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Textbook 3rd Year 2019 : ENGINEERING MECHANICS

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Thambi Durai
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DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DOC.NO. : TKEC/MECH/ACADEMIC/1 DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK SUBJECT CODE & NAME: STAFF INCHARGE: UNIT - I (TWO MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. QUESTIONS REMARKS Define Fourier s Law of Conduction MAY/JUN 2013 What is lumped system analysis? When is it use? MAY/JUN 2013 Define time constant for a temperature sensor APR/MAY 2014 Define Coefficient of Thermal conductivity. NOV/DEC 2009. Write the Poisson's equation for heat conduction. APRMAY 2010 What is heat generation in solids? Give examples. APR/MAY 2011 What-do you understand by critical radius of insulation? OCT/NOV 2013 What is lumped analysis OCT/NOV 2013 What do you understand by critical radius of insulation and give its expression? Define fin efficiency and effectiveness. What is the functional meaning of the term "infinite fin". APR/MAY 2014 What are the two methods of heat conduction in solids? NOV/DEC 2011 What is the purpose of attaching fins to a surface? What are the different types of fin profiles? Give some examples of heat transfer in engineering. Define Temperature field. What is Poisson's equation for heat flow? Give examples for initial'&; boundary conditions. What is meant by Transient heat conduction? What is meant by thermal resistance? What is the function of insulating materials? UNIT - I (SIXTEEN MARKS) DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK S.NO 1. 2. 3. 4. 5. 6. QUESTIONS REMARKS a. An electrical wire of 10 m length and 1 mm diameter dissipates 200 W in air at 25 C. The convection heat transfer coefficient between the wire surface and air is 15 W/m2K. Calculate the critical radius of insulation and also determine the temperature of the wire if it is insulated to the critical thickness of insulation b. A furnace wall consists of three layers. The inner layer of 10 cm thickness is made of firebrick (k =1.04 W/mK). The intermediate layer of 25 cm thickness is made of OCT/NOV 2015 masonry brick (k = 0.69 W/mK) followed by a 5 cm thick concrete wall (k = 1.37 W/mK). When the furnace is in continuous operation the inner surface of the furnace is at 800 C while the outer concrete surface is at 50 C. Calculate the rate of heat loss per unit area of the wall, the temperature at the interface of the firebrick and masonry brick and the temperature at the interface of the masonry brick and concrete. a.What is meant lumped capacity? What are the physical assumptions necessary for a lumped capacity unsteady state analysis to apply? (4) (iii)A slab of Aluminum 5 cm thick initially at 200 C is suddenly immersed in a liquid at 70 C for which the convection heat transfer co-efficient is 525 W/m2K. Determine the temperature at a depth of 12.5 mm from one of the faces 1 minute after the immersion. Also calculate the energy removed per unit area from the plate during 1 minute of immersion. Take P = 2700 bar, Cp = 0.9 kJlkg. OK, k=215W/mK, = 8.4X 10-5 m2/s b.Define the Biot and Fourier numbers c. Explain the different modes of heat transfer with appropriate expressions. A composite wall is formed of a 2.5 cm copper plate (k = 355 W/m.K), a 3.2 mm layer of asbestos (k = 0.110 W/m.K) and a 5 cm layer of fiber plate (k = 0.049 W/m.K). The wall is subjected to an overall temperature difference of 560 C (560 C on the Cu plate side and O C on the fiber plate side). Estimate the heat flux through this composite ~all and the interface temperature between asbestos and fiber plate. A steel tube k=43.26 W/mK of 5.08 cm 10 and 7.62 cm 00 is covered with 2.54 cm of asbestos Insulation k=0.208 W/mK The inside surface of the tube receives heat by convection from a hot gas at a -temperature of 316 C with heat transfer coefficient ha=284 W/m2K while the outer surface of Insulation is exposed to atmosphere air at 38 C with heat transfer coefficient of 17W/m2K Calculate heat loss to atmosphere for 3 m length of the tube and temperature drop across each layer. A pipe consists of 100 mm internal diameter and 8 mm thickness carries steam at 170 C. The convective heat transfer coefficient on the inner surface of pipe is 75 W/m2C. The pipe is insulated by two layers of insulation. The first layer of insulation is 46 mm in thickness having thermal conductivity of 0.14 W/m C. The second layer of insulation is also 46 mm in thickness having thermal