Papers by Mohd Sobri Takriff
Chemical Engineering Science, 2016
Hydrodynamic instabilities emerged both in axial as well as radial direction. Instabilities creat... more Hydrodynamic instabilities emerged both in axial as well as radial direction. Instabilities created at the steam water interface and propagated towards the walls. These instabilities produce pressure stresses in a non-deterministic way. Both hydrodynamic instabilities and their induced stresses are asymmetric in nature. The strength of these instabilities varies along radial as well as axial directions.
Mathematical Problems in Engineering, 2013
This paper presents the application of a mathematical model for simulation of the swirling flow i... more This paper presents the application of a mathematical model for simulation of the swirling flow in a tube induced by elliptic-cut and classical twist tape inserts. Effects of the twist ratio (y=2.93, 3.91, and 4.89) and cut depth (w=0.4, 0.8, and 1.4 cm) on heat transfer enhancement (Nu) and friction factor (f) in laminar flow are numerically investigated. The simulation is carried out using commercial CFD package (FLUENT-6.3.26) to grasp the physical behaviour of the thermal and fluid flows of a constant heat-fluxed tube fitted with elliptic-cut twist tape in the laminar flow regime for the Reynolds number ranging from 200 to 2100. The simulated results matched the literature correlations of plain tube for validation with 8% variation for Nusselt number and 10% for friction factor. The results show that the heat transfer rate and friction factor in the tube equipped with elliptic-cut twist tape (ECT) are significantly higher than those fitted with classical twist tape (CTT). Moreov...
Journal of Central South University of Technology, 2010
The inhibition ability of 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT), ethylenediaminetetr... more The inhibition ability of 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT), ethylenediaminetetra-acetic acid (EDTA) and thiourea (TU) for mild steel corrosion in 1.0 mol/L HCl solution at 30 ℃ was investigated. Tafel polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the influence of these organic compounds as corrosion inhibitors of mild steel in 1.0 mol/L HCl solution at 30 ℃. The inhibition mechanism was discussed in terms of Langmuir isotherm model. Results obtained from Tafel polarization and impedance measurements are in a good agreement. The inhibition efficiency increases with the increase of the inhibitor concentration. The adsorption of the inhibitors on the mild steel surface follows Langmuir adsorption isotherm and the free energy of adsorption ∆G ads indicates that the adsorption of APTT, EDTA, and TU molecules is a spontaneous process and a typical chemisorption.
Chemical Engineering Communications, 2002
An investigation on oscillatory flow in a baffled column was carried out to determine the effects... more An investigation on oscillatory flow in a baffled column was carried out to determine the effects of various operating parameters on interstage backmixing. Among parameters studied in this work were liquid flow rate, liquid viscosity, oscillation frequency, and oscillation amplitude. The results of this study indicated that the interstage backmixing had a maximum value under nonflow condition but decreased with
The study was carried out to determine the effect of pulsating frequencies exiting from a hot cir... more The study was carried out to determine the effect of pulsating frequencies exiting from a hot circular air jet on the local heat transfer of a flat impingement aluminium plate. The velocity profile of a steady heated circular air jet and pulsating air jet at frequencies of 10 and 20 Hz was measured in the first part of the study. The same set-up was used to measure the heat flux of the pulsating jet impinging on a flat aluminium plate. The heat flux of the heated air jet impinging on the plate was measured using a heat flux micro-sensor at radial positions between 0 to 12 cm away from the stagnation point. Measurement of the heat flux was used to calculate the local heat transfer coefficient and local Nusselt Number for steady air jet and for air jet pulsating frequencies of 10 and 20 Hz. The Reynolds number used were 16 000, 23 300 and 32 000. Results obtained show that the local Nusselt number calculated at all measurement point for pulsating jet were higher than the local Nusselt number for steady jet. The results for pulsating jet Nusselt number was higher than the steady jet Nusselt number for the value of frequencies measured are due to the higher localised heat transfer. The higher Nusselt number obtained at localized radial positions can be due to the higher instantaneous velocity as was shown from the velocity profile plotted in the first part of the experiment. The relationship between the two results shows that higher flow velocity and turbulence intensity gives higher localized heat transfer.
Abstract The study was carried out to determine the effect of pulsating frequencies on the local ... more Abstract The study was carried out to determine the effect of pulsating frequencies on the local and average heat transfer characteristic of a heated circular air jet. The velocity profile of a heated circular pulsating air jet was measured in the first part of the study. The same set-up was used to measure the heat flux of the pulsating jet impinging on a wall. The heat flux of the heated air jet impinging on the plate was measured using a heat flux microsensor at different radial positions. Measurement of the heat flux was used to calculate the average ...
