Gives
k=0.12W/m°c
h0=35W/m2°c
r1=2mmr2=1+0.8=2.8mm
Q1˙=2πkl1ln(r1r2)+2πr2lh01∆t
Q1˙=k1ln(r1r2)+r2h012πl∆t
Put value
Q1˙=0.121ln(22.8)+0.0028×3512πl∆t
Q1˙=0.02803+10.20402πl∆t
Q1˙=10.23212πl∆t
Q1˙=2πl∆t×0.09773
Critical radius
rc=h0k=350.12=0.0034285m=3.4285mm Q2˙=k1ln(r1rc)+rch012πl∆t
Put value
Q2˙=0.121ln(23.4285)+0.0034285×3512πl∆t
Q2˙=4.491+8.3332πl∆t
Q2˙=12.82452πl∆t
Q2˙=2πl∆t×0.07797
Percentage increase and heat loss
=Q1˙Q2˙−Q1˙×100=0.097730.07797−0.09773×100=20.21 Heat loss=20.21%
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