Film condensation of mercuryCondensation en film du mercureFilmkondensation von quecksilberплэнoчнaя кoндэнcaция pTyTи

Measurements of vapour-to-surface temperature difference and heat flux for film condensation of mercury on a vertical plane square (side 40mm) nickel-plated copper surface are reported. Thermocouples, accurately located and spaced through the copper condensing block served to measure, by extrapolation, the temperature at the copper-nickel interface and from the temperature gradient, the heat flux. Special care was taken to ensure that the results were not vitiated by the presence in the vapour of non-condensing gases. The results have higher relative precision than other recent heat-transfer measurements for condensation of metals since the present observations were made under conditions (metal used, vapour temperature and condensation rate) for which the vapour-to-surface temperature difference was larger than in the earlier work. The observed vapour-to-surface temperature differences are substantially greater than those given by the Nusselt theory of film condensation. By attributing the excess temperature drop to the vapour-liquid interface, the results are compared with theoretical expressions for interphase matter transfer. As in other recent work, values for the correction factor (or apparent “condensation coefficient”) varied from near unity down to about 0.6. The precision of the present results is such as to reveal a dependence of the correction factor on the condensation rate as well as on the vapour pressure. It was found that both could be satisfactorily correlated by a single dimensionless variable.     

Design and analysis of a wireless power transfer system with alignment errors for electrical vehicle applications

In this study, a 15 kW wireless power transfer system with high frequency and large air gap for electrical vehicle battery charge systems is designed and co-simulations with ANSYS-Maxwell and Simplorer software are performed. The air gap between the primary and the secondary windings are determined as 20 cm for the 15 kW wireless power transfer system. Operation of the designed system for different operation conditions such as completely aligned windings (ideal condition) and windings with alignment errors, which can occur because of user error or another reason, are analyzed and obtained results are reported. The resonant frequency of the designed system which has a 60 × 60 cm secondary winding and a 60 × 100 cm primary winding is 17.702 kHz, and the maximum efficiency of the system is obtained as 75.38% for completely aligned windings. The distribution and density of the electromagnetic flux, and variation of efficiency versus load level of the system and responses of the system in case of different alignment errors are also investigated and reported for both ideal operation conditions and in case of alignment errors.     

A phenomenological model for heat transfer in freeboard of fluidized beds

A phenomenological model was developed to predict heat transfer to tubes located in the freeboard region of gas fluidized beds. The model is concerned with the conductive/convective mechanism of heat transfer. For high temperature applications, an additional contribution by thermal radiation would need to be incorporated. The model considers that the tube surface experiences alternating contact with a dense emulsion phase and a lean void phase. Contributions by dense and lean phases are represented by transient conduction and convection mechanisms, respectively. Particletube contact information was obtained experimentally for a wide range of operating conditions at room temperature and pressure. Predictions of the model were compared with measured heat transfer coefficients. Over a 20-fold range in magnitudes of heat transfer coefficients, the model successfully predicted the measured values with an average deviation of 44 percent.     

An improved PTS scheme based on a novel discrete invasive weed optimization algorithm for PAPR reduction in the UFMC signal

Neural Computing and Applications - Multicarrier transmission strategy provides great benefits in wireless communication technology. For this reason, all of the waveform contenders proposed for the...     

Electron–Electron Interactions in Sb-Doped SnO<Subscript>2</Subscript> Thin Films

Electrical conductivity and Hall-effect measurements on undoped and Sb-doped SnO₂ thin films prepared by the sol–gel technique were carried out as a function of temperature (55 K to 300 K). Structural characterizations of the films were performed by atomic force microscopy (AFM) and x-ray diffraction (XRD). A doping-induced metal–insulator transition (MIT) was observed. On the metallic side of the transition, the experimental data were interpreted in terms of electron–electron interactions (EEI). The existence of EEI was confirmed by excellent agreement between theoretical and experimental data. The experimental data on the insulator side of the transition were analyzed in terms of variable-range hopping (VRH) conduction. A complete set of parameters describing the properties of the localized electrons, including hopping energy, hopping distance, and the value of the density of states at the Fermi level, was determined.     

Design and performance analysis of the three-level isolated DC-DC converter with the nanocyrstalline core transformer

In this study, an isolated three-level DC-DC converter is proposed for high power and high conversion ratio applications such as fuel cells. The proposed system consists of a single phase three-level inverter, a medium frequency transformer and a diode rectifier unit. In the proposed system, a DC supply voltage is converted to a medium frequency AC voltage via a three-level inverter instead of the conventional two-level inverter. Since the three-level inverter generates an AC waveform with multiple steps, lower voltage harmonics and lower EMI levels than conventional two-level inverter are achieved. Thus, the three-level inverter provides higher efficiency value. The medium frequency transformer enables high voltage conversion ratio and provides galvanic isolation as well. The output voltage of the medium frequency transformer is converted to the DC voltage and thus the DC-DC conversion is achieved. According to simulation and experimental results, it is seen that the proposed DC-DC converter structure provides higher power density and higher efficiency values than conventional system.     

Bidirectional intensity modulated/direct detection optical OFDM WDM-PON system

In this paper, we have evaluated a bidirectional wavelength division multiplexing passive optical network(WDM-PON) employing intensity modulated/direct detection optical orthogonal frequency division multiplexing(IM/DD-OFDM). The proposed system employs 100 Gbit/s 16 quadrature amplitude modulation(16-QAM) downstream and 5 Gbit/s on-off keying(OOK) upstream wavelengths, respectively. The proposed system is considered low-cost as non-coherent IM/DD OFDM technology and a simple reflective semicond...     

High-performance solar-blind photodetectors based on Al/sub x/Ga/sub 1-x/N heterostructures

Design, fabrication, and characterization of high-performance Al/sub x/Ga/sub 1-x/N-based photodetectors for solar-blind applications are reported. Al/sub x/Ga/sub 1-x/N heterostructures were designed for Schottky, p-i-n, and metal-semiconductor-metal (MSM) photodiodes. The solar-blind photodiode samples were fabricated using a microwave compatible fabrication process. The resulting devices exhibited extremely low dark currents. Below 3fA, leakage currents at 6-V reverse bias were measured on p-i-n samples. The excellent current-voltage (I--V) characteristics led to a detectivity performance of 4.9/spl times/10/sup 14/ cmHz/sup 1/2/W/sup -1/. The MSM devices exhibited photoconductive gain, while Schottky and p-i-n samples displayed 0.09 and 0.11 A/W peak responsivity values at 267 and 261 nm, respectively. A visible rejection of 2/spl times/10/sup 4/ was achieved with Schottky samples. High-speed measurements at 267 nm resulted in fast pulse responses with greater than gigahertz bandwidths. The fastest devices were MSM photodiodes with a maximum 3-dB bandwidth of 5.4 GHz.