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Heat Sink (heat + sink)

Distribution by Scientific Domains

Engineering	38%
Physics and Astronomy	19%

Selected Abstracts

A Comparison of Four Mohs Tissue Preparation Methods Using Porcine Skin

DERMATOLOGIC SURGERY, Issue 9 2010
FRCPC, WILLIAM LEAR MD
OBJECTIVE Mohs surgery relies on high-quality, rapid tissue preparation and processing. This study evaluated four currently performed tissue preparation and processing methods for speed of processing and depth of cut into the tissue block to achieve a complete high-quality section. METHODS The following four methods were tested: cryoEMBEDDER, float, heat sink, and slide. Standardized specimens of porcine skin were used to ensure uniformity. We measured the time required for a technician to flatten, embed, and cut to the first complete section of each specimen. Additionally, we measured the depth in microns required to cut into an embedded specimen to achieve a complete section. RESULTS There were advantages and disadvantages of each method, and our findings suggest that the heat sink and float methods are more time efficient but that the slide and cryoEMBEDDER methods require less cutting into the specimen to obtain a complete section. The cryoEMBEDDER device used in this study was loaned by cryoEMBEDDER (Salt Lake City, Utah). [source]

The Uncertainty in SCHF-DT Thermal Conductivity Measurements of Lotus-Type Porous Copper

ADVANCED ENGINEERING MATERIALS, Issue 10 2009
Hiroshi Chiba
Abstract Lotus-type porous metals with many straight pores are attractive for use as heat-sinks because a large heat-transfer capacity can be obtained, due to the small diameter of the pores. In order to use lotus-type porous copper effectively as a heat sink, it is important to know the effective thermal conductivity considering the effect of pores on heat conduction in the material. Since these metals have anisotropic pores, a steady-state comparative longitudinal heat-flow method for measuring thermal conductivity, referring to an ASTM standard, is better than other methods. So far, the effective thermal conductivity of lotus-type porous copper has been measured by using specimens of different thickness (the SCHF-DT method). In this paper, the uncertainty in the effective thermal conductivity of a specimen measured using this method was evaluated by comparison between numerical analysis and current experimental data. The following conclusions were drawn: 1) The uncertainty showed good agreement with the uncertainty analysis; 2) The contribution of the thermal grease thickness was large, based on a combined standard uncertainty analysis; and, 3) The effective thermal conductivity perpendicular to the pores of lotus copper can be measured within 10% uncertainty by this method. [source]

Study on heat transfer characteristics of porous metallic heat sink with conductive pipe under bypass effect

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2009
Sheng-Chung Tzeng
Abstract The work investigated the forced convection heat transfer of the heat sink situated in a rectangular channel by considering the bypass effect. The fluid medium was air. The relevant parameters were the Reynolds number (Re), the relative top by-pass gap (C/H), and the relative side by-pass gap (S/L). The size of the heat sink was 60 mm (L)×60 mm(W)×24 mm(H). Two heat sinks were employed as test specimens: (A) the 0.9-porosity aluminum foam heat sink and (B) the 0.9-porosity aluminum foam heat sink with a 20 mm diameter copper cylinder. The copper cylinder was used as a conductive pipe of heat sink. The average Nusselt number was examined under various forced convection conditions. Experimental results demonstrate that increasing by-pass space decreased the Nusselt number. Besides, the average Nusselt number of mode B heat sink was higher than that of mode A heat sink by 30% for the case without by-pass flow. The heat transfer enhancement by the copper cylinder would decline as the by-pass space grew. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20247 [source]

A comparison of forest and moorland stream microclimate, heat exchanges and thermal dynamics

