Physical Sciences

Slotting Fins of Heat Exchangers To Provide Thermal Breaks

Heat exchangers that include slotted fins (in contradistinction to continuous fins) have been invented. The slotting of the fins provides thermal breaks that reduce thermal conduction along flow paths (longitudinal thermal conduction), which reduces heat-transfer efficiency. By increasing the ratio between transverse thermal conduction (the desired heat-transfer conduction) and longitudinal thermal conduction, slotting of the fins can be exploited to (1) increase heat-transfer efficiency (thereby reducing operating cost) for a given heat-exchanger length or to (2) reduce the length (thereby reducing the weight and/or cost) of the heat exchanger needed to obtain a given heat-transfer efficiency. By reducing the length of a heat exchanger, one can reduce the pressure drop associated with the flow through it. In a case in which slotting enables the use of fins with thermal conductivity greater than could otherwise be tolerated on the basis of longitudinal thermal conduction, one can exploit the conductivity to make the fins longer (in the transverse direction) than they otherwise could be, thereby making it possible to make a heat exchanger that contains fewer channels and therefore, that weighs less, contains fewer potential leak paths, and can be constructed from fewer parts and, hence, reduced cost.

Posted in: Briefs, Physical Sciences, Heat exchangers, Performance upgrades, Conductivity

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Methane Clathrate Hydrate Prospecting

Methane hydrate deposits would be detected indirectly through thermal, magnetic, and electric measurements. A method of prospecting for methane has been devised. The impetus for this method lies in the abundance of CH4 and the growing shortages of other fuels. The method is intended especially to enable identification of subpermafrost locations where significant amounts of methane are trapped in the form of methane gas hydrate (CH4·6H2O). It has been estimated by the U.S. Geological Survey that the total CH4 resource in CH4·6H2O exceeds the energy content of all other fossil fuels (oil, coal, and natural gas from non-hydrate sources). Also, CH4·6H2O is among the cleanest-burning fuels, and CH4 is the most efficient fuel because the carbon in CH4 is in its most reduced state. The method involves looking for a proxy for methane gas hydrate, by means of the combination of a thermal-analysis submethod and a field submethod that does not involve drilling. The absence of drilling makes this method easier and less expensive, in comparison with prior methods of prospecting for oil and natural gas.

Posted in: Briefs, TSP, Physical Sciences, Alternative fuels, Methane, Thermal testing, Mining vehicles and equipment

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Detecting Edges in Images by Use of Fuzzy Reasoning

Human visual processing is partly imitated in order to harness some of its power. A method of processing digital image data to detect edges includes the use of fuzzy reasoning. The method is completely adaptive and does not require any advance knowledge of an image.

Posted in: Briefs, TSP, Physical Sciences

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Foam Sensor Structures Would Be Self-Deployable and Survive Hard Landings

A document proposes systems of sensors encased in cold hibernated elastic memory (CHEM) structures for exploring remote planets. The CHEM concept was described in two prior NASA Tech Briefs articles, including “Cold Hibernated Elastic Memory (CHEM) Expandable Structures” (NPO-20394), Vol. 23, No. 2 (February 1999), page 56 and “Solar Heating for Deployment of Foam Structures” (NPO-20961), Vol. 25, No. 10 (October 2001), page 36. To recapitulate: Lightweight structures that can be compressed for storage and later expanded, then rigidified for use are made from foams of shape-memory polymers (SMPs). According to the instant proposal, a CHEM sensor structure would be fabricated at full size from SMP foam at a temperature below its glass-transition temperature (Tg). It would then be heated above Tg and compacted to a small volume, then cooled below Tg and kept below Tg during launch, flight, and landing. At landing, the inelastic yielding of the rigid compacted foam would absorb impact energy, thereby enabling the structure to survive the landing. The structure would then be solar heated above Tg, causing it to revert to its original size and shape. Finally, the structure would be rigidified by cooling it below Tg by the cold planetary or space environment. Besides surviving hard landing, this sensor system will provide a soft, stick-at-the-impact- site landing to access scientifically and commercially interesting sites, including difficult and hard-to-reach areas.

Posted in: Briefs, TSP, Physical Sciences

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Real-Gas Effects on Binary Mixing Layers

This paper presents a computational study of real-gas effects on the mean flow and temporal stability of heptane/ nitrogen and oxygen/ hydrogen mixing layers at supercritical pressures. These layers consist of two counter- flowing free streams of different composition, temperature, and density. As in related prior studies reported in NASA Tech Briefs, the governing conservation equations were the Navier-Stokes equations of compressible flow plus equations for the conservation of total energy and of chemicalspecies masses. In these equations, the expressions for heat fluxes and chemicalspecies mass fluxes were derived from fluctuation-dissipation theory and incorporate Soret and Dufour effects. Similarity equations for the streamwise velocity, temperature, and mass fractions were derived as approximations to the governing equations. Similarity profiles showed important real-gas, non-ideal-mixture effects, particularly for temperature, in departing from the error-function profile, which is the similarity solution for incompressible flow. The temperature behavior was attributed to real-gas thermodynamics and variations in Schmidt and Prandtl numbers. Temporal linear inviscid stability analyses were performed using the similarity and error-function profiles as the mean flow. For the similarity profiles, the growth rates were found to be larger and the wavelengths of highest instability shorter, relative to those of the error-function profiles and to those obtained from incompressible-flow stability analysis. The range of unstable wavelengths was found to be larger for the similarity profiles than for the error-function profiles.

