Mixed convection over a semi-infinite horizontal plate

Mixed convection over a horizontal plate has been studied by the method of series truncation for the two cases where the buoyancy effects aid and oppose the main flow. From the Navier-Stokes equations in parabolic coordinates the equations for the first truncation are obtained. The numerical results show that the predictions are very accurate for heat transfer over the entire mixed convection domain. The skin friction predictions are accurate only for moderately large buoyancy effects. In the buoyancy dominated flow the heat transfer is over estimated by four percent and skin friction by thirty percent.

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Zusammenfassung Gemischte Konvektion entlang einer horizontalen Platte wurde untersucht mit Hilfe der Methode der abgebrochenen Reihen. Die beiden Fälle in denen der Auftrieb die Hauptströmung unterstützt und behindert wurden betrachtet. Die Reihen wurden von den Navier-Stokes'schen Gleichungen in parabolischen Koordinaten erhalten. Die numerischen Ergebnisse sind sehr genau für den Wärmeübergang im ganzen Gebiet der gemischten Konvektion. Die Wandreibung wird nur im Falle von mässig grossen Auftriebseffekten genau vorausgesagt. Bei grossem Auftrieb wird der Wärmeübergang um vier Prozent und die Reibung um dreissig Prozent überschätzt.

     

N-methylation of etioporphyrin I and octaalkyl-5-azaporphyrins : X-ray structure of trans-Na,Nb-dimethyletioporphyrin I triiodide

Improved procedures are reported for the preparation of mono-, di- and tri-N-methyl-etioporphyrin I. Demethylation of N_a, N_b, N_c-trimethyletioporphyrin I under acidic, basic or thermal conditions gives N_a, N_b-dimethyl etioporphyrin I. N-Methylation of octaalkyl-5-azaporphyrins leads, in general, to mixtures of the isomeric mono-, di- and tri-N-alkylated 5-azaporphyrins. An X-ray crystal structure of N_a,N_b-dimethyl etioporphyrin I triiodide confirms the trans arrangement of the N-Me groups. The two N-methylated pyrrole rings are twisted 27° to each other.     

Vibrational Dynamics and Heat Capacity of Trans‐1,4‐Polyisoprene (α‐Form)

Vibrational dynamics of the α‐polymorphic form of trans‐1‐4‐polyisoprene is described using Higg's method and the Urey‐Bradley force field. Characteristic features of dispersion profiles such as repulsion and bunching are reported. A comparison with the β‐form is presented and possible reasons for variation in heat capacity are discussed.     

Forced convection over a semi-infinite flat plate

The problem of forced convection heat transfer over a semi-infinite flat plate is treated by the method of series truncation, so as to yield results valid from leading edge to far downstream (0 < -R ₀< ∞). Results are presented for Prandtl number Pr = 0.1, 0.7, and 10. It is found that the effect of leading edge on heat transfer is smaller than on skin friction.     

Synthesis and characterization of nano-structured Th1?x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m²/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm³/g.     

Mixed convection over a semi-infinite vertical flat plate

The problem of mixed convection over a semi-infinite vertical flat plate is studied by the method of series truncation for both cases when buoyancy adds and opposes the main flow. The present analysis is valid from leading edge to far downstream. The solutions show that the results are very accurate over an entire flow regime spanning from pure forced convection to moderately large free convection flows. In the buoyancy dominated limit the heat transfer is underestimated by 4 percent and skin friction is overestimated by 22 percent.

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Zusammenfassung Das Problem der gemischten Konvektion entlang einer vertikalen ebenen Platte wurde untersucht mit Hilfe der Methode der abgebrochenen Reihen, um Ergebnisse für kleine und mittlere Reynoldszahlen zu geben, verglichen mit den Grenzschicht-Resultaten in der Literatur, die fürRe gültig sind. Es wurde gefunden, dass die Methode gute Ergebnisse gibt für alle drei Regionen (erzwungene Konvektion dominierend im Nahgebiet, freie Konvektion dominierend im Ferngebiet, und das Zwischengebiet) in die das Strömungsfeld bei Grenzschichtrechnungen aufgeteilt worden ist; nicht nur für genügend grosseR _x sondern auch für sehr kleine Werte vonR _x .