TECHNOLOGY AREA(S): Air Platform
OBJECTIVE: Demonstrate a 30kW refrigerant-air condenser design with 50 percent improvement in volumetric heat transfer capacity and no more than 10 percent increase in pressure drop per kW of heat exchanged compared to state-of-the- art compact condensers.
DESCRIPTION: Advances in manufacturing techniques and heat transfer enhancement schemes have enabled realization of heat exchanger designs with high thermal load capacity in small volumetric footprints. Emerging heat exchanger technologies such as advanced channel geometries, surface modifications (e.g., split dimples ), active flow manipulation (e.g., synthetic jets  or oscillating surfaces ) and conformal structurally integrated core architectures [4, 5] can be combined to obtain significant improvements in heat exchanger energy density. When combined with computational fluid dynamics (CFD) and heat transfer tools, novel heat transfer enhancement approaches, channel configurations, and packaging can be customized to suit specific applications, constraints, and operating conditions. The possibility also exists to incorporate heat exchangers in irregular and/or confined spaces, thereby providing maximum utilization of volume real estate. Additionally, passive flow manipulation geometries and channel designs can be optimized for heat transfer and pressure losses, which can reduce or even eliminate the efficiency and capacity penalties associated with flow devices contained in highly confined volume envelopes. The incorporation of game-changing, high capacity vapor cycle systems (VCS) onboard both future and current aircraft hinges on the ability to occupy the smallest volume possible, and acquire, transport, and reject waste heat from electronics, crew, and weapon systems. However, increasing air vehicle loads require evaporators and condensers (especially if air-cooled) that occupy prohibitively large volumes, which decreases the available space for mission systems, fuel, and weapons. This represents a serious capability shortfall in which the thermal management system (TMS) is unable to scale to meet new, more severe mission demands. The intent of this program is to both improve capacity and reduce integration risks associated with VCS in future or current aircraft by significantly reducing the volume footprint of two-phase heat exchangers. There are two approaches that can be combined to attain this objective: 1. Enhanced energy density (compared to conventional plate-fin designs); this could be achieved by leveraging advanced manufacturing techniques and flow regime-tailored heat transfer intensification schemes 2. Conformal geometry permitting the UCHX to be designed around available space in the equipment bay; this will likely require advanced manufacturing techniques - such as additive manufacturing - to realize irregular, non-rectilinear shapes. The viability of this technology will be demonstrated by development of a subscale, air-cooled condenser prototype with 30 kW capacity, and having an enhanced volumetric energy density of no less than 50 percent, and increased pressure drop (per kW capacity) of no greater than 10 percent, as compared to currently employed state-of-the-art aerospace air condenser designs (typically plate-fin cross-flow) at a variety of representative operating conditions. Because utilizing air as a sink requires considerable volume, the technical concepts, fabrication methodologies and design practices developed in this program will open multiple transition paths to high-capacity TMS onboard future air vehicle architectures without requiring additional volume real estate. This technology could also be applied to improve the energy density of other HX types, including evaporators, cold plates, air-air HXs, and air-liquid HXs. Coordination and/or partnership with an original equipment manufacturer (OEM), first tier subsystem company and/or weapons system company (WSC) in order to gain insight into realistic operational requirements is highly encouraged.
PHASE I: Design viable UCHX design solutions for a notional aerospace air-R134a condenser. The deliverables are: 1. Fabrication protocol for HX; demonstrate manufacturing capability to produce heat exchanger channels and integrated heat transfer enhancement structures 2. Candidate UCHX design to be compared against baseline air-R134a condenser.
PHASE II: Produce full-scale prototype of selected UCHX design to compare to current baseline. Prototype testing will demonstrate satisfaction of heat exchanger performance targets and compliance with the volume and integration restrictions in a representative HX equipment bay environment. Deliverables include final report, technical documentation for UCHX prototype, prototype testing results, and fabricated UCHX prototype.
PHASE III: This is an enabling technology for upgrading heat sink capacity, while reducing cost and schedule risks associated with insertion of new equipment in the airframe due to reduced volume requirements. These same benefits extend to most weapon systems where heat exchangers are critical to operation.
1: Elyyan, M.A., Tafti, D.K., "A novel split-dimple interrupted fin configuration for heat transfer augmentation," Int. J. Heat Mass Transfer 52 (2009) 1561-1572.
2: Yu, Y., Simon, T.W., Zhang, M., Yeom, T., North, M.T., and Cui, T., "Enhanced heat transfer in air-cooled heat sinks using piezoelectrically-driven agitators and synthetic jets," Int. J. Heat Mass Transfer 68 (2014) 184-193.
3: Leal, L., Miscevic, M., Lavieille, P., Amokrane, M., Pigache, F., Topin, F., Nogarede, B., and Tadrist, L., "An overview of heat transfer enhancement methods and new perspectives: focus on active methods using electroactive materials," Int. J. Heat Mass Transfer 61 (2013) 505-524.
4: Thompson, S.M., Aspin, Z.S., Shamsaei, N., Elwany, A., and Bian, L., "Additive manufacturing of heat exchangers: a case study on a multi-layered Ti-6Al-4V oscillating heat pipe," Additive Manufacturing 8 (2015) 163-174.
5: Norfolk, M., and Johnson, H., "Solid-state additive manufacturing for heat exchangers," J. Manufacturing 67 (2015) 655-659.
6: AF173-006 SITIS Q&A with accompanying tables. (Uploaded in SITIS on 9/15/16)
KEYWORDS: Heat Exchangers, Air-air, Thermal Management