QUIZ TEST-1 - being mechanical

EME-504 / Prof. A.K. Srivastava Date: 27 / 08 / 2011

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SHRI RAMSWAROOP MEMORIAL COLLEGE OF ENGG. & MANAGEMENT

B.Tech. [SEM V (ME-51, 52, 53, 54)] QUIZ TEST-1

(Session: 2011-12)

HEAT AND MASS TRANSFER (EME-504)

Roll No.

(To be filled by the Student) Note: All questions are compulsory. Part – A

(Questions from Tutorial Sheet) [10 Marks]

Q1) A hot plate is exposed to an environment at 1000 c. The Temperature profile of the environmental fluid is given as Tc = 60+40y+0.1y2. The thermal conductivity of the plate is 40W / mo k. Calculate the heat transfer coefficient. (Q. No. 1) [5] Q2) A hollow cylinder with inner radius 30mm and outer radius 50mm is heated at the inner surface at the rate of 105w/m2, and dissipates heat by convection from the outer surface into a fluid at the temp. of 1000

C with a heat transfer coefficient of 400 w/m2 . There is no energy generation and the thermal conductivity of the solid is assumed to be constant at 15 w/m 0 k. calculate the temp. of inside and outside surfaces of the cylinder.(Q. No. 7) [5] Part – B [20 Marks] Q-1). What is the purpose of insulation? Obtain and expression for critical thickness of insulation for a hollow

cylinder. [3 + 3]

Q-2). A furnec is constructed with 10 cm of fine clay and 50 cm of red brick. The inside surface temperature

is 12000 C and outside air temperature is 500 C determine the heat loss from 1 m2 of the furnace wall and the temperature at the layer enter phase. Thermal conductivity for the wall material is: Fine clay k = 0.28 (1+0.000893t) W/m0 K. Red brick k = 0.75 W/m0 K.

[7] Q-3). A 2mm diameter wire with 0.8mm a thick layer of insulation (k=0.15 W/m0 K.)is used in a certain

electric heat application . The insulated surface is exposed to atmosphere with convective heat transfer coefficient 40 W/m2 K. What percentage change in heat transfer rate would occur if critical thickness of insulation is used? It may be assumed that temperature difference between surface of the wire and surrounding air remains unchanged.

[7]

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Academic/26 Refer/WI/ACAD/18

Time: 1 Hour Max. Marks: 30


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Q1) A plate wall of fire clay brick 25cm thick is having a temp 13500c and 500c on two sides. The thermal conductivity of fire clay varies as- K=0.838(1+0.0007T) where T is in 0 C. Calculate the heat loss per m2 through the wall. (Q. No. 2) [5]

Q2) A hollow sphere of inside radius 4cm and outside radius 6cm is electrically heated at the inner surface at the constant rate of 105w/m2. At the outer surface it dissipates heat by convection to a fluid at temp.100 0

C and a heat transfer coefficient of 450 w/m2 K. the thermal conductivity of the solid is 20 w/m 0 k. Calculate the inner and outer surface temperatures. (Q. No. 8) [5]

Part – B [20 Marks] Q-1). What is the purpose of insulation? Obtain and expression for critical thickness of insulation for a hollow

cylinder. [3 + 3]





[7]

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Q-1). 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. 9) [5]

Q4) A wall is constructed of several layers, the first layer consist of brick ( K=0.66w/m 0 k), 25cm thick , the second layer 2.5 cm thick plaster (K=0.7 w/m 0 k).The third layer 10 cm thick lime stone ( K=0.66w/m 0

k) and outer layer of 1.25cm thick plaster (K=0.7 w/m 0 k). the heat T/F coefficient on interior and exterior of the wall fluid layers are 5.8 W/m2 0 K and 11.6 W/m2 0 K respectively find-

a) The overall heat transfer coefficient; b) Overall thermal resistance per m2; c) Rate of heat T/F per m2 of the interior of the room is at 260 C while outer air is at -70 C; d) Temperature of junction between limestone. (Q. No. 4) [5] . Part – B [20 Marks] Q-1). What is the purpose of insulation? Obtain and expression for critical thickness of insulation for a hollow

cylinder. [3 + 3]





[7] __________X__________




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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 – (Q. No. 5) [5] KA= 0.4(1+0.008T) KB= 0.5(1+0.008T) Where T is in 0 C. the thickness LA=10cm, LB=5cm The inside temp of slab A is 600 0 C and outside temp of slab is 300C.

