Effect of the angle of attack of a rectangular wing on the heat transfer enhancement in channel flow at low Reynolds number

Convective heat transfer enhancement can be achieved by generating secondary flow structures that are added to the main flow to intensify the fluid exchange between hot and cold regions. One method involves the use of vortex generators to produce streamwise and transverse vortices superimposed to the main flow. This study presents numerical computation results of laminar convection heat transfer in a rectangular channel whose bottom wall is equipped with one row of rectangular wing vortex generators. The governing equations are solved using finite volume method by considering steady state, laminar regime and incompressible flow. Three-dimensional numerical simulations are performed to study the effect of the angle of attack α of the wing on heat transfer and pressure drop. Different values are taken into consideration within the range 0° < α < 30°. For all of these geometrical configurations the Reynolds number is maintained to Re = 456. To assess the effect of the angle of attack on the heat transfer enhancement, Nusselt number and the friction factor are studied on both local and global perspectives. Also, the location of the generated vortices within the channel is studied, as well as their effect on the heat transfer enhancement throughout the channel for all α values. Based on both local and global analysis, our results show that the angle of attack α has a direct impact on the heat transfer enhancement. By increasing its value, it leads to better enhancement until an optimal value is reached, beyond which the thermal performances decrease

Effect of rectangular winglet pair roll angle on the heat transfer enhancement in laminar channel flow

Convective heat transfer enhancement can be achieved by generating secondary flow structures that are added to the main flow to intensify the fluid exchange between hot and cold regions in the system. One method involves the use of vortex generators to produce streamwise and transverse vortices on the top of the main flow. This study presents numerical computation results on laminar convection heat transfer in a rectangular channel which bottom wall is equipped with rectangular winglet pair vortex generators. The governing equations are solved using finite volume method by considering steady state, laminar regime and incompressible fluid. Three dimensional numerical simulations are performed to study the effect of the generators\u27 roll-angle β on the flow and heat transfer characteristics. Different values of roll-angle β in the range [20°–90°] are considered, while maintaining a constant angle of attack (α = 30°) for all the cases. The influence of the Reynolds number is also studied for values 456 and 911 (based on the channel hydraulic diameter). Both local and global analyses of the thermal performances are carried out using parameters such as the Nusselt number and the friction coefficient. In addition, the position and strength of the longitudinal vortices created are presented and discussed, highlighting their effect on the heat transfer rates throughout the duct, for the various generators\u27 roll-angles. Finally, from both local and global investigations, it is found that the optimal values of the roll-angle, determined for each Reynolds number, are not necessarily 90°, which corresponds to the widely used configuration in the open literature

Effect of the angle of attack of a rectangular vortex generator on the heat transfer in a parallel plate flow

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Heat transfer enhancement in channel flow downstream a rectangular winglet pair vortex generator

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Intensification des transferts par génération de vorticité

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Heteromeric KV2/KV8.2 Channels Mediate Delayed Rectifier Potassium Currents in Primate Photoreceptors.

Silent voltage-gated potassium channel subunits (KVS) interact selectively with members of the KV2 channel family to modify their functional properties. The localization and functional roles of these silent subunits remain poorly understood. Mutations in the KVS subunit, KV8.2 (KCNV2), lead to severe visual impairment in humans, but the basis of these deficits remains unclear. Here, we examined the localization, native interactions, and functional properties of KV8.2-containing channels in mouse, macaque, and human photoreceptors of either sex. In human retina, KV8.2 colocalized with KV2.1 and KV2.2 in cone inner segments and with KV2.1 in rod inner segments. KV2.1 and KV2.2 could be coimmunoprecipitated with KV8.2 in retinal lysates indicating that these subunits likely interact directly. Retinal KV2.1 was less phosphorylated than cortical KV2.1, a difference expected to alter the biophysical properties of these channels. Using voltage-clamp recordings and pharmacology, we provide functional evidence for Kv2-containing channels in primate rods and cones. We propose that the presence of KV8.2, and low levels of KV2.1 phosphorylation shift the activation range of KV2 channels to align with the operating range of rod and cone photoreceptors. Our data indicate a role for KV2/KV8.2 channels in human photoreceptor function and suggest that the visual deficits in patients with KCNV2 mutations arise from inadequate resting activation of KV channels in rod and cone inner segments.SIGNIFICANCE STATEMENT Mutations in a voltage-gated potassium channel subunit, KV8.2, underlie a blinding inherited photoreceptor dystrophy, indicating an important role for these channels in human vision. Here, we have defined the localization and subunit interactions of KV8.2 channels in primate photoreceptors. We show that the KV8.2 subunit interacts with different Kv2 channels in rods and cones, giving rise to potassium currents with distinct functional properties. Our results provide a molecular basis for retinal dysfunction in patients with mutations in the KCNV2 gene encoding KV8.2

