SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-183 (AirForce)
Title:  Nanofluids for Heat Transfer Enhancement in Aircraft Systems
Research & Technical Areas:  Air Platform

  Objective:  Develop a nanofluid thermal management system concept for enhancing heat transfer performance and weight/volume savings of at least 25 percent in aircraft heat exchangers that use PAO and jet fuels.
  Description:  Thermal engineers strive constantly to improve the performance of the thermal management (TM) systems used in advanced aircraft. New materials and processes are candidate improvement strategies and a lot of testing and qualifications are necessary. Nanofluids (NFs) are evolving coolant materials which offer the potential for heat transfer performance enhancements. This concept for improving the thermophysical properties of coolants is a fairly new research area. NFs have been found to exhibit up to 150 percent higher thermal conductivity and 3 times enhancement in critical heat flux (CHF) compared to the basic fluids from which the NFs are produced. A variety of finer nanoparticles are available commercially in substantial quantities to enable the production of NF suspensions. A wealth of research data is available in this new area to start exploring the benefits in real application scenarios. Cooling, the major subset of TM problems, related to aircraft systems is a big technical challenge for the designers and airframe integrators. The advent of nanoparticles processing methods and their unique properties (such as thousand times larger surface-to-volume ratio and ability to remain in suspension indefinitely) spawned the idea of designer-coolant development using carbon nanotube (CNT), Al2O3, Cu, CuO, etc. in coolants such as poly alpha olefin (PAO), water, and ethylene glycol. The long term chemical and mechanical effects of nanoparticle additives on the flow lines and pumps are yet unknown. The Air Force (AF)seeks novel exploitation and technology maturation strategies of the single phase NF concept, including the cost versus benefit aspects, for AF applications involving PAO or liquid-to-air heat exchangers (HXs).

  PHASE I: Select key elements and establish a preliminary design, analysis, and experimental approach for quantitatively demonstrating the concept of heat transfer enhancement using NFs. This shall include assessment of candidate aircraft HX specifications for running laboratory experiments.
  
  PHASE II: Perform detailed design, analysis, fabrication, and testing of a proof-of-concept test bed for hardware. Analyze results and optimize heat transfer enhancement parameters for real application scenarios. Develop molecular dynamic models to corroborate test results. Project possible weight/volume savings and new TM options. Five gallons of new nanofluid coolant shall be delivered to the AF.

  DUAL USE COMMERCIALIZATION: Military application: Military applications include cooling systems improvements in tactical air platforms and cargo aircraft. Commercial application: Commercial applications include retrofitting of improved HXs into the fleet of various airlines, terrestrial heat exchanger systems, and automobiles using similar cooling devices.

  References:  1. Choi, S.U.S., Zhang, Z.G., Yu, W., Lockwood, F.E., and Grulke, E.A., “Anomalous thermal conductivity enhancement in nanotube suspensions,” <i>Applied Physics Letters</i>, Vol. 79, No. 14, 1 Oct 2001, pp. 2252-2254. 2. You, S.M. and Kim, J.H., “Effect of nanoparticles on critical heat flux of water in pool boiling heat transfer,” <i>Applied Physics Letters</i>, Vol. 83, No. 16, 20 October 2003, pp. 3374-3376. 3. Keblinski, Pawel, Eastman, Jeffery A., and Cahill, David G., “Nanofluids for Thermal Transport,” <i>Materials Today</i>, June 2005, pp. 36-44.

Keywords:  heat exchanger (HX), thermal management (TM), nanofluid (NF), heat transfer enhancement, poly alpha olefin (PAO), carbon nanotube (CNT)

Questions and Answers:
Q: What I am wondering is the concept including the development of a novel technology to study the NFs in micro/nano scale. As I know, the possible heat transfer mechanisms of NFs have been initiated, but obtaining a micro/nano scale-level understanding of how heat is transferred in NFs remains the greatest challenge. An advanced experiment to study the micro/nano scale heat transfer behavior is required. I appreciate if you could provide more information about it.
A: The main driving force behind this solicitation is a desire to allow industry to explore what is feasible with nanofluids. We are not necessarily looking for the development of a wonder-fluid, but just incremental steps towards advancing the state-of-the-art. If a fluid could be developed that had similar viscosity and temperature range to an existing working fluid, such as polyalphaolefin (PAO) or jet fuel, or even water-glycol, but with increased thermal conductivity and/or heat capacity, that would be a large step towards advancing the state of thermal management fluids. The amount of these increases in individual properties is not being specified in the solicitation, because it is unknown what amount of increase is really feasible. Also, it may be that the price of increasing these desired properties is increased viscosity or chemical / mechanical incompatibility to the point that the fluid is not practical. If the temperature range of existing fluids could be extended significantly, or if the thermal properties of fluids could be increased by orders of magnitude, that would be good, but it may not be reasonable to require that for this Phase I effort. It is more to explore what is feasible, and what is not.
That said, the goal in the topic is listed as using the improved performance of nanofluids to reduce the weight / volume of the liquid / air heat exchanger system by 25%, so there does need to be some thought given to the potential application side of these fluids. The actual methodology to be used for the experimentation showing this improved performance of the nanofluid, which would then lead to this 25% savings in the heat exchanger, is not being specified at this time.
Q: What I am wondering is the concept including the development of a novel technology to study the NFs in micro/nano scale. As I know, the possible heat transfer mechanisms of NFs have been initiated, but obtaining a micro/nano scale-level understanding of how heat is transferred in NFs remains the greatest challenge. An advanced experiment to study the micro/nano scale heat transfer behavior is required. I appreciate if you could provide more information about it.
A: The main driving force behind this solicitation is a desire to allow industry to explore what is feasible with nanofluids. We are not necessarily looking for the development of a wonder-fluid, but just incremental steps towards advancing the state-of-the-art. If a fluid could be developed that had similar viscosity and temperature range to an existing working fluid, such as polyalphaolefin (PAO) or jet fuel, or even water-glycol, but with increased thermal conductivity and/or heat capacity, that would be a large step towards advancing the state of thermal management fluids. The amount of these increases in individual properties is not being specified in the solicitation, because it is unknown what amount of increase is really feasible. Also, it may be that the price of increasing these desired properties is increased viscosity or chemical / mechanical incompatibility to the point that the fluid is not practical. If the temperature range of existing fluids could be extended significantly, or if the thermal properties of fluids could be increased by orders of magnitude, that would be good, but it may not be reasonable to require that for this Phase I effort. It is more to explore what is feasible, and what is not.
That said, the goal in the topic is listed as using the improved performance of nanofluids to reduce the weight / volume of the liquid / air heat exchanger system by 25%, so there does need to be some thought given to the potential application side of these fluids. The actual methodology to be used for the experimentation showing this improved performance of the nanofluid, which would then lead to this 25% savings in the heat exchanger, is not being specified at this time.

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