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Technical Paper

Comparative Analysis of Thermal Management Architectures to Address Evolving Thermal Requirements of Aircraft Systems

2008-11-11
2008-01-2905
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.
Technical Paper

System Evaluation of Cavitation Enhanced Heat Transfer in Microchannels

2006-11-07
2006-01-3062
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.
Technical Paper

The Heat Transfer Effects of Nanotube Surfaces Treatments and a Means for Growing the Nanotube Coated Surfaces

2006-11-07
2006-01-3067
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.
Technical Paper

The Evolution of Microchannel Heat Transfer

1999-04-06
1999-01-1357
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.
Technical Paper

The Heat Pump Thermal Bus - An Alternative to Pumped Coolant Loops

1999-04-06
1999-01-1356
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.
Technical Paper

ZERO-ODP REFRIGERANTS FOR LOW TONNAGE CENTRIFUGAL CHILLER SYSTEMS

1996-05-01
961320
This paper investigates the use of several zero-ozone depleting potential (zero-ODP) HFC refrigerants, including HFC-134a, HFC-227ca, HFC-227ea, HFC-236ea, HFC-236cb, HFC-236fa, HFC-245cb, and HFC-254cb, for centrifugal chiller applications. We took into account the thermodynamic properties of the refrigerant and aerodynamic characteristics of the impeller compression process in this evaluation.. For a given operating temperature lift, there are significant differences in the pressure ratio required by each refrigerant and this variation in pressure ratio directly affects compressor size, efficiency, and performance. A comparison of the HFC refrigerant candidates with CFC-114 shows that HFC-236ea, HFC-227ca and HFC-227ea are viable alternatives for centrifugal water chillers. HFC-236ea has properties closest to CFC-114, and will result in comparible performance, but will require a slightly larger impeller and a purge system.
Technical Paper

DEVELOPMENT OF HFC-134a ABSORBENTS FOR THE CHEMICAL/MECHANICAL HEAT PUMP

1996-05-01
961321
This paper will describe the screening and development of absorbents for HFC-134a in the chemical/mechanical heat pump. The absorbents must have low volatility, low melting point, high solubility for HFC-134a vapor, high heat of mixing with HFC-134a, suitable vapor pressure/temperature concentration characteristics when mixed with HFC-134a, low toxicity, low flammability, and thermal stability. A screening procedure was used to select approximately 15 absorbents for experimental evaluation. Measurement of the key physical and thermodynamic properties of the absorbent/HFC-134a mixtures, such as vapor pressure/temperature/concentration properties, materials compatibility, and thermal stability, is described. From these measurements, activity coefficients, enthalpy of mixing, and entropy of mixing of the liquid solution were determined.
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