Influence of rib height on the local heat transfer distribution and pressure drop in a square channel with 90° continuous and 60° V-broken ribs

Internal channel cooling is employed in advanced gas turbines blade to allow high inlet temperatures so as to achieve high thrust/weight ratios and low specific fuel consumption. The objective of the present work is to study the effect of rib height to the hydraulic diameter ratio on the local heat transfer distributions in a double wall ribbed square channel with 90° continuous attached and 60° V-broken ribs. The effect of detachment of the rib in case of broken ribs on the heat transfer characteristics is also presented. Reynolds number based on duct hydraulic diameter is ranging from 10,000 to 30,000. A thin stainless steel foil of 0.05 mm thickness is used as heater and infrared thermography technique is used to obtain the local temperature distribution on the surface. The images are captured in the periodically fully developed region of the channel. It is observed that the heat transfer augmentations in the channel with 90° continuous attached ribs increase with increase in the rib height to hydraulic diameter ratio (e/D) but only at the cost of the pressure drop across the test section. The enhancements caused by 60° V-broken ribs are higher than those of 90° continuous attached ribs and also result in lower pressure drops. But, with an increase in the rib height, the enhancements are found to decrease in channel with broken ribs. The effect of detachment incase of broken ribs is not distinctly observed. The heat transfer characteristics degraded with increase in the rib height in both attached and detached broken ribbed cases.     

Thermal and hydraulic characteristics of turbulent nanofluids flow in a rib–groove channel

Thermal and hydraulic characteristics of turbulent nanofluids flow in a rib–groove channel are numerically investigated. The continuity, momentum and energy equations were solved by means of a finite volume method (FVM). The top and bottom walls of the channel are heated at a constant temperature. Nine different rib–groove shapes are considered in this study, which are three different rib shapes with three different groove shapes including rectangular, triangular and trapezoidal and they are interchanged with each other. Four different types of nanoparticles Al₂O₃, CuO, SiO₂, and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 25 nm to 80 nm, are dispersed in different base fluids (water, glycerin, engine oil) are used. In this study, several parameters such as different Reynolds numbers in the range of 5000 < Re < 20000, and different rib–groove aspect ratios in the range of 0.5 ≤ AR ≤ 4 are also examined to identify their effects on the heat transfer and fluid flow characteristics. The results indicate that the rectangular rib–triangular groove has the highest Nusselt number among other rib–groove shapes. The SiO₂ nanofluid has the highest Nusselt number compared with other nanofluid types. The Nusselt number increased as the nanoparticle volume fraction, Reynolds number and aspect ratio increased; however, it decreased as the nanoparticle diameter increased. It is found that the glycerin–SiO₂ shows the best heat transfer enhancement compared with other tested base fluids.     

On the current distribution at the channel – rib scale in polymer-electrolyte fuel cells

Experimental results based on in-situ measurements at the interface between the catalyst layer and the gas diffusion layer (GDL) on the cathode side at the channel – rib scale show an interesting variation of the current density distribution as the mean current density is increased. It is found that the local current density below the rib median axis corresponds to a maximum at low to intermediate mean current densities and to a minimum when the mean current density is sufficiently high. Also, the higher is the current density, the more marked the minimum. From numerical simulations, it is shown that the current density distribution inversion phenomenon is strongly correlated to the liquid water zone development within the GDL.     

Numerical Study on the Suppression of Shock Induced Separation on the Non-Adiabatic Wall

IntroductionThe supersonic flow inevitably encounters the shockwaves that are in contact with the solid walls on which theturbulent boundary layer is developed. This sitUationproduces locally a complex phenomenon known as shockwave/turbulent boundary layer interaction. Basic stlldiesof the complex combinations of heat transfer andcompressibility are required to understand their effects onthe turbulent boundary layer characteristics. If the shockwave is strong enough, then the boundary layer c…     

Effects of Heterogeneous Condensation on the Transonic Flow Fields on a Bump Model

In the present study, effect of the heterogeneous condensation on the characteristics of shock wave generated on the bump model in the transonic flow field was investigated numerically. As a result, it was found that, for the flow field with steady adiabatic shock wave on the bump model, the condensation with heterogeneous nucleation has a strong effect on the whole flow field, and it reduced the strength of the shock. Furthermore, the total pressure loss was dependent on the concentration of the solid particles per unit volume.     

