Thermodynamics and Heat Transfer

National Diploma in Mechanical Engineering Section A: COMPULSORY Answer ALL inquiries 1-12 1. An obstruction temperature gadget has an opposition R0 = 100 ? at 0o C. In the event that the obstruction RT = 197. 7 ? in an oil shower, what is the temperature of the oil in the shower, given that RT = R0(1+? T)? Take R0 = 100 ? R0 = opposition at 0o C ? = 3. 9083 x 10-3/o C (2 imprints) NDE Thermodynamics and Heat Transfer Exam 2008 Name: _______________________________________ Peruse all the guidelines before beginning Do not open this paper until educated Time permitted: 2 hours (in addition to 5 minutes understanding time) Attempt ALL inquiry in Section A (questions 1 †12) Attempt any TWO from Section B (questions 13-15) Answer the inquiries in the spaces gave on the inquiry paper. Utilize the rear of the past page whenever required. In the event that you endeavored each of the three inquiries in area B, at that point cross out the inquiry you don’t need stamped. The marker will stamp the initial 2 inquiries not crossed out. Show all important working. Imprints will be granted for strategy just as right answers Add your name to the highest point of this page 3. A steel shaft has a measurement of 25. 0 mm at 20 °C. A metal holding neckline has an inward breadth 24. 95 mm at a similar temperature. In the event that the pole is cooled to 0 °C, discover the temperature to which the holding neckline must be warmed if is to have a freedom of 0. 10 mm when it is fitted to the pole. Take ? Steel = 12 x 10-6/oCand ? Metal = 19 x 10-6/oC. (4 imprints) 2. A steel throwing (C = 460 J/kgK) of mass 2. 4 kg is cooled from 350 °C by putting in a holder of 12 kg of water (C = 4200 J/kgK) at 18 °C. Accepting no warmth is moved to the holder, compute the last temperature. (4 imprints) Instructions: Attachments: Marking: Formulae, immersed water tables Individual imprints are appeared on each question. There are an aggregate of 70 imprints speaking to half of your last imprint in this subject. At least 40% in this test is a necessity for course finishing Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 2 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 4. Warmth was added to 10 kg of immersed fluid water at a weight of 2 bar at the pace of 20 kW for 10 minutes. Given the accompanying data from the soaked water table, and accepting immaculate protection: hf = 505 kJ/kg, hfg = 2202 kJ/kg, hg = 2707 kJ/kg, Ts = 120. 2 °C a. Discover the dryness division of the steam after the underlying 10 minutes. (4 imprints) 5. For the total burning of acetylene, C2H2: a. Record the reasonable burning condition (2 imprints) b. Decide the stoichiometric air to fuel mass proportion (5 imprints) Atomic loads: H = 1, C = 12, O = 16, N = 14 Air piece: 23% oxygen, 77% nitrogen (by mass) . Figure the time (in minutes and seconds) for which the steam must be warmed at a similar rate so as to turn out to be completely dry. (3 imprints) 6. Set up a named sketch of a manometer slanted at 5o to a flat datum. In the event that the manometer contains oil with a thickness of 800 kg/m3, and an adjustment in the weight applied to it is 50 Pa, discover the oil redire ction in mm. (4 imprints) O f il de lect particle 5o Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 3 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 4 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 7. Clarify for the Seebeck impact and how it might be applied to temperature estimation. (3 imprints) 10. Locate the all out warmth move, per m2, through the divider demonstrated as follows. Disregard radiation. Air temperature â€5 °C h = 10 W/m2K Brick 70 mm thick k = 2. 3 W/mK Air Gap R = 1. 5 m2K/W (5 imprints) Surface temperature 25 °C Gib 9 mm k = 0. 1 W/mK 8. The non-stream vitality condition is given as Q †W= ? U. Express the condition as it applies to: a. Isothermal b. Polytropic, and c. Adiabatic procedures . (3 imprints) 9. 50 liters of oxygen at 200C has a weight of 850 kPa (abs). Discover the weight if its volume is decreased to 100 liters at: a. steady temperature Batts R = 2. 2 b. 850C 11. A cold receptacle is 400 mm long, 200 mm high, 200 mm profound and is produced using material 2 cm thick with a coefficient of warm conductivity of 0. 