99年化工原理期末考试题

Final Examination for Unit Operations of Chemical Engineering Grade 99 2001 12 25 Name Student No Class Score 1 45 points True or false or fill the black or choose the correct answer 1 In a laminar flow the frictional coefficient Fanning Factor f is inversely proportional to Re 2 At heat transfer by conduction q heat flow rate is always constant 3 When a fluid passes through a pipe the total mechanical energy in section 1 inlet is always equal to that in section 2 outlet 4 When the inlet and outlet temperatures are fixed LMTD logarithmic mean temperature difference is always larger than that of arithmetic mean temperature 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 The orifice meter belongs to flow rate meter while the rotameter is flow rate meter A constant pressure drop B constant area C variable pressure drop D variable area 7 There are often two kinds of condensation processes in industry which are 1 2 respectively 8 If the inlet and outlet temperatures of fluids are fixed the LMTD of countercurrent flow is always larger than that of parallel current flow without phase heat transfer 9 In order to avoid the cavitation the following is feasible A increase the operating temperature B decrease the diameter of suction pipe C install the valve or fittings in the suction pipeline D reduce the frictional loss in the suction pipeline 10 The expression of Newton s Cooling law is 11 The orifice meter is used to measure the rotameter is utilized to measure the Pitot tube is used to measure A average velocity in the orifice B volume flow rate in the orifice C average velocity in annular space between the float and tube wall D volume flow rate in annular space between the float and tube wall E local velocity in the pipe F average velocity in the pipe 12 A single spherical particle settles freely in static fluid in which the settling obeys Stoke s Law laminar flow If the diameter of particle decreases the settling velocity ut will when the density of particle reduces ut will the density of fluid increases ut will the temperature increases ut will 13 The methods of adjusting volume flow rate of centrifugal pump are 1 2 3 The commonest way in practice is 14 Air flows along the tube and saturated vapor passes through the shell in a shell tube exchanger In order to enhance heat transfer which way is feasible in practice as follows A increase vapor velocity B employ superheated vapor C increase air velocity D set up the baffle in the shell 15 When fouling scale and pipe wall resistances are ignored and the difference between hi and ho is very huge overall heat transfer coefficient U is close to wall temperature is close to A larger h B smaller h C average value between hi and ho D uncertain 16 There are many ways to remove solid particles in a mixture give three of them 1 2 3 17 If the temperature drop To between the saturated vapor and pipe wall is double in a vertical tube the condensation heat transfer film coefficient h will increase to of original value A 2 1 4 B 21 4 C 23 4 D 2 18 Based on the temperature distribution as shown in figure which has largest heat resistance and which has the largest thermal conductivity if the thickness of each layer is the same A layer A B layer B C layer C 19 The removal of uncondensable gas in the condensing vapor will A Increase condensing film coefficient B Decrease condensing film coefficient C Do not change condensing film coefficient D Be uncertain 20 Which statement is correct in the following A The filtration rate is equal to the washing rate in a filter press B The filtration ending rate is equal to the washing rate in a filter press C The filtration ending rate is 4 times as much as the washing rate in a filter press D The filtration ending rate is 1 4 times as much as the washing rate in a filter press 21 Water 0 001 kg m s 1000 kg m3 passes through a pipe of diameter di 0 001 m and length L 2 m with the average velocity 1 m s Re The flow pattern is the maximum velocity umax is the frictional loss hf is the expression of velocity distribution is 2 15 points A slurry with incompressible cake is filtered by a 1m2 filter press at constant pressure If the filtering constant K is 10 m2 atm min operating pressure difference p is 2 atm and the septum resistance can be ignored Find 1 the filtrate volume in m3 when the filtering time is 10 min 2 if the septum resistance must be considered and equivalent filtrate volume Ve is 1 m3 what is the equivalent filtration time te 3 what is the filtrate volume V in m3 when the filtering time is 10 min for case 2 4 what is the filtration rate dV dt when the filtering time is 10 min for case 1 3 20 points Water is transported by a pump efficiency of pump 65 from tank 1 to tank 2 as shown in Figure The total equivalent length of pipe is 200 m including all local frictional loss The pipeline is 89x4 5 mm the orifice coefficient of Co and orifice diameter do are 0 61 and 20 mm respectively Frictional coefficient is 0 025 and the readings of vacuum gauge in tank 1 and pressure gauge in tank 2 are 200 mm Hg and 49000N m2 respectively Find 1 Water mass flow rate in kg s when the reading R of U pressure gauge in orifice meter is 600 mm Hg H2O 1000 kg m3 Hg 13600 kg m3 2 Developed head H of pump in m H2O 3 Practical power P of pump in kw 10m 2 1 4 20 points A single pass 1 1 shell tube exchanger is made of many 25 2 5 mm tubes Organic solution u 0 5m s m mass flowrate 15000kg h Cp 1 76 kJ kg oC 858 kg m3 passes through the tube The te