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The combined effect of NaCl salinity and iron deficiency on biomass production, iron homeostasis, photosynthetic activity and antioxidant status were studied in Foeniculum vulgare: a biannual Apiaceae with pastoral potential. Plants were grown in hydroponic conditions for 21 days under two concentration of iron: 1 (low) or 40 µM Fe3+-EDTA (sufficient), in the absence or presence of 75 mM NaCl. When individually applied, both Fe deficiency and salinity notably restricted shoot and whole dry weight (DW) with a more marked effect under combined stresses. This may linked to a significant decrease in stomatal conductance, CO2 assimilation rate (84%) and transpiration rate (66%). Although, the relatively better tolerance to Fe deficiency combined with salinity could be explained by the capacity of this species to maintain higher root system and root/shoot DW ratio. Salinity has a negative impact on Fe-use efficiency (24%) when combined with a low Fe supply that means that iron is primarly used in shoot sodium (Na+) excretion. Phenolic analysis showed the relevance of caffeic and cinnamic acid derivatives in leaves and roots proving their modulation under D and (D + S) treatments. Antioxidant activities as well as inhibitory capacity towards LOX enzyme were ound to be altered under D and (D + S) conditions as rescued by the lowest IC50 and EC50 values. Overall, F. vulgare constitues a promising model to ameliorate the tolerance of the cultivated fennel species under low Fe soils and/or saline regions. [ABSTRACT FROM AUTHOR]

This paper deals with an experimental study of heat transfer in a Poiseuille-Rayleigh-Bénard flow. This situation corresponds to a mixed convection phenomenon in a horizontal rectangular channel uniformly heated from below. Flow visualisation and temperature measurements were achieved in order to describe the flow regimes and heat transfer behaviour. The classical measurement techniques such employing thermocouples give local measurement on one hand and on other hand they often disturb the flow. As the flow is three-dimensional, these techniques are not efficient. In order to not disturb the flow, a non-intrusive method is used for thermal measurement. The Planar laser Induced Fluorescence (PLIF) was implemented to determine thermal fields in the fluid. Experiments conducted for various Reynolds and Rayleigh numbers allow to determine the heat transfer and thus to propose correlation for Nusselt number for a mixed convection flow in Poiseuille-Rayleigh-Bénard configuration. First a description of the use of this technique in water flow is presented and then the obtained results for various Reynolds and Rayleigh numbers allow to propose a correlation for the Nusselt number for such configuration of mixed convection. The comparison between the obtained heat transfer and the pure forced convection one confirms the well-known result that the convective heat transfer is greatly enhanced in mixed convection. Indeed, secondary flow induced by buoyant forces contributes to the refreshment of thermal boundary layers and so acts like mixers, which significantly enhances heat transfer. [ABSTRACT FROM AUTHOR]

This paper deals with a mixed convection water flow in a horizontal rectangular duct, uniformly heated from one lateral vertical wall and thermally insulated elsewhere. The supplied heat flux induces a secondary flow, which structure is constituted of one longitudinal roll in the considered aspect ratio (Γ = 1.9), embedded into a return flow of possibly large stream wise extension (up to twenty channel heights). Such situation induces helicoidal trajectories for the fluid flow particles, which contributes to a heat transfer enhancement compared to purely forced convection flow. [ABSTRACT FROM AUTHOR]

comprehensive numerical study was carried out to study the thermal performances of a solar collector equipped with partitions attached to its glass cover. This technique is used to favorise and increase the heat transfer coefficient between the working fluid, (air) and the absorber in the solar collector. A specifically developed numerical model based on the finite-volume method and the SIMPLER algorithm is used for the solution of the mass, momentum and energy transfer governing equations. The discretized equations are solved iteratively by an algorithm based on a preconditioned conjugate gradient method. Concerning the radiation exchange, we consider that the working fluid is transparent, so only the solid surfaces contribute to the radiation exchange and assumed to be diffuse-gray. A complete parametric study is made for various partitions length Lp, aspect ratio A and Rayleigh numbers Ra for Prandtl number Pr = 0.71. Results are reported in terms of isotherms, streamlines and average Nusselt-numbers along the absorber plate. [ABSTRACT FROM AUTHOR]

A study of dynamic regimes in Bénard-Marangoni convection was carried out for various Prandtl and Marangoni numbers in small aspect ratio geometries (Γ = 2.2 and 2.8). Experiments in a small hexagonal vessel, for a large range of the Marangoni number (from 148 to 3636), were carried out. Fourier spectra and an auto-correlation function were used to recognize the various dynamic regimes. For given values of the Prandtl number (Pr = 440) and aspect ratio (Γ = 2.2), mono-periodic, bi-periodic and chaotic states were successively observed as the Marangoni number was increased. The correlation dimensions of strange attractors corresponding to the chaotic regimes were calculated. The dimensions were found to be larger than those obtained by other authors for Rayleigh-Bénard convection in aspect ratio geometries of the same order. The transition from temporal chaos to spatio-temporal chaos was also observed. For Γ = 2.2, when larger values of the Marangoni number were imposed (Ma = 1581 for Pr = 160 and Ma = 740 for Pr = 440), spatial modes were involved through the convective pattern dynamics. [ABSTRACT FROM AUTHOR]

The aim of this paper is to show the effect of secondary flows caused by natural convection on the laminar-turbulent hydrodynamic transition. It is not a question of measuring a critical threshold value of Reynolds number of transition but only to estimate the degree of turbulence in the transition regime, i.e. weak turbulence in the case of superposition (mixed convection) or not (forced convection) of secondary flows on the forced flow. This is possible thanks to the application of the wavelet transform. The calculation of the Hölder exponent, associated with the maximum value of the singularity spectrum for two configurations, vertical (forced convection) and horizontal (mixed convection) allows the degree of turbulence to be measured in both cases. The variation of the Hölder exponent versus the Reynolds number has enabled it to be shown that the secondary flows stabilise the main flow and stifle the beginnings of the turbulence during the regime of transition to turbulence; these kinds of results have also been shown in literature. Generally, large-sized secondary flows (for example Dean's flows) stabilise the turbulence. Our work confirms this, through an experiment carried out in identical conditions for mixed convection (horizontal flow) and forced convection (vertical flow). [ABSTRACT FROM AUTHOR]