High Heat Flux Burnout in Subcooled Flow Boiling

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Spring Inserts for the Intensification of the Heat Exchange Process during Boiling in Vertical Tubes——Optimization of Geometric Parameters

The paper presents new criteria for calculation of heat transfer coefficients and flow resistance during boiling inside vertical tubes with spring inserts, developed on the basis of own experimental research. Calculations of the geometric parameters of the spring insert were carried out using the Nelder-Mead optimization method for various optimization criteria (maximizing the increase ratios for heat transfer coefficient and flow resistance, minimizing entropy, own optimization criterion). The results of optimization calculations were verified by the optimization procedures available in Statistica.     

Critical Heat Flux in Flow Boiling—Review of the Current Understanding and Experimental Approaches

ABSTRACT

A comprehensive review of current literature on subcooled flow boiling with a focus on the mechanistic modeling of the departure from nucleate boiling is presented. This review covers parametric trends, other reviews on the topic, previous modeling approaches, applicable measurement techniques for two-phase flow, and an extensive literature review on mechanistic models for the prediction of critical heat flux (CHF). The models have been carefully deconstructed to give an overview about differences and similarities in the respective modeling approaches. Drawing on previously successful application of measurement techniques for two-phase flow, recommendations for future experimental investigation regarding specific parameters of the respective models are given for the refinement of the current modeling approaches of CHF phenomena.     

Advancements in the Field of Direct Steam Generation in Linear Solar Concentrators—A Review

Direct steam generation in parabolic trough or linear Fresnel collectors represents one interesting technological option for concentrating solar electricity production. Today's state of the art characterized by the first commercial plants in operation is a result of more than 20 years of intensive research on this topic. This article provides a review on the key results from research that includes physical effects like heat transfer and pressure drop in horizontal boiler tubes, plant layout considerations, and thermal storage options. An overview on test and demonstration facilities as well as on commercial plants is given, leading to an outlook on the next generation of direct steam generation systems.     

Analytical Solution of Melting in a Subcooled Semi-infinite Solid with Boundary Conditions of the Second Kind

The melting problem in a semi-infinite region with constant heat flux boundary condition is solved by a semi-expect method and an integral approximate method. Effect of subcooling on the transient solid-liquid interface location and surface temperature are also discussed in this paper.     

Influence of Lubricant on the Nucleate Boiling Heat Transfer Performance of Refrigerant—A Review

This review provides an overview of the lubricant on the heat transfer performance pertaining to nucleate boiling. It appears that the effect of individual parameter on the heat transfer coefficient may be different from study to study. This is associated with the complex nature of lubricant and some compound effects accompanying the heat transport process. Some important effects such as oil concentration, heat flux, geometric configuration, saturation temperature, thermodynamic and transport properties, miscibility, foaming, and additional surface active agent are reported and discussed. In general, the heat transfer coefficient is impaired provided the oil concentration is sufficient high (e.g., >7%), and this is applicable to smooth and structured tubes. But normally structured tubes tend to suffer more from lubricant, yet this is especially conspicuous when the size of the reentrant channel is small. On the other hand, foaming and partial miscibility seem to benefit the heat transfer coefficient.     

Emission analysis of the effect of carbon nanowires in biodiesel–ethanol blends

The present work is dedicated to study of diesel–biodiesel–ethanol blends in a diesel engine using addition of various concentrations of carbon nanowires. Algae oil from microalgae has the potential to become a sustainable fuel source as biodiesel. The Neochloris oleoabundans algal oil was extracted by mechanical extraction method. The transesterification reaction of algal oil with methanol and base catalyst was used for the production of biodiesel. Experimental investigation results were studied for various parameters, such as exhaust emission of carbon monoxide, hydrocarbon, oxides of nitrogen gases, smoke, and carbon dioxide.     

A Study of the Influence of Solid Particles on Boiling Hysteresis

Experiments have been performed to determine the effects on boiling hysteresis of locally fluidized particlescontained in a liquid that serves as coolant for electronic equipment.The results show that locally fluidizedparticles can diminish boiling hysteresis.     

