SHRI RAMSWAROOP MEMORIAL COLLEGE OF ENGG. & MANAGEMENT B.Tech. [SEM V (ME-51, 52, 53, 54)] QUIZ TEST-1 (Session: )

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1 QUIZ TEST-1 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) The inside temperature of a furnace wall ( k=1.35w/m.k), 200mm thick, is C. The heat transfer coefficient at the outside surface is a function of temperature difference and is given byh= ΔT (W/ m 2. K) Where ΔT is the temperature difference between outside wall surface and surroundings. Determine the rate of heat transfer per unit area, if the surroundings temperature is 40 0 C [Q. No.1] [5] Q2) An electric cable of 10 mm in diameter has a sheathing of insulation for which the value ok K is 0.1 W/m- K. Find the relative diameter of sheathing which will keep the wire at the same temperature as if it were bare. h( heat transfer coefficient from the surface of sheathing)= 10 W/m 2 -K. [Q. No.11] [5] Q1. a) Define Log mean area for hollow cylinder and obtain an expression for the same. [1+2] b) Using unidirectional general Fourier s Conduction Equation under steady state without heat generation in cylindrical coordinate system, obtain an expression for the temperature distribution and heat transfer through a hollow cylinder of constant thermal conductivity. [2+2] Q2. A hollow sphere of inside radius 4 cm and outside radius 6 cm is electrically heated at the inner surface at a constant rate of 10 5 w/ m 2. At the outer surface it dissipates heat by convection into a fluid at a temperature of 100 and a heat transfer coefficient of 450 w/ m 2 K. The thermal conductivity of the solid is 20 W/ m-k. Calculate the inner and outer surface temperature. [2+2+2] Q3. a) A 30 meters long pipe, 5 cm in diameter is to be protected by a covering of hair felt for which K = 0.04 W/ m- K. Calculate the thickness of lagging to prevent if the rate of water is 25 kg/ hr. The temperature of water entering into pipe the pipe is 10 and air temperature is -20. Take heat transfer coefficient from water to pipe = 30 W/ m 2. K and heat transfer coefficient from outer surface of insulation to air = 5 W/ m 2 - K. [5] b) Briefly explain the purpose of insulation. What is critical thickness of insulation? [1+1] Date: 08/09/2012

2 QUIZ TEST-1 (Session ) Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) The temperature distribution in a plate of thickness 20 mm is given by T( 0 C) = 10x + 6 x Assume no heat generation in the plate. calculate rate of heat flux on two sides of the plate. Also calculate rate of temperature change with respect to time, if k = 300W/m.k, ρ = 5800 kg/ m 3 and C = 420 J/ kg.k. [Q. No. 2] [ ] Q2) An electric cable 10 mm in diameter is to be insulated with rubber. The insulated cable is exposed to air at 20 C. Find the most economical thickness of the rubber insulation from heat transfer point of view assuming the cable surface temperature of 60 C in bare as well as in insulation condition. Assume the following data: K( Rubber)= 0.14 W/m-K. h t (Heat transfer coefficient on the surface of cable or on insulation surface) = 7 W/m 2 -K. Also find the percentage increase in current carrying capacity when more economical insulation thickness is provided.[q. No. 12] [3+2] Q1. a) Define Log mean area for hollow cylinder and obtain an expression for the same. [1+2] b) Using unidirectional general Fourier s Conduction Equation under steady state without heat generation in cylindrical coordinate system, obtain an expression for the temperature distribution and heat transfer through a hollow cylinder of constant thermal conductivity. [2+2] Q2. A hollow sphere of inside radius 4 cm and outside radius 6 cm is electrically heated at the inner surface at a constant rate of 10 5 w/ m 2. At the outer surface it dissipates heat by convection into a fluid at a temperature of 100 and a heat transfer coefficient of 450 w/ m 2 K. The thermal conductivity of the solid is 20 W/ m-k. Calculate the inner and outer surface temperature. [2+2+2] Q3. a) A 30 meters long pipe, 5 cm in diameter is to be protected by a covering of hair felt for which K = 0.04 W/ m- K. Calculate the thickness of lagging to prevent if the rate of water is 25 kg/ hr. The temperature of water entering into pipe the pipe is 10 and air temperature is -20. Take heat transfer coefficient from water to pipe = 30 W/ m 2. K and heat transfer coefficient from outer surface of insulation to air = 5 W/ m 2 - K. [5] b) Briefly explain the purpose of insulation. What is critical thickness of insulation? [1+1] Date: 08/09/2012

