Control-Oriented Modeling of Integrated Flash Boiling for Rapid Transient Heat Dissipation

Flash boiling is a heat transfer process with promise for rapid transient cooling for pulsed, episodic heat loads. While real-time control is needed to use flash boiling for thermal management, the highly nonlinear dynamics of flash boiling do not lend themselves to simple feedback control methods. Here, a control-oriented switched-mode dynamic model of a three-component flash boiling process is presented for use in model-based control design. The switched-mode model uses logic to toggle between three system modes to capture critical dynamics in the flash boiling process: evaporator filling, flash evaporation, and compression. By deactivating unnecessary dynamic states, the mode-switching maintains simulation stability in the presence of highly transient thermodynamic property evaluations near the saturation dome. The model runs faster than real time in part by holding inactive dynamic states constant while in a given mode. Simulated pressure dynamics are compared against experimental data collected on a prototype test bed. The normalized root-mean-square error between the simulated and experimental evaporator pressure is less than 7% for each experimental trial. The results show that the proposed model effectively captures the dominant dynamics of the flash boiling process, thereby enabling future model-based design and control of the process.