conductivity of 0.46 W/mC. Ambient air temperature = 33 C. The convective heat transfer coefficient from the outer surface of pipe = 12 W/m2C. Thermal conductivity of steam pipe = 46 W/m C. Calculate the heat loss per unit length of pipe and determine the interface temperatures. Suggest the materials used for insulation. Two square plates, each of 5 m2 area, are separated by a gap of 6 mm. One plate, whose surface emissivity is 0.7, is at a temperature of 900 K. The other plate has surface emissivity of 0.95 and a temperature of 300 K. Assuming the plates to be much larger than the nan, calculate the net radiation heat exchange between the OCT/NOV 2013 -plates. If a thin polished metal sheet of surface emissivity 0.15 on both sides is interposed between two plates, calculate the steady state temperature and new net radiation exchange through the system. Calculate how many times the heat loss by radiation will be reduced. DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 7. 8. 9. 10. (i) Discuss the general arrangement of parallel flow, counter flow and cross flow heat exchangers. (ii) In a double pipe counter flow heat exchanger 10000 kg/h of an oil having a specific heat of 2095 J/kgK is cooled from 80*C to 50*C by 8000 kg/h of water entering at 25*C. Determine the heat exchanger area for an overall heat transfer coefficient of 300 W/M2K. Take Cp for water as 4180 J/kgK. A composite wall consists. of 10 cm thick layer of building brick, k = 0.7 W/mK and 3 cm thick plaster, k = 0.5 W/mK. An insulating material of k = 0.08 W/mK is to be added to reduce the heat transfer through the wall by 40%. Find its thickness. (10) 06. Circumferential aluminium fins of rectangular profile (1.5cmwide and 1mm thick) are fitted on to a 90 mm engine cylinder with a pitch of 10 mm. The height of the cylinder is 120 mm. The cylinder base temperature before and after fitting the fins are 200 C and 150 C respectively. Take ambient at 30 C and h(average) =100 W/m K. 2 Estimate the heat dissipated from the finned and the unfinned s urface areas of cylinder body. A steel tube k=43.26 W/mK of 5.08 cm 10 and 7.62 cm 00 is covered with 2.54 cm of asbestos Insulation k=0.208 W/mK The inside surface of the tube receives heat by convection from a hot gas at a -temperature of 316 C with heat transfer coefficient h =284 W/m K while the outer 2 a surface of Insulation is ex posed to atmosphere air at 38 C with heat transfer coefficient of 17 W/m2K Calculate heat loss to atmosphere for 3 m length of the tube and temperature drop across each layer A composite wall is formed of a 2.5 cm copper plate (k = 355 W/m.K), a 3.2 mm layer of asbestos (k = 0.110 W/m.K) and a 5 cm layer of fiber plate (k = 0.049 W/m.K). The wall is subjected to an overall temperature difference of 560 C (560 C on the Cu plate side and O C on the fiber plate side). Estimate the heat flux through this composite ~all and the interface temperature between asbestos and fiber plate UNIT - II (TWO MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. QUESTIONS REMARKS What is the reciprocity relation for view factor OCT/NOV 2013 What is a radiation shield and how is net radiation transfer -between two surfaces affected by an intervening shield OCT/NOV 2013 What do you mean by Reynolds colburn analogy APR/MAY 2014 When water at a mean temperature of 40 C flows through a square tube 5m long, the flow is fully developed and the wall temperature is maintained at 90 C. What will be the convective heat transfer coefficient APR/MAY 2014 What is lumped system analysis? When is it used? APR/MAY 2011 In which mode of heat transfer is the convection heat transfer coefficient usually higher, natural or forced convection? Why? APR/MAY 2011 Define thermal boundary layer thickness APR/MAY 2010 What do you understand by free and forced convection? APR/MAY 2010 Define grashof number NOV/DEC 2014 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Name four dimensions used for dimensional analysis NOV/DEC 2014 What is Convective heat transfer? Sketch formation of boundary layer and show laminar, transition & turbulent flow Write down differential equation for Continuity of fluid flow. Define velocity boundary layer thickness APR/MAY 2015 What is Colburn analogy? Distinguish between laminar and turbulent flow APR/MAY 2015 Give examples for free convection. Sketch, temperature and velocity profiles in free convection on a vertical wall. Define momentum thickness. What are the uses of dimensional analysis? UNIT - II (SIXTEEN MARKS) S.NO 1. 2. 3. 4. 