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T650(E)(A12)TAPRIL EXAMINATIONNATIONAL CERTIFICATEFLUID MECHANICS N5(8190205)12 April (X-Paper)09:00–12:00Drawing instruments and nonprogrammable calculators may be used.This question paper consists of 6 pages sheet and 1 formula sheet.

(8190205)-2-T650(E)(A12)TDEPARTMENT OF HIGHER EDUCATION AND TRAININGREPUBLIC OF SOUTH AFRICANATIONAL CERTIFICATEFLUID MECHANICS N5TIME: 3 HOURSMARKS: 100NOTE:If you answer more than the required number of questions, only therequired number of questions will be marked. Work you do not want to bemarked must be clearly crossed out.INSTRUCTIONS AND INFORMATION1.Answer any FIVE of the SIX questions in this question paper.2.Read ALL the questions carefully.3.Number the answers according to the numbering system used in this questionpaper.4.Use the value of g 9,81 m/s2.5.ALL units must at least be shown in the answers.6.Write neatly and legibly.

(8190205)-3-T650(E)(A12)TQUESTION 11.11.2Define the density of a fluid. Mention the units of density and indicate how itis determined.(3)An unknown liquid substance has a mass of 18,5 grams and occupies avolume of 23,4 ml (millilitres).Calculate the density of the unknown liquid substance.1.3(2)A shaft of 80 mm diameter revolves concentrically in a fixed bearing of80,5 mm in diameter and 100 mm in length. The annular space is full of oiland it has been found that a torque of 1,85 Nm is required to drive the shaft at1 000 r/min.Calculate the following:1.3.1the absolute coefficient of viscosity of the oil(9)1.3.2the power loss due to viscous forces(2)1.3.3the critical velocity of this oil when it flows in a pipe of 75 mmdiameter, if the critical Reynolds number is 2 300 and the density ofthe oil is 780 kg/m3(4)[20]QUESTION 22.12.2Make a neat sketch and describe the operation of a pressure gauge whichworks on the Bourdon principle. Clearly label ALL the parts of the gauge.(6)An accumulator is loaded with 40 kN weight. The ram has a diameter of30 cm and stroke of 3 m. Its friction loss is 5% of the entire weight. It takestwo minutes to fall through its full stroke. It delivers 7,5 litres of hydraulic oilthrough a pump.Calculate the following:2.2.1work supplied by the accumulator(4)2.2.2intensity of pressure of the water(2)2.2.3pressure head(2)2.2.4work supplied by the pump per second(2)2.2.5total work supplied per second by the hydraulic machine(2)2.2.6power delivered by the hydraulic machine

(8190205)-4-T650(E)(A12)TQUESTION 33.1A closed container has the dimensions of 4 m x 2 m x 3 m high and containsoil to a depth of 2,25 m. The oil has a relative density of 0,85. The pressureabove the oil is 50 kPa above the atmospheric pressure.Calculate the following:3.23.1.1resultant horizontal forces against each wall of the container(6)3.1.2position of the centre of pressure(5)The half section of a ship is shown in the figure below. The side is vertical toa depth of 1 m below the waterline and then it curves to the centre line in theform of a parabolic arch, the axis of the parabola being a horizontal line 1 mbelow the waterline. Determine the magnitude and direction of the resultanthydrostatic thrust per meter of length of the half section. The density ofseawater is 1 025 kg/m3.water1m2,5 m3m(9)[20]

(8190205)-5-T650(E)(A12)TQUESTION 44.1Define the following terms in relation to the patterns of fluid flow:4.1.1streak line or filament line4.1.2path line4.1.3stream line(3 x 2)4.2(6)Two different liquids need to be mixed in the ratio 5 : 1 in relation to theirvolumes. The final quantity of the mixed liquid must be 2 /s. A branched pipewill be used to carry out this process.Determine the following:4.2.14.2.24.2.34.2.4the diameter of the delivery pipe needed if the flow velocity shouldnot exceed 2 m/s(3)the diameter of the other two pipes if their velocities should notexceed 2 m/s(6)the weight flow at the delivery if the average density of the fluid is920 kg/m3(2)if the flow at the delivery is laminar or turbulent and the viscosity ofthe liquid is 0,6 Pa(3)[20]QUESTION 55.15.2Give TWO advantages and TWO disadvantages of orifice plates or orificemeters as flow-measuring equipment.(4)A 50 mm diameter pipe has a filter in it with a shock constant of 3 (k 3).The pipe is 5 m long and has a friction coefficient of 0,001 (f 0,001). L ratio of the system. D Determine the total length/diameter 5.3(4)A 40 mm diameter orifice plate is used to measure the flow rate of a liquidwith a relative density of 0,82. The coefficient of discharge of the orifice is0,65 and the pipe line has a diameter of 75 mm.Calculate the difference in height of the mercury levels of the manometerconnected over the orifice if the flow rate is constant at 9 /s.

