Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 6 Articles
Brilliant Green has been used as a photosensitized in photogalvanic cell for solar energy conversion. EDTA was used as an electronic donor (reductant) and sodium lauryl sulphate (surfactant) was used as an anionic micelle for greater photoejection of electrons. The photopotential and photocurrent without surfactant was found to be 610 mV and 68 mV respectively whereas with surfactant their values were found to be 652 mV and 76 µA respectively. The effect of various parameters on the electrical output of the cell has been studied. The current voltage (i-V) characteristics of the cell has also been observed. Performance of the cell was determined in dark at its power point....
This paper presents analytical and experimental studies on optimization of the gas delivery and current collection\r\nsystem in a proton exchange membrane (PEM) fuel cell for the objective of reducing ohmic loss, thereby achieving\r\nhigher power density. Specifically, the dimensions of current collection ribs as well as the rib distribution were\r\noptimized to get a maximized power density in a fuel cell. In the modeling process, the power output from a fixed\r\narea of membrane is calculated through analysis of an electrical circuit simulating the current from electrochemical\r\nreaction flowing to the current collectors. Current collectors of two-dimensional ribs and three-dimensional pillars\r\nwere considered. Analyses found that three-dimensional pillars allow higher power density in a PEM fuel cell.\r\nConsidering the mass transfer enhancement effect, three-dimensional pillars as current collectors in gas flow field\r\nmay be a good choice if the fuel cell operates at low current density and there is no liquid water blocking the flow\r\nchannels. The analyses did not consider the existence of liquid water, meaning the current density is not very high.\r\nThe study concluded that decreasing the size of both the current collector and its control area yields a significant\r\nbenefit to a higher power density. A preliminary experimental test in a PEM fuel cell has verified the conclusion of\r\nthe analytical work....
Coal-based electric power generation remains the basic source of obtaining energy. With increasing pressure to\r\nreduce CO2 emissions, improving power unit efficiency has become an issue of utmost significance. Surely, one of\r\nthe possibilities to improve the efficiency of new power units is raising the steam parameters. With improved power\r\nplant efficiency, there is a lower demand for power of almost all auxiliary equipment except the boiler feed pump.\r\nThe reason for this is that the power needed to drive the feed pump is an almost linear function of the steam\r\npressure. This means that, even though the steam mass flow (and, consequently, the feed water mass flow) is\r\nreduced and the efficiency of feed pumps is improved, their power increases. For this reason, it is very important to\r\nfind the optimum drive of the boiler feed pump. The main aim of the conducted analysis was to compare various\r\ndrive options of the boiler feed pump for a conceptual ultra-supercritical 900-MW steam power unit. The following\r\ndrive configurations of the boiler feed pump were presented and compared:\r\n A frequency-controlled electric motor\r\n A condensing turbine fed with steam extraction from the immediate-pressure turbine\r\n An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the\r\nlow-pressure turbine\r\n A backpressure turbine fed with steam from a hot reheat steam line operating in parallel with the\r\nintermediate-pressure turbine\r\n An extraction-backpressure turbine fed with steam from a cold reheat steam line with bleeds shifted from the\r\nintermediate-pressure turbine (the master cycle idea).\r\nThe analysis of the operation of the 900-MW unit with various configurations of the feed pump drive was carried\r\nout for three load levels: for the nominal mass flow of live steam and for the partial mass flow of 75% and 50%....
An economic analysis has been performed to compare four nuclear fuel cycle options: a once-through cycle (OT), DUPIC recycling,\r\nthermal recycling using MOX fuel in a pressurized water reactor (PWR-MOX), and sodium fast reactor recycling employing\r\npyroprocessing (Pyro-SFR). This comparison was made to suggest an economic competitive fuel cycle for the Republic of Korea.\r\nThe fuel cycle cost (FCC) has been calculated based on the equilibrium material flows integrated with the unit cost of the fuel\r\ncycle components. The levelized fuel cycle costs (LFCC) have been derived in terms of mills/kWh for a fair comparison among\r\nthe FCCs, and the results are as follows: OT 7.35 mills/kWh, DUPIC 9.06 mills/kWh, PUREX-MOX 8.94 mills/kWh, and Pyro-SFR\r\n7.70 mills/kWh. Due to unavoidable uncertainties, a cost range has been applied to each unit cost, and an uncertainty study has\r\nbeen performed accordingly. A sensitivity analysis has also been carried out to obtain the break-even uranium price (215$/kgU)\r\nfor the Pyro-SFR against the OT, which demonstrates that the deployment of the Pyro-SFR may be economical in the foreseeable\r\nfuture. The influence of pyrotechniques on the LFCC has also been studied to determine at which level the potential advantages of\r\nPyro-SFR can be realized....
Earlier works have suggested that the energy correlations in a spallation source may influence the neutron noise measurements\r\nin an ADS. For the calculation of this effect not only the generally known and used one-particle spectrum is needed but also the\r\nso-called two particle spectrum, which describes also the energy correlations. Since measured data are not available for the energy\r\ncorrelation of the neutrons from a single spallation event, the physical models of the MCNPX code have been used to investigate\r\nthe effect. The calculational model has been successfully validated with measurements of the number distribution of spallation\r\nneutrons. The simulated one- and two-particle energy distributions and spectra proved that the energy correlations exist and have\r\nan important effect in low multiplicity spallation events and in thin targets. On the other hand, for thick targets this effect appears\r\nnegligible and the factorization of the two-particle spectrum seems an acceptable approximation. Further investigations are in\r\nhand to quantify the actual effect of the energy correlations on the neutron noise measurements....
Mathematical expressions have been employed to estimate global solar radiation on horizontal from relative sunshine duration for\r\ntwo weather stations in the United Arab Emirates (UAE), which are Abu Dhabi and Al Ain. These expressions include the original\r\nAngstrom-Prescott regression function (linear), quadratic function, third-order function, single-termexponential function, power\r\nfunction, logarithmic, and linear-logarithmic function. The predicted values were compared to the measured values using number\r\nof statistical methods to validate the goodness of the fits, such as residual analysis and goodness of fit statistics. All the used\r\nmathematical models performed generally well in both cities of Abu Dhabi and Al Ain, with all values of the coefficient of\r\ndetermination (R2) higher than 75%. Specifically, the linear Angstrom-Prescott model estimated the average monthly global\r\nradiation on horizontal best for the city of Abu Dhabi, providing the second lowest mean absolute percentage error (MAPE)\r\nof 1.89% and the highest value of R2, which is approximately 94%, while the third-order model proved to be the best estimator for\r\nthe city of Al Ain, providing the lowest MAPE value (3.06%) and a corresponding R2 of 83%....
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