HYDROLOGICAL PROCESSES, Issue 7 2008
David M. Hannah
Abstract Although the importance of riparian forest in moderating stream temperature variability is recognized, most previous research focuses on conifer harvesting effects and summer maximum temperature with highly variable findings. This article compares stream temperature, microclimate and heat exchange dynamics between semi-natural forest and moorland (no trees) reaches in the Scottish Cairngorms over two calendar years to provide a longer-term perspective. Mean daily water column temperature is warmer for moorland than forest in late winter,early spring, but cooler in summer. Daily water column temperature range is greater for moorland than forest. Streambed temperature dynamics are markedly different between reaches, reflecting contrasting groundwater,surface water (GW,SW) interactions. Mean, minimum and maximum daily air temperature is cooler, humidity is lower, and wind speed is much higher for moorland than forest on average. Net radiation is the dominant heat sink in autumn,winter and major heat source in spring,summer for moorland and summer for forest. Net radiation is greater in summer and lower in winter for moorland than forest. Sensible heat is an energy source in autumn,winter and sink in spring,summer, with loss (gain) greater in summer (winter) for moorland than forest. Latent heat is predominantly a sink for both reaches, with magnitude and variability higher for moorland than forest. Streambed heat flux is much smaller than fluxes at the air,water interface, with moorland and forest illustrating seasonal and between-reach differences attributable to different GW,SW interactions. Seasonal patterns in stream energy budget partitioning are illustrated schematically. To our knowledge, this is the first such study of mixed woodland, which generates notably different results to work on coniferous forest. This research provides a process basis to model stream thermal impact of changes in forest practice, and so inform decision making by land and water resource managers. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Thermal and hydrodynamic characteristics of constructal tree-shaped minichannel heat sink

AICHE JOURNAL, Issue 8 2010
Yongping Chen
Abstract A three-dimensional thermal and hydrodynamic model for constructal tree-shaped minichannel heat sink is developed. The heat and fluid flow in the constructal heat sink with an inlet hydraulic diameter of 4 mm are numerically analyzed, taking into consideration conjugate heat transfer in the channel walls. The pressure drop, temperature uniformity, and coefficient of performance (COP) of the constructal tree-shaped heat sink are evaluated and compared with those of the corresponding traditional serpentine flow pattern. The results indicate that the constructal tree-shaped minichannel heat sinks have considerable advantages over the traditional serpentine flow patterns in both heat transfer and pressure drop. The strong and weak heat flow can be effectively allocated in tree-shaped flow structures; hence, the inherent advantage of uniform temperature on the heating surface in the constructal tree-shaped heat sink is demonstrated. And in tree-shaped flow structures, the local pressure loss due to confluence flow is found to be larger than that due to diffluence flow. In addition, an aluminum constructal tree-shaped minichannel heat sink is fabricated to conduct the verification experiment. The experimentally measured temperature distribution and pressure drop are in agreement with the numerical simulation, which verifies that the present model is reasonable. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Performance improvement of a combined double-way thermochemical sorption refrigeration cycle with reheating process

AICHE JOURNAL, Issue 2 2010
Tingxian Li
Abstract A reheating process is proposed aimed at improving the system performance of a combined double-way thermochemical sorption thermodynamic cycle based on adsorption and resorption refrigeration. The reheating process causes an increase in the driving equilibrium temperature difference, which promotes the reaction rate and thus improves the global conversion of sorbent. Experimental results showed that the proposed reheating process is an effective technique for improving the performance of the combined double-way cycle. The improvement in the COP ranged between 12 and 48% in the different cycle conditions, when compared with the combined double-way cycle without reheating. The low pseudo-evaporation temperature and high heat sink temperature can further improve the system performance. The COP obtained with the combined double-way cycle without reheating was 0.57, when the heat sink, evaporation, and pseudo-evaporation temperatures were 25, 10, and 10°C, respectively. However, at the same cycle conditions, the COP increased to 0.64 when the proposed reheating process was introduced in the combined double-way sorption cycle. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Titan's damp ground: Constraints on Titan surface thermal properties from the temperature evolution of the Huygens GCMS inlet

