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Thermal Convexity of Tubular Heat Exchangers in Steady State
Get PDFThis paper deals with the thermal convexity of heat exchangers in steady state: (Th,c(x)=γh,c(x)Tc,in+(1- γh,c(x))Th,in with 0 ≤ γh,c(x) ≤ 1). This method assesses the spatial distribution of the thermal convexity factors of both fluids along a tubular heat exchanger in counter-current flow and co-current flow arrangement. Analytical expressions of the thermal convexity coefficients are in exponential form. According to the flow configuration two linear functions are proposed for the hot and the cold fluid. The slope of these two functions corresponds to the exponential factor. The estimations of the exponential factor thanks to the steady state convexity coefficient profile provide results that are in good agreement with those obtained from correlations
Time Series in the Study of Seismic Regime of Vrancea (Romania) Seismic Zone
Get PDFIn the series of monthly number of earthquakes is present long-term systematic component. The assumption about stationary of the average value and the variance is rejected. Statistically significant autocorrelation coefficients mean that the time series is not random, and there is some connection between successive levels. In order to predict a series of exponential smoothing method was used. Best model is simple seasonal for the logarithm of the levels, and Winters additive for the square root level of the original series. The research of time series confirms that the ARIMA (0, 1, 2) x (1, 0, 1) s model can be used to the analysis and prediction of uniform non-stationary time series with a nonlinear trend, such as a polynomial of low degree. Prediction for 2012 is computed using simple Simple seasonal, Winters and ARIMA models
Investigating the Relationship between Porosity and Compressive Strength for Porous Concrete as a Sustainable Pavement
Get PDFIn this study, the relationship between porosity and compressive strength for porous concrete (PC) was investigated. The effect of mixture design parameters particularly, water-to-cement ratio (W/C) and size of aggregate on the porosity and compressive strength of PC was evaluated. To investigate the role of W/C and aggregate size on this testing procedure, the experiments were performed on specimens of two aggregates size and four range of W/C. The PC mixtures were made with W/C in the range of 0.28-0.34, 350kg/m3 cement content and 19.5mm and 9.5 maximum size of aggregate. PC mixes were made from each aggregate and were tested. The results showed that the W/C and aggregate size are key parameters which significantly affect the porosity of PC. Investigation of compressive strength and porosity for the various mix designs showed a clear dependence on these parameters. The measured values fall within the expected range obtained from a review of the literature. Compressive strength of coarse porous concrete (CPC) is smaller than compressive strength of fine porous concrete (FPC) and the porosity of CPC are bigger than porosity of FPC. In general, increased W/C yields a smaller porosity and higher compressive strength. This approach can reduce the number of trial batches needs for target performance of PC samples
Matrix Transforms of Summability Domains of Normal Series-to-Series Matrices
Get PDFIn the present paper matrix transforms of summability domains CSA of normal series-to-series matrices A are investigated. Let M be a matrix and B a triangular series-to-series matrix. Necessary and sufficient conditions for M to be a transform from CSA into CSB are found. For application the special case, when A is a series-to-series Riesz matrix, are studied
Determination of Drying Characteristics of Some Vegetables
Get PDFDrying is, removing the water effect of distorting structure, from the food products with the effect of heat. Direct sun drying, greenhouse drying and supported by solar panel greenhouse combinations were done for drying vegetables. Eggplant, cauliflower, leeks, broccoli were dried. Dry matter and water activity values were measured for each of products on the systems of directly in the sun drying, drying in the greenhouse, the panel + greenhouse. Improvements of the conditions in the greenhouse and then with some modifications should be established such as optimization of the air velocity is thought to be achieved by faster drying
Determination of Pressure-Temperature Conditions of Retrograde Symplectic Assemblages in Granulites and Amphibolites
Get PDFSymplectites form during post-orogenic fast uplift processes in orogenic belts, and retrograde Symplectic assemblages mainly consist of plagioclase + quartz ± orthopyroxene ± clinopyroxene in mafic granulites or plagioclase + hornblende + quartz ± biotite in amphibolites, usually rimming relict garnet porphyroblasts. Such Symplectic assemblages resulted from retrograde reactions between garnet and other peak-metamorphic minerals by nearly isothermal decompression (ITD), so the Symplectic mineral assemblages could not be at equilibrium with the relict garnet rims and thus the so-called “local equilibrium†between garnet rims and the Symplectic assemblages does not exist. Thus, the P-T conditions of the Symplectic assemblages are best determined using only the Symplectic mineral compositions. This is best accomplished using garnet-free thermobarometers, i.e., two-pyroxene or hornblendeplagioclase thermometer in combination with the hornblende-plagioclase-quartz or applying the clinopyroxeneplagioclase-quartz geobarometer to minerals within the symplectites. Taking two mafic granulite samples and two amphibolite samples as examples, reasonable ITD P-T paths from the metamorphic peaks to retrogression stages have been derived, but P-T paths obtained using the relict garnet rims and the Symplectic minerals gave anomalous results. These examples demonstrate that the P-T conditions of the retrograde Symplectic assemblages cannot be estimated using chemical compositions of the decomposed, relict garnet rims in this case
