The improved model of the shell-and-tube steam-water heat exchanger is presented. A nonlinear PID control law is proposed for such exchanger for mitigation of output temperature variations because of fluid flow oscillations. Simulation results are given to estimate the effectiveness of the proposed approach. The disturbance limiting control law is also presented. The control law ensures the increase of precision of stabilization of the temperature in the outlet of the heat exchanger on the assumption of the minimum of the heat flow rate (performance criterion) under the action of disturbances of the heating agent flow rate.