Loading...
Search for: efficiency
0.007 seconds
Total 1663 records

    An applicable method for efficiency estimation of operating tray distillation columns and its comparison with the methods utilized in HYSYS and Aspen Plus

    , Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 51, Issue 10 , October , 2015 , Pages 1393-1402 ; 09477411 (ISSN) Sadeghifar, H ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    Developing general methods that rely on column data for the efficiency estimation of operating (existing) distillation columns has been overlooked in the literature. Most of the available methods are based on empirical mass transfer and hydraulic relations correlated to laboratory data. Therefore, these methods may not be sufficiently accurate when applied to industrial columns. In this paper, an applicable and accurate method was developed for the efficiency estimation of distillation columns filled with trays. This method can calculate efficiency as well as mass and heat transfer coefficients without using any empirical mass transfer or hydraulic correlations and without the need to... 

    Promotion of low-carbon economy through efficiency analysis: A case study of a petrochemical plant

    , Article International Journal of Environmental Research ; 2020 Keivani, E ; Abbaspour, M ; Abedi, Z ; Ahmadian, M ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2020
    Abstract
    Over the past few decades, industrial development has caused a dramatic increment in greenhouse gas (GHG) emissions, as a leading cause of climate change. Modifying the industrial plants' environmental performance is the main pillar of improving efficiency that can reduce the waste of resources and make achieving lower-cost global emission reduction targets of the Kyoto protocol's clean development mechanism (CDM) possible. Considering the essentiality of knowledge-based research in increasing the awareness of policymakers by providing better access to accurate and reliable information, an analytical survey on efficiency in oil, gas, and petrochemical industries has been conducted by... 

    Suggestions to improve "manual welding efficiency" in terms of "welder tool time" for developing countries (based on a case study: Iranian petrochemical projects)

    , Article Annual Conference of the Canadian Society for Civil Engineering 2007: Where the Road Ends, Ingenuity Begins, Yellowknife, NT, 6 June 2007 through 9 June 2007 ; Volume 2 , 2007 , Pages 1091-1100 Mortaheb, M ; Ruwanpura, J. Y ; Dehghan, R ; Khoramshahi, F ; Sharif University of Technology
    2007
    Abstract
    "Manual Welding" is normally a major part of activities which constitutes to the expansion and productivity of construction industry. This research aims to identify and evaluate the factors impacting welder efficiency enhancement and can lead to construction productivity improvement. The "tool time" has been used as a yard stick to assess welder productive time and welding efficiency. A total of 162 samples in three working categories of piping, vessels and steel structures were chosen for study and evaluation. A series of work sampling studies by direct observation as well as continuous monitoring indicate that almost 35.5% of a typical welding day is taken away by non productive times.... 

    SELM: Software engineering of machine learning models

    , Article 20th International Conference on New Trends in Intelligent Software Methodologies, Tools and Techniques, SoMeT 2021, 21 September 2021 through 23 September 2021 ; Volume 337 , 2021 , Pages 48-54 ; 09226389 (ISSN); 9781643681948 (ISBN) Jafari, N ; Besharati, M. R ; Hourali, M ; Sharif University of Technology
    IOS Press BV  2021
    Abstract
    One of the pillars of any machine learning model is its concepts. Using software engineering, we can engineer these concepts and then develop and expand them. In this article, we present a SELM framework for Software Engineering of machine Learning Models. We then evaluate this framework through a case study. Using the SELM framework, we can improve a machine learning process efficiency and provide more accuracy in learning with less processing hardware resources and a smaller training dataset. This issue highlights the importance of an interdisciplinary approach to machine learning. Therefore, in this article, we have provided interdisciplinary teams' proposals for machine learning. © 2021... 

    Nonparametric frontier analysis models for efficiency evaluation in insurance industry: A case study of Iranian insurance market

    , Article Neural Computing and Applications ; Vol. 24, issue. 5 , April , 2014 , pp. 1153-1161 ; ISSN: 09410643 Rahmani, I ; Barati, B ; Majazi Dalfard, V ; Hatami-Shirkouhi, L ; Sharif University of Technology
    Abstract
    Performance evaluation and efficiency analysis is considered to be one of the critical responsibilities of the management department. This paper investigates and assesses the efficiency and performance of Iranian insurance companies through nonparametric frontier analysis (FA) models. The two well-known nonparametric FA models, data envelopment analysis (DEA) and free disposal hull, are utilized to separate the efficient companies from the inefficient companies, and two well-known super-efficiency analysis models are utilized to rank the efficient units. For the further analysis, critical inputs are also identified for inefficient companies using DEA sensitivity analysis which is a powerful... 

