Effect of gravity

Our prior discussion on surface tension again offers some insight. Since the surface tension and adhesive forces scale down with the lengths of the liquid, solid, and vapor boundaries, they drop much slower in comparison to the gravity force on a liquid droplet that is proportional to the volume of the droplet. Hence we could envision that at some smaller scale, the surface tension would be a much more dominant force compared to gravity, and if so, the effect of gravity onto the shape of the droplet would be negligible. 

Simulated shapes of water droplets of different volumes on silver surfaces. 

Amnon Yariv, Photonics Optical Electronics in Modern Communications. New York Oxford University Press, 2007. 

Meyer-Arendt, Introduction to Classical and Modern Optics. London Prentice-Hall, 1972. 

Tunable microlens arrays actuated by various thermo-responsive hydrogel structures, Journal of Micromechanics and Microengineering, vol. 20, p. 115035, Nov 2010. 

---

In inclined or vertical pipes, the flow regimes are similar to those described for horizontal pipes when both gas- and Hquid-flow rates are high. At lower flow rates, the effects of gravity are important and the regimes of flow are quite different. For Hquid velocities near 30 cm/s and gas velocities near... 

A method for measuring the uniaxial extensional viscosity of polymer soHds and melts uses a tensile tester in a Hquid oil bath to remove effects of gravity and provide temperature control cylindrical rods are used as specimens (218,219). The rod extmder may be part of the apparatus and may be combined with a device for clamping the extmded material (220). However, most of the mote recent versions use prepared rods, which are placed in the apparatus and heated to soften or melt the polymer (103,111,221—223). A constant stress or a constant strain rate is appHed, and the resultant extensional strain rate or stress, respectively, is measured. Similar techniques are used to study biaxial extension (101). 

The abihty to remove heat from electrophoretic systems has severely limited the maximum capacity of these systems in terms of how large or thick the systems can be. Electrophoretic separations have been performed on space flights because the effect of gravity in outer space is small and mixing from heating is negligible. Whereas electrophoresis in outer space has been accompHshed (10), the economics for a scaleable process have not (see Space processing). 

Combined Effect of Gravity Forces, Wind, and Mechanical Ventilation... 

The combined effect of gravity forces, wind, and mechanical ventilation on the pressure across the opening is illustrated in Fig. 7.102. 

Centrifugation is the application of rotational velocity to enhance the effect of gravity and intensify the separation of phases. It can be applied in two distinct ways... 

Lift/gravity dijferential Lift, which is designed into a machine-train s rotating elements to compensate for the effects of gravity acting on the rotor, is another source of imbalance. Because lift does not always equal gravity, there is always some imbalance in machine-trains. The vibration component due to the lift/gravity differential effect appears at the fundamental or 1 x frequency. 

The small pore size and the uniform distribution result in capillary forces which should allow wicking heights and thus battery heights of up to 30 cm. Due to the cavities required for gas transfer and under the effect of gravity, the electrolyte forms a filling profile, i.e., fewer cavities remain at the bottom than at the top. Therefore with absorptive glass mats a rather flat battery... 

The effect of gravity on the liquid and vapor parameters in the inlet and outlet cross-section is presented in Figs. 8.12 and 8.13. It is seen that an increase in the gravity is accompanied by a significant growth of the liquid pressure (Fig. 8.12a). At the same time an increase of the vapor pressure in the outlet cross-section is observed. However, the rate of liquid and vapor pressure growth are very different. This causes an increase of the difference AP = gravity... 

Fig. 8.12a,b The effect of gravity on inlet liquid pressure and pressure difference between the inlet and outlet cross-section of the capillary (a) the dependence of (g), (b) the dependence of AP(g), (AP = — Pout). Reprinted from Peles et al. (2000) with permission... 

Strehlow R.A., Noe K.A., and Wherley B.L., The effect of gravity on premixed flame propagation and extinction in a vertical standard flammability tube, Proc. Combust. Inst., 21 1899-1908,1986. 

TT( is nondimensionalized by the flame transit hme T( = 3/Sl. Here, 7 is the normalized gas expansion ratio. Because of the difference in density between the fresh and burnt gas, gravity will also influence the d5mamics of the flame front. The effect of gravity has been included through a Froude number, Fr = Sl/ Sg), positive for a flame propagating downward. Similar expressions have been derived by Matalon and Matkowski [13], and by Frankel and Sivashinsky [14]. 

As 100% vaporization is approached, there is not sufficient liquid flowing in the system to continuously wet the entire tube wall, and thus dry spots appear. Transition Zone III is characterized by the initial appearance of these dry spots, and Region IV is characterized by a completely dry tube wall and a dispersed flow pattern. Due to the effects of gravity, dry spots... 

Compensatory mechanisms in the circulatory system are needed to counteract the effects of gravity. Two important mechanisms include ... 

The inhibition of sympathetic tone to the venous system (capacitance vessels) results in increased pooling of blood in the venous vascular bed with consequent decreased venous return to the heart and decreased cardiac output. This phenomenon is more pronounced in upright positions because of the effect of gravity. The hemodynamic effects of ganglionic blockers include decreases in cardiac output, renal blood flow, cerebral blood flow and orthostatic hypotension(20,21). 

---