On the Numerical Modeling of Impinging Jets Heat Transfer—A Practical Approach

This article compares steady-state and transient simulations in predicting impinging jet heat transfer. The configurations tested are H/D = 2 and 6, Re = 10,000, 20,000, 23,000, and 30,000. The variables considered are: turbulence model (LES, k-?, k-ω, V2F), discretization schemes, mesh density and topology, inlet velocity profile, and turbulence. The V2F model performs best for the steady state simulations. The inlet velocity profile plays an important role. Mesh topology and distribution is also important. The turbulence created in the shear layer plays a stronger role than the inlet turbulence. The LES model reproduces the turbulent structures with a useful degree of accuracy.     

Subcooled Boiling in the Ultrasonic Field—On the Cause of Microbubble Emission Boiling

Subcooled quasi-pool boiling for water and for ethanol aqueous solutions of 10% by weight (10wt%) and 50wt% and ethanol in an ultrasonic field was experimentally performed for the upward flat heating surface of a copper block with 10 mm diameter under atmospheric conditions. Tested liquid subcooling was 15 K, 20 K, and 25 K for water and aqueous solutions of ethanol and 20 K, 30 K, and 40 K for 100wt% ethanol. At 20 K of liquid subcooling for water and ethanol aqueous solutions, no microbubble emission boiling (MEB) has been observed in quasi-pool boiling. Even if MEB occurs, the heat flux levels off and it turns easily to film boiling. In an ultrasonic field, MEB occurs remarkably. Then the heat flux increases to higher than the ordinary critical heat flux as observed in highly subcooled boiling. The experimental results show that the ultrasonic vibration introduces instability of the interface of liquid and vapor and accelerates MEB at 20 K of liquid subcooling for water and aqueous solutions of ethanol. At 15 K of liquid subcooling for water and aqueous solutions, no effect of ultrasonic vibration is observed. However, at 25K of liquid subcooling, the ultrasonic vibration extends MEB region to higher superheating of the heating surface for aqueous solutions of ethanol. The maximum heat flux in MEB decreases with increasing of ethanol concentration and becomes critical heat flux for 100wt% ethanol. No effect of ultrasonic vibration on boiling is observed for the 100wt% ethanol in these experiments.     

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

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.     

Revenue prospects of photovoltaic in Germany—Influence opportunities by variation of the plant orientation

The fixed feed-in tariff under the Renewable Energy Sources Act in Germany particularly encourages photovoltaic systems with the highest possible annual yield, regardless of their temporal generation profile. Consequently, a large part of the installed photovoltaic systems in Germany have a southern orientation. This paper examines how the optional German market premium scheme incentivizes the installation of photovoltaic systems with a more demand-oriented electricity production. For this purpose, the measure ‘energy yield elasticity (of market value)’ was developed and calculated by using historical market data. The results show that some of the plant orientations that are deviating from the southern reference could have led to an increase in the market value in the last few years. However, these would not have been high enough to more than compensate for the financial losses that were formed as a result of the annual energy yield declines. The merit order effect could change this situation in the future.     

On the importance of the long-term seasonal component in day-ahead electricity price forecasting: Part II — Probabilistic forecasting

A recent electricity price forecasting study has shown that the Seasonal Component AutoRegressive (SCAR) modeling framework, which consists of decomposing a series of spot prices into a trend-seasonal and a stochastic component, modeling them independently and then combining their forecasts, can yield more accurate point predictions than an approach in which the same autoregressive model is calibrated to the prices themselves. Here, we show that further accuracy gains can be achieved when the explanatory variables (load forecasts) are deseasonalized as well. More importantly, considering a novel extension of the SCAR concept to probabilistic forecasting and applying two methods of combining predictive distributions, we find that (i) SCAR-type models nearly always significantly outperform the autoregressive benchmark but are in turn outperformed by combined SCAR forecasts, (ii) predictive distributions computed using Quantile Regression Averaging (QRA) outperform those obtained from historical simulation and bootstrap methods, and (iii) averaging over predictive distributions generally yields better probabilistic forecasts of electricity spot prices than averaging over quantiles. Given that probabilistic forecasting is a concept closely related to risk management, our study has important implications for risk officers and portfolio managers in the power sector.     

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.     

