Materials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Mechanism and Prevention of Scale Formation in Boilers1871072ENH. MulIer-SteinhagenChemical & Petroleum Engineering, University of SurreyJournal Article19700101Nucleate boiling heat transfer coefficients may be strongly reduced by scale formation, even for conditions where the bulk foulant concentration is well below the saturation concentration. Due to the mechanism of micro-layer evaporation, the local concentration at the heat transfer surface can be considerably increased, causing the formation of scale and changes in bubble frequency and bubble departure diameter. The interaction between scale formation and bubble formation is studied with a precision pool boiling test apparatus in conjunction with a microprocessor-controlled camera and video equipment. The effects of EDTA which is commonly used as an antifouling agent in industrial boilers, on saturated pool boiling in the presence of foulants are discussed.https://www.ije.ir/article_71072_b9f9073422c473bdc22df569a0e4450d.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Application of a One-Dimensional Computer Model to Flood Routing in Narrow Rivers91471073ENK.W. TomlisonCivil Engineering, Teesside PolytechnicV. NassehiChemical & Petroleum Engineering, University LoughboroughJournal Article19700101This paper deals with the development of a computer model for flood routing in narrow rivers. Equations describing the propagation of a flood wave in a channel-flood plain system are presented and solved using an implicit finite difference scheme. Particular emphasis has been given to the treatment of the friction term in the governing equation of motion.https://www.ije.ir/article_71073_2f44fbec710debf6daedb2de08d4adc6.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Nonresonant Excitation of the Forced Duffing Equation152471074ENJ. F. GeerSystems Science, Watson School of Engineering, Applied Science and TechnologyJournal Article19700101We investigate the hard nonresonant excitation of the forced Duffing equation with a positive damping parameter E. Using the symbolic manipulation system MACSYMA, a computer algebra system. we derive the two term perturbation expansion by the method of multiple time scales. The resulting approximate solution is valid for small values of the coefficient e As the damping parameter e increases, the accuracy of this solution degrades. In order to obtain an improved approximate solution to the given time dependent initial value problem, a hybrid perturbation-Galerkin method is applied to the perturbation solution. The hybrid method is based on Galerkin s method for determining an approximate solution to a differential equation using the perturbation solutions as trial functions. This hybrid method has the potential of overcoming some of the drawbacks of the perturbation method and the Galerkin method when they are applied separately, while combining some of the good features of both. We compare these two solutions for various values of e and W (the frequency of the external force) and demonstrate the effectiveness of the hybrid method. Both the perturbation and hybrid solutions are also compared to a fourth order Runge- Kutta solution of the Dufting equation. For small values of e, the hybrid solution is very close to the numerical solution for most values of W while the perturbation solution slightly overestimates the numerical solution. For larger values of ethe perturbation solution deviates from the numerical solutton very rapidly while the hybrid method remains close to the numerical model.https://www.ije.ir/article_71074_2a5771c58b1ee230e577c9b5a9138757.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201A Non-Sinusoidal Reference Wave for Pwm Ac Drives253671075ENA. SeifiElecterical Engineering, University of TabrizS. H. HosseiniElecterical Engineering, University of TabrizJournal Article19700101In this paper we propose a suitable reference wave for Pulse Width Modulation (PWM) AC Drives. Staircase reference waves whose levels are calculated to eliminate certain harmonics are studied and a certain staircase reference waveform with L levels is constructed. When L is made very large in limit, this staircase waveform approaches a continuous one which is called Quasine (Quasi + Sine). This approach compared to the classical harmonic elimination method has the advantage that the magnitude of non-triplen harmonics is reduced. A computer program by TURBO PASCAL 6 was developed to enable us to have a comparison between the harmonic contents of output voltage for various reference waveforms.https://www.ije.ir/article_71075_f89b54de029df49a362620b6d84347a2.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Second Moment of Queue Size with Stationary Arrival Processes and Arbitrary Queue Discipline374471076ENRasoul HajiIndustrial Engineering, Sharif University of TechnologyJournal Article19700101In this paper we consider a queuing system in which the service times of customers are independent and identically distributed random variables, the arrival process is stationary and has the property of orderliness, and the queue discipline is arbitrary. For this queuing system we obtain the steady state second moment of the queue size in terms of the stationary waiting time distribution of a similar queuing system in which the queue discipline is first-in-first-out.https://www.ije.ir/article_71076_8f44bc21ffcdacd6cd2b16274511a1c7.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Heat Transfer and Carryover in the Dryout of a Heated Vertical Tube455871077ENA. HeydariMechanical Engineering, Sharif University of TechnologyJournal Article19700101This work concerns dryout experiments in which a tube, initially containing water, filled up or partially filled and at 1,2 or 3 atmosphere pressures, is heated. The initial water column experience three thermal regions. The first region, called the first period, involves heating of the tube until saturation conditions are obtained in the water. Boiling of the water in the tube causes swelling with overflow at the top of the tube. which happens during the second period. The second period ends when the overflow ceases. Hereafter, the liquid content of the tube diminishes because of evaporation, its level falls and exposes the tube wall to vapor, and the temperature of the exposed tube rises. This occurrence is called dryout; the period in which it occurs is called the third period. The experimental results of 44 dryout experiments are the histories of dry-out level collapsed liquid level, and tube wall temperatures. The analytical objective is the prediction of the temperature~ collapsed liquid level and the dryout histories during the three periods. The temperature history of the first period is predicted according to a result of Jaeger [4]. The collapsed liquid level, quench front and the transient height of the two-phase level during the second period are predicted by a model developed by Lahey [6]. Once dryout begins, a drift flux model by Sun et al [10] predicted the hisotory of the dry-out and the collapsed liquid level. The wall temperature above the dryout level is predicted using a model by Yeh et al. [5]. Good agreements between the experimental results and the predictions were found for the first and third periods hut the duration of the second period could not he correctly predicted.https://www.ije.ir/article_71077_842825449ec853d40d0c1edc063b487c.pdfMaterials and Energy Research CenterInternational Journal of Engineering1025-24956119930201Stochastic Synthesis of Drouths for Reservoir Storage Design (RESEARCH NOTE).596371078ENA. R. SoltaniStatistics, Shiraz UniversityE. RaeissiGeomatics Engineering, Shiraz UniversityN. SamaniGeomatics Engineering, Shiraz UniversityJournal Article19700101Time series techniques are applied to Ghara-Aghaj flow records, in order to generate forecast values of the mean monthly river flows. The study of data and its correlogram shows the effect of seasonality and provide no evidence of trend. The autoregressive models of order one and two (AR1, AR2), moving average model of order one and ARMA (1,1) model are fitted to the stationary series, where the AR2 model yields results which are statistically compatible with the past records. For a better understanding of the behavior the spectral analyses of the data and exhaustive statistical tests are also provided. Synthetic data generated by AR2 model together with historical data are then used to obtain reservoir storage for varying design periods, and draft rates. For this, the Stall's method which is a more sophisticated form of mass curve is employed. Results are given as two design curves.https://www.ije.ir/article_71078_2a964dcefc84b05a0368f8749617389b.pdf