exam paper 2009 - “K W V UNIVERSITY Murdoch Examinations...

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Unformatted text preview: “K W V UNIVERSITY Murdoch Examinations - Semester 1, 2009 €. Unit EXM224 PRINCIPLES OF UNIT OPERATIONS Exam Type : Internal & External Reading time : 10 minutes (Note taking allowed onto Exam Paper ONLY) Exam Duration : 3 hours INSTRQQTIQNS This paper contains 3 pages and 5 questions. Spend 30-35 minutes on each question. All questions are of equal value with respect to marks. Attempt all questions and answer in the answer booklet provided. 0 Marks will be allocated for stating relevant equations, assumptions and units in your calculations. EXAMINATI ID L WED CLOSED BOOK EXAM ANSWER BOOKLET Provided by the gandidgte CALCULATOR (NO QWERTY KEYBOARD) Question 1 A ventun' meter is used to measure the flow rate of an incompressible fluid. ii a 2 2 . . v v Bernoulli equation 3‘- + Z1 + 4 = —p—2~ + 22 + -—2— r 2g 7 2g 1(a) Use the equation of continuity to derive the relationship between velocities v1 and V2 at points 1 and 2 in which the cross-sectional area at point 1 is four times that at point 2. [4 marks] 1(b) Use the Bernoulli equation for the system to prove that __ 15 p Q2 p] p 2 2 A12 [6 marks] 1(c) Suppose this meter is used to measure the flow rate of a stream of water, using mercury (SG = 13.6) as the manometer fluid. Calculate the pressure drop pl-pz which satisfies a manometer reading h = 52 cm. [5 marks] 1(d) Calculate the volumetric flow rate. Pipe diameter at point 1 is 20 cm and the discharge coefficient is 0.96. [3 marks] 1(e) What are the disadvantages of a venturi meter ? [2 marks] Question 2 2(a) Briefly discuss how you would obtain the friction factor for a (i) fluid flow through a pipe, (ii) particle settling in a fluid. [4 marks] 2(b) Briefly explain the behaviour of a Newtonian non-settling slurry. [2 marks] 2(c) A slurry has 50% solids by mass of clay particles (SG of clay = 2.65). Calculate (i) the solids concentration in % solids by volume in the slurry, and [2 marks] (ii) the slurry viscosity (viscosity of water = 0.001 N s m'z). [2 marks] 2(d) The slurry described in part 2(e) is pumped through a horizontal 5 cm diameter, smooth pipe. The average velocity of flow is 5 cm s". Calculate the rate at which solids are transported (t h"). [3 marks] 2(e) Verify laminar conditions for the slurry flow described in parts 2(c) and 2(d) and calculate the head loss per unit length of pipe. [7 marks] Assume that the head loss in a smooth pipe carrying a Newtonian fluid under laminar flow conditions may be calculated using the Hagen-Poiseuille equation: hf =32uLv p g D2 and the slurry viscosity is given by Ei=1+2.scv+locv2 no where CV is the volume fraction of solids and no = viscosity of fluid. gum; 3(a) (i) Calculate the mass flow rate of air (t h") required to dead roast a sulphide containing 80% F632 and 20% SiOz to produce Fe203 and $02 at 550°C in a fluid bed roaster. Solid feed rate = 80 t/day Air (21% 02, 79% N2) input = 110% of theoretical air (Fe =56, S=32, O = 16, N = 14) [10 marks] (ii) Calculate the vol% composition of the exit gas from the roaster. [5 marks] 3(b) A slurry (A) containing 40% solids by mass is fed into a solid/liquid separation unit at a slurry feed rate of 150 t h". The two output streams (B and C) from the solid/liquid separation unit contain pure water (B) and filter cake (C) containing 20% water by mass. Sketch a block diagram to show the flow of A, B and C and calculate the weight flow rates of the two output streams B and C. [5 marks] Question 4 Gold in the form of the aurocyanide ion is adsorbed from leach solutions onto activated carbon granules. A stirred tank containing 100 m3 of solution containing 1 ppm gold is treated with 1 kg of suspended carbon granules which can be assumed to be spherical with diameter 1 mm. The mass transfer correlation for mass transport to suspended particles is given by Sh = 2.0 + 0.6 or“ .Sc"3 = de/D where Gr = d3.(ps - pL) .g/(pL.v2), Sc = v/D and d is the particle diameter, g = 980 cm 3'2 is the acceleration due to gravi , ty 2 D = 1 x 10‘5 cm s'1 is the diffilsion coefficient of aurocyanide ions, pg = 2.0 g cm‘3 is the density of the carbon granules and m, =1.0 g cm'3 is the density of the solution, v = 0.01 cm 4(a) 4(b) 4(0) 4(d) 2 s'1 is the kinematic viscosity and k, is the mass transfer coefficient. Calculate the mass transfer coefficient to the carbon granules in cm s". [6 marks] Assuming that the rate of adsorption of gold is controlled by mass transport of aurocyanide ions to the surface of the granules, calculate the initial rate of gold adsorption in terms of Au mg min"l . [9 marks] Without making any additional calculations, sketch the shape of the curve that could be expected for the concentration of gold in the solution in the reactor as a filnction of time after adding the carbon. What assumption have you made? [3 marks] Suggest two methods (with reasons) for improving the rate of adsorption of gold. [2 marks] Question 5 5(a) 5(1)) A wall of a furnace 0.244 m thick is constructed of material having a thermal conductivity 1.30 W m'1 K". The wall will be insulated on the outside with material having an average thermal conductivity 0.346 W m'1 K", so the heat loss from the furnace will be equal to or less than 1830 W m'z. The inner and outer surface temperatures are 1315 °C and 26 °C respectively. Calculate the thickness of insulation required. AT 21%) [10 marks] A small oxidized horizontal metal tube with an outside diameter 25 mm, length 60 cm and surface temperature 315 °C is in a very large furnace enclosure with fire-brick walls surrounding air at 815 °C. Calculate the total heat transfer to the tube by convection and radiation. Emissivity of metal tube = 0.66 116 for horizontal cylinder = 1.32(AT/D)“4 ) (T1 /100)4 — (T2/100)4 (T1 ' T2) q: h, = s(5.676 [10 marks] End of Question Paper a. v t ...
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exam paper 2009 - “K W V UNIVERSITY Murdoch Examinations...

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