16.11. A stirred-tank heating process and its block diagram are shown in Fig. P16-11. The control system is tuned by the Ziegler-Nichols method, and the ultimate frequency u is 2rad/min. (a) Determine the value of Kc by the Ziegler-Nichols method of tuning. (b) What is the length of the pipe between the tank and the measuring element? (c) What are the gain margin and the phase margin for the control system when Kc is set to the Ziegler-Nichols value found in part (a) ? FIGURE P16-11