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Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER- VI • EXAMINATION SUMMER-2017
Subject code: X61903 Date: 04/05/2017
Subject Name: Heat and Mass Transfer
Time: 10.30AM to 01:00PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

An insulated steam pipe of 16cm diameter is covered with 4cm thick layer of insulation (k=0.9 and carries process steam. Determine the percentage change in the rate of heat loss if an extra 2cm of thick layer of lagging (k=1.25 is provided. Given that surrounding temperature remains constant and the heat transfer co-efficient for both the configurations is 12w/m2-deg
07

A furnace emits radiation at 20000k. treating it as a black body radiation
Calculate the
Monochromatic radiant flux density at wavelength.
Wave length at which emission is maximum and the corresponding radiant flux density.
Total emissive power,
07
Q.2

A steam pipe 50 mm diameter and 2.5m long has been placed horizontally and exposed to still air at 250c. If the pipe wall temperature is 2950 determine the rate of heat loss. at the mean temperature of 1600c, the thermo-physical properties of air are,
3.64*10-2w/m-deg,
Pr 0.682
v 30.09*10-6 m2/s
β 2.31*10-3 per k
07

What is meant by critical radius of insulation? A thin cylinder with radius r is lagged to an outer radius ro with an insulating material of thermal conductivity k. show that the maximum steady radial heat transfer rate occurs when ro where ho is heat transfer rate against ro for all value of ro between r and infinity.
07
OR

Derive an equation of heat Transfer by conduction through composite wall
07
Q.3

Discuss shape factor algebra and salient features of the shape factor.
07

Discuss planck law and Stefan boltzman law of radiation
07
OR
Q.3

Derive equation of heat transfer by radiation between two non black infinite parallel planes.
07

Derive governing differential equation for temperature distribution of constant area extended surface.
07
Q.4

Derive the relationship between the effectiveness and number of transfer units for a counter flow heat exchanger.
07
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In a food processing plant, a brine solution is heated from a temperature of -120c to -650c in a double pipe parallel flow heat exchanger by water entering at 350c and leaving at 20.50c at the rate of 9 kg/min. determine the heat exchanger area for an overall heat transfer co-efficient of 860 w/m2k.
07
OR
Q.4

Derive equation of LMTD for parallel flow heat exchanger.
07

Discuss fick's law of mass transfer.
07
Q.5

Discuss significance of Reynolds number, Grashof number and Prandtl number for convection heat transfer.
07

Derive the two dimensional momentum equation for the hydrodynamic boundary layer on a flat plate.
07
OR
Q.5

Prove that in heat transfer by natural convection the nusselt number is a function of prandtl number and grashof number
07

Explain film condensation and drop wise condensation.
07