فهرست مطالب محمدرضا جعفری نصر

The removal of carbon dioxide due to environmental problems is still of great interest to researchers. In this study, simulation of carbon dioxide removal by absorption four amine base solvents including; monoethanolamine (MEA), diethanolamine (DEA), methyl diethanolamine (MDEA) and aminomethylpropanol (AMP) in a polypropylene hollow fiber membrane reactor is investigated. A comparative study for solvents by multi-physics Comsol software based on fluid dynamics (CFD) calculations is performed. The results showed that the best adsorption rate was obtained by MEA solvent with 88% CO2 absorption rate. The absorption of carbon dioxide by each amine-based solvents in the references is investigated separately. The simulation results are validated separately for each solvent. An acceptable consistency is obtaned between the present simulation data and the results of others given refrences. Finally, as a result of this study, it is shown that the present simulation is powerfully provided suitable and alternative data for carbon dioxide removal by each four traditional amine-based solvents in compare with the available experimental data.

Bioheat transfer plays an important role in analyzing living systems due to its ability to diagnose and treat the disease. Recently, CFD has been increasingly used in biomedical researches of coronary artery disease because of its high hardware and software performance that makes it possible to identify and treat the risk factors for coronary artery disease progression. The purpose of this paper was to investigate blood flow and heat transfer in normal state and in several cases of plaque with a real geometric model of a vessel in an artery by using a commercial Software. Blood is considered as a non-Newtonian and non-compressible fluid and viscosity is modeled using Carreau equations. Unlike many previous studies, the inlet velocity is considered to be transient (pulsatile) and heat transfer has been investigated with the assumptions of constant blood inlet temperature and constant vessels wall temperature and the outlet wall heat transfer has been calculated. A real geometric model in different plaque progressions has been studied as well. Plaque progression in the artery, increases the wall pressure and shear stress, which is very dangerous in cases of severe blockage and may cause high risk of rupture. Increased plaque also reduces the blood heat transfer to the artery’s walls. The results show that there is a change between 10-70% in the dynamic parameters after clogging, but there is no significant change in the outlet temperature.

In this study, the process of single stage mixed natural gas liquefaction is reviewed, then process energy optimization and economic analysis are followed. The effect of specific energy consumption optimization on the costs of cooling equipment was investigated. The basis of this study is PRICO process and due to some limitations and concerns for Iran, it is tried to develop a new modified process so that the available process restrictions would expel and finally the recommended process optimized by genetic algorithm. Mole flow of refrigerant, low pressure and high pressure of refrigerant in the cycle, are the most important operational parameters that were selected by sensitivity analysis. The total energy consumption of compressors reached 1413.8 kW and decreased by 11 percent. Results showed optimization of the specific energy consumption increases the cost of the heat exchanger, due to the reduction of heat exchanger temperature driving force and need to higher heat transfer area. However, the operating cost of compressors can be reduced.

Mixed refrigerant is widely used in the natural gas liquefaction process, and this makes it important to optimize the parameters affecting this process. In this research, a PRICO process with mixed refrigerant was optimized by using Non-dominated Sorting Genetic Algorithm (NSGAII). In this optimization, energy consumption and the surface of heat exchanger were optimized simultaneously to eliminate the adverse effect of the surface of heat exchanger increase due to the single-objective optimization of the energy consumption observed in the previous papers. Molar flow rates of mixed refrigerant compounds including methane, ethylene, propane, isopentane and nitrogen, outlet pressures of the first and second compressors and outlet pressure of the cooling cycle valve were considered as optimization variables. Also, the considered objective functions were performed on sensitive analysis towards optimization variables Moreover, the optimization solutions were presented as a set of optimal solutions called Pareto optimal fronts whose results showed the contradiction of the two objective functions well. Afterwards, multi-objective optimization results were compared with single-objective minimization results. Ultimately, comparison results showed that the surface of heat exchanger in multi-objective optimization was reduced by 54% in comparison with  single-objective optimization (energy optimization).

The most important elements in liquefaction process are heat exchangers that are Plate Fin or Spiral Wounded. In this paper, IRAN LNG liquefaction cycle is simulated using Aspen-Hysys software. Then a procedure for designing plate fin heat exchanger is developed. Moreover, the paper also presents a new method to select the best secondary surface. The obtained surfaces by traditional simulation for cold and warm ends of heat exchanger and overall heat transfer coefficient are 3001 m2, 1933 m2 and 425 W/m2.K. After designing the optimized heat exchanger using the newly developed Rapid Design Algorithm (RDA), the obtained surfaces for cold and warm ends and the overall heat transfer coefficients were 575 m2 and 842 W/m2.K, respectively. This study shows a significant reduction in designing a compact heat exchanger with cold end surface, warm ends surface, and an increase in overall heat transfer coefficient which are 2.5, 3.3 and 2 times lower and higher, respectively.

