Johnner P. Sitompul

MODELING AND SIMULATION OF DEEP-BED GRAIN DRYERS

This paper concerns with heterogeneous modeling of deep-bed grain dryers based on two-phase model by taking into account coupled heat and mass transfer within grains. This model also consider axial mass and heat dispersion in the fluid phase. The dynamic two-phase equations are solved numerically by finite difference with alternating direction implicit method algorithm, and then applied to simulate humidity and temperature profile of drying gas across dryers together with moisture content and temperature of grains. The capabilities of these models were compared with experimental data obtained from available literatures, under drying conditions such as temperature and absolute humidity of drying gas and moisture content of grains. The simulation results show that the dynamic of corn drying within the bed is well predicted by the two-phase model.

Modelling and Simulation of Momentum, Heat, and Mass Transfer in a Deep-Bed Grain Dryer

Abstract This article concerns the modelling and simulation of a deep-bed grain dryer in a large diameter-column. Two-dimensional (2D) models of deep-bed grain dryers were built by considering simultaneously momentum, heat, and mass transfer in the drying phase together with coupled heat and mass balance in the grain phase. The dynamic equations are solved numerically by using finite difference method. The momentum equations are applied to simulate pressure drop and velocity field of the drying air across the bed. The mass and heat balance in the two phases determine the profile of temperature and moisture content in both phases. Further, drying rate curves for various temperature of inlet drying gas together with moisture content of grain were simulated. The simulated profiles are in close agreement with experimental data.

A COMPREHENSIVE MATHEMATICAL AND NUMERICAL MODELING OF DEEP-BED GRAIN DRYING

ABSTRACT This paper deals with comprehensive mathematical and numerical modeling of deep-bed grain drying. In order to build the process model, it is necessary to analyze the transport in both grain and gas phases. Experimental works were carried out for a layer of grain bed in order to validate the models. The models consider momentum, energy, and mass conservation within grain and drying air phase. The two-dimensional dynamic equations of energy and mass conservation are solved numerically by finite-difference method (FDM) and utilizing alternating direction implicit algorithm within grain and drying air phase, while momentum conservation are solved by finite difference method by utilizing Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. Furthermore, the models will be applied in consideration with developing and designing dryer in order to simulate humidity and temperature profiles of the drying gas together with moisture content and temperature of grain across dryer in term of the dryer performance. The simulations show that the models can be used to predict the dynamic drying characteristic profiles as well as the superficial velocity of drying air phase across dryer.

Systems-level analysis of Escherichia coli response to silver nanoparticles : the roles of anaerobic respiration in microbial resistance

Despite extensive use of silver nanoparticles for antimicrobial applications, cellular mechanisms underlying microbial response to silver nanoparticles remain to be further elucidated at the systems level. Here, we report systems-level response of Escherichia coli to silver nanoparticles using transcriptome-based biochemical and phenotype assays. Notably, we provided the evidence that anaerobic respiration is induced upon exposure to silver nanoparticles. Further we showed that anaerobic respiration-related regulators and enzymes play an important role in E. coli resistance to silver nanoparticles. In particular, our results suggest that arcA is essential for resistance against silver NPs and the deletion of fnr, fdnH and narH significantly increases the resistance. We envision that this study offers novel insights into modes of antimicrobial action of silver nanoparticles, and cellular mechanisms contributing to the development of microbial resistance to silver nanoparticles.

Synthesis of PDLLA/PLLA-bentonite nanocomposite through sonication

This paper concerns the synthesis of poly(D,L-lactic acid)/poly(L-lactic acid) bentonite nanocomposites. Poly (D,L-lactic acid) (PDLLA) was synthesized using lactic acid through the ZnO-catalyzed direct polycondensation method at vacuum pressure and poly(L-lactic acid) (PLLA) was synthesized with L-lactide by ring-opening polymerization method. The PDLLA/PLLA-bentonite nanocomposite films were synthesized using the solvent casting method. The nanoclay, bentonite, was prepared using the solution-intercalation method by dissolving the nanoparticles into chloroform before sonication. In this study, PDLLA/PLLA-bentonite nanocomposite films were produced using variable amounts of nanoclay and sonication times during the mixing of PDLLA/PLLA and bentonite. The properties of the PDLLA/PLLA nanocomposites were then characterized using the X-ray Diffraction (XRD), Universal Testing Machine (UTM), Water Vapor Permeability (WVP) tests, and the enzymatic biodegradability test. The XRD test was used to measure the int...

Experimental study on the effect of freezing medium temperature on exergy efficiency

This paper evaluates the effect of variable temperatures of a freezing medium on exergy efficiency, based on experimental data. The experiments were conducted with variable temperatures at the first, second, and third stages of the freezing course. The results show that the third stage was the most reversible stage. Irreversibility of the first stage was affected by freezing temperature of both the first and second stage. The study implies that scheduling of the freezing temperature is important for reducing the total irreversibility of the process, and the temperature has to be determined consecutively from the third to the first stage.