METEORITICS & PLANETARY SCIENCE, Issue 11 2006
Ralph D. Lorenz
The model parameters are adjusted to match the recorded temperature history of a nearby heater, taking into account heat losses by conduction to the rest of the probe and to Titan's cold atmosphere. The model suggests that after impact when forced convective cooling ceased, the inlet temperature rose from ,110 K to an asymptotic value of only ,145 K. This requires that the inlet was embedded in a surface that acted as an effective heat sink, most plausibly interpreted as wet or damp with liquid methane. The data appear inconsistent with a tar or dry, fine-grained surface, and the inlet was not warm enough to devolatilize methane hydrate. [source]

Copper-filled macroporous Si and cavity underneath for microchannel heat sink technology

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008
F. Zacharatos
Abstract Thermal management in ICs becomes essential as integration density and total power consumption increase. The use of microchannels in high power density electronics cooling is a well-known technique for heat transfer. In this work we developed Cu-filled macroporous Si channels with a Cu-filled cavity underneath, which may be used as heat sinks in high power density electronics cooling. Macroporous Si is formed by electrochemical dissolution of bulk Si, while pore filling with copper is achieved by electro-deposition. Using appropriate design, the resulting composite material may be fabricated on selected areas on the silicon substrate for use as heat sink on Si. The surface area is defined by patterning. The macroporous Si structure is composed of either randomly distributed pores or pores arranged in two-dimensional (2-D) arrays, fabricated by pre-patterning the Si surface before anodization so as to form pore initiation pits. The pore size in this work was 5,m, while the porous layer and the cavity underneath had both a thickness of 40 ,m. Copper deposition proceeds first by filling the micro-cavity underneath the porous layer. This is achieved by linearly increasing the applied potential during electro-deposition. After full Cu-filling of the cavity, pore filling starts from the bottom of each pore and proceeds laterally, while no nucleation takes place on pore wall. In this way, homogeneous copper wires within pores may be fabricated. The Cu/Si composite material is appropriate for forming channels with improved heat transfer within the Si wafer. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Current spreading and thermal effects in blue LED dice

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2007
K. A. Bulashevich
Abstract We have applied simulations to study current the spreading and heat transfer in blue III-nitride light-emitting diodes (LEDs) with the focus on self-heating and its effect on the device characteristics. A conventional planar design of an LED die is considered for the heat sink through a sapphire substrate. The computations predict a great current crowding at the contact electrode edges, resulting in a non-uniform temperature distribution over the die. The thermal effect on the current-voltage characteristic, output optical power, and series resistance of the diode is analyzed and the theoretical predictions are compared with available observations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Study on heat transfer characteristics of porous metallic heat sink with conductive pipe under bypass effect

Optimization of a finned heat sink array based on thermoeconomic analysis

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2007
S. Z. Shuja
Abstract The design and specification of heat sinks for electronic systems is not easily accomplished through the use of standard thermal design and analysis tools since geometric and boundary conditions are not typically known in advance. A second-law based thermoeconomic optimization procedure is presented for a finned heat sink array. This involves including costs associated with material, and irreversible losses due to heat transfer and pressure drop. The influence of important physical, geometrical and unit cost parameters on the overall finned array are optimized for some typical operating conditions that are representative of electronic cooling applications. The optimized cost results are presented in terms of ReD, ReL, ,P / ,H, and q for a finned system in a graphical form. In addition the methodology of obtaining optimum parameters for a finned heat sink system which will result in minimum operating cost is demonstrated. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Thermal performance of aluminium-foam CPU heat exchangers