The traditional laboratory work based on guided assignment will not be adequate within the outcom... more The traditional laboratory work based on guided assignment will not be adequate within the outcome based learning environment. Innovative approaches that require active involvement of the students in the learning activities are necessary in ensuring that the targeted learning outcomes are achieved. The Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, introduced open ended laboratory work in 2008 as part of the effort to provide suitable learning environment for the students to achieve the learning outcomes. This paper describes a comparison study between traditional and open ended laboratory; the implementation of the open ended laboratory and its impact on the overall students learning experience with emphasis on programme outcomes. The open ended laboratory assignment was first implemented in the first semester of the 2008-2009 academic years. The students are divided in groups of four and were only given a statement on their laboratory assignment. They are required to determine the objectives and the scope of the laboratory assignment, to identify the necessary apparatus and prepare the step by step methodology. Each group is required to prepare a report on the above elements and present the results. They are graded based on the originality of their idea, results and discussion from the laboratory assignment and oral presentation. Initially the students had some difficulties because they were not familiar with such laboratory assignment. However, the performance was improved in the proceeding semesters and they are better prepared for their final year research project.
American Journal of Engineering and Applied Sciences, 2009
Abstract Problem Statement: Applications of impingement jets in industry for heating and cooling ... more Abstract Problem Statement: Applications of impingement jets in industry for heating and cooling purposes requires a high convective heat transfer coefficient. Numerous studies have been conducted to improve the convective heat transfer coefficient for a steady impinging jet. A pulsating jet has a very high potential in replacing steady jet after it been found able to increase the heat transfer coefficients at certain pulsating frequencies. The objectives of this study were to;(i) determine the velocity profile of a circular pulsating air ...
Outcome based engineering education (OBE) requires continual quality improvement (CQI) to ensure ... more Outcome based engineering education (OBE) requires continual quality improvement (CQI) to ensure that the students achieved the intended learning outcomes. Students are the most important stakeholder in the OBE learning environment and their input in the CQI process is needed to ensure that improvement measures that were put in place as a result of CQI are relevant and suitable. This paper reports the process of obtaining students' feedback, how the information was processed and the improvement measures that were implemented at the department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia (UKM). Students' feedback were obtained via an online course assessment system, students dialog session and exit survey among the graduating class. Based on the inputs, improvements were made on the teaching and learning activities such as the introduction of integrated projects in the second and third year curriculum, open-ended laboratory assignments, formalization of industrial visits and lectures as part of the learning activities, Chem-e-car project and poster presentation session. Improvements that were introduced based on the feedbacks from the students have help to the students to achieve the intended learning outcomes and have received positive feedback from the stakeholders.
Desalination, 2003
This paper presents a modified Donnan-Steric-Pore model (DSPM) to predict the rejection of mixtur... more This paper presents a modified Donnan-Steric-Pore model (DSPM) to predict the rejection of mixture of NaCI:Na 2 SO 4 in nanofiltration (NF) membrane based on the extended Nernst-Planck equation with the incorporation of charge and steric effects for the transport of ions inside ...
Corrosion Science, 2009
The corrosion protection of mild steel in a 2.5 M H 2 SO 4 solution by 4,4-dimethyloxazolidine-2-... more The corrosion protection of mild steel in a 2.5 M H 2 SO 4 solution by 4,4-dimethyloxazolidine-2-thione (DMT) was studied at different temperatures by measuring changes in open circuit potential (OCP), potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Corrosion current densities calculated from EIS data were comparable to those obtained from polarisation measurements. Results showed that DMT inhibited mild steel corrosion in a 2.5 M H 2 SO 4 solution and indicated that the inhibition efficiencies increased with the concentration of inhibitor, but decreased proportionally with temperature. Polarisation curves showed that DMT is a mixed-type inhibitor. Changes in impedance parameters suggested the adsorption of DMT on the mild steel surface, leading to the formation of protective films. The DMT adsorption on the mild steel surface followed the Langmuir adsorption isotherm. The kinetic and thermodynamic parameters for dissolution and adsorption were investigated. Comprehensive adsorption (physisorption and chemisorption) of the inhibitor molecules on the mild steel surface was suggested based on the thermodynamic adsorption parameters.
