Related questions with answers

A concrete wall with a surface area of $20 m^2$ and a thickness of 0.30 m separates conditioned room air from ambient air. The temperature of the inner surface of the wall $(T_1)$ is maintained at $25^\circ C.$ (a) Determine the heat loss (W) through the concrete wall for three thermal conductivity values of (0.75, 1, and $1.25 W/m \cdot K)$ and outer wall surface temperatures of $T_2 = −15, −10, −5, 0, 5, 10, 15, 20, 25, 30,$ and $38 ^\circ C$ (a total of 11 data points for each thermal conductivity value). Tabulate the results for all three cases in one table. Also provide a computer generated graph [Heat loss, $\dot{Q}(\mathrm{W})$ vs. Outside wall temperature, $T_2 (^\circ C)]$ for the display of your results. The results for all three cases should be plotted on the same graph. (b) Discuss your results for the three cases.

A wall has inner and outer surface temperatures of 16 and $6^{\circ} \mathrm{C}$ , respectively. The interior and exterior air temperatures are 20 and $5^{\circ} \mathrm{C}$ , respectively. The inner and outer convection heat transfer coefficients are 5 and $20 \mathrm{W} / \mathrm{m}^{2} \cdot \mathrm{K}$ , respectively. Calculate the heat flux from the interior air to the wall, from the wall to the exterior air, and from the wall to the interior air. Is the wall under steady-state conditions?

Write a vector equation for the line through (6,-11) that is perpendicular to the vector $\langle 4,3\rangle$ .

Question

A concrete wall, which has a surface area of $20 \mathrm{m}^{2}$ and is 0.30 m thick, separates conditioned room air from ambient air. The temperature of the inner surface of the wall is maintained at $25^{\circ} \mathrm{C}$ , and the thermal conductivity of the concrete is $1 \mathrm{W} / \mathrm{m} \cdot \mathrm{K}$ . (a) Determine the heat loss through the wall for outer surface temperatures ranging from $-15^{\circ} \mathrm{C}$ to $38^{\circ} \mathrm{C}$ , which correspond to winter and summer extremes, respectively. Display your results graphically. (b) On your graph, also plot the heat loss as a function of the outer surface temperature for wall materials having thermal conductivities of 0.75 and $1.25 \mathrm{W} / \mathrm{m} \cdot \mathrm{K}$ . Explain the family of curves you have obtained.

Solutions

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Solution A

Solution B

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We are given the following data:

\begin{align*} A&=20\mathrm{~m^2}\\\\ L &=0.30\mathrm{~m}\\\\ T_i &=25\mathrm{\degree{C}}\\\\ k&=1\:\frac{\text{W}}{\text{m}\cdot{\text{K}}}\\\\ \end{align*}

Required: $\cdot$ The heat loss through-plane wall in extreme summer and extreme winter and plotting it on the graph. $\cdot$ Plot the heat loss as a function of the outer surface temperature for wall materials.