98年化工原理期中考试题.doc

Final for Unit Operations of Chemical EngineeringGrade 98, 2000/12/27 Name Student No. Class Score 1. (40 points) True or false or fill the black or choose the correct answer(1) ( ) In a laminar flow, the velocity distribution is parabolic.(2) ( ) In a laminar flow, the frictional loss is proportional to velocity square.(3) ( ) In the fully-developed turbulent flow, Fanning factor f is independent of Re. (4) ( ) If the volumetric flow rate increases, the developed head H of centrifugal pumps will increase as well.(5) ( )When the developed head H is the same, one pump can develop more volume flow rate than that two same pumps which work in parallel.(6) For laminar flow in a pipe, when the diameter increases and flow rate keeps constant, Fanning factor f will ( ); and frictional loss will ( ).(7) In SI system, the dimension of viscosity is ( ), and its unit is ( ).(8) When the temperature of fluid to be transported increases, the maximum lift of suction will ( ). If the velocity of suction pipe decreases, the maximum suction lift will ( ).(9) The expression of Newtons Law of viscosity is ( ).(10) When the pipe installation changes from horizontal to vertical position and the velocity keeps unchanged, the frictional loss will be .A. increased; B. decreased; C. the same; D. uncertain(11) A single spherical particle settles freely in static fluid, in which the settling obeys Stokes Law (laminar flow). If the diameter of particle decreases, the settling velocity ut will ( ); when the density of particle increases, ut will ( ); the density of fluid increases, ut will ( ); the viscosity of fluid increases, ut will ( ) (12) The methods of adjusting volume flow rate of centrifugal pump are (1) ; (2) ; (3) ;The commonest way in practice is ( ).(13) If the flow is laminar in a pipe, its characteristics are (1)( ); (2)( ); (3)( ), respectively. (14) For a rectangular channel with length a and width b, the equivalent diameter de is ( ).(15) The capacity of gravity dust settling chamber depends on ( )A) the length of the dust settling chamber.B) the height of the dust settling chamber.C) the bottom area of the dust settling chamberD) the volume of the dust settling chamber(16) The reading in a gauge is 10 m H2O = N/m2 (absolute pressure), and the reading of a vacuum gauge is 380 mm Hg= m H2O(absolute pressure)= N/m2 (gauge pressure) if the atmospheric pressure is 1 atm.(17) When the flow rate is fixed, the maximum suction lift Za will if the velocity of discharged pipe increases. When the flow rate is fixed, Za will if the frictional loss in the suction pipe increases.(18) ( ) In order to avoid the cavitation, the adjusted valve can be installed in suction pipeline.(19) ( ) Water need not to be added during the start of reciprocating pump because it has priming function.20 The filter basic equation is derived based on ( ) 2. (20 points) A slurry is filtered by a 0.1 m2 filter press at constant pressure. The cake is incompressible. The filter basic equation is as follows:(q + 10)2 = 250 (t + 0.4)where q: m3/m2; t: minFind 1) how much filtrate is obtained after 249.6 min, in m3? 2) if the pressure drop decreases to 50% of original value, how much filtrate can be got after 249.6 min, in m3?3) The filtration rate at 249.6 min in case 1, in m3/min3. (20 points) A liquid with density 900 kg/m3) and viscosity m=30 cp flows from tank 1 to tank 2 by the pipeline with inner diameter 40 mm. The surface of liquid in two tanks keeps constant. When the valve is closed, the readings of gauges A and B are 8.82104 N/m2 and 4.41104 N/m2, respectively. When the valve is open, the total length of pipeline is 100 m including all local frictional equivalent length, find:(1) the volumetric flow rate in the pipe, in m3/h?(2) when the valve is open, what happens to the readings of gauges A and B, explain simply why?Hint: for laminar flow, f=16/Re or l=4f=64/Re For turbulent flow, l=0.3145/Re0.254 (20 points) A single pass (1-1) shell-tube exchanger is made of many 252.5 mm tubes. Organic solution, u=0.5m/s, m(mass flowrate)= 15000kg/h, Cp=1.76 kJ/kg. oC, r=858 kg/m3, passes through the tube. The temperature changes from 20 to 50 oC. The saturated vapor at 130 oC condenses to the saturated water, which goes through the shell. The individual heat transfer coefficients hi and ho in the pipe and shell are 700 and is 1.0104 W/m2 oC, respectively. The thermal conductivity k of pipe wall is 45 W/m. oC. If the heat loss and resistances of fouling can be ignored, find(1) Overall heat transfer coe