Thermodynamics and Heat Transfer

Nationwide Diploma in Mechanical Engineering Part A: COMPULSORY Reply ALL questions 1-12 1. A resistance temperature machine has a resistance R0 = 100 ? at 0o C. If the resistance RT = 197. 7 ? in an oil tub, what’s the temperature of the oil within the tub, provided that RT = R0(1+? T)? Take R0 = 100 ? R0 = resistance at 0o C ? = Three. 9083 x 10-Three /o C (2 marks) NDE Thermodynamics and Warmth Switch Examination 2008 Identify: _______________________________________
Learn all of the directions earlier than beginning Don’t open this paper till instructed Time allowed: 2 hours (plus 5 minutes studying time) Try ALL query in Part A (questions 1 – 12) Try any TWO from Part B (questions 13-15) Reply the questions within the areas supplied on the query paper. Use the again of the earlier web page if required. If you happen to tried all three questions in part B, then cross out the query you don’t need marked. The marker will mark the primary 2 questions not crossed out. Present all related working.
Marks will likely be awarded for technique in addition to appropriate solutions Add your identify to the highest of this web page Three. A metal shaft has a diameter of 25. zero mm at 20°C. A brass retaining collar has an inner diameter 24. 95 mm on the similar temperature. If the shaft is cooled to zero°C, discover the temperature to which the retaining collar should be heated if is to have a clearance of zero. 10 mm when it’s fitted to the shaft. Take ? Metal = 12 x 10-6 /oCand ? Brass = 19 x 10-6 /oC. (four marks) 2. A metal casting (C = 460 J/kgK) of mass 2. four kg is cooled from 350°C by putting in a container of 12 kg of water (C = 4200 J/kgK) at 18°C.

