rodzaj: materiały konferencyjne w czasopiśmie

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rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: Plate-fin and tube heat exchangers (PFTHE) are made of round, elliptical, oval or flat tubes to which continuous fins (lamellas) are attached. Liquid flows inside the tubes and gas flows outside the tubes perpendicularly to their axes and parallel to the surface of continuous fins. Experimental studies of multi-row plate-fin and tube heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes when the air velocity in front of the exchanger is less than approximately 3.5 m/s when a Reynolds number based on an equivalent hydraulic diameter equal to the distance between tube rows in the direction of air flow is less than 10,000. In the subsequent rows of tubes up to about the fourth row the heat transfer coefficient decreases. In the fifth and further rows, it can, that the heat transfer coefficient is equal in each tube row. It is necessary to find the relationships for the air-side Nusselt number on each tube row to design a PFTHE with the appropriate number of tube rows. The air-side Nusselt number correlations can be determined experimentally or by CFD modeling (Computational and Fluid Dynamics). The paper presents a new mathematical model of the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are different. The heat transfer coefficient on an analyzed tube row was determined from the equality condition of mass- average air temperature differences on a given tube row determined using the analytical formula and CFD modeling. The results of numerical modeling were compared with the results of the experiments.]]>

rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: Aeroelastic properties, such as free vibrations of multilayered composite cylindrical shells, are investigated in the present paper. It is well known that the eigenmode (eigenvalue) analysis is a crucial point in the estimations/calculations of the divergence and flutter speeds characterizng dynamic instability. In this study the maximization problem of eigenfrequencies and eigenmodes is discussed, especially from the point of view of stacking sequences of composite panels. A special attention is focused on two types of the shell wall construction: a) angle-ply ±θ and b) symmetrical discrete laminates built of layers oriented at 0, ±45 and 90. The analytical formulae is derived with the use of the Rayleigh-Ritz method for simply supported cylinders. It allows us to solve the optimum problem easily for angle-ply fibre orientations. For symmetrical laminates with discrete fibre orientations the optimal solutions are searched for using finite element analysis combined with genetic or evolutionary algorithms. The influence of geometrical parameters describing the cylindrical panel is also demonstrated herein. ]]>

rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: The paper presents an innovative solution of the self-adjusting system of the wind turbine with horizontal axis, consisting of two-blade, carousel rotor with vertical axis and twoposition self-adjusting mechanism. The procedure of computing power and propeller torque of rotor with self-adjusting system as a function of the angle of wind attack, the design and principles of operation of the adjusting turbine were presented. And also the proposal to use it as a self-adjusting system on the wind direction and at the same time as a protection of the main rotor HAWT (Horizontal Axis Wind Turbine) against excessive speed in strong winds. The proposed system can replace the most common solution like the directional rudder or the auxiliary wind motor, which generally requires the generator rotor brake.]]>

rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: This work concerns atomic potentials applied in the description of carbon nanotubes mechanical behavior. The explicit relations of interatomic forces for different interatomic potentials have been derived. The fluctuations in the values of interatomic potential, interatomic force, elastic constant and Young’s modulus have been put forward to elucidate the similarities and differences between potentials. The present analysis may be helpful in the equivalent continuum modelling of carbon nanotubes and nanocomposites.]]>

rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: The buckling loads and the post-buckling behavior of the perfect and imperfect delaminated plate are investigated in the paper. For this purpose the concise formulations enabling to derive pre- and post-buckling behaviour of plates with embedded delaminations is presented. The computations are made using FE package NISA II and Mathematica package. Obtained results for buckling loads and the post-buckling behaviour are compared with the experimental results. The Digital Image Correlation (DIC) technique is employed to verify the uniformity and homogeneity of deformations. ]]>

rodzaj: materiały konferencyjne w czasopiśmie

Abstrakt: This paper proposes an e ective method for determining thermal stresses in structural elements with a three-dimensional transient temperature field. This is the situation in the case of pressure elements of complex shapes. When the thermal stresses are determined by the finite element method (FEM), the temperature of the fluid and the heat transfer coefficient on the internal surface must be known. Both values are very difficult to determine under industrial conditions. In this paper, an inverse space marching method was proposed for the determination of the heat transfer coefficient on the active surface of the thick-walled plate. The temperature and heat flux on the exposed surface were obtained by measuring the unsteady temperature in a small region on the insulated external surface of a pressure component that is easily accessible. Three di erent procedures for the determination of the heat transfer coefficient on the water-spray surface were presented, with the division of the plate into three or four finite volumes in the normal direction to the plate surface. Calculation and experimental tests were carried out in order to validate the method. The results of the measurements and calculations agreed very well. The computer calculation time is short, so the technique can be used for online stress determination. The proposed method can be applied to monitor thermal stresses in the components of the power unit in thermal power plants, both conventional and nuclear.]]>