5. QUESTIONS a. Define reynold s,nessult and prandtl number b. Sketch the boundary layer development of a flow over a flat plate and explain the significance of the boundary layer. Air at 200 kPa and 200 C is heated as it flows through a tube with a diameter of 25 mm at a velocity of 10 m./sec. The wall temperature is maintained constant and is 20 C above the air temperature all along the length of tube. Calculate: (i) The rate of heat transfer per unit length of the tube. (ii) Increase in the bulk temperature of air over a 3 m length of the tube. Air at 400 K and 1 atm pressure flows at a speed of 1.5 m/s over a flat plate of 2 m long. The plate is maintained at a uniform temperature of 300 K. If the plate has a width of 0.5 m, estimate the heat transfer coefficient and the rate of heat transfer from the air stream to the plate. Also estimate the drag force acting on the plate A 5-cm-thick iron plate fk = 60 W /m C), c P = 460 J/(kg C), p = 7850 kg/m3 , and a = 1.6 x 10"5 m2/s] is initially-at T, = .225 C. Suddenly, both surfaces are exposed to an ambient at T = 25 C with a heat transfer coefficient h = 500 W/m2 C. Calculate the center temperature at t = 2 min after the start of the cooling. Calculate the energy removed from the-plate per square meter during this time. A steel rod of diameter D = 2cm, length L = 25 cm, and thermal conductivity k = 50 W/(m C) is exposed to ambient air at T = 200C with a heat transfer coefficient, h = 64 W/(m2 C). If one end of the rod is maintained at a temperature of 120 C, calculate the heat loss from the rod. REMARKS OCT/NOV 2015 OCT/NOV 2013 OCT/NOV 2013 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 6. 7. 8. 9. 10. A thermometer pocket is inserted in a pipe of 150mm diameter carrying hot air. The pocket is made of brass (k = 70 W/m C). The inner and outer diameter of the pocket are 10 mm and 15 mm respectively. The heat transfer coefficient between the pocket and air is given by Nu = 0.174 ( R e ) 0 6 1 8 , Reynolds number (Re) of airflow = 25000 Take k (air) = 0.035 W/m C and depth of pocket = 50 mm Find the actual error in temperature measurement if the pipe wall is at 50 C and air temperature is 150 C. Cylindrical cans of 150 mm length and 65 mm diameter are to be cooled from an initial temperature of 20 C by placing them in a cooler containing air at a temperature of 1 C and a pressure of 1 bar. Determine the cooling rates when the cans are kept in horizontal and vertical positions. The dry bulb and wet bulb temperature recorded by a thermometer in moist air are 27 C and 17 C respectively. Determine the specific humidity of air assuming the following values. Pr = 0.74, Sc = 0.6, Cp = 1.004kJ/kg.K, p = 1.0132 x 105 N/m2 The water is heated in a tank by dipping a plate of 20 cm X 40 cm in size. The temperature of the plate surface is maintained at 100 C. Assuming the temperature of the surrounding water is at 30 C, Find the heat loss from the plate 20 cm side is in vertical plane. A 6 - m long section of an 8 cm diameter horizontal hot water pipe passes through a large room in which the air and walls are at 20 C. The pipe surface is at 70 C and the emissivity of the pipe surface is 0.7. Find the rate of heat loss from the pipe by natural convection and radiation APR/MAY 2014 APR/MAY 2014 APR/MAY 2011 UNIT - III (TWO MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. QUESTIONS REMARKS Define bulk temperature APR/MAY 2011 List the various promoters used for maintaining dropwise condensation APR/MAY 2011 State Newton's law of cooling OCT/NOV 2013 Differentiate free and forced convection OCT/NOV 2013 Explain why the Fluorescent lamps are more efficient than incandescent bulbs. What is the law of superposition applicable to shape factor in Radiative heat transfer? What are the factors are involved in designing a heat exchangers? Give expression for heat transfer coefficient in Nucleate boiling. What is effectiveness of a heat exchange? APR/MAY 2010 Draw heat flux curve for various regions of flow boiling. Give the expression for NTU. APR/MAY 2010 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 12. 13. 14. 15. 16. 17. 18. 19. 20. What is LMTD? What is Excess temperature in boiling? What is flow boiling? How heat exchangers are classified? Mention the difference between free and forced convection. NOV/DEC 2004 What is the importance of boundary layer? NOV/DEC 2004 How is the Reynolds number in condensation defined? What is meant by condensation? Define Drop wise condensation UNIT - III (SIXTEEN MARKS) S.NO 1. 2. 3. 4. 5. 