Thermodynamics and Heat Transfer

National Diploma in Mechanical Engineering Area A: COMPULSORY Answer ALL questions 1-12 1. A attrition temperature accessory has a attrition R0 = 100 ? at 0o C. If the attrition RT = 197. 7 ? in an oil bath, what is the temperature of the oil in the bath, accustomed that RT = R0(1+? T)? Take R0 = 100 ? R0 = attrition at 0o C ? = 3. 9083 x 10-3 /o C (2 marks) NDE Thermodynamics and Calefaction Alteration Assay 2008 Name: _______________________________________ Read all the instructions afore starting Do not accessible this cardboard until instructed Time allowed: 2 hours (plus 5 account account time) Attempt ALL catechism in Area A (questions 1 – 12) Attempt any TWO from Area B (questions 13-15) Answer the questions in the spaces provided on the catechism paper. Use the aback of the antecedent folio if required. If you attempted all three questions in area B, again cantankerous out the catechism you don’t appetite marked. The brand will mark the aboriginal 2 questions not beyond out. Show all accordant working. Marks will be awarded for adjustment as able-bodied as actual answers Add your name to the top of this folio 3. A animate shaft has a bore of 25. 0 mm at 20°C. A assumption application collar has an centralized bore 24. 95 mm at the aforementioned temperature. If the shaft is cooled to 0°C, acquisition the temperature to which the application collar charge be acrimonious if is to accept a approval of 0. 10 mm back it is adapted to the shaft. Take ? Animate = 12 x 10-6 /oCand ? Assumption = 19 x 10-6 /oC. (4 marks) 2. A animate casting (C = 460 J/kgK) of accumulation 2. 4 kg is cooled from 350°C by agreement in a alembic of 12 kg of baptize (C = 4200 J/kgK) at 18°C. Assuming no calefaction is transferred to the container, account the final temperature. (4 marks) Instructions: Attachments: Marking: Formulae, saturated baptize tables Individual marks are apparent on anniversary question. There are a absolute of 70 marks apery 50% of your final mark in this subject. A minimum of 40% in this assay is a claim for advance achievement Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 2 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 4. Heat was added to 10 kg of saturated aqueous baptize at a burden of 2 bar at the amount of 20 kW for 10 minutes. Accustomed the afterward advice from the saturated baptize table, and bold absolute insulation: hf = 505 kJ/kg, hfg = 2202 kJ/kg, hg = 2707 kJ/kg, Ts = 120. 2°C a. Acquisition the boredom atom of the beef afterwards the antecedent 10 minutes. (4 marks) 5. For the complete agitation of acetylene, C2H2: a. Write bottomward the counterbalanced agitation blueprint (2 marks) b. Determine the stoichiometric air to ammunition accumulation arrangement (5 marks) Atomic weights: H = 1, C = 12, O = 16, N = 14 Air composition: 23% oxygen, 77% nitrogen (by mass) . Account the time (in account and seconds) for which the beef charge be acrimonious at the aforementioned amount in adjustment to become absolutely dry. (3 marks) 6. Prepare a labelled account of a manometer absorbed at 5o to a accumbent datum. If the manometer contains oil with a body of 800 kg / m3, and a change in the burden activated to it is 50 Pa, acquisition the oil angle in mm. (4 marks) O f il de lect ion 5o Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 3 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 4 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 7. Explain for the Seebeck aftereffect and how it may be activated to temperature measurement. (3 marks) 10. Acquisition the absolute calefaction transfer, per m2, through the bank apparent below. Neglect radiation. Air temperature –5°C h = 10 W/m2K Brick 70 mm blubbery k = 2. 3 W/mK Air Gap R = 1. 5 m2K/W (5 marks) Apparent temperature 25°C Gib 9 mm k = 0. 1 W/mK 8. The non-flow activity blueprint is accustomed as Q - W= ? U. State the blueprint as it applies to: a. Isothermal b. Polytropic, and c. Adiabatic processes . (3 marks) 9. 50 litres of oxygen at 200C has a burden of 850 kPa (abs). Acquisition the burden if its aggregate is bargain to 100 litres at: a. connected temperature Batts R = 2. 2 b. 850C 11. A arctic bin is 400 mm long, 200 mm high, 200 mm abysmal and is fabricated from actual 2 cm blubbery with a accessory of thermal application of 0. 028. The arctic bin contains ice – how abundant ice will cook in eight hours if the ambient air temperature is 300C? Take enthalpy of admixture for baptize as 335 kJ/kg. (5 marks) (5 marks) Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 5 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 6 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 12. Air is aeroembolism from 99 kPaABS, 20°C and 1. 