Author: Mehmet ArikPublisher:
ISBN:
Category :
Languages : en
Pages : 462
Book Description
Enhancement of Pool Boiling Critical Heat Flux in Dielectric Liquids
Author: Mehmet ArikNanoscale Modification of Key Surface Parameters to Augment Pool Boiling Heat Transfer and Critical Heat Flux in Water and Dielectric Fluids
Author: Eric Christopher ForrestPublisher:
ISBN:
Category :
Languages : en
Pages : 130
Book Description
(Cont.) Results indicate that the low global warming potential fluorinated ketone may be a viable alternative in the cooling of electronic devices. Additionally, results demonstrate that enhancement of boiling heat transfer is possible for well-wetting dielectric fluids, with 40% enhancement in the critical heat flux using dilute suspensions of aluminum or silica nanoparticles in the fluorinated ketone.
Hydrodynamic Aspects of Boiling Heat Transfer
Author: N. ZuberEvaluation of External Surface Modification Techniques to Enhance Pool Boiling of Dielectric Fluids
Author: Farhan ModyPublisher:
ISBN:
Category : Dielectrics
Languages : en
Pages : 75
Book Description
"The miniaturization trend of transistors and increase in packing density of electronic devices has resulted in high heat flux generation, which has created a need for efficient heat removal systems. The present research is an experimental study of pool boiling using plain copper chip and microchannel chip with boiling surface of 34.5mm x 32mm. Three dielectric fluids, Perfluoro-2-methylpentane (PP1), perfluoro-methyl-cyclopentane (PP1C), and fluorocarbon (FC-87) were used in a closed loop pool boiling system to determine their performance at atmospheric pressure. The pool boiling results have been compared with literature for a boiling surface of 10 mm x 10 mm to study the effect of heater size. To improve the performance of the pool boiling system, we desire high critical heat flux and low surface temperatures. In the current study, we introduced two external structures fitted on the test surfaces for regulating the flow of vapor through specific structures and generating independent liquid-vapor pathways without any deposition and/or chemical surface modifications of the test surface. Firstly, an array of hollow conical structures (HCS) called volcano manifold are printed using additive manufacturing technique. A critical heat flux (CHF) of 28.1 W/cm2, 38.3 W/cm2 and 32.5 W/cm2 was achieved for volcano manifold with plain copper chip using PP1, PP1C and FC87 respectively giving 19%, 33% and 6.5% enhancement in CHF respectively as compared to a plain chip without volcano manifold. Secondly, dual taper manifold having taper angle of 15° is printed using a stereolithography (SLA) additive manufacturing technique. Plain chip with dual taper manifold gave the CHF of 25.6 W/cm2, 31.7 W/cm2 and 32.3 W/cm2 for PP1, PP1C and FC-87, respectively. These results indicate a deterioration in CHF caused by vapor constriction. In addition, the heater size effect was studied by comparing the pool boiling performance of a plain copper boiling surface of 34.5 mm x 32 mm (Large heater) with 10 mm x 10 mm (Small heater) from published literature for all three refrigerants. It was noted that 31%, 66% and 104% increment in maximum heat transfer coefficient was obtained for PP1, PP1C and FC-87 respectively with larger heater over smaller heater at CHF. The geometrical parameters of the enhancement structures were based on published results for water. The results show that the external surface modification techniques require further geometrical parameter optimization as the current designs based on water performance caused vapor constriction effects that caused performance deterioration for dielectric fluids."--Abstract.
Measurement and Prediction of the Pool Boiling Critical Heat Flux in Highly Wetting Liquids
Author: Abhay Ashok WatwePool Boiling Heat Transfer with Highly-wetting Dielectric Fluids
Author: Seung Mun YouNanofluids
Author: S. M. Sohel MurshedPublisher: Nova Science Publishers
ISBN: 9781633216778
Category : Nanofluids
Languages : en
Pages : 0
Book Description
As an emerging research field, nanofluids have sparked immense interest from researchers around the world and have been a subject of intensive research in recent years. Because of their fascinating thermophysical properties and heat transfer performances, as well as enormous potential applications, nanofluids are considered the next generation heat transfer fluids. This book covers a wide range of topics from preparation methodology, properties, and theories to applications of nanofluids. In addition to the state-of-the-art reviews and analysis on the key areas of nanofluids including thermophysical and heat transfer properties of carbon nanotube and magnetic nanofluids, viscosity of metal oxide nanofluids and pool boiling of nanofluids, this book presents extensive experimental and theoretical research efforts on thermal conductivity, viscosity, convective heat transfer, capillary wetting, and transport properties of nanofluids. Studies on the application of nanofluids in droplet-based microfluidic technology are presented. Another new area of nanofluid-based optical engineering is explored in this book. It also introduces a new class of nanofluids named-ionanofluids. Featuring contributions from some of the leading researchers in the field, this book is a unique reference source and an invaluable guide to scientists, researchers, engineers, industrial people, graduate and postgraduate students, as well as academicians across the science and engineering disciplines.