Q2) A tube having outside diameter 2cm is maintained at a uniform temperature T1 and is covered with an insulation (k=0.20Wm/K) to reduce heat loss. Heat is dissipated from the outer surface of insulation by natural convection with Ha =15 W/m2K into the ambient air at T∞. Determine the critical thickness of insulation. Calculate the ratio of heat loss from the tube with insulation to that without insulation for (a) the thickness of insulation equal to the critical thickness and (b) the thickness of insulation 2cm thicker then the critical thickness. (Q. No. 10) [5]

. Part – B [20 Marks] Q-1). What is the purpose of insulation? Obtain and expression for critical thickness of insulation for a hollow

cylinder. [3 + 3]





[7] __________X__________




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Q1) A pipe 300mm in outer dia. is insulated by material of thermal conductivity of 0.23 w/m 0 k. the outer dia. of insulation is 500mm. The insulation is placed with an eccentricity of 50mm. calculate the heat loss from the pipe of its inner and outer surface of insulation are subjected to a temperature difference of 250 0 C. (Q. No. 6) [5]

Q2) Determine the maximum current that a 1 mm diameter bare aluminum(k=204Wm/K)wire can carry

without exceeding a temperature of 200 0 C. The wire is suspended in air at temperature 250 C and h=10 W/m2K. the electrical resistance of this wire per unit length is 0.037Ω/m. (Q. No. 12) [5]

Part – B [20 Marks] Q-1). What is the purpose of insulation? Obtain and expression for critical thickness of insulation for a hollow

cylinder. [3 + 3]





[7]

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EME-504 / Prof. A. K. Srivastava Date: 17 / 10 / 2011

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B.Tech. [SEM III (ME 51, 52, 53 & 54)] QUIZ TEST-3

(Session: 2011-12)

HEAT & MASS TRANSFER Time: 1 hour (EME-504) Max. Marks: 30

Roll No.

(To be filled by the Student) Note: All questions are compulsory.

Part – A (Questions from Tutorial Sheet) [10 Marks]

Q1. Water at 250C and 1.5m/sec. enters a long brass (k=110W/m0K) condenser tube with inner dia. Of 1.34 cm. and outer dia. of 1.58cm. The heat transfer coefficient for condensation at outer surface of the tube is 12,000 w/m2 0K. Calculate overall heat transfer coefficient based on outer surface of the tube. The properties of water at 25°C are---ρ=996kg/m3,µ=8.6x10-4kg/m-sec Kf= 0.614w/m°k,Pr=5.85, Nu=0.023Re0.8x Pr0.4 (Q.No.1) [5] Q2. The dry and saturated stream at 420C is condensed over a 60cm square vertical plate maintained at 280C. Calculate the following- (Q.No.13) [3+2]

I. Film thickness, local heat transfer, coefficient at 30cm from the top edge. II. Average heat transfer and local heat transfer rate. III. What would be the heat transfer coefficient if the plate is inclined at 300C with the horizontal?

Properties of steam at 420C, hfg=2402kJ/kg, ρv=0.0561 kg/m3

The properties of fluid at 350C from TABLE‐ ρ=994kg/m3, µ=728x10‐6kg/m‐sec, Kf= 0.625w/m°k

Part – B [20 Marks] Q1. Define the effectiveness of Heat Exchanger. Obtain an expression for the parallel flow heat exchanger as Given: є = [1- exp -NTU (1+R)] / (1+R) [2+5] Q2. Calculate the rate of diffusion of water vapor from a pool of water at the bottom of a well 6 meters in height to dry air flowing over the top of the well. Assume the entire system is at 250 C and 1 atm. If the well diameter is 3 meters, then find the total weight of water diffused per hour from the surface of water I the well. [3+3] Q3. Steam at 0.065 bar condenses on a vertical plate 0.6 m square. If the surface temperature of the plate is maintained at 150 C. Estimate the rate of condensation. [2+4+1] Ts = 37.70 C, hfg (at 0.065 bar) = 2412 x 103 J/Kg The properties of water at mean temperature of (37.7+15)/2 = 26.40 C are listed below: ρ = 1000 kg/m3, µ = 864 x 10-6 Kg/m-sec, k = 0.913 w/m0K. __________X__________



