6 - Bulk transport

Abstract

This chapter explores bulk flow properties of fluids. The physical rules governing flow in any system apply to bulk flow of fluids, liquids, or gases in the body. Flow takes place down gradients of pressure, and its rate is affected by the size and resistance of the flow channels. When a fluid passes along a smooth-walled tube, the layers of fluid in contact with the walls experience drag due to friction. Fluids flow only when there is a net pressure difference between two points. Flow of blood depends upon contraction of heart muscle to produce pressure within the ventricular chambers. Low Reynold's numbers are found almost everywhere in the circulatory and respiratory systems. The parts of the systems most likely to show turbulent flow are tubes of relatively large radius with rapid linear flow rates. Suspended particles are affected by flow and they affect it. The velocity profile results in the more massive white blood cells lying along the axis of flow with the red cells in the surrounding layers. The presence of suspended particles directly affects the flow of blood. The effective viscosity of a mixture of particles and fluid changes according to the concentration and the orientation of particles.