This paper introduces research and development of a modern non-invasive device for determining flows and velocity fields. This device is based on the ultrasonic method. The measured fluid flow is surrounded by appropriate ultrasonic transmitters and receivers, which communicate with each other. A physical principle of this method consists in an interaction of sound waves with a flow, which generates a certain delay in sound waves transmission. The found quantity is thus time delay. The device is being designed as a flowmeter and with advanced and extended postprocessing as a tomograph, which reconstructs a 3D vector field for big volumes. This whole process requires the following: development of an appropriate design of the ultrasonic flowmeter and tomograph, testing the signal transfer and also various postprocessing methods on a measurement accuracy, building of a special verification experimental equipment and building of an electronic device as a control unit and data acquisition system.
The shaft torque of a simple paddle mixer was measured when mixing granular materials in a cylindrical vessel in dependence on the material properties and certain geometrical parameters. The results were correlated semi-empirically and relations were found for determining the critical depth and critical moment of the granular bed. A dimensionless equation was found by dimensional analysis for determining the shaft torque of the mixer for subcritical depths of bed and by extrapolation to blades of infinitely large diameter the correctness of the derivation was shown.The shaft torque required in mixing granular materials is important not only in designing mixing equipment but also yields information about the force relations in the granular material. There are only a few articles in the literature dealing with this problem: Weighardt\ Iiyama and Aoki2, Lastovcev and Chvalnov 3 .The main contribution of this paper consists in using the theoretically derived value of the stress on the mixer blade in deriving . the semi-empirical correlations. This stress was obtained from the shapes of the slip surfaces in the vicinity of the blade 4 . Further the interesting concept of the critical depth of the granular bed and the corresponding critical torque are introduced.
Experimental
ApparatusFor the experimental work we modified a drill press (Fig. 1) to serve as the basis of the mixing unit. The mixer shaft 1 was driven by an el-motor 9. The system of V-belt transmissions enabled us to change the shaft rpm's over the range 1 to 400 rpm. The mixing shaft torque was measured indirectly by measuring the torque exerted on the mixing vessel 1 0 which was mounted on the rotable shaft 3. The principle of measuring the torque by a balance is clear from the figure. The
Abstract.This article deals with numerical investigation of flow in plate heat exchangers. These are counterflow heat exchangers formed by plates. These plates are shaped by the ridges to intensify heat transfer. The objective of the work is the investigation of effect of straight oblique triangular ridges for increasing of heat transfer and pressure losses. The ridges on adjacent plates intersect and thus form a channel of complex shape. The research includes various types of ridges with different fillets and ridges spacing.The work also investigates the number of ridges that is necessary for optimization calculations. Obtained data are analysed and the heat transfer coefficient and pressure loss are evaluated. Conclusion describes the effect of fillets, ridges pitch and number of ridges.
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