دوماهنامه مهندسی شیمی ایران
پیاپی 19 (آذر و دی 1384)

“Calcium sulfate is the majority of dissolved salts in commercial and industrial waters. Calcium sulfate is negative soluble versus temperature in water. Accordingly the saturation concentration adjacent to the heat transfer area will dwindle beneath the bulk concentration. Hence the surplus salt will deposit on the heat transfer surface and a fouling resistance will be established by two independent mechanisms. The first one is mass diffusion associated with mass transfer mechanism and the second is the evaporation of bubbles on the heat transfer surface. Averting of salt deposition is not straightforwardly practicable, but estimation of this heat resistant as a function of operating parameter is significant. Optimizing the heat flux to reduce sedimentation process and consequently minimizing the running cost is one reasons. In addition is necessary to provide an accurate schedule for overhauling program and fuel consumption for a predetermined running system. In the current research, the fouling resistance of calcium sulfate scale is modeled as a function of time, heat flux and bulk concentration.

In this study, Surface Tension of Aqueous Solution of Alkanolamines (MDEA and DEA) has investigated as a function of concentration and temperature (in the range 298.15-328.15K).Temperature dependence of surface tension is linear. Using Experimental Results published in literatures, line parameters have determined. Concentration dependence can be described, using an exponential function. The best coefficients for mentioned function calculated, using error minimizing method. Combination of temperature and concentration dependence results in an overall relationship for surface tension prediction. Such a relationship is useful in column design and optimization (minimizing problems such as flooding and foaming).

The major problems occurred with conventional purification of feed and extraction of product, causes the necessity of investigation and introduction of the more advanced procedures. Supercritical fluid extraction which uses a dense gas near or above its critical point as the solvent is one of the advanced methods of extraction in recent years. This method has found many industrial applications such as the chemical, petroleum, environmental, biochemical, food, pharmaceutical and polymers. In this paper the properties of a supercritical fluid is presented and after comparison by the gas and liquid state the application of this kind of fluid is introduced in different fields and industries. For a number of physical, practical and economic reasons carbon dioxide is the fluid of choice in most SCF processes, with its friendly environmental property.

Several models have been reported on growth kinetics of microbial systems. Monod equation is a well-known growth model, due to its simple assumptions. Nutrient uptake is affected by nutrient reserves within the cells and the physiological behavior of the microorganisms. In growth-kinetic studies, the type of nutrient should be considered in addition to its concentration. Phosphate, one of the main substrates, is stored within the cells which can be utilized under starvation conditions. In the present study, the applications and limitations of Monod model in cell growth under limitation of accumulating nutrients have been reviewed with special interest to yeast cells.

One of the techniques that have been used in production of granules is spray drying process. Mechanical strength is very important parameter in transport of granules. In this study the granulation mechanism was investigated by hallow granule model and drying time was calculated using solid – liquid separation filtration analogy. Also, the effects of slurry physical characteristics on spray drying conditions were evaluated.

This research has been done to optimize the process parameters for pomegranate juice powder production in a spray dryer. Fruit juices can be replaced by fruit juice powders. Food drying is a good way for preserve them so fruit juice drying increases the shelf life and decrease the product wasting. Also it eases the transportation of them.The produced powder easily mixed with other food ingredients and dissolves in water, so in addition to its use as a fast drink, it can be used in souses, desserts and other foods.In this work, a pilot of spray dryer used and the effect of different parameters like temperature, feed concentration, feed rate and amount of different additives were tested. The resulting powder was tested for its properties and also its organoliptic characteristics were tested.

High current density performance of polymer electrolyte fuel cell (PEM) is known to be limited by transport of reactant and products. In addition, at high current densities excessive amount of water is generated and condenses, filling the pores of electrode with liquid water, and hence limiting the reactant transport to active catalyst. This phenomenon known as flooding, is an important limiting factor of PEM performance. When some magnet particles are deposited in the catalyst layer of a cathode and magnetized, the cell performance has been improved compared with that of non-magnetized case. Numerical simulation to explain this phenomenon shows that the repulsive Kelvin force caused by the magnet particles manages the liquid water and gas flow in the porous electrode layer. In addition, the saturation level of liquid water (s) near the catalyst interface decreases with increasing the residual magnetic flux density of the magnet particles, and this method improves the cell performance by decreasing the value of s and making more pore space for oxygen gas that decreases the diffusion looses in cathode. At last we considered disadvantages of this method and calculated cell performance with a realistic sight.

This article has tried to assess different approaches to critical properties estimation of different substances critical properties studied in this article include: critical temperature, critical pressure and critical volume. Different methods have been presented for estimating substances so far, methods with absolutely different ways of functioning. As the matter of fact the present article is a general assessment and categorization of these methods and equations. This categorization has first been presented by authors. Methods of group contribution and riazi have been studied in this article. In riazi method which is the last method presented in the article, there is no need to knowledge of the chemical and molecular structure of combinations and having known only the normal boiling point and the density, one can estimate the critical properties while in group contribution approach which includes different methods it self, molecular combinations and the chemical structures ought to be exactly defined, every single one of group contribution methods contributes a variety of substances combinative and properties as well.

Emissions produced by power plants have an important effect on environment. Therefore, reducing these emissions considered an economic issue and performance criterions have a special importance. Nitrogen oxides, carbon dioxide, sulfur dioxide and mercury are the main emissions in electricity generation thermal power plants. Having been studied these emissions, some of the most current methods and also future technologies are introduced in this paper to reduce these emissions.