Assuming no warmth is transferred to the container, calculate the ultimate temperature. (four marks) Directions: Attachments: Marking: Formulae, saturated water tables Particular person marks are proven on every query. There are a complete of 70 marks representing 50% of your last mark on this topic. A minimal of 40% on this examination is a requirement for course completion Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 2 Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering four.
Warmth was added to 10 kg of saturated liquid water at a stress of two bar on the fee of 20 kW for 10 minutes. Given the next data from the saturated water desk, and assuming excellent insulation: hf = 505 kJ/kg, hfg = 2202 kJ/kg, hg = 2707 kJ/kg, Ts = 120. 2°C a. Discover the dryness fraction of the steam after the preliminary 10 minutes. (four marks) 5. For the entire combustion of acetylene, C2H2: a. Write down the balanced combustion equation (2 marks) b. Decide the stoichiometric air to gasoline mass ratio (5 marks) Atomic weights: H = 1, C = 12, O = 16, N = 14 Air composition: 23% oxygen, 77% nitrogen (by mass) . Calculate the time (in minutes and seconds) for which the steam should be heated on the similar fee as a way to develop into absolutely dry. (Three marks) 6. Put together a labelled sketch of a manometer inclined at 5o to a horizontal datum. If the manometer accommodates oil with a density of 800 kg / m3, and a change within the stress utilized to it’s 50 Pa, discover the oil deflection in mm. (four marks) O f il de lect ion 5o Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page Three Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08
Web page four Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering 7. Clarify for the Seebeck impact and the way it could also be utilized to temperature measurement. (Three marks) 10. Discover the full warmth switch, per m2, by way of the wall proven under. Neglect radiation. Air temperature –5°C h = 10 W/m2K Brick 70 mm thick ok = 2. Three W/mK Air Hole R = 1. 5 m2K/W (5 marks) Floor temperature 25°C Gib 9 mm ok = zero. 1 W/mK eight. The non-flow power equation is given as Q – W= ? U. State the equation because it applies to: a. Isothermal b. Polytropic, and c. Adiabatic processes . (Three marks) 9. 50 litres of oxygen at 200C has a stress of 850 kPa (abs). Discover the stress if its quantity is lowered to 100 litres at: a. fixed temperature Batts R = 2. 2 b. 850C 11. A cold bin is 400 mm lengthy, 200 mm excessive, 200 mm deep and is constituted of materials 2 cm thick with a coefficient of thermal conductivity of zero. 028. The chilly bin accommodates ice – how a lot ice will soften in eight hours if the ambient air temperature is 300C? Take enthalpy of fusion for water as 335 kJ/kg. (5 marks) (5 marks) Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 5
Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 6 Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering 12. Air is compressed from 99 kPaABS, 20°C and 1. 5 litres to a quantity of zero. 2 litres (5 marks) in keeping with the legislation PV1. 25 = C. Discover the next; a. Decide the mass of the gasoline Part B Reply any TWO questions from questions 13-15 13. A steam pipe is 75 mm exterior diameter and is 80 m lengthy. It conveys steam at a fee of 1000 kg/h at a stress of two Mpa. The steam enters the pipe with a dryness fraction of zero. eight and is to depart the pipe with a dryness of not lower than zero. 96. The pipe should be insulated – the fabric for use has a thermal coefficient of conductivity of zero. 08 W/mK. If the temperature drop throughout the pipe is negligible, discover the minimal thickness of insulation required to satisfy the circumstances. The temperature on the outer floor of the insulation is 27 0C. (10 marks) b. Decide the ultimate stress c. Decide the ultimate temperature Finish of Obligatory part. Reply solely TWO of the remaining questions. Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08
Web page 7 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page eight Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering Reply query 13 right here 14. A one-shell-pass, eight-tube-passes warmth exchanger is used to warmth glycerine from 25oC to 60oC at mass movement fee of 3000 kg /h. The heating liquid is water which enters the thin-walled, 12 mm diameter tubes at 90oC with a mass movement fee of 26 kg / min. On the shell facet the convective warmth switch coefficient is 2000 W / m2 Ok and on the water facet the corresponding worth is 2400 W / m2K.
After a while in operation a fouling issue of zero. 0004 m2 Ok / W develops on the outer tube surfaces. Take cGLYCERINE = 2. 43 kJ / kg Ok and cWATER = four. 2 kJ / kg Ok. Calculate: Glycerine in Water Glycerine out a. The speed of warmth switch within the machine earlier than fouling happens. (1 mark) b. Outlet temperature of water. (2 marks) c. Log imply temperature distinction (LMTD). (2 marks) d. Coefficient of warmth switch after fouling has developed. (2 marks) e. Complete size of tube required, utilizing “soiled” coefficient of warmth switch (Three marks) Thermo examination November 2008 last. doc Model 23-Sep-08 Mechanical Consortium Printed 11/04/08 Web page 9 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 10 Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering Reply query 14 right here Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 11 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 12 Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering Reply query 15 right here 15.
Argon gasoline flows steadily by way of a turbine. The movement is solely adiabatic. Entry circumstances are 900 kPaABS at 450o C with a velocity of 80 m/s by way of an inlet measuring 75 mm x 80 mm. Argon leaves the turbine at 150 kPaABS at a velocity of 150 m/s. Work output from the turbine is 250 kW. Given the next very best gasoline properties for argon R = 208. 1 J /kg Ok and cp = 520. Three J /kg Ok, discover: a. Mass movement 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 (Three marks) b. Outlet temperature of the gasoline. Assume change of top negligible. 7 marks) Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 13 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 14 Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering Further web page for working if required Saturated water properties Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 15 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 16
Nationwide Diploma in Mechanical Engineering Nationwide Diploma in Mechanical Engineering Thermodynamics and Warmth Switch Formulary PV = mRT Q kA’t x P1V 1 = P2 V 2 T1 T2 Saturated water properties 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 ? ¦ « ©ok i ? » « » « » « » ¬ ? 2S rlk ‘t x mcv ‘T F A for all processes Q Q H V AT four hA’T 5. 67 x10 eight P Ugh ‘U W OUTPUT 100 INPUT Q V W m2 Ok four Ok= Q UA’t Imply t Imply ? 1 ? 2 §? · ln ? 1 ? ?? ? © 2? 2 § V2 V12 m? h2 h1 ? 2 © T1 m h2 h1 S. T. P. = zero°C and 101. Three kPa N. T. P. = 15°C and 101. Three kPa Cwater = 4200 J/kgK For Air Cp = 1005 J/kgK Cv = 718 J/kgK R = 287 J/kgK ? =1. four Q W mc p T2 g z2 · z1 ? ? ? Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 17 Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 18 Nationwide Diploma in Mechanical Engineering Thermo examination November 2008 last. doc Model 23-Sep-08 ?Mechanical Consortium Printed 11/04/08 Web page 19

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