Chapter 15, Problem 27P

To determine

To find: The exhaust temperature.

Answer to Problem 27P

  $T_L={248}^{\circ }C$

Explanation of Solution

Given Data:

  $T_H=350°C$

Efficiency $=30\%$

Formula Used:

  $e_c=1-\frac{T_L}{T_H}$

Calculation:

  $\begin{array}{l}{e}_c=1-\frac{T_L}{T_H}\\ 0.39=1-\frac{\left(273+350\right)}{T_H}\\ 0.61=\frac{623}{T_H}---(1)\end{array}$

The lower temp be made T that raises the efficiency to 0.49

  $\begin{array}{l}0.49=1-\frac{T}{T_H}\\ 0.51=\frac{T}{T_H}---(2)\end{array}$

Now divide eqn 1 by 2 ,

  $\begin{array}{l}\frac{61}{51}=\frac{623}{T}\\ T=\frac{623\times 51}{61}\\ =512K\\ T_L={248}^{\circ }C\end{array}$

Temperature of heat source $T_H={639}^{\circ }C$