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Part – A (Questions from Tutorial Sheet) [10 Marks] Q1. A thin walled concentric tube heat exchanger is used to cool engine oil from 1600 to 600 and water, which is available at 250C acts as a coolant. The oil and water flow rates are 2 Kg/Sec. and the diameter of the inner tube is 0.5m and corresponding value of overall heat transfer coefficient is 250 w/m2 0K. How long must the heat exchanger be to accomplish the desired cooling? (Q.No.2) [5] Take Cp of water = 4.187 kj/kg0K Cp of engine oil = 2.035 kj/kg0K Q2. Saturated steam at 900C and 70kρa is condensed on outer surface of a 1.5m long 2.5m dia. Vertical tube maintained at uniform temperature of 700C. Assuming film wise condensation, calculate the heat transfer rate on the tube surface use properties of water at 800C. (Q.No.9) [5]

Hfg=2309 KJ/kg. ρ= 974kg/m3 kf

=0.668w/m0K µ=0.355x10-3kg/m.sec

Part – B [20 Marks] Q1. Define the effectiveness of Heat Exchanger. Obtain an expression for the parallel flow heat exchanger as Given: є = [1- exp -NTU (1+R)] / (1+R) [2+5] Q2. Calculate the rate of diffusion of water vapor from a pool of water at the bottom of a well 6 meters in height to dry air flowing over the top of the well. Assume the entire system is at 250 C and 1 atm. If the well diameter is 3 meters, then find the total weight of water diffused per hour from the surface of water in the well. [3+3] Q3. Steam at 0.065 bar condenses on a vertical plate 0.6 m square. If the surface temperature of the plate is maintained at 150 C. Estimate the rate of condensation. [2+4+1] Ts = 37.70 C, hfg (at 0.065 bar) = 2412 x 103 J/Kg The properties of water at mean temperature of (37.7+15)/2 = 26.40 C are listed below: ρ = 1000 kg/m3, µ = 864 x 10-6 Kg/m-sec, k = 0.913 w/m0K.

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(Session: 2011-12)


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Part – A (Questions from Tutorial Sheet) [10 Marks] Q1. A heat exchanger is required to cool 55,000 kg/h of alcohol from 660C to 400C using 40,000 kg/hr. of water entering at 50C calculate for a parallel flow heat exchanger: (Q.No.3) [3+2]

I. Exit temperature of water II. Heat transfer rate

III. Surface area required

Take overall heat transfer coefficient V=580 W/m2 0K. Take Cp (alcohol) =3760 j/kg0K Cp of (water) = 4180 j/kg0K. Q2. A vertical plate 350 mm height and 420 mm wide at 400C is exposed to saturated steam at 1 atom. Calculate- (Q.No.10) [(1x3)+2]

I. film thickness at the bottom of the plate II. maximum velocity at the bottom of the plate

III. total heat flow of the plate Assume vapor density is small as compared to that of the condensate. Properties of steam & condensate at Tsat=1000C, hfg=22.7x103J/kg at Tf =700C,µ= 406x10-6kg/m-sec , Kf= 0.668w/m°k, ρ=977.8kg/m3 Part – B [20 Marks] Q1. Define the effectiveness of Heat Exchanger. Obtain an expression for the parallel flow heat exchanger as Given: є = [1- exp -NTU (1+R)] / (1+R) [2+5] Q2. Calculate the rate of diffusion of water vapor from a pool of water at the bottom of a well 6 meters in height to dry air flowing over the top of the well. Assume the entire system is at 250 C and 1 atm. If the well diameter is 3 meters, then find the total weight of water diffused per hour from the surface of water in the well. [3+3] Q3. Steam at 0.065 bar condenses on a vertical plate 0.6 m square. If the surface temperature of the plate is maintained at 150 C. Estimate the rate of condensation. [2+4+1] Ts = 37.70 C, hfg (at 0.065 bar) = 2412 x 103 J/Kg The properties of water at mean temperature of (37.7+15)/2 = 26.40 C are listed below: ρ = 1000 kg/m3, µ = 864 x 10-6 Kg/m-sec, k = 0.913 w/m0K.

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Q1. A simple heat exchanger consisting of two concentric flow passages is used for heating 1110 kg/h of oil (Sp heat=2.1 kj/kg0K) from a temp. of 270C to 490C. The oil flows through the inner pipe made of copper (OD=2.86, ID=2.54) and the surface heat transfer coefficient on the oil side is 635 W/m2 0K. The oil is heated by hot water supplied at the rate of 390kg/h and at inlet temperature of 930C. The water side heat transfer coefficient 1270 W/m2 0K. Take the thermal conductivity of copper to be 350 W/m 0K. And the fouling factors on the oil and water sides to be o.ooo1 and o.ooo4 m2 0K/W. what is the length of heat exchanger for

I. Parallel flow (Q.No.4) [3+2] II. Counter flow

Q2. A vertical plate 500mm high and 200mm wide is used to condense saturated steam at 1 atom. At what surface temperature must the plate be maintained to achieve a condensation rate of 24.4kg/hr.? Properties of steam at 1atm, Tsat=1000C, hfg=2257x103J/kg (i) Ts=840C, Tf=920C, ρ = 964 kg/m3, µ =306 x 10-6 Kg/m-sec, kf = 0.667 w/m0K (ii) Ts=800C, Tf=900C, ρ = 965.3 kg/m3,µ =314.8 x 10-6 Kg/m-sec, kf = 0.684 w/m0K.