The scope of this article is to provide a solution for the challenge against more popularity of multi-stage flash distillation applications compared to membrane processes in brackish water desalination. Adequate integration of exist 197 ton per hour MSFD unit and solar direct steam generation technology has been considered as an alternative renewable energy source to achieve solar LP steam. So, as the result of this modification, in each of three units, 17.8 MW of fossil energy is replaced by solar energy during day time. The rate of produced steam is 327,800 ton per year. The amount of natural gas saving is 25,041 ton and this leads to reduction in CO2 production up to 78680 ton per year.

Using of twisted tubes is one of the most promising technique to increase heat transfer between hot and cold fluids. In this study, the ratio of oval cross sections and number of twists in the Reynolds range of 1000 to 15000 were analyzed by computational fluid dynamics tools. The ratio of oval cross sections between 1 and 2.5 and the number of twists between 0 and 3 are considered for a case study. Basically, increasing the Reynolds number, increasing the cross section diameter ratio, and increasing the number of twists increase the Nusselt number and the friction factor simultaneously. In this case study, the ratio of oval cross sections 1.67 and the length of the twisted of 3 (0.6 m), reveal the best performance to achieve the optimal pressure drop and Nusselt number, respectively.

In a process unit, reducing the energy consumption, increasing the production capacity and economic profit of the process, have been always considered and various methods, including thermodynamic methods and mathematical methods, have been improved for this purpose. In present study, atmospheric distillation process of Tehran refinery has been optimized by two different methods and their results, have been reported. By the first method, in which optimization has been performed by Aspen Analyzer software, based on pinch technology (as the thermodynamic method), comparisons between real situation and based ideal design, show the difference about 34%. The required number of units by ideal design is reported 21, the utility consumption is 1.3´ 105 kW and required area is 2.2´ 104 m2. The second method, performed optimization by GAMS software which is based on synheat model as the mathematical method. The required number of units is reported 28, the utility consumption is 5.2´ 104 kW and required area is 6.6´ 103 m2. In present study with the use of HeVi software, the results of mathematical optimization is visualized in the form of grid diagram for heat exchangers and streams

Heat treatment furnaces play an important role in refinery and petrochemical systems. The emission of a huge amount of environmental pollutants such as nitrogen oxides (NOx) and carbon dioxide (CO2), along with the cost of repairs and periodic overhauls have given more attention to the optimization of the furnaces. Flameless combustion as a newly emerging process, with features such as reducing emissions of pollutant gases, uniform distribution of temperature profile along with reducing thermal stresses, and noise pollution in the torch, promising to change the conventional combustion systems and move them toward emission, operational, and maintenance costs reduction. In this study, the burner made by Sholeh-Sanat Company was investigated using the computational fluid dynamics under pre-heating conditions and oxygen concentrations of 3 and 6%. The furnace performance was considered in steady flameless conditions with eddy-dissipation concept (EDC). Flameless combustion characteristics were obtained in the torch and compared to conventional combustion; moreover, the temperature peaks were eliminated, and the temperature profile became more uniform. Also, in the 6% state, the mass fraction of nitrogen oxides and carbon dioxide compounds were observed to be about 400 and 3000 times decreasing respectively. Working under 3% mode, more uniform temperature profile and less nitrogen oxides were observed.

In this study, optimization of a waste heat recovery system (WHRS) that works by an organic Rankine cycle (ORC) from a cement plant is investigated. Energy and economic models of the system are presented. The energy model and thermo-economic model are developed according to the first law of thermodynamics and specific exergy costing method respectively. To design ORC, there are two major issue that are considered here. One issue with recperator and another without that. The first law of thermodynamic as an objective function to maximize the efficiency and economic objective function to minimize the total cost of electricity produced are used. Optimization methodology is based on genetic algorithm and performed by EES software. Also in order to determine the effect of the fluids on the cycle, three fluid included R245fa, R123 and n-pentene are examined and their results is discussed. The results showed that in the case of thermodynamics optimization without recuperator, R123 with 17.76% has the highest efficiency compared with the other fluids and with recuperator versus R123 with 20% is the best fluid. Moreover in thermoeconomic optimization R123 has the lowest total production cost compared with the other fluids with 0.199€/hr and 0.315€/hr in cycle without recuperator and with recuperator respectively. Here, it can be concluded that for the thermal recovery of medium-temperature sources, in thermodynamic optimization and thermoe-conomic optimization, R123 can be identified as a good choice for ORC cycles.

