Showing papers on "Heat sink published in 2013"

A comprehensive review on passive heat transfer enhancements in pipe exchangers

Abstract: Enhancing heat transfer surface are used in many engineering applications such as heat exchanger, air conditioning, chemical reactor and refrigeration systems, hence many techniques have been investigated on enhancement of heat transfer rate and decrease the size and cost of the involving equipment especially in heat exchangers. One of the most important techniques used are passive heat transfer technique. These techniques when adopted in Heat exchanger proved that the overall thermal performance improved significantly. This paper reviews experimental and numerical works taken by researchers on this technique since 2004 such as twisted tape, wire coil, swirl flow generator,… etc. to enhance the thermal efficiency in heat exchangers and useful to designers implementing passive augmentation techniques in heat exchange. The authors found that variously developed twisted tape inserts are popular researched and used to strengthen the heat transfer efficiency for heat exchangers. The other techniques used for specific work environments are studied in this paper. Twisted tape inserts perform better in laminar flow than turbulent flow. However, the other several passive techniques such as ribs, conical nozzle, and conical ring, etc. are generally more efficient in the turbulent flow than in the laminar flow.

Thermal and hydrodynamic analysis of microchannel heat sinks: A review

Abstract: An impressive amount of investigation has been devoted to enhancing overall thermal and hydrodynamic performance of microchannel heat sinks. The small size of microchannel heat sinks and their ability to dissipate heat generated by modern electronics makes them the first choice for the electronic cooling systems in most devices. In this paper, a comprehensive review of available studies regarding non-circular microchannel heat sinks, with emphasis on rectangular microchannels, was presented and analyzed. This review looked into the methodologies used to analyze and optimize the overall performance of microchannel systems along with channel geometries, flow conditions, the coolants used, structural materials, optimization tools and finally, the form in which the final outcome of each study was presented. The review showed that earlier studies (from 1981 to 1999) were largely conducted using experimental or analytical approaches while more recent studies (from 2000 to the end of 2012) showed a dependency on numerical simulations and evolutionary algorithms. In addition, they also showed that laminar was the prevailing flow condition as out of the 69 articles reviewed, 54 employed laminar flows. Furthermore, the use of liquid coolants was preferable over gaseous coolants. Recent developments in nanofluids are providing alternative coolants that are quickly establishing as coolants to be reckoned with.

L10 FePtX–Y media for heat-assisted magnetic recording

Abstract: Highly chemically ordered L10 FePtX–Y nano-granular films with high perpendicular magnetic anisotropy are key media approaches for future heat-assisted magnetic recording (HAMR). They are sputtered at elevated temperature on glass disks coated with adhesion, heat sink, and texturing layers. Adding X = Ag reduces the required deposition temperature and X = Cu lowers the Curie temperature. Current seed layers are NiTa for adhesion and heat sink and well-oriented MgO (002) layers for highly textured FePtX(002) grains surrounded by Y = carbon and/or other segregants. Magnetic anisotropies larger than 4.5 × 107 erg cm−3 and coercivities beyond 5 Tesla have been achieved. The combination of thermal conductivity and Curie temperature determines the required laser power during recording. Key goals are to optimize media, heads, head-disk-spacing, and read-back channels to extend the areal density to 1.5–5 Tb in−2. Head and media in heat-assisted magnetic recording1. LD, laser diode; TFC, thermal fluctuation control; NFT, near field transducer. 1Lidu Huang et al., “HAMR Thermal Modeling Including Media Hot Spot”, APMRC 2012.

Recent Advances in High-Flux, Two-Phase Thermal Management

Abstract: Recent developments in applications such as computer data centers, electric vehicle power electronics, avionics, radars, and lasers have led to alarming increases in heat dissipation rate, which now far exceeds the capability of air cooling schemes and even the most aggressive single-phase liquid cooling schemes. This trend is responsible for a recent transition to two-phase cooling, which capitalizes upon the coolant's latent heat rather than sensible heat alone to achieve several order-of-magnitude increases in heat transfer coefficient. Three two-phase cooling configurations have surfaced as best contenders for the most demanding applications: mini/microchannel, jet, and spray. This study will explore the implementation of these configurations into practical cooling packages, assess available predictive tools, and identify future research needs for each. It is shown that the design and performance assessment of high-flux, two-phase cooling systems are highly dependent on empirical or semiempirical predictive tools and, to a far lesser extent, theoretical mechanistic models. A major challenge in using such tools is the lack of databases for coolants with drastically different thermophysical properties, and which cover broad ranges of such important parameters as flow passage size, mass velocity, quality, and pressure. Recommendations are therefore made for future research to correct any critical knowledge gaps, including the need for robust computer algorithms. Also discussed is a new class of “hybrid” cooling schemes that capitalize upon the merits of multiple cooling configurations. It is shown that these hybrid schemes not only surpass the basic cooling configurations in heat dissipation rate, but they also provide better surface temperature uniformity.

Heat and mass transfer in a Jeffrey fluid over a stretching sheet with heat source/sink

Abstract: This article studies the combined effect of heat and mass transfer in Jeffrey fluid over a stretching sheet in the presence of heat source/heat sink. The surface temperature and the concentration are assumed to vary according to power law form. The arising non-linear coupled partial differential equations are reduced to a set of coupled non-linear ordinary differential equations and then exact solutions are derived by power series method using Kummer’s confluent hyper-geometric functions. The effects of emerging parameters on the velocity, temperature and concentration profiles are shown and examined. It is observed that the velocity increases with an increase in Deborah number. Further the temperature is a decreasing function of Deborah number. Thermal boundary layer thickness decreases by increasing the wall temperature and heat sink parameters.

Numerical Predictions of the Flow and Thermal Performance of Water-Cooled Single-Layer and Double-Layer Wavy Microchannel Heat Sinks

Abstract: Various microchannel heat sinks for dissipating heat loads have received great attention. Wavy channels are recognized to be suitable to enhance the heat transfer, and are successfully applied in heat-exchange devices. In this article, three kinds of water-cooled microchannel heat sinks, such as a rectangular straight microchannel heat sink, a single-layer wavy microchannel heat sink and a double-layer wavy microchannel heat sink, have been designed and the corresponding laminar flow and heat transfer have been investigated numerically. The effects of the wave amplitude on heat transfer, pressure drop, and thermal resistance are also observed. Results show that for removing an identical heat load, the overall thermal resistance of the single-layer wavy microchannel heat sink decreases with increasing volumetric flow rate, but the pressure drop is increased greatly. At the same flow rate, the double-layer wavy microchannel heat sinks can reduce not only the pressure drop but also the overall thermal resist...