Numerical simulation of transient startup characteristics in pump-driven two-phase flow systems

Abstract

The pump-driven two-phase flow system is widely used in electronic cooling due to its high heat transfer efficiency and stable temperature control. However, transient startup behaviors, crucial for reliability in dynamic thermal environments, remain poorly understood. This study addresses this gap by developing a simulation model using AMESim software with R134a as the working fluid, investigating the effects of heat load, pump speed and cooling water temperature on startup dynamics. Results reveal three distinct startup types: Type I rising startup, Type II rising startup, and Type I falling startup. As the heat load increases from 2 kW to 5 kW, the system transitions from Type I to Type II, with the cold plate wall temperature decreasing by up to 27%. At 2 kW and 5 kW, the system exhibits Type I upward and Type II upward startup behaviors, respectively. Type II startup demonstrates reduced overshoot, enabling quicker approach to quasi-steady state. At 2 kW, the system exhibits both single-phase and two-phase heat transfer, with the latter lowering the temperature by 2.26◦C. Excessive subcooling can induce temperature oscillations within the evaporator. At a pump speed of 200 r/min, Type I upward startup is observed; however, increased speeds result in wall temperature overshoot. Furthermore, raising the cooling medium temperature from 10◦C to 40◦C elevates the evaporator wall temperature by 51.67%. By integrating quantitative metrics for overshoot, response time and subcooling effects, this work provides actionable insights for optimizing pump-driven two-phase systems in high-heat-flux electronic cooling applications.