Design and experimental investigation of a shell-and-tube phase change thermal storage unit for data center waste heat

The low-grade waste heat from expanding data centers needs to be recovered to prevent massive energy waste and exergy loss. This paper specifically designed and developed a high-efficiency phase-change thermal storage device (PCTSD) tailored for residual heat recovery in data centers. A highly thermally conductive composite phase change material (CPCM) was prepared consisting of 94wt% paraffin wax, 5wt% expanded graphite, 1wt% Cu. PCTSD employed the shell-and-tube heat exchanger configuration integrated with a multi-channel finned tube structure, substantially increasing the heat transfer area. An experimental platform was established to evaluate metrics such as energy storage efficiency, energy storage time etc., and other parameters under varying operating conditions. The study showed that the CPCM had a thermal conductivity nearly ten times higher than pure paraffin, leading to a reduction in energy storage time. An increase in the temperature difference between the heat-carrying fluid and the phase-change temperature served to expedite the rate of thermal energy storage. Simultaneously, appropriately increasing fluid flow rate enhanced convective heat transfer, shortening storage time and improving efficiency. Under the condition of Qv =2 L/min and P =280 W, the phase-change thermal energy storage apparatus attained its peak overall thermal storage efficiency of 94.75%. The charging and discharging durations were 21.75 and 21.08 minutes, respectively—significantly shorter than under other flow conditions. This process demonstrated a more homogeneous temperature profile across the cross-sectional area of the thermal storage unit—with phase change progression kept in synchronization, leading to a notable boost in heat transfer efficiency. As a result, the system exhibited improved waste heat recovery and overall energy storage performance.