Wyniki wyszukiwania - Biblioteka Nauki

1

Pomiary oporów przepływu jednofazowego w minikanałach

100%

Dutkowski K.

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tom R. 56, nr 5

503-506

PL

W artykule przedstawiono wyniki badań dotyczących oporów jednofazowego przepływu wody (Re = 6 414) oraz powietrza (Re = 22 865) minikanałami. Jako minikanały zastosowano rurki ze stali nierdzewnej o całkowitej długości 500 mm i 15 różnych średnicach wewnętrznych (0,21 - 2,30 mm). Wyznaczono współczynnik strat liniowych podczas ruchu laminarnego, burzliwego i granicę przejścia z zakresu laminarnego w burzliwy. Wyniki badań porównano z wielkościami teoretycznymi znanymi z mechaniki płynów kanałów konwencjonalnych.

EN

The paper presents results of experimental investigations of pressure drop in minichannels, with use of water and air as the working fluids. The test section was made from stainless steel pipes of internal diameters equal to 0.21, 0.31, 0.45, 0.55, 0.64, 0.80, 1.05, 1.10, 1.30, 1.35, 1.40, 1.60, 1.68, 1.94 and 2.30 mm. The experiments were conducted for the Reynolds number up to Re = 6 414 and Re = 22 865 for water and air, respectively. A friction factor is presented as a function of the Reynolds number. The experimental friction factor is compared with the results obtained from theoretical equations of Hagen-Poiseuille and Blasius. There was determined the boundary of transition to the turbulent flow. The deviation of all the results of experimental investigations was not greater than š 20% related to the friction factor coefficient theoretical value. On the basis of the experimental investigations performed, one can state that: - contradictory reports concerning a sooner transition to the turbulent flow different from those occurring in conventional channels were not confirmed; - the friction factor of laminar flow can be correctly predicted by the conventional correlation λ=64/Re; - the friction factor of turbulent flow can be correctly predicted by Blasius correlation, which is valid for conventional channels; - the theory of single-phase flow in conventional channels was found to produce valid predictions for experimental results.

2

Pomiary oporów przepływu dwufazowego w minikanałach

100%

Dutkowski K.

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tom R. 56, nr 5

507-511

PL

W artykule przedstawiono wyniki badań oporów przepływu mieszaniny woda-powietrze w minirurkach. W badaniach zastosowano 10 minirurek ze stali nierdzewnej o średnicy wewnętrznej dw = 0,64 ÷ 2,30 mm. Badania przeprowadzono w zakresie parametrów: masowe natężenie przepływu wody 0,15 ÷ 59 kg/h, powietrza 0,004 ÷ 0,7 kg/h, udział masowy powietrza w mieszaninie dwufazowej x = 0,0003 ÷ 0,22, gęstość strumienia masy mieszaniny (w?) = 46 ÷ 8582 kg/(m2os). Wykazano brak możliwości wykorzystania klasycznych metod obliczenia oporu przepływu dwufazowego.

EN

The paper presents results of experimental investigations of frictional pressure drop in minichannels. Air-water mixture was used as working fluid. The test section was made from stainless-steel pipes of internal diameters equal to 0.64, 1.05, 1.10, 1.30, 1.35, 1.40, 1.60, 1.68, 1.94 and 2.30 mm. Investigations were performed for mass flux of 46 ÷ 8582 kg/(m2 s) and gas quality from 0.0003 to 0.22. The superficial velocity ranges of water and air were 0.1 ÷ 8.6 m/s and 0.9 ÷ 63.9 m/s, respectively. The results of experimental investigations were compared with the theoretical values obtained from the homogeneous equilibrium model (HEM). The dynamic viscosity coefficient was calculated using correlations proposed by: Owens, Mc Adams, Ackers, Cicchitti, Dukler, Beattie & Whaley, Lin. It was found that none of the tested correlations could predict the two-phase pressure drop satisfactorily. Even though there exist papers which confirm the suitability of the classical separated flow methods of Lockhart-Martinelli and Friedel for calculations of the frictional pressure drop of the two-phase flow in minichannels, the experimental study conducted by the author confirms the existence of substantial limitations. The classical correlations of Lockhart-Martinelli and Friedel can be only treated as primary estimation of resistances in the adiabatic two-phase flow in tubular minichannels. Experiments confirmed the need for introducing corrections and modifications to the classical method to obtain results reliable in case of minichannels.

3

Przyczyny i skutki niestabilnej pracy parowników chłodniczych

51%

Bohdal T. , Czapp M. , Dutkowski K.

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tom nr 8

332-338