Heat transfer and flow of a thermodependent and yield stress fluid

In this paper, we study the flow of a fluid possessing a yield stress, in a cylindrical pipe being the wall heated with a constant flux; experimental and numerical results being presented here. We are interested in the influence of the different parameters on the Nusselt number, and in the pressure variation. We propose a model which enables us to estimate the Nusselt number and pressure variation, which takes into account the variation of the physical properties due to temperature variations. The proposed correlations agree well with experimental measurement.

---

Wärmeübertragungs- und Strömungsverhalten eines Fluids mit temperatur- und scherspannungsabhängigem Fließvermögen

Zusammenfassung In dieser Arbeit wird das Strömungsverhalten eines Fluids mit temperatur- und scherspannungsabhängigem Fließvermögen in einem mit konstanter Wärmestromdichte beaufschlagten Kreisrohr untersucht. Hierbei fallen experimentell und numerisch gefundene Ergebnisse an. Besonders interessiert der Einfluß verschiedener Parameter auf die Nusselt-Zahl und den Druckverlust. Es wird ein Modell zur Berücksichtigung der Auswirkung temperaturabhängiger Stoffwerte auf beide Intensitätsparameter vorgeschlagen. Die hieraus resultierenden Korrelationen stimmen gut mit den experimentellen Befunden überein.

---

Nomenclature a, b K =a e ^–bT - C f friction factor - C f* reduced friction factor - C _p specific heat capacity (J/Kg/°C) - D internal diameter (m) - h heat transfer coefficient (W/m² °C) - H free energy - Hb Herschel-Bulkley number - K fluid consistency (Pa · sⁿ) - L axial length (m) - mass flow (Kg · m^–3) - n flow behaviour index - Nu Nusselt number - p pressure (Pa) - Pe Peclet numberRe ·Pr=Re _g ·Pr _g - Pr Prandtl numberPr _g =kC _p / - Pr _g generalised Prandtl numberPr _g =kC _p /(U ₀/D ^n–1 - r radial coordinate (m) - R pipe radius (m) - R _c plug radius - Re Reynolds number - Re Metzner Reynolds number (Ostwald fluid) - Re _g generalised Reynolds number - Re _s Metzner Reynolds number (Herschel-Bulkley fluid) - t time (s) - T temperature (°C) - T _e entrance temperature (°C) - T _m mean temperature (°C) - T _p wall temperature (°C) - U ₀ mean velocity (m/s) - u axial velocity (m/s) - v radial velocity (m/s) - X ⁺ Cameron number - y, r radial coordinate (m) - z axial coordinate (m) Greek symbols R _c /R - exponent used forNu - shear rate (s^–1) - (3n + 1)/4n - * /((1 –a)) - thermal conductivity (W/m °C) - _a apparent viscosity (Pa · s) - density (kg/m³) - shear stress (Pa) - ₀ wall shear stress (Pa) - =b _p D/2 - _p heat flux (W/m²) - =1+2n/2n+1+2n ²/(2n+1)(n+1) ² - p*/z p*/z=p/z/p/z (isothermal) Indices p wall - i axial index - j radial index     

Understanding the interactions between artemisinin and cyclodextrins: spectroscopic studies and molecular modeling

Artemisinin extracted from Artemisia annua L. proved to be currently, with its derivatives, the most effective drugs against simple and severe malaria, and is also effective on the chloroquine-resistant forms. The advantageous effect of some cyclodextrins (CDs) on artemisinin solubilization was demonstrated by different authors. The present work aims to confirm the effect of several CDs on artemisinin solubilization and to analyse the complexes formed between these CDs and artemisinin in order to understand their solubilization capacities. In this context, solubility studies, liquid-state NMR spectroscopy (¹H NMR studies and ROESY experiments) as well as theoretical studies (molecular modeling) have been performed. Randomly methylated-βCD, Crysmeb^? and hydroxypropylated-γCD were also found to improve the aqueous solubilization of artemisinin as well as βCD, γCD and hydroxypropylated-βCD whose effects were already demonstrated. The best solubilization ability was found with Crysmeb^?. The spectroscopic studies showed a lot of interactions between artemisinin and all the CDs studied, but mainly outside the cavity. Molecular modeling confirmed that artemisinin and CDs formed non-inclusion complexes.     

Densitometric HPTLC Quantification of 2-Azaanthraquinone Isolated from Mitracarpus scaber and Antimicrobial Activity against Dermatophilus congolensis

JPC – Journal of Planar Chromatography – Modern TLC - 2-Azaanthraquinone (benzo[g]isoquinoline) isolated from Mitracarpus scaber has been found to have in-vitro antimicrobial activity...