On the origin of viscoelastic Taylor–Couette instability resulted from normal stress differences

Mahmood Norouzi,M.H. Sedaghat,M.M. Shahmardan,M.R.H. Nobari 한국유변학회 2015 Korea-Australia rheology journal Vol.27 No.1

In this paper, the effect of normal stress differences on the viscoelastic Taylor–Couette instability is studied numerically. The governing equations are discretized using FTCS finite difference method on a staggered mesh based on the artificial compressibility algorithm. Using the CEF model as the constitutive equation and the Carreau–Yasuda model as the viscometric functions, the flow between rotating cylinders has been studied for a range of radius ratios, Taylor numbers and rheological properties. It is shown that increasing the first normal stress difference destabilizes the flow field while increasing the negative second normal stress difference stabilizes the flow field. The main contribution of the current study is an answer to thisquestion: How do the first and second normal stress differences affect the stability of viscoelastic flowbetween rotating cylinders? For this reason, we used the order of magnitude technique to obtain a force balancerelation in the core region of flow. Based on this relation and numerical simulation, the origin of viscoelasticTaylor–Couette instability resulted from normal stress differences are studied in detail. Furthermore, a two dimensional analytical solution for the main flow velocity component between finiterotating cylinders is carried out considering the end effect of stationary walls

Numerical study of vortex shedding in viscoelastic flow past an unconfined square cylinder

Mahmood Norouzi,Seyed Rasoul Varedi,Mahdi Zamani 한국유변학회 2015 Korea-Australia rheology journal Vol.27 No.3

In this paper, the periodic viscoelastic shedding flow of Giesekus fluid past an unconfined square cylinder is investigated numerically for the first time. The global quantities such as lift coefficient, Strouhal number and the detailed kinetic and kinematic variables like normal stress differences and streamlines have been obtained in order to investigate the flow pattern of viscoelastic flow. The effects of Reynolds number and polymer concentrations have been clarified in the periodic viscoelastic flow regime. Our particular interest is the effect of mobility parameter on the stability of two dimensional viscoelastic flows past an unconfined square cylinder. To fulfill this aim, the mobility parameter has been increased from 0 to 0.5 for different polymer concentrations. Results reveal that mobility factor noticeably affects the amplitude of lift coefficient and shedding frequency more strongly at higher polymer concentrations

An experimental investigation on impact process of Boger drops onto solid surfaces

Samira Mandani,Mahmood Norouzi,Mohammad Mohsen Shahmardan 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.2

In this paper, the impact dynamics of Boger drops on dry solid surfaces is investigated experimentally. The effects of viscosity, surface wettability, and impact velocity on the spreading and receding behavior of the Newtonian and viscoelastic drops are studied in detail. They are impinged upon Plexiglas and glass substrates, which have hydrophilic properties, at the impact velocities 4.03 m/s and 4.22 m/s. The polyacrylamide drops spread out more widely and recede more rapidly than the glycerin drops. The impact velocity and the liquid viscosity have more influence on the spreading phase. However, the surface wettability shows only a minute effect on the spreading phase but a very significant effect on the receding phase. On the receding stage, the effect of impact velocity was only observed on the behavior of the low-viscosity drops. Therefore, when the low-viscosity drops impact on a hydrophilic substrate, the higher impact velocity, the receding velocity is increased.

Effects of viscous dissipation on heat convection of viscoelastic flow inside isothermal channels and tubes

Seyed Zia Daghighi,Mahmood Norouzi 한국유변학회 2018 Korea-Australia rheology journal Vol.30 No.4

In the present paper, analytical solutions for thermal convection of the Finitely Extensible Nonlinear Elastic model with Peterlin’s closure (FENE-P) in isothermal slits and tubes are presented by considering the viscous dissipation effects for the first time. Temperature distributions are derived in closed form, namely the HeunT function, and Frobenius series solutions for the slit and the tube flows, respectively. The effects of fluid elasticity, the Brinkman number and the extensibility parameter on the thermal convection characteristics of FENE-P fluid flows are investigated in detail. Generally, the Brinkman number causes a fall in the Nusselt number, but a rise in the centerline temperature. The results reveal that during the cooling process the Nusselt number experiences a decrease with the Brinkman number, while the centerline temperature rises. However, during the heating process the former increases and the latter decreases. As the main innovation of this study, the results show a strong relation between the Nusselt number and the Brinkman number and also between the centerline temperature and the Brinkman number.

Dissipative particle dynamics modeling of MR fluid flow in a novel magnetically optimized mini-MR damper

Ghafarian Eidgahi Moghadam Mohsen,Shahmardan Mohammad Mohsen,Norouzi Mahmood 한국유변학회 2022 Korea-Australia rheology journal Vol.34 No.4

Magnetically optimization of mini-MR damper with focused on MR fluid properties and damper construction is investigated using dissipative particle dynamics method as a molecular scale modeling technique. To select a suitable MR fluid, the effect of diameter and weight of magnetic particles on damping force of 10 N as set point is studied. The results show damping force increases by increasing diameter of magnetic particles and finally trends to a constant value while changes nonparabolic by enhancement of their weight. The results of studies on structural parameters of damper show that by increasing gap size of flow passage, damping force increases while enhancement in inner diameter of cylinder and piston length has reverse effect. Optimum design of MR damper completed by investigation on electrical coils in terms of their arrangement and step wise distribution of magnetic fi eld strength as our major innovation. To optimum operating conditions of MR damper at minimum electrical energy consumption and hysteresis level, the scenario of three segment coils in length of 3, 5, and 7 mm at base relative magnetic strength of 40% with 15% difference in steps by utilizing 140CG MR fluid as agent fluid are selected.

