Experimental and Numerical Study of Twin Underexpanded Impinging Jets

In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visualizing density fields using schlieren method. Numerical calculations were also conducted by solving unsteady three dimensional compressible Navier-Stokes equations with Baldwin-Lomax turbulence model. The main parameters for the dual jets are the non-dimensional distance between the two nozzle centers HID covering 1.5, 2.0, the nozzle to plate separation LID 2.0, 3.0,4.0 and 5.0 and the pressure ratio defined by po/pb 1.0~6.0, where D is the diameter of each nozzle exit, p0 the stagnation pressure and pb the back pressure. It is found that the agreement between the experiments and the calculations is good. The fountain flow at the middle of the two jets is observed both in the experiments and the calculation. According to FFT analysis of the experiments for the twin jets, relatively low frequency (up to 5     

Configuration of Shock Waves in Two-Dimensional Overexpanded Jets

An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio pe/pb of the nozzle exit pressure pe to the back pressure pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio pe/pb, even if the pe/pb is under overexpanded conditions.     

Analytical Study on Impingement Heat Transfer with Single—Phase Free—Surface Circular Liquid Jets

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Calculation of Vertical Mixing in Plane Turbulent Buoyant Jets on the Basis of the Algebraic Model of Turbulence

An algebraic model of turbulence,involving buoyancy forces,is used for calculating velocity and temperaturefields in plane turbulent vertical jets in a non-homogeneous stagnant medium.A new approach to the solution ofthe governing system of partial differential equations (continuity,conservation of momentum,heat (buoyancy),turbulent kinetic energy,dissipation rate and mean quadratic temperature fluctuation) is suggested which isbased on the introduction of mathematical variables.Comparison is made between the results of the presentcalculations with experimental and numerical data of other authors.     

A Multi—Criteria Decision Making Procedured for the Analysis of an Energy System

In the course of improving and/or designing an energy system,either purely economic criteria,although theoverriding criteria,or purely energy-based criteria,although the emphasized criteria,can not separately handlereal-world situations in a satisfactory manner.The economic effectiveness and the energy efficiency mustbe considered simultaneously to demonstrate the conflicting and non-commensurable characteristics of thesemultiple criteria.An iterative and interactive approach to formulating and solving non-linear multi-criteria decision makingproblems for the analysis of an energy system is proposed.It allows the decision maker(DM)to learn fromthe available information and dynamically change his mind.Criterion functions can be treated as objectivefunctions,as constraints or as something in between by the DM.After a series of iterations and interactiveprocedures,a preferred solution can be made among the non-inferior sets considering thermodynamic criteriaand economic criteria simultaneously.A simple example for design of a heat exchanger is used to illustrate theprocedure.     

Application of Rainbow Schlieren Deflectometry for Axisymmetric Supersonic Jets （Comparison of Experiments with Numerical Analysis）

This paper analyzes the correctly-expanded supersonic jet from a convergent-divergent
axisymmetric nozzle by using numerical simulation of turbulent flow.And the calculated density
distributions in this flow are compared with the present experimental data using rainbow schlieren
deflectometry.The value of the density from the experimental data agrees well with the results
calculated by this simulation.Therefore,the present method of the measurement using rainbow
schlieren deflectometry is useful for the measurement of the density of the correctly-expanded
supersonic jet.     

Study of the Thermal Behavior of Multi Tube Tank in Heat Recovery from Chimney—Analysis and Optimization

This work discusses the utilization of multi tube tank heat exchanger for waste heat recovery. The thermal behavior of the system is studied in order to understand the contribution of the different heat transfer modes governing the system. As application, heating water in residential application from chimney heat recovery is considered. A prototype illustrating the suggested system is implemented and tested. Different waste heat scenarios by varying the quantity of burned firewood (heat input) are experimented. The temperature at different parts of the system and the gas flow rates of the exhaust pipes are measured. Measurements showed that the temperature of 95 L tank of water can be increased by 68°C within one hour. Obtained results show that the convection and radiation exchanges at the bottom surface of the tank have a considerable impact on the total heat transfer rate of the water (as high as 70%). Moreover, the proposed system allows saving 9.8 L of gasoline, 10.6 L of diesel or 15 kg of wood for 12 hours of chimney operation.     

