# Rate of Heat Transfer of a Composite Pipe

1. Jul 11, 2017

### dzj633

1. The problem statement, all variables and given/known data
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: Ao=π*do
Inside area of pipe: Ai=π*di
q12=hrA1(T1-T2)
hr=σε1(T1+T2)(T12+T22)

3. 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?

2. Jul 11, 2017

### Nidum

The mechanism for heat transfer in this problem is conduction ?

3. Jul 11, 2017

### dzj633

Okay... With that being said i need to use these equations:
qk=(ΔT)/(Rk steel + Rk plastic)
Rk steel= (ln |ro steel/ri steel|) / (2πkl)
Rk plastic= (ln |ro plastic/ri plastic|) / (2πkl)

and use 1 m for the length of the pipe?