New emissions targeting strategy for site utility of process industries

A new procedure for environmental targeting of co-generation system is presented. The proposed method is based on the concepts of pinch technology for total site targeting of fuel, power, steam, environmental impacts and total annualized cost with considering emissions taxes. This approach provides a consistent, general procedure for determining mass flow rates and efficiencies of the applied turbines. This algorithm utilizes the relationship of entropy with enthalpy and isentropic efficiency. Also, the life cycle assessment (LCA) as a well-known tool for analyzing environmental impacts on a wide perspective with reference to a product system and the related environmental and economic impacts have been applied. In this regard, a damage-oriented impact analysis method based on Eco-indicator 99 and footprints analysis was considered. In addition, the present work demonstrates the effect of including both sensible and latent heating of steam in the extended Site Utility Grand Composite Curve (ESUGCC). It is shown that including sensible heating allows for better thermal matching between the processes. Furthermore, the other representation YSUGCC as the other form of Site Utility Grand Composite has been proposed. Two case studies were used to illustrate the usefulness of the new environmental targeting method.     

A Novel Self-aligned and Maskless Process for Formation of Highly Uniform Arrays of Nanoholes and Nanopillars

Fabrication of a large area of periodic structures with deep sub-wavelength features is required in many applications such as solar cells, photonic crystals, and artificial kidneys. We present a low-cost and high-throughput process for realization of 2D arrays of deep sub-wavelength features using a self-assembled monolayer of hexagonally close packed (HCP) silica and polystyrene microspheres. This method utilizes the microspheres as super-lenses to fabricate nanohole and pillar arrays over large areas on conventional positive and negative photoresist, and with a high aspect ratio. The period and diameter of the holes and pillars formed with this technique can be controlled precisely and independently. We demonstrate that the method can produce HCP arrays of hole of sub-250 nm size using a conventional photolithography system with a broadband UV source centered at 400 nm. We also present our 3D FDTD modeling, which shows a good agreement with the experimental results.     

Investigating peak stresses in fitting and repair patches of buried polyethylene gas pipes

Nowadays, polyethylene composes a large number of natural gas distribution pipelines installed under the ground. The focus of the present contribution is two fold. One of the objectives is to investigate the applicability of polyethylene fittings in joining polyethylene gas pipes which are electrofused onto the pipe ends and buried under the ground, by estimating stress distribution using finite element method. The second objective is to study the effectiveness of polyethylene repair patches which are used to mend the defected pipelines by performing a finite element analysis to calculate peak stress values. Buried polyethylene pipelines in the natural gas industry, can be imposed by sever loadings including the soil-structure interaction, traffic load, soil’s column weight, internal pressure, and thermal loads resulting from daily and/or seasonal temperature changes. Additionally, due to the application of pipe joints, and repair patches local stresses superimposed on the aforementioned loading effects. The pipe is assumed to be made of PE80 resin and its jointing socket, and the repair patch is PE100 material. The computational analysis of stresses and the computer simulations are performed using ANSYS commercial software. According to the results, the peak stress values take place in the middle of the fitting and at its internal surface. The maximum stress values in fitting and pipe are below the allowable stresses which shows the proper use of introduced fitting is applicable even in hot climate areas of Ahvaz, Iran. Although the buried pipe is imposed to the maximum values of stresses, the PE100 socket is more sensitive to a temperature drop. Furthermore, all four studied patch arrangements show significant reinforcing effects on the defected section of the buried PE gas pipe to transfer applied loads. Meanwhile, the defected buried medium density polyethylene gas pipe and its saddle fused patch can resist the imposed mechanical and thermal loads of 22°C temperature increase. Moreover, increasing the saddle fusion patch length to 12 inches reduces the maximum stress values in the pipe, significantly.     

Kinetic,isotherm and thermodynamic study of nitrate adsorption from aqueous solution using modified rice husk

In this article, we prepared anionic sorbent using rice husk (RC). Anionic rice husk (ARC) structural characteristics and adsorption properties for nitrate removal from aqueous solution were investigated. The sorption of NO₃^? by batch method is carried out. The optimum conditions of sorption were found to be: a sorbent dose of 0.4 g in 100 mL of NO₃^? solution, contact time of 90 min, pH = 7. In optimum condition, removal efficiency was 94.3% for the NO₃^?. The nitrate adsorption process was well described by the pseudo-second-order kinetic model, and the experimental isotherm data fitted well with the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated and the results showed that the adsorption of nitrate on ARC was spontaneous and exothermic in nature. The effect of other anions were also studied and was found that the anions reduced the nitrate adsorption in the order of carbonate > chloride > phosphate > sulphate. ARC was used for the removal of NO₃^? from real wastewater (urban wastewater) that high performance of adsorbent was considerable.     