Intra-Urban Air Temperature Distribution, Urban Heat Island and Thermal Comfort Implications in A Subtropical City
Get PDFUnlike most of the Brazilian hot-humid cities, subtropical Curitiba experiences thermal discomfort due to cold during most of the year, with the coldest air temperature occurring in winter. Due to rapid urbanization, the Metropolitan Area has been faced with critical environmental problems. Urban microclimate patterns exhibit considerable variability; particular areas of the city alternate between cool islands and heat islands, resulting in different outdoor thermal comfort levels. The objective of this work is twofold: 1) to characterize intra-urban air temperature differences and their impact on outdoor thermal comfort in Curitiba; 2) to assess the yearlong Urban Heat Island (UHI) effect and its effect on indoor thermal comfort levels. For that, a series of independent measurements and field monitoring campaigns, both outdoors and indoors, were analyzed. Results point to a great variability in intra-urban temperature differences and derived outdoor comfort levels. With regard to predicted UHI effects in low-cost dwellings, indoor comfort due to heat was found to prevail over the year; the 'net effect' between heat stress in summer and cold stress in winter point towards a prevalence of heat stress indoors
Direct Numerical Simulation Modeling of Multidisciplinary Transport during Li-Ion Battery Charge/Discharge Processes
Get PDFWe develop a direct numerical simulation (DNS) model of multidisciplinary transport coupled with electrochemical reactions during Li-ion battery charge/discharge processes based on the finite volume (FV) numerical technique. Different from macroscopic models, the DNS model is based on microstructure of composite electrodes and solves component-wise transport equations. During DNS, the input physical properties are intrinsic material properties, not effective physical properties for macroscopic models. Since the interface of solid and electrolyte phase is evidently differentiated in DNS, the occurrence of electrochemical reactions is prescribed exactly on the interface of solid and electrolyte phase. Therefore, the DNS model has the potential to unravel the underlying mesoscopic pore-scale mechanisms of multi-disciplinary transport coupled with electrochemical reactions and thus can provide insightful information of the involved processes, as well as enables the design and optimization of electrodes, including microstructures inside electrodes. One test case, in which the electrode microstructure is reconstructed with a purely random reconstruction method, is considered. Simulation results corroborate the validity of the DNS model
Some Physical, Chemical and Electrical Properties of the Polyphosphate LiMII 2(PO3)5 (M=Cu, Zn, Cd, Ba, Pb) Glasses
Get PDFThe polyphosphate glasses with the general formulae LiMII 2(PO3)5 (M=Cu, Zn, Cd, Ba, Pb) were prepared by using the melt-quench technique. They are characterized by X-ray diffraction (XRD), density measurements and differential thermal analysis (DTA). The results show that the glass transition temperature and molar volume increase nonlinearly with increasing of the bivalent cation atomic weight in the sequence Cu<Zn<Cd<Pb<Ba. Measurements of the ionic conductivity were made in the frequency range of 20 - 106 Hz and the temperature range 25 - 300°C. It is found that the Conductivity of the LiZn2(PO3)5 and LiCu2(PO3)5 glasses are much lower than those of the other samples. The differences in conduction properties are discussed based on the structural and atomic properties of the glass components
Introduction of SOFC Technology into Cuban Energy Sector: Technical and Sustainability Analysis
Get PDFThe feasibility of integrating a solid oxide fuel cell (SOFC) technology into the Cuban energy sector is analyzed. In this context, two scenarios for power generation are assessed: the first (existing) combines a bagasse cogeneration unit and diesel combustion engines and for the second (future), diesel engines are replaced by a SOFC feed with ethanol and integrated into the sugar factory. The environmental impact (greenhouse gases), exergy efficiency, and a renewability parameter are considered as indicators for the assessment of the studied scenarios through a multifunctional unit (9.86t/h sugar, 2.195t/h of hydrated ethanol (96% w/w) and 847kWh of electricity) approach. The SOFC scenario shows significant advantages from an environmental point of view, obtaining a reduction of 55% greenhouse emissions and 60% fossil fuel consumption. At the same time, the overall process efficiency (38%) and renewability index (0.93) are higher than for the existing scenario. Furthermore, health impacts and their corresponding external cost related to airborne emissions (primary and secondary pollutant) are estimated applying the Uniform World Model (UWM). In this sense, the results show that the use of a SOFC technology involves a reduction of health impacts in 25.76 YOLL yr-1 (12%) and external costs of 52175 US$ yr-1 (12%). The potentiality of SOFC technology implementation into Cuban energy sector is assessed using a Strengths, Weaknesses, Opportunities and Threats (SWOT) approach. Nowadays, the main threat of implementation of this technology is associated to competitive energy market