Sharif Digital Repository

Utilizing the cold energy of liquefied natural gas can reduce the demand of burning fossil fuels for work production and employing refrigeration cycles for seawater desalination. A novel low-temperature cascade power generation cycle combined with a seawater freeze desalination system is proposed to retrieve the cold energy from liquified natural gas. Binary working fluids are utilized to decrease the irreversibilities of the power cycle and enhance the energy recovery efficiency. The effects of the important temperatures of the cycle, pinch temperature of the heat exchangers, number of turbines and their efficiency on the cycle performance are investigated. Optimization of the work... 

The current study presents a numerical investigation on turbulent hydrothermal characteristics in a wavy passage equipped with discontinuous twisted tapes. The working fluid is water and passage walls are kept under constant wall temperature. The effect of Reynolds number (Re = 2500, 4500, 6500, 8500 and 10500), twist angle (TA = 90∘ and 180∘) and inclination angle (IA = 15∘ and 30∘) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF), energy efficiency factor (EEF) and entropy generation rate are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and... 

The optimum design of a high capacity double inlet pulse tube refrigerator based on second law of thermodynamics has been presented in this paper. Second law is applied to calculate the work loss in the regenerator and to optimize the cryocooler performance. To investigate the behavior of the pulse tube refrigerator, mass and energy balance equations are applied to several control volumes of the cryocooler cycle. A complete system of conservation equations is employed to solve the regenerator analytically. The proposed model reports the cooling capacity of 110 W at 80 K cold end temperature at frequency of 50 Hz, orifice conductance of 0.4 and double inlet coefficient of 0.6, with 2.4 kW net... 

Microdialysis-based continuous glucose measuring systems are desirable candidates for accurate and biologically safe monitoring of glucose level in diabetic patients. However, it is necessary to improve these systems by utilizing highly reliable non-enzymatic sensors instead of enzymatic ones, while lowering the size and lessening the dialysis fluid consumption. Our purpose is to design an implantable integrated microfluidic device for regular nonenzymatic microdialysis-based glucose measurement. We report a novel nonenzymatic microfluidic glucose sensor based on Pt-Ni nanoparticles - multiwalled carbon nanotubes/screen-printed carbon electrode (Pt-Ni NPs-MWCNTs/SPE). Devised microfluidic... 

Recent developments of superconductive industry require cryocoolers with cooling power higher than one Watt in the 70-80 K temperature range. High capacity pulse tube cryocoolers assure the cooling power required for operation of superconducting devices. The purpose of this paper is to investigate the influence of the pressure wave generator on high capacity pulse tube cryocooler performance. In this respect the hydrodynamic and thermal behavior of the cryocooler is explained by applying the mass and energy balance equations to different components of the cryocooler cycle. A linear temperature profile is assumed in the regenerator and nodal analysis technique is employed to simulate the tube... 

Recent developments of superconductive industries require cryocoolers with cooling power higher than 1 W in the 70-80 K temperature range. High capacity pulse tube cryocoolers assure the cooling power required for operation of superconducting devices. This paper presents numerical simulation of a high capacity pulse tube cryocooler, intended to provide more than 200 W cooling power at 80 K. In this respect the behavior of the cryocooler is explained by applying the mass and energy balance equations to different components of the cryocooler. Nodal analysis technique is employed to simulate the tube section behavior numerically. To perform the system optimization the influence of key operating... 

One of the methods to increase the hardness of metals, mostly used in aerospace and automobile industries, where light parts with high strength is needed, is precipitation hardening. Nano-precipitates can strongly influence the mechanical properties of materials, especially in a dynamic case. In the present work, attempts have been made so as to make Nano-particles dynamically precipitate in IF steels. Investigating the structure by the means of SEM and AFM resulted in understanding that the precipitates were in nano-size. The micro-hardness of samples was measured as well. © BHR Group 2007 Industrial Processes for Nano and Micro Products  

In this paper, a finite point method is employed to solve the incompressible laminar Stokes flow. A moving least-squares approximation, using linear and quadratic basis functions, in conjunction with a point collocation method, has been utilized to discretize the governing equations. Two examples, including the driven cavity and the fully developed channel flow, are solved showing the accuracy and applicability of the method. In summary, the solutions for the linear basis case exhibit a large sensitivity to the size of the domain of influence of the weighting function, in contrast to the quadratic basis case  

In the present research an experimental investigation is performed to explore the effects of working fluid, heat input, ferrofluid concentration, magnets location, and inclination angle on the thermal performance of an Open Loop Pulsating Heat Pipe (OLPHP). Obtained results show that using ferrofluid can improve the thermal performance and applying a magnetic field on the water based ferrofluid decreases the thermal resistance. It shows that at an inclination angle of the OLPHP to be zero, the thermal performance of the present OLPHP reduces. Best heat transfer capability was achieved at 67.5 degree relative to horizontal axis for all of working fluids. Variation of the magnets location... 

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a... 