Numerical Study of the Effect of Imaginary Circle Diameter and Initial Flow Field on the Aerodynamic Field in a Tangentially Fired Furnace

INTRoDUCTIoNInthetangeatiallyfiringsystempulverized-coal-and-airjetsareinjectedintothefurnacethIoughslotbtirnersinfourcornersofthefUInace.Theaxesofburnersaretangellttooneorsevera1imaginarycir-clesinproperordertoformastablerotationalfireballwithhightemperatureinoperation.Sotheimag-inarydiameterofiisanimportantgeometricstructureparameterindesigningatangentiallyfiredfurnace,whichistheemphasisofthisstudy.Atpresent,theimaginarycirclediameterrkiisusuallydesignedwithsmallvalueandtheconcentricfir…     

Boiling of HFE—7100 on a Straight Pin Fin

IntroductionSeveral books had summarized inveshgationsanalyzing fins with a consent heat tusfer coefficient(e.g., see Kem and Kraus[']). When boiling occurs on a fin,the heat transfer coefficient along the fin is definitely notconstant. Inveshgated by the Pioneering works of Haleyand Westwatefv and Lai and Hsu['l, fin boiling ProCesshas received extensive attention. ~sl41 and Liaw andYehul reviewed the related lit~. BOth the heattransfer rate from the fin base, as well as the feasibleoper…     

Selection of the Relevant Turbulence Model in a CFD Simulation of a Flow Disturbed by Hydraulic Elbow——Comparative Analysis of the Simulation with Measurements Results Obtained by the Ultrasonic Flowmeter

The article is an attempt to compile the results of CFD liquid flow simulation through pipeline section containing hydraulic elbow with the results of ultrasonic flow measurements. To carry out the measurements behind the flow disturbing element (hydraulic elbow), an ultrasonic flowmeter with applied head set in accordance with the Z-type system was used. For comparative purposes, a flow simulation for 3 different turbulence models (k-epsilon, SST and SSG) was performed. It was found that with a proper ultrasonic flowmeter heads configurations, it is possible to measure the flow rate disturbed by the hydraulic elbow at any distance from the source of the disturbance. It has to use appropriate correction factor that can be determined by knowing the flow velocity profile equation. Based on comparison of CFD simulation results with experimental data, the accuracy/ purposefulness of using individual turbulence models in the case of discussed hydraulic installation was evaluated.     

Nucleate Boiling in Large Arrays of Impinging Water Sprays

The nucleate boiling of subcooled water, under 100 cm² square arrays of impinging sprays, was experimentally investigated. Three types of commercially available full cone pressure nozzles, of distinct flow capacities, allowed for runs where the average impinging coolant mass flux spanned the 0.3–7.2 kg/m²-s range. Array geometry was varied adjusting nozzle-to-nozzle and nozzle-to-impingement surface distances. Experimental construction allowed for good drainage of spent coolant and unrestricted air entrainment to spray cones. The average heat flux through the heated, upward-facing, copper impingement surface was found to be equal to the sum of single-phase and nucleate boiling heat flux components. The phase-change component was experimentally observed to depend upon wall excess temperature only. The proposed heat transfer correlation reproduces original experimental data with a mean absolute error of 10.6%. Non-critical-heat-flux (non-CHF) cooling capacity and efficiencies of up to, respectively, 2000 kJ/kg and 83% were observed.     

Flow Pattern and Heat Transfer Behavior of Boiling Two—Phase flow in Inclined Pipes

Movable Electrical Conducting Probe (MECP), a kind of simple and reliable measuring transducer, used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper. When the test pipe is set at different inclination angles, several kinds of flow patterns, such as bubble, slug, churn, intermittent, and annular flows, may be observed in accordance with the locations of MECP. By means of flow pattern analysis, flow field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented as expected in some flow pattern zones.The results of the investigation, measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow, as well as for turbine vane liquid-cooling design.     

