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Identification of a fluid for two phase capillary pumped cooling systems

Final Report Summary - DIPHASICFLUID (Identification of a fluid for two phase capillary pumped cooling systems)

Executive Summary:
The DIPHASICFLUID project aimed at finding new fluids for two phase capillary pumped cooling systems (CPL). Those systems being used under severe conditions during operation, from very cold weather situations to very hot conditions, the specifications that the fluid must meet are very challenging with respect to phase transition temperatures. Properties to be considered are also numerous and the problem to be solved ends up to be a multi-objective one. Among the phenomena to be taken care of, heat transfer is related to the vaporization enthalpy and the heat capacity; viscosity and density are related to the fluid flowing through the pipes; surface tension is related to the ability to wet the porous wick where heat transfer occurs and to pump the fluid. None of the existing fluids (acetone, methanol, ethanol, ammonia for instance) are satisfactory. Besides those fluids also display inappropriate effects in terms of toxicity, safety, which must be improved and add new products requirements.
As an all-around search in databases and suppliers portfolio could be very time consuming and unable to cover all properties at the same time, the project implemented a strategy for finding solutions based on the use of property prediction tools and first-principle thermodynamic models, to orient the search towards suitable chemical families. Since it was forecasted that pure compound fluids may not be found, mixture candidates were also looked at. This defined an additional challenge because mixtures are reputedly exhibiting non ideal behavior which can be described only by nonlinear property predictions models and those are difficult to run in a large scope search. The project was split in several tasks. The first task (WP1) consisted in building a mathematical performance function encompassing all the property specifications and in screening out unsuitable chemical families in order to define an electronic signature of the ideal fluid. Second, a systematic computer-based search was run to obtain a list of candidate fluids (WP2). It combined two existing computer tools: a bottom-up approach that constructs molecules with feasible chemical synthesis pathways starting from a core molecule; and a top-down search based on group contribution property estimation methods to explore new pure compounds and mixtures built from a pool of chemical fragments. The third task (WP3) intended to narrow the candidate list by updating the performance function of each candidate through the refining of property values either extracting them from databases or predicting them with more accurate first-principle methods. The fourth task concerned the fluid choice (WP4). The fifth task was devoted to experimental measurements of selected fluids (WP5). A coordination tasks (WP6) oversaw the whole project and took care of the dissemination issues.
The project has been successful. With the help of the efficient strategy combining computer-based calculation and experiments, several tens of thousands of molecules covering all chemical families were screened. Not a single molecule achieved the maximum performance regarding all properties, but suitable chemical families were identified and drawbacks of the most promising single molecules were pointed out. Hence, mixtures were screened with the idea of benefiting from synergies in the mixture where one compound property could compensate the far-from-target property value of another compound in the mixture. With that in mind, several hundred mixtures were imagined, their property predicted and verified through experiments. Ultimately, the project found several fluid mixture candidates which performance was validated. Additionally, new cooling fluids suitable for other applications have been found. Both fluids are undergoing patenting at the time of the project end and could be used in future exploitation.

Project Context and Objectives:
see attached document

Project Results:
see attached document

Potential Impact:
see attached document

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