Dilated flow channel

The main reason why volumetric capacity is normally estimated in a relatively crude manner, as a proportion of swept volume , is that derivations of transport efficiency are generally secondary to assessments of the density condition of the solid in the conveyed state. The product as fed is in a dynamic condition, so the best simple assessment is to assume a loose poured measurement of product density. This value can be adjusted up or down, to take account of the speed of the feed screw and the assessed packing characteristics of the flow channel from the hopper. Material carried within the normal feeder speed range of 15-100 r/min tends to be relatively dense at low speeds but more dilated at the faster speed. 

However, the aperture, fluid velocity and the permeability increase with stress ratio increment when stress ratios are enough large to cause shear dilation of fractures K is large than 3.5). These results show that the shear-induced flow channeling has very important impact on permeability of fractured rock mass and shouldn t be neglected. 

Another group of drugs that relax heart muscle are the calcium-channel blockers. One example is nifedipine, shown in Figure 14.46. Muscle contraction is initiated as a nerve impulse signals calcium ions to enter muscle cells. As their name implies, calcium-channel blockers inhibit the flow of calcium ions into muscles, thereby inhibiting muscle contraction. The heart rate slows down, and muscles of blood vessels relax and dilate, lowering blood pressure. 

Calcium channel blockers, such as verapamil (Calan , Covera , Isoptin , Verelan), diltiazem (Cardizem , Dilacor , Tiazac ), and nimodipine (Nimotop ), inhibit the flow of calcium ions into the cells that line blood vessel walls. This changes the way the blood vessels surrounding the brain dilate and constrict and provides relief from migraines. 

Since acute DIN appears to be dose related, pharmacokinetic and pharmacodynamic monitoring is an important means of preventing toxicity. However, the persistent presence of therapeutic or low cyclosporine concentrations cannot preclude nephrotoxicity. Calcium channel blockers may antagonize the vasoconstrictor effect of cyclosporine by dilating glomerular afferent arterioles and preventing acute decreases in renal blood flow and glomerular filtration. Lastly, decreased doses of cyclosporine or tacrolimus, primarily when used in combination with other non-nephrotoxic immunosuppressants, may minimize the risk of toxicity, but this may increase the risk of chronic rejection. 

These are a relatively recent development and act by increasing the efflux of potassium ions in smooth muscle cells of blood vessels. This leads to hyperpolarization of vascular smooth muscle thereby reducing the excitability and bringing about vasodilation. The resulting vasodilation in coronary arterioles improves blood flow to the myocardium. This, in combination with a reduction in both afterload (dilation of arteries) and preload (dilation of veins), relieves the angina. Nicorandil is an example of a potassium channel activator. 

VARIANT ANGINA Variant angina results from reduced flow rather than increased demand, and Ca channel blockers have proven efficacy. In these patients, these drugs can attenuate ergonovine-induced vasospasm, suggesting that protection in variant angina is due to coronary dilation rather than to alterations in peripheral hemodynamics. 

EXERTIONAL ANGINA Ca + channel antagonists also are effective in the treatment of exertional angina. Their utility may result from an increase in blood flow owing to coronary arterial dilation, from a decrease in myocardial demand (secondary to a decrease in arterial blood pressure, heart rate, or contractility), or both. These drugs decrease the number of anginal attacks and attenuate exercise-induced ST-segment depression. 

Minoxidil (loniten) is efficacious in patients with the most severe and drug-resistant forms of hypertension. A small fraction of minoxidil is metabolized by hepatic sulfotransferase to the active molecule, minoxidil N-O sulfate. Minoxidil sulfate activates the ATP-modulated channel in smooth muscle, causing hyperpolarization and relaxation of arteriolar smooth muscle. Minoxidil produces arteriolar vasodilation with essentially no effect on capacitance vessels. Minoxidil preferentially increases blood flow to skin, skeletal muscle, the GI tract, and the heart. The disproportionate increase in blood flow to the heart may have a metabolic basis, in that administration of minoxidil is associated with a reflex increase in myocardial contractility and in cardiac output. The cardiac output can increase by as much as three- to fourfold, primarily due to enhanced venous return to the heart. The increased venous return probably results from enhanced flow in vascular beds with a fast response for venous return to the heart. The adrenergic increase in myocardial contractility contributes to the increased cardiac output, but is not the predominant factor. The renal effects of minoxidil are complex it dilates renal arteries, but systemic hypotension produced by the drug actually can decrease renal blood flow. Renal function usually improves in patients who take minoxidil for the treatment of hypertension, especially if renal dysfunction is secondary to hypertension. Minoxidil potently stimulates renin secretion, an effect mediated by renal sympathetic stimulation. 

Figure 8 shows some examples of the channelling flow effect due to the fracture dilation. Note that all models have the same reference legend. One line indicates the flowrate of lO mvsec and the flowrates smaller than this value are not drawn in Figure 8. 

Prominent channelling effect is observed during the increase of differential stresses. This is due to both anisotropic stress and the dilation of the fractures. Results show that well-connected fractures of larger apertures are the major pathways for fluid flow in fractured rock and pathways can be significantly changed after application of stress. 

Wasan and his research group focused on the field of interfacial rheology during the past three decades [15]. They developed novel instruments, such as oscillatory deep-channel interfacial viscometer [20,21,28] and biconical bob oscillatory interfacial rheometer [29] for interfacial shear measurement and the maximum bubble-pressure method [15,29,30] and the controlled drop tensiometer [1,31] for interfacial dilatational measurement, to resolve complex interfacial flow behavior in dynamic stress conditions [1,15,27,32-35]. Their research has clearly demonstrated the importance of interfacial rheology in the coalescence process of emulsions and foams. In connection with the maximum bubble-pressure method, it has been used in the BLM system to access the properties of lipid bilayers formed from a variety of surfactants [17,28,36]. 

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