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MARKING GUIDELINENATIONAL CERTIFICATEAPRIL EXAMINATIONPOWER MACHINES N5APRIL This marking guideline consists of 8 pages.
MARKING GUIDELINE-2POWER MACHINES N5T.(E)(A.)TQUESTION 11.1U 60p 1,96 389860400 m / sU 0,4 Ci\Ci 1.2 1.3pDN(3)U0,44000,41000 m / s(3)Diagram on next page.
MARKING GUIDELINE-3POWER MACHINES N5T.(E)(A.)T(8)
MARKING GUIDELINE1.4-4POWER MACHINES N5T.(E)(A.)T1.4.1Cri 645 m/s(1)1.4.2Cre 567,6 m/s(1)1.4.3Ce 330 m/s(1)1.4.4Fc m(cfi - cfe )100(375 - 325)6083,333 N(3)[20]QUESTION 22.12.2The efficiency of any boiler is defined by the ratio of heat transferred to feedwaterin converting it to steam divided by the heat suppliedby thecomplete combustion of the fuel.2.2.1EE \Total Heat h 2.2.2h1 Total Heat Transferred22572257 EE2257 11,225278,4 kJ / kgTotal Heat100 Calorific Value 125278,4 100 30000184,26 %(6)158 kJ / kgHeat GainedM s (h2 - h1 ) Heat LostMf Cv hh2 Mf Cv h h1Ms 1775 30000 0,8426 158180002650,692 kJ / kgAt 2500 kPa the hg for dry steam is 2801 kJ / kg .\ The steam is wet , because hg is greater than h2 .Copyright reserved(4)(6)Please turn over
MARKING GUIDELINE2.2.3-5POWER MACHINES N5 hwetT.(E)(A.)Thf xhfghw - hfhfg2650,692 - 962 1839 0,918\ The steam is 91,8% dry. x(4)[20]QUESTION 33.1PV R PVV MT rT115 11, 75 2930, 2243 kJ / kg.KQ M Cp (T2 - T1 )Cp QM (T2 - T1 ) 3.2 800,75(399 - 293)1,0063 kJ / kg.K Cp - CvCp - R1,0063 - 0,2243 0,782 kJ / kg.K M Cv(T2 - T1 ) 3.33.43.5MRTRCvDUV1Copyright reserved 0,75 0,782(399 - 293) 62,169 kJ (3)(3)(3)(3)Mr 0, 751, 75 0, 42857 m3(2)Please turn over
MARKING GUIDELINE3.6V2 -6POWER MACHINES N5T.(E)(A.)TMRT2P20,75 0,224 3991150,58289 m 3orV2 0, 42857 3992930,5836 m3 P2 (V2 - V1 ) 3.7WDV1T2T1 115(0,58289 - 0,42857 ) 17,7468 kJ(3)orWD mR (T2 - T1 ) 0, 75 0, 224 ( 399 - 293) 17,81 kJ(3)[20]QUESTION 44.1Vs (V1 - V3 ) Copyright reservedp D2 L4p 0, 222 0,3140, 01178 m3(3)Please turn over
MARKING GUIDELINE4.2V3V1V4-7POWER MACHINES N5 0,055(V1 - V3 ) 0,055 0,01178 0,00065 m 3 Vs Vc 0,01178 0,00065 0,01243 m 3 æPV3 çç 3è P4T.(E)(A.)T1ön ø1 æ 650 ö 1, 350,00065ç è 98 ø0,00264 m 3 V1 - V4 0,01243 - 0,00264 0,00979 m 3 \Ve4.3Pf V fTfVf P1 (V1 - V4 )T1P1 (V1 - V4 ) T fPf T198 ( 0, 01243 - 0, 00264 ) 288101,325 2910, 00937 m3\Free Air Delivered / min4.4h vol Copyright reserved(9) 0, 00937 N0, 00937 650 6, 0905 m3 / min(5)V1 - V4 100 V1 - V310,00979 100 0,01178 183,1 %(3)[20]Please turn over
MARKING GUIDELINE-8POWER MACHINES N5T.(E)(A.)TQUESTION 55.1Fµh10, 33 6 9,81 19, 424 N L2 - r12 0, 332 - 0,132 w1 \ N1h2m h19,81( 6 1,8 ) - 19, 4241,8 0, 303 w1 602p 10, 231 602 p97, 7 r / min L2 - r2 2 0,332 - 0, 212 \N2g ( M m) - F µ10, 231 rad / s w20, 303 m 5.2µ Mg 0, 255 mg ( M m) - F µm h29,81( 6 1,8 ) - 19, 4241,8 0, 255 11,153 rad / s w2 602p (12)11,153 602 p106,5 r / min(8)[20]TOTAL:Copyright reserved100