Thermal Analysis of Plastic Serpentine-Type Microchannel Evaporators

2007 ◽  
Author(s):  
Boris Kosoy ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Removal Rate ◽  
Flow Characteristics ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
High Heat Transfer ◽  
Micro Channels

Recently, microchannel liquid cooling technology showed very high heat transfer coefficients enabling high heat fluxes at allowable wall temperatures. It promises to be a potential solution to high flux electronics. This paper presents result of two related areas in the field of microchannel heat transfer. First, experimental results of serpentine-type fluoroplastic evaporated thermosyphons for microchannel applications are presented. R11 and R113 were used as working fluid, and it was shown that R11 has higher heat removal rate than R113. Flow distribution and flow characteristics (liquid, vapor, mixture etc) are discussed. Later discussion is extended towards key issues in mini and micro channels, and proposed correlations will be discussed. It is our great honor to contribute to Prof. Sadik Kakac symposium to celebrate his 75th birthday. We feel privileged knowing him and learning from his scientific books, papers, and personal discussions. We wish him a happy, healthy, and long life.

High Efficiency Heat Sinks from Polycrystalline Diamond Grown by CVD Method

2006 ◽  
Vol 956 ◽  
Author(s):  
Oleg A. Voronov ◽  
Gary S. Tompa ◽  
Veronika Veress
Keyword(s):  
Heat Transfer ◽  
Semiconductor Lasers ◽  
High Efficiency ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Measuring System ◽  
High Heat Transfer ◽  
Micro Channels

ABSTRACTWhile absolute power levels in microelectronic devices are relatively modest (a few tens to a few hundred watts), heat fluxes can be significant (through 50 W/cm2 in current electronic chips and up to 2000 W/cm2 in semiconductor lasers). Diamond heat sinks enable heat transfer rates well above what is possible with standard thermal management devices. We have fabricated heat sinks using diamond, which has the highest temperature thermal conductivity of any known material. Polycrystalline diamonds manufactured by chemical vapor deposition (CVD) are machined by laser and combined with metallic or ceramic tiles. Cooling by fluid flow through micro-channels enhances heat removal. These unique attributes make diamond based heat sinks prime contenders for the next generation of high heat load sinks. Such devices could be utilized for efficient cooling in a variety of applications requiring high heat transfer capability, including semiconductor lasers, microprocessors, multi-chip modules in computers, laser-diode arrays, radar systems, and high-flux optics, among other applications. This paper will review test designs, heat flux measuring system, and measured heat removal values.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Experimental Investigation of Area Ratio on Microjet Array Heat Transfer

2009 ◽  
Author(s):  
Gregory J. Michna ◽  
Eric A. Browne ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Area Ratio ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
High Heat Transfer

Electronics cooling is becoming increasingly difficult due to increasing power consumption and decreasing size of processor chips. Heat fluxes in processors and power electronics are quickly approaching levels that cannot be easily addressed by forced air convection over finned heat sinks. Jet impingement cooling offers high heat transfer coefficients and has been used effectively in conventional-scale applications such as turbine blade cooling and the quenching of metals. However, literature in the area of microjet arrays is scarce and has not studied arrays of large area ratios. Hence, the objective of this study is to experimentally assess the heat transfer performance of arrays of microjets. The microjet arrays were fabricated using MEMS processes in a clean room environment. The heat transfer performance of several arrays using deionized water as the working fluid was investigated. Inline and staggered array arrangements were investigated, and the area ratio (total area of the jets divided by the surface area) was varied between 0.036 and 0.35. Reynolds numbers defined by the jet diameter were in the range of 50 to 3,500. Heat fluxes greater than 1,000 W/cm2 were obtained at fluid inlet-to-surface temperature differences of less than 30 °C. Heat transfer performance improved as the area ratio was increased.

Preliminary Results of Pressure Drop Modeling During Flow Boiling in Open Microchannels With Uniform and Tapered Manifolds (OMM)

2013 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Full Potential ◽  
Transfer Coefficients ◽  
Open Microchannel

Flow boiling with microchannel can dissipate high heat fluxes at low surface temperature difference. A number of issues, such as instabilities, low critical heat flux (CHF) and low heat transfer coefficients, have prevented it from reaching its full potential. A new design incorporating open microchannels with uniform and tapered manifold (OMM) was shown to mitigate these issues successfully. Distilled, degassed water at 80 mL/min is used as the working fluid. Plain and open microchannel surfaces are used as the test sections. Heat transfer and pressure drop performance for uniform and tapered manifold with both the surfaces are discussed. A low pressure drop of 7.5 kPa is obtained with tapered manifold and microchannel chip at a heat flux of 263 W/cm2 without reaching CHF. The pressure drop data is further compared with the homogenous model and the initial results are presented.

