ON LINE MICROCOMPUTER CONTROL OF HEAT EXCHANGER

Abstract

The present work deals with the On-line Computer control of the exit temperature of a steam heated, fintube, double pipe, heat exchanger by manipulating coolent flow rate through the inner tube using a stepper motor controlled valve. For control, an IBIv compatible PC/XT equipped with AD/DA and I/O timer card was used. For the control of stepper motor, a ste-pper motor driver card was developed. Temperature measurment at the inlet and exit of the inner tube and the steam was done by - using IC transducer A0590. The control algorithms used for the present study were basically those of J.Fuhrman, R.Mutharasan and D. Coughanowr with slight modifications. The inputs to the algorithm are inlet temperature of coolant, steam: temperature and inlet coolant flowrate. The control parameter was flow rate of coolant. The different parameters in the control algorithm, which need tunning were tunned through simulation. For simulation an emperical model was fitted to the experimental transient response of exit temperature of the heat exchanger. It was observed that the experimental results closely follow the simulation profile, and the desired temperature was acheived in 18 sec, with a rise time of 3 seconds. On the other hand the exit temperature takes around 45 seconds to reach 97% of the desired temperature when no controller i$ used. From the simulated results it was clear that the desired temperature can be a the ived, even within shorter time interval of four second, provided the time constant of stepper motor cohtrol valve which is around 2.5 seconds at present is reduced to a value less than 1 second. The software developed for the imp3bmentation of the control algorithm was developed in advanced.version of BASIC (BAS ICA) . The AD/DA conversion routines and the porthandling was also done in BASICA.