In two phase capillary pumped cooling systems, the selection of a suitable fluid is a critical issue. Many properties have to be considered : 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. Temperature limits must be set because the CPL apparatus may undergo severe conditions during operation, from very cold weather situations to very hot conditions. Therefore the problem of finding a fluid is a multi-objective problem, considering that numerous properties need to be matched. 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.
Rather than undertaking a trial and error search through existing chemicals, we have proposed to run a systematic search that implements a computer aided molecule and mixture design approach based on reverse engineering. Such a strategy combines both bottom-up and top-down approaches to find fluids that can match a large set of specification together. Then the best chemical structure which properties match the set of target properties is imagined with the help of computer synthesis tools.
The project is split in several tasks. The first task (WP1) consists in building a mathematical performance function encompassing all the property specifications and screen potentially interesting chemical families in order to define an electronic signature of the ideal fluid. Second, a systematic computer-based search is run to result in a list of candidate fluids (WP2). It combines two existing computer tools from the partners : 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. Third, the candidate list is narrowed 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 (WP3). The fourth task should concern the fluid choice (WP4). The fifth task is dedicated to experimental measurements (WP5). A coordination tasks (WP6) oversees the whole project.