Sharif Digital Repository

Electrospray cooling is experimentally examined for high volumetric flow rates (80 mL/h) stabilized by a novel hemispherical nozzle. Stability of the Taylor cone-jet mode of this nozzle is increased by interaction of the discharging liquid with the outer wall of a hemispherical cap, installed at the tip of a simple nozzle. The liquid can then be discharged at high flow rates at the same mode. The liquid is ethanol and the test surface temperature as well as the cooling heat flux are measured. The results of the surface temperature, the heat flux and the heat transfer coefficient are compared between the three cases. The first and main case is the electrospray using the novel hemispherical... 

In this study, the influence of volumetric flow rate and inclination angle of air jet is evaluated on the performance of a Saccardo ventilation system in a straight rectangular tunnel in case of fire. Simultaneous effects of volumetric flow rate and inclination angle of jet exiting the Saccardo nozzle on the behavior of smoke plume is considered by studying the structure of velocity profile before the fire source. It is found that this factor has a remarkable influence on the behavior of smoke plume and therefore, on the temperatures experienced near the fire. Besides, the influence of tunnel slope on the performance of the Saccardo system to sweep the plume is investigated. It is shown that... 

It is widely accepted that under reservoir conditions there exists some degree of block to block interaction that may result in capillary continuity. The formation of liquid bridges causing capillary continuity between blocks will significantly affect ultimate recovery. In this work a mechanistic model with original thought from hydrology for a given steady feeding volumetric flow rate from an upper block (under both gravity and matrix capillary pressure effects) is developed which considers the formation, growth and detachment of pendant liquid droplets perpendicular to the horizontal fracture (assuming to be smooth and parallel walled) between blocks. The length of detached liquid droplet... 

Spray cooling characteristics of a flow blurring injector are investigated experimentally. Variations of the flow rates and the distance from the nozzle to the test surface are examined in terms of the cooling heat flux. The liquid flow rate is varied from 200 to 1200 mL/h. The effect of the air flow rate from 6 to 18 L/min is also studied and heat transfer coefficients are obtained. Depending on different effective parameters, the maximum cooling heat flux is measured between 61 and 193 W/cm2. Owing to formation of fine droplets at higher air flow rates, the maximum cooling heat flux is improved by about 60%. The present data is generated for a flow blurring type of injector to have four... 

In this study the effects of melt temperature and flow rate of cooling gas on the characteristics of silver nanoparticles have been studied. Transmission electron microscopy and dynamic light scattering techniques have been employed to monitor morphology and particle size of the product. Measurements reveal that higher melt temperatures and higher cooling gas flow rates can decrease particle size. Silver nanoparticles with an average particle size of 35 nm and specific surface of 18.489 m2/g have been obtained at a melt temperature of 1,130 °C with argon flow rate of 20 liters per minute  

Relative permeability is used to describe quantitatively simultaneous transport of two or more immiscible phases through a porous medium. Accurate estimates of relative permeability curves depend on the method of estimation and are desired to obtain reliable predictions of flow behavior. To compare the accuracy of relative permeability estimation of implicit and explicit methods, primary drainage experiments of water by a sample oil fluid have been studied. The experiments performed on a horizontal glass type micromodel as a model of porous media sample under different fixed high flow rates condition to negate capillary pressure effects. The relative permeability of oil and water phases is... 

Reduction in ship resistance, in order to decrease fuel consumption and also achieve higher speeds, has been the topic of major research over the last three decades. One of the most attractive ideas in this field is micro bubble drag reduction, which attempts to obtain optimum injection flow rate based on ship specifications. The model test results of a 70 cm catamaran model was used to quantify the effect of air injection rate on drag reduction, and to estimate a simple formulation for calculating an efficient injection rate by considering the main parameters of the ship, such as: length, width and speed. The test results show that excessive air injection decreases the drag reduction... 

This study attempts to investigate a new way for cooling PV cell using natural vapor as coolant. The performance of solar cell was examined on simulated sunlight. The natural vapor encountered backside of PV cell vertically in various distribution and different mass flow rates. Also, the effect of natural vapor temperature in cooling performance was analyzed. Results indicated that the temperature of PV cell drops significantly with increasing natural vapor mass flow rate. In detail, the PV cell temperature decreased about 7 to 16°C when flow rate reaches 1.6 to 5grmin-1. It causes increasing electrical efficiency about 12.12% to 22.9%. The best performance of PV cell can be achieved at high... 