The “anomalous heat effect” is a normal event in the cold fusion phenomenon – On the paper “excess heat evolution from nanocomposite samples under exposure to hydrogen isotope gases” by Kitamura et al. Published in the int. J. Hydrogen Energy 43, pp. 16,187–16,200 (2018) –

The anomalous heat effect reported in the paper, “Excess heat evolution from nanocomposite samples under exposure to hydrogen isotope gases” by Kitamura et al. published in the Int. J. Hydrogen Energy 43, pp. 16,187–16,200 (2018), is investigated in the science of the cold fusion phenomenon (CFP) established in these 30 years. It is concluded that the effect is a normal event in the CFP consistent with many events observed in materials with various components and compositions composed of host elements and hydrogen isotopes.     

Energy demand in the fifteen European Union countries by 2010 —: A forecasting model based on the decomposition approach

This paper develops a forecasting model based on the complete decomposition method. The forecasting model allows the trend effect, the rebound effect and dematerialization/materialization to be estimated. To demonstrate the model, a case analysis of the probable energy demand in the 15 European Union (EU) countries up to 2010 has been made. The results show that the aggregate energy demand in the 15 EU countries by the end of 2010 will have increased from 258 to 426 Mtoe compared to the 1997 level, and dematerialisation will have increased from 73 to 225 Mtoe.     

Final Shape of Precision Molded Optics: Part I—Computational Approach,Material Definitions and the Effect of Lens Shape

Coupled thermomechanical finite element models were developed in ABAQUS to simulate the precision glass lens molding process, including the stages of heating, soaking, pressing, cooling and release. The aim of the models was the prediction of the deviation of the final lens profile from that of the mold, which was accomplished to within one-half of a micron. The molding glass was modeled as viscoelastic in shear and volume using an n-term, prony series; temperature dependence of the material behavior was taken into account using the assumption of thermal rheological simplicity (TRS); structural relaxation as described by the Tool-Narayanaswamy-Moynihan (TNM)-model was used to account for temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain. In Part I of this two-part series, the computational approach and material definitions are presented. Furthermore, in preparation for the sensitivity analysis presented in Part II, this study includes both a bi-convex lens and a steep meniscus lens, which reveals a fundamental difference in how the deviation evolves for these different lens geometries. This study, therefore, motivates the inclusion of both lens types in the validations and sensitivity analysis of Part II. It is shown that the deviation of the steep meniscus lens is more sensitive to the mechanical behavior of the glass, due to the strain response of the newly formed lens that occurs when the pressing force is removed.     

Selected Papers From the Seventh HEFAT Conference—Heat Transfer,Fluid Mechanics,and Thermodynamics in Society

This editorial provides an overview of a special issue dedicated to the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, HEFAT2010, which took place July 19–21, 2010, in Antalya, Turkey. All papers for this conference were peer reviewed and almost 150 papers were accepted. Of these papers, eight were selected for this issue and were peer reviewed for a second time according to journal standards. The eight articles focus on recent developments of heat transfer and include the acidity and method of preparation of nanofluids on nucleate pool boiling, industrial boiler circulation, spray cooling of electronic components, freezing in a horizontal plate freezer with CO₂ as refrigerant in a cascade refrigeration system, thermal simulation of a pulsing heat pipe, condensation of R22 retrofits, vertically downward-blowing single-jet air curtains in cold rooms, and a gravity-assisted heat pipe air-to-air cooler. This issue of Heat Transfer Engineering is the seventh special journal issue dedicated to selected papers from the HEFAT conferences.     

Investigations of Interaction of the Main Flow with Root and Tip Leakage Flows in an Axial Turbine Stage by Means of a Source／Sink Approach for a 3D Navier—Stokes Solver

IntroductionFundamental stUdies of losses in tUrbomachinery in-dicate that, besides giving rise to losses of work, leakageflows contribute to the overall creation of entropy andkinetic encrgy losses. Some entropy is created in thelabyrinth seals and in passages between the fixed androtating pats of turbomachinery. CFD computations inlabyrinth seal geometries enable the evaluation of theentropy ereation PrOCesses there. CFD-based analysis canm1nindze the mass fiow rates of the tip leakage a…     

Contrastive study between the biomass energy utilization structure and the ecotype energy utilization structure in rural residences — A case in Hunan province,China

