TTC Technologies (United States)

This paper demonstrates a low-loss photo patternable polymer waveguide material platform based on benzocyclobutene (BCB) that works in both liquid resins and dry film formats. By precise control of molecule design and refractive index between the core and clad layers, we minimized material absorption at target wavelengths, achieving a propagation loss value of <0.1 dB/cm at 850 nm and <0.3 dB/cm at 1310 nm at the system level based on cutback measurements. We patterned these waveguides on silicon and PCB substrates with laser direct imaging (LDI) or mask aligner, with sub-10 μm accuracy. Moreover, our patterned waveguides maintain thermal stability, with <±5% change in optical loss after multiple reflow processes and 1000 h at 85 °C and 85% humidity (HAST) tests. Lastly, we introduce our modeling framework, predicting transmission, mode profile, and optimal performance of waveguides while considering varying geometries, coupling designs, bend radii, and pitch sizes.

Analytical tools for modern aviation heat exchangers (HEXs), such as those that are additively manufactured, have to be advanced and smart. To develop such tools, procedures are presented in this paper that obviate the need for the standard -number-of-transfer-units method of analysis, enable multiple-rating capabilities, and support the generation and exporting of lookup tables that could be readily inserted into a system-level multidisciplinary design optimization platform. Three practical optimization procedures are evaluated and compared for their ability to efficiently handle the design variables and the performance rating, constraints, and objective functions in the optimization of aviation thermal management components and subsystems. Modern database management techniques are also implemented to enable the generation of the training data that are required for building intelligence into the developed HEX software. The mathematical and qualitative details of the heat transfer aspects of a few of these capabilities are presented in this paper, as are two case studies pertaining to optimization where we compare two of the developed approaches. To the knowledge of the authors, no previous studies have addressed the issues resolved in this paper.

Aerospace system efficiency improvement and capacity growth has fueled demand for innovative, affordable and scalable thermal management technologies. Recent advancements in additive manufacturing (AM) and materials has extended the thermal design space for heat exchangers, cold plates, heat sinks, and heat pipes. Novel heat transfer enhancement techniques, along with design and system interface innovations, offer attractive cooling solutions for use in numerous aircraft systems. These advances are becoming increasingly relevant in aircraft systems as customers are demanding the use of air-cooling instead of liquid-cooling with minimal impact on overall energy conversion efficiency, installed volume and weight. This paper provides an overview of Boeing-led advances in analysis, design, fabrication and testing of next generation heat transfer devices. A case study is presented to provide insight into a methodology for selection of heat transfer surfaces and design optimization for an air-to-air heat exchanger. Design considerations are presented for additive manufacturing of the thermal management devices using a range of high performance materials including aluminum, titanium, stainless steel, and conductive polymer composites.

This paper reports on the use of CFD-based exergy calculation procedure in the multi-disciplinary design and optimization of a complete aircraft system. The procedure is a multi-level one which is based on physical decomposition of the overall system into various sub-systems and utilizes the iterative local/global optimization procedure for system level optimization to avoid the implicit nesting of optimization loops. The procedure thus allows each subsystem to be modeled to a level of detail desired at the subsystem level. Formulation of the CFDbased exergy calculation and results are presented, as is the procedure for both single point and multi-point optimization of the air-frame subsystem of the aircraft. Results from CFD-based modeling are further compared with those from traditional methods based on empirical formulation.

This paper investigates the low-velocity filtration combustion of lean methane–air mixtures occurring in inert packed beds by using a modified one-temperature model, considering the axial thermal diffusion owing to the convective gas–solid heat transfer. Based on the scaling analysis of various transport terms in different conservation equations, a high-activation energy asymptotic method is applied in the flame zone and results in a set of powerful analytical solutions for combustion macrocharacteristics under the fully developed conditions. These are then combined with the eigenvalue method of the modified one-temperature model in the whole flow region to study the flame behaviour analytically and numerically. Our results have shown that the combustion wave velocity is a key characteristic parameter in the filtration combustion process. Compared with other existing theoretical results, the present analytical solutions demonstrate the intricate relationships among the combustion wave velocity, the flame speed, the peak flame temperature and the effects of the variable thermo-physical properties, and show better prediction performance for the combustion wave velocity, the flame speed and the peak flame temperature. Excellent agreements with experimental results have been observed, especially for very lean filtration combustion with stream-wise propagating combustion fronts.