Lorentz force is the pumping basis of many electromagnetic micropumps used in lab-on-a-chip. In this paper a novel reciprocating single-chamber micropump is proposed, in which the actuation technique is based on Lorentz force acting on an array of microwires attached on a membrane surface. An alternating current is applied through the microwires in the presence of a magnetic field. The resultant force causes the membrane to oscillate and pushes the fluid to flow through microchannel using a ball-valve. The pump chamber (3 mm depth) was fabricated on a Polymethylmethacrylate (PMMA) substrate using laser engraving technique. The chamber was covered by a 60 μm thick hyper-elastic latex rubber... 

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... 

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... 

A reciprocating single-chamber micropump is designed and experimentally tested. The actuation technique of the pump is based on Lorentz force acting on an array of low-weight microwires placed on a flexible membrane surface. A square-wave electric current (5.6 and 7.8 A) with a low-frequency range (5.6 to 7.6 Hz) is applied through the microwires in the presence of a perpendicular magnetic field (0.08 to 0.09 T). The resultant oscillating Lorentz force causes the membrane to oscillate with the same frequency, and pushes the fluid to flow toward the outlet using a high-efficiency ball-valve. The micropump has exhibited a maximum efficiency of 2.03% with a flow rate as high as 490 μl/s and... 

This Paper presents simulation of Electroosmotic phenomenon in a capillary using an extended hybrid finite-volume-element method. Most of the last electroosmotic phenomenon studies in microchannels do not take into consideration the effect of reservoirs and pressure drops occurred at the inlet and outlet of the microchannel. This neglect may lead to a few drawbacks. For example, the incorrect pressure drops can significantly alter the flow patterns and mass flow rates in microchannels. As a remedy the use of reservoirs at the two ends of a microchannel has been recently practiced as a novel strategy to overcome this drawback. However, this remedy needs careful attention because the resulting... 

In a vortex engine, oxidizer issues tangentially at the end of the chamber, consequently a cool vortex flows toward the head, being mixed with fuel, a secondary vortex of combustible reactants swirls coaxial with the first vortex to the nozzle exit. Therefore radiation heat transfer from flame to the chamber wall causes to increase wall temperature; meanwhile highly convective coolant flow of outer vortex reduces the wall temperature. In this paper the rate of total heat transfer and radiative heat are measured experimentally and convective cooling is calculated as the difference between the above mentioned quantities. The rate of heat transfer to the chamber wall is calculated using... 

A comprehensive model for pervaporation in thin membrane channels was developed to study the effect of changing temperature and concentration on mass flux. This model consists of momentum, energy and species mass balances along and across the membrane in the flow channel. A computational fluid dynamics (CFD) code was written in C++ programming language to solve the coupled non-linear transport equations in the channel by finite volume method. The Semi-Implicit Pressure Link Equation (SIMPLE) CFD algorithm is used to modify the dependent variables in each of the iterations. The effect of variation of temperature and concentration on transport and thermodynamic properties were considered by... 

Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex engine are compared with a similar axial flow type engine. A detector sensitive to emission from C2* excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2* emission from flame. Mixtures of Propane and Butane with air enriched by oxygen are used as fuel and oxidizer. The effects of equivalence ratio and oxidizer mass flow rate... 

Valveless piezoelectric micropumps are in wide practical use due to their ability to conduct particles with absence of interior moving mechanical parts. The objective of this paper is to obtain the fluid flow response to actuation frequency of a passive diffuser valve under harmonic pressures. In this regards a 2D model of a micropump valves and chambers is analyzed. The analysis is performed for 10Kpa back pressure on micropump chamber and actuation frequencies within the range of 1 Hz to 10 KHz. Results show the highest velocity in the direction of diffuser axis occurs at the narrow diffuser neck while flow direction reverses every half period. For low frequencies, a parabolic velocity... 

Relationship between respiratory sounds and flow has always been of interest for researchers and physicians. However, the flow-sound relationship at very low flow rate has been questionable because breath sounds must exceed a minimum flow in order to be audible and different from the background noise. This study aimed to find the minimum critical flow rates for respiratory sounds to be audible and different from background noise. Tracheal and lung sound signals of healthy subjects in two groups of adults (12 subjects) and children (9 subjects) were studied. The values of minimum critical flow were determined comparing the spectrogram of the respiratory sounds at very low flow with that of...