Local Convective Heat Transfer from Small Heaters to Impinging Submerged Axisymmetric Jets of Seven Coolants with Prandtl Number Ranging from 0.7 to 348

INTRODUCTIoNJetimpingementhasbeenextensivelyemployedintechnicalprocessestoproducerelativelyhighheat/massfluxes.Incomparisonwiththeheat/masstransferratesprovidedbyconventionaltechniqueswithfluidfiowsparalleltotheheat/masstransfersur-face,aremarkableincreaseintransfercoefficientscanbeobtainedinthisfashion.Inmostcasesairisusedastheworkingmedium.Examplesofairjetapp1icationsincludecoolingofturbinebladesandelectroniccom-ponents,annealingofmetallicandplasticsheets,dry-ingoftextilesandpaper,andtem…     

Theoretical Analysis of Hydraulic Jump on Extremely Small Size Liquid Jet Impingement

INTR0DUCTI0NWhenliquidjetsverticallyimpingeonahorizontalplane,theliquidspreadsoverthesurfaceasathinlayerboundedbyahydraulicjumpbeyondwhichthedepthoftheliquidismuchgreater.Totheauthor'sknowledge,thehydraulicjumphasbeenprovedtooc-curwheneverthefilmspreadsfarenough.Itischarac-terizedbyasignificantreductioninfilmaverageveloc-ityandacorrespondinglysharpincreaseintheliquidfilmthickness.Asinallconvectiveheattransfersituations,theflowfieldofanimpingingliquidjetcontrolstheheattransfercharacteristic…     

One—Dimensional Analysis of Melting in an External Artery Heat Pipe

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Self-similar characteristics of underexpanded,cryogenic hydrogen and methane jets

Underexpanded, cryogenic hydrogen and methane jets were measured using laser Raman scattering diagnostic. The jets were released from 1 mm to 1.25 mm orifices for the stagnation pressure ranges of 2–6 bar and temperature ranges of 37–46 K (hydrogen) and 112–189 K (methane). Raman signals are inherently small, thus a denoising algorithm was developed to substantially reduce the noise hindering the statistical analysis of the data. The time-averaged concentration and temperature data were plotted to show a hyperbolic decay law along the jet centerline and a Gaussian distribution in the radial direction. The concentration fluctuations of the cryogenic jets are similar to those of warm jets, the centerline RMS mass fraction decays similarly to the mean mass fraction, and the highest radial concentration fluctuations appear in the shear layer. Thus, the self-similar characteristics of the cryogenic jets are comparable with room-temperature jets for the present test conditions.     

小喷嘴间距撞击流的径向射流速度分布

采用热线风速仪对小喷嘴间距撞击流产生的径向射流的速度分布进行了实验研究.研究结果表明,径向射流在各个r.2D的径向断面上的速度分布具有相似性,呈高斯分布.在撞击面上无因次径向射流速度随着无因次径向距离的增大先增大后减小,而与喷嘴直径(D)、喷嘴间距(L)和出口气速无关.无因次径向速度在达到最大值前,与无因次径向距离成正比,在达到最大值后,无因次径向速度与无因次径向距离的1.33次方成反比.在撞击面上径向射流速度的最大值与出口气速成正比,与无因次喷嘴间距的0.551次方成反比.当L/D1时,无因次最大径向速度的位置随无因次喷嘴间距的增加而增加,当L/D1时,无因次最大径向速度的位置保持不变.     

Development and demonstration plant operation of an opposed multi-burner coal-water slurry gasification technology

The features of the opposed multi-burner (OMB) gasification technology, the method and process of the research, and the operation results of a pilot plant and demonstration plants have been introduced. The operation results of the demonstration plants show that when Beisu coal was used as feedstock, the OMB CWS gasification process at Yankuang Cathy Coal Co. Ltd had a higher carbon conversion of 3%, a lower specific oxygen consumption of about 8%, and a lower specific carbon consumption of 2%–3% than that of Texaco CWS gasification at the Lunan Fertilizer Plant. When Shenfu coal was used as feedstock, the OMB CWS gasification process at Hua-lu Heng-sheng Chemical Co. Ltd had a higher carbon conversion of more than 3%, a lower specific oxygen consumption of about 2%, and a lower specific coal consumption of about 8% than that of the Texaco CWS gasification process at Shanghai Coking & Chemical Corporation. The OMB CWS gasification technology is proven by industrial experience to have a high product yield, low oxygen and coal consumption and robust and safe operation.     

Release and dispersion modeling of cryogenic under-expanded hydrogen jets

In the present work performed within the framework of the SUSANA EC-project, we address the release and dispersion modeling of hydrogen stored at cryogenic temperatures and high pressures. Due to the high storage pressures the resulting jets are under-expanded. Due to the low temperatures the choked conditions can be two-phase. For the release modeling the homogeneous equilibrium model (HEM) was used combined with NIST equation of state for hydrogen. For the dispersion modeling the 3d CFD methodology was used combined with a) a notional nozzle approach to bridge the expansion to atmospheric pressure region that exists near the nozzle, b) the ideal gas assumption for hydrogen and air and c) the standard (buoyancy included) k–ε turbulence model. Predicted release choked mass fluxes are compared against 37 experiments from literature. Predicted steady state hydrogen concentrations along the jet axis are compared against five dispersion experiments from literature as well as the Chen and Rodi correlation and the behavior of the proposed release and dispersion modeling approaches is assessed.     