Heteromeric KV2/KV8.2 Channels Mediate Delayed Rectifier Potassium Currents in Primate Photoreceptors.

Silent voltage-gated potassium channel subunits (KVS) interact selectively with members of the KV2 channel family to modify their functional properties. The localization and functional roles of these silent subunits remain poorly understood. Mutations in the KVS subunit, KV8.2 (KCNV2), lead to severe visual impairment in humans, but the basis of these deficits remains unclear. Here, we examined the localization, native interactions, and functional properties of KV8.2-containing channels in mouse, macaque, and human photoreceptors of either sex. In human retina, KV8.2 colocalized with KV2.1 and KV2.2 in cone inner segments and with KV2.1 in rod inner segments. KV2.1 and KV2.2 could be coimmunoprecipitated with KV8.2 in retinal lysates indicating that these subunits likely interact directly. Retinal KV2.1 was less phosphorylated than cortical KV2.1, a difference expected to alter the biophysical properties of these channels. Using voltage-clamp recordings and pharmacology, we provide functional evidence for Kv2-containing channels in primate rods and cones. We propose that the presence of KV8.2, and low levels of KV2.1 phosphorylation shift the activation range of KV2 channels to align with the operating range of rod and cone photoreceptors. Our data indicate a role for KV2/KV8.2 channels in human photoreceptor function and suggest that the visual deficits in patients with KCNV2 mutations arise from inadequate resting activation of KV channels in rod and cone inner segments.SIGNIFICANCE STATEMENT Mutations in a voltage-gated potassium channel subunit, KV8.2, underlie a blinding inherited photoreceptor dystrophy, indicating an important role for these channels in human vision. Here, we have defined the localization and subunit interactions of KV8.2 channels in primate photoreceptors. We show that the KV8.2 subunit interacts with different Kv2 channels in rods and cones, giving rise to potassium currents with distinct functional properties. Our results provide a molecular basis for retinal dysfunction in patients with mutations in the KCNV2 gene encoding KV8.2

Degradation of Cadmium Yellow Paint: New Evidence from Photoluminescence Studies of Trap States in Picasso's Femme (époque des "demoiselles d'Avignon")

Paints based on cadmium sulfide (CdS) were popular among artists beginning in the mid-19th century. Some paint formulations are prone to degrade, discoloring and disfiguring paintings where they have been used. Pablo Picasso's Femme (époque des "Demoiselles d'Avignon") (1907) includes two commercial formulations of CdS: one is visibly degraded and now appears brownish yellow, while the other appears relatively intact and is vibrant yellow. This observation inspired the study reported here of the photoluminescence emission from trap states of the two CdS paints, complemented by data from multispectral imaging, X-ray fluorescence spectroscopy, micro-FTIR, and SEM-EDS. The two paints exhibit trap state emissions that differ in terms of spectrum, intensity, and decay kinetics. In the now-brownish yellow paint, trap state emission is highly favored with respect to near band edge optical recombination. This observation suggests a higher density of surface defects in the now-brownish yellow paint that promotes the surface reactivity of CdS particles and their subsequent paint degradation. CdS is a semiconductor, and surface defects in semiconductors can trap free charge carriers; this interaction becomes stronger at reduced particle size or, equivalently, with increased surface to volume ratio. Here, we speculate that the strong trap state emission in the now-brownish cadmium yellow paint is linked to the presence of CdS particles with a nanocrystalline phase, possibly resulting from a low degree of calcination during pigment synthesis. Taken together, the results presented here demonstrate how photoluminescence studies can probe surface defects in CdS paints and lead to an improved understanding of their complex degradation mechanisms