天大化工原理-英文版课件-CHAPTER 4 Basic Equations of Fluid Flow.pptVIP

2. Layer flow with free surface where = gravity force = shear stress on lower surface of control volume A = area of lower surface of control volume A = bL The total mass flow rate of the fluid then is Discussion of the assumptions: 1. No shear stress acting on the interface of liquid and gas(air) Shear force will increase if the vapor(or gas) shear exist. 2. Laminar flow A critical Re number of 2100 has often been used for layer flow, but film thickness measurements indicated a transition at Re around 1200. Deviation of predicted values from that of measurements Alternate form of Reynolds number For circular pipe The Reynolds number for flow down a flat plate is defined by the equation. 3. Angular-momentum equation(角动量方程) Analysis of the performance of rotating fluid-handling machinery such as pumps, turbines, and agitators is facilitated by the use of force moments and angular momentum. Equation (4.53) is the angular momentum equation for steady two-dimensional flow. Applications of Eq. (4.53) are given in Chaps. 8 and 9. 4.4 MECHANICAL ENERGY EQUATION** 1. Energy equation for potential flow; Bernoulli equation without friction 2. Bernoulli equation(柏努利方程): correction for effects of solid boundaries 3. Kinetic energy of stream 4. Correction of Bernoulli equation for fluid friction 5. Pump work in Bernoulli equation 1. Energy equation for potential flow; Bernoulli equation without friction For this steady unidirectional flow process, Eq.(4.45) In fps units (c) for a stationary fluid, density is constant Eq. (4.58a) become (d) to identify the streamline or stream tube, to choose definite upstream and downstream stations, and to choose datum surface. EXAMPLE 4.4. Brine, specific gravity 60°F /60°F = 1.15, is draining from the bottom of a large open tank through a 50-mm pipe. The drainpipe ends at a point 5 m below the surface of the brine in the tank. Considering a streamline starting