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- Wärmeübertragung (2)
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Structured sheets have addition to increased bending
stiffness considerable potential for lightweight. Unsteady turbulent flows around the plain and hexagonal sheets were
analyzed numerically and experimentally in order to determine the heat transfer intensity between sheet surfaces and surrounding air flows. To obtain experimental results for later validations of numerical results, a measurement facility was designed and constructed. Flow patterns around metal Sheets were measured under various flow conditions e.g. the effects of different temperatures, heating powers and flow velocities on the
heat transfer intensity were studied. Numerically provided results demonstrated a good match between theoretical calculations and experiments. For all investigated patterns, the structured hexagonal sheets achieved significantly higher heat Transfer intensity than the plain sheets.
Unsteady turbulent flows with solid particles of different sizes in the cyclone were studied numerically and experimentally. The grid studies and influence of the boundary condition prescription on the flow behavior in the cyclone and the effectiveness of the particle separation were studied firstly numerically.
The turbulent flow was calculated by means of Large Eddy Simulations and this flow problem was calculated parallel using eight processors. It was found theoretically that pressure at the bottom outlet of the cyclone has a significant impact on the particle separation. This impact of the pressure at the cyclone function was examined also using experiments and pressure distributions for different flow rate intensities for several locations in the cyclone were determined. These experimental results can be used for a validation of numerical results. Furthermore, the larger losses were observed in the immersion tube due to higher flow velocity and impulse exchange in the vortex core.
В статье приведены результаты исследования производственных допусков при водоструйной резке методом трехмерных (3D) измерений: отклонения формы были показаны путем трехмерного справнения отсканированных образцов. Размеры были измерены также с использованием двухмерных (2D) срезов отсканированных образцов. Определено, что чистая водоструйная резка имеет тенденцию отделять мягкие материалы, такие как пластмасса, фольга, пена или бумага, а также пища. В отличие от чистой водоструйной резки, абразивная резка используется для твердых материалов, таких как сталь, керамика, стекло. Вычислено оптимальное давление для обработки материалов. Особое значение уделено разделению композитных материалов, которое не может быть удовлетворительно осуществлено с использованием обычных методов.
This paper investigates experimentally and numerically the aero-acoustic noise generated by airflow around sheet metals with periodic hills of three different geometries named KMT, PWO and WAB used in automotive industry.
Each sheet was tested experimentally in a wind tunnel at airflow of free-stream-velocity of 18 m/s and Reynold’s number based on the respective sheet thickness in the range of 1800-4200. The experiment was based on measuring the aero-dynamic sound generated by each sheet using a microphone. Moreover, it was based on measuring the velocity fluctuation after the sheets trailing edge by a Hot Wire Anemometer (HWA). Finally, an acoustic camera was used to locate the locations of sound sources in the flow. On the other hand, the numerical analysis used turbulence model as Large Eddy Simulation with Kinetic Energy Transport as a sub-grid model. Ffowcs-Williams & Hawkings model was used to predict the acoustic sources.
Agreements were found between the trend of acoustic noise
produced from experiment and numerical simulation over some
ranges of frequency. The experiment has showed that the three
sheets had comparable sound pressure level over the whole
spectrum while the numerical results have showed that KMT
sheet has achieved significant loudness at frequencies under 400
Hz while the WAB sheet has achieved significant quietness at
frequencies below 400 Hz. The velocity contours obtained from
the simulation showed that flow is laminar over some length
before it changes to turbulent at a transition point. This
behavior agrees with other data presented for long sheets
subjected to flow of similar values of Reynolds Number.
Das Ziel der Untersuchung ist die Entwicklung eines neuen Konzeptes für Wärmetauscher sowie die experimentellen und numerischen Untersuchung an den wärmeübertragenden Flächen. Für die experimentelle Untersuchung wurde eine neue Messanlage gebaut und die Untersuchungsverfahren für die thermodynamischen Tests definiert. Die Strömung mit Wärmeübergang wurde mit der Hilfe der numerischen Simulation untersucht. Die Ergebnisse wurden mit den experimentellen Ergebnissen vergleichen und zeigten eine hohe Übereinstimmung. Außer den thermodynamischen Untersuchungen wurden auch Studien der Luftqualität durchgeführt. In diesem Fall geht es um eine numerische Studie zur CO2 Verteilung im Raum. Eine niedrige erforderliche Frischluftzufuhr führt oft zu einem niedrigen Energieverbrauch