A gas-pressurized coaxial tubular flow-loop apparatus for module-scale barocaloric heat transfer measurements

Barocaloric materials offer a promising route toward solid-state cooling and pressure-tunable thermal energy storage, but most experimental studies rely on small-sample high-pressure calorimetry that does not capture heat transfer behavior at practical module scales. Here, we present a gas-pressurized module-scale barocaloric heat-transfer apparatus that represents the first reported module-level implementation of gas-mediated hydrostatic actuation. The apparatus uses a gas-mediated hydrostatic pressure system to actuate a gram-scale active material bed while a separate liquid flow loop supplies or removes heat through an adjacent coaxial heat transfer channel, thereby decoupling pressure delivery from thermal exchange. Using microencapsulated paraffin as a model pressure-tunable phase change material, we demonstrate two complementary measurement modes based on temperature scanning and step-temperature operation. Temperature-scanning measurements reproduce the bimodal solid-solid and solid-liquid transition behavior observed by differential scanning calorimetry with high fidelity, resolving an upward shift in transition temperature and the disappearance of the lower-temperature solid-solid transition peak with increasing pressure (to 18.6 MPa). Step-temperature measurements further demonstrate the ability of the apparatus to probe transient heat penetration and transformation behavior under cyclic thermal boundary conditions. These results establish the gas-pressurized coaxial flow-loop architecture as a scalable platform for investigating barocaloric heat transfer, finite-rate transformation behavior, and pressure-tunable phase transitions under system-relevant thermal boundary conditions.