Sub.: heat transfer

Ministry of Higher Education and Scientific Research
University of Babylon /College of Material s Engineering
Dept. of Eng. of Polymers and Petrochemical Industries
First month Examination (2016-2017)
Sub.: heat transfer Date:14/ 12/2016
Stage: Third NOTE: Answer Three Questions Time:1.5Hrs.
Q1) Consider the plane wall with uniformly distributed heat sources .The thickness of the wall in the x direction is ?x, and it is assumed that one dimensional and steady state . The heat generated per unit volume is? q, and we assume that the thermal conductivity does not vary with temperature. Show that the heat-conduction equation?(?^2 T)/(?x^2 )+q ?/k=0?

Q2) An aluminum rod 2.0 cm in diameter and 12 cm long protrudes from a wall that is maintained at 250?C. The rod is exposed to an environment at 15?C. The convection heat-transfer coefficient is 12 W/m2•?C. Calculate the heat lost by the rod? k=204 W/m.0C
Q3) A hot steam pipe having an inside surface temperature of 250?C has an inside
diameter of 8 cm and a wall thickness of 5.5 mm. It is covered with a 9-cm layer of
insulation having k=0.5W/m•?C, followed by a 4-cm layer of insulation having
k=0.25 W/m•?C. The outside temperature of the insulation is 20?C. Calculate the
heat lost per meter of length. Assume k=47 W/m•?C for the pipe?

Q4) A 2-kW resistance heater wire whose thermal conductivity is k=15 W/m • °Chas a diameter of D=4 mm and a length of L=0.5 m, and is used to boil water (Figure 1). If the outer surface temperature of the resistance wire is Ts=105°C, determine the temperature at the center of the wire ?


Figure(1)





Good luck
Head of the Department: Examiner:
Assist. Prof. Dr. Nizar .J.Hadi Mr.Qusai A.M