Yusuf Uludag

Removal of mercury from aqueous solutions via polymer-enhanced ultrafiltration

Separation of mercury from aqueous solutions by continuous polymer-enhanced ultrafiltration (PEUF) was investigated. Polyethyleneimine (PEI) was added to the solutions as the complexing agent before circulating the solution in a laboratory-scale continuous ultrafiltration system. Effects of mercury-to-polymer ratio, pressure drop and feed solution circulation rate on retention of mercury and permeate flux were studied. Constant retention values close to unity were obtained until a critical mercury-to-polymer ratio was exceeded. For higher metal loadings, retention values decreased linearly. Permeate flux increased linearly with pressure drop and was not affected by other parameters such as metal loading and feed circulation rate. Therefore, concentration polarization was not a problem for the studied range of variables.

Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration

Performance of continuous polymer enhanced ultrafiltration (PEUF) method was investigated for removal of mercury and cadmium from binary mixtures. This method includes the addition of polyethyleneimine (PEI) as a water soluble polymer to bind the metals, which was followed by ultrafiltration operation performed on both laboratory and pilot scale systems. The influence of various operating parameters such as temperature, metal/polymer ratio, presence of calcium ions and pH on retention of metals and permeate flux was investigated. To investigate the possibility of selective separation of mercury and cadmium, experiments were conducted for binary solutions at different pH and loading ratios. It was seen that the retention of mercury decreased and permeate flux increased when the temperature increased. The increased pH and decreased metal/polymer ratio, loading (L), resulted in higher retention of both metals. Shapes of retention vs. pH or L curves were very similar for both metals. Retentions stay almost constant at a value very close to unity until a critical L or pH value was reached, then, R decreases almost linearly with L or pH. However, retention of cadmium was affected more than that of mercury as the pH decreased and L increased. This leads to the selective separation of mercury and cadmium. At low pH values (about 5) and at high L values (about 0.3), mercury was removed by ultrafiltration operation while almost all cadmium passed through the membrane. At pH 5.5 and cadmium/polymer ratio about 0.35 and mercury/polymer ratio about 0.39, the highest separation factor was obtained as 49.

Effects of Spray Drying Temperature and Additives on the Stability of Serine Alkaline Protease Powders

In this study, after production by recombinant Bacillus subtilis (BGSC-1A751), carrying pHV1431::subc gene in the complex medium and separation of solids from the fermentation broth, serine alkaline protease (SAP) was dried in order to investigate the stabilization during spray drying and subsequent storage. The effect of air inlet temperature of the spray dryer between T = 70 and 130°C and the effect of protective additives, glucose and maltodextrin, at 0–2% (w/v) on SAP activity during spray drying and storage stability of obtained SAP powders at 4°C for a long period (6 months) were evaluated. Increasing drying air inlet temperature generally resulted in an increase in activity loss; moreover, higher absorbance peaks observed at wave number 1061 cm−1 of the IR spectrums when drying temperature is increased indicates the structural change in the SAP molecule. In most cases presence of additives provided higher activities both after drying and during storage period compared to no additive case. Drying the enzyme with 1% (w/v) glucose at T = 110°C resulted in the highest enzyme activity after drying and storage processes.

Heat and mass transfer mechanisms in drying of a suspension droplet: A new computational model

A new computational single-droplet drying model is presented. The model considers heat and mass transfer simultaneously together with the receding evaporation front approach. A spherical droplet under constant drying conditions is considered. Computations are performed to predict the drying of colloidal silica-water suspension and skimmed milk. It is shown that the results agree well with those of experimental observations available in the literature.

Numerical method for optimizing stirrer configurations

A numerical approach for the numerical optimization of stirrer configurations is presented. The methodology is based on a parametrized grid generator, a flow solver, and a mathematical optimization tool, which are integrated into an automated procedure. The flow solver is based on the discretization of the Navier-Stokes equations by means of the finite-volume method for block-structured, boundary-fitted grids with multi-grid acceleration and parallelization by grid partitioning. The optimization tool is an implementation of a trust region based derivative-free method. It is designed to minimize smooth functions whose evaluations are considered expensive and whose derivatives are not available or not desirable to approximate. An exemplary application illustrates the functionality and the properties of the proposed method.

