Question 11.22: Determine the radiation heat-transfer coefficient for the pi...

Thermodynamics and Heat Power

Determine the radiation heat-transfer coefficient for the pipe of Illustrative Problem 11.21.

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The upper temperature is given as 120°F and the temperature difference Δ is 120 − 70 = 50°F. Using Figure 11.25, $h_{r}$ = 1 1. 8 and $h_{r}=F_{e} F_{A} h_{r}=1 \times 0.79 \times 1.18=0.93$ . As a check, using the results of Illustrative Problem 11.19,

\begin{aligned}h_{r}=\frac{Q}{A \Delta t} &=\frac{214.5}{[\pi(3.5 / 12)] \times 5(120-70)} \\&=0.94 Btu / h \cdot ft .^{2} \cdot{ }^{\circ} F\end{aligned}

11.25

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