Sharif Digital Repository

ABSTRACT: Experimental study of the performance of a gas centrifuge can be appreciably simplified if instead of isotopic mixtures, a binary mixture of gases with large molecular weight difference is used. The current study undertook this approach by injecting a 53%–47% (w/w) mixture of “Freon12-Freon22” into a gas centrifuge. The two parameters, whose investigation was the objective of the current study were: the feed flow rate (F), and the clearance between tail scoop and the rotor wall (d). The results demonstrated that changing the scoop-wall clearance has the most significant effect on the cut (θ), so that by fixing “d”, “θ” becomes nearly invariant. The head separation factor (α)... 

Particle dispersion in the vortex flow has been one of the most interesting subjects in recent years. Bidirectional vortex flow field is an industrial sample of rotating flow which is used to obtain advantages of better mixing and combustion. In this work penetration and dispersion quality of particles which are entering from various positions on the vortex engine walls have been numerically predicted. Head side, end side, and sidewall are considered as the entering positions. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, and density of entering particles are assumed to be known. If the particle length scale is considered not to be comparable with the... 

Development of design and production technology of centrifugal pumps for achieving better performance and less energy consumption in these devices has increasingly been taken into consideration. This is due to the fact that centrifugal pumps have an important contribution in industrial applications and energy consumption around the world. Accordingly, the international standards of centrifugal pumps, urge more precise analysis systems for obtaining the performance curves of these pumps. For this reason, a complete, precise and real-time monitoring and performance analysis system for centrifugal pumps is introduced in this paper. The pump characteristics are measured by precise measuring... 

During recent years centrifugal-based microfluidic devices known as Lab-on-a-CD have attracted a lot of attentions. Applications of these CD-based platforms are ubiquitous in numerous biological analyses and chemical syntheses. Mixing of different species in microscale is one of the essential operations in biochemical applications where this seemingly simple task remains a major obstruction. Application of centrifugal force, however, may significantly improve the flow agitation and mixing, especially when it is combined with the Coriolis force which acts perpendicular to centrifugal force. In this study, mixing process in minichambers located on a rotating platform under a periodic... 

The Lab On a CD (LOCD), also known as Centrifugal Microfluidics, has evolved into a sophisticated platform for performing biomedical assays due to its marvelous miniaturization and accurate simulation of biological reactions. Among the numerous applications of the LOCD is fluid mixing. In this paper a centrifugal, serpentine micromixer is simulated and reformed toward better mixing performance. The micromixer was chosen to be curved as a curved design was found to be thrice as functional and compact as a rectilinear design, mixing-wise. The two angular velocity and opening radius parameters were originally hypothesized to affect mixing performance. Effect of angular velocity was studied over... 

In this paper, a method has been presented to study the free vibration of a rotating shell consisting of p coupled conical shells. This method considers the Coriolis and centrifugal forces as well as the initial hoop tension resulting from rotation of the shell. Matrix transform and power series methods were employed to solve the equations. The advantage of using the matrix transform approach is that the dimension of the coefficient matrix, which is finally constructed to obtain the natural frequencies of a shell made of p cones, remains 8×8. The obtained results were validated with the help of existing special cases of the studied problem reported in the literature, and by means of FEM... 

Design of centrifugal compressors can be accomplished using methods provided in text books and open literature. In this general approach, after determination of dimensions in meridional plane, blade profiles are designed using aerodynamic methods. Then, some blades are trimmed at the beginning to avoid inlet blockage. But there is no clear guidance on how this trimming must be performed. With this widely implemented method, splitter blades have the same profile as main ones. In this research, blade profiles and dimensions of the compressor impeller are not changed while the effect of changes in the position and angle of splitters leading edge are investigated. An optimization scheme is... 

In this research, multi-level optimization of the profile of the splitter blades of a turbocharger compressor is performed using genetic algorithm in order to improve its performance. Successive corrections of the profile at hub, mid-span, and shroud of the splitter blades, with the objective of decreasing the incidence losses at the leading edge and adjustment of the blade loading at the shroud, result in an impeller having improved splitter blades. The impeller flow field analysis shows that the optimization has been successful in reducing the flow leakage at the shroud region as well as the losses in the leading edge region. Although numerical simulations predict a decrease by 0.5% in... 

A fully coupled numerical analysis using Biot's theory with u-p formulation considering variable permeability during liquefaction is used in this study to simulate liquefaction induced lateral spreading phenomenon. A centrifuge test performed on liquefiable soil at Rensselaer Polytechnic Institute is simulated using the developed model. The numerical results are in good agreement with experimental observations. A number of numerical simulations under different geometric, site-specific, and ground acceleration parameters have been carried out in the course of this study. Based on the statistical analysis conducted on the results of 31 different models, a new relation is proposed for... 

Diabetes mellitus is a global endemic with a rapidly increasing prevalence in both developing and developed countries. Recently, hemoglobin A1c has been recommended by the American Diabetes Associations as a possible substitute for fasting blood glucose for the diagnosis of diabetes, because it is an indicator of long-term glycemic control. Also, centrifugal microfluidic systems have good potential for use in the point of care testing systems. In this study, a centrifugal microfluidic disc was designed and manufactured to measure hemoglobin A1c in whole blood using an immunoturbidimetry based method. Also, a new passive valve, named septum valve, was presented to precisely control the entry... 

