M. Nabil Esmail

Rheological properties of carboxymethyl cellulose

This work is a complete and comprehensive study of the rheological properties of carboxymethyl cellulose (CMC) solutions. The study was carried out using the computer controlled RheoStress RS100 system of Haake. CMC concentration in the test solutions ranged by weight from 1 to 5%. This range was sufficiently wide to reveal the nearly Newtonian behavior at the lower end of concentrations, and the definitely pseudoplastic, thixotropic, and viscoelastic behaviors of CMC solutions at the higher end of concentrations. The scope of the study included measurements of steady-state parameters, transient shear stress response, and yield stress. In addition, the thixotropic, creep recovery, and dynamic responses of solutions with high concentrations were measured.

Conversion of syngas to hydrocarbons in a tube-wall reactor using CoFe plasma-sprayed catalyst: experimental and modeling studies

Abstract Catalyst activity and product selectivity studies of the conversion of synthesis gas to various hydrocarbon fractions were performed in a single-tube tube-wall reactor (TWR) using a CoFe plasma-sprayed catalyst with the operating conditions: temperature 250–275°C, pressure 0.1–1.03 MPa, exposure velocity 139–722 μms −1 , and a H 2 :CO ratio of 2.0. The catalyst activity in terms of CO conversion was highest (98.5% m/m ) at an exposure velocity of 139 μms −1 , temperature of 275°C, and in the pressure range 0.69–1.03 MPa. The selectivity to hydrocarbons was 43–50% ( m/m ) in the pressure range 0.69–1.03 MPa whereas the selectivity to C 5 + hydrocarbons was over 40% of the total hydrocarbons produced. The production of propylene was higher than ethylene under similar process conditions. The performance of the TWR was predicted by a numerical model. The model is based on the complete two-dimensional transport equations and reaction rate equations, developed for the CoFe catalyst. Predictions are made for the temperature along the axis of the reactor, for CO and H 2 conversions as functions of the reactor length and the exposure velocity, and the axial H 2 O and CO 2 concentrations.

THE EFFECT OF SUBSTRATE GEOMETRY ON DYNAMIC CONTACT ANGLES IN SURFACE WETTING

Dynamic contact angles play a central role in the problem of wetting of surfaces. A solid surface is moving steadily through the free surface of a liquid. The angle between the plunging solid surface and the liquid free surface at the line of solid-liquid contact is the dynamic contact angle. This work compares experimentally measured dynamic contact angles of horizontally rotating rolls of different diameters with those of circular fibers, and tapes. The comparison also includes dry and pre-wet surfaces. Dynamic contact angles depend on the geometry of the wetted substrate. Specifically the geometry through its curvatures affects the surface tension forces at the contact line. Smaller diameter rolls generate smaller angles. In wetting of circular fibers the angles are the smallest compared to tapes and rolls. Flat dry tapes form the largest angles when they are wetted. This implies that the curvatures of the circular rolls and fibers contribute to the balance of surface energies at the contact line. Pre-...

A deficient spline function approximation to fourth-order differential equations

Abstract An approximate spline solution is developed for the initial value problem of a fourth-order ordinary differential equation. The approximation is based on deficient spline polynomials of degree m = 8 and deficiency 4. The existence and uniqueness of the solution, which satisfies a Lipschitz condition, are proved. The consistency, stability, and consequently convergence of the solution are established. Furthermore, the method is proved to be of order 9, and the errors are limited by the relation ‖S (i) (x) − y (i) (x)‖ = O(h 9 − i ), i = 0(1)8.