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2006
H. Mahdi
Abstract This study investigates the performance of existing central processing unit (CPU) heat exchangers and compares it with aluminium-foam heat exchangers in natural convection using an industrial set-up. Kapton flexible heaters are used to replicate the heat produced by a computer's CPU. A number of thermocouples are connected between the heater and the heat sink being used to measure the component's temperature. The thermocouples are also connected to a data-acquisition card to collect the data using LabVIEW program. The values obtained for traditional heat exchangers are compared to published data to validate experiments and set-up. The validated set-up was then utilized to test the aluminium-foam heat exchangers and compare its performance to that of common heat sinks. It is found that thermal resistance is reduced more than 70% by employing aluminium-foam CPU heat exchangers. The results demonstrate that this material provides an advantage on thermal dissipation under natural convection over most available technologies, as it considerably increases the surface-area-to-volume ratio. Furthermore, the aluminium-foam heat exchangers reduce the overall weight. Copyright © 2005 John wiley & Sons, Ltd. [source]

Thermal and hydrodynamic characteristics of constructal tree-shaped minichannel heat sink

Copper-filled macroporous Si and cavity underneath for microchannel heat sink technology

Determining Thermal Test Requirements for Automotive Components

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 2 2004
Dustin S. Aldridge
Abstract Component thermal response is dependent upon numerous factors including the atmospheric temperature, heat sinks and sources, vehicle use time, etc. The number of significant thermal cycles and time at temperature for many components will be related to the number of times the engine is started. This paper provides a methodology to determine the number of significant thermal cycles and time at temperature a product will experience in 10 years which will depend upon engine starts. These calculations provide the basis for an accelerated test requirement to qualify the product based upon customer usage measurements. Because of the trace ability and linkage, the methodology is more marketable to internal and external customers, and less likely to be questioned or arbitrarily overruled. It also enables relative severity assessments for historical customer requirements compared with field needs. Copyright © 2004 John Wiley & Sons, Ltd. [source]

The sting at the end of the tail: Damaging winds associated with extratropical cyclones

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 597 2004
K. A. Browning
Abstract Strong surface winds often accompany the low-level jets that occur along the cold fronts of extratropical cyclones, but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone. The most damaging extratropical cyclones go through an evolution that involves the formation of a bent-back front and cloud head separated from the main polar-front cloud band by a dry slot. When the cyclone attains its minimum central pressure, the trailing tip of the cloud head bounding the bent-back front forms a hook which goes on to encircle a seclusion of warm air. The most damaging winds occur near the tip of this hook,the sting at the end of the tail. Observations of the Great Storm of October 1987 in south-east England are re-examined in some detail to study this phenomenon. The cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations. Air within these circulations leaves the hooked tip of the cloud head (and enters the dry slot) much faster than the rate of travel of the cloud-head tip, implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds. The circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds. Regardless of how important this role may be, the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds. Copyright © 2004 Royal Meteorological Society [source]

Enhanced energy efficiency and reliability of telecommunication equipment with the introduction of novel air cooled thermal architectures

BELL LABS TECHNICAL JOURNAL, Issue 2 2010
Domhnaill Hernon
In the past, thermal management was an afterthought in the design process of a product owing to the fact that heat dissipation loads and densities were minute and did not adversely affect component reliability. In fact, it may be stated that, historically, the sole purpose of thermal management was to ensure component operation below a critical temperature thereby providing reliable equipment operation for a given time period. However, this mindset has evolved in recent years given current economic and energy concerns. Climate change concern owing to vast green house gas emissions, increasing fuel and electricity costs, and a general trend towards energy-efficiency awareness has promoted thermal management to the forefront of "green" innovation within the information and communications technology (ICT) sector. If one considers the fact that up to 50 percent of the energy budget of a data center is spent on cooling equipment and that two percent of the United States' annual electricity is consumed by telecommunications equipment, it becomes obvious that thermal management has a key role to play in the development of eco-sustainable solutions. This paper will provide an overview of the importance of thermal management for reliable component operation and highlight the research areas where improved energy efficiency can be achieved. Novel air-cooled thermal solutions demonstrating significant energy savings and improved reliability over existing technology will be presented including three dimensional (3D) monolithic heat sinks and vortex generators. © 2010 Alcatel-Lucent. [source]