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//Variable declaration:
D2 = 0.5/10**3 //External diameter of needle (m)
h3 = 12 //Heat transfer coefficient (W/m^2.K)
L = 1 //Insulation thickness (m)
T1 = 95 //Reactant temperature ( C)
T3 = 20 //Ambient air temperature ( C)
k1 = 16 //Thermal conductivity of needle (W/m.K)
k3 = 0.0242 //Thermal conductivity of air (W/m.K)
D3 = 2/10**3 //Diameter of rubber tube (m)
//Calculation:
r2 = D2/2 //External radius of needle (m)
r3 = D3/2 //Radius of rubber tube (m)
Rt1 = 1/(h3*(2*%pi*r2*L)) //Thermal resistance ( C/W)
Q1 = (T1-T3)/Rt1 //Rate of heat flow in the absence of insulation (W)
Bi = h3*D2/k1 //Biot number
Nu = h3*D2/k3 //Nusselt number
R2 = log(r3/r2) //Thermal resistance of needle ( C/W)
R3 = 1/(h3*(2*%pi*r3*L)) //Thermal resistance of rubber tube ( C/W)
Rt2 = R2+R3 //Total thermal resistance ( C/W)
Q2 = (T1-T3)/Rt2 //Rate of heat loss (W)
//Result:
printf("1. The rate of the heat loss from the hypodermic needle with the rubber insulation is : %.2f W .",Q1)
printf(" The rate of the heat loss from the hypodermic needle without the rubber insulation is : %.2f W .",Q2)
printf("2. The Biot number is : %f",Bi)
printf(" The nusselt number is : %.3f ",Nu)
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