    Solving a new mixed integer non-linear programming model of the multi-skilled project scheduling problem considering learning and forgetting effect on the employee efficiency

    , Article IEEE International Conference on Industrial Engineering and Engineering Management ; 18 November , 2014 , Pages 400-404 ; ISSN: 21573611 ; ISBN: 9781479909865 Mehmanchi, E ; Shadrokh, S ; Sharif University of Technology
    Abstract
    In this paper, we propose a new mathematical programming model to tackle the multi-skilled project scheduling problem. Considering the effect of learning and forgetting on the human skills, an exponential learning function has been developed by assuming the efficiency of employees performing activities to be dynamic. Taking the nonlinearity of the function into account, we use separable programming to acquire an appropriate linear approximation for it. Moreover, the proposed model allows us to relax some of the binary variables linearly without any modifications. At the end, the final model is tested with some instances and is solved by CPLEX in order to confirm the implemented... 

    Aspects of alkaline flooding: Oil recovery improvement and displacement mechanisms

    , Article Middle East Journal of Scientific Research ; Volume 18, Issue 2 , 2013 , Pages 258-263 ; 19909233 (ISSN) Sedaghat, M. H ; Ahadi, A ; Kordnejad, M ; Borazjani, Z ; Sharif University of Technology
    2013
    Abstract
    Alkaline flooding is one of the newest chemical enhanced oil recovery (EOR) methods. Alkaline generates in situ surfactants when in reacts with acid content of the oil. This economic surfactant generated in oil-water interface, reduces interfacial tension (IFT) significantly that leads to increase in oil recovery by extracting oil from tiny pores. In this study, three alkaline i.e. Na2CO3, NaOH and KOH in various concentrations were flooded in a glassy micromodel to detect displacement mechanisms and compare oil recovery. According to the results, increase in alkaline concentration leads to increase in recovery. However, in this case, alkaline type does not play a significant role. In... 

    Supercritical extraction of cocoa butter from cocoa seed, using pure carbon dioxide, carbon dioxide with ethanol as co-solvent and ethane

    , Article Middle East Journal of Scientific Research ; Volume 13, Issue 8 , 2013 , Pages 1010-1015 ; 19909233 (ISSN) Salajegheh, D ; Vaziri, A ; Bastani, D ; Sharif University of Technology
    2013
    Abstract
    The effective parameters such as particle size, temperature, pressure and extraction time on supercritical carbon dioxide extraction of cocoa butter form cocoa seed were studied in order to find the optimum conditions for extraction. Particle size from whole cocoa nibs to one millimeter diameter, extraction temperature from 35°C to 55°C, extraction time from 2 to 8 hours and extraction pressure from 5 to 20 MPa were investigated and optimized. The optimum results (according to the limitation of the apparatus) of 5.2% extraction efficiency, suggests that pure CO2 is not a suitable solvent for extraction of cocoa butter in the investigated range of parameters and therefore the use of a... 

    Effect of crystallinity and morphology of TiO2 nano-structures on TiO2:P3HT hybrid photovoltaic solar cells

    , Article Applied Solar Energy (English translation of Geliotekhnika) ; Volume 51, Issue 1 , January , 2015 , Pages 34-40 ; 0003701X (ISSN) Boroomandnia, A ; Kasaeian, A. B ; Nikfarjam, A ; Akbarzadeh, A ; Mohammadpour, R ; Sharif University of Technology
    Allerton Press Incorporation  2015
    Abstract
    A comparative study has been made of hybrid solar cells based on poly(3-hexylthiophene) (P3HT) and different nano-structures of TiO2. Electrospinning, which is a low cost production method for large area nanofibrous films, was employed to fabricate TiO2 nanofibers and spin coating method was employed to fabricate organic-inorganic hybrid solar cells based on P3HT and TiO2 nanostructures. The performance of the hybrid solar cells was analyzed for four density levels of the TiO2 nanostructure. It was found that higher densities of TiO2 leads to more interface area and generates excitons, so that the power conversion efficiency increases to... 

    Simple and rapid determination of effective Murphree component efficiencies for operating absorbers, strippers and distillation columns filled with any type of trays

    , Article Separation and Purification Technology ; Volume 139 , January , 2015 , Pages 104-108 ; 13835866 (ISSN) Sadeghifar, H ; Sharif University of Technology
    Elsevier  2015
    Abstract
    Estimating efficiency of an operating column has to be distinguished from that of a column being designed. This crucial point has been totally overlooked in the literature. All the methods and models available for predicting the Murphree efficiencies of tray columns have been developed for the design case. They generate their own mass and heat transfer rates and empirical parameters rather than produce true transfer rates by using operating column (realistic) data, especially the specifications of outlet streams. In addition, most of these methods are limited in application and insufficient in accuracy, especially if applied outside the range of conditions under which they were formulated.... 