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4 QUIZ TEST-1 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) The temperature distribution across a wall 1m thick at a certain instant of time is given by- T(x) = x-50x 2 where T is in 0 C and x is in meter. The uniform heat generation of 1000W/m 3 is present in wall of area 10m 2 having the properties of p= 1600kg/m 3, k= 40W/m 0 K, C= 4kj/kg 0 k a) Determine the rate of heat transfer entering the wall (x=0) and leaving the wall(x=1m) b) Determine the rate of change of internal energy of wall c) Determine the time rate of temperature change at x=0,.05m [Q. No. 3] [1+2+2] Q2) The maximum current carrying capacity of an electric cable of 10 mm in diameter is increase 11.2% by providing the insulation and without increasing the cable surface temperature above 60 C which is permissible. Assuming the surrounding air temperature 20 C and heat transfer coefficient on bare or insulated cable 10 W/m 2 -K, find the conductivity of the insulating material required for the purpose. [Q. No. 13] [5]. Q1. a) Define Log mean area for hollow cylinder and obtain an expression for the same. [1+2] b) Using unidirectional general Fourier s Conduction Equation under steady state without heat generation in cylindrical coordinate system, obtain an expression for the temperature distribution and heat transfer through a hollow cylinder of constant thermal conductivity. [2+2] Q2. A hollow sphere of inside radius 4 cm and outside radius 6 cm is electrically heated at the inner surface at a constant rate of 10 5 w/ m 2. At the outer surface it dissipates heat by convection into a fluid at a temperature of 100 and a heat transfer coefficient of 450 w/ m 2 K. The thermal conductivity of the solid is 20 W/ m-k. Calculate the inner and outer surface temperature. [2+2+2] Q3. a) A 30 meters long pipe, 5 cm in diameter is to be protected by a covering of hair felt for which K = 0.04 W/ m- K. Calculate the thickness of lagging to prevent if the rate of water is 25 kg/ hr. The temperature of water entering into pipe the pipe is 10 and air temperature is -20. Take heat transfer coefficient from water to pipe = 30 W/ m 2. K and heat transfer coefficient from outer surface of insulation to air = 5 W/ m 2 - K. [5] b) Briefly explain the purpose of insulation. What is critical thickness of insulation? [1+1] Date: 08 / 09 / 2012

5 QUIZ TEST-1 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) Find steady heat flow through a composite slab make of two material A & B. The thermal conductivity of two materials vary linearly with temperature as K A = 0.4( T) K B = 0.5( T) Where T is in 0 C. the thickness L A =10cm, L B =5cmThe inside temp of slab A is C and outside temp of slab is 30 0 C. [Q. No. 4] [5] Q2) An electric current of 300 amp. is passed through a stainless steel wire 2.5 mm in diameter. The resistivity of the stainless steel wire may be taken as 70 μ ohm-cm and the length of the wire is 1.5 m. if the outer surface temperature of the wire is maintained at 180 C, calculate the centre temperature of the wire. For stainless steel, take K = 25 W/ m-k. [Q. No. 8] [5]. Q1. a) Define Log mean area for hollow cylinder and obtain an expression for the same. [1+2] b) Using unidirectional general Fourier s Conduction Equation under steady state without heat generation in cylindrical coordinate system, obtain an expression for the temperature distribution and heat transfer through a hollow cylinder of constant thermal conductivity. [2+2] Q2. A hollow sphere of inside radius 4 cm and outside radius 6 cm is electrically heated at the inner surface at a constant rate of 10 5 w/ m 2. At the outer surface it dissipates heat by convection into a fluid at a temperature of 100 and a heat transfer coefficient of 450 w/ m 2 K. The thermal conductivity of the solid is 20 W/ m-k. Calculate the inner and outer surface temperature. [2+2+2] Q3. a) A 30 meters long pipe, 5 cm in diameter is to be protected by a covering of hair felt for which K = 0.04 W/ m- K. Calculate the thickness of lagging to prevent if the rate of water is 25 kg/ hr. The temperature of water entering into pipe the pipe is 10 and air temperature is -20. Take heat transfer coefficient from water to pipe = 30 W/ m 2. K and heat transfer coefficient from outer surface of insulation to air = 5 W/ m 2 - K. [5] b) Briefly explain the purpose of insulation. What is critical thickness of insulation? [1+1] Date: 08/09/2012

6 QUIZ TEST-1 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) Find the heat flow through the given configuration per square meter (a) without bolt. (b) with bolt. K( magnesia) = 0.1 W/ m- K [1+2+2] K( steel bolt) = 25 W/ m- K K (brick) = 1 W/ m- K Assume one bolt is fitted per m 2 area of the surface. [Q. No. 6] Q2) An insulated steam pipe having outside dia. of 30mm is to be covered with two layers of insulation each having thickness of 20mm. The thermal conductivity of one material is five times that of the other. Assuming that the inner and outer surface temperature of composite insulations are fixed, how much heat transfer will be increased when the better insulation material is next to the pipe then it is to the outer layer. [Q. No 15] [5] Q1. a) Define Log mean area for hollow cylinder and obtain an expression for the same. [1+2] b) Using unidirectional general Fourier s Conduction Equation under steady state without heat generation in cylindrical coordinate system, obtain an expression for the temperature distribution and heat transfer through a hollow cylinder of constant thermal conductivity. [2+2] Q2. A hollow sphere of inside radius 4 cm and outside radius 6 cm is electrically heated at the inner surface at a constant rate of 10 5 w/ m 2. At the outer surface it dissipates heat by convection into a fluid at a temperature of 100 and a heat transfer coefficient of 450 w/ m 2 K. The thermal conductivity of the solid is 20 W/ m-k. Calculate the inner and outer surface temperature. [2+2+2] Q3. a) A 30 meters long pipe, 5 cm in diameter is to be protected by a covering of hair felt for which K = 0.04 W/ m- K. Calculate the thickness of lagging to prevent if the rate of water is 25 kg/ hr. The temperature of water entering into pipe the pipe is 10 and air temperature is -20. Take heat transfer coefficient from water to pipe = 30 W/ m 2. K and heat transfer coefficient from outer surface of insulation to air = 5 W/ m 2 - K. [5] b) Briefly explain the purpose of insulation. What is critical thickness of insulation? [1+1] Date: 08/09/2012

