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Mulyazmi,National University of Malaysia | Mulyazmi,Bung Hatta University | Daud W.R.W.,National University of Malaysia | Majlan E.H.,National University of Malaysia | Rosli M.I.,National University of Malaysia
International Journal of Hydrogen Energy | Year: 2013

The design of a proton exchange membrane (PEM) fuel cell system is important for the optimization of the function of supporting parameters in the fuel cell. The water balance in a PEM fuel cell is investigated based on the water transport phenomena. In this investigation, the diffusion of water from the cathode side to the anode side of the cell is observed to not occur at 20% relative humidity at the cathode (RHC) and 58% relative humidity at the anode (RHA). The minimum concentration of condensed water at the cathode side is observed at a cathode gas inlet relative humidity of 40% RHC-92% RHC and at temperatures between 343 K and 363 K. RHC operating conditions that are greater than 90% and at a temperature of 363 K increased the concentration of condensed water and occurred quickly, which result in a water balance that became difficult to control. On the anode side, the condensation of water is observed at operating temperatures of 353 K and 363 K. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Desmiarti R.,Bung Hatta University | Li F.-S.,Gifu University
ITB Journal of Engineering Science | Year: 2011

The sorption and the degradation capacity of natural estrogens in freshwater environmental system in Japan were performed. Batch experiments were examined in water-sediment suspensions using six layers of sediment under aerobic and anaerobic conditions. The results indicated that the water-sediment partition coefficient of E1 (K d E1) was higher than E2 (K d E2). The degradation rate of E1 (k E1) was smaller than E2 (k E2). Under aerobic and anaerobic conditions, E1 was formed from E2. The degradation rate of E2 (k E2) from the surface to bottom of sediment layers was estimated fell in the range from 0.114 to 0.026 h -1 and 0.05 to 0.014 h -1 under aerobic and anaerobic conditions, respectively.

Sulong A.B.,National University of Malaysia | Ramli M.I.,National University of Malaysia | Hau S.L.,National University of Malaysia | Sahari J.,National University of Malaysia | And 3 more authors.
Composites Part B: Engineering | Year: 2013

Highly filled conductive fillers (>60 vol%) for conductive polymer composites (CPCs) cause the degradation of rheological and mechanical properties. This study investigated the rheological properties of highly filled metal powder (SS316L) in a polymer matrix composite combined with carbon nanotubes (CNTs) and Graphite (G). The effects of filler concentrations and chemical functionalization on the mechanical and electrical properties of the resulting CPC were determined. Feedstocks with different concentrations were injection molded, and the molded specimens were subjected to tests of tensile strength, three-point bending, hardness, and three-point probe electrical conductivity. The feedstock of CNTs/G/SS316L can be injection molded from 28 vol% polypropylene (PP). The functionalized CPC shows higher strength and elongation than as-produced CPC based on the tensile and flexural tests. The highest flexural and tensile strengths are 80 and 35 MPa, respectively. The functionalized CPC also exhibits higher hardness and better electrical properties than as-produced CPC. Thus, functionalization with CNTs and Graphite enable the reinforcement and formation electrical conducting networks between metal- and carbon-based fillers within a polymer matrix. © 2013 Elsevier Ltd. All rights reserved.

Suherman H.,National University of Malaysia | Suherman H.,Bung Hatta University | Sahari J.,National University of Malaysia | Sulong A.B.,National University of Malaysia
Advanced Materials Research | Year: 2011

Electrical properties of carbon nanotubes-based epoxy nanocomposites for high electrical conductive plate were investigated. Dispersion and incorporation mechanism between two conductive fillers with different sizes (CNTs and Graphite) in the polymer matrix are the key factors in the fabrication of high electrical conductivity plate. Different variation of carbon nanotubes (CNTs) (1∼10 wt %) and Graphite (G) (60 ∼ 69 wt %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by the internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in terms of variation of G and CNTs concentration were measured by the four point probe for in a plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are effective ways to produce high electrical conductive nanocomposites. The highest electrical conductivity was reached on 104.7 S/cm by addition 7.5 wt% of CNTs. Dispersion quality of G and CNTs in the epoxy matrix was observed on the fractured surface by scanning electron microscopic. © (2011) Trans Tech Publications, Switzerland.

The aim of this study was to analyze the teachers' understanding on the concept of limits and derivative and the way they deliver the subjects to their students. The study was divided into two main phases during two years of research. This research was conducted in 7 high schools vary from general, Islamic and occasional schools. The participants of the study were 20 in-service mathematics teachers from 7 high schools. Questioners were given to find out how teachers' understanding on the concepts and how they organized their class. The teachers' level of complexity on the subject was analyzed by Structure of the Observed Learning Outcome (SOLO) Taxonomy, and teachers' class organizations was analyzed by assessing and classifying their responds written on the questioner sheets and discussion with the selected participants. Based on the data, it can be figured out that the most teachers' position were on third level out of five level of SOLO Taxonomy. Data also told us that half of the teachers experienced the difficulties in teaching the concept due to their limitations on mastering subject. Data also showed that there is a relevance between teachers' level of understanding and teachers' ability in delivering subject to their students. © Published under licence by IOP Publishing Ltd.