    Performance of polyacrylamide/Cr(III) gel polymer in oil recovery from heterogeneous porous media: An experimental study

    , Article Korean Journal of Chemical Engineering ; Volume 33, Issue 12 , 2016 , Pages 3350-3358 ; 02561115 (ISSN) Kargozarfard, Z ; Riazi, M ; Ayatollahi, S ; Shahnazar, S ; Sharif University of Technology
    Springer New York LLC 
    Abstract
    Water channeling due to reservoir heterogeneity is an important factor that could decrease the displacement efficiency of a water flooding process. In this study, the ability of polyacrylamide/ chromium acetate system on altering water path in heterogeneous layered media was investigated using glass bead micromodels. After the relevant parameters were optimized, a series of water and gel injection experiments were conducted in glass bead micromodel. The experimental results show that sweep efficiency is basically controlled by gel strength. The gel strength has a minor impact on the oil recovery from the higher permeable zone, whereas the oil recovery from the lower permeable zone is a... 

    Computational study on design parameters of a solar chimney

    , Article International Conference on Sustainable Mobility Applications, Renewables and Technology, 23 November 2015 through 25 November 2015 ; 2015 ; 9781467395298 (ISBN) Esfidani, M. T ; Raveshi, S ; Shahsavari, M ; Sedaghat, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    Abstract
    Today, the production of energy and electricity is one of the major concerns of mankind. Electricity generation by solar energy is considered as one of the alternatives to fossil fuels. Solar chimneys mechanism is based on a natural phenomenon. In this process the solar energy heat up the earth's surface and the surrounding air. Due to the density difference between cold air and warm air, heated air ascends and causes air circulation. In this study, mathematical modelling of solar chimney and governing equations of this system will be discussed. In order to validate the numerical results, upwind velocity in chimney has been compared with a reliable reference results. As well as, the... 

    Antimicrobial wound dressing containing silver sulfadiazine with high biocompatibility: In vitro study

    , Article Artificial Organs ; Volume 40, Issue 8 , 2016 , Pages 765-773 ; 0160564X (ISSN) Mohseni, M ; Shamloo, A ; Aghababaei, Z ; Vossoughi, M ; Moravvej, H ; Sharif University of Technology
    Blackwell Publishing Inc 
    Abstract
    Many patients all over the world suffer from acute wounds caused by traumas or burns. In most crucial cases, skin regeneration cannot be promoted spontaneously, and skin grafts are applied as the main treatment. However, this therapy has some drawbacks which motivate researchers to develop wound dressings. In this study, electrospun mats consisting of polycaprolactone (PCL) and polyvinyl alcohol (PVA) incorporated with silver sulfadiazine (SSD) are proposed to be used as antimicrobial wound dressings with the capability of cell seeding. Various amounts of SSD were loaded into PVA nanofibers, and the effects of SSD particles on the morphological characteristics of nanofibers, mechanical... 

    Synthesis and characterization of new triphenylamine-based dyes with novel anchoring groups for dye-sensitized solar cell applications

    , Article Journal of Materials Science: Materials in Electronics ; Volume 28, Issue 2 , 2017 , Pages 1859-1868 ; 09574522 (ISSN) Salimi Beni, A ; Hosseinzadeh, B ; Azari, M ; Ghahary, R ; Sharif University of Technology
    Springer New York LLC  2017
    Abstract
    Three new chromophores based on the triphenylamine (MM, DM, DN) with various novel electron withdrawing anchoring groups have been synthesized for use in dye-sensitized solar cells (DSSCs). The sensitizers were characterized by 1H and 13C NMR, Mass, UV–Vis, and electrochemical analysis. The HOMO and LUMO electron distributions of the sensitizers were calculated using density functional theory on a B3LYP level for geometry optimization. The DSSC device based on DM dye showed the best photovoltaic performance among MM and DN dyes: maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 98 %, short circuit current (JSC) of 4.58 mA/cm2, open circuit voltage (VOC) of... 

    Efficient solutions of interval programming problems with inexact parameters and second order cone constraints

    , Article Mathematics ; Volume 6, Issue 11 , 2018 ; 22277390 (ISSN) Sadeghi, A ; Saraj, M ; Mahdavi Amiri, N ; Sharif University of Technology
    MDPI AG  2018
    Abstract
    In this article, a methodology is developed to solve an interval and a fractional interval programming problem by converting into a non-interval form for second order cone constraints, with the objective function and constraints being interval valued functions. We investigate the parametric and non-parametric forms of the interval valued functions along with their convexity properties. Two approaches are developed to obtain efficient and properly efficient solutions. Furthermore, the efficient solutions or Pareto optimal solutions of fractional and non-fractional programming problems over R + n S (0) are also discussed. The main idea of the present article is to introduce a new concept for... 

