On moving heat sources

The two-dimensional thermal problem due to relative motion of a medium and a suddenly activated circular heat source is solved for several boundary conditions. The solutions can be interpreted as for a moving heat source in a stationary medium or a medium moving past a stationary heat source. Uniform and non-uniform temperature, and uniform and non-uniform heat flux boundary conditions are considered. The effect of velocity and radial direction on the temperature distribution is examined. Average, steady-state Nusselt numbers are derived. The transient response of a continuous line source is obtained as a limiting case of the prescribed heat flux solution. Received on 24 September 1996     

Use of compression wave focusing for the production of a superjet

The principle of focusing compression waves by their reflection from nonflat surfaces is well-known. The invention in [1] postulates for this purpose the use in a pulsed hydrojet of a piston with a specially shaped surface. In this paper, the use of focusing is investigated numerically for the production of superjets.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 153–156, September–October, 1976.     

Fatigue crack growth rate in ferrite-martensite dual-phase steel

An empirical study is made on the fatigue crack growth rate in ferrite-martensite dual-phase (FMDP) steel. Particular attention is given to the effect of ferrite content in the range of 24.2% to 41.5% where good fatigue resistance was found at 33.8%. Variations in ferrite content did not affect the crack growth rate da/dN when plotted against the effective stress intensity factor range ΔK_eff which was assumed to follow a linear relation with the crack tip stress intensity factor range ΔK. A high ΔK_eff corresponds to uniformly distributed small size ferrite and martensite. No other appreciable correlation could be ralated to the microstructure morphology of the FMDP steel. The closure stress intensity factor K_cl, however, is affected by the ferrite content with K_cl/Kmax reaching a maximum value of 0.7. In general, crack growth followed the interphase between the martensite and ferrite.Dividing the fatigue crack growth process into Stage I and II where the former would be highly sensitive to changes in ΔK and the latter would increase with ΔK depending on the R = σ_min/σ_max ratio. The same data when correlated with the strain energy density factor range ΔS showed negligible dependence on mean stress or R ratio for Stage I crack growth. A parameter α involving the ratio of ultimate stress to yield stress, percent reduction of area and R is introduced for Stage II crack growth so that the da/dN data for different R would collapse onto a single curve with a narrow scatter band when plotted against αΔS.     

Finite element stability analysis of pre-twisted Beck's column

Summary This paper presents a stability and vibration analysis of a pre-twisted cantilever column subjected to vertical and follower loads at its free end. The investigation is carried out using finite element modelling where the effects of transverse shear deformation and rotatory inertia are taken into account in deriving the element matrices. By using the assembly procedure and imposing the boundary conditions, a relationship between the load and vibration frequency is obtained. The critical, divergence and flutter, loads are calculated by evaluating the relationship and shown in figures for various values of non-conservativeness parameter, of twist angle, and those of rigidity ratio.

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Untersuchung der Stabilität des verwundenen Beck-Stabes mit Finiten Elementen

Übersicht Dieser Aufsatz stellt eine Stabilitäts- und Schwingungsuntersuchung des vorverwundenen, einseitig eingespannten Stabes dar, der an seinem freien Ende vertikalen und mitgehenden Lasten ausgesetzt ist. In der Untersuchung wird die Methode der finiten Elemente angewendet, und in der Herleitung der Elementmatrizen werden die Einflüsse der Schubspannungen infolge der Querkraft und der Rotationsträgheit berücksichtigt. Eine Beziehung zwischen der Last und der Schwingungsfrequenz wird dadurch ermittelt, daß man die Gesamtssystemmatrix bildet und die Randbedingungen anwendet. Durch die Auswertung der Beziehung werden die kritischen Divergenz- und Flatterlasten für verschiedene Werte des Nichtkonservativitätsparameters, des Verwindungswinkels und des Steifigkeitsverhältnisses ermittelt und in Bildern dargestellt.