On the Controlling Factor of Catalyst Temperature in C3H8—Air Mixture

Catalytic combustion of propane-air mixture was investigated.Platinum catalysts over a flat stainless steel with γ-alumina washcoat were employed.The employed burner has three catalysts set parallel to the mixture flow,spaced at an interval of 5,10 and 15 mm.Both experiment and numerical simulation were made at inlet temperature of 553 K,inlet velocity of 3 to 7 m/s and equivalence ratio of 0.3 to 0.5.In the numerical simulation,two-dimensional,steady state model was developed to calculate the temperature and species concentration in gas-phase.In this model.chemical reaction on the catalyst surface and that in the gas phase were assumed to occur in three-steps.The numerical results show good agreement with experimental results.It was found that the properties of the catalyst strongly affect the catalyst surface temperature.Especially,the thermal conductivity of catalyst has a great effect,while the emissivity of catalyst has less effect.     

Nucleate Boiling of n-Pentane in a Horizontal Confined Space

An experimental study was carried out on n-pentane nucleate boiling at atmospheric pressure and saturation temperature for different gap sizes. The boiling was investigated in a confined space delimited by two horizontal discs, a heated surface and an adiabatic surface, for distances varying between 0.1 mm and 13 mm. Tests were carried out on heated surfaces of 12 mm and 20 mm diameter. The effects of the gap size on the partial boiling curve and the diameter of the heated surface were studied. A dimensionless analysis was carried out and a correlation to describe the phenomenon of confined nucleate boiling is presented.     

Critical Heat Flux of Boiling Heat Transfer in a Moderate Narrow Space

INTanDUCTI0NBoilingheattransferandcriticalheatflux(CHF)inaconfinednarrowspacehavebeenstudiedexperi-melltallybyanumberofinvestigatorsinthepastfewdecades.However,thereisnoanypopularlyacceptedmodelintheheattransferinnarrowspaceboiling,althoughsomepopularknowledgeabouttheboilingheattransferinthenarrowspacehavebeenacceptedbymanyresearchers.Theknowledgecanbecon-cludedasthatthenucleateboilingheattransferisenhancedatlowheatfluxregionanddeterioratedathighheatfiuxregi0nespeciallyatCHF.Theenhanceme…     

Influence of Tube's Diameter on Boiling Heat TransferPerformance in Small Diameter Tubes

INTaoDUCTIONReclitlydry-troeeVaPoratorofairconditioningmaChineandreffigeratorhavebeendevefoPinginthedirectionofusingsmalldiamtertube.TheHITACHICo.conductedaserlesofeVaPoratfonhe8ttransferexperimeats,usingthethinwallcoppertubesofinnerdiamter9.52nun,8mm,7mmand5nunre-spectivelytheworkingmediawasHCFC22(qualityx=o.6)I'].TheresulthasshoWnthatheeVaPo-rationheattransfercoefficielltsweresghcatlyincreasedwiththedecreasingoftubediameter.EVaThorationheattransfercoefficientofa5.onuninnerdiare…     

Study on the Effect of the Side Secondary Air Velocity on the Aerodynamic Field in a Tangentially Fired Furnace with HBC—SSA Burner

INTroDUCTIONThe Horizontal Bias Combustioll Pulverized Coal(HBC) burner for tangential firing system has advantages of improving flame stabilization, slaggingresistance, pollution control and high combustionefficiency[']. However, in the thin and tall furnace firedwith coal with strong slagging telldency) it is possiblethat slagging occurred on water-cooled wall, especiallywhen the cross-sectional and volumetric heat releaserate are very high in the burner domain.The HBC burner with Si…     

Analytical and Numerical Study on the Uniformity of Temperature Difference Field in Heat Exchangers

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Investigation of Boiling Heat Transfer of Binary Mixture from Vertical Tube Embedded in Porous Media

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