300MW对冲燃烧锅炉NOx排放特性及经济性试验研究

针对某电厂一台300 MW前后墙对冲燃烧锅炉,通过上层停运磨通入一次风,改变磨煤机组合、机组负荷、炉膛氧量以及一次风温、一次风量等参数,研究了不同燃烧方式对NOx排放及锅炉经济性的影响,提出了锅炉高效低污染运行的合理方式。     

Numerical investigation of the flammable extent of semi-confined hydrogen and methane jets

The effect of surfaces on the extent of high pressure horizontal unignited jets of hydrogen and methane is studied using computer fluid dynamics simulations performed with FLACS Hydrogen. Results for constant flow rate through a 6.35 mm diameter pressure relief Device (PRD) orifice from 100 barg, 250 barg, 400 barg, 550 barg and 700 barg compressed gas systems are presented for both horizontal hydrogen and methane jets. To quantify the effect of a horizontal surface on the jet, the jet exit is positioned at various heights above the ground ranging from 0.1 m to 10 m. Free jet simulations are performed for comparison purposes. Also, for cross-validation purposes, a number of cases for 100 barg releases were simulated using proprietary models developed for hydrogen within commercial CFD software PHOENICS. It is found that the presence of a surface and its proximity to the jet centreline result in a pronounced increase in the extent of the flammable cloud compared to a free jet.     

Study of several impinging jets

IntroductionIn the aeronautics field, engine manufacturers arecontinually confronted with the cooling problemsassociated with walls being in contact with overheatinggases. In such situations, the film-cooling technique iscommonly used to protect the first stage of a gas tllrbinerotor or stator from the ever-increasing temperatUre ofthe combustion products. In some critical cases, a moreeffective cooling can be achieved by the presence of anarray of cold air jets impinging on the other side of …     

330MW对冲燃烧锅炉燃烧和污染物排放的数值模拟

分别对330MW对冲锅炉在额定负荷、55％额定负荷工况下的流场、温度场、煤粉颗粒场和NOx场进行了模拟研究,模拟结果与实际运行经验吻合较好。通过研究得出了一些有参考价值的数据,对大型对冲燃烧锅炉的设计优化和安全运行具有较为重要的参考价值。     

前后墙对冲燃烧锅炉降低飞灰含碳量的燃烧调整试验

分析了浙江浙能长兴发电有限公司3号锅炉飞灰含碳量升高的原因,指出磨煤机研磨能力下降、煤粉过粗、煤粉浓度分配不均匀以及局部缺氧燃烧等是主要原因;介绍了针对巴威DRB-XCL旋流燃烧器的特点,通过采取调整燃烧器调风盘、内、外二次风叶片角度以及提高炉膛氧量等措施,从而降低锅炉飞灰含碳量2%~3%,解决了3号炉飞灰含碳量高的问题,提高了机组运行的经济性。     

Analysis of jet flames and unignited jets from unintended releases of hydrogen

A combined experimental and modeling program is being carried out at Sandia National Laboratories to characterize and predict the behavior of unintended hydrogen releases. In the case where the hydrogen leak remains unignited, knowledge of the concentration field and flammability envelope is an issue of importance in determining consequence distances for the safe use of hydrogen. In the case where a high-pressure leak of hydrogen is ignited, a classic turbulent jet flame forms. Knowledge of the flame length and thermal radiation heat flux distribution is important to safety. Depending on the effective diameter of the leak and the tank source pressure, free jet flames can be extensive in length and pose significant radiation and impingement hazard, resulting in consequence distances that are unacceptably large. One possible mitigation strategy to potentially reduce the exposure to jet flames is to incorporate barriers around hydrogen storage equipment. The reasoning is that walls will reduce the extent of unacceptable consequences due to jet releases resulting from accidents involving high-pressure equipment. While reducing the jet extent, the walls may introduce other hazards if not configured properly. The goal of this work is to provide guidance on configuration and placement of these walls to minimize overall hazards using a quantitative risk assessment approach. The program includes detailed CFD calculations of jet flames and unignited jets to predict how hydrogen leaks and jet flames interact with barriers, complemented by an experimental validation program that considers the interaction of jet flames and unignited jets with barriers.