Model Based Predictive Control of Nucleate Boiling

Abstract

Conventional, liquid phase, forced-convection cooling systems enjoy elevated levels of heat transfer when operated in the Nucleate Boiling regime. Under such conditions, coolant flow rates can be greatly reduced leading to a significant reduction in pumping effort, a downsized cooling system and a subsequent increase in operational lifetime. In order to control heat transfer reliably, a closed-loop control system is necessary which requires a measurement or estimation of the instantaneous heat transfer coefficient. This work presents a control technique for Nucleate Boiling focused on automotive applications and based around a specially built laboratory test rig. The control system calculates the necessary coolant flow rate from an estimated heat flux. The simplicity of the control system is complemented by the complexity of estimating the instantaneous heat flux. Three techniques for estimating this heat flux are presented relying on measured system variables. Results for the third and most practical, technique are presented taken from the laboratory test rig.