Journal of The Taiwan Institute of Chemical Engineers, 2010
Advanced Materials Research, 2010
The morphology and kinetics of the localized corrosion of aluminum alloy (AA)2024-T3 (UNS A92024)... more The morphology and kinetics of the localized corrosion of aluminum alloy (AA)2024-T3 (UNS A92024) at the open-circuit potential were investigated by in situ atomic force microscopy (AFM) scratching. The addition of metavanadate to chloride solutions resulted in outstanding corrosion inhibition. Samples exposed to 0.1 M sodium chloride (NaCl) with no inhibitor developed a trench-like attack at the periphery of large Al-Cu-Fe-Mn-(Si) intermetallic phases. The addition of dilute metavanadate markedly reduced the kinetics of the attack. In addition, most S-phase particles remained free of attack. Higher concentrations of metavanadate increased protection even further so that only high AFM tip forces could induce pitting corrosion. Corrosion attack was immediately observed when AA2024-T3 samples were exposed to chloride solutions containing orange decavanadates. The attack nucleated on the exposed surface but not under the AFM tip. The attack grew continuously, accompanied by gas evolution and formation of corrosion products. Optical inspection after the test indicated severe corrosion damage, confi rming an overall poor performance of orange decavanadate solutions as corrosion inhibitors.
Research on Chemical Intermediates
Inhibition of corrosion of nickel–aluminum bronze alloy (NAB) by use of 4-amino-5-phenyl-4H-1,2,4... more Inhibition of corrosion of nickel–aluminum bronze alloy (NAB) by use of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol (APTT) was investigated by monitoring weight loss and open-circuit potentials (OCP), and by use of electrochemical impedance spectroscopy (EIS). Quantum chemical data were calculated by use of the density functional theory (DFT) model. Results showed that APTT inhibits corrosion of NAB alloy fairly well. The efficiency of inhibition increases with increasing concentration of APTT, and adsorption of the inhibitor obeys the Langmuir adsorption isotherm model. Negative values of adsorption free energy indicate chemical adsorption is spontaneous. The theoretical study showed that sulfur and nitrogen atoms (S, N7 and N8) were the reactive sites.
Journal of Applied Sciences, 2009
The inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) in 2... more The inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) in 2.5 M H2SO4 solution and the effect of hydrodynamic condition on inhibition process were studied. The hydrodynamic condition experiments are simulated by rotating cylinder electrode (RCE). Change of open circuit potential (OCP) with immersion time and potentiodynamic polarization were used to study the effect of hydrodynamic conditions on the inhibition process. Results obtained from changes of open circuit potential (OCP) with immersion time, and potentiodynamic polarization are in good agreement and indicated that the inhibition process was flow velocity dependence.
Research on Chemical Intermediates
The inhibition ability of phthalhydrazide (PTD) for mild steel in 1 M HCl at 30 °C was investigat... more The inhibition ability of phthalhydrazide (PTD) for mild steel in 1 M HCl at 30 °C was investigated by electrochemical measurements [impedance spectroscopy (EIS) and potentiodynamic polarization techniques] and quantum chemical calculations. The frontier molecular orbital energy E HOMO (highest occupied molecular orbital), E LUMO (lowest unoccupied molecular orbital), and the Mulliken charge distribution were calculated and are discussed. Results showed that the inhibition efficiency of PTD increased with inhibitor concentration. The maximum corrosion inhibition efficiency was 77.6% at 2 mM PTD. Adsorption of the inhibitor followed the Langmuir adsorption isotherm. Adsorption of inhibitor molecules on mild steel surface occurred spontaneously and chemically. Quantum chemical calculations showed that the low performance of PTD as a corrosion inhibitor is due to the large energy gap (E HOMO − E LUMO).
Corrosion Science, 2010
The corrosion inhibition of mild steel in a 2.5 M H 2 SO 4 solution by 4-amino-5-phenyl-4H-1, 2, ... more The corrosion inhibition of mild steel in a 2.5 M H 2 SO 4 solution by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) was studied at different temperatures, utilising open circuit potential, potentiodynamic and impedance measurements. The results indicate that APTT performed as an excellent mixed-type inhibitor for mild steel corrosion in a 2.5 M H 2 SO 4 solution and that the inhibition efficiencies increased with the inhibitor concentration but decreased proportionally with temperature. The kinetic and thermodynamic parameters for adsorption of APTT on the mild steel surface were calculated. A chemisorption mechanism of APTT molecules on the mild steel surface was proposed based on the thermodynamic adsorption parameters.
Materials Chemistry and Physics, 2010
Corrosion Science, 2010
A relationship between quantum chemical parameters for three triazole compounds and their inhibit... more A relationship between quantum chemical parameters for three triazole compounds and their inhibition ability was studied using electrochemical measurements (potentiodynamic polarization and EIS), molecular dynamic method and quantum chemical calculations. Electrochemical measurements results revealed that the inhibition efficiencies increased with the concentration of inhibitors. The molecular dynamic method results showed that the higher interaction potential between the inhibitor and metal surface, the higher the inhibition efficiency. The quantum chemical calculation results showed that the triazole ring is the active site in these inhibitors and they can absorb on Fe surface by donating electrons to Fe d-orbital.
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Papers by Mohd Sobri Takriff