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Abstract

The results of experimental investigations of heat transfer and a friction factor in an air channel of the minichannel heat exchanger are presented. The main aim of the analysis was to examine an influence of geometrical parameters of the fin shape with two geometries on heat transfer and flow characteristics of the air channel. The test rig was designed to monitor the parameters of the airflow during cooling by the minichannel heat exchanger. The analysis was conducted with the airflow in the range of 1–5 m/s. The temperature of the evaporation in a refrigeration system was set at 288.15 K. The energy balance of the refrigeration system was carried out. A numerical model describes the airflow through a part of the heat exchanger. Numerical simulations were validated with the experimental data. Numerical methods were used to evaluate the performance of the system and possibilities to improve the fin geometry. The characteristics of the friction factor (a measure of the pressure loss in the airflow) and the Colburn j-factor (heat transfer performance) were calculated. For the maximal velocity of the airflow, the Colburn factor was equal to 0.048 and the evaporator capacity equaled 1914 W.
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Bibliography

[1] Islam S., Islam M.S., Abedin M.Z.: Review on heat transfer enhancement by louvered fin. Int. J. Eng. Mater. Manufact. 6(2021), 60–80.
[2] Muszynski T., Kozieł S.M.: Parametric study of fluid flow and heat transfer over louvered fins of air heat pump evaporator. Arch. Thermodyn. 37(2016), 3, 45–62.
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[5] Gunnasegaran P., Shuaib N.H., Abdul Jalal M.F.: The effect of geometrical parameters on heat transfer characteristics of compact heat exchanger with louvered fins. ISRN Thermodyn. (2012), 1–10.
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[7] Amirnordin S.H., Didane H.D., Norani Mansor M., Khalid A, Suzairin M.S., Raghavan V.R.: Pressure drop and heat transfer characteristics of louvered fin heat exchangers. Appl. Mech. Mater. 465-466(2014), 500–504.
[8] Chan Kang H., Jun G.W.: Heat transfer and flow resistance characteristics of louver fin geometry for automobile applications. J. Heat Transfer. 133(2011), 1–6.
[9] Okbaz A., Olcay A.B., Cellek M.S., Pinarbasi A.: Computational investigation of heat transfer and pressure drop in a typical louver fin-and-tube heat exchanger for various louver angles and fin pitches. EPJ Web Conf. 143(2017), 02084.
[10] Park J.S., Kim J., Lee K.S.: Thermal and drainage performance of a louvered fin heat exchanger according to heat exchanger inclination angle under frosting and defrosting conditions. Int. J. Heat Mass Transf. 108(2017), 1335–1339.
[11] Liu X., Chen H., Wang X., and Kefayati G.: Study on surface condensate water removal and heat transfer performance of a minichannel heat exchanger. Energies 13(2020), 5, 1065
[12] Saleem A., Kim M.H.: CFD analysis on the air-side thermal-hydraulic performance of multi-louvered fin heat exchangers at low Reynolds numbers. Energies 10(2017), 6, 1–24.
[13] Bohdal T., Charun H., Sikora M.: Heat transfer during condensation of refrigerants in tubular minichannels. Arch. Thermodyn. 33(2012), 2, 3–22.
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Authors and Affiliations

Michał Jan Kowalczyk
1
Marcin Łęcki
1
Artur Romaniak
1
Bartosz Warwas
1
Artur Gutkowski
1

  1. Lodz University of Technology, Institute of Turbomachinery, Wólczanska 217/221, 93-005 Łódz, Poland
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Abstract

The embryology of two species, Deschampsia antarctica , a native species, and Poa annua , an alien species in the Antarctic we studied. Flowering buds of plants growing in their natural habitats on King George Island and generative tissues of both plant species grown in a greenhouse were analyzed. Adaptations to autogamy and anemogamy were observed in the flower anatomy of both species. The microsporangia of the evaluated grasses produce a small number of three−celled pollen grains. Numerous pollen grains do not leave the microsporangium and germinate in the thecae. Deschampsia antarctica and P. annua plants harvested in Antarctica developed a particularly small number of microspores in pollen chambers. In D. antarctica , male gametophytes were produced at a faster rate: generative cells in pollen did not become detached from the wall of the pollen grain, they were not embedded in the cytoplasm of vegetative cells, and they divided into two sperm cells situated close to the wall. The monosporous Polygonum type of embryo sac development was observed in the studied species. The egg apparatus had typical polarization, and the filiform apparatus did not develop in synergids. Large antipodals with polyploidal nuclei were formed in the embryo sacs of D. antarctica and P. annua . Poa annua was characterized by numerous antipodal cells which formed antipodal tissue in the chalazal region of the embryo sac. Three distinct antipodals with atypical, lateral position in the vicinity of the egg apparatus were observed in D. antarctica. The diaspores of the investigated grass species were characterized by small size, low weight and species−specific primary and secondary sculpture of the testa and caryopsis coat.
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Authors and Affiliations

Irena Giełwanowska
Wioleta Kellmann-Sopyła

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