Babylon university
College of materials engineering
Department of polymers and petrochemicals industrials
engineering
Subject: Heat transfer Class: Third year
Heat transfer Examples
Prepared by Mr.Qusai A.Mahdi
Example:- Flow Water flows inside a tube of 20mm diameter
and 3m long flows at a velocity of 0.03 m/s .The water gets
heated from 40oC to120 oC while passing through the tube.The
tube wall is maintained at constant temperature of 160oC.Find
heat transfer rate?
Given:
Diameter, D = 0.020 m Length, L = 3 m Velocity, U = 0.03 m/s
Inner temperature of water, Ti= 40oC
Outer temperature of water, To= 120oC
Wall temperature, Tw= 160 oC
To find: Heat transfer rate ( Q )
Solution: Bulk mean Temperature
Tb= (Ti +To) / 2 = 80 oC
Properties of water at 80oC (HMT Data book, Pg: 21)
?= 974 kg/m3
?= 0.364 x 10 -6 m2/s
Pr = 2.22
k = 0.6687 W/mK
Re = (Um Dh/?) = 1648.35
Since Re < 2300, flow is laminar.
For laminar flow
Nu = 3.66 (HMT Data book, Pg: 123)
Um=0.03 m/s
D=0.02m
Tw=160 oc
Ti=40 oC T0=120 oC
3m
Babylon university
College of materials engineering
Department of polymers and petrochemicals industrials
engineering
Subject: Heat transfer Class: Third year
Heat transfer Examples
Prepared by Mr.Qusai A.Mahdi
Average heat transfer coefficient,
h = Nu k / Dh =122.39 W/m2K
The Heat transfer rate is
Q = h A (Tw-Tm) = h ?DL (Tw-Tb)
Q=122.39 W/m2K*?*(0.02m) *(4m)(120-40)K
Q = 1845.29 W
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