     

The two-dimensional velocity shift caused by the use of a rotating mirror in PIV flow field measurements

A theoretical analysis of the two-dimensional velocity shift by the use of a rotating mirror in PIV flow field measurements has been carried out by the application of ray optics. The velocity shift has been calculated directly in the flow field co-ordinates. In dimensionless form the results are also available in the image plane. It is shown that the distribution of the velocity shift over the entire observation field may not usually be assumed to be uniform (and may vary by up to 20%). The effect of the layout and arrangement of the rotating mirror on the velocity shift and its distribution has been analysed. In addition, the sensitivity of the velocity shift to the design tolerances and imperfections of the rotating mirror is given.     

Probe diagnosis of a flow of particles desorbed from the surface of a solid by a low-density plasma jet

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 5, pp. 144–150, September–October, 1993.     

Pool boiling from GEWA surfaces in water and R-113

Pool boiling heat transfer measurements are reported for water and R-113 with several horizontal cylindrical test sections: plain, T-finned GEWA-T (with various gaps) and standard low fin GEWA-K. With R-113 the enhancement is a well-behaved function ofS _T , reaching a maximum of 2 atS _T = 0.25 mm. With distilled water, the performance depends in a more complex way on gap width. The maximum enhancement of 1.6 is obtained atS _T =0.35 mm. Visual observations of the actual test sections and models indicated a complex liquid-vapor exchange mechanism. Bubble generation with adjacent liquid feed was observed at random locations around the periphery of the test section. A semi-theoretical equation was developed which correlates the experimental data quite well.

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Sieden bei freier Konvektion von GEWA-Oberflächen in Wasser und R-113

Zusammenfassung Es wird über Wärmeübergangsmessungen beim Sieden unter freier Konvektion mit Wasser und R-113 an verschiedenen zylindrischen, horizontal angeordneten Versuchsobjekten berichtet, die folgende Oberflächenbeschaffenheiten hatten: glatt, T-berippt GEWA-T (mit unterschiedlichen Abständen) und serienmäßig mit niedrigen Rippen versehen GEWA-K. Bei R-113 ist die Verbesserung im Wärmeübergang eine erwartungsgemäße Funktion vonS _T , die einen Maximalwert von 2 beiS _T =0,25 mm erreicht. Bei destilliertem Wasser hängt das Verhalten in komplizierter For von der Lückenweite ab. Die maximale Verbesserung liegt bei 1,6 und wird fürS _T =0,35 mm erreicht. Optische Beobachtungen an den Versuchsobjekten und Modellen zeigten einen komplizierten Flüssigkeits-Dampf-Austauschmechanismus. Es wurde Blasenbildung mit benachbartem Flüssigkeitszustrom an willkürlich wechselnden Stellen um die Peripherie des Versuchsobjektes beobachtet. Eine halbtheoretische Gleichung wurde entwickelt, welche die experimentellen Daten gut wiedergibt.

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Nomenclature A surface area - A _t tunnel/channel wall area - A liquid film area - C _q constant in natural convection correlation - C _T constant in GEWA-T Model - D outside diameter - D _b base diameter (fin root diameter) - D _tc diameter at thermocouple location - h heat transfer coefficient - h _fg latent heat - h _t heat transfer coefficient at the tunnel wall - k _l thermal conductivity of liquid - L length of test section - N _A number of active nucleation sites - ql latent heat transfer rate - q heat flux - q_ex natural convection heat flux - q latent heat flux - S _t GEWA-T gap width - T wall-minus-saturation temperature difference - T _gn vapor temperature - T _s saturation temperature - T _w wall temperature - x, y constants in natural convection correlation - liquid film thickness - surface tension Dedicated to Prof. Dr.-Ing. U. Grigull's 75th birthday     

Burnett simulation of flow and heat transfer in micro Couette flow using second-order slip conditions

The conventional Burnett equations with second-order velocity slip and temperature jump conditions were applied to the steady-state micro Couette flow of a Maxwellian monatomic gas. An analytical approach as well as a relaxation method was used to determine the velocity slip and temperature jump at the wall. Convergent solutions to the Burnett equations were obtained on arbitrary fine numerical grids for all Knudsen numbers (Kn) up to the limit of the equations’ validity. The Burnett equations with second-order slip conditions indicate a much better agreement with DSMC data over the first-order slip conditions at high Kn. The convergent Burnett solutions were obtained in orders of magnitude quicker than that with the corresponding DSMC simulation. The augmented Burnett equations were also introduced to model the flow but no obvious improvement in the results was found.