7 QUIZ TEST-2 Time: 1 Hour HEAT & MASS TRANSFER Note: Q1) A copper plate of 2mm thick is heated up to C and then quenched into water at 20 0 C. Find the time required for the plate reached the temp of 40 0 C. Assume the following Data. h( heat transfer coefficient on the surface of the plate ) = 80w/m 2 -K Plate dimensions =30cm*30cm, Cp (specific heat of copper) = 0.4 KJ/kg-K, P (density of water) 8800kg/m 3. [Q.NO.1 (TUTE-2)][5] Q2) Determine the flow of heat from a round iron rod of 10 cm length having diameter 1.6cm. The surface heat conductance is 25W/m 2 -K. The base temp of rod is C and atmospheric temp is 30 0 C. Conductivity of the rod material is 40W/m-K. Assume that the fin is insulated at the tip. [Q.NO.9 (TUTE-2)] [5] Q1) (a) Obtain an expression for the temperature distribution and heat flow for a fin of finite length with insulated tip. [4] (b) Define effectiveness of a fin. [2] Q2) (a) Pin fins are provided to increase the heat transfer rate from a hot surface, which of the following arrangement will give higher transfer rate a better performance : (i) 6 fins of 10 cm length (ii) 12 fins of 5 cm length Take k for fin material 200 W/m-k, h = 20 W/m 2 K, c/s area of fin = 2 cm 2, parameter of fin = 4 cm, fin base temperature = 230 C, surrounding air temperature = 30 C [5] (b) Explain the significance of Bi number, F 0 number in transient state heat conduction [2] Q3) (a) Explain lumped parameter analysis and thermal time constant. [2+1] (b) An egg with mean diameter of 40 mm and initially at 20 C is placed in a boiling water pan for 4 minutes and found to be boiled to consumer s taste. How long a similar egg for same consumer be boiled after taken from a refrigerator at 5 C. Take the following properties for the egg: k = 10 W/m- C, ρ = 1200 kg/m 3, C= 2kJ/kg C, h = 100 W/m 2 C. [4] EME-504/Prof. A. K. Srivastava Date: 25 /09 /2012

8 QUIZ TEST-2 Time: 1 Hour HEAT & MASS TRANSFER Note: Q1) One thousands spheres made of copper of diameter 10mm are annealed in the annealing furnace. Initial temp of the spheres =20 0 C, Temp of annealing furnace =400 0 C The properties of copper are given as: h= 3W/m-k Cp=0.4kj/kg-k, p=8200kg/m 3 Find the time required for the spheres to reach the temp of C. [Q.NO.3 (TUTE-2)][5] Q2) Twelve thin brass fins (K=65 W/m-K) of 0.8mm thick are placed axially on a 5 cm diameter cylinder which stands vertically and is surrounded by air at 40 0 C. The fins extend 2.5 cm from the cylinder surface. The heat transfer coefficient on the surface of the fins is 20 W/m-K. What is the rate of heat transfer to the air per meter length of cylinder when its surface is at C? Take following data L= 2.5cms, 2δ= 0.08cms, h=20w/m 2 -k, K= 65W/m-K, θ 0 =110 0 C. [Q.NO.10 (TUTE-2)] [5] Q1) (a) Obtain an expression for the temperature distribution and heat flow for a fin of finite length with insulated tip. [4] (b) Define effectiveness of a fin. [2] Q2) (a) Pin fins are provided to increase the heat transfer rate from a hot surface, which of the following arrangement will give higher transfer rate a better performance : (i) 6 fins of 10 cm length (ii) 12 fins of 5 cm length Take k for fin material 200 W/m-k, h = 20 W/m 2 K, c/s area of fin = 2 cm 2, parameter of fin = 4 cm, fin base temperature = 230 C, surrounding air temperature = 30 C [5] (b) Explain the significance of Bi number, F 0 number in transient state heat conduction [2] Q3) (a) Explain lumped parameter analysis and thermal time constant. [2+1] (b) An egg with mean diameter of 40 mm and initially at 20 C is placed in a boiling water pan for 4 minutes and found to be boiled to consumer s taste. How long a similar egg for same consumer be boiled after taken from a refrigerator at 5 C. Take the following properties for the egg: k = 10 W/m- C, ρ = 1200 kg/m 3, C= 2kJ/kg C, h = 100 W/m 2 C. [4] EME-504/Prof. A. K. Srivastava Date: 25 /09 /2012 X

9 QUIZ TEST-2 Time: 1 Hour HEAT & MASS TRANSFER Note: Q1) Brass wire of 0.5mm diameter is annealed in annealing furnace at a temp of C. Find the time required for the wire reached the temp of C if the temp of wire before passing into furnace is 30 0 C. h=30w/m 2 -k, p=8600kg/m 3, Cp=0.4kj/kg-k for brass. Assume the length of the wire is 10 meters. [Q.NO.4 (TUTE-2)][5] Q2) One end of the long rod is inserted into a furnace with the other end projecting into the outside the air. After steady state is reached, the temp of the rod measured at two points 10cms apart and found to be C and 91 0 when the ambient temp is 28 0 C. If the rod is 2cms in diameter and h=15 W/m 2 -k, what is the thermal conductivity of the rod? [Q.NO.11 (TUTE-2)] [5] Q1) (a) Obtain an expression for the temperature distribution and heat flow for a fin of finite length with insulated tip. [4] (b) Define effectiveness of a fin. [2] Q2) (a) Pin fins are provided to increase the heat transfer rate from a hot surface, which of the following arrangement will give higher transfer rate a better performance : (i) 6 fins of 10 cm length (ii) 12 fins of 5 cm length Take k for fin material 200 W/m-k, h = 20 W/m 2 K, c/s area of fin = 2 cm 2, Parameter of fin = 4 cm, fin base temperature = 230 C, surrounding air temperature = 30 C [5] (b) Explain the significance of Bi number, F 0 number in transient state heat conduction. [2] Q3) (a) Explain lumped parameter analysis and thermal time constant. [2+1] (b) An egg with mean diameter of 40 mm and initially at 20 C is placed in a boiling water pan for 4 minutes and found to be boiled to consumer s taste. How long a similar egg for same consumer be boiled after taken from a refrigerator at 5 C. Take the following properties for the egg: k = 10 W/m- C, ρ = 1200 kg/m 3, C= 2kJ/kg C, h = 100 W/m 2 C. [4] EME-504/Prof. A. K. Srivastava Date: 25 /09 /2012