Aim: The aim of this study was to assess the relationship between microRNAs and viral and immunological markers in HIV-1 infection. Materials & methods: The expression level of miRNAs was evaluated in 60 HIV-1 patients and 20 healthy controls using real-time PCR assays. Results: The results showed that among all miRNAs, miR-29 and miR-150 were significantly downregulated in HIV-1 patients compared with healthy controls, while miR-155 and miR-223 were significantly upregulated compared with healthy controls (p < 0.001 for all comparisons). Conclusion: The mentioned miRNAs seem to influence the clinical progression of HIV-1 infection in naive patients. Moreover, determining the profiles of... 

Microfluidics has been becoming more and more popular over last two decades. The reason for this, is inherent features of microfluidics including low consumption of samples and reagents, high sensitivity, short analysis time, and low cost. As well as, centrifugal microfluidics as a subset of microfluidics has been able to prove itself as a helpful tool in analytic assays. The main application of centrifugal microfluidic devices is being used in point-of-care testing systems. Herein, we presented a microfluidic disc for measuring hemoglobin(Hb) concentration in the EDTA-anticoagulated venous blood using cyanmethemoglobin method. In this experiment, at first a hand-made standard solution was... 

This paper presents a comprehensive 3D numerical simulation of reacting flows in micro scale dimension through centrifugal, or Lab-On-a-CD (LOCD), and pressure-driven, or Lab-On-a-Chip (LOC) devices. Three different serpentine channel configurations (rectangular, triangular and sinusoidal) are investigated. In these configurations, two chemical species enter from two inlets and according to an irreversible chemical reaction, start yielding other species. Both Newtonian and generalized Newtonian fluids are considered in the simulations and the results are compared for both LOC and LOCD devices. Besides, the effects of different parameters such as the aspect ratio of channels’ cross section,... 

Inertial particle focusing as a powerful passive method is widely used in diagnostic test devices. It is common to use a curved channel in this approach to achieve particle focusing through balancing of the secondary flow drag force and the inertial lift force. Here, we present a focusing device on a disk based on the interaction of secondary flow drag force, inertial lift force, and centrifugal forces to focus particles. By choosing a channel whose cross section has a low aspect ratio, the mixing effect of the secondary flow becomes negligible. To calculate inertial lift force, which is exerted on the particle from the fluid, the interaction between the fluid and particle is investigated... 

A rotating closed loop pulsating heat pipe (RCLPHP) was experimentally investigated as a passive heat sink for rotary equipment cooling. The effects of heat input, rotational speed, filling ratio, and working fluid on the thermal resistance of RCLPHP were studied. Pure water and ethanol were used as working fluids with filling ratios of 30%, 50%, and 70% by volume, and the RCLPHP was tested at four rotational speeds: 200, 400, 600, and 800 rpm. The results showed that the best filling ratio for both water and ethanol is 50% and proved that the RCLPHP is able to work efficiently in a wide range of rotational speed. Moreover, it was observed that at the optimum filling ratio for ethanol and... 

In this paper, vibration analysis of rotating laminated composite cylindrical shells using a combination of the layerwise theory and wave propagation approach is investigated. This combination enables us to study all the conventional boundary conditions in our analysis. Results obtained have been compared with those available in the literature and a good agreement has been observed. In contrast to the Equivalent Single Layer theories (ESL), the layerwise theory is constructed on the basis ofC°- continuity through the laminate thickness. For the surface of the shell, a displacement field based on the wave propagation approach is proposed. The effect of Coriolis and centrifugal accelerations... 

Dynamic compaction (DC) is a common soil improvement technique, used extensively worldwide. DC treatment design is usually based upon empirical relations and past experience. The common problem with all empirical relations is oversimplification of the mechanisms, and the use of parameters that are highly dependent on engineering judgement. In this paper, a developed finite-element code is used for modelling the impact behaviour of dry and moist sandy soil. The code is verified against the results of centrifuge tests. Then the validity of the popular Menard empirical relation for determination of improvement depth in DC design is investigated. The effect of initial relative density, tamper... 

Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance. Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow field is simulated using Reynolds Stress Transport Model (RSM). The... 

Dynamic compaction (DC) is a popular soil improvement method that is extensively used worldwide. DC treatment design is usually carried out based on past experiences and empirical relations. To establish a rational design approach, all important factors affecting the DC process should be taken into account. In this paper, a finite element code is developed for modeling the impact behavior of dry and moist granular soils. The code is verified with the results of some centrifuge tests. Several analyses were conducted in order to study the effects of energy/momentum per drop, tamper base radius, and number of drops on compaction degree, compacted depth, and extension of the improved zone in the... 

The liquefaction phenomenon is usually accompanied by a large amount of settlement. Based on the observations made in past earthquakes, ground improvement by densification is one of the most useful approaches to reduce the liquefaction-induced settlement. Currently, there is no analytical solution for evaluation of the amount of settlement and tilting of footings that are constructed on densified ground surrounded by liquefiable soil. A number of factors, such as underlying soil properties, dimensions of the footing and earthquake loading characteristics, cause the problem to become complicated. In this paper, the dynamic response of shallow foundations on both liquefiable and...