دوماهنامه مهندسی شیمی ایران
پیاپی 117 (مهر و آبان 1400)

In this paper, the performance of a typical glass flat plate solar collector is evaluated experimentally by the test bench designed and constructed at Research Institute of Petroleum Industry (RIPI) in the city of Tehran. The results of five experimental tests including thermal performance evaluation, effective heat capacity, time constant, radiation angle correction factor and pressure drop are presented according to the Iranian National Standardization Organization (INSO) standard 7129. The results show that the highest thermal efficiency of the tested collector based on the gross surface area is 42.5% in ideal temperature conditions.In addition, its effective heat capacity is 42618 J/K and its time constant is obtained equal to106 seconds. Furthermore, its radiation angle correction factor is 0.85 for incident angle of 45o and the pressure drop of the tested collector is about 500 Pa for its working mass flow rate.

In this study, the single-leaf of parsley and also bulk of particles at temperatures of 46, 58, and 68°C and the thickness of 0.13 to 0.17 mm and the period from 0 to 140 minutes in a laboratory fixed bed dryer dried. Also, the single leaf of parsley and the mass dried in the sun. To dry the parsley in the dryer, five samples were considered for each temperature and the weight of samples during the drying process is continuously recorded until changes in the volume of samples to zero. Then the influence of parameters such as the temperature of the drying rate is examined. Equilibrium time and humidity were observed to be 140 minutes and 0.0003, respectively. Also, the process kinetics curve shows that more drying occurs in the descending phase due to the low external resistance to mass and heat transfer. In studying the effect of temperature, it was observed that with increasing temperature from 46 to 68℃, parsley reaches equilibrium humidity with a greater slope. Then drying process of a single leaf, and parsley mass, using feed-forward neural networks and leading, was modeled and the results of the neural network with the results obtained from experimental data were compared. The best result by a feed-forward neural network for single-leaf parsley with Levenberg - Marquardt algorithm, and 13 neurons and the coefficient of determination 0.9987 and parsley mass with nine neurons optimized and coefficient 0.9993obtainedwhich demonstrates the high accuracy of the artificial neural network.

The fabrication of polypropylene composites using various types of reinforcements to improve the mechanical properties has received much attention in recent years. In this paper, enhancing the mechanical properties of polypropylene composites by adding different classes of natural and synthetic particle and fiber reinforcements were reviewed. Accordingly, it was found that the fabrication of polypropylene composites leads to an increase either in the strength of samples and corresponding mechanical properties. Moreover, surface modification and processing reinforcements, especially natural fibers via chemical and physical methods were studied. The results show an increase in the adhesion of reinforcements surface inside the polypropylene, which results in strength enhancement and improving the mechanical properties of polypropylene composites. The evidence from this study points towards the idea that the increased use of modified natural fibers in polylropylene composites and those natural or synthetic reinforcements which form hybrid composites provide promising research topics in the future.

Microalgae with reserves of carbohydrates, high growth rate have been introduced as one of the most promising sources for bioethanol production. In this study, after culturing mixed microalgae species in photobioreactors, a nitrogen starvation strategy was used to increase the accumulation of carbohydrates in microalgae. Then, the sugars in the biomass were extracted using enzymatic hydrolysis by cellulase enzyme. For the first time, the enzymatic hydrolysis of microalgae is investigated by considering the dynamic conditions of the fluid inside the reactor. The results showed that increasing the system agitation more than the enzyme concentration affects the hydrolysis efficiency. At high speeds of 250 rpm, where the flow regime changes from slow to turbulent, the amount of sugar released is much higher than the values at low speeds of the stirrer. Also, adding baffle increases the mass transfer rate by preventing the formation of vortices and consequently increases the hydrolysis efficiency. But changingthe type of stirrer does not have a significant effect onthe hydrolysis process. Also in this study, the effect of agitation during the hydrolysis process was investigated by evaluating the mass transfer rate.

One of the strategic goals in the Persian Gulf Star Oil Refinery has been to change the use of the Kerosene Hydrotreater with the Sour Naphtha service. The purpose of this study is to simulate and evaluate the shell and tube heat exchangers at the outlet of kerosene Hydrotreater unit’s reactor for Naphtha service which has been studied as part of a massive, change usage project. The simulation results with the HTRI software Version 6.32, showed that in change of useage with the new service andthe without considering fouling, the amount of heat transfer ofthe mentioned heat exchangers will be sufficient for heat transfer of 22.2 Mega Watt. However, due to the fouling of the heat exchangers andthe need of the reactor to reach a temperature of 310 degrees Celsius and the temperature conditions at the end of catalyst life due to coke, it was inevitable that worst operating conditions had to be considered.The simulation results showed that heat transfer surface area of heat exchangers must be increased by 24% to achieve the actual operating conditions.Suggestions for compensating the heat transfer surface area, including increasing the number of tube to 1370 branches for each of heat exchangers, Increase length of the tubes to 6400 mm, changethe shell structure from type E to F or adding a new heat exchanger similar to the existing system, in series with those, was proposed that latter was considered as a more economical solution.

Static mixers are applied for increasing the mixing in chemical reactors as well as for increasing the heat transfer coefficient in heat exchangers. In the study, fluid flow characteristics in tubes equipped with modified static mixers with different geometric parameters were investigated by computational fluid dynamics. The classic twisted tape, perforated twisted tape, and V-Cut twisted tape were evaluated for Reynolds numbers between of 3000 to 19000. The fluid flow and pressure drop for the mixers were investigated. The validated simulation results were employed to train the artificial neural network model. Reynolds number and geometric parameters of the mixers were used as input variables of the neural network for predicting the friction factor. The model accuracy for estimating the friction factor was investigated and a relative error of less than 1% was obtained. The main relative errors for all data in classical, V-Cut, and perforated twisted tape were 0.75%, 0.57%, and 0.52%, respectively, and for validation data were 1.1%, 0.92%, and 0.62%. 30% of the data were randomly selected for the neural network to prove the model validity.