10 QUIZ TEST-2 Time: 1 Hour HEAT & MASS TRANSFER Note: Q1) A steel ball of 5 cm diameter at C is suddenly placed in a controlled environment maintained at C. Taking the following data, find the time required for the ball to attain a temp of C. Cp=450J/kg- 0 C, K=35W/m-K, h=10w/m 2 -K, p=800kg/m 3. Find also the rate of cooling. [Q.NO.5 (TUTE-2)] [5] Q2) The temp of air in a reservoir is measured with the aid of mercury-in-glass thermometer placed into steel protective well filled with oil. The thermometer shows the temp at the end of well 84 0 C. How large is the measurement error due to transfer of heat by conduction along the protective well if the temp at the base of well is 40 0 C. The well is 12cms long, its thickness is 1.5mm and thermal conductivity of well material is 55.8 W/m- 0 C, h (heat transfer coefficient between well and air). = 23.8W/m 2-0 C. [Q.NO.12 (TUTE-2)] [5] Q1) (a) Obtain an expression for the temperature distribution and heat flow for a fin of finite length with insulated tip. [4] (b) Define effectiveness of a fin. [2] Q2) (a) Pin fins are provided to increase the heat transfer rate from a hot surface, which of the following arrangement will give higher transfer rate a better performance : (i) 6 fins of 10 cm length (ii) 12 fins of 5 cm length Take k for fin material 200 W/m-k, h = 20 W/m 2 K, c/s area of fin = 2 cm 2, parameter of fin = 4 cm, fin base temperature = 230 C, surrounding air temperature = 30 C. [5] (b) Explain the significance of Bi number, F 0 number in transient state heat conduction. [2] Q3) (a) Explain lumped parameter analysis and thermal time constant. [2+1] (b) An egg with mean diameter of 40 mm and initially at 20 C is placed in a boiling water pan for 4 minutes and found to be boiled to consumer s taste. How long a similar egg for same consumer be boiled after taken from a refrigerator at 5 C. Take the following properties for the egg: k = 10 W/m- C, ρ = 1200 kg/m 3, C= 2kJ/kg C, h = 100 W/m 2 C. [4] X EME-504/Prof. A. K. Srivastava Date: 25 /09 /2012

11 QUIZ TEST-2 Time: 1 Hour HEAT & MASS TRANSFER Note: Q1) A household iron has a surface area of 0.05m 2 and is made of stainless steel with total weight of 1.4 kg and 500W capacity. The heat transfer coefficient on the surface of iron fin with its surrounding air is 17 W/m 2 C where the temp of surrounding air is 30 0 C. How long after being turned on, will the iron fin reached C if it is originally at surrounding temp.take ρ(iron steel) =7820kg/m 3, k (iron steel) 17.3W/m- 0 C, C p (iron steel) = 460.8J/kg- 0 C. [Q.NO.6 (TUTE-2)] [5] Q2) A plane wall is fitted with rectangular fins of thermal conductivity of 50 W/m-K and profile area of 1.75cm 2. The atmospheric temp is 30 0 C and surface conductance is 200 W/m 2 -k. If fin base temp is C, find the maximum heat dissipation possible from one meter width of fin. [Q.NO.14 (TUTE-2)] [5] Q1) (a) Obtain an expression for the temperature distribution and heat flow for a fin of finite length with insulated tip. [4] (b) Define effectiveness of a fin. [2] Q2) (a) Pin fins are provided to increase the heat transfer rate from a hot surface, which of the following arrangement will give higher transfer rate a better performance : (i) 6 fins of 10 cm length (ii) 12 fins of 5 cm length Take k for fin material 200 W/m-k, h = 20 W/m 2 K, c/s area of fin = 2 cm 2, parameter of fin = 4 cm, fin base temperature = 230 C, surrounding air temperature = 30 C [5] (b) Explain the significance of Bi number, F 0 number in transient state heat conduction. [2] Q3) (a) Explain lumped parameter analysis and thermal time constant. [2+1] (b) An egg with mean diameter of 40 mm and initially at 20 C is placed in a boiling water pan for 4 minutes and found to be boiled to consumer s taste. How long a similar egg for same consumer be boiled after taken from a refrigerator at 5 C. Take the following properties for the egg: k = 10 W/m- C, ρ = 1200 kg/m 3, C= 2kJ/kg C, h = 100 W/m 2 C. [4] EME-504/Prof. A. K. Srivastava Date: 25 /09 /2012