Hepatic Steatosis: Prevalence and Host/Viral Risk Factors in Iranian Patients with Chronic Hepatitis B Infection

Poortahmasebi, Vahdat,Alavian, Seyed Moayed,Keyvani, Hossein,Norouzi, Mehdi,Mahmoodi, Mahmood,Jazayeri, Seyed Mohammad Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.9

Background: In chronic hepatitis B (CHB), the presence of hepatic steatosis (HS) seems to be associated with known host and viral factors which may influence the long-term prognosis of chronic hepatitis B (CHB), probably leading to cirrhosis and hepatocellular carcinoma (HCC). Different from chronic hepatitis C (CHC), factors associated with HS in CHB are not clearly explored. Materials and Methods: 160 CHB patients were divided into two groups depending on the results of liver biopsy. Group I consisted of 71 patients with confirmed steatosis. Group II comprised 89 patients without steatosis. The groups were compared in terms of basal characteristics, body mass index (BMI), liver enzymes (ALT, AST, ALP), serum fasting blood sugar (FBS) and lipids, hepatitis B e antigen (HBeAg), viral load, and histological findings. Results: In terms of host factors, male gender, older age, BMI, high serum FBS and lipid levels were associated with HS. On the other hand, ALT levels, the HAI scores of necroinflammation and stage of fibrosis did not associate with HS. On multivariate analysis, parameters of sex, BMI, cholesterol and FBS levels were independently associated with HS. Regarding viral factors, HBeAg negativity was significantly associated with HS (81.7%, p value 0.006), but not HBV DNA level (p value 0.520). Conclusions: HS in CHB appears to be unrelated to the status of HBV replication. However, fibrosis progression in CHB is related to variable host factors. HS may be enhanced through these factors in HBV chronic patients.

Effects of Elastic forces on Viscous Dissipation in Forced-Convection Heat Transfer of Viscoelastic Fluid

Ali Minaeian,Juyong Jeong,Mahdi Nili-Ahmadabadi,Mahmood Norouzi,Kyung Chun Kim 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.08

Optimal determination of rheological parameters for herschel-bulkleydrilling fluids using genetic algorithms (GAs)

Reza Rooki,Faramarz Doulati Ardejani,Ali Moradzadeh,Hossein Mirzaei,Vassilios Kelessidis,Roberto Maglione,Mahmood Norouzi 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

The rheological properties of a drilling fluid directly affect flow characteristics and hydraulic performance. Drilling fluids containing bentonite mixtures exhibit non-Newtonian rheological behavior which can be described with a high degree of accuracy by the three-parameter Herschel-Bulkley (HB) model. To deter\-mine the HB parameters, standard statistical techniques, such as the non-linear regression (NL) method are routinely used. However, sometimes they provide non physically acceptable solutions which could produce wrong values of the significant hydraulic parameters which affect drilling operations. To obtain more accu\-rate results, the Golden Section (GS) method was subsequently developed by Kelessidis et al. (2006). In this work a different technique was developed using the Genetic Algorithms (GAs) to provide an easy-to-use tool in order to determine the three parameters of the Herschel-Bulkley model more accurately. To eval\-uate the accuracy of the GAs method, experimental viscometric data sets of drilling fluids were taken from the literature and the results were compared with the ones obtained by using the NL and GS techniques. The results show that the GAs and the GS methods provide similar results with very high correlation coef\-ficients and small sum of square errors for most of the samples exhibiting negative yield stress values by the NL technique, while giving similar to the NL technique for the samples that were predicted with positive yield stress. However, in some cases, the GAs method gives better and more realistic results than the GS method.

Optimal determination of rheological parameters for herschel-bulkley drilling fluids using genetic algorithms (GAs)

Rooki, Reza,Ardejani, Faramarz Doulati,Moradzadeh, Ali,Mirzaei, Hossein,Kelessidis, Vassilios,Maglione, Roberto,Norouzi, Mahmood 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.3

The rheological properties of a drilling fluid directly affect flow characteristics and hydraulic performance. Drilling fluids containing bentonite mixtures exhibit non-Newtonian rheological behavior which can be described with a high degree of accuracy by the three-parameter Herschel-Bulkley (HB) model. To determine the HB parameters, standard statistical techniques, such as the non-linear regression (NL) method are routinely used. However, sometimes they provide non physically acceptable solutions which could produce wrong values of the significant hydraulic parameters which affect drilling operations. To obtain more accurate results, the Golden Section (GS) method was subsequently developed by Kelessidis et al. (2006). In this work a different technique was developed using the Genetic Algorithms (GAs) to provide an easy-to-use tool in order to determine the three parameters of the Herschel-Bulkley model more accurately. To evaluate the accuracy of the GAs method, experimental viscometric data sets of drilling fluids were taken from the literature and the results were compared with the ones obtained by using the NL and GS techniques. The results show that the GAs and the GS methods provide similar results with very high correlation coefficients and small sum of square errors for most of the samples exhibiting negative yield stress values by the NL technique, while giving similar to the NL technique for the samples that were predicted with positive yield stress. However, in some cases, the GAs method gives better and more realistic results than the GS method.