(8190205)-6-T650(E)(A12)TQUESTION 6A water turbine has a wheel with the vanes mounted at a mean diameter of 0,4 m androtates at 716,19 r/min. A stream of water at an angle of 20 leaves the nozzle at40 m/s and flows over the vanes at a rate of 20 kg/s. There is a loss of 10% relativevelocity when the water passes over the vanes and the vanes and nozzle are arrangedin such a way that no axial thrust occurs.Determine the following:6.1inlet blade tip angle by drawing an inlet vector diagram(7)6.2velocity at which the water leaves the turbine by drawing the outlet vectordiagram(6)6.3theoretical power output of the turbine according to the diagram(4)6.4diagram efficiency of the turbine(3)[20]TOTAL:

(8190205)T650(E)(A12)TFLUID MECHANICS N5INFORMATION SHEET m;vP F;ARe l subs tan ce; waterPwhere v vPi Po subs tan ce water2 ;RFviscous Vg 1111 V ; KeK KcVt K gVFhydrostati c g A y ; hrec tan gular W R gV A Crand where K g P and K c E 2,5 Ig2d or hat angle Sin 2 y where3AyI g ( rec tan gular ) or Specific gP ghPabsolute Pgauge Patmospheri c ;FSurface tension 2 R ;Ke Specific bd 3 D4or I g ( circular ) 1264 Q or V A1 u1 A2 u 2 ; m V ; W g m g A u ; HW gQH pump P1u12P2u 22 Z1 H total Z 2 motor turbine hloss (J / N, m) g 2g g 2g turbine Turbine head ;W pump Pump head ; W Fx 100 ; mRe uD hloss (J / N ) or m :2 1 u2hs 1 ; Cc 2 gu2hs k;2ghs u1 u 2 22goFinlet m u1 P1A1oandFlat Plate : Stationary F Au 2Curved :Um L u2hf 4 f e d T 2 ghs h (1 Cv2 ); Dn60Fexit m u 2Moving F A u u m 2X Direction Fx Au 2 (1 Cos )o;P mVw t u m ;

MARKING GUIDELINENATIONAL CERTIFICATEAPRIL EXAMINATIONFLUID MECHANICS N512 APRIL This marking guideline consists of 17 pages.

MARKING GUIDELINE 1 MARK -2FLUID MECHANICS N5T650(E)(A12)T1MARK2QUESTION 11.1The density of a fluid could be defined as the mass per unit volume atstandard temperature and pressure. . The unit for density is kg/m. Thedensity is determined by dividing the mass in kg by the volume in m 3. ρ 1.2m kg kg/m V m3 (3)FIND DENSITY18,5mass 18,5 10 -3 kg1 00023,4 ml23,4 mlVolume 23,4 10 -3 l 23,4 10 6 m331 000 ml/l1 000 l/mm ρ V18,5 10 3 kgρ 23,4 10 6 m3 790,5kg/m 380,5 mmGIVEN : N 1 000 r/m T 1,85 Nm80mm1.3(2)100 mm

MARKING GUIDELINE1.3.1-3FLUID MECHANICS N5T650(E)(A12)TA π D π 0,08 0,1 0,02513 m 2 2 π N 2 π 1000 Rad/sω 104,719 Rad/s60 20 0,08mx ω R 104,719 Rad/s 4,188 m/s2 D d 0,0805 0,08Cr 0,00025 m22 T μ A x D 2 Crμ Cr T A x D 2 0,00025 m 1,85 Nm 0,02513 m 2 4,188 m/s 0,08 m μ 0,1098 Ns/m 2 1.3.21.3.3 1 000 R/s 1,85 Nm 60 193 WORPower Loss ω T 104,719 Ras/s 1,85 193 WattsPower loss ρ u d μμ Re μ ρ d0,1 098 Ns/m 2 300 780 kg/m 3 0,075 m 4,316 m/s (2)Re (4)[20]

MARKING GUIDELINE-4FLUID MECHANICS N5T650(E)(A12)TQUESTION 22.1The fluid pressure is applied to the inside of the flattened phosphor-bronze tubeand it tends to straighten out. This movement of the loose end of the tube iscommunicated through the gearing system to the pointer. The magnifiedmovement of the pointer then indicates the pressure applied on the scale whichis marked off in either Pa, kPa, MPa, PSI, mwater, etc. (6)2.2Given: Total weight 40 000 NDia. of ram 0,3 mStroke 3 m Friction loss 5%t 2 minDelivery vol. 7,5 litre