Hydrodynamic modeling of traffic jams in intracellular transport in axons

Irregularities in intracellular traffic in axons caused by mutations of molecular motors may lead to “traffic jams”, which often result in swelling of axons causing such neurodegenerative diseases as Alzheimer's disease and Down syndrome. Hence, it is of particular interest to mathematically model the formation of traffic jams in axons. This paper adopts the hydrodynamic continuity equations for intracellular transport of organelles as developed by Smith and Simmons [D.A. Smith, R.M. Simmons, Models of motor-assisted transport of intracellular particles, Biophysical Journal 80 (2001) 45–68.] whereas the Kerner and Konhäuser [B.S. Kerner, P. Konhäuser, Cluster effect in initially homogeneous traffic flow, Physical Review E 48 (1993), R2335–R2338.] model for traffic jams in highway traffic is applied to predict the velocity field. It is observed that combination of the two sets of equations can comprehensively predict the traffic jams in axons without the need to any additional assumption or modification.     

On the use of body biasing to improve linearity in low LO-power CMOS active mixers

In a radio-frequency (RF) transceiver, the linearity of the mixer has a profound effect on the overall transceiver performance. In many RF transceivers, active mixers are used due to their higher gain which also improves the overall receiver noise figure. In a typical RF active mixer where the transistors in the LO stage switch abruptly, most of the nonlinear distortions come from the transconductance or RF stage and thus the linearity of the mixer can be enhanced by proper design of the RF stage. In low-power receivers, however, to reduce the power consumption of the local oscillator (LO) circuit, the amplitude of LO signal is low and thus the switching of the transistors in the LO stage of the mixer is gradual. In this paper, we propose a technique to improve the linearity of such low-power mixers by enhancing the linearity of the LO stage. In particular, body biasing is utilized in the LO stage to improve the linearity. To verify the effectiveness of the proposed technique, two proof-of-concept double-balanced down-conversion active mixers have been designed and fabricated in 0.13-µm CMOS. The maximum IIP3 of +2.7 dBm and −4.9 dBm at a conversion gain of 13 dB and 16 dB are achieved for the first and second prototype respectively. For a 2.4 GHz RF input signal and an intermediate-Frequency (IF) of 50 MHz, the first prototype consumes 2.4 mW from a 1.2 V supply while the second one consumes only 780 µW from a 0.7 V supply.     

Entropy generation for microscale forced convection: Effects of different thermal boundary conditions,velocity slip,temperature jump,viscous dissipation,and duct geometry

This work presents closed form solutions for fully developed temperature distribution and entropy generation due to forced convection in microelectromechanical systems (MEMS) in the Slip-flow regime, for which the Knudsen number lies within the range 0.001 < Kn < 0.1. Two different cross-sections are analyzed, being microducts (composed of two parallel plates) and micropipes, with the effects of viscous dissipation being included. Invoking the temperature jump equation, two different thermal boundary conditions are investigated, being isothermal and isoflux walls. Expressions are presented for the local and bulk temperature profiles, the Nusselt number, the Bejan number, and the entropy generation rate in terms of the key parameters. Though the results are obtained for the microscale problems, they can be generalized to the macroscale counterparts by letting Kn = 0.     

Application of metal foams in air-cooled condensers for geothermal power plants: An optimization study

Optimized design of metal foam heat exchangers, as replacements for finned-tubes in air-cooled condensers of a geothermal power plant, is presented here. Two different optimization techniques, based on first and second law (of thermodynamics) are reported. While the former aims at the highest heat transfer rate with as low pressure drop as possible, the latter minimizes the generated entropy in the thermodynamic system. Interestingly, the two methods lead to the same optimal design. The new design has been compared to the conventional air-cooled condenser designed and optimized by using the commercially available software ASPEN. It is shown that while the heat transfer rate increases significantly (by an order of magnitude) compared to the finned-tube for the same main flow obstruction height, the pressure drop increase is within an acceptable range. Further comparison between the two systems are carried out, making use of Mahjoob and Vafai's performance factor developed specifically for metal foam heat exchangers.     