028. The nippy receptacle con tains ice †what amount ice will liquefy in eight hours if the surrounding air temperature is 300C? Take enthalpy of combination for water as 335 kJ/kg. (5 imprints) (5 imprints) Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 5 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 6 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering 12. Air is packed from 99 kPaABS, 20 °C and 1. 5 liters to a volume of 0. 2 liters (5 imprints) as per the law PV1. 25 = C. Locate the accompanying; a. Decide the mass of the gas Section B Answer any TWO inquiries from questions 13-15 13. A steam pipe is 75 mm outside width and is 80 m long. It passes on steam at a pace of 1000 kg/h at a weight of 2 Mpa. The steam enters the channel with a dryness part of 0. 8 and is to leave the channel with a dryness of at the very least 0. 96. The funnel must be protected †the material to be utilized has a warm coefficient of conductivity of 0. 08 W/mK. In the event that the temperature drop over the funnel is immaterial, locate the base thickness of protection required to meet the conditions. The temperature at the external surface of the protection is 27 0C. (10 imprints) b. Decide the last weight c. Decide the last temperature End of Compulsory segment. Answer just TWO of the rest of the inquiries. Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 7 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 8 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer question 13 here 14. A one-shell-pass, eight-tube-passes heat exchanger is utilized to warm glycerine from 25oC to 60oC at mass stream pace of 3000 kg/h. The warming fluid is water which enters the meager walled, 12 mm measurement tubes at 90oC with a mass stream pace of 26 kg/min. On the shell side the convective warmth move coefficient is 2000 W/m2 K and on the water side the comparing esteem is 2400 W/m2K. After some time in activity a fouling variable of 0. 0004 m2 K/W creates on the external cylinder surfaces. Take cGLYCERINE = 2. 43 kJ/kg K and cWATER = 4. 2 kJ/kg K. Figure: Glycerine in Water Glycerine out a. The pace of warmth move in the gadget before fouling happens. (1 imprint) b. Outlet temperature of water. (2 imprints) c. Log mean temperature distinction (LMTD). (2 imprints) d. Coefficient of warmth move subsequent to fouling has created. (2 imprints) e. Complete length of cylinder required, utilizing â€Å"dirty† coefficient of warmth move (3 imprints) Thermo test November 2008 last. doc Version 23-Sep-08 Mechanical Consortium Printed 11/04/08 Page 9 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 10 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer question 14 here Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 11 Thermo t est November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 12 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Answer question 15 here 15. Argon gas streams consistently through a turbine. The stream is altogether adiabatic. Passage conditions are 900 kPaABS at 450o C with a speed of 80 m/s through a gulf estimating 75 mm x 80 mm. Argon leaves the turbine at 150 kPaABS at a speed of 150 m/s. Work yield from the turbine is 250 kW. Given the accompanying perfect gas properties for argon R = 208. 1 J/kg K and cp = 520. 3 J/kg K, discover: a. Mass progression of argon Inlet 75 mm x 80 mm p = 900 kPaABS T = 450oC V = 80 m/s 250 kW p = 150 kPaABS V = 150 m/s (3 imprints) b. Outlet temperature of the gas. Accept change of tallness unimportant. 7 imprints) Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 13 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 14 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Extra page for working whenever required Saturated water properties Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 15 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 16 National Diploma in Mechanical Engineering National Diploma in Mechanical Engineering Thermodynamics and Heat Transfer Formulary PV = mRT Q kA't x P1V 1 = P2 V 2 T1 T2 Saturated water properties P V1n 1 P 2 V2 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 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 procedures 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 Mean t Mean ? 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 test Novembe r 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page 17 Thermo test November 2008 last. doc Version 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Page