Steady fully developed mixed convection flow in a vertical parallel plate microchannel with bilateral heating and filled with porous material

This study investigated analytically the hydrodynamic and thermal behaviour of a fully developed laminar, viscous, incompressible fluid in a vertical parallel plate microchannel taking into account the velocity slip and thermal jump at the walls. The governing equations are expressed in a dimensionless form using the dimensionless quantities. The method of undetermined coefficient was employed to obtain the closed-form expression for velocity, which is used to determine the skin friction. The solution obtained is then presented graphically and the results are discussed for various dimensionless parameters entering the problem. During the course of investigation, it is found that the critical values of the mixed convection parameter Gre (which is the ratio of the Grashof number Gr to the Reynolds number Re) led to flow reversal decrease with increase in Darcy number, while it increases with increase in Knudsen number Kn. Also, the Nusselt number Nu is found to increase with increasing Darcy number.

Repeated increases in blood flow, independent of exercise, enhance conduit artery vasodilator function in humans

This study aimed to determine the importance of repeated increases in blood flow to conduit artery adaptation, using an exercise-independent repeated episodic stimulus. Recent studies suggest that exercise training improves vasodilator function of conduit arteries via shear stress-mediated mechanisms. However, exercise is a complex stimulus that may induce shear-independent adaptations. Nine healthy men immersed their forearms in water at 42°C for three 30-min sessions/wk across 8 wk. During each session, a pneumatic pressure cuff was inflated around one forearm to unilaterally modulate heating-induced increases in shear. Forearm heating was associated with an increase in brachial artery blood flow ( P < 0.001) and shear rate ( P < 0.001) in the uncuffed forearm; this response was attenuated in the cuffed limb ( P < 0.005). Repeated episodic exposure to bilateral heating induced an increase in endothelium-dependent vasodilation in response to 5-min ischemic ( P < 0.05) and ischemic handgrip exercise ( P < 0.005) stimuli in the uncuffed forearm, whereas the 8-wk heating intervention did not influence dilation to either stimulus in the cuffed limb. Endothelium-independent glyceryl trinitrate responses were not altered in either limb. Repeated heating increases blood flow to levels that enhance endothelium-mediated vasodilator function in humans. These findings reinforce the importance of the direct impacts of shear stress on the vascular endothelium in humans.

Numerical Simulation of Upward Two-Phase Flow in Narrow Channel Between Two Flat Plates With Bilateral Heating

The convection heat transfer characteristic in narrow channel is superior. Therefore, narrow channels are suitable for being manufactured into compact heat transfer components with high heat transfer performance. This new technology of heat transfer enhancement with no source is widely applied to various fields such as microelectronic heat sink, cryogenic industry, chemical industry, aeronautic & astronautic industry and nuclear engineering. In integrated reactor, the coolant channels between the plate fuels are narrow channels. As to the investigation of two-phase flow and heat transfer in narrow channels, reports are focused on experimental research with low pressure, at home and abroad, but reports on numerical simulation research are relatively small. Based on separated flow, a theoretical two-fluid model predicting for upward flow in a rectangular narrow channel with bilateral heating has been developed in this paper. The theoretical model is based on fundamental conservation principles: the mass, momentum and energy conservation equations of liquid films and the momentum conservation equation of vapor core. The model assumed that liquid film covers the surface of the channel while the vapor with entrained droplets flows in the central core. And there exists the mass transfer between the liquid droplets in the vapor core and the liquid films. Through numerically solving these equations, liquid film thickness, radial velocity and temperature distribution in liquid films and heat transfer coefficient are obtained. The calculated results shows that the width of the narrow channel, heat pattern, heat flux have great influences on heat transfer coefficient and the thickness of liquid film. The heat transfer coefficient will increase with the decrease of the channel width. That is, the heat transfer may be enhanced with small rectangular narrow channel. But when the channel width is less than a certain value, the model may not be proper anymore. So the further research should be necessary. As the applications of the present model, the critical heat flux and critical quality are calculated.