Band 16, Heft 4

Nanofluids has significant effect on heat transfer enhancement for comparatively high Reynolds number than to low Reynolds number flow. Whereas, vibration effects reduces in significance as Reynolds number increases. This study combined these two method of heat transfer enhancement i.e. use of nanofluid flow through pipe under vibration. A grid independent CFD model used for the study was validated in various aspects such as it was validated for variation of local Nusselt number, isothermal vibrational flow and non-isoviscous viscosity model so that one could believe the results obtained from the model. A valid CFD simulations has been done to investigate the effect on heat transfer to fluid flowing from pipe subjected to a constant heat flux. Al 2 O 3 -water based nanofluid was used as Newtonian fluid as it exhibits Newtonian behavior at low concentration (∅ < 2%). In order to make it non-Newtonian in nature, mixture of Al 2 O 3 nanoparticles and 0.5 wt% aqueous CMC solution was used. Temperature dependent viscosity and thermal conductivity relations were considered for nanofluid so that it can be effectively model as single phase fluid including factors like liquid layering, Brownian motion etc. Simulations were done for different Reynolds number, volume fraction and solid particle diameter and results were presented in the form of ratio of heat transfer coefficient of vibration flow to steady-state flow. At low Reynolds number flow, a significant increment was observed for non-Newtonian nanofluid and its effect increases for volume fraction and solid particle than that of Newtonian nanofluid for the range of simulation parameters used.

In the current work, the high temperature water gas shift reaction assessment for hydrogen generation and its purification was carried out in reactors integrating hydrogen or carbon dioxide perm-selective membranes. Indeed, the performance of the high temperature water gas shift reaction was analyzed under adiabatic conditions through a mathematical model developed for this purpose. The main results indicate that both membrane reactors provide under some conditions a complete carbon monoxide conversion. As a result the dual phase membrane presents a great separation capacity of carbon dioxide. This gives us the opportunity to obtain a high purity of hydrogen. Thus, it can be concluded that the concept of the membrane reactor that used for carbon dioxide separation could be a veritable competitor and a great promise candidate for replacing the Pd based membrane reactors which is used for hydrogen separation.

The conversion of CO 2 to methanol holds great promise, as it offers a pathway to reduce CO 2 level in the atmosphere and also produce valuable components. In this study, a typical methanol synthesis plant for CO 2 conversion was numerically modeled. Effect of fresh feed to plant parameters (i.e., pressure and CO 2 concentration) as well as the influence of recycle ratio on the reactor performance was investigated. Hence, all essential equipment, including compressor, mixer, heat exchanger, reactor, and liquid–vapor separator were considered in the model. Then, at the best operating conditions, thermal behavior and components distribution along the length and radius of the reactor were predicted. Finally, the effect of inert gases was investigated in the methanol production process and the results were compared with the conventional route (CR), which uses natural gas for methanol synthesis. The results revealed that in the absence of inert gases and by employing a recycle stream in the process, CO 2 hydrogenation leads to 13 ton/day production of methanol more than CR. While in the feedstock containing 20% inert gases, which is closer to the realistic case, methanol production rate is 45 ton/day lower than CR. These findings prospect a promising approach for the production of green methanol from carbon dioxide and hydrogen.

Debottlenecking and estimating fouling in a clarifier piping system for the expansion of an existing chemical manufacturing facility in the U.S. Gulf Coast was analyzed and modified. The existing clarifier piping system fitting data was gathered for the real-world operation from the field. This data was used in the Applied Flow Technology (AFT) Fathom, a program used to study hydraulic systems. The hydraulic results with and without recommended piping modifications along with changing piping roughness factors were also analyzed. The two piping roughness factor cases tested were roughness of 0.152 mm and fouling of 25.4 mm. The AFT Fathom results showed that without piping modifications and specifying fouling of 25.4 mm, required flow cannot be established due to insufficient driving force for liquid movement. The measured field flow data confirmed that the reduced clarifier capacity was due to high pressure losses in the hydraulic system. Also, it was found that the existing clarifier nozzle was inadequately designed originally, and replacing the nozzle showed an increase in the clarifier capacity due to reduced entrainment of the air. These modifications were further adapted in the plant expansion and operations were validated using the actual plant data. The plant data matched closely with the estimated capacities of the clarifiers. AFT Fathom hydraulic software was effective in predicting a fouling severity in the clarifier piping system and debottlenecking of the clarifier capacity was done. The conclusions derived from this study can be used all over the world where clarifiers are utilized.

Fluidized Catalytic Cracking (FCC) is a complex process that arises due to feed composition, non-linearities, and dynamic mass and heat interactions in its components. FCC is difficult to model and monitor in industries, and one of the key reasons is that they are multivariable processes. Such processes are highly interacting and that makes the process of controlling even more difficult. The interaction between loops can be quantified easily by dRGA. An easy and effective way of controlling multivariable processes is to implement a centralized control system, considering the interactions between measured and manipulated variables. In this study, a centralized control system is designed for the riser section of the FCC unit. The dRGA method is modified to enhance the closed-loop response by formulating an optimization problem and obtaining an optimal controller settings. A rigorous simulation studies show an 826% reduction in ISE values, a 309% reduction in IAE values, and a 262% reduction in ITAE value of T r i s ${T}_{ris}$ from the dRGA method to the modified dRGA method. Further, IAE values for Y l p g ${Y}_{lpg}$ are reduced by 29% from dRGA to modified dRGA method and 34% from synthesis to modified dRGA method.

The purpose of presented research is the mathematical simulation and sensitivity analysis of ethylene dichloride synthesis (EDC) through direct chlorination of ethylene in a bubble column reactor at steady state condition. In the first step, the reactor is heterogeneously simulated based on the energy and mass balance equations by coupling the mass and energy, kinetic, equilibrium, and population balance models. In the considered process, the gaseous ethylene and chlorine are dispersed and dissolved in the liquid medium and converted to EDC at the presence of a homogeneous catalyst. The population balance model is applied to calculate the heat and mass transfer area along the reactor. To investigate the accuracy of established model, the results of simulation are compared with the plant data. It is confirmed that temperature, pressure, rate of mass transfer, breakage, and coalescence phenomena change the bubble diameter and distribution in the chlorination reactor. In the second step, the effects of operating pressure and temperature on the EDC production rate are investigated by the developed model. In the third step, considering EDC production rate as the cost function the optimal operating temperature of reactor is developed at steady state condition. Based on the obtained results, the optimal operating temperature is 357 K and EDC production at the optimal condition is 23.79 mol s −1 .