GEOHEX: The Test Bench for Condensing Heat Transfer
In the GEOHEX project, one of the main objectives was to understand how the new materials and coatings developed by the consortium could improve the performance of geothermal heat exchangers. Achieving this required reproducing controlled condensation conditions in the laboratory, carefully observing surface behavior during the transition from dropwise to film condensation. Spike therefore designed and built a dedicated test bench to analyze the condensation mechanism on treated plates, using an experimental approach that combined engineering rigor with direct observation of the phenomenon.
Spike’s Role in Test Bench Design
Spike oversaw the entire development of the facility, from mechanical design to definition of the thermo-fluidic circuit, through to the integration of instrumentation and control systems. The test bench was conceived to study R134a condensation on specially prepared surfaces, with the ability to vary plate geometry and surface treatment. The system served as a fundamental tool for evaluating the effect of nano- and micro-structured surfaces on droplet formation, liquid film dynamics, and overall thermal efficiency.
A Condenser with Optical Window for Phenomenon Observation
A distinctive feature of the system is the double backlit optical window, which allowed high-quality video recording of the condensation process. This setup enabled analysis of the transition between dropwise and film condensation, study of droplet dynamics, and correlation of surface morphology with thermal behavior. The condenser was tested both horizontally and vertically, with the possibility of slight tilting to evaluate how small orientation changes influenced condensate distribution.
Plant Configuration and Technical Instrumentation
The test bench is equipped with a 7 °C water circuit to cool the plate and a 35 °C R134a condensation circuit. The system is designed to operate up to 9 bar working pressure, 14.5 bar maximum pressure, and 16 bar design pressure. All necessary instrumentation—including temperature, pressure, and flow sensors—was integrated into the circuit and connected to a PLC that manages startup, monitoring, and data acquisition.
FEM Simulations and Structural Validation
During the design phase, Spike used Comsol Multiphysics to evaluate the mechanical behavior of the condenser under high-pressure conditions. FEM analyses showed the stress distribution within the exchanger body and confirmed the robustness of the chosen geometry under expected operating conditions. This numerical work was combined with real testing, ensuring safety and stability during experiments.
A Critical Facility for GEOHEX Material Validation
The condensation test bench built by Spike played a crucial role in the experimental activities of the GEOHEX project. This infrastructure made it possible to directly observe how advanced coatings influenced droplet nucleation, coalescence, and liquid film flow. The collected data contributed to the comparative evaluation of surfaces, enabling the identification of configurations capable of improving geothermal heat exchanger thermal performance and reducing fouling risk. The facility represented a key step in transferring advanced material results from laboratory testing to real-world applications.