Piston-driven laminar flow and heat transfer in a plane channel with a sudden expansion

 This paper presents a numerical study of piston-driven heat transfer and fluid flow in a plane channel containing a sudden expansion. The numerical method employed is based on a control-volume-based finite element method for incompressible flow with a staggered and moving grid and SIMPLER algorithm for pressure-velocity coupling. The numerical results show a good agreement with the experimental data reported in the literature. Results concerning time and space evolution of the thermal and flow fields are presented for different values of the expansion ratio, the initial clearance volume, and the piston velocity. Received: 20 April 2002 / Accepted: 23 January 2003     

Crystallization behavior of poly(lactic acid)/elastomer blends

Differential Scanning Calorimetry (DSC) was used to evaluate the crystallization behavior of poly(lactic acid) and its blends with elastomer. It has been observed that the cold crystallization temperature of the blends decreased as the weight fraction of elastomer increased as well as the onset temperature of cold crystallization also shifted to lower temperature. In non-isothermal crystallization experiments, the crystallinity of poly(lactic acid) increased with a decrease in the heating and cooling rate. The melt crystallization of poly(lactic acid) appeared in the low cooling rate (1, 5 and 7.5 °C/min). The presence of low elastomer tends also to increase the crystallinity of poly (lactic acid). The DSC thermogram at ramp of 10 °C/min showed the maximum crystallinity of poly(lactic acid) is 36.95% with 20 wt% elastomer contents in blends. In isothermal crystallization, the cold crystallization rate increased with increasing crystallization temperature in the blends. The Avrami analysis showed that the cold crystallization was in two stages process and it was clearly seen at low temperature. The Avrami exponent (n) at first stage was varying from 1.59 to 2 which described a one-dimensional crystallization growth with homogeneous nucleation, whereas at second stage was varying from 2.09 to 2.71 which described the transitional mechanism to three dimensional crystallization growth with heterogeneous nucleation mechanism. The equilibrium melting point of poly(lactic acid) was also evaluated at 176 °C.     

Modeling and Optimization of Nanofluid Flow in Flat Tubes Using a Combination of CFD and Response Surface Methodology

In this paper, modeling and optimization of Al₂O₃–water nanofluid flow in horizontal flat tubes is performed using a combination of computational fluid dynamics (CFD) and response surface methodology (RSM). At first, nanofluid flow is solved numerically in various flat tubes using CFD techniques and the heat transfer coefficient () and pressure drop () in tubes are calculated. The numerical simulations are performed using two phase mixture model by FORTRAN programming language. The flow regime and the wall boundary conditions are assumed to be laminar and constant heat flux respectively. In the second step, numerical data of the previous step will be used for a parametric study, modeling and optimization of nanofluid flow in flat tubes using the RSM technique.It is shown that the results include important design information on nanofluid parameters in flat tubes. The important design information about the relationship between design variables and responses will not be achieved without the simultaneous use of CFD and optimization approaches.     

Investigation of nickel deposition onto section and central longitudinal surfaces of AA1370 aluminum electrical wire with and without a weak permanent magnetic field

In this work a special regard is given to the morphology of the nickel deposited layers, onto AA1370 aluminum section and central longitudinal surfaces, with and without a weak magnetic field oriented in parallel and perpendicular to the coated surface in modified Watt bath. The obtained results show the formation of honeycomb structure nickel deposits for samples treated with weak parallel oriented field under approximately 0.3 A/cm₂, and partial dendritic structure nickel deposit for samples treated with weak perpendicular oriented magnetic field, the perimeter deposits with and without magnetic field is different to the deposits in the remain surface. We attributed the defect of nickel deposits on the surfaces with and without magnetic field to the distribution of the intermetallics particles and we attributed the honeycomb structure to the escapement of hydrogen and oxygen.     

