Question

A 20cm-thick cement mortar wall for a warehouse has a temperature on the inside-21°C and outside 26°C. a) What is the temperature difference between the inside and outside in: a. Kelvin (convert inside and outside temperatures to Kelvin and then subtract) b. Celsius b) What is the heat loss through a 4m x 4m section of this wall

Answer 1

Answer:

a).a. 5K

   b. 5°C

b). 480 W

Explanation:

Given:

Thickness of mortar, L = 20 cm  = 0.2 m

Inside temperature, $T_{in}$ = 21°C

                                                           =21+273 = 294 K

Outside temperature, $T_{out}$ = 26°C

                                                           =26+273 = 299 K

a). Temperature difference in --

  a) Kelvin

      ΔT = $T_{out}$ - $T_{in}$

         = 299 - 294

         = 5 K

  b). Celcius

       ΔT = $T_{out}$ - $T_{in}$

             = 26 -21

             = 5°C

b). We know thermal conductivity for cement mortar is k = 1.2 W / m-K

For steady state we know

$Q = \frac{\Delta T}{\frac{L}{K.A}}$

$Q = \frac{5}{\frac{0.2}{1.2\times 2\times 2}}$

$Q = 480$ W