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Advances in aircraft technology have brought about a necessity for new aircraft thermal management architectures in order to maintain reasonable cost, size, weight, and power requirements of the overall thermal system. Two-phase cooling technologies such as vapor-compression systems have demonstrated significant benefits and offer a serious option for emerging new aircraft thermal management applications. Although vapor-compression technology offers a steady state solution to many of the limitations of existing aircraft thermal management systems, industry concerns about transient behavior need to be addressed. The purpose of this research was to investigate transient effects on the vapor compression system when the majority of the onboard thermal loads are cooled directly with the vapor-compression system and how these systems operate under the rapid thermal transients that a military aircraft experiences during combat missions.

Recent advances in aircraft technology have raised much concern over the manner in which aircraft thermal management is carried out. These advances range from the incorporation of high-power electronics to transporting thermal loads at high temperatures. These types of technological advances have brought about a necessity for new aircraft thermal management architectures in order to maintain reasonable cost, size, weight, and power requirements of the overall system. The objective of this study is to address the requirements and performance aspects of existing system configurations in an effort to identify inefficiencies and highlight potential areas for improvement. As a result of this study, a new aircraft thermal management architecture, which can best be described as a vapor-compression thermal bus, is proposed as a replacement for existing technology.

A method of augmenting natural convection, low-Reynolds-number single-phase forced convection and boiling heat transfer by using nanotube coated heat transfer surfaces is described, as well as a unique method of growing these nanotube surfaces from the heat transfer metal alloy, thereby achieving excellent adhesion. This paper discuses side-by-side experiments where nanotube coated and uncoated surfaces are compared. Data on the positive effects of nanotube coating the axial grooves of copper-water heat pipes is also included. Applications for this technology include improved natural convection heat sinks, enhanced boiling surfaces and improved heat pipes. The nanotube coating is also demonstrated to be a low-cost coating and has been successfully grown on several alloys.

Mainstream Engineering Corporation and Rensselaer Polytechnic Institute previously introduced a new method of enhancing two-phase heat transfer in microchannels. Micro-orifices, 20 μm wide, were entrenched at the inlet of 227-μm (hydraulic diameter) microchannels to provide flow stability and induce hydrodynamic cavitation. Significant heat transfer enhancement was recorded during supercavitating flow conditions in comparison to non-cavitating flows with minimal pressure-drop penalty. This paper examines the usefulness of this approach from a systems perspective. Results are compared to predicted values in microchannel passages without orifices. Recommendations are made to improve the performance of the entire thermal management system.

This paper describes new advances in compressor technology for space-based human health maintenance and countermeasure systems. Specifically, NASA is developing an on-board hyperbaric chamber to treat decompression sickness in crewmembers during long-term space missions. Presently, they do not have pressurization, oxygen delivery, or environmental control subsystems that will operate in zero gravity. Commercial, earth-based compressors typically require gravity-circulated lubrication oil for bearings. An innovative, lubrication-free compressor was designed for space-based hyperbaric chamber pressurization and oxygen delivery subsystems. Compressor components were fabricated and the potential of the new compressor was experimentally validated. The compressor, including power and control equipment weighs 80% less than, occupies 84% less space than, and uses 43% less power than state-of-the-art, commercial, terrestrial systems.

This paper describes the performance benefits and current technology progress of an active heat pump loop (HPL) thermal control bus for spacecraft and planetary thermal control applications. Having initiated this research more than 14 years ago, this paper also briefly highlights the technical developments and obstacles overcome during this 14-year development. This paper discusses the unique features of the HPL approach that make it an attractive design choice for future manned thermal control applications: the use of an heat pump to reject heat to space at a temperature above the heat acquisition temperature, the use of non-toxic thermally stable working fluids, and the use of high-performance lubrication-free (gravity independent) refrigeration compressors. The HPL approach has the performance benefits of a traditional two-phase pumped loop thermal bus coupled with the simplicity of a single-phase pumped loop.

High-density electronics packaging requires new advancement in thermal management. New efforts to standardize three-dimensional electronics packages provide the opportunity to standardize thermal management systems for the first time. Microchannel cooling, a high heat flux technology, is the leading candidate for standardization of earth- and space- based electronics packages. This paper looks at the developments in microchannel cooling that make it more advantageous than other high heat flux techniques and the work that remains to achieve a standardized thermal management system.

This paper will describe a patent-pending approach of using a vapor compression system to also provide a forced two-phase indirect heat transfer loop. This system can be configured with water boiler peak cooling thermal control hardware to avoid the high ambient temperatures associated with supersonic low altitude flight. Due to the very short duration of this high ambient condition, water boiler transient cooling techniques have potential. The water boiler can also be used for ground based cooling when flight-line ground cooling carts are unavailable. The use of a PID controller to accurately control the cold plate temperatures when used with a solenoid activated by-pass circuit will be described.