MARKING GUIDELINE2.2.12.2.22.2.3-5FLUID MECHANICS N5T650(E)(A12)Tπ x 0,3 24 0,07068 m 2stroke of ram L 3 mFriction 5% Net load on accumulato r taking friction (when descends)95F 40 000 x100 38 000 NTime taken by ram to fall through full stroket 2 min 2 x 60 120 seconds 120 seconds 3 m ( stroke)1 second x m/s3Distance moved by ram in one second 120 0,025 m/sWater supplied by pump Q 7,5l/s7,5l/s 1 000 0,075 m 3 /s WORK SUPPLIED BY THE ACCUMULATO R Work done by accumulato r per second Force x distance 38 000 x 0,025 m/s 950 Nm/s Area of ram INTENSITY OF PRESSURE OF WATERFPressure P Area of ram38 000N 0,07068 m 2 53 7634,4 N/m 2 (4)(2)PRESSURE HEADP xg537634,4 1000 x 9,81 54,805mPr essure head H

MARKING GUIDELINE2.2.42.2.52.2.6 -6FLUID MECHANICS N5T650(E)(A12)TWORK SUPPLIED BY PUMP / sWater sup plied by pump Q 7,5l / s7,5l / s 1000 0,0075m 3 / s Total work sup plied x g x H x Q 1000 x 9,81 x 54,805 x 0,2023 4032,258Nm / s (2) Total work Work supplied by accumulaot Work supplied bypump 950 4 032,258 4982,258 Nm/s Total work supplied per second1 0004 982,258 1 000 4,982 kW Power delivered (2) (2)[20]Please turn over

MARKING GUIDELINE-7FLUID MECHANICS N5T650(E)(A12)TQUESTION 33.1Given4 m 2 m 3 m HighPressure 50 kPaDepth 2,25 m OIL 850 kg/m 32,25 m3mOil2m4m3.1.1Consider 2 by 3 wallF1 P A 50 10 3 2 3 300 kN F2 ρgA y 850 kg/m 3 9,81 m/s 2 2,25 m 2 m 2,25 m2 42,214 kNFRe sul tan t F1 F2 300kN 42,214kN 342,214kN Consider 4 by 3 wallF1 P A 50 10 3 Pa 4 m 3 m 600 kN F2 ρgA y 850 kg/m 3 9,81 m/s 2 2,25 m 4 m 84,427 kNFResultant F1 F22,25 m2 600 kN 84427 kN 684,427 kN

MARKING GUIDELINE-8FLUID MECHANICS N53.1.2T650(E)(A12)TWallhF1F2FR1 2,2531,5m F1 1,5 m from top1 F2 2,25 m from top 3 2.25 3 Take moments about top of WallCWM ACWM F1 1,5 F2 2,25 FR h 600 1,5 84,427 2,25 684,427 hh

MARKING GUIDELINE3.2-9FLUID MECHANICS N5AT650(E)(A12)TBWater line1mRVC2,5 m 1 025 kg/m3HD3mFIND FORCE AND DIRECTION 2 Area ABCD 3 m 1 m 3 m 1,5 m 3 2 6mHORIZONTAL COMPONENTH ρgAy 1 025 kg/m 3 9,81 m/s 2 2,5 m 1 m 2,52 31422,656 N 31,423 kNVERTICAL COMPONENTV ρg 1 025 kg/m 3 9,81 m/s 2 6 m 3 60331,5 N 60,332 kN RESULTANTR 2 H2 V 2 R 31422,656 N 2 60331,5 2 68,0241 kN

MARKING GUIDELINE-10FLUID MECHANICS N5T650(E)(A12)TDIRECTIONVTanθ H Tan 1 θ60331,531422,656 62,488 0 62 0 29 '(9)[20]QUESTION 44.14.24.1.1A streak line or filament line is formed when particles of some dyeor colouring is injected into the stream during experimental work toform a line in the flow and make it visible. 4.1.2The velocity of any particle is a vector quantity having magnitudeand direction which vary from at any moment to moment. The pathfollowed by a particle is called a path line. 4.1.3A steam line in fluid flow is defined as the curve which if formed atany instant in time when the positions of successive particles isjoined, and which is tangential to the direction of motion of theparticles. (3 x 2)Given: 920 kg/m 35A 0,6 Pa.sC 2 l/s CU C 2 m/sB1Ratio 5 : 1 by volume

MARKING GUIDELINE4.2.1-11FLUID MECHANICS N5T650(E)(A12)T U A CC C AC CUC 0,002 m 3 /s2 m/s 0,001 m 2π d2 0,001 m 24But0,001 m 2 4 π 0,03568 m 35,68 mm dC4.2.2 CAB BUT A 5 B 5 CB(3)B C B60,002 m 3 /s 6 3,333 10 4 m 3 /s 5 And AB 5 3,333 10 4 m 3 /s 1,667 10 3 m 3 /s AB BVB3,333 10 4 m 3 /s2 m/s 1,6665 10 4 m 2 4 1,6665 10 4 m 2π 0,014567 m 14,567 mmdB