Digital sinusoidal PWMs for a micro-controller based single-phase inverter,Part 1: Principles of digital sinusoidal PWM generation

Nowadays, Digital Sinusoidal Pulse Width Modulation (DSPWM) is playing a major role in the generation of pure sinusoidal waveforms using micro-controller based inverters (Kawabata, Miyashita and Yamamoto 1991 Kawabata, T., Miyashita, T. and Yamamoto, Y. 1991. “Digital Control of Three-Phase PWM Inverter With LC Filter,”. IEEE Transactions on Power Electronics, 6: 62–72.  [Google Scholar]; Herrmann, Langer and Broeck 1993 Herrmann, U., Langer, H. G. and Broeck, H. V.D. 1993. “Low Cost DC to AC Converter for Photovoltaic Power Conversion in Residential Applications,”. 24th Annual IEEE Power Electronics Specialists Conference. 1993, Seattle, WA, USA.  [Google Scholar]; Ying-Yu 1995 Ying-Yu, T. “DSP-Based Fully Digital Control of a PWM DC-AC Converter for AC Voltage Regulation,”. 26th Annual IEEE Power Electronics Specialists Conference. Atlanta, GA.  [Google Scholar]; PICREF-1 1997 PICREF-1. 1997. Uninterruptible Power Supply Reference Design Vol. 2004. Microchip Technology [Google Scholar]; Shih-Liang, Meng-Yueh, Jin-Yi, Li-Chia and Ying-Y 1999 Shih-Liang, J., Meng-Yueh, C., Jin-Yi, J., Li-Chia, Y. and Ying-Yu, T. 1999. “Design and Implementation of an FPGA-Based Control IC for AC-Voltage Regulation,”. IEEE Transactions on Power Electronics, 14: 522–532.  [Google Scholar]; The Electrical Engineering Handbook 2000 The Electrical Engineering Handbook. 2000. , 2nd ed., New York: CRC Press LLC.  [Google Scholar]; Koutroulis, Chatzakis, Kalaitzakis and Voulgaris 2001 Koutroulis, E., Chatzakis, J., Kalaitzakis, K. and Voulgaris, N. C. 2001. “A Bidirectional, Sinusoidal, High-Frequency Inverter Design,”. IEE Proceedings-Electric Power Applications, 148: 315–321.  [Google Scholar]; Skvarenina 2002 Skvarenina, T. L. 2002. “The Power Electronics Handbook,”. In Industrial Electronics Series, Edited by: Irwin, J. D. New York: CRC.  [Google Scholar]; Pop, Chindris and Dulf 2004 Pop, O., Chindris, G. and Dulf, A. 2004. “Using DSP Technology for True Sine PWM Generators for Power Inverters,”. 27th International Spring Seminar on Electronics Technology: Meeting the Challenges of Electronics Technology Progress, 1: 141–146.  [Google Scholar]; Zhongyi, Mingzhu and Yan 2005 Zhongyi, H., Mingzhu, L. and Yan, X. “Core Techniques of Digital Control for UPS,”. IEEE International Conference on Industrial Technology.  [Google Scholar]). The types of DSPWM that can be generated depend on the micro-controller hardware resources and are therefore limited, but provide performance benefits not possible with an analogue controller. For instance, digital controllers offer a programmable solution and therefore more flexibility, as advanced algorithms and additional features can be added to the system in software instead of hardware (Monti, Santi, Dougal, and Riva 2003 Monti, A., Santi, E., Dougal, R. A. and Riva, M. M. 2003. “Rapid Prototyping of Digital Controls for Power Electronics,”. IEEE Transactions on Power Electronics, 18: 915–923.  [Google Scholar]; Brush 2005 Brush, L. “Trends in Digital Power Management: Power Converter and System Demand Characteristics,”. Twentieth Annual IEEE Applied Power Electronics Conference and Exposition. Austin, TX [Google Scholar]). Digital controllers are also less sensitive to environmental conditions and show precise behaviour compared with their analogue counterparts (Skvarenina 2002 Skvarenina, T. L. 2002. “The Power Electronics Handbook,”. In Industrial Electronics Series, Edited by: Irwin, J. D. New York: CRC.  [Google Scholar]). This two-part article looks at the benefits and limitations of three major DSPWMs for a single-phase full-bridge inverter and investigates their performance. In Part 1, the theory of the three major DSPWMs are presented, including mathematical models and simulation results. It looks at the PWM patterns required to generate these DSPWMs and the benefits and limitations of each. To evaluate the proposed mathematical models and simulation results, a 2kVA single-phase full-bridge inverter was developed and the DSPWMs implemented. In Part 2, experimental results from the implementation of the DSPWMs on the prototype 2kVA inverter are presented, which confirms the validity of the proposed analysis in Part 1. Moreover, the performance, including efficiency and losses (switching, conduction, and transformer) of the different DSPWMs implemented on the 2kVA inverter under different loads were examined and recommendations presented.