6. QUESTIONS AIR at 2 m/s, 27 C, and 1 atm flows over a flat plate, Calculate (i) Boundary Layer Thickness at x = 20 cm & 40 cm (ii) Mass flow which enters the boundary layer between x=20 cm and x = 40 cm. Assume unit depth in z direction. Air at 80 kg/h flows through a 10 cm internal diameter tube. At a particuiai point, the pressure and temperature of air are 1.5 bar and 333 K respectively. Whilst the surface temperature of the tube is maintained at 380 K. Find heat transfer coefficient and rate from 1m length of the tube in this region. Consider laminar film condensation of a stationary vapour on a vertical flat plate of length L and width b. Derive an expression for the average heat transfer coefficient. State the assumptions made. Hot gases enter a finned tube, cross flow heat exchanger with a flow rate of 1.5 kg/s and a temperature of 250 C. The gases are used to heat water entering the exchanger at a flow rate of 1 kg/s and an inlet temperature of 35 C. On the gas side, the overall heat transfer coefficient and the area are 100 W/m2.K and 40 m2 respectively. What is the rate of heat transfer by the exchanger and what are the gas and water exit temperatures? Assume Cp of gas as 1.0 kJ/kg.K. A 1-shell 2 tube pass steam condenser consists of 3000 brass tubes of 20 mm diameter. Cooling water enters the tubes at 20 C with a mean flow rate of 3000 kg/s. The heat transfer coefficient for condensation on the outer surfaces of the tubes is 15500 W/m2.K. If the heat load of the condenser is 2.3x 108 W when the stem condenses at 50 C determine hi and estimate (a) the outlet temperature of the cooling water (b) the overall heat transfer coefficient (c) the tube length per pass using the NTU method.(d) the rate of condensation of steam if hf q = 2380 kJ/kg. A cross flow type heat exchanger with steam condensing inside tubes at 100 C is used to heat air from 20 C. The air side may be taken as mixed. The effectiveness of the heat exchanger is found as 0.7. If the area is 20m2 and overall heat transfer coefficient based on this area is 150 W/m2K, determine the heat transfer rate. Determine the extra area required if a fouling resistance of 0.0006 m2K/ W is experienced REMARKS OCT/NOV 2013 OCT/NOV 2013 APR/MAY 2011 APR/MAY 2011 APR/MAY 2014 APR/MAY 2014 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 7. 8. 9. 10. Dry steam at 2.45 bar condenses on a vertica1 '.ub; f h igh t of 1m at 117 C. Estimate the thickness of the condensa e Hm and tne local heat transfer coefficient at a distance 0.2 m from th e upper end of the plate. APR/MAY 2010 Derive th" L MT D for a parallel flow heat exchanger stating the assumptions APR/MAY 2010 Water is to be boiled at atmospheric pressure in a mechanically polished stainless steel pan placed on top of a heating unit. The inner surface of the bottom of the pan is maintained at lO8 C. The diameter of the bottom of the pan is 30 cm. Assuming Csf = 0.0130. Calculate (i) the rate of heat transfer to the water and ii) the rate of evaporation of water. Water enters a cross flow Heat exchanger (both fluids unmixed) at 5 C and flows at the rate of 4600 kg/h to cool 4000 kg/h of air that is initially at 40 C. Assume the overall heat transfer coefficient value to be 150 W/m2K For an exchanger surface area of 25m2 Calculate the exit temperature of air and water UNIT - IV (TWO MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. QUESTIONS REMARKS Define Radiation heat transfer What are the effects of non-condensable gases during condensation? OCT/NOV 2013 What are fouling factors in heat exchangers? OCT/NOV 2013 What is Intensity of radiation? APR/MAY 2011 Define LMTD of a heat exchanger. APR/MAY 2011 What do you understand by thermal radiation? APR/MAY 2011 What is Radiation Shield? Distinguish between Absorptive & Transitivity of radiation. Draw and indicate the regimes of heat transfer experienced in flow boiling. APR/MAY 2014 Draw the Pool boiling heat transfer characteristics curve and mark the critical heat flux and Leiden frost point APR/MAY 2014 Differentiate Opaque body & perfectly transparent surface. What is mean beam length in Gas Radiation? Find the temperature of the sun assuming as a black body, if the intensity of radiation is Maximum at the wave length of 0.5^. Distinguish between Reflectivity & Transitivity. APR/MAY 2010 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 15. 16. 17. 18. 19. 