Finite volume simulation of 2-D steady square lid driven cavity flow at high reynolds numbers

In this work, computer simulation results of steady incompressible flow in a 2-D square lid-driven cavity up to Reynolds number (Re) 65000 are presented and compared with those of earlier studies. The governing flow equations are solved by using the finite volume approach. Quadratic upstream interpolation for convective kinematics (QUICK) is used for the approximation of the convective terms in the flow equations. In the implementation of QUICK, the deferred correction technique is adopted. A non-uniform staggered grid arrangement of 768x768 is employed to discretize the flow geometry. Algebraic forms of the coupled flow equations are then solved through the iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. The outlined computational methodology allows one to meet the main objective of this work, which is to address the computational convergence and wiggled flow problems encountered at high Reynolds and Peclet (Pe) numbers. Furthermore, after Re > 25000 additional vortexes appear at the bottom left and right corners that have not been observed in earlier studies.

Rheological characterization of polyethylene glycol based TiO2 nanofluids

Rheological characterization of TiO2 nanoparticle dispersions in polyethylene glycol (PEG 200) is presented over 1–10 wt% particle mass fraction range in terms of shear viscosity, thixotropy and linear viscoelasticity. A stress controlled rheometer fitted by a cone-and-plate system was employed for the rheological measurements between −10°C and 40°C. The non-linear viscoelastic experiments revealed that TiO2-PEG 200 nanofluid exhibits a shear thinning behavior when particle mass fraction exceeds 1%. No appreciable change in the shear viscosity versus shear rate behavior was detected over the course of four days of dispersion storage. At high particle concentrations the dispersions had a yield stress that was determined by fitting the results through Herschel-Bukley model. Within the studied range of particle concentration, no evidence of thixotropic behavior was observed. In addition, relative viscosity measured at high shear region was found to be independent of the temperature. On the other hand, strong temperature dependency was observed at low shear region particularly at high temperatures. Storage and loss moduli of the TiO2-PEG 200 nanofluid were determined by frequency sweep measurements with applied stresses in the linear viscoelastic region. It was found that when the applied stress is lower than the corresponding yield stress TiO2-PEG 200 nanofluid showed a gel structure especially at high particle mass concentration.

Numerical Analysis of Viscoelastic Fluids in Steady Pressure-Driven Channel Flow

The developing steady flow of Oldroyd-B and Phan-Thien-Tanner (PTT) fluids through a two-dimensional rectangular channel is investigated computationally by means of a finite volume technique incorporating uniform collocated grids. A second-order central difference scheme is employed to handle convective terms in the momentum equation, while viscoelastic stresses are approximated by a third-order accurate quadratic upstream interpolation for convective kinematics (QUICK) scheme. Momentum interpolation method (MIM) is used to evaluate both cell face velocities and coefficients appearing in the stress equations. Coupled mass and momentum conservation equations are then solved through an iterative semi-implicit method for pressure-linked equation (SIMPLE) algorithm. The entry length over which flow becomes fully developed is determined by considering gradients of velocity, normal and shear stress components, and pressure in the axial direction. The effects of the mesh refinement, inlet boundary conditions, constitutive equation parameters, and Reynolds number on the entry length are presented. [DOI: 10.1115/1.4006696]

Theoretical investigation of effects of flow oscillations on ultrasound Doppler velocity measurements

Effects of flow oscillations on spectrum of Ultrasound Doppler Velocimetry (UDV) signals were investigated theoretically and numerically. A laminar pipe flow with a superimposed oscillating component was considered. Negative impact of oscillation on the ultrasound signal hence on the flow images was observed in the form of spreading of spectral ultrasound signal energy around mean component, leading to image artifacts. Both analytical and numerical results revealed the strong effect of a group of parameters including Doppler frequency, flow oscillation amplitude and frequency. Exceeding a particular value of the group, 1.45, resulted in artifacts in the flow images. Revealing the mechanisms involved in the deteriorations associated with the flow oscillations is potentially useful in UDV studies involving random flow fluctuations such as turbulence.

Theoretical and experimental investigation of fluid rheology effects on modulated ultrasound propagation

A mathematical model is developed and presented to capture the effect of viscoelastic nature of a material on modulated ultrasound (US) pulses. The model is established by considering perturbation of material elements subject to modulated US pulses and by introducing the exponential relaxation of the perturbed fluid elements with a spectrum of time constants. Both the model and experimental findings revealed that consecutive perturbation of a material via the modulated US pulses enabled to probe the relaxation times of similar order of magnitudes to the frequency of the US modulation while filtering out the impact of other relaxation times on the US measurement. The US experimental results were verified by those of a conventional rheometer. Hence carrying out measurements at different US modulation frequencies in the Hz ranges seems to allow one to obtain the relaxation time spectrum of the investigated material in the time scales of milliseconds to seconds.