Development and Validation of a Micro-CT Compatible Experimental Platform for Frost Formation Studies
Frost formation on evaporator surfaces continues to limit the performance of air-source heat pumps, yet its three-dimensional evolution under realistic conditions remains insufficiently characterised. Performing such studies inside laboratory Micro-CT systems is technically challenging: the CT scanner’s confined space, moisture sensitivity, and strict temperature limits prohibit the use of conventional cooling and air-delivery hardware. Existing frost rigs generally cannot supply independently controlled humidity and temperature at sub-zero conditions within a compact, rotating environment without risking condensation on CT optics. This work presents a Micro-CT-compatible experimental platform that overcomes these limitations by designing a compact, co-rotating architecture in which all air-temperature conditioning and cooling occur inside the CT scanner. The system combines a micro-wind tunnel (MWT) with a counter current copper-in-copper spiral heat exchanger (CiC–SHXC), enabling precise control of temperature, humidity, and flow rate while maintaining all external surfaces above 18 °C for moisture-safe operation. A two-track development strategy was adopted. Track 1 consisted of ex-situ laboratory validation to assess condensation behaviour, frost-growth dynamics, thermal stability, and overall operational safety. Track 2 focuses on the integration strategy to allow the complete MWT, CiC–SHXC, and thermal-oil loop within the CT chamber, supplied by an external psychrometric generator and an LN2-assisted oil chiller. The ex-situ tests demonstrated stable Peltier operation down to –15 °C, reproducible condensation–freezing transitions, and condensation-free external surfaces for coolant temperatures down to approximately -20 °C. Analytical modelling further shows that the CiC–SHXC provides near-isothermal outlet control across all operating modes without unintended subcooling of airstreams. The resulting platform establishes a robust basis for future time-resolved Micro-CT studies of frost evolution and for developing physically grounded frost-growth and defrost models relevant to next-generation heat-pump systems.