Oil flows through a horizontal pipe made of oxidised steel with emissivity of $0\mathrm{.}79,$ length of $4\mathrm{.}88m$ and an outside surface area of $87\mathrm{.}3m^2.$ Inlet temperature is $130C$ and outlet is $70C.$ The pipe is not thermally insulated and the ambient air temperature is $20C.$ Wind effect can be neglected.

With the aid of APPENDIX A$,$ calculate the heat loss to the surrounding due to convection and radiation. If polished steel with emissivity of $0\mathrm{.}07$ is used instead of oxidised steel, what would be the loss of heat? Comment on the results.

Information:

Thermal conductivity of steel

$=54\frac{W}{m}*K$

Viscosity of air at $20C$

$=1\mathrm{.}8{10}^{-5}Pa.s$

Density of air at $20C$

$=1\mathrm{.}2k\frac{g}{m^3}$

Prandtl Number

$=0\mathrm{.}71$