Question:

An industrial freezer is designed to operate with an internal air temperature of $ - 20^\circ C$. when the external air temperature is $25^\circ C$ and the internal and external heat transfer coefficients are $12W/m^2K$ and $8W/m^2K$, respectively. The walls of the freezer are composite construction, comprising of an inner layer of plastic ($k = 1W/mK$, and thickness of 3 mm), and an outer layer of stainless steel ($k = 16W/mK$, and thickness of $1mm$). Sandwiched between these two layers is a layer of insulation material with $k = 0.07W/mK$. Find the width of the insulation that is required to reduce the convective heat loss to $15W/m^2$.

This question has single correct option

A. $595mm$

B. $195mm$

C. $198mm$

D. $175mm$

Answer:

B. $195mm$