12 QUIZ TEST-3 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) A counter flow double pipe heat exchanger using superheated steam is used to heat the water at a rate of 3 kg/ s.the steam enters the exchanger at 180 and leaves at 130. The inlet and outlet temp of water are 30 and 80, respectively. The overall heat transfer coefficient is 820 W/ m 2. K. Calculate the heat transfer area required.what would be the increase in surface area, if fluids flow in parallel? Take C p of water as kj/ kg. k. [Q. No.1] [3+2] Q2) Saturated under atmospheric pressure condenses on a vertical surface 100 cm high. If the temperature of the surface is maintained at 80 0 C. Calculate at 50 cm from the top of the plate. (1) The film thickness (2) The mean velocity (3) The local heat transfer coefficient (4) Average heat transfer coefficient for the whole surface (5) Total heat flow per hour metre width of the plate The properties of water at( )/ 2 = 90 are given below: ρ = kg/ m 3 Cp = 4203 j/ kg k k = W/ m. K µ = kg/ m-s h fg = 2270 kj/ kg [Q. No.12] [1x5] Q1. a) Define the terms NTU and Effectiveness of a heat exchanger. [1+1] b) Steam enters a counter flow heat exchanger, dry and saturated at 10 bar leaves at 350.The mass flow rate of steam is 800kg/min. The gas enters the heat exchanger at 650 and mass flow rate is 1350kg/min. If the tubes are 30 mm dia and 3m long then determine the no. of tubes required. Neglect the resistance offered by metallic tubes. Use the following data- For steam T sat =180 (at 10 bar) C ps =271 kj/kg,h s =600 W/m 2 For gas C pg =1 KJ/Kg h g =250 w/m 2 [5] Date: 22/10/2012

13 Q2. a) Differentiate between Film wise condensation & Drop wise condensation. [2] b) Water at atmospheric pressure is to be boiled in polished copper pan. The diameter of the pan is 350mm and is kept at 115.Calculate the following(1) Power of the burner (2)rate of evaporation in kg/h (3)Critical heat flux for these conditions [2+2+1] The thermo physical properties of water from table at 100 C are ρ l(=ρf) =958.4 kg/m 3, ρ v =.5955 kg/m 3 Cpl (Cpf) = 4220J/kg K. µ l=(µf) =279x10-6 Ns/m 2 Prl =(Prf) =1.75,hfg=2257 KJ/kg, n=1, σ= 58.9x10-3 N/m, Csl =.013 Q3. a) State Fick s law of diffusion. Explain the significance of diffusion coefficients in mass transfer phenomenon. [1+1] b) What is steady state equi-molar counter diffusion? Obtain an expression for diffusion rate in case of steady state equi-molar counter diffusion. [1+3] Date: 22/10/2012 Page-2

14 QUIZ TEST-3 (Session ) Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) Steam in a condenser of a steam power plant is to be condensed at a temp of 30 cooling water from a nearby lake, which enters the tube of a condenser at 14 and leaves at 22. The surface area of tubes is 45 m 2 and overall heat transfer coefficient is 2100 W/m 2. Calculate the mass flow rate of cooling water needed and rate of steam condensation in the condenser. [Q. No. 2] [3+2] Q2) Obtain the outside average heat transfer coefficient for 20 mm outside diameter and 50 cm long tube when it is in vertical position and exposed to steam.take temperature of the steam as 100 and tube surface temperature is 96.The properties of water film at the average temperature are, ρ = kg/ m 3 k = W/ m. K h fg = 2240 kj/ kg Cp = 4200 j/ kg k µ = kg/ m-s L = 0.5 m [Q. No. 13] [5] Q1. a) Define the terms NTU and Effectiveness of a heat exchanger. [1+1] b) Steam enters a counter flow heat exchanger, dry and saturated at 10 bar leaves at 350.The mass flow rate of steam is 800kg/min. The gas enters the heat exchanger at 650 and mass flow rate is 1350kg/min. If the tubes are 30 mm dia and 3m long then determine the no. of tubes required. Neglect the resistance offered by metallic tubes. Use the following data- For steam T sat =180 (at 10 bar) C ps =271 kj/kg,h s =600 W/m 2 For gas C pg =1 KJ/Kg h g =250 w/m 2 [5] Q2. a) Differentiate between Film wise condensation & Drop wise condensation. [2] b) Water at atmospheric pressure is to be boiled in polished copper pan. The diameter of the pan is 350mm and is kept at 115.Calculate the following(1) Power of the burner (2)rate of evaporation in kg/h (3)Critical heat flux for these conditions [2+2+1] Date: 22/10/2012

15 The thermo physical properties of water from table at 100 C are ρ l(=ρf) =958.4 kg/m 3, ρ v =.5955 kg/m 3 Cpl (Cpf) = 4220J/kg K. µ l=(µf) =279x10-6 Ns/m 2 Prl =(Prf) =1.75,hfg=2257 KJ/kg, n=1, σ= 58.9x10-3 N/m, Csl =.013 Q3. a) State Fick s law of diffusion. Explain the significance of diffusion coefficients in mass transfer phenomenon. [1+1] b) What is steady state equi-molar counter diffusion? Obtain an expression for diffusion rate in case of steady state equi-molar counter diffusion. [1+3] Date: 22/10/2012 Page-2

