<div><p>Performance of drag reduction agents with elevated temperature for geothermal & DHN applications; surfactant- and polymer-type DRAs assessed. Read more about <a itemtype="1" pagetype="project" class="siteLink ptproject" resolved="true" href="https://www.tno.nl/en/sustainable/subsurface/geo-energy/heat-energy-transition-source-user/cost-reduction-geothermal-district-heat/">DRAGLOW</a>.</p></div>

High Temperature & Salinity (HTS) Flow Loop

Thema:: Geo energy

A unique test facility for geothermal & district heating network innovation. Shaping the future of heat together and unlock innovations and new possibilities in geothermal and district heating: TNO’s High Temperature Salinity (HTS) Flow Loop provides a unique testing environment for innovation in geothermal and district heating networks for pushing the limits of energy infrastructure.

What is the HTS Flow Loop?

The HTS Flow Loop is a state-of-the-art testing facility developed by TNO to support research and development in the geothermal and district heating network (DHN) sectors. Designed for flexibility and cost-efficiency, it enables rigorous testing of high-temperature, high-salinity fluid systems under controlled conditions.

With corrosion-resistant construction, precision instrumentation, and adaptable configurations, the HTS Flow Loop offers a robust platform for experimental setups that simulate the toughest operational environments.

Capabilities

The HTS Flow Loop supports a wide range of experimental setups and performance evaluations, including:

Scaling behaviour analysis on novel pipe wall materials and heat exchangers
Descaling solution performance testing
Corrosion behaviour of materials under geothermal conditions
Exchange filter efficiency studies
Drag Reduction Agent (DRA) testing, including thermal and flow behaviour
Component performance testing for DHN systems (e.g., heat exchangers, pumps, valves)
Mineral recovery investigations from brine

Technical specifications

An overview of the key technical specifications of the HTS Flow Loop:

Materials: Hastelloy, Titanium, Duplex & Mo-Steel
Temperature range: 10–90 °C in tanks & up to 115 °C in piping
Flow rate: –20 to 20 m³/h
Pressure range: 0 to 10 barg
Salinity: Up to saturation; supports various compositions (e.g., Na, Ca, Pb & Cl)
Tank 1: 1 m³, thermally insulated, heat wrapping, stirrer for brine preparation
Tank 2: 1 m³, compressed air outflow for downstream boundary control
Pump: Centrifugal, 0–20 m³/h
Test loop: 1” & 2” insulated piping, heat wrapped, 5 m sections
Instrumentation: pH, temperature, flow, pressure, differential pressure, level gauge, sampling ports
Control system: Pre-programmed sequences with built-in safety protocols

High temperature and Salinity Flow Loop website image — High temperature and Salinity Flow Loop

Previous projects and case studies

The HTS Flow Loop has played a central role in pioneering projects aimed at improving the performance, sustainability, and safety of geothermal and DHN systems:

Performance of drag reduction agents with elevated temperature for geothermal & DHN applications; surfactant- and polymer-type DRAs assessed. Read more about DRAGLOW.

Testing cation-exchange filters to selectively remove heavy metal ions and avoid NORM scale in surface equipment.

Assessing the readiness of suppliers to move from metal-based to composite-based geothermal systems.

Collaborate with us

TNO welcomes collaboration with industrial partners, academic institutions, and government agencies. Whether you’re developing new materials, optimising system performance, or shaping future energy policy, the HTS Flow Loop provides the ideal environment to turn ideas into proven solutions.

We are happy to think along with you — discuss your challenges with us and start a geothermal or DHN research project. Together with the HTS Loop, we are ready to meet your needs.