Design and Simulation of Conventional and Intelligent Controllers for Temperature Control Of Shell and Tube Heat Exchanger System

Abstract

temperature. The hot fluid (water) then flows from the process tank and passes through the tube-side of the heat exchanger. Cold fluid (water) flows from the reservoir tank into the shell side of the heat exchanger. The disturbance tank is provided to study the performance of designed controllers for disturbance rejection. There are two thyristor drives that regulate the voltage and current to the heaters in order to regulate the temperature of the water in process and disturbance tank. The cold and hot water inlet flow to the shell and tubes respectively are manipulated using pneumatic control valves. The flow rate of the hot water is treated as disturbance variable. The hot water inlet temperature is maintained with ± 0.5 0 C variation using an inbuilt digital PID controller. The experiment is carried out in co-current mode. The hot water outlet temperature is considered as the controlled variable. whereas the cold water flow rate to the shell side is treated as the manipulated variable. The cold water is supplied at the room temperature. The inlet and outlet temperatures of the shell and tube side fluid are measured using the RTDs. A differential pressure transmitter (DPT) is used to measure the cold water flow rate. The inlet flow of the cold water can be varied in the range of 0-350 LPH and that of hot water between 0-250 LPH. All the sensors and interfaced with a 16 bit data acquisition system (Advantech ADAM 5000 series hardware). A PC is used to log the data and also perform the functions of the controller. The process parameters are obtained from real time using MATLAB scientific package and the communication standard used is RS232. Fig.2 shows the photograph of the real time experimental setup and the specifications of the heat exchanger set up are tabulated in Table I. TABLE I SPECIFICATION OF HEAT EXCHANGER SETUP. B. Procedure for obtaining process parameters The process reaction curve can be obtained by giving a step change in the manipulated variable. It is one of the widely followed process identification technique [2] and [3]. This method is used for identifying parameters of the shell and tube heat exchanger at each region. For each of these regions a step change in cold water inflow rate is given in both positive and negative directions and the corresponding reaction curves are obtained as shown in Fig.2. Fig.2. Process reaction curve to obtain the transfer function. The transfer functions obtained are tabulated in TABLE II. Using average transfer function ,the controller parameters are obtained. The Ziegler-Nichols rule often leads to a rather oscillatory response to set point changes. According to Zeigler-Nichols tuning, the controller parameters are obtained and tabulated in Table III.