Forced Convection Boiling in Microchannels for Improved Heat Transfer

2006 ◽  
Author(s):  
Thomas B. Baummer ◽  
Ebrahim Al-Hajri ◽  
Michael M. Ohadi ◽  
Serguei V. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Surface Areas ◽  
Feed Pressure ◽  
Wide Range

This paper presents experimental results from research investigating the heat transfer capabilities of microchannel surfaces using a novel force-fed boiling and evaporation technique. The evaporative surfaces being investigated consist of a series of parallel, high-aspect ratio, open topped microchannels. The different sample surfaces vary in channel density, channel aspect ratio, and channel width and have heat transfer surface areas up to ten times their nominal surface areas. Liquid enters the channels of the evaporative surface from above through a developed system of feed channels. This method organizes a liquid-vapor circulation at the boiling surface that results in dissipation of very high heat fluxes in the boiling/thin film evaporation mode. By using the force-fed boiling technique, nominal area heat transfer rates of 100,000 W/m2-K have been achieved with HFE-7100 as the working fluid [1]. In force-fed boiling, the many very short microchannels are working in parallel; therefore the feed pressure and pumping power are very low. This technique may prove valuable to a wide range of heat transfer applications, particularly for heat removal at high heat flux surfaces.

scholarly journals Experimental validation of pressure drop models during flow boiling of R134a – effect of flow acceleration and entrainment

2018 ◽  
Vol 240 ◽  
pp. 03010
Author(s):  
Tomasz Muszynski ◽  
Rafal Andrzejczyk ◽  
Carlos Dorao
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
High Heat ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Flow Acceleration ◽  
High Heat Transfer

A crucial step to assure proficient work of power and process apparatus is their proper design. A wide array of those devices operates within boiling or condensation of the working fluid to benefit from high heat transfer rates. Two-phase flows are associated with high heat transfer coefficients because of the latent heat of evaporation and high turbulence level between the liquid and the solid surface. Predicting heat transfer coefficient and pressure drop is a challenging task, and has been pursued by researchers for decades. In the case of diabatic flows, the total pressure drop is due to the change in kinetic and potential energy. The article presents detailed boiling pressure drops data for R134a at a saturation temperature of 19.4°C. Study cases have been set for a mass flux varying from 300 to 500 kg/m2s. Presented data along with the data reduction procedure was used to obtain the momentum pressure drop values during flow boiling. The study focuses on experimental values of momentum pressure drop component and its prediction based on various void fraction models and entrainment effects.

scholarly journals Entropy Generation and Heat Transfer Performance in Microchannel Cooling

Entropy ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 191 ◽  
Author(s):  
Jundika Kurnia ◽  
Desmond Lim ◽  
Lianjun Chen ◽  
Lishuai Jiang ◽  
Agus Sasmito
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Heat Transfer Performance ◽  
Second Law Of Thermodynamics ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Performance ◽  
Cooling Channel ◽  
High Heat Transfer ◽  
Microchannel Cooling

Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250–1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.

Enhancement of heat transfer in a square channel by roughened surfaces in rib-elements and turbulent flow manipulation

2017 ◽  
Vol 27 (7) ◽  
pp. 1571-1595 ◽  
Author(s):  
Jian Liu ◽  
Gongnan Xie ◽  
Bengt Ake Sunden ◽  
Lei Wang ◽  
Martin Andersson
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Research Work ◽  
Flow Characteristics ◽  
High Heat ◽  
The Novel ◽  
Content Type ◽  
Flat Surfaces ◽  
Square Channel ◽  
High Heat Transfer

Purpose The purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties. Design/methodology/approach The novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work. Findings Based on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling. Originality/value The novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

Numerical Investigation on the Effect of Transversal Septa on Forced Convection in Circular Tubes

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Circular Tubes ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry, solar energy heater, etc. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. In this paper a numerical investigation is carried out on forced convection in circular tubes with septa heated by constant fluxes and characterized by different shapes. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, when the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa may significantly augment pressure drops. The fluid is air and properties are function of temperature. Septa of the same material of the tube are introduced and several shapes and arrangements are analyzed as well as different Reynolds numbers, baffle spacings and heat fluxes applied on the external surface. The investigation is accomplished by means of the commercial code Fluent. A k-e turbulence model is used with enhanced wall treatment options. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients, friction factors and pressure drops for different values of heat flux, Reynolds numbers and baffle spacings. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

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