Pool Boiling from Enhanced Structures Under Confinement
Author: Camil-Daniel GhiuPublisher:
ISBN:
Category : Ebullition
Languages : en
Pages :
Book Description
A study of pool boiling of a dielectric liquid (PF 5060) from single-layered enhanced structures was conducted. The parameters investigated were the heat flux, the width of the microchannels and the microchannel pitch. The boiling performance of the enhanced structures increases with increase in channel width and decrease in channel pitch. Simple single line curve fits are provided as a practical way of predicting the data over the entire nucleate boiling regime. The influence of confinement on the thermal performance of the enhanced structures was also assessed. The main parameter investigated was the top space (0 mm 3{13 mm). High-speed visualization was used as a tool . For the total confinement (= 0 mm), the heat transfer performance of the enhanced structures was found to depend weakly on the channel width. For>0 mm, the enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. The maximum heat flux for a prescribed 85 °C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime. A semi-analytical predictive model applicable to pool boiling under confinement is developed. The model requires a limited number of empirical constants and is capable of predicting the experimental heat flux within 30%.
Advances in Heat Transfer
Author: Young I. ChoPublisher: Academic Press
ISBN: 0123815290
Category : Science
Languages : en
Pages : 459
Book Description
Advances in Heat Transfer fills the information gap between regularly scheduled journals and university-level textbooks by providing in-depth review articles over a broader scope than in journals or texts. The articles, which serve as a broad review for experts in the field, will also be of great interest to non-specialists who need to keep up-to-date with the results of the latest research. This serial is essential reading for all mechanical, chemical and industrial engineers working in the field of heat transfer, graduate schools or industry. Provides an overview of review articles on topics of current interest Bridges the gap between academic researchers and practitioners in industry A long-running and prestigious series
Enhanced Pool Boiling Heat Transfer by Flow Modulation and Contact Line Augmentation Over Cylindrical Tubes
Author: Indranil M. JoshiPublisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 71
Book Description
"The miniaturization trend in electronics has spurred the development of efficient thermal management solutions. Single phase techniques are reliable but are limited by large fluid temperature differences and pressure drop. Two phase cooling has very little pressure drop with large heat absorption capacity. Boiling stands out as one of the most effective methods of heat dissipation which utilizes phase change. However, the design of two-phase systems is limited by the critical heat flux condition where a vapor layer prevents the liquid from contacting the heater surface. The current research study is directed towards increasing the CHF and maintaining low wall superheats to design efficient heat removal systems. In this study, different surface modification techniques are studied with an aim to identify various mechanisms that affect the heat transfer. Different surface enhancements in the form of Circumferential rectangular microchannels(CRM) and fin are used over cylindrical surface. Cylindrical tube with outer diameter of 15 mm was used for testing with water as working fluid. Tubular surface with fin attached performed the best yielding the CHF of 115 W/cm2 at wall superheat of 18oC which translated to an enhancement of 76%. The best performance of 110 W/cm2 at 9 oC without reaching CHF was obtained amongst CRM. Different mechanisms were identified by analyzing the results from pool boiling experiments. Area enhancement and contact line substantially affected the heat transfer performance in CRM. Area enhancement increased performance by providing additional area for heat transfer. Contact line region has higher heat flux. Single bubble growing over multiple grooves has increased contact line density which increases heat transfer performance. Increment in CHF was obtained by employing any one of these surface enhancements. High speed imaging enabled to analyze the behavior of bubble after nucleation on the fin surface thus deciphering the flow modulation over the cylindrical surface. Presence of bubble diverter at the bottom surface ensured higher evaporative momentum force towards the cylindrical surface. This displaced nucleating bubble at the bottom away from the fin, enabling liquid to rewet the surface. This allowed the formation of separate liquid vapor pathways which resulted in increased performance."--Abstract.