Sharif Digital Repository

Due to its unique properties, helium has extensive applications in various fields such as medicine, life sciences, electronic industries, welding, meteorology, and the industries which require low-temperature cooling. Also, designing the cryogenic distillation columns is one of the complex aspects of these plants. In the present study, the distillation column of a helium extraction plant from natural gas has been simulated by means of theta method of convergence. The required thermodynamic properties were determined from the Enhanced Predictive Peng-Robinson (E-PPR 78) equation of state, which has high accuracy in predicting the thermodynamic properties of natural gas componens. The... 

Access to potable water with standard quality is an inevitable component of human’s lives. Freeze desalination, by consuming lower energy compared to other techniques, relies on the exertion of a cold source which is then accompanied by simultaneous rejection of impurities from water. Regarding this, a numerical study on freeze desalination a hollow cylinder is carried out to determine the effects of the design variables such as heat flux, hydraulic diameter, initial salt concentration, and freezing time on the ice mass, ice salinity, ice generation speed, and Nusselt number on a cold surface of the inner tube. Results show that increasing the value of heat flux from -250 W/m^2 to -1000... 

Spiral-wound heat exchangers have special applications in industry due to their high efficiency, especially in low temperature ranges (cryogenic) such as gas liquefaction cycles; However, due to drastic changes in properties, the mechanism of flow and heat transfer in this type of exchangers has not been fully studied yet. Therefore, accurate modeling of fluid flow on both sides of tubes and shells as well as heat transfer between them can be very important in analyzing and designing this type of exchangers and optimizing them to increase the efficiency of the exchanger and the cycle. In this study, the focus is on the flow and heat transfer of supercritical fluid inside helical tubes of... 

Cryogenic distillation of air is the only method of large-scale production of high-purity oxygen and nitrogen. The falling film column, due to its lower pressure drop and higher heat transfer, is gaining attention. In this method, the heat and mass transfer take place simultaneously on a vertical wall. The present study aims at providing a numerical framework based on a finite volume approach to simulate the falling film distillation column, focusing on the high-pressure column of an air separation unit. Due to the heat integration, filmwise condensation is expected to happen on the surface of the column. An innovative sub-model is developed to evaluate condensation heat transfer... 

Heat exchangers are one of the most important components used in liquefaction cycles and overall efficiency of the cycle mainly depends on the heat exchangers effectiveness. It has been shown that the effectiveness of these equipments should be high enough to be able to liquefy a gas. Spiral heat exchangers are used frequently in cryogenic industry and specially in Helium liquefaction industry due to their specific characteristics, however according to literature review it turns out that little study is done in the field of simulation and geometrical parameter investigation of these kind of heat exchangers, so in this study the design and simulation of these cryogenics heat exchangers are... 

Inhencemant of automobile radiator heat performance is the purpose of this study. Radiator fin shape, coolant fluid properties and influence of nanofluid studied in this research. Plain fin, louvered fin and vortex generator fin is choosen and design. With flow simulation influence of fin shape on heat performance is studied. After that, with considering radiator coolant fluid, the effect of antifreezing on fin heat transfer is evaluated. Then by addin nanoparticles to water and antifreezing solution, effect of nanofluid on heat transfer is evaluated. Results show that with increasing the air velocity for all geometries in the study , heat transfer and pressure drop is increased. But heat... 

Cryogenic temperature is below than 123 Kelvin and any physical study that occurs below this temperature is Cryogenic science. Cryogenic has varaiety of application in medical, industry, food, oil and gas etc. Based on this paper and its relavant source spiral wound HE is one of the most optimum HE for cryogenic application specially for helium liquification cycle. In order to liquefy helium in helium cycle efficiency of spiral wound HE shall be over than 85 percent. For this reason and special fluid behavour in low temperature considering property variation, heat in leak and axial conduction is vital for calculating efficiency in cryogenic temperature of helium liquification cycle. In this... 

Freeze desalination as a water refining method has attracted a lot of attention due to its potential in lowering process energy consumption compared to other methods. This method is based on the fact that the dissolved salt is drained from the saline water during its freezing. The current study conducts a parametric study on freezing saline water in a cylindrical container to investigate the impact of geometric and functional factors affecting the desalination quality. This has been done by examining the aforesaid factors in the form of dimensionless parameters such as thermal Grashof number, solutal Grashof number, and Jacob number. In addition, in order to improve the desalination, a novel... 

As today's tremendous advance occurred in biotechnology and nanotechnology, the microfluidic devices made a new success that was not possible with the traditional equipments. It was useful in such a way that by using a microliter volume of that fluid, we could have the ability to use it in biologics, medicine, aerospace, cooling electronic systems and medical discovery. One of the main component of fluidic microsystems are micropumps in which they divide into two types. Reciprocating micropumps have been worked by stimulating electromagnetic micropumps which is based on Lorentz law. In this project, we try to investigate the impact of effective parameters in the movement of the mercury mass.... 

Cryogenic is the study of physical phenomena at temperatures below 123 Kelvin. One of the applications of cryogenic science is the liquefaction of gases. In the liquefaction cycles of gases, such as helium liquefaction, fluidization occurs in the pressure reducing valve but temperature of the gas should be greatly reduced before it enters the pressure reducing valve. For this purpose, high-performance heat exchangers should be used. Spiral Wound is one of the heat exchangers that has ability to achieve over 90% efficiency due to its structure. Researchs in the field of design and simulation of spiral heat exchangers are limited and are done with a lot of simple assumptions such as constant... 