(Q.No.11) [5] Part – B [20 Marks] Q1. Define the effectiveness of Heat Exchanger. Obtain an expression for the parallel flow heat exchanger as Given: є = [1- exp -NTU (1+R)] / (1+R) [2+5] Q2. Calculate the rate of diffusion of water vapor from a pool of water at the bottom of a well 6 meters in height to dry air flowing over the top of the well. Assume the entire system is at 250 C and 1 atm. If the well diameter is 3 meters, then find the total weight of water diffused per hour from the surface of water in the well. [3+3] Q3. Steam at 0.065 bar condenses on a vertical plate 0.6 m square. If the surface temperature of the plate is maintained at 150 C. Estimate the rate of condensation. [2+4+1] Ts = 37.70 C, hfg (at 0.065 bar) = 2412 x 103 J/Kg The properties of water at mean temperature of (37.7+15)/2 = 26.40 C are listed below: ρ = 1000 kg/m3, µ = 864 x 10-6 Kg/m-sec, k = 0.913 w/m0K. __________X__________



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Part – A (Questions from Tutorial Sheet) [10 Marks] Q1. Consider a very long concentric tube heat exchanger having hot and cold water inlet temperature of 850C and 150C 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 following modes of operations-

I. Counter flow (Q.No.6) [3+2] II. Parallel flow

Q2. Dry saturated steam at a pressure of 2.45bar condenses on the surface of a vertical tube of height 1 m. the tube surface temperature is kept at 1170C. Estimate the thickness of the condensate film and local heat transfer coefficient at a distance of 0.2m from the upper end of the tube. (Q.No.12) [3+2] Properties of steam at p=2.45bar, Tsat=126.70C, hfg=2183x103J/kg At Tf=121.850C ρ = 943 kg/m3,µ = 237 x 10-6 Kg/m-sec, k = 0.686 w/m0K. Part – B [20 Marks] Q1. Define the effectiveness of Heat Exchanger. Obtain an expression for the parallel flow heat exchanger as Given: є = [1- exp -NTU (1+R)] / (1+R) [2+5] Q2. Calculate the rate of diffusion of water vapor from a pool of water at the bottom of a well 6 meters in height to dry air flowing over the top of the well. Assume the entire system is at 250 C and 1 atm. If the well diameter is 3 meters, then find the total weight of water diffused per hour from the surface of water in the well. [3+3] Q3. Steam at 0.065 bar condenses on a vertical plate 0.6 m square. If the surface temperature of the plate is maintained at 150 C. Estimate the rate of condensation. [2+4+1] Ts = 37.70 C, hfg (at 0.065 bar) = 2412 x 103 J/Kg The properties of water at mean temperature of (37.7+15)/2 = 26.40 C are listed below: ρ = 1000 kg/m3, µ = 864 x 10-6 Kg/m-sec, k = 0.913 w/m0K.

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B.Tech. [SEM V (ME 51, 52, 53 & 54)] QUIZ TEST-4

(Session: 2011-12)


Roll No.


Part – A (Questions from Tutorial Sheet) [10 Marks] Q1. Calculate the shape factor for the configuration shown in the figure given below:- (Q.No.1)

a) A sphere of diameter d inside a cubical box of length L = d [2] b) Hemispherical surface closed by a plane surface [1] c) End and side of circular tube of equal length and diameter d [2]

r 1=d 1 2 2 F13 = 0.17

(a) (b) (c)