20. State Kirchhoff s law. APR/MAY 2010 What is mean beam length in Gas Radiation? What is the equation for radiation between two gray bodies? State the difference between film wise and drop wise condensation. OCT/NOV 2004 Sketch the temperature variations in parallel flow and counter flow heat exchangers. OCT/NOV 2004 Write down the heat transfer equation for Radiant exchange between infinite parallel gray planes. UNIT - IV (SIXTEEN MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. QUESTIONS Dry saturated steam at a pressure of 2.45 bar condenses on the surface of a vertical tube of height 1 m. The tube surface temperature is kept at 117 C.Estimate the thickness of the condensate film. A parallel flow heat exchanger has hot and cold water stream running through it. the flow rates are 10 and 25 kg/min respectively. Inlet temperatures are 75 C and 25 C on hot and cold sides. The exit temperature on the hot side should not exceed 50 C. Assume h; = h 0 = 600 W/m2K. Calculate the area of heat exchanger using e - NTU approach. Two large parallel planes with emissivity s 0.35 and 0.85 exchange heat by radiation. The planes are respectively 1073K and 773K. A radiation shield having the emissivity of 0.04 is placed between them. Find the percentage reduction in radiation heat exchange and temperature of the shield. Consider a cylindrical furnace with outer radius - height - 1 m. The top (surface 1) and the base (surface 2) of the furnace have emissivity s 0.8 & 0.4 and are maintained at uniform temperatures of 700 K and 500 K respectively. The side surface closely approximates a black body and is maintained at a temperature of 400 K. Find the net rate of radiation heat transfer at each surface during steady state operation. Assume the view factor from the base to the top surface as 0.38. Two very large parallel planes exchange heat by radiation. The emissivity s of the planes are respectively 0.8 and 0.3. To ^i, imize the radiation exchange between the planes, a polished aluminum radiation shield is placed between them. If the emissivity of the shield is 0.04 on both sides, find the percentage reduction in heat transfer rate. Derive the radiation exchange between (i) Large parallel gray surfaces and (ii) Small gray bodies Two large parallel plates of 1mx1m spaced 0.5m apart in a very large room whose walls are at 27 C. The plates are at 900 C and 400 C with emissivities 0.2 and 0.5 Respectively. Find the net heat transfer to each plate and to the room. 8. What are the radiation view factors and why they are used? (04) Determine the view factor (F1-4) for the figure shown below. (12) 9. In an industrial facility, air is to be preheated before entering a furnace by geothermal water at 120 C flowing through the tubes of a tube bank located in a duct. Air enters the duct at 20 C and 1 atm with a mean velocity of 4.5 m/s, and flows over the tubes REMARKS OCT/NOV 2013 OCT/NOV 2013 APR/MAY 2011 APR/MAY 2011 APR/MAY 2010 APR/MAY 2010 APR/MAY 2014 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 10. in normal direction. The outer diameter of the tubes is 1.5 cm, and the tubes are arranged in line with longitudinal and transverse pitches of SL = ST = 5 cm. There are 6 rows in the flow direction with 10 tubes in each row. Determine the rate of heat transfer per unit length of the tubes. Water is to be heated from 15 C to 65 C as it flows through a 3 cm internal Diameter 5 m long tube. The tube is equipped with an electric resistance beater that provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat generated in the heater is transferred to the water in the tube. If the system is to provided hot water at a rate of 10 L/min, determine the power rating of the resistance heater. Also estimate the inner surface temperature of the tube at the exit. APR/MAY 2014 UNIT - V (TWO MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. QUESTIONS REMARKS What is meant by mass transfer? What is Diffusion mass transfer? What is the Molar Diffusion velocity? Define Mass concentration. Define Molar concentration What is Counter diffusion? Define mass transfer fluxes. What is the governing equation for Transient Diffusion? Give equation for Counter diffusion. Define Fourier number & Biot number for mass transfer. What are the factors considered in evaporation of water into air? What does the view factor represent? When the view factor from a surface to itself is zero? APR/MAY 2011 What is the physical meaning of Schmidt number? APR/MAY 2011 Define molar concentration. APR/MAY 2010 What is mass average velocity? APR/MAY 2010 Helium diffuses through a plane, plastic membrane 1 mm thick. The concentration of helium in the membrane is 0.02 k mol/m3 at the inner surface and 0.005 k mol/m3 at the outer surface. If the binary diffusion coefficient of helium with respect to the plastic is 10"9 m2/s, what is the diffusion flux of helium through the plastic? APR/MAY 2014 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DOC.NO. : TKEC/MECH/ACADEMIC/1 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK 17. 