Helium is known as a strategic material due to its unique properties and applications in the development of advanced industries. Currently, natural gas is the only source from which helium can be produced economically. The United States, Qatar, Algeria, and Russia have the largest share of helium production, respectively. In this research, the process of helium extraction from natural gas and its liquefaction, independent of LNG production based on helium in South Pars gas of Iran, which is the largest helium reservoir in the world, were designed and simulated.In the helium liquefaction section, the speed and accuracy of the process simulation were improved by developing a home code based on... 

This research aims to develop a numerical tool for design and performance evaluation of spiral wound heat exchanger (SWHE) in the cryogenic temperature range. This type of heat exchangers are used in gas liquefaction cycles due to their compact structure and ability to achieve high effectiveness values. High sensitivity of liquefaction cycles yield to heat exchanger effectiveness, effect of some physical phenomena in cryogenic temperature range, and complicated shell-side flow structure of SWHEs, turns the design and performance evaluation of cryogenic SWHEs into a challenging issue. Consequently, first of all, the geometrical parameters of SWHE were introduced and made dimensionless. In... 

Correct and timely extraction of smoke is very important in fire incidents. Statistics show that more than seventy percent of fire casualties are caused by breathing toxic gases. One of the destructive factors in the operation of the smoke exhaust system is the plugholing phenomenon. In this phenomenon, due to the improper design of the ventilation system, the exhaust vent extracts air instead of smoke. The plugholing phenomenon causes the accumulation of smoke in the structure, therefore it is essential to know this phenomenon to prevent it. In this research, the plugholing phenomenon in the smoke extraction process has been investigated by the numerical simulation method. To investigate... 

Optimization of Plate-Fin Heat Exchnagers, which have various applications in different cryogenic processes nowadays, can have a significant role in improving process efficiency as well as decreasing their capital and operationl costs. In this study, is introduced a procedure to optimize the performance of multi-stream multi-phase Plate-Fin Heat Exchangers, implementing Genetic Algorithm optimization method. In this study, the simulation of the multi-stream multi-phase Plate-Fin Heat Exchanger is carried out by Aspen EDR, a leading software in simulation and design of different types of heat exchangers. The software is then integrated to external software to automate the simulation... 

Cryogenics is the study of materials and their behavior at temperatures below -150 degrees Celsius, where gases can liquefy or even solidify. Cryogenics investigates the properties of matter at these cold temperatures, revealing unique physical properties and behaviors that cannot be observed under normal conditions. It is not easy to reach this temperature range and special methods are used to achieve it. The Gifford-McMahon (GM) cycle is one of the most famous thermodynamic cycles for achieving ultra-cold temperatures. When there are limitations for supercooling in terms of space and dimensions, the use of this cycle is more considered. One of the most important parts of this cycle is the... 

Gas liquefication in low temperatures is one of the most challenging fields in engineering due to complexity of its thermodynamic analisys and fabrication of equipments. Heat Exchangers are one of the most important equipments in these prosseces. High prices of Heat Exchangers in these facilities makes their Optimal and cost effective design, of crucial importance. In this thesis three dimensional model of a Plate Fin Heat Exchanger is thoroughly investigated. Fistly, by means of Aspen Heat Exchanger design Software a counter flow Heat Exchanger is designed. This HX is to be placed in Collins cycle, so, working fluid in both hot and cold streams is Helium Gas. The HX then by means of ANSYS... 

Gas liquefaction is one of the main applications of Cryogenics science. Due to the unique properties of Helium, it is a strategic product in the world. Therefore, appropriate and applicable analysis should be used to investigate and optimize the Helium liquefaction cycles. In the current study, the goal is to find the optimal point with the help of energy and exergy analysis based on economic criterion, for the various parameters of Collins’ cycle. In order to simulate the cycle, a computer code is developed. First, sensitivity analysis of different parameters affecting the exergy efficiency and liquid fraction of the cycle has been done. Then, Artificial Neural Network and Genetic Algorithm... 

Many studies have been conducted in plate heat exchangers. However, some effective parameters on the performance have been less considered. It has been demonstrated that heat exchanger performance increases with more uniform flow distribution. It is possible to make the flow distribution more uniform by installing a baffle inside the header. The ‘gap’ or the distance between this baffle and the inlet is one of the important parameters in determining performance but is has been mostly overlooked by previous studies. This study investigates the effects of inlet baffle place on heat exchanger performance. Another important factor is the header geometry. Elongation and reduction in header... 

Smoke must be exhausted, as the first action, in probable fire in subways, underground transportation systems and mines in order to survive people exposed to it. To achieving this purpose, the axial fan should be used to move the smoke to the exit lines. These fans should be had same performances in suction and discharge directions (main and reverse directions). This means flow rate should be the same at main and reverse directions. Therefore, fully reversible axial flow fans should be used in emergency ventilations. The fully reversible axial flow fans have same efficiencies in suction and discharge directions. The symmetric profiles should be used in manufacturing of the blades of these... 

In the present study, performance of a novel fan namely bladeless fan has been evaluated. The aerodynamic and aeroacoustic performances are studied by using 3D simulation of this fan. Mass conservation equation, momentum conservation equations and noise equations of FfowcsWilliams-Hawkings numerically solved to investigate performance of this fan. Firstly, fan cross section profile was designed by Eppler airfoil 473 instead of the prior profile as a modification then effect of different geometrical parameters on the performance is examined. These parameters are height of cross section, angle of output flow with respect to fan axis, thickness of output airflow, hydraulic diameter and aspect...