Sulaimon S.,University of Technology Malaysia | Aziz A.A.,University Of Maiduguri | Nasution H.,Bung Hatta University
Applied Mechanics and Materials | Year: 2013

According to Montreal Protocol, HCFC22 (hydro chlorofluorocarbon), a commonly used refrigerant in domestic refrigeration and air-conditioner, must be phased out owing to its environmental problem. Several natural substances including ammonia, carbon dioxide, water and hydrocarbon (HC) such as propane (HC290) and butane (HC600) and their mixtures have immerged as close substitute. Literature showed that pure HC refrigerant may not be suitable enough because of the difference in operating pressure and volumetric cooling capacity when compared with HCFC22. The main objective of this study is to theoretically investigate different ratios of HC refrigerants HC290/HC600 mixtures flowing through adiabatic capillary tube using homogenous model. In this study, the percentage by volume of HC290 was varied from 30 to 40 % in a step of 5%. The pressure at the two extreme ends and temperature along the capillary tube, using HCFC22 refrigerant, which was used as benchmark, was experimentally determined in the air-conditioning (AC) system. Comparing the model results with the experimental data showed that HC refrigerants HC290/HC600 in ratio 35%/65% gave 2.95% minimum error and thus it can be used as a substitute to HCFC22 in the split-type AC system. © (2013) Trans Tech Publications, Switzerland.

Desmiarti R.,Bung Hatta University | Li J.,Gifu University | Li F.,Gifu University
Water, Air, and Soil Pollution | Year: 2012

The behavior of estrone (E1) and 17β-estradiol (E2) in relatively closed water environment was studied by continuous flow experiment using sediments from a freshwater reservoir. For this, four sediment columns (two oxic ones and two anoxic ones) were employed, which were structured by packing 30 cm of undisturbed sediment and 60 cm of overlying water collected from two sites within a reservoir. A mass balance model that considered the influent flux, the effluent flux, mass transfer, sorption, and biodegradation was proposed to describe the behavior of E2 and E1 in the columns. The results indicated that the water-sediment partition coefficient of E1 (K E1 d) was higher than E2 (K E2 d). The degradation rate of E1 (k E1) was smaller than E2 (k E2). Under both oxic and anoxic conditions, E1 was formed from E2. Furthermore, to clarify the impact of the model parameters such as the hydraulic retention time (HRT), K d, and k on the behavior of E2 and E1, variance analysis was performed based on the results of model simulations. The results showed that the concentrations of E2 and E1 in the column effluent were controlled most significantly by the sorption capacity of the natural estrogens onto sediment particles, with the determined contributory ratios changing in the order of sorption > HRT > degradation. © Springer Science+Business Media B.V. 2012.

Nasution H.,Bung Hatta University | Nasution H.,University of Technology Malaysia | Jamaluddin H.,University of Technology Malaysia | Syeriff J.M.,University of Technology Malaysia
Telkomnika | Year: 2011

Reducing energy consumption and to ensure thermal comfort are two important considerations for the designing an air conditioning system. An alternative approach to reduce energy consumption proposed in this study is to use a variable speed compressor. The control strategy will be proposed using the fuzzy logic controller (FLC). FLC was developed to imitate the performance of human expert operators by encoding their knowledge in the form of linguistic rules. The system is installed on a thermal environmental room with a data acquisition system to monitor the temperature of the room, coefficient of performance (COP), energy consumption and energy saving. The measurements taken during the two hour experimental periods at 5-minutes interval times for temperature setpoints of 20°C, 22°C and 24°C with internal heat loads 0, 500, 700 and 1000 W. The experimental results indicate that the proposed technique can save energy in comparison with On/Off and proportional-integral-derivative (PID) control.

Suherman H.,National University of Malaysia | Suherman H.,Bung Hatta University | Sulong A.B.,National University of Malaysia | Sahari J.,National University of Malaysia
Ceramics International | Year: 2013

The main challenges for commercialization of a single-filler graphite (G) polymer-matrix composite as bipolar plates are its low electrical conductivity and flexural strength. The minimum requirements set by the US Department of Energy (DOE) are the electrical conductivity and flexural strength to be greater than 100 S/cm and 25 MPa, respectively. In this study, the electrical conductivity of a G/epoxy (EP) composite (single filler) is only 50 S/cm (in-plane conductivity) at 80 wt% G. However, flexural strength is greater than 25 MPa. Using carbon nanotubes (CNTs) as the second filler at a concentration of 5 wt% in a CNTs/G/EP nanocomposite resulted in the in-plane and through-plane electrical conductivity and flexural strength being 180 S/cm, 75 S/cm, and 45 MPa, respectively. The density of the CNTs/G/EP nanocomposite is also less than that of G/EP composite, which demonstrates that a total weight reduction is achievable. © 2012 Elsevier Ltd and Techna Group S.r.l.

Suherman H.,National University of Malaysia | Suherman H.,Bung Hatta University | Sahari J.,National University of Malaysia | Sulong A.B.,National University of Malaysia
Ceramics International | Year: 2013

This paper focused on using a conductive polymer composite (CPC) as a potential replacement for the conventional graphite bipolar plate used in polymer electrolyte membrane fuel cells (PEMFC). Based on the requirements established by the US Department of Energy (DOE), the in-plane electrical conductivity and flexural strength are required to be greater than 100 S/cm and 25 MPa, respectively. The high filler loading is needed to satisfy the high in-plane electrical conductivity. However, the high filler loading reduces the flexural strength and manufacturability of the composite. In this study, the composites were prepared by compounding using an internal mixer followed by compression moulding. The combination of 10 vol% carbon black (CB) as the second filler with synthetic graphite/epoxy (SG/EP) resulted in the following composite properties: 150 S/cm (in-plane conductivity), 55 S/cm (through-plane conductivity), and 38.8 MPa (flexural strength). Used as the second filler, the CB, which had a small-sized diameter, formed conductive networks that filled the voids between the SG and polymer matrix. The in-plane electrical conductivity and flexural strength of the CB/SG/EP composites at the optimum composition exceeded the requirement for bipolar plate applications. © 2013 Elsevier Ltd and Techna Group S.r.l.

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