天大化工原理-英文版课件-2. Blowers and Compressor.ppt

Exercise 1 Water(? = 1000 kg/m3) is transported from a low tank to a high tank. When the valve at C is open,the following data are detected: flow rate q, head H, pressure at inlet of pump p1, pressure at outlet of pump p2 and shaft power PB. Classification Positive-displacement meters Thermal meter 热丝[电]式仪表 Selection the flowmeter Applicability of the instrument to the specific problem Rangeability Accuracy Cost of install and operation C0 is determined experimentally. It varies considerably with changes in β and with Reynolds number at the orifice Reo. FIGURE 8.19 Overall pressure loss in orifice meters. EXAMPLE 8.4 4. Rotameter (Area meter ) tapered glass tube Write Bernoulli equation between upsteam a and downstream b . a represents the position right below the float, b is the up-surface of the float, volumetric flow rate Impact tube (冲压管） a : parallel to the direction of the flow. ps Actual pitot tube, a correction factor should be applied. * Now one of the following variation is conducted, determine the change in q,H,p1,p2 and PB. 1 open the valve C wider; 2 transport another liquid (? =1260kg/m3) 8.5 Measurement of flowing fluids Type of flowmeters Venturi meter（文丘里流量计） Orifice meter（孔板流量计） Rotameter（转子流量计） Pitot tube（测速管） 1. Type of flowmeters According the sensing element ,the meters can be classed as : Sensing element Pressure drop Area different Thermal Magnetic Full-Bore meters Insertion meters Measure the average velocity Measure velocity at one point. Venturi meter Orifice meter Rotameters V-element Pitot tube throat section is called文氏喉 2.Venturi meter 文丘里流量计(head meter压差流量计) short conical inlet section a long discharge cone Enough straight pipe a b Writing the Bernoulli equation for incompressible fluids across station a and station b. the continuity relation (assume the density is constant): Cv, : Venturi coefficient volumetric flow rate mass flow rate (8.37) (8.38) The basic equation of venturi meter For a well-designed venturi, t