13.2 A stirred-tank blending system with a bypass stream is shown in Fig. E13.2. The control objective is to control the composition of a key component in the exit stream, x4. The chief disturbance variables are the mass fractions of the key component in the inlet streams, x1 and x2. Using the following information, discuss which flow rate should be selected as the manipulated variable: (i) inlet flow rate w2, (ii) the bypass fraction f, or (iii) exit flow rate, w4. Your choice should reflect both steady-state and dynamic considerations. Available Information: (a) The tank is perfectly mixed. (b) Constant physical properties can be assumed because the composition changes are quite small. (e) Because the variations in liquid level are small, h does not have to be controlled. (d) The bypass piping results in a negligible time delay. (1 - fw1 *1 w1 *2 w2 fwi V X3 X4 W4 W3