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وزارة التعليم العالي و البحث العلمي
Ministry of Higher Education&
Scientific Research
University of Technology
Materials Engineering Department لوجيةوالجامعة التكن
قسم هندسة المواد
Date: / / 2012
Final Examination
(2011-2012) Class:2
nd
Subject: heat Transfer &Fluid
Allowed time: 3Hr
Examiner: Dr. Ayad K. Hassan
Note: answer five questions
Use Tables Allowed
Q1:- A house has a composite wall of wood, fiberglass insulation, and plaster board as
indicated in the sketch. On a cold winter day the convection heat transfer coefficients are
ho=60 W/m2 .K and hi=30 W/m
2 .K. the total wall surface area is 350 m
2.
a- Determine a symbolic expression for the total thermal resistance of the wall,
including inside and outside convection effects for the prescribed conditions.
b- Determine the total heat loss through the wall.
c- If the wind were blowing violently, raising ho to 300 W/m2 .K, determine the
percentage increase in the heat loss. ....( 20 mark)
Thermal conductivity of plaster board Kp=0.17 W/m.K ,
fiberglass insulation Kb=0.038 W/m.K and plywood siding Ks=0.12 W/m.K
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Q2:- The temperature of a gas stream is to be measured by a thermocouple whose
junction can be approximated as a 1-mm-diameter sphere, as shown below. The properties
of the junction are K= 35 W/m·°C, ρ= 8500 kg/m3, and Cp =320 J/kg · °C, and the
convection heat transfer coefficient between the junction and the gas is h= 210 W/m2·°C.
Determine how long it will take for the thermocouple to read 99 percent of the initial
temperature difference. Assume Ti=0oC, T∞= 100
oC and T(t)=99
oC ….(20 mark)
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Q3:- An aluminum pin fin has a diameter of 4mm and length of 20 mm. calculate the heat
dissipated when the base temperature is 600 K, the fluid temperature is 400 K, and heat
transfer coefficient is 100 W/m2.K . take KAL=180 W/m.K Assume that the fin is insulated
end ….(20 mark)
Q4:- A: Derive the nodal temperature equation for the case of an exterior corner node
with one adjacent side insulated and one adjacent side to a convective heat transfer, as
shown in Fig bellow. (10 marks)
B: Two large parallel plate are at T1=800K, ϵ1=0.3, T2=400K, ϵ2=0.7. Calculate the heat
transfer rate between the two plans. where σ =5.67X10-8
W/m2.K
4 (10 marks)
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Q5:- Air at 27 oC and 1 atm flows over a flat plate at speed of 2 m/s. Calculate the
hydrodynamic boundary layer thickness and thermal boundary layer thickness at
distance 20 cm from the leading edge of the plate. Assume that the plate is heated over its
entire length to a temperature of 60 oC. Calculate the heat transferred in a first 20 cm
Assume unit depth in the z-direction. …. (20 mark) ----------------------------------------------------------------------------------------------------------------------------
Q6 -: A thin (16 cm) diameter circular horizontal plate is maintained at 130oC in a large
room at (24oC) the plate convicts heat from both its top and bottom surfaces. Determine
the rate of heat input in to the plate necessary to maintain the temperature of (130oC)
….(20 mark)
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List of laws
Forced convection
For laminar flow over plate :
For turbulent flow over plate
Natural convection
Horizontal plate
Nuavrg =cRam
Upper surface heat: c=0.15, m=1/3
Lower surface heat: c=0.27, m=1/4
GOOD LUCK
m,n
m,n-1
m-1,n
h,T∞
dx
dy