Improved cooling fluids for aircraft
Capillary pumped loops (CPLs) are two-phase thermal management systems. They use capillary surface tension to circulate a cooling fluid between an evaporator and a condenser. Unlike conventional heat pipes, CPLs separate liquid and vapour flow – hence the name two-phase. Conventional fluids are only partially compatible with all aerospace requirements and many do not meet environmental objectives. A new fluid is required. The EU funded the project DIPHASICFLUID (Identification of a fluid for two phase capillary pumped cooling systems) to find a solution. The fluid must optimise a variety of different parameters such as heat transfer capability, viscosity, density and operating temperature. Computers are well suited to such a task, and scientists used reverse engineering to identify candidate molecules and mixtures based on predefined performance requirements. Researchers developed a mathematical performance function based on weighted contributions of target properties according to their importance. Inclusion of the effects of chemical parameters on each property of the performance function enabled them to identify several ideal candidate fluid mixtures. The team then conducted both bottom-up and top-down searches for new candidates. The bottom-up algorithm focused on renewable materials with feasible chemical synthesis pathways. The top-down computer tool used property estimation methods to investigate new pure compounds and mixtures. Based on chemical fragments identified with each method, candidate fluids were constructed and compared, enabling identification of similar molecules. To narrow down the candidate list, researchers updated the performance function of each candidate by refining property values either by extracting them from databases or predicting them with first-principle methods. Experimental work led to the identification of several cooling fluids suitable for aircraft thermal management systems. In these mixtures, the properties of one compound can compensate for property values far from the target of another compound. Improved cooling fluids with lower environmental impact will be an important contribution to the sustainability and competitive position of the EU aerospace industry. They will also have important benefits for operator health and safety. DIPHASICFLUID outcomes are harnessing the power of computers to quickly match desired performance with chemical properties for an optimised solution.
Keywords
Cooling fluids, aircraft, thermal management, capillary pumped loops, DIPHASICFLUID