Plate heat exchangers have recently widely used in most of the industries especially in food industry. Some factors on efficiency of this equipment such as fouling are so important in design. In this study the crystal sedimentation of calcium sulphate from cane water on the sole plate heat exchanger is simulated. In order to validate the determined sedimentation rate, the designed was compared with the available experimental data. Moreover, the effect of fouling on the velocity, temperature, and the amount of heat exchanger duty factors were studied. However, the temperature and duty will be decreased during the time of process by sedimentation. In this paper, Rapid Design Algorithm (RDA) was utilized to analyze the design. The result showed that amount of heat transfer was so dependent on the rate of fouling. For instance, for flow 0.08 (kg/s), the amount of required heat transfer surface is increased from 0.12 to 0.65 (m2) when the deposition of fouling on surface is considered.

In this study, thermal, exergetic analysis and performance evaluation of seawater and fresh wet cooling tower and the effect of parameters on its performance is investigated. Base on the definition of an economic model for capital and variable costs, an optimized efficiency of a cooling tower has been evaluated. With modeling of a cooling tower and using of experimental results and a developed code in EES, this study has been performed. Due to lack of fresh water, seawater cooling is an interesting choice for future of cooling, so the effect of seawater in the range of 1 g/kg to 60 g/kg for salinity on the performance has been studied. Effect of changing the salinity of the water on performance and parameters which are related to exergy has been compared with a cooling tower which used fresh water. Results showed that decreasing of air efficiency about 3%, increasing water efficiency about 1.5% are some of these effects. Moreover with the formation of fouling the performance of cooling tower decreased about 15% which this phenomenon and its effects like increase in output water temperature and tower excess volume have been shown.

Optimizing energy consumption is important for reducing environmental degradation and reducing operating costs. In this project, Pinch technology is used at the Butanol Recovery Unit to save energy. The Utilities include cooling water (20 ̊C) and pressure steam for exchanging heat with a mixture of water and butanol with different mixing rates. By reducing the optimal minimum temperature difference between hot and cold currents of 5°C (ΔTmin = 5 ̊C), the thermal load of the hot and cold Utilities can be reduced. This work by targeting of around 16% and 6%, will be decrease for hot and cold Utilities, respectively. In this project with targeted goals, operating costs per year can be reduced up to 13.3 percent in ideal condition. With increasing and lowering of new area the capital costs will increase to 31,662 $ an additional surplus on initial spending. Energy saving costs are reduced by up to 10.1%, with a return on investment of 5.9 year.

LNG production is an intense and complex process, in which the liquefaction accounts for more than 50% of costs. In recent years, design engineers have been made several attempts to optimize this process. The main objective was to increase the production yield and capacity, and minimize the costs. The most important process equipment in liquefaction stage is devoted to compact heat exchangers of Plate Fin or Spiral Wounded types. This article described the simulation of liquefaction cycle of Iran LNG project with triple mixed refrigerant to provide a new method for designing the plate heat exchanger used in this cycle; in addition, a simple method was introduced for selecting the best secondary surface based on the conceptual development of the volume performance index (VPI). The designed exchanger had the minimum surface area and volume. The reduction of required heat transfer surface area had a significant role in the reduction of investment capital cost in LNG production process. The liquefaction cycle of Iran LNG was fully investigated in this article as an industrial case. According to the simulation, the cold and hot surface areas of the plate heat exchanger, used in the given process, are as large as 3001m2 and 1933m2 with the overall heat transfer coefficient of 425 W/ m2K°; whereas, designing this exchanger by developed rapid design algorithm (RDA) significantly can be reduced the required cold and hot surface areas by 5.2 and 3.3 times, respectively. The overall heat transfer coefficient was also increased by 2 times.

LNG project is intrinsically a complex process that accompanied with liquefaction section. It almost dedicates the 50% of total project costs. Liquefaction section is the key point of this process and designers are commonly interested to keep the costs in lowest level and affect the process activeness. The most important elements in liquefaction process are heat exchangers that made by Plate Fin or Spiral Wounded types. In this paper, as a first step, a LNG liquefaction cycle with triple mixed refrigerator is simulated and then a new procedure for designing of plate fin heat exchanger is developed. A method also for selection of the best secondary surface based on volume performance index is presented. As a result the designed heat exchangers gives lowest volume and lower heat exchanger surface would have important role in reduction of investment costs. As a case study, a feedstock, belonging to pre-cooling unit of Iran LNG project, was used. The calculated surfaces by traditional simulation of cold and hot ends surfaces of heat exchanger and overall heat transfer coefficient (OHTC) are 3001 m2, 1933 m2 and 425 W/m2.K respectively. After designing an optimum geometry with new developed rapid design algorithm (RDA), the obtained surfaces for cold and hot ends and the overall heat transfer coefficient were 575 m2 and 842 W/m2.K respectively. The outcomes of this study revealed that a great significant reduction in design an industrial compact heat exchanger with cold and hot end surfaces about 5.2, 3.3 times lower respectively and about 50 percent increase in OHTC.