Theoretical Analysis on the Air-Condition Cabin Technique for Satellite Temperature Adjustment on the Ground

The aim of this paper is to study the heat transfer mechanism of the air-condition cabin technique for satellite temperature adjustment on the ground before the launch of those satellites with pressurized structure. By the study, the temperature of the satellite can be set appropriately, and this is very important to the initial satellite temperature after the satellite operates in orbit. In the paper, the simplified physical model is provided and the mathematical equations are obtained, thereafter, the experimental data are compared with the theoretical analysis. The quantitative conclusions from the theoretical analysis can be used to direct the design or the experiment of the temperature adjustment. Finally, we can conclude that, the temperature variation rule of the satellite is exponential, and the temperature adjustment process can be predicted by the exponential formula, which is obtained from the theoretical analysis.     

Hazard Analysis on One-Room Building Fires

INTRODUCTIONInsomepublicbuildings,suchastheaters,cinemas,inwhichtheamoulltofthecombustibleandthepersonnUJnberarebothlarge,butthewidthoftheexitisoftenlimited,thefirehazardisoftenveryhigh.Insuchbuildingfires,firesmokeisthemajorcauseforcasualties[1'2].Themainreasonisthatsmokeisacomplexmixtureconsistedofmanytoxicgasesandothercomponellts,spreadingfasterthanflame,andreducingvisibility.Inthefollowingsections,amodelforpredictingthedeathnUmberinaone--roombuildingfireisproposed,numericalsibilation…     

Study on Thermo-Conductive Plastic Finned TubeRadiators

INTRODUCTIONAir-coolingtechnologyinwater-savingtypeelec-tricpowerindustryfeaturedbyheattransferunderthec0nditi0noflowtemperatureandsmalltempera-turedifferencehasbeengreatlydeveloped[l,2'3].Withthedevelopmellt0ftheelectricpowerindustryinagreatnumberofwatershortageregions,powersta-tionsusingaircoolingradiat0rshavebecomeanim-portantsubjectinvestigatedathomeandabroad.Atpresent,alargenumberofcoolingelementsinusearealuminumtubeswithaluminumfins,steeltubeswithsteelfinsandflatsteeltubeswithaluminu…     

Effect of Pressure on Minimum Fluidization Velocity

Minimum fluidization velocity of quartz sand and glass bead under different pressures of 0.5,1.0,1.5 and 2.0MPa were investigated.The minimum fluidization velocity decreases with the increasing of pressure.The influ-ence of pressure to the minimum fluidization velocities is stronger for larger particles than for smaller ones.Based on the test results and Ergun equation,an experience equation of minimum fluidization velocity is pro-posed and the calculation results are comparable to other researchers' results.     

Study on an Undershot Cross-Flow Water Turbine

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water tur- bines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after at- taching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effec- tive head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine ef- ficiency. Also, the runner with no bottom plate differed from rtmners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full ro- tational speed range compared with that found in runners that had a bottom plate.     

Study on γ-butyrolactone for LiBOB-based electrolytes

To solve the problems of LiBOB-based electrolytes, small salt solubility and low conductivity, a sort of cyclic carboxylate, γ-butyrolactone (GBL) was applied in the lithium-ion battery electrolyte as the main solvent of lithium bis(oxalate)borate (LiBOB). LiBOB–GBL electrolyte exhibits good electrochemical stability, which is suitable to be the candidate of the lithium-ion battery electrolyte. Using GBL as the solvent of the LiBOB salt can increase the solubility and conductivity dramatically. At room temperature, LiFePO₄/LiBOB–GBL/Li half cell shows satisfying cycle performance with no capacity fading in the first 50 cycles and promising capacity performance with stable discharge capacity of about 125 mAh g⁻¹. EA is mixed with GBL to get lower viscosity solvent. In LiFePO₄/Li half cell with 0.5 C discharge rate, 0.2 M LiBOB–GBL/EA (1:1, wt) electrolyte exhibits best at room temperature and 0.7 M LiBOB–GBL/EA (1:1, wt) electrolyte exhibits best at elevated temperature.     

Study on the Effects of Flow in the Volute Casing on the Performance of a Sirocco Fan

The flow at the exit from the runner blade of a centrifugal fan with forward curved blades (a sirocco fan) sometimes separates and becomes unstable. We have conducted many researches on the impeller shape of a sirocco fan, proper inlet and exit blade angles were considered to obtain optimum performance. In this paper, the casing shape were decided by changing the circumferential angle, magnifying angle and the width, 21 sorts of casings were used. Performance tests, inner flow velocity and pressure distributions were measured as well. Computational fluid dynamic calculations were also made and compared with the experimental results. Finally, the most suitable casing shape for best performance is considered.     