16 QUIZ TEST-3 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) Find the surface area required in a counter flow steam superheater in which the steam enters at 180 in a dry saturated state and leaves at 250 with an increase of enthalpy of 159kj/ kg. The hot combustion gases (C p = 1.05 kj/ kg.k ) enter the super heater at 510. The steam flow rate is 1000kg/ h, the hot gas flow rate is 2000 kg/ h and overall heat transfer coefficient is 26 W/ m 2.k. [Q. No. 4] [5] Q2) 12 cm outside diameter and 2m long tube is used in a big condenser to condense the steam at 0.4 bar. Estimate the unit surface conductance in vertical position and in horizontal position also. Also find the amount of condensate formed per hour in both cases. The saturation temperature of the steam = 74.5 Average wall temperature = 50 The properties of water at( )/ 2 = 62.7 are given below: ρ = kg/ m 3 k = 0.65 W/ m. K µ = kg/ m-s h fg = 2480 kj/ kg [Q. No. 14] [3+2]. B Part Q1. a) Define the terms NTU and Effectiveness of a heat exchanger. [1+1] b) Steam enters a counter flow heat exchanger, dry and saturated at 10 bar leaves at 350.The mass flow rate of steam is 800kg/min. The gas enters the heat exchanger at 650 and mass flow rate is 1350kg/min. If the tubes are 30 mm dia and 3m long then determine the no. of tubes required. Neglect the resistance offered by metallic tubes. Use the following data- For steam T sat =180 (at 10 bar) C ps =271 kj/kg,h s =600 W/m 2 For gas C pg =1 KJ/Kg h g =250 w/m 2 [5] Q2. a) Differentiate between Film wise condensation & Drop wise condensation. [2] Date: 22/ 10 / 2012

17 b) Water at atmospheric pressure is to be boiled in polished copper pan. The diameter of the pan is 350mm and is kept at 115.Calculate the following(1) Power of the burner (2)rate of evaporation in kg/h (3)Critical heat flux for these conditions [2+2+1] The thermo physical properties of water from table at 100 C are ρ l(=ρf) =958.4 kg/m 3, ρ v =.5955 kg/m 3 Cpl (Cpf) = 4220J/kg K. µ l=(µf) =279x10-6 Ns/m 2 Prl =(Prf) =1.75,hfg=2257 KJ/kg, n=1, σ= 58.9x10-3 N/m, Csl =.013 Q3. a) State Fick s law of diffusion. Explain the significance of diffusion coefficients in mass transfer phenomenon. [1+1] b) What is steady state equi-molar counter diffusion? Obtain an expression for diffusion rate in case of steady state equi-molar counter diffusion. [1+3] Date: 22/ 10 / 2012 Page-2

18 QUIZ TEST-3 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) A counter flow heat exchanger is employed to cool 0.55 kg/s (Cp = 2.45 kj/kg ) of oil from Q 115 to 4 by the use of water. The inlet and outlet temperatures of cooling water are 15 and 75, respectively. The overall heat transfer coefficient is expected to be 1450W/m 2 k. Using NTU method, calculate the following: (a) The mass flow rate of water, (b) effectiveness of heat exchanger and (c) the surface area required. [Q. No. 6] [1+2+2] Q2) Steam at 100 is condensing on vertical drum having a diameter of 20 cm and a temperature of 90. If drum is vertical how long must it be to condense 100 kg of steam per hour? The properties of the condensing water at mean temperature are given : ρ= kg/ m 3 k = W/ m. K µ = kg/ m-s h fg = 2270 kj/ kg ν = m 2 /sec [Q. No. 15] [5] B Part Q1. a) Define the terms NTU and Effectiveness of a heat exchanger. [1+1] b) Steam enters a counter flow heat exchanger, dry and saturated at 10 bar leaves at 350.The mass flow rate of steam is 800kg/min. The gas enters the heat exchanger at 650 and mass flow rate is 1350kg/min. If the tubes are 30 mm dia and 3m long then determine the no. of tubes required. Neglect the resistance offered by metallic tubes. Use the following data- For steam T sat =180 (at 10 bar) C ps =271 kj/kg,h s =600 W/m 2 For gas C pg =1 KJ/Kg h g =250 w/m 2 [5] Q2. a) Differentiate between Film wise condensation & Drop wise condensation. [2] b) Water at atmospheric pressure is to be boiled in polished copper pan. The diameter of the pan is 350mm and is kept at 115.Calculate the following(1) Power of the burner (2)rate of evaporation in kg/h (3)Critical heat flux for these conditions [2+2+1] Date: 22 / 10 / 2012

19 The thermo physical properties of water from table at 100 C are ρ l(=ρf) =958.4 kg/m 3, ρ v =.5955 kg/m 3 Cpl (Cpf) = 4220J/kg K. µ l=(µf) =279x10-6 Ns/m 2 Prl =(Prf) =1.75,hfg=2257 KJ/kg, n=1, σ= 58.9x10-3 N/m, Csl =.013 Q3. a) State Fick s law of diffusion. Explain the significance of diffusion coefficients in mass transfer phenomenon. [1+1] b) What is steady state equi-molar counter diffusion? Obtain an expression for diffusion rate in case of steady state equi-molar counter diffusion. [1+3] Date: 22 / 10 / 2012 Page-2