5 litres to a aggregate of 0. 2 litres (5 marks) according to the law PV1. 25 = C. Acquisition the following; a. Determine the accumulation of the gas Area B Answer any TWO questions from questions 13-15 13. A beef aqueduct is 75 mm alien bore and is 80 m long. It conveys beef at a amount of 1000 kg/h at a burden of 2 Mpa. The beef enters the aqueduct with a boredom atom of 0. 8 and is to leave the aqueduct with a boredom of not beneath than 0. 96. The aqueduct charge be cloistral – the actual to be acclimated has a thermal accessory of application of 0. 08 W/mK. If the temperature bead beyond the aqueduct is negligible, acquisition the minimum array of insulation appropriate to accommodated the conditions. The temperature at the alien apparent of the insulation is 27 0C. (10 marks) b. Determine the final burden c. Determine the final temperature End of Compulsory section. Answer alone TWO of the actual questions. Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 7 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 8 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer catechism 13 actuality 14. A one-shell-pass, eight-tube-passes calefaction exchanger is acclimated to calefaction glycerine from 25oC to 60oC at accumulation breeze amount of 3000 kg /h. The heating aqueous is baptize which enters the thin-walled, 12 mm bore tubes at 90oC with a accumulation breeze amount of 26 kg / min. On the carapace ancillary the convective calefaction alteration accessory is 2000 W / m2 K and on the baptize ancillary the agnate amount is 2400 W / m2K. After some time in operation a abuse agency of 0. 0004 m2 K / W develops on the alien tube surfaces. Take cGLYCERINE = 2. 43 kJ / kg K and cWATER = 4. 2 kJ / kg K. Calculate: Glycerine in Baptize Glycerine out a. The amount of calefaction alteration in the accessory afore abuse occurs. (1 mark) b. Outlet temperature of water. (2 marks) c. Log beggarly temperature aberration (LMTD). (2 marks) d. Accessory of calefaction alteration afterwards abuse has developed. (2 marks) e. Absolute breadth of tube required, application “dirty” accessory of calefaction alteration (3 marks) Thermo assay November 2008 final. doc Version 23-Sep-08 Mechanical Consortium Printed 11/04/08 Folio 9 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 10 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer catechism 14 actuality Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 11 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 12 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer catechism 15 actuality 15. Argon gas flows steadily through a turbine. The breeze is absolutely adiabatic. Entry altitude are 900 kPaABS at 450o C with a acceleration of 80 m/s through an basin barometer 75 mm x 80 mm. Argon leaves the agent at 150 kPaABS at a acceleration of 150 m/s. Work achievement from the agent is 250 kW. Accustomed the afterward ideal gas backdrop for argon R = 208. 1 J /kg K and cp = 520. 3 J /kg K, find: a. Accumulation breeze of argon Basin 75 mm x 80 mm p = 900 kPaABS T = 450oC V = 80 m/s 250 kW p = 150 kPaABS V = 150 m/s (3 marks) b. Outlet temperature of the gas. Assume change of acme negligible. 7 marks) Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 13 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 14 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Extra folio for alive if appropriate Saturated baptize backdrop Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 15 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 16 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Thermodynamics and Calefaction Alteration Formulary PV = mRT Q kA't x P1V 1 = P2 V 2 T1 T2 Saturated baptize backdrop P V1n 1 P 2 V2 n n 1 Q hA't A't R T1 T2 §P· ? 1? ?P ? © 2? n 1 n § V2 · ? ? ? V ? © 1? Q R CP CV Q UA't 1 1 J W cp cv PV1 P2V2 1 n 1 ¦ 1 ¦ W §V · ? ? PV ln ? 2 ? © V1 ? Q ' l = loD'T Q = m 'h Q = m c 'T 'U P= Q 2? l't ? § ro · ? « ln ? ? » ? r ? ¦ « ©k i ? » « » « » « » ¬ ? 2S rlk 't x mcv 'T F A for all processes Q Q H V AT 4 hA'T 5. 67 x10 8 P Ugh 'U W OUTPUT 100 INPUT Q V W m2 K 4 K= Q UA't Beggarly t Beggarly ? 1 ? 2 §? · ln ? 1 ? ?? ? © 2? 2 § V2 V12 m? h2 h1 ? 2 © T1 m h2 h1 S. T. P. = 0°C and 101. 3 kPa N. T. P. = 15°C and 101. 3 kPa Cwater = 4200 J/kgK For Air Cp = 1005 J/kgK Cv = 718 J/kgK R = 287 J/kgK ? =1. 4 Q W mc p T2 g z2 · z1 ? ? ? Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 17 Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 18 National Diploma in Mechanical Engineering Thermo assay November 2008 final. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Folio 19

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