Study on Prompt NO_X Emission in Boilers

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Experimental Study on Hydrocarbon Fuel Thermal Stability

The.thermal stability characteristics of kerosine-type fuels are examined using a heated-tube apparatus whichallows independent control of fuel pressure,fuel temperature,tube-wall temperature and fuel flow rate.Thismethod is identified simply as a“constant wall temperature method”.It is different from a previous widely usedmethod,which is identified as a“constant heat flux method”.It is a single-pass system.Rate of deposition onthe tube walls are measured by weighing the test tube before and after each test.For a fuel temperature of 250℃,it is found that deposition rates increase continuously with increase in tube-wall temperature.This finding contradicts the results of previous studies which had led to the conclusion thatdeposition rates increase with increase in wall temperature up to a certain value(around 650 K)beyond whichany further increase in wall temperature causes the rate of deposition to decline.The present results show clearly that the constant wall temperature method is more suitable for assessing thethermal stability of gas turbine fuels.     

Influences of the Exhaust Flow on the Boundary Layer Flow on the Wafer Surface in Spin Coating System

Recently, development of high technology has been required for the formation of thin uniform film in manufacturing processes of semiconductor as the semiconductor become more sophisticated. Spin coating is usually used for spreading photoresist on a wafer surface. However, since rotating speed of the disk is very high in spin coating, the dropped resist scatters outward and reattaches to the film surface. So, the scattered resist is removed by the exhaust flow generated at the gap between the wafer edge and the catch cup. It is seriously concerned that the stripes called Ekman spiral vortices appears on the disk in the case of high rotating speed and the film thickness increases near the wafer edge in the case of low rotating speed, because it prevent the formation of uniform film. The purpose of this study is to make clear the generation mechanism of Ekman spiral vortices and the influence of exhaust flow on it Moreover the influence of the catch cup geometry on the wafer surface boundary layer flow is investigated.     

Analysis on influence factors of China's CO2 emissions based on Path–STIRPAT model

With the intensification of global warming and continued growth in energy consumption, China is facing increasing pressure to cut its CO₂ (carbon dioxide) emissions down. This paper discusses the driving forces influencing China's CO₂ emissions based on Path–STIRPAT model—a method combining Path analysis with STIRPAT (stochastic impacts by regression on population, affluence and technology) model. The analysis shows that GDP per capita (A), industrial structure (IS), population (P), urbanization level (R) and technology level (T) are the main factors influencing China's CO₂ emissions, which exert an influence interactively and collaboratively. The sequence of the size of factors' direct influence on China's CO₂ emission is A>T>P>R>IS, while that of factors' total influence is A>R>P>T>IS. One percent increase in A, IS, P, R and T leads to 0.44, 1.58, 1.31, 1.12 and −1.09 percentage change in CO₂ emission totally, where their direct contribution is 0.45, 0.07, 0.63, 0.08, 0.92, respectively. Improving T is the most important way for CO₂ reduction in China.     

Hazard Analysis on One—Room Building Fires

First, a calculation method for available safety egress time (shortly called ASET) and requirement safety egress time (shortly called RSET) in a one-room building fire is proposed and a model for predicting the death number caused by the fire is established in this paper. Then, numerical simulations are performed, and the following laws are discovered: (1) At the beginning of the fire, the smoke layer falls slowly; as the fire develops, it falls rapidly. (2) The hypotheses on the fire source, the combustion properties of the combustibles, and the width of the exit and the person number in the room are important factors which affect the death number in the fire.     

Pure Jatropha Oil for Power Generation on Floreana IslandlGalapagos： Four Years Experience on Engine Operation and Fuel Quality

In the small country of Ecuador, all environmental risks of the production and consumption of fossil fuels can be observed by damages through oil exploration in the amazonite rainforest and two tank ship accidents close by Galapagos Islands causing death of 10,000 marine iguanas and other species. Now Ecuador plans to replace all environmentally dangerous diesel generators from all four inhabited Galapagos Islands by a hybrid system using 100% renewable energy for electricity production. Since 2010 a hybrid system of two Jatropha oil generators with an electrical power of 69 kW （kWel） and a photovoltaic plant with an electrical peak power of 21 kW （kWpeak） is successfully providing electricity from renewable energy for inhabitants and tourists of Floreana Island. After more than 15.000 engine operation hours of each engine there is no engine defect. For fuel supply, the so-called ＂Living Fence＂ concept collecting Jatropha seeds by farmers and families from already existing 6,000 km hedges on Ecuadorian mainland was chosen to comply with highest biofuel sustainability standards. The Jatropha oil is produced in a decentralized so-called CompacTropha oil mill container following the ambitious German fuel quality standard DIN51605. Since 2010 Floreana project successfully demonstrates that it is possible to replace diesel gen sets by generators fueled with pure Jatropha oil from decentralized sustainable production.