    Energy efficient cultivation of microalgae using phosphorescence materials and mirrors

    , Article Sustainable Cities and Society ; Volume 41 , 2018 , Pages 449-454 ; 22106707 (ISSN) Helali Esfahani, H ; Shafii, M. B ; Roshandel, R ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In the present study, two novel annular photobioreactors (PBR) were developed to enhance microalgae growth. One of these photobioreactors used mirrors outside the PBR, while the other one utilized phosphorescence materials inside the PBR. The results of the study suggested that the use of mirrors and phosphorescence materials led to 70% and 30% increase, respectively, in the light intensity without any additional energy consumption. Further, the results revealed that when compared with the base case, the biomass concentration increased by 91% and 24% in PBR with mirrors and phosphorescence materials, respectively. In conclusion, an improvement in PBRs resulted in efficient light to biomass... 

    Holographic diffusers: application for indoor infrared communications

    , Article International Journal of Wireless Information Networks ; Volume 4, Issue 4 , 10-01 , 1997 , pp 259-274 ; 1572-8129 Pakravan, M. R ; Simova, E ; Kavehrad, M ; Sharif University of Technology
    1997
    Abstract
    Diffused infrared transmission is one of thepreferred techniques used in indoor wirelesscommunications. Tolerance to shadowing and a lack ofalignment requirements are among the many advantagesoffered by this technique compared to the line-of-sighttechniques. However, it has its disadvantages, namelyhigh path loss and multipath dispersion. The limitationimposed by eye-safety requirements restricts the transmitted power. Therefore, efficient useof transmitted optical power is the key for practicalbroadband infrared systems. In this paper, we report onusing a holographic diffuser for shaping of infrared radiation pattern in an indoorinfrared transmission system. The holographic diffusershave... 

    Relay selection for multi-source network-coded D2D multicast communications in heterogeneous networks

    , Article Wireless Networks ; Volume 26, Issue 8 , 2020 , Pages 6059-6076 Kalbkhani, H ; Shayesteh, M. G ; Sharif University of Technology
    Springer  2020
    Abstract
    Multicast service is considered as a useful transmission mode for future mobile social services to deliver the traffic to multiple mobile users simultaneously. Device-to-device (D2D) multicast communication enables multiple proximate users to share the contents of their common interests directly. This paper aims to present a relay selection scheme for multi-source network-coded D2D multicast communication underlying heterogeneous cellular network which consists of macrocells and femtocells. We propose two methods for selecting efficient relays from the set of femtocell base stations (FBSs). The first method, named destination-blind relay selection, identifies those idle FBSs that can... 

    A bi-objective model for scheduling of multiple projects under multi-skilled workforce for distributed load energy usage

    , Article Operational Research ; 2021 ; 11092858 (ISSN) Javanmard, S ; Afshar Nadjafi, B ; Taghi Akhavan Niaki, S ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    Abstract
    Satisfying the clients' uncompromising priorities is a challenge for decision makers of organizations that face multiple projects. This paper considers an organization with a multi-skilled workforce working on several predetermined projects under time-of-use energy tariffs where distributed load energy usage is the primary concern of energy suppliers. This paper also considers different time-of-use energy tariffs, which are among the most common strategies to reach a more balanced energy utilization. The problem is stated as a bi-objective mixed-integer programming model containing two conflicting objectives; to minimize the total cost of the multi-skilled workforce and obtain a sustainable... 

    Fog harvesting: combination and comparison of different methods to maximize the collection efficiency

    , Article SN Applied Sciences ; Volume 3, Issue 4 , 2021 ; 25233971 (ISSN) Sharifvaghefi, S ; Kazerooni, H ; Sharif University of Technology
    Springer Nature  2021
    Abstract
    Fog harvesting is an unconventional source of water that can be used in some regions with water scarcity to overcome water shortages. The most commonly used collectors are meshes which have intrinsic limitations, the most important of which are clogging and aerodynamic deviation of droplets around the wires. Here, three techniques are compared and combined to overcome these limitations, i.e., replacing the mesh with an array of vertical wires, addition of a hydrophobic layer to the wires, and forcing the ionized droplets to move toward the wires by applying an electric field. The combination of these techniques was found to result in higher fog harvesting efficiency compared to each...