Posted in: Briefs, TSP, Physical Sciences

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System Measures Optical Spectrum Components While Preserving Spatial Detail of Object Surface

An imaging spectrograph system performs data analysis with no need for a frame grabber or PC. Conventional commercial spectrometers or spectrophotometers are usually able to measure optical spectrum from a specified surface area at one point. This is done either with one detector scanning the spectrum in narrow wavelength bands or with an array detector, in which case all the spectral components are acquired at once. If one desires to measure the spectrum at several spatial locations of the specified surface, the target under examination or the measuring instrument has to be mechanically scanned.

Posted in: Briefs, Physical Sciences

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Reconditioned Test Equipment as a Key Driver in Reducing Life Cycle Support Costs

Previously owned test and measurement equipment has been purchased for over 50 years by the United States military, agencies of the Federal gov- ernment, and prime contractors that support these organizations. Yet, despite the significant amount of previously owned equipment purchased regularly, there are very few guidelines (either official or understood) for the research and procurement of this equipment. There are many reasons why an engineer or organization may choose to procure previously owned test equipment assets; however, they are generally one or all of the following: Need to save money. Need to save time over delivery of a new asset. Need to replace with an exact model/configuration that is no longer available as new. Electronic Test Equipment — commonly referred to in the military as TMDE (Test, Measurement and Diagnostic Equipment) or GPETE (General Purpose Electronic Test Equipment) — has been a key component in the lifecycle management of electronic systems since the earliest communication systems were deployed in field, air, and shipboard programs. Today, this equipment continues to play a valuable role in maintaining operational readiness for our military services. In many cases, when a new system is being deployed or repair is required to an existing one, the engineer and/or procurement official will have the option of purchasing new test equipment or previously owned. The availability of previously owned equipment in these cases is usually correlated to the degree in which the equipment is new, cuttingedge technology usually found in design work. The vast majority of federal and military projects, however, typically involve manufacturing, maintenance, or production that relies on “proven” previously deployed and tested technology. Hence, there is usually adequate supply of previously owned equipment. If this is the case, the decision to purchase new or used may be influenced by budget or urgency. Purchasing previously owned equipment may end up costing less than 50% of the list price of the new asset, and may be delivered more quickly. However, there are factors that would-be purchasers of previously owned equipment should keep in mind: Search for the model within one’s own company/organization. If it is not available inside the department or organization and you choose to procure previously owned equipment, always know your source. Specifically, who is guaranteeing quality, warranty, and right of return? The best way to procure this asset is through an informal bidding process where only bona fide test equipment dealers are invited to compete. Do not allow substitutions unless it is clearly understood that the asset will work as configured. If delivery is the main issue, make sure the asset is definitely available from the dealer and that the manufacturer/distributor is unable to expedite delivery. Avoid buying from end users directly, as there are hidden costs that make this an unacceptable choice for anyone other than organizations with complete evaluation, calibration, and repair facilities. Because military systems evolve and, in many cases, have their operational life extended, the original test systems must still be available and maintainable. Today, two factors combine to make system support more difficult. First, the lifespan of military systems is being extended as the government struggles with the dual budget pressures of being squeezed by rising personnel costs and being hit by massive increases in the acquisition cost of new systems. Therefore, in many cases, the procedures to test older systems are based on test equipment that, if removed, must be replaced with product that is a form, fit, and function substitution, or proper system functionality will be at serious risk, requiring a software rewrite and a complete system re-validation. Second, product lifecycles are shortening even as the move to Commercial Off the Shelf (COTS) equipment accelerates. Manufacturers are not stocking spares for long-term support to the extent they did in the past. This makes test equipment harder to support and maintain. The manufacturer’s solution may be to supply a replacement instrument. Before integrating such a replacement instrument, the support facility must consider the switching costs carefully, including physical size and weight, power consumption, cooling requirements, electrical specifications, programming language and interface, and software drivers. Replacing an instrument in a test system with anything other than an original piece of equipment requires engineering expertise, not only in the understanding of the original test procedure, but also the characteristics of the original Device Under Test (DUT) and the specifications and capabilities of the original instrument. So what are the alternatives when a critical system needs to be replicated, repaired, or made more reliable and maintainable? The answer lies in the use of “exact replacement” instruments that are drawn from a broad pool of existing products in the commercial and government sectors. By applying a rigorous inspection, evaluation, and reconditioning process, existing instruments can be brought up to “new” standards with a useful life equal to the original. In most cases, it is possible to source a broad range of exact replacement equipment from the secondary market supply chain. There are many suppliers in this chain that operate refurbishing programs that can bring an existing malfunctioning unit up to the condition and specifications of a new unit, making it a “zero time” product that performs as if it were a new item. Reconditioned instruments provide a viable and cost-effective way to extend the life of existing support systems. Using products from the commercial and government secondary market also allows significant cost savings in current and future maintenance requirements. This article was written by Peter Ostrow, President and CEO of TestMart/NAVICPmart, San Bruno, CA. For more information, visit www.navicpmart.com.

Posted in: Briefs, Physical Sciences, Life cycle analysis, Recycling, Cost analysis, Test equipment and instrumentation

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