20 QUIZ TEST-3 Time: 1 Hour HEAT AND MASS TRANSFER Note: All questions are compulsory. Q1) Consider a very long concentric tube heat exchanger having hot and cold water inlet temperature of 85 and 15 respectively. The flow rate of hot water is twice that of cold water. Assuming equivalent cold and hot water specific heat, determine the heat water outlet temperature for the Counter flow [Q. No. 11] [5] Q2) Determine the rate of diffusion of water vapour from a pool of water at the bottom of a well which is 6m deep and 2.5 m in diameter to dry ambient air over the top of the well. The entire system may be assumed at 30 and one atmospheric pressure. The diffusion coefficient is m 2 / sec. [Q. No 16] [5] B Part Q1. a) Define the terms NTU and Effectiveness of a heat exchanger. [1+1] b) Steam enters a counter flow heat exchanger, dry and saturated at 10 bar leaves at 350.The mass flow rate of steam is 800kg/min. The gas enters the heat exchanger at 650 and mass flow rate is 1350kg/min. If the tubes are 30 mm dia and 3m long then determine the no. of tubes required. Neglect the resistance offered by metallic tubes. Use the following data- For steam T sat =180 (at 10 bar) C ps =271 kj/kg,h s =600 W/m 2 For gas C pg =1 KJ/Kg h g =250 w/m 2 [5] Q2. a) Differentiate between Film wise condensation & Drop wise condensation. [2] b) Water at atmospheric pressure is to be boiled in polished copper pan. The diameter of the pan is 350mm and is kept at 115.Calculate the following(1) Power of the burner (2)rate of evaporation in kg/h (3)Critical heat flux for these conditions [2+2+1] The thermo physical properties of water from table at 100 C are ρ l(=ρf) =958.4 kg/m 3, ρ v =.5955 kg/m 3 Cpl (Cpf) = 4220J/kg K. µ l=(µf) =279x10-6 Ns/m 2 Prl =(Prf) =1.75,hfg=2257 KJ/kg, n=1, σ= 58.9x10-3 N/m, Csl =.013 Date: 22/10/2012

21 Q3. a) State Fick s law of diffusion. Explain the significance of diffusion coefficients in mass transfer phenomenon. [1+1] b) What is steady state equi-molar counter diffusion? Obtain an expression for diffusion rate in case of steady state equi-molar counter diffusion. [1+3] Date: 22/10/2012 Page-2

22 QUIZ TEST-4 Time: 1 Hour HEAT & MASS TRANSFER Note: Attempt all Questions. Q1) An Industrial furnace in the form of a black body emits radiation at 3000 K. Calculate the following- (a) monochromatic emissive power (radiant flux density) at 1 µm wavelength. (b) wavelength at which the emission is the maximum. (c) total emissive power (d) compare the total emissive power of furnace if it is assumed as a real surface having emissivity equal to 0.8. [ Q.NO.1 (TUTE 4)][ ] Q2) Determine the number of shields required to keep the temperature of the outside surface of a hollow brick lining of a furnace at 100 when the temperature of the inside surface of the lining is 500. Take the emissivity of brick lining as well as for shield as 0.87.Heat transfer to the surrounding from the outer surfaces takes place by radiation and convection.the heat transfer coefficient for the natural convection is given by h a =1.24(ΔT) 0.33 W/M 2 K,Air temp.=25 0 C.Neglect the heat transfer by conduction and convection in the brick-lining. [Q.NO.13 (TUTE-4)] [5] Q1) (a) State and explain Stefan Boltzman Law Of radiation. Derive an expression for the total emissive power of a black body. [1+3] b) Obtain an expression for the shape factor of an irregular cavity with respect to itself. [2] Q2) Two large parallel planes having emissivities of 0.5 and 0.5 are maintained at temperature of 800 and 300 respectively. A radiation shield having an emissivity of 0.05 on both sides is placed between the two planes. Calculatea) Heat transfer per unit area without shield [3] b) Also find the temperature of the shield; and heat transfer per unit area with shield. [2+2] Q3) a) Explain the concept of black body and differentiate it with grey body. [1+2] b) A grey body (ε= 0.82) emits the same amount of heat as black body at 300. Find out the required temperature of grey body. If a black body at 1000 K and a grey body at 1200 K emit the same amount of heat; then find out the emissivity of grey body. [4] EME-504/Prof. A. K. Srivastava Date: 17 /11 /2012

23 QUIZ TEST-4 Time: 1 Hour HEAT & MASS TRANSFER Note: Attempt all Question. Q1) A domestic hot water tank ( 0.5 m dia and 1 m high ) is installed in a large space. The ambient temperature is 25. if the tank surface is oxidised copper with an emissivity of 0.8. Find the heat loss from the tank surface at temperature of 80 by radiation. What should be the reduction in heat loss if a coating of aluminium point having an emissivity of 0.3 is given to the tank? [ Q. NO.2( Tute-4)] [3+2] Q2). Two large parallel planes with emissivities 0.4 ( T = 500 K ) and 0.8 ( T= 700 K ) exchange heat. Find the net heat radiated by them and percentage reduction in heat transfer when polished aluminium radiation shield ( ε= 0.04 ) is placed between them. [ Q. N0. 12, Tute-4] [5] Q1) (a)state and explain Stefan Boltzman Law Of radiation. Derive an expression for the total emissive power of a black body. [1+3] b) Obtain an expression for the shape factor of an irregular cavity with respect to itself. [2] Q2) Two large parallel planes having emissivities of 0.5 and 0.5 are maintained at temperature of 800 and 300 respectively. A radiation shield having an emissivity of 0.05 on both sides is placed between the two planes. Calculatea) Heat transfer per unit area without shield [3] b) Also find the temperature of the shield; and heat transfer per unit area with shield. [2+2] Q3).a) Explain the concept of black body and differentiate it with grey body. [1+2] b) A grey body (ε= 0.82) emits the same amount of heat as black body at 300. Find out the required temperature of grey body. If a black body at 1000 K and a grey body at 1200 K emit the same amount of heat; then find out the emissivity of grey body. [4] X EME-504/Prof. A. K. Srivastava Date: 17 /11 /2012