Corrosion monitoring of hydrogen by HUP probe in the presence of sulphide and thiourea

The effect of sulphide and thiourea on hydrogen uptake during the corrosion of steel in deaerated pH3 has been studied using an electrochemical hydrogen probe incorporating a solid electrolyte (HUP) and lead dioxide (PbO₂) as a reference electrode. This probe has been used for the quantitative determination of the hydrogen activity generated during the corrosion of steel. The sensor voltage implies an average equivalent hydrogen pressure in uncharged steel of 2 × 10^?18 atmospheres. During the corrosion of steel, this value increases by very large amounts; thus in deaerated pH3, the equivalent pressure rose by 10^24.5 in the presence of 200 ppm sulphide and by 10² in the presence of 100 ppm thiourea. Weight loss and AC impedance methods were also performed under the same conditions as the hydrogen measurements. The hydrogen probe data were correlated with a.c impedance and weight loss results in order to understand the effect of S^2? and thiourea on hydrogen uptake.     

A practical approach for modelling and control of biomass pyrolysis pilot plant with heat recovery from combustion of pyrolysis products

A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to improve energy balance of the process and to be environmentally friendly by avoiding rejection of pyrolysis pollutants fumes into the atmosphere. The high number of parameters involved in a pyrolysis process makes it difficult to specify an optimum procedure for charcoal yield and pyrolysis cycle durability. So the knowledge of the essential parameters which govern the kinetics mechanisms of the biomass thermal decomposition and the combustion of pyrolysis gases is very useful to understand the operating cycle of the plant. In the present study a thermochemical model is developed in order to simulate and control the operating cycle of the system. The effect of the inlet molar air flow rate on the temporal evolution of biomass mass loss rate and temperatures in the different active zones of the pilot plant as well as the determination of the critical inlet molar air flow rate for which accidental runaway of combustion reactions occurs are presented. To avoid this accidental phenomenon a Proportional-Integral-Derived (PID) anticipated regulation is used in order to control temperatures evolution in the different zones of the device and avoid the runaway of combustion reactions.     

Nonlinear feedback control and trajectory tracking of vehicle

This paper mainly studies nonlinear feedback control applied to the nonlinear vehicle dynamics with varying velocity. The main objective of this study is the stabilisation of longitudinal, lateral and yaw angular vehicle velocities. To this end, a nonlinear vehicle model is developed which takes both the lateral and longitudinal vehicle dynamics into account. Based on this model, a method to build a nonlinear state feedback control is first designed by which the complexity of system structure can be simplified. The obtained system is then synthesised by the combined Lyapunov–LaSalle method. The simulation results show that the proposed control can improve stability and comfort of vehicle driving. Moreover, this paper presents a lemma which ensures the trajectory tracking and path-following problem for vehicle. It can also be exploited simultaneously to solve both the tracking and path-following control problems of the vehicle ride and driving stability. We also show how the results of the lemma can be applied to solve the path-following problem, in which the vehicle converges and follows a designed path. The effectiveness of the proposed lemma for trajectory tracking is clearly demonstrated by simulation results.     

Optimization of rotor speed based on stretching,efficiency, and viscous heating in nonintermeshing internal batch mixer: Simulation and experimental verification

Optimization of rotor speed based on stretching, efficiency, and viscous heating in nonintermeshing internal batch mixer has been investigated using polymer melt. A practical optimization technique was followed for optimization. Four different rotor speeds were used and characterized numerically with viscous dissipation and stretching. The heat distribution between rotor edge and mixer wall was calculated. Stretching experienced by the fluid was analyzed and the result was verified experimentally using particle tracking method. Exponential increase of energy dissipation between the rotor edge and the barrel at higher speed highlighted the importance of choosing the thermal properties of the polymer to avoid thermal degradation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of thermal degradation on the impact properties of PVC compounds

An instrumented drop weight impact test was used to study the effect of thermal degradation on the impact properties of PVC compounds. The impact resistance of the aged compounds related well with their weight loss and hence, with thermal degradation. Each compound showed a specific weight loss percentage that correlated with a 50% loss in its impact properties (failure point), irrespective of the aging temperature. The results were also used to estimate a thermal index (TI) of each compound in a rapid and reliable way.     

Contribution of flow deformation to the shrinkage of injection molded PVC

The viscoelastic nature of PVC cannot be ignored during the injection molding process. Strains imposed on the compound during the injection stage display recovery dynamics that are indicative of the temperature at which the strains were imposed. A mathematical model, employing “approximate” time-temperature modulus relationships, provided the basis for interpreting the shrinkage data. A distribution map of the various relative temperatures attained within the part during injection was determined.