GEOHEX: The Test Bench for Single-Phase Heat Transfer
Within the GEOHEX project, one of the main objectives is the development of advanced materials and coatings capable of improving the performance of heat exchangers used in geothermal applications. To achieve this, it was necessary to build experimental facilities able to reproduce real operating conditions and evaluate the effect of nanostructured surfaces on heat transfer. The first of these installations is the single-phase liquid–liquid heat-exchange test bench, designed and built by Spike as a platform to test the behavior of treated plates and quantify the performance gains achievable compared to conventional materials.
Spike’s Role in the Design of the Facility
Spike is responsible for the complete mechanical, hydraulic, and instrumentation design of the test bench. The system was conceived to study in detail the heat transfer between an organic fluid and a simulated geothermal brine, operating under high pressure and with precise control of the operating conditions. The work included numerical modeling, component sizing, material selection, and the development of a fully accessible and modular configuration. The facility also integrates a PLC-based control system that manages startup, monitoring, and data acquisition, ensuring stable and repeatable testing.
The Heart of the Test Bench: The Replaceable-Plate Heat Exchanger
The test bench includes a heat exchanger specifically designed to allow rapid installation of plates coated with GEOHEX materials. The compact geometry, built in stainless steel, is configured to permit plate extraction without disassembling the entire circuit. This design made it possible to compare different surface treatments while keeping all other operating conditions constant, providing a rigorous evaluation method to determine the effectiveness of nanostructured surfaces in improving the heat-transfer coefficient.
Test Bench Configuration and Instrumentation
The test bench is built on a two-level structure: the upper level is dedicated to process components—such as heat exchangers, valves, auxiliary tanks, and the operator panel—while the lower level houses pumps, the chiller, the electrical panel, the gas recovery unit, and the vacuum system. Connections are made using copper and stainless-steel piping, and the instrumentation includes pressure, temperature, and flow sensors. This configuration enables complete monitoring of the system’s thermal and fluid-dynamic behavior, with all data collected in real time by the PLC.
Operating Conditions and System Performance
The bench is designed to operate with organic fluid R134a at temperatures between 35 and 25 °C and geothermal brine at 170 °C, at an operating pressure of 10 bar, with a maximum pressure of 16 bar and a design pressure of 25 bar. These conditions reproduce typical preheating scenarios for geothermal fluids, challenging the plates treated with nanoporous coatings or other surface treatments developed within the GEOHEX project.
Support from Numerical Modeling
During the design phase, Spike used COMSOL Multiphysics to verify the mechanical and thermal behavior of the exchanger. Simulations included Von Mises stress analysis at high pressure, fluid-velocity distributions, temperature maps on the surfaces, and assessments of flow symmetry. These results made it possible to optimize the internal geometry and ensure uniform thermal profiles under realistic operating conditions.
A Key Facility for Validating GEOHEX Materials
The single-phase heat-transfer test bench represents one of Spike’s main contributions to the GEOHEX project. Thanks to this facility, it is possible to compare the thermal performance of different treated surfaces in a standardized way, verify corrosion resistance, and assess exchanger behavior under operating conditions typical of geothermal plants. This laboratory installation provides the experimental foundation for validating the advanced materials developed by the consortium, contributing to the creation of more efficient, durable, and sustainable heat exchangers for the geothermal sector.