Passive versus active operator work in automated process control-a job design case study in a control centre

An evaporatorʹs time-constant (tc) equation has been developed as part of a mathematical model describing the time-dependent behaviour of a refrigeration system. The magnitudes of the evaporatorʹs tc were approximately 2 and 5 s, respectively for 100 and 50% loads imposed on the refrigerator. As a result of a step change in the inletʹs water-temperature, the magnitudes of both tc and the two-phase heat-transfer coefficient (ftp) for the refrigerant system were altered. Although a step decrease in the inlet-waterʹs temperature led to large increase in tc the systemʹs behaviour stabilized quickly because ftp had also increased significantly. The predictions of this investigation showed that such an analysis is highly sensitive to the accuracy of the equations used to calculate both tc and ftp and this makes the experimental verification of this model desirable.