The purposes of this study are to look into the actuality of rural residential energy consumption in Hunan province, China, to improve rural residential energy utilization structures, and to protect the environment. An investigation on rural residential energy consumption was carried out in the villages of Xintian and Jiangwan in the spring and summer of 2005. Biomass energy is used in Xintian while biogas is popularized in Jiangwan. A questionnaire survey covered basic information of residences in the two villages, and energy consumption data of each family in the spring and summer were also recorded continuously. The characteristics of energy utilization structures of the two villages, the one with biomass energy utilization structure and the other with the ecotype energy utilization structure, are contrasted, and seasonal variance characteristics of energy consumption in spring and summer are analyzed. Sequentially, influence factors of rural residential energy consumption are further discussed qualitatively and quantificationally. Environmental benefit is assessed finally when biogas substitutes biomass energy. Conclusions are summarized as follows: In Xintian, a complicated energy structure is still dominant, where biomass energy accounts for a significant proportion and manifold energy resources exist simultaneously; the energy consumption is high; categories of energy resources used by households vary between spring and summer. The energy structure is definitely better in Jiangwan, where the ratios of commercial energy and ecotype energy used are both higher than those in Xintian and the ratio of biomass energy is smaller. Categories of used energy resources are also more constant in spring and summer. The total energy use amount of each season in Xintian is larger than that in Jiangwan respectively, while there is little difference in the efficiency energy use amount of each season between the two villages. Qualitative and quantitative analyses show that the accessibility of local energy resources, the domestic economical level, governmental energy policies, and consumption conceptions of farmers affect energy utilization structures definitely, while the efficiency of cookers, the number of family members, and annual income have effect on energy consumption amounts. Environmental analysis shows that the usage of biogas makes a great contribution in optimizing the energy consumption structure, reducing energy consumption, discharging less harmful gases and keeping the ecosystem in balance. The comparison between biomass energy and ecotype energy provides instructions for future development of rural residential energy consumption in China.     

Free convection in a vertical,porous annulus with constant heat flux on the inner wall—experimental results

Steady-state natural convection in a concentric, tall, vertical annulus filled with saturated, porous media is experimentally studied when the inner wall is heated by applying a constant heat flux and the outer wall is isothermally cooled. Temperature profiles and heat transfer rates are obtained for two sets of aspect and radius ratios, A = 14.4, k = 3.5 and A = 11.08, k = 14. The use of several solid-fluid combinations indicates a divergent behavior by Nusselt vs Rayleigh number curves, as also reported by previous investigators. An analysis of present and previous experimental data shows that the Nusselt number for a given Rayleigh number decreases as the ratio of solid and fluid thermal conductivities increases and vice versa.     

Gasoline,diesel and climate policy implications—Insights from the recent evolution of new car sales in Germany

With the aid of detailed automobile sales data this paper looks into changes in car attributes and CO₂ emissions in Germany in the years 1998−2008, both at aggregate level and within individual car segments. New car CO₂ emissions have not decreased at the expected levels because of negligible downsizing and increasing power of diesel cars. Interestingly, today there are relatively more models available with higher-than-average emission levels than in the late 1990s. We further constructed matched pairs of gasoline and diesel models in order to explore how their power and emissions ratio has evolved during the same decade. Results imply that German consumers may not have chosen to buy the diesel powered matched pair of a gasoline car they would have bought a few years earlier; instead they selected among the variety of diesel cars available in the market, and preferred a more powerful diesel car than what they might have bought otherwise. These findings reinforce the view that low-carbon transport policies must address the issue of changes in vehicle size and performance, which compromise the environmental effectiveness of regulations. In contrast to current EU regulations, CO₂-related standards should discourage increases in a vehicle's weight and power.     

Genetic diversity by AFLP analysis within Jatropha curcas L. populations in the State of São Paulo,Brazil

The genetic diversity of 5 populations of Jatropha curcas L. (Euphorbiaceae), a species cultivated in tropical countries and used in biodiesel production, was analyzed by amplified fragment length polymorphism (AFLP). Plants from distinct populations found in the State of São Paulo, Brazil, had their genetic diversity characterized by using three primer combinations. The number of polymorphic bands obtained reached 184 and the base pair length of bands ranged from 75 to 350, with average PIC values of 0.418. Accessions from the Aguas de Santa Barbara population presented the highest percentage of polymorphic loci (89.76%), followed by the populations of Catanduva (84.24%), Jales (80.98%), Jurucê (78.80%) and Taquaritinga (70.65%). Plants collected from the populations of Taquaritinga and Jales presented the smallest and highest genetic diversities, respectively, measured by using both Nei's genetic variability index (h = 0.2242 and 0.2973) and Shannon's index (I = 0.3359 and 0.4319). The results obtained indicated that 73.1% of genetic variability corresponds to intrapopulational variation and 26.8% to variation among populations. The clustering dendrogram using Jacquard showed four clusters. Three clusters with low genetic diversity grouped most of individuals collected in distinct regions (63.3% JU, 47.0% JA and 82.5% TA) and the fourth with the higher genetic diversity was composed with basically individuals collected in CA and AS, but it also had samples collected in JU, JA and TA, where it is possible to select individuals to be included in breeding programs.