The aim of this paper is to design and numerically simulate the mass-transfer compartment and piezoelectric micropump of an implantable integrated microfluidic device for regular microdialysis-based nonenzymatic measurement of glucose level in diabetic patients. The device function is based on the process that the piezoelectric micropump pumps the dialysis fluid into the mass-transfer compartment microchannels, where the interstitial fluid (ISF) glucose diffusion into this dialysis fluid gives it a glucose content, then detected and measured in the sensor section. This diffusion takes place through the semipermeable membranes located in the microchannels at the base of the hollow... 

High capacity pulse tube refrigerator (HCPTR) is a new generation of cryocoolers tailored to provide more than 250 W of cooling power at cryogenic temperatures. The most important characteristics of HCPTR when compared with other types of pulse tube refrigerators are a powerful pressure wave generator, and an accurate design. In this paper the influence of geometrical and operating parameters on the performance of a double inlet pulse tube refrigerator (DIPTR) is studied. The DIPTR is modeled applying the nodal analysis technique, using mass, momentum and energy conservation equations. The model is able to compute instantaneous flow field throughout the system and calculate cooling capacity... 

Three-dimensional cell culture and the forming multicellular aggregates are superior over traditional monolayer approaches due to better mimicking of in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform-sized multicellular aggregates. Microfluidic technology describes a platform of techniques comprising microchannels to manipulate the small number of reagents with unique properties and capabilities suitable for biological studies. The focus of this review is to highlight recent studies of using microfluidics, especially droplet-based types for the formation, culture, and... 

Purpose - This paper sets out to present a fully explicit smoothed particle hydrodynamics (SPH) method to solve non-Newtonian fluid flow problems. Design/methodology/approach - The governing equations are momentum equations along with the continuity equation which are described in a Lagrangian framework. A new treatment similar to that used in Eulerian formulations is applied to viscous terms, which facilitates the implementation of various inelastic non-Newtonian models. This approach utilizes the exact forms of the shear strain rate tensor and its second principal invariant to calculate the shear stress tensor. Three constitutive laws including power-law, Bingham-plastic and... 

Abstract: We propose a novel method for producing unequal sized droplets through breakup of droplets. This method does not have the disadvantages of the available methods and also reduces the dependence of the droplets volume ratio on the inlet velocity of the system by up to 26 percent. The employed method for investigating the proposed system relies on 3D numerical simulation using the VOF algorithm and the results have been obtained with various valve ratios for both the micro- and nanoscale. The results indicate that the droplet length during the breakup process increases linearly with time. The droplet length at the nanoscale is smaller than that at the micro scale. It has been shown... 

Parabolic trough solar collector (PTC) is one of the most mature and widely used type of solar energy harnessing devices. Therefore, investigation of the effect of various operational conditions on the overall efficiency of these devices has been topic of substantial interest in the recent decade. Moreover, utilization of nanoparticles as a useful additive to the working fluid should be examined thoroughly to optimize the collector's outputs. To do so, in the present study, energy and exergy efficiencies of a typical PTC as a function of several involving parameters are numerically calculated. These parameters are nanoparticle volume fraction (from 0 to 5 percent), environment wind speed... 

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Because in such systems the surface structure plays a key role, in this study, we explore the performance of the hierarchical nanostructures. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. We consider a flow between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics method. The size of the nanostructures and the distance between them have been studied to find whether a design with a maximum flow rate exists. The nanostructures have two parts, a bigger part on... 

Access to clean water is one of the challenges of the 21st century. Thus water purification is inevitable. One method of water treatment is purification by magnetic particles in the presence of magnetic field. The contaminants are attached to the magnetic particles and then by applying a magnetic field, magnetic particles and, thus, the pollutants can be collected. For the optimal design of a water treatment system, the effect of important parameters in the design, such as magnetic fields, particle size, and Reynolds number are determined numerically by modeling and simulating the water treatment process. Two methods are used to create the magnetic field: permanent magnet and coils. It is... 

Nanofluids are widely used as the continuous phase during droplet formation in microsystems due to their impressive features such as excellent thermal, magnetic, and interfacial properties. Although it is well-known that nanofluids are susceptible to exhibit non-Newtonian behavior even at a low concentration of nanoparticles, effects of non-Newtonian behavior of nanofluids have not been studied on droplet formation thus far. In this study, oil-in-water droplet formation with a relatively high viscosity ratio of the immiscible phases was studied numerically in a T-junction microchannel. To inspect the non-Newtonian effects of aqueous nanofluids on droplet formation, empirical data on the... 

In this paper, a modified finite-volume Eulerian-Lagrangian localized adjoint method (FVELLAM) extended for convection-diffusion problems with a non-linear flux function is introduced. Tracking schemes are discussed using viscous Burgers' equation. It is shown that in order to have smooth results, only the new time level values should be used in tracking process. Then, the proposed method is employed to study immiscible incompressible two-phase flows in porous media. Various one- and two-dimensional test cases involving internal sources and sinks are solved and accuracy of solution and performance of the method are investigated by comparing the results obtained using FVELLAM with those of...