Numerical simulation of forced convection over a periodic series of rectangular cavities at low Prandtl number

Convective heat transfer in laminar conditions is studied numerically for a Prandtl number Pr = 0.025, representative of liquid lead–bismuth eutectic (LBE). The geometry investigated is a channel with a periodic series of shallow cavities. Finite-volume simulations are carried out on structured orthogonal curvilinear grids, for ten values of the Reynolds number based on the hydraulic diameter between Re_m = 24.9 and Re_m = 2260. Flow separation and reattachment are observed also at very low Reynolds numbers and wall friction is found to be remarkably unequal at the two walls. In almost all cases investigated, heat transfer rates are smaller than the corresponding flat channel values. Low-Prandtl number heat transfer rates, investigated by comparison with Pr = 0.71 results, are large only for uniform wall temperature and very low Re. Influence of flow separation on local heat transfer rates is discussed, together with the effect of different thermal boundary conditions. Dependency of heat transfer performance on the cavity geometry is also considered.     

A Highly Luminescent Tetrahydrocurcumin IrIII Complex with Remarkable Photoactivated Anticancer Activity

Curcumin has chemopreventative properties against a variety of tumours, but has poor bioavailability. Here, two new bis-cyclometallated iridium(III) complexes have been prepared, featuring the natural product curcumin (CUR) or its reduced form, tetrahydrocurcumin (THC), as bidentate, anionic O O-binding ligands. The iridium THC complex is highly luminescent in deoxygenated solution and efficiently generates singlet oxygen under aerated conditions, whereas in the CUR analogue, other non-radiative decay pathways are competitive. The complexes are rapidly taken up by a variety of human tumour cell lines from solutions of micromolar concentration. They show negligible cytotoxicity in the absence of irradiation. When briefly irradiated with visible light, Ir-THC becomes highly phototoxic, inducing rapid apoptosis within 2 h. The results show the high potential of such complexes as sensitizers in photodynamic therapy (PDT).     

On the generalized mean curvature

We study some properties of graphs whose mean curvature (in distributional sense) is a vector Radon measure. In particular, we prove that the distributional mean curvature of the graph of a Lipschitz continuous function u is a measure if and only if the distributional divergence of T u is a measure. This equivalence fails to be true if Lipschitz continuity is relaxed, as it is shown in a couple of examples. Finally, we prove a theorem of approximation in W ^(1,1) and in the sense of mean curvature of C ² graphs by polyhedral graphs. A number of examples illustrating different situations which can occur complete the work.     

On sets with variational mean curvature in L^{n}(\mathbf{R}^{n})

In this paper we give an example of a singular set with finite perimeter in the plane which is a subgraph with variational curvature in $L^2(\mathbf R ^2)$ . This is a extension to the class of graphs of a well celebrated example suggested by De Giorgi, where the boundary of the set was the union of two spiral curves.     

Experimental investigation of combined forced and free convection in horizontal and inclined tubes

Summary This investigation considers the effects of free convection on the laminar flow of water through a circular duct having essentially constant wall heat transfer rate per unit length of the duct and circumferentially uniform wall temperature. The effect of the Reynolds and Rayleigh number variations on heat transfer results has been analysed for both horizontal and inclined pipe. The experiment has covered the range of the inlet Reynolds number from 200 to 2300, and of the Rayleigh number from 6,000 to 70,000. The effect of pipe inclination has been investigated for slope angle values up to 60°, with laminar ascending flow.

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Sommario L'indagine é volta alla determinazione sperimentale dei coefficienti di scambio termico in regime di convezione mista per acqua in moto laminare entro un condotto a sezione circolare. Allo scopo di consentire il confronto dei risultati con le previsioni teoriche, l'esperienza è stata condotta cercando di approssimare le condizioni al contorno di flusso termico uniforme lungo l'asse del tubo e di temperatura uniforme in senso circonferenziale. La dipendenza dei coefficienti di scambio termico dai numeri di Reynolds e di Rayleigh è stata analizzata sia per condotto orizzontale che inclinato. La sperimentazione ha coperto il campo di valori compreso tra 200 e 2300 del numero di Reynolds all'ingresso, e tra 6000 e 70000 del numero di Rayleigh. L'influenza dell'inclinazione sullo scambio termico è stata esaminata, per moto laminare ascendente, tra 0 e 60° sull'orizzontale.

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Research supported by C.N.R., grant no. 81.002.77.07.