B.Tech. Fifth Semester (Chemical Engineering) (CGS)
10153 : Heat Transfer : S CH 01
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Pages : 4 AW - 31458
Time : Three Hours Max. Marks : 80
Notes : Answer three questions from Section A and three questions from Section B.
Assume suitable data wherever necessary.
Illustrate your answer necessary with the help of neat sketches.
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Use of slide rule logarithmic tables, Steam tables, Moller's Chart, Drawing instrument, Thermodynamic table for moist air, Psychrometric Charts and Refrigeration charts is permitted.
SECTION - A
- a) A pipe 100 mm ID & 8 mm thickness is carrying a steam at 170°C. The convective heat transfer coeff. on the inner surface of pipe is 75W/ m²°C. The pipe is insulated by two layers of insulation. The first layer of insulation is 46 mm in thickness having thermal conductivity of 1.4W/m°C. The second layer of insulation is also 46 mm having thermal conductivity 0.46 W/ m°C . Ambient temperature = 33°C thermal conductivity of steam pipe =46 W /m°C. The convective heat transfer coeff. from the outer surface of pipe 12W/m²°C. Calculate the heat loss per unit length of pipe. Also determine the interface temperature. 7
b) Define the terms :--- Content provided by FirstRanker.com ---
i) Economic thickness of insulation. 2
ii) Critical thickness of insulation. 2
iii) Extended surfaces. 3
OR - a) Derive expression for temperature distribution under one dimensional steady state heat conduction for composite wall. 7
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b) A steam pipe of outer diameter 120 mm is covered with two layers of lagging inside layer 45 mm thick (k =0.08 W/m°C ) & outside layer 30 mm thick (k =0.12W /m°C). The pipe conveys steam at a pressure of 20 bar with 50°C super heat. From steam table temperature t; =262.4°C . The outside temperature of lagging is 25°C. If the steam pipe is 30 m long determine —
i) Heat lost per hour &
ii) Interface temperature of lagging. 7 - a) Draw and discuss the temperature profile of parallel flow and countercurrent flow heat exchanger. 6
b) Explain the following :--- Content provided by FirstRanker.com ---
i) Reynold's Number
ii) Prandtl Number
iii) Grashoff Number. 4
OR - a) Define the term convection. 4
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b) Ethylene glycol is to be heated from 20°C to 54°C in a tube having 50 mm I.D. The tube wall is maintained at a constant temperature of 85°C. The flow velocity through the tube is 2m/sec. the physical properties of E.G. at average temperature = 37°C are
p=1104kg/m³, Cp =2460J/ kgk
µ=0.0107N-S/m², k =0.255W / mk,
µw =0.0029N ~S/m²
Calculate the length of heat exchanger tube. 10 - a) Explain Wilson plot with significance. 7
b) What is mean by film condensation? Obtain an expression for following equation.
hvy = 0.943 [ k³ ?² g (?L —?V) ? ] / [ µ.L(Tv ~Ts)] ^0.25 valid for laminar flow in condensation film. 6
OR - a) The effectiveness of counter flow heat exchanger is greater than parallel flow heat exchanger. Justify. 6
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b) A vertical plate 500 mm high & maintained at 30°C is exposed to saturated steam at atmospheric pressure calculate —
i) rate of heat transfer &
ii) the condensate rate per hour per meter of the plate width for film condensation. 7
Data :
?=980.3kg/m³ k= 664x10?³ W /m°C--- Content provided by FirstRanker.com ---
µ=434x10?6 kg/m.s & ? =2257kJ /kg.
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- Calculate the heat transfer coefficient for fluid flowing through a tube having 40 mm I.D. at a rate of 5000 kg/hr.
Data :
µ=0.004N.s/m², ?=1.07g/cm³--- Content provided by FirstRanker.com ---
sp.heat =2.72kJ / kg .k
k=0.256W/m.k
Use Dittus — Boelter equation. 13
SECTION -B
- a) The flow rates of hot & cold water stream through a parallel flow heat exchanger are 0.2 kg/s & 0.5 kg/s respectively. The inlet temperature on the hot & cold sides are 75°C & 20°C respectively. The exit temperature of hot water is 45°C. If the individual heat transfer coefficients on both sides are 650W /m²°C. Calculate the area of the heat exchanger. 6
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b) A counter flow heat exchanger is employed to cool 0.55 kg/s (Cp=245kJ /kg°C) of oil from 115°C to 40°C by the use of water. The inlet and outlet temperatures of cooling water are 15°C & 75°C respectively. Take U=1450W/ m²°C. Using NTU method, calculate the following —
i) the mass flow rate of water.
ii) the effectiveness of the heat exchanger.
iii) The surface area required. 8
OR - a) Draw and discuss the working of plate type heat exchanger with the help of diagram. Mention the industrial applications of it. 9
b) Discuss the different types of fouling in heat exchanger. 5 - a) 10000 kg/hr of solution containing 5% solute is to be concentrated to 25% solute. Steam is available at a temperature 135° C. Feed solution enters at 35° C. BPR of the solution is 5°C. Calculate -
1) Water evaporated per hr.
2) Steam consumption per hr.--- Content provided by FirstRanker.com ---
3) Steam economy
4) Heat Transfer area. 7
Data :
Sp. heat of water is 4180 J/kg k.
Latest heat of condensation = 2180 kJ/kg--- Content provided by FirstRanker.com ---
Latent heat of vaporization = 2253 kJ/kg
U=2907W/m²k.
b) Define & Explain the term. 6
i) Capacity of Evaporator.
ii) Economy of Evaporator.--- Content provided by FirstRanker.com ---
iii) True Boiling point rise.
OR - a) Discuss the working and industrial applications of falling film evaporator with figure. 8
b) Define the phenomenon boiling and explain pool boiling curve with neat diagram. 5 - a) Define Radiation and give an expression for Net radiation exchange between black bodies separated by non - absorbing medium. 7
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b) Explain the terms
i) Emissivity.
ii) Total Emissive power
iii) Grey body 6
OR - a) Discuss the following laws of radiation.
i) Kirchhoff's Law
ii) Planck's Law. 7
b) Calculate the following for an industrial furnace in the form of a black body and emitting radiation at 3500° C.
i) Monochromatic emissive power at 1.2 µm length.--- Content provided by FirstRanker.com ---
ii) Wavelength at which the emissions is maximum.
iii) Maximum Emissive Power,
iv) Total Emissive Power.
v) Total Emissive Power if it is assumed as a real surface with emissivity equal to 0.9. 6
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