18. 19. 20. Differentiate between convective and diffusion mass transfer. APR/MAY 2014 What are the analogy between Heat and Mass Transfer OCT/NOV 2013 Define Schmidt and Sherwood numbers OCT/NOV 2013 What are fouling factors in heat exchangers? UNIT - V (SIXTEEN MARKS) S.NO 1. 2. 3. 4. 5. 6. 7. 8. QUESTIONS A mixture of 0 2 and N2 with their patiia! pressures in the ratio 0.21 to 0.79 ic in a container at 25 C. Calculate the molar concentration, the mass density, the mole fraction and the mass fraction of each species for a total pressure of 1 bar. What would be the average molecular weight of the mixture? Air at 25 C and atmospheric pressure flows with a velocity of 3 m/s inside a 10 mm diameter tube of 1 m length. The inside surface of the tube contains a deposit of naphthalene. Determine the average mass transfer coefficient for the transfer of naphthalene from the pipe surface into the air. A steel sphere of radius 60 mm which is initially at a uniform temperature of 325 C is suddenly exposed to an environment at 25 C; with convection heat transfer coefficient 500 W/m2K Calculate the temperature at a radius 36 mm and the heat transferred 100 seconds after the sphere is exposed to the environment. Two identical circular plates each with area 1m2 and emissivity 0.5 are arranged facing each other in a large room. The emissive power of the plates is 30 kW/m2 and 3kW/m2 respectively. The temperature of the surrounding is 27 C. The surface of the plates facing each other only are radiating energy, find (i) Distance between the plates; (ii) Temperature of the plates; (iii) Heat transfer to the surrounding from the plates. Assume the shape factor between the plates as 0.6. Determine the number of shields required to be fixed in between the outer and inner walls (of a furnace) that are to be maintained at 100 C and 500 C respectively if the emissivity of the wall lining as well as for shield is 0.87. Heat transfer to the surroundings from the outer surface takes place by radiation and convection. The heat transfer coefficient for natural convection is given by ha = 1.44 (At)0 3 3 W/m2oC Ta (air temperature) = 25 CNeglect the heat transfer by conduction and convection between the brick lining. The tire tube of a vehicle has a surface area 0.62 m2 and wall thickness 12 mm. The tube has air filled in it at a pressure 2.4 x 105 N/m2. The air pressure drops to 2.3 x 105 N/m2 in 10 days. The volume of air in the tube is 0.034 m3. Calculate the diffusion coefficient of air in rubber at the temperature of 315K. Gas constant value = 287. Solubility of air in rubber tube = 0.075m3 of air/m3 of rubber tube at one atmosphere Air at 1.01 bar and 30 C flows past a tray full of water with a velocity of 2 m/s. The partial pressure of water vapour is 0.7 kPa and the saturation pressure is 3.17 kPa. The tray measures 40 cm along the flow direction and has a width of 20 cm. Calculate the evaporation rate of water if the temperature on the water surface is 25 C. Assume the following properties for air: density, p 1.2 kg/m3, kinematic viscosity, v = 15 x 10-6 m2/s and diffusivity, D = 0.145 m2/h. Write short notes on the following: (i) Analogy between heat and mass transfer REMARKS OCT/NOV 2013 OCT/NOV 2013 APR/MAY 2014 APR/MAY 2014 APR/MAY 2011 APR/MAY 2011 DEPARTMENT RECORDS The Kavery Engineering College, Mecheri, Salem District. DOC.NO. : TKEC/MECH/ACADEMIC/1 DEPARTMENT OF MECHANICAL ENGINEERING ACADEMIC YEAR:2016-2017 DATE : PAGE : OF YEAR/SEM/SEC: III /V /A QUESTION BANK (ii) Evaporation process in the atmosphere. A mixture of 02 and N2 with their partial pressures in the ratio 0.21 to 0.79 is in a container at 25 C. Calculate the molar concentration, the mass density, the mole fraction and the mass fraction of each species for a total pressure of 1 bar. What would be the average molecular weight of the mixture? Dry air at 20 C (p = 1.2 kg/m3, v = 15 x lQ-6 m2/s, D = 4.2 x lQ-5 m2/s) flows over a 10. flat plate of length 50 cm which is covered with a thin layer of water at a velocity of 1 m/s. Estimate the local mass transfer coefficient at a distance of 10 cm from the leading edge and the averagemass transfer coefficient. PREPARED BY APPROVED BY 9. Staff in charge Revision No: 00 Revision Level History: From To Teaching Coordinator Reason for revision HOD Principal Revision Date Authorised By

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