Q2. A thermo flask has a double walled bottle and the space between the walls is evacuated so as to reduce the heat flow. The bottle surfaces are silver plated and emissivity of each surface is 0.025. If the content of the bottle are at 375 K, find the rate of heat loss from the thermos bottle to the ambient air at 300 K. What thickness of the cork (k=0.03 W/m-deg) would be required if the same insulating effect is to be achieved by the use of cork? (Q.No.5) [3+2] Part – B [20 Marks] Q1. Obtain an expression for heat transfer between two non-black parallel surfaces. Also, state the assumptions made. [5+2] Q2. A pipe with a surface temperature of 480 K is kept within a large enclosure whose walls are at 380 K. Presuming the pipe surface to be black, calculate the coefficient of radiant heat transfer. If the heat transfer coefficient including the effect of radiation and convection is 34.9 W/m2-deg, find the convective heat transfer coefficient. [6] Q3. Three mild steel spheres of diameters 20 cm, 30 cm & 40 cm are placed concentrically. The surface of the innermost sphere is maintained at 800 K while that of the outermost sphere is 200 K. Assuming that the walls are extremely thin and there is perfect vacuum in the annular space between the sphere. Determine the steady state temperature of the intermediate sphere. The emissivity of each surface is 0.2 . [7] __________X__________


1


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Q1. Determine the radiation heat flux between two closely spaced, black parallel plates radiating only to each other if their temp. are 850 K and 425 K respectively. Recalculate the heat flux presuming that each of the parallel plates has an emissivity of 0.5. In each case, the plates have an area of 4m2. (Q.No.3) [3+2] Q2. A 250 x 250 mm ingot casting, 1.5 m high and at 1225 K temperature is stripped from its mold. The casting is made to stand on the end on the floor of a large foundry whose wall, floor and roof can be assumed to be at 300 K temp. Make calculation for the rate of radiant heat interchange between the casting and the room. The casting material has an emissivity of 0.85. Take Stefan Boltzman constant = 5.67 x 10-8 W/m2k4. (Q.No.6) [5]

Part – B [20 Marks] Q1. Obtain an expression for heat transfer between two non-black parallel surfaces. Also, state the assumptions made. [5+2] Q2. A pipe with a surface temperature of 480 K is kept within a large enclosure whose walls are at 380 K. Presuming the pipe surface to be black, calculate the coefficient of radiant heat transfer. If the heat transfer coefficient including the effect of radiation and convection is 34.9 W/m2-deg, find the convective heat transfer coefficient. [6] Q3. Three mild steel spheres of diameters 20 cm, 30 cm & 40 cm are placed concentrically. The surface of the innermost sphere is maintained at 800 K while that of the outermost sphere is 200 K. Assuming that the walls are extremely thin and there is perfect vacuum in the annular space between the sphere. Determine the steady state temperature of the intermediate sphere. The emissivity of each surface is 0.2 . [7] __________X__________



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Q1. A large plane perfectly insulated on one face and maintained at the fixed temp. T1 on the bare face, has an emissivity of 0.84 and loses 250 W/m2 when exposed to surroundings at nearly 0 K. the radiant heat loss from another plane of the same size is 125 W/m2 when bare face having emissivity 0.42 and maintained at temp. T2 is exposed to the same surroundings. Subsequently these two planes are brought together so that the parallel bare faces lie only 1 cm apart and the heat supply to each is so regulated that their respective temp. T1 and T2 remain unchanged. Determine the net heat flux between the planes. (Q.No.4) [5] Q2. An enclosure measures 1.5 m x 1.75 m with a height of 2 m. under steady state equilibrium conditions, the walls and ceiling are maintained at 525 K and floor at 400 K. Determine the net radiation of floor. Є1 (emissivity of ceiling and wall) = 0.85 Є2 (emissivity of floor) = 0.75 (Q.No.8) [5]




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Q1. A domestic hot water tank, 0.5 m diameter and 1m high, is located in a large space effectively forming black surroundings. The surface emissivity and temperature are 0.8 and 350 K, and the temperature of the surroundings is 295 K. estimate the heat loss by radiation from the tank, and suggest the possibility to reduce this heat loss. (Q.No.7) [3+2] Q2. A steel tube 5 cm outside diameter and 2 m long is at 500 K temperature. This tube is located centrally in (i) a large brick room having wall temperature 300 K and (ii) a square brick conduit of 20 cm side and at 300 K. if the emissivity of steel and the brick are 0.8 and 0.95 respectively, make calculation for the rate of heat loss by radiation from the tube in each case and comment on the results. (Q.No.10) [2+3]




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Q1. The flat floor of a hemispherical furnace is at 800 K and has an emissivity of 0.5. The corresponding values for the hemispherical roof are 1200 K 0.25. Determine the net radiation heat transfer from the roof to floor. (Q.No.9) [5] Q2. Two large parallel planes with emissivity 0.4 are maintained at different temperature and exchange heat only by radiation. What percentage change in net radiative heat transfer would occur if two equally large radiation shields with surface emissivity 0.04 introduced in parallel to the plates? (Q.No.13) [5]



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QUIZ TEST-1 - being mechanical