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1

Analysis of a possible application of a small power plant in the Organic Rankine Cycle, which apply waste heat from a combustion engine

Żabski J., Gumkowski S.

Eco-Energetics : technologies, environment, law and economy

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2018

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T. 1

127--135

EN

Some considerations on the waste heat treatment, heat and power combined generation and principles of the Organic Rankine Cycle and its application are produced. A thermodynamic screening of eight working fluids for Organic Rankine Cycle (ORC) was carried out. All investigated agents were single component fluids. The considered ORC systems operated at the upper temperature in the range Tmax=146-185°C and the lower one Tmin=27-37°C. The highest pressure in the cycles equalled pmax=3500 kPa and pmin=85 kPa. The cycles were run at subcritical pressures and the saturated vapour line was of the overhanging type in all cases. Heat regeneration was not considered in this paper. The heat source for the ORC system was heated air exhausted from the cooling system of an opposed-piston engine. The temperature of this heat at the inlet to ORC was equal to Th,in=230°C. Air was also the heat sink for the ORC with the inlet temperature Tcold,in=20°C. The power output of the ORC, neglecting electric generator efficiency, was kept in the range N=10-11 kW. Calculated thermal efficiencies h held values between 0.121 and 0.164.

2

Biomass drying: Experimental and numerical investigations

Żabski J., Lampart P., Gumkowski S.

Archives of Thermodynamics

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2018

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Vol. 39, no 1

39--73

EN

Results of experimental and numerical investigations of wood chips drying are described in the paper. Experiments are carried out on two test facilities: a small laboratory rig and a larger pre-prototype dryer. Both facilities are thorough-circulation convective air dryers. The first one is a batch dryer, whereas the second one is a continuous dryer with wood chips flowing down by gravity from a charging hopper to a gutter with the aid of screw-conveyor. The latter is considered a half scale model (preprototype) for professional drying installations. A low feeding rate of wood chips into the pre-prototype dryer makes the process quasi-stationary and the difference between it and a batch drying is negligible. So, most experiments at this facility were carried out as batch dryers with non-agitated packed beds. The investigations exhibit the same linear correlation between the mass of evaporated water from the packed bed and the drying air velocity for both facilities. Numerical analysis of the drying process is conducted using the Ansys Fluent software enriched in drying capabilities by means of self-written procedures – user defined functions. Simulations confirmed a phenomenon of a drying front observed in the small laboratory rig. A thin layer of wood chips comprises the whole heat exchange and moisture evaporation phenomenon. The drying front travels downstream in the course of the process separating the already dried layer and still wet layer.

3

Implementation of the first period of convective drying in a commercially available CFD package

Żabski J.

Transactions of the Institute of Fluid-Flow Machinery

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2015

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nr 128

139--157

EN

The issue of the drying of woodchips is investigated in this paper. The most widespread type of the solid drying is a packed bed convective drying process with hot air as a working medium that is considered here. A comprehensive survey has proven a severe shortage of 3D drying-oriented computational fluid dynamics (CDF) packages for handling packed beds. This work was carried out by means of User Defined Procedures (UDF) – self written codes in C implemented in a commercially available CFD package – Ansys Fluent. A strongly flattened fixed bed of woodchips was investigated whose dimensions equaled to 1.5 m×1.5 m×0.2 m in length, width and height, respectively. In theoretical modeling woodchips were assumed as spheres of unique size settled in a cubic layout. The first period of drying was taken into consideration with the inlet air temperature 60 ◦C and humidity 0%. The temperature of the packed bed was set to the wet bulb temperature 21 ◦C. The vapor flux was implemented as a source term in the continuity equation. The core part of the UDF was a DEFINE_SOURCE macro that comprised the source term for evaporating water and partially the liquid water storage. As a result the drying air was humidified from initial 0%, to 22% along the bed, at a constant air enthalpy. The air temperature decreased from 60 ◦C to 38 ◦C, and the drying rate fell from 0.22 to 0.10 kg/m3s.

4

Influence of the negative and positive jet of wake on laminar-turbulent transition in a boundary layer

Żabski J., Wierciński Z.

Journal of Theoretical and Applied Mechanics

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2009

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Vol. 47 nr 4

797-814

EN

In this paper, the results of experimental investigations relating to the influence of negative and positive jet of the wake on laminar-turbulent transition in the boundary layer on a flat plate are described. Using the technique of phase averaging and wavelet analysis, the investigations were carried out in an aerodynamic tunnel with a low level of turbulence in the external stream. The existence of serious differences was noted between the influence of the negative and positive jets due to strong velocity impulses appearing in the area behind the negative jet in the place of the local minimum of the velocity. However, behind the positive jet such strong disturbances appear later, not directly in the region behind the jet. These impulses do not show any signs of chaos and fortuity, therefore they should be rather classified as determined disorder. Moreover, the region of calm behind the positive jet, well-known in the literature, remains also in the area of entirely disturbed flow.

PL

W pracy przedstawiono badania eksperymentalne dotyczące wpływu ujemnego i dodatniego strumienia śladu spływowego na przejście laminarno-turbulentne w warstwie przyściennej na płaskiej płycie. Badania przeprowadzono w tunelu aerodynamicznym o niskim poziomie turbulencji przepływu zewnętrznego, wykorzystując technikę fazowego uśredniania i analizy falkowej. Stwierdzono istnienie poważnych różnic między oddziaływaniem ujemnego i dodatniego strumienia w postaci silnych impulsów prędkości pojawiających się w obszarze za ujemnym strumieniem w miejscu o lokalnego minimum prędkości. Za dodatnim strumieniem takie silne zaburzenia pojawiają się później i nie bezpośrednio za nim. Ponadto regiony uspokojenia za dodatnim strumieniem, dobrze znane z literatury, są dobrze widoczne także w rejonie całkowicie zaburzonego przepływu.

5

Extended Reynolds analigy for different flow conditions of the heated plate

Wierciński Z., Kaiser M., Żabski J.

Prace Instytutu Lotnictwa

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2007

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Nr 4(191)

83-91

EN

The investigation of the extended Reynolds analogy of the transitional boundary layer on the heated plate with different onflow condition was carried out. The coefficients of intermittency were determined on the basis of the tree-parametric cumulative distribution function of Weibull using the local shear stress Cf and Stanton number St distributions along the plate which are experimentally measured. For the unsteady flow with wakes the extended Reynolds analogy coefficient s is equal to 1.10 while for the flow without unsteadiness it is equal to 1.0. Finally, using the cumulative distribution function of Weibull the formula was proposed for the Prandtl number distribution in the region of laminar-turbulent transition.

PL

W pracy przedstawiono rezultaty badań rozszerzonej analogii Reynoldsa w warstwie przyściennej na grzanej płycie w różnych warunkach jej opływu. Na podstawie pomiarów lokalnego współczynnika oporu Cf oraz liczby Stantona wzdłuż płyty w strumieniach o różnym poziomie turbulencji wyznaczono rozkład współczynnika intermitencji jako trójparametrowej dystrybuanty rozkładu Weibulla. Dla niestacjonarnego przepływu ze śladami spływowymi wartość współczynnika rozszerzonej analogii Reynoldsa wynosi 1.10, zaś w pozostałych badanych przypadkach wartość tego współczynnika wynosi 1. Ponadto, zaproponowano zastosowanie rozkładu współczynnika intermitencji w postaci dystrybuanty trójparametrowego rozkładu Weibulla do wyznaczenia rozkładu liczby Prandtla w obszarze przejścia laminarno-turbulentnego w warstwie przyściennej dla przepływów o różnym poziomie niestacjonarności.