Hybrid Nanofluids for Enhanced Liquid Cooling in Pumped Loops

Pumped liquid cooling loops circulating glycol-based coolant are widely used in combat vehicles to regulate engine temperature. These coolants make use of engineered additives to further reduce potential for freezing, corrosion, cavitation, and other attributes to ensure high system reliability. However, they exhibit relatively poor thermal properties in comparison to many liquids used in heat transfer applications. This results in higher operating temperatures, larger interface heat exchangers, and more demanding heat rejection requirements, including fan power, than would otherwise be necessary. Fluids with improved thermal properties are needed in order to reduce size, mass, power, and fuel consumption, and to improve reliability in next generation combat vehicles. To address this critical need, Creare and the Massachusetts Institute of Technology (MIT) are coordinating development of an advanced hybrid nano-engineered fluid for enhanced liquid cooling. The enhanced fluid combines solid-phase inorganic nanoparticles with inorganic nano-scale phase change material (PCM) droplets, known as a phase change dispersions (PCDs). The nanoparticles are designed for attraction to the interface of the PCM droplets, where they stabilize the material in a Pickering emulsion, forming the nano-encapsulated PCD; excess unbonded nanoparticles are freely suspended in the fluid. The hybrid role of the nanoparticles in stabilizing the PCM and providing enhanced thermal conductivity is a novel, highly-compelling aspect of the proposed effort. Based on prior work at MIT, we expect that this will provide up to 3¢5x increase in the coolantÆs effective heat capacity, in addition to increases in thermal conductivity up to 50%. This hybrid nano-engineered solution has the potential to greatly reduce cooling loop size, mass, and energy consumption, while ensuring long-term reliable operation of combat vehicles operating in extreme conditions. In Phase I, we plan to identify, develop, and evaluate a test matrix of nano-encapsulated phase change dispersions, aimed at demonstrating measurable benefits to thermal properties of Army engine coolants, including thermal conductivity and effective heat capacity. For candidate solutions demonstrating greatest potential, we will conduct further screening evaluations to evaluate changes to heat transfer coefficient, pumping power, and to assess susceptibility to foaming, cavitation, and corrosion. In Phase II, MIT and Creare will continue work to refine and optimize the candidate nano-engineered fluids down-selected from the Phase I study, and will continue with longer-term laboratory trials at more aggressive environmental conditions. We will also produce and deliver additional quantities of fluid to facilitate further dedicated study by the Army.