24 QUIZ TEST-4 Time: 1 Hour HEAT & MASS TRANSFER Note: Attempt All Questions. Q1). A small sphere with a surface temperature of 573 K is located at the geometric centre of a large sphere with an inner surface temperature of 298 K. the outside diameter of the small sphere is 6 cm, and inside diameter of the large sphere is 3.6cm. assuming that both side approach black body behavior, determine how much of the emission from the inner surface of the large sphere is incident upon the outer surface of the small sphere.what is the net exchange of heat between the two spheres? [Q.NO.3(TUTE-4)][5] Q2). Determine in watts radiation heat loss from each meter of 20 cm diameter heating pipe when it is placed centrally in the brick duct of square section 30 cm side. Temperature of the pipe surface = 200 Brick duct temperature = 20 Emissivity of the pipe surface = 0.8 Brick duct emissivity = 0.9 Assume only radiation heat transfer between pipe and brick duct. If system is in steady state condition then find the surface heat transfer coefficient of the brick duct assuming the temperature of the surrounding of the duct is 10 [Q.NO.7 (TUTE-4)] [3+2] Q1) ) State and explain Stefan Boltzman Law Of radiation. Derive an expression for the total emissive power of a black body. [1+3] b) Obtain an expression for the shape factor of an irregular cavity with respect to itself. [2] Q2) Two large parallel planes having emissivities of 0.5 and 0.5 are maintained at temperature of 800 and 300 respectively. A radiation shield having an emissivity of 0.05 on both sides is placed between the two planes. Calculatea) Heat transfer per unit area without shield [3] b) Also find the temperature of the shield; and heat transfer per unit area with shield. [2+2] Q3).a) Explain the concept of black body and differentiate it with grey body. [1+2] b) A grey body (ε= 0.82) emits the same amount of heat as black body at 300. Find out the required temperature of grey body. If a black body at 1000 K and a grey body at 1200 K emit the same amount of heat; then find out the emissivity of grey body. [4] X EME-504/Prof. A. K. Srivastava Date: 17 /11/2012

25 QUIZ TEST-4] Time: 1 Hour HEAT & MASS TRANSFER Note: Attempt all Questions. Q1. Liquid air boiling at -153 is located in a spherical container of 320 mm. The container is surrounded by a concentric spherical shell of diameter 360 mm in a room at 27. The space between the two spheres is evacuated. The surface of the spheres are flushed with aluminium (ε = 0.03). Taking the latent heat of vaporisation of liquid air as 210 KJ/ Kg. Find the rate of evaporation of liquid air.[q.no.4 (TUTE-4)] [5] Q2 To reduce the heat flow, the vacuum is provided between two walls of a thermos-bottle. The surface of both walls are silvered (ε = 0.02) which are towards each other. The contents of the bottle have a temperature of 100 and the ambient temperature is 24. Find the rate of heat loss from the thermos bottle. If the same insulating effect is required with the use of cork, find the thickness of cork required. Take the value of K of cork as W/ m-k. Assume inner wall has the temperature of the content and outer wall has the temperature of surrounding atmosphere. [Q.NO.8 (TUTE-4)] [5] Q1 State and explain Stefan Boltzman Law Of radiation. Derive an expression for the total emissive power of a black body. [1+3] b) Obtain an expression for the shape factor of an irregular cavity with respect to itself. [2] Q2 Two large parallel planes having emissivities of 0.5 and 0.5 are maintained at temperature of 800 and 300 respectively. A radiation shield having an emissivity of 0.05 on both sides is placed between the two planes. Calculatea) Heat transfer per unit area without shield [3] b) Also find the temperature of the shield; and heat transfer per unit area with shield. [2+2] Q3).a) Explain the concept of black body and differentiate it with grey body. [1+2] b) A grey body (ε= 0.82) emits the same amount of heat as black body at 300. Find out the required temperature of grey body. If a black body at 1000 K and a grey body at 1200 K emit the same amount of heat; then find out the emissivity of grey body. [4] X EME-504/Prof. A. K. Srivastava Date: 17 /11 /2012

26 QUIZ TEST-4 Time: 1 Hour HEAT & MASS TRANSFER Note: Attempt all Questions. Q1 Determine the heat lost by radiation per meter length of 8 cm diameter pipe at 300 if (a) Located in a large room with red brick walls at a temperature of 27. (b) Enclosed in a 16 cm diameter red brick conduit at a temperature of 27. Take ε = ( steel pipe ) = 0.79 and ε =( brick conduit )= 0.93 [Q.NO.6 (TUTE-4)] [3+2] Q2 The amount of energy falling on a 50 cm 50 cm on horizontal thin metal plate insulated to bottom is 950 W/ m 2. If the emissivity of the plate surface is 0.8 and the ambient temperature is 30, find the equilibrium temperature of the plate.avg. convection heat transfer coefficient for the plate surface h a =5.6 w/m 2 K. [Q.NO.10 (TUTE-4)] [5] Q1) State and explain Stefan Boltzman Law Of radiation. Derive an expression for the total emissive power of a black body. [1+3] b) Obtain an expression for the shape factor of an irregular cavity with respect to itself. [2] Q2) ) Two large parallel planes having emissivities of 0.5 and 0.5 are maintained at temperature of 800 and 300 respectively. A radiation shield having an emissivity of 0.05 on both sides is placed between the two planes. Calculatea) Heat transfer per unit area without shield [3] b) Also find the temperature of the shield; and heat transfer per unit area with shield. [2+2] Q3.a) Explain the concept of black body and differentiate it with grey body. [1+2] b) A grey body (ε= 0.82) emits the same amount of heat as black body at 300. Find out the required temperature of grey body. If a black body at 1000 K and a grey body at 1200 K emit the same amount of heat; then find out the emissivity of grey body. [4] EME-504/Prof. A. K. Srivastava Date: 17 /11 /2012