Rate of Heat Transfer of a Composite Pipe

[dzj633]

Homework Statement

A composite pipe made of steel pipe ( ks = 16 W/m.K) of inner and outer radius of 0.5 and 1.0 cm and a plastic pipe (kp = 0.092 W/m.K) of inner and outer radius of 1 and 1.25 cm, respectively. If the inner surface of the steel is maintained at 900 °C and outer surface of plastic is maintained at 300 °C. The rate of heat transfer per unit length is close to?

2. Relevant equation
Outside area of pipe: A_o=π*d_o
Inside area of pipe: A_i=π*d_i
q₁₂=h_rA₁(T₁-T₂)
h_r=σε₁(T₁+T₂)(T₁²+T₂²)

The Attempt at a Solution

Sigma is boltzmann's constant (6.6667E-8 W/m^2.K^4) I do not know if these equations are the right ones to use because i cannot find an equation for the emissivity. What equation am i missing to solve?

 

[Nidum]

The mechanism for heat transfer in this problem is conduction ?

 

[dzj633]

Okay... With that being said i need to use these equations:
q_k=(ΔT)/(R_{k steel} + R_{k plastic})
R_{k steel}= (ln |r_{o steel}/r_{i steel}|) / (2πkl)
R_{k plastic}= (ln |r_{o plastic}/r_{i plastic}|) / (2πkl)

and use 1 m for the length of the pipe?