فصلنامه مهندسی معدن
پیاپی 25 (زمستان 1933)

Moving a train in tunnel, due to restrictions on the walls, causing the air to moving forward. This phenomenon is called the piston effect. Piston effect creates piston wind on exit corridor of subway stations which may cause inconvenience to passengers particularly during the cold seasons of year. Most of the calculations carried out on the piston wind at exit corridor of subway stations are based on three-dimensional modelling and dynamic mesh method using ANSYS and FLUENT software. Despite having high precision, these methods have disadvantages too, like heavy mathematical computation and necessity of using super computers which limits applicability of this method. In this study new method based on one dimensional equations of fluid motions using MATLAB software has been developed. Validation of this model has been examined based on data from Taleghani Metro Station in Tehran. Comparison of real data with model calculation approves high accuracy of proposed model.

Backbreak and subject of reduction in the bench dip respect to the blasthole dip have the important role on the stability and design of remained bench wall after blasting. Effects of parameters of blastholes and charging due to surface mines including: blasthole diameter, blastholes spacing, burden, stemming, blasthole length, blasthole dip, under drilling, charge quantity in each delay and powder factor on the backbreak distance and varying the reduction of bench dip angle (β) respect to the blastholes dip angle (α) have been investigated by various blasting operations in Eyvughly gypsum mine, Rashakan limestone mine, Sungun copper mine and Gholghohar iron mine in this research. Each parameter of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip increases with an increase of blasthole diameter, blastholes spacing, burden, stemming and blasthole length. The parameters of Lb and () show better correlations with the blasthole diameter and blastholes spacing (S). The parameters of Lb and dont show correlation with the three parameters of under drilling (U), charge quantity in each delay and powder factor. The multivariable relationships between parameters of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip () with the combination of five blasthole parameters including: diameter, blastholes spacing (S), burden (B), stemming and blasthole length were obtained by statistic analysis using SPSS program with correlation coefficient (R) of 0.948 and 0.960 respectively. The amount of backbreak distance (Lb) and varying the reduction of bench dip respect to the blastholes dip can be predicted and controlled using the obtained multivariable relationships. The parameters of blastholes have important effects on the backbreak and dips of mine benches, and proposed relationships can be useful for stability analysis and design of mine benches due to the blasting operations.

In this paper, size distribution of nano-microbubbles produced by a nano-micro bubble generator was measured by the reliable and fast method of laser diffraction. The effects of key parameters including time, type and concentration of frother, gas flow rate and gas type on size distribution of nano-microbubbles were investigated. Measurement results of nano-microbubble size as a function of time showed that simultaneously with the reduction of the absolute zeta potential of nano-microbubbles and the amount of dissolved oxygen in the solution, size of nano-microbubbles was decreased. Increased concentration of frother as well as affecting conventional sized bubbles reduced the average size of nano-microbubbles. Results also showed that the nanobubbles produced with Aerofroth65 were smaller than those formed with MIBC and Pine oil. This is because surface tension reduction by Aerofroth65 is more significant than by MIBC and Pine oil. Increased aeration rate (air and oxygen) from 0.1 to 0.3 l min-1, reduced the average size of nano-microbubbles. Nano-microbubbles generated in the presence of oxygen had smaller average size relative to air nano-microbubbles because of higher dissolution of oxygen in water in comparison with air and also the higher absolute value of surface zeta potential.

blasting operations with regard to influencing other parts of the mineral extractionprocess (loading, hauling and crushing) is of major importance. In this operation theassessment criteria in addition to achieving the desired fragmentation is reduction ofundesirable phenomena such as back-break and fly-rock. several parameters such as geometric properties,rock mass properties and characteristics of explosives affect blasting pattern.As the problem is multi criteria, utilization of useful methods that satisfyoperational objectives (desired fragmentation, reduction of back-break and fly-rock)is necessary.In this research in which Gol-E-Gohar Iron ore mine is considered as a case study,in the first with using multiple attribute decision making model (TOPSIS), efficient pattern from the patterns carried out in the mine based on the objectives is selected.in the second part of the research has been tried to improve the values of these objectives using goal programming(GP) model.