Development and evaluation of a Thermally Capacitive Heat Exchanger (TCHX)

Many electronic devices run under relatively stable power loads, allowing traditional thermal management systems to operate in steady state. However, some electronic components display unpredictable and highly dynamic operational regimes, characterized by sudden increases in thermal load. These situations require a specialized thermal management solution with high, quickly-accessible thermal capacity, enabling short-term energy storage during operation and gradual heat dissipation over more extended periods. While energy storage alone is insufficient due to inherent capacity limits, a system that transfers heat to the environment and simultaneously provides extra energy buffering during thermal pulses is highly desirable. In this study, a novel thermal management concept, termed “Thermally Capacitive Heat Exchanger” (TCHX), is developed and explored. The TCHX employs solid–liquid phase change, integrated into a heat exchanger structure. The prototype includes three coaxial pipes, where the inner pipe and outer annulus function as flow passages for hot and cold heat transfer fluids (HTFs). In contrast, the middle annulus contains the PCM, which adds thermal capacity, and carefully designed fins that facilitate heat transfer across it. However, the system suggested, designed, built and explored in this work is not a usual “triple-pipe” heat exchanger or PCM storage unit, explored to some extent in the existing literature. The novel design allows for an actual heat transfer between the hot and cold fluids, whereas a built-in latent heat storage serves to compensate for the mismatch between the instantaneous thermal load to be removed and the available cooling capacity. A dedicated experimental setup was built around the unit to assess its performance under different thermal conditions. The experimental study included several typical operation cases, including charging, discharging, and hybrid scenarios involving simultaneous heat accumulation and transfer at various rates. Each hybrid experiment demonstrated the unit's dual-mode operation: steady state and transient. At steady state with no energy accumulation, the heat transfer rate ranged from 180 to 240 W, depending on the operational regime. During the transient stage, the TCHX acted as a thermal buffer between the HTFs, where the heat input from the hot stream exceeded the heat removed by the cold one, and the surplus energy was accumulated in the unit. In this stage, the peak heat transfer rate from the hot HTF reached 700 W. A dimensionless parameter called dominance was introduced in this study to serve as a possible “scenario classifier” for the TCHX operational regimes. A simplified numerical model was developed to predict the system's behavior trends under various scenarios. The model was validated for two distinct hybrid-operation cases, and then used to perform a numerical study of additional cases, going much beyond the specific configurations explored experimentally. In particular, it revealed the dominance effects on geometrically identical configurations, along with the effect of the configurations themselves on the device performance at the same dominance. The results of the current study demonstrate that the TCHX prototype has potential as a modular “building block” for future scalable thermal management systems.