Experimental Investigation of CO2 Transport through Combined Membrane Absorber and Regenerator

Greenhouse gases such as carbon dioxide have been known to contribute significantly to global warming, which in turn has resulted in serious global environmental problems. Carbon dioxide is the main gaseous contaminant in the atmosphere, representing about 80% of greenhouse gases. It is reported that industry and power plants using fossil fuels such as coal-combustion power generators produce half of the CO2 emissions. These emissions create the need for low energy-consumption, and efficient technologies for the capture and removal of CO2 from gas mixtures produced by industrial sources. Conventional gas absorption processes for the removal of CO2 including chemical absorption by alkanolamine solutions suffer from many drawbacks such as flooding, foaming, entraining, channeling, and high capital and operating costs. The effort of this research is to work on the possibilities of enhancing the efficiency of these processes to reduce the effect of their drawbacks by using Hollow fiber membrane Contactor (HFMC) as a new gas separation process. In this study several membrane contactors such as homemade Polyvinylidenefluoride (PVDF), commercial Polytetrafluoroethylene (PTFE) and Perfluoroalkoxy alkane (PFA) were individually fabricated as an absorption process, the gas mixture of CO2/N2 flowed on one side of a hydrophobic microporous membrane while several liquid absorbent, such as Monoethanolamine (MEA), Diethanolamine (DEA) and Sodium Hydroxide (NaOH) flowed on the other side of membrane for comparison purpose. The CO2 gaseous contaminant diffused from the gas phase to the membrane gas–liquid interface and is absorbed in the liquid. The Result revealed that homemade PVDF has the highest removal rate and PFA has the lowest removal efficiency, in addition, although the removal performance by NaOH gave better removal efficiency, by contrast, it suffered from poor regeneration, therefore, DEA became more favorable in overall performance because of its higher regeneration rate. The effects of operation parameters such as gas and liquid flow rates and packing ratio on performance of CO2 removal were analyzed. The results reveal that, regardless of the type of the membrane module used and liquid solvent, increase in liquid flow rate and packing ratio and a decrease in gas flow rate, give the best system performance in the absorption process. The rich solution may be sent to another membrane contactor for stripping to remove the absorbed gases and regenerate the solvent. In the stripping unit, the operating parameters such as temperature, gas flow rate and liquid follow rate were examined to investigate their effect on the stripping performance. Results determined that temperature has the focal effect on stripping performance regardless of the type of the solvent, increase in temperature increases stripping efficiency. In addition, higher stripping performance was found to be at high solvent liquid flow rate, low sweep gas flow rate. Using a suitable membrane configuration could be considered as a way to prevent wetting. The generated lean solution is then recycled to the absorption unit and the CO2 transport in combined absorber and stripper units were evaluated by time. Various membrane modules using several aqueous amine solutions such as MEA, DEA and NaOH at different heat of regeneration were examined to investigate their impact on membrane wetting and overall performance. Results revealed that DEA shows the optimum performance at high heat of regeneration. A mathematical model was applied to predict the CO2 removal in gas liquid membrane contactor. Model results were in good agreement of the experimental data

An adaptive policy-based vertical handoff algorithm for heterogeneous wireless networks

The next generation of wireless networks is envisioned as convergence of heterogeneous radio access networks. Since technologies are becoming more collaborative, a possible integration between IEEE 802.16 based network and previous generation of telecommunication systems (2G, ..., 3G) must be considered. A novel quality function based vertical handoff (VHO) algorithm, based on proposed velocity and average receive power estimation algorithms is discussed in this paper. The short-time Fourier analysis of received signal strength (RSS) is employed to obtain mobile speed and average received power estimates. Performance of quality function based VHO algorithm is evaluated by means of measure of quality of service (QoS). Simulation results show that proposed quality function, brings significant gains in QoS and more efficient use of resources can be achieved.<br /

Three new records of Megaspilidae (Hymenoptera, Ceraphronoidea) from Iran

In the present study, thirty specimens of Megaspilidae (Hymenoptera, Ceraphronoidea) were collected by Malaise-traps from different area of Fars province in southern Iran. Three species namely, Dendrocerus laticeps (Hedicke, 1929), D. perlucidus Alekseev, 1983 and Conostigmus fasciatipennis Kieffer, 1907 are new records for Iran

Comparing the Comparative Efficiency of System Marginal Price and Pay as Bid Auctions in Electricity Markets

System marginal price auction and pay as bid auction are common auctions in electricity markets. The present article discusses the impacts of selecting between different common auctions in electricity markets (system marginal price auction and pay as bid auction) on production efficiency, total efficiency and average expected price in an asymmetric information situation, where each player’s information about the marginal cost of the competitor is incomplete. A model is designed to conduct the comparative study of alternative auction mechanisms. The model is based on two profit maximizing players, with full information about their marginal cost and incomplete information about their competitor. Assumptions which has been used to construct the model are based on Iran’s electricity market structure. The outcome indicates that although production efficiency in alternative auction mechanism do not differ from each other, expected price under system marginal price auction is lower than pay as bid mechanism. Vice versa occurs in total efficiency

A Comparative Study of Iran’s Electricity Market Auction Mechanism and System Marginal Price Auction Mechanism

The present article discusses the impacts of selecting between different common auctions in electricity markets (system marginal price auction and pay as bid auction) on production efficiency, total efficiency and average expected price in an asymmetric information situation, where each player’s information about the marginal cost of the competitor is incomplete. A simple model is designed to conduct the comparative study of alternative auction mechanisms. The model is based on two profit maximizing players, with full information about their own marginal cost and incomplete information about their competitor. Assumptions which have been used to construct the model are based on Iran’s electricity market structure. The outcome indicates that although players bid functions in alternative auction mechanism differ from each other, the production efficiency, total efficiency and the average expected price are equivalent

Comparing four different methods for the management of ectopic pregnancy: A cross-sectional study

Background: Ectopic pregnancy (EP) is one of the major causes of maternal mortality during the first trimester of pregnancy. Objective: Four treatment methods for EP including single-dose methotrexate (SD-MTX), double-dose methotrexate, expectant and surgical management were considered. Materials and Methods: In this cross-sectional study, the clinical characteristics of 365 women aged 15-44 yr who had been diagnosed with EP were reviewed from March 2017 to March 2019 in hospitals affiliated to Shiraz University of Medical Sciences, Shiraz, Iran. Receiver operating characteristics curves were plotted to determine the cut-off points for size of ectopic mass and beta-human chorionic gonadotropin (β- hCG) that suitably discriminated between double-dose methotrexate and surgery management. Results: The most common site of EP was adnexa. According to the receiver operating characteristics analysis, surgery was the best plan for the women with an ectopic mass &gt; 34.50 mm in diameter or with an initial β-hCG level &gt; 6419 mIU/ml. The β-hCG levels in the women successfully treated with SD-MTX were significantly lower than in those with failed treatment (p = 0.02). The SD-MTX group had a higher success rate and significantly shorter duration of hospitalization, and so this was a more effective medical treatment in comparison with the double-dose protocol. Conclusion: Surgery is proposed as the best option for the cases with large ectopic mass or high β-hCG level. SD-MTX had a higher success rate and shorter hospital stay than the double-dose protocol, and so was found to be an efficient and safe alternative. Further randomized clinical trials with larger sample sizes are recommended to validate the current results. Key words: Ectopic pregnancy, Methotrexate