Question

B. A wire of 6.5 mm diameter at a temperature of 60°c is to be insulated by a material having k=0.174 w/m°c. Convection heat transfer coefficient (h) =8.772 w/m °c. The ambient temperature is 20°c. For maximum heat loss, what is the minimum thickness of insulation and heat loss per meter length? Also find percentage increase in the heat dissipation too.

Answer 1

Dont put such a big question

Answer 2

Answer:

0.0167 m

118.1%

Explanation:

rcritical=k/h=0.174/8.772=0.0199

tinsulation=rcritical-radius=0.0199-0.00325=0.0167 m

Qbare=hA(Ts-Ta)=8.772*2*3.14*0.00325*(60-20)=7.1206 W

Rinsulation=ln(rcritical/radius)/(2*pi*k*L)=ln(0.0199/0.00325)/(2*3.14*0.174*1)=1.66 C/W

Rconvection=1/(A*h)=1/(2*3.14*1*0.0199*8.772)=0.9151 C/W

Rtotal=0.9151+1.66=2.5757 C/W

Qsheath=(Ts-Ta)/Rtotal=(60-20)/2.5757=15.53 W

Percent increase=100%*(15.53-7.1206)/7.1206=118%