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.