Sharif Digital Repository

This paper presents a theoretical framework for the energy and exergy evaluation of a basic as well as three modified Organic Rankine Cycles (ORCs). The modified ORCs considered incorporating turbine bleeding, regeneration and both of them. The results demonstrate that evaporator has major contribution in the exergy destruction which is improved by increase in its pressure. The results confirm that the integrated ORC with turbine bleeding and regeneration has the highest thermal and exergy efficiencies (22.8% and 35.5%) and the lowest exergy loss (42.2 kW) due to decrease in cold utility demand and high power generation  

To attain an ongoing electricity economy, developing novel widespread electricity supply systems based on diverse energy resources are critically important. Several photovoltaic (PV) technologies exist, which cause various pathways to produce electricity from solar energy. This paper evaluates the competition between three influential solar technologies based on photovoltaic technique to find the optimal pathways for satisfying the electricity demand: (1) multicrystalline silicon; (2) copper, indium, gallium, and selenium (CIGS); and (3) multijunction. Besides the technical factors, there are other effective parameters such as cost, operability, feasibility, and capacity that should be... 

In the natural gas transmission network, from supply points to demand nods there are various technological options that include processing, transportation, conversion and gas distribution. Comprehensive analysis of natural gas network requires evaluation of different chains of gas flow through various levels based on economical and environmental criteria subject to technical and operational constraints such as feasibility, operability and reliability of different alternatives. To aid decision-making process in the sector of natural gas, a generic optimization-based model has been developed for assessing long term energy issues related to planning and design of natural gas supply systems. The... 

A novel frequency synthesizer architecture for reducing spur level is presented. By using a feedforward path a new zero in the transfer function is generated which enables us to increase the capacitor tied to the control voltage line and thus reducing spur level. A fast settling technique is also used to compensate the effect of spur reduction technique on settling time. Different blocks of frequency synthesizer are implemented in MATLAB/Simulink. Simulations show 13 dB improvement in reference spur level compared to conventional architecture for a 2.4 GHz frequency synthesizer  

Gaseous reduction of manganese ores has been studied as it is beneficial for both understanding the common ferromanganese production process and the development of new processes. Thermodynamics, kinetics, and the mechanisms of reduction by methane have been reviewed, supported by thermodynamic calculations from the commercial HSC Chemistry and FactSage software. While there were similarities in reduction process by CO and H2, methane was a more efficient reductant and yielded reduction levels beyond MnO, which was due to the large thermodynamic driving force for carbide formation by metastable methane. The practical aspects of gaseous reduction by methane, such as application of a... 

In this paper, a low power active phase shifter in 0.18 μm CMOS technology, operating from 5 to 6 GHz, for WLAN applications is presented. Design equations for this novel structure, which consists of two current steering stages, transconductance stage and DACs, are derived, thoroughly. This phase shifter has a range of 360° with 5.625° phase resolution. The power consumption is 35 mW. The RMS phase error is only 0.3°. The simulated power gain, input P1dB, and NF are 4 dB, -0.8 dBm and 6 dB, respectively  

This paper presents a new single-loop single-stage second order sigma-delta modulator. The circuit based on switched capacitor components just uses one Op-Amp to realize second order noise shaping. The modulator demonstrated 85 dB DR in 8kHz bandwidth, dissipating 135 μW from a 2.5 V supply. © 2002 IEEE  

An area and power-efficient second order sigma-delta modulator is presented. At system level, we propose a new single-loop single-stage modulator that uses only one class-AB op-amp to realize a second order noise shaping for speech band applications. The modulator shows 86 dB DR in 4 kHz speech bandwidth. It consumes 125 μw from a 2.5 V supply  

The design of a power-efficient second-order Δ/∑ modulator for voice-band is presented. At system level, a new single-loop, single-stage modulator is proposed. The modulator employs only one class-AB op-amp to realize a second-order noise shaping for voice-band applications. The modulator is designed in a 0.25μm standard CMOS process, and exhibits 86 dB dynamic range (DR) for a 4 kHz voice-bandwidth. The proposed modulator consumes 125μW from a 2.5 V supply. © Springer Science + Business Media, LLC 2006  

Characterization and calcination behavior of a low-grade manganese ore, as a part of Mn ferroalloys production, was studied by XRF, ex-situ XRD, in-situ XRD, and SEM-EDS techniques. Calcination experiments were carried out at and up to 900 °C (1173 K) in air and argon atmospheres. The samples were in particles and powder forms. The results indicated that both quartz and calcite phases in the ore exhibit a bimodal spatial distribution; as relatively large regions and finely distributed in the Mn- and Fe-containing phases. By Rietveld analysis of the in-situ XRD data, the reactions occurring upon heating during the calcination process were deduced. Thermal decomposition and reactive diffusion... 

This study is a novel attempt in developing of an Artificial neural network (ANN) model integrated with a thermodynamic equilibrium approach for downdraft biomass gasification integrated power generation unit. The objective of the study is to predict the net output power from the systems derived from various kinds of biomass feedstocks under atmospheric pressure and various operating conditions. The input parameters used in the models are elemental analysis compositions (C, O, H, N and S), proximate analysis compositions (moisture, ash, volatile material and fixed carbon) and operating parameters (gasifier temperature and air to fuel ratio). The architecture of the model consisted of one... 

This dataset includes 1032 runs from a biomass downdraft gasifier integrated with power production unit that is fed by 86 different types of biomasses from different groups (e.g. wood and woody biomasses, herbaceous and agricultural biomasses, animal biomasses, mixed biomasses and contaminated biomasses) and under various operating conditions. The dataset covers elemental and proximate analysis of various biomasses, operation conditions and the net output power from the biomass gasification-power production (BG-PP) in each case/run. This article has been submitted via another Elsevier journal as a co-submission, titled “Artificial neural network integrated with thermodynamic equilibrium... 

A new single-bit cascaded 2-2 σ/δ (Sigma-Delta) modulator with only two op-amps, instead of four ones in conventional modulators, to decrease the static power consumption and area, is designed for GSM transceiver applications. The circuit consists of two new single op-amp, second-order, and low-pass loop filters to achieve a fourth-order quantization noise shaping. The modulator shows 84dB DR (Dynamic Range) for GSM signal bandwidth, while consuming 2.3mW from a 2.5V supply voltage. © 2003 IEEE