and characterization of o/w nano and microemulsions containing Crodamol PC® as the oil phase. An influence of surfactants system applied in formulations on the properties of the obtained emulsions has been studied. The emulsions were prepared by phase inversion composition method. The measurement of the internal phase droplet size and the study of rheological properties were done. The obtained results showed that the prepared transparent emulsion systems are nano and microemulsion formulation. Moreover, it was concluded that the microemulsions stability and the size of the internal phase droplets depended on the type and the concentration of emulsifier and on the ratio of water phase to oil. Rheological studies have confirmed that the obtained microemulsions showed pseudoplastic behaviour.

Open access

Tadeusz Bohdal, Małgorzata Sikora, Katarzyna Widomska and Andrii M. Radchenko

Abstract

The experimental research of environmentally friendly refrigerant HFE-7100 condensation in pipe minichannels was conducted. During the investigations of HFE-7100 condensation in a minichannel with internal diameter 2 mm together with visualization of flow patterns was made. Visualization results were compared with existing flow structure maps. The identification of the range of flow patterns occurrence during the condensation process of low-pressure refrigerant HFE-7100 was made. The tests were performed throughout the whole range of condensation process.

Open access

Tadeusz Bohdal, Katarzyna Widomska and Małgorzata Sikora

Abstract

The paper presents the results of experimental heat transfer and pressure drop during condensation of the single component refrigerant R134a and zeotropic mixtures R404A, R407C, and R410A in tube minichannels of internal diameter from the range 0.31-3.30 mm. The local values and the average of heat transfer coefficient and pressure drop in the whole range of the change in mass quality were measured. On the basis of the obtained test results there was illustrated the influence of the change of mass vapor quality, the mass flux density, and the inner diameter of channel on the studied parameters. These results were compared with the calculation results based on the relations postulated by other authors. The discrepancy range was ± 50%. On the basis of given test results own correlation was developed to calculate the heat transfer coefficient and pressure drop of tested refrigerants which presents the obtained results in a range of discrepancy of ±25%.

Open access

Tomasz Oszako, Katarzyna Sikora, Małgorzata Borys, Katarzyna A. Kubiak and Miłosz Tkaczyk

Abstract

In the last decades, a new wave of oak decline has been observed in Poland. The most important pathogenic organisms involved in this phenomenon are probably soil-borne pathogens Phytophthoragenus, especially P. quercina. In this work, we sought to test the influence of elevated CO2 concentration on the susceptibility of oaks (Quercus robur L.) to infection by P. quercina. In order to test the susceptibility of oak fine roots to infection, we applied phosphite-based fertiliser Actifos in 0.6% concentration. One-year-old oak seedlings were grown for one year in greenhouse with either an ambient atmosphere (400 ppm CO2) or an elevated (800 ppm) concentration of CO2. Oaks grown at the elevated CO2 concentration developed longer shoots as proved by statistically significant differences. However, there was no difference in the development of root systems. The application of Actifos had a positive significant effect on the development of shoots and the surface area of fine roots under the elevated CO2 concentration.

Open access

Tadeusz Bohdal, Henryk Charun and Małgorzata Sikora

Abstract

The present paper describes the results of experimental investigations of heat transfer during condensation of R134a, R404A and R407C in pipe minichannels with internal diameters 0.31-3.30 mm. The results concern investigations of the local heat transfer coefficient. The results were compared with the correlations proposed by other authors. Within the range of examined parameters of the condensation process in minichannels made of stainless steel, it was established that the values of the heat transfer coefficient may be described with Akers et al., Mikielewicz and Shah correlations within a limited range of the mass flux density of the refrigerant and the minichannel diameter. On the basis of experimental investigations, the authors proposed their own correlation for the calculation of local heat transfer coefficient.