Amer Nordin Darus

MOICA: A novel multi-objective approach based on imperialist competitive algorithm

A novel multi-objective evolutionary algorithm (MOEA) is developed based on imperialist competitive algorithm (ICA), a newly introduced evolutionary algorithm (EA). Fast non-dominated sorting and the Sigma method are employed for ranking the solutions. The algorithm is tested on six well-known test functions each of them incorporate a particular feature that may cause difficulty to MOEAs. The numerical results indicate that MOICA shows significantly higher efficiency in terms of accuracy and maintaining a diverse population of solutions when compared to the existing salient MOEAs, namely fast elitism non-dominated sorting genetic algorithm (NSGA-II) and multi-objective particle swarm optimization (MOPSO). Considering the computational time, the proposed algorithm is slightly faster than MOPSO and significantly outperforms NSGA-II.

Mixed convection heat transfer of nanofluids over backward facing step having a slotted baffle

Mixed convection heat transfer over a 2-D backward facing step with an inclined slotted baffle by using nanofluids is numerically investigated. Continuity, momentum and energy equations were solved by using Finite Volume Method with SIMPLE algorithm to link the pressure and velocity fields. Different Reynolds numbers from 50 to 400 were applied. In addition, the downstream wall of the step from 10 ⩽ X ⩽ 15 was subjected to a uniform heat flux of 10,000 W/m2 while the upper wall and the baffle are kept insulated. Five different geometries (without baffle, with a vertical solid baffle, with a solid inclined baffle, with two inclined slotted baffle) were compared to find the best for heat transfer enhancement. Different nanoparticles such as Al2O3, CuO, ZnO and SiO2 with different volume fractions from 0% to 4% and different nanoparticle diameter from 20 to 50 nm were considered with water as a base fluid to explore the best nanofluid for heat transfer enhancement. It is clearly shown that nanofluids with more nanofluid volume fraction and small nanoparticle diameter affect the heat transfer considerably. Results clearly illustrated that SiO2 with 4% volume fraction and 20 nm nanoparticle diameter shows the best performance for heat transfer enhancement in compared with other nanoparticles. It is also found that the inclined baffle has the maximum average Nusselt number along the heated wall with high pressure drop and skin friction coefficient. However, by increasing Reynolds number, the inclined slotted baffle at D = 0.5 had an appropriate average Nusselt number and minimal changes of pressure drop and skin friction which can be considered as the appropriate geometry.

Simulation of forced convection in a channel with nanofluid by the lattice Boltzmann method

This paper presents a numerical study of the thermal performance of fins mounted on the bottom wall of a horizontal channel and cooled with either pure water or an Al2O3-water nanofluid. The bottom wall of the channel is heated at a constant temperature and cooled by mixed convection of laminar flow at a relatively low temperature. The results of the numerical simulation indicate that the heat transfer rate of fins is significantly affected by the Reynolds number (Re) and the thermal conductivity of the fins. The influence of the solid volume fraction on the increase of heat transfer is more noticeable at higher values of the Re.

A modified imperialist competitive algorithm for constrained optimization of plate-fin heat exchangers

In this study, to handle the design optimization of plate-fin heat exchangers, a constrained version of a newly introduced evolutionary algorithm, the imperialist competitive algorithm, is proposed. Imperialist competitive algorithm was initially established for unconstrained optimization problems and different strategies such as penalty functions were employed to handle the constraints in the previous studies. In the proposed constrained imperialist competitive algorithm, a feasibility-based ranking is employed in the imperialist competitive algorithm method. Seven design parameters and various constraints are considered for the design optimization in which minimum weight and minimum total annual cost were considered as the autonomous objective functions. The results are compared with those obtained by a genetic algorithm approach combined with a static penalty function scheme. Also, a comparison between the proposed algorithm and the original imperialist competitive algorithm is performed. The simulation results show that both the proposed algorithm and imperialist competitive algorithm are of higher accuracy than the genetic algorithm, which is commonly used. Also, the numerical experiment indicates that the modification in the imperialist competitive algorithm leads to better performance of the algorithm.

SIMULATION STUDIES OF GAS-SOLID IN THE RISER OF A CIRCULATING FLUIDIZED BED

A numerical parametric study was performed on the influence of various riser exit geometries on the hydrodynamics of gas-solid twophase flow in the riser of a Circulating Fluidized Bed (CFB). A Eulerian continuum formulation was applied to both phases. A two fluid framework has been used to simulate fully developed gas-solid flows in vertical riser. A two dimensional Computational Fluid Dynamics (CFD) model of gas-particle flow in the CFB has been investigated using the code FLUENT. The turbulence was modeled by a k-e turbulence model in the gas phase. The simulations were done using the geometrical configuration of a CFB test rig at the Universiti Teknologi Malaysia (UTM). The CFB riser column has 265 mm (width), 72 mm (depth) and 2.7 m height. The riser is made up of interchangeable Plexiglas columns. The computational model was used to simulate the riser over a wide range of operating and design parameters. In addition, several numerical experiments were carried out to understand the influence of riser end effects, particle size, gas solid velocity and solid volume fraction on the simulated flow characteristics. The CFD model with a k-e turbulence model for the gas phase and a fixed particle viscosity in the solids phase showed good mixing behaviour. These results were found to be useful in further development of modeling of gas solid flow in the riser. However, computational fluid dynamics (CFD) is emerging as a very promising new tool in modeling hydrodynamics. While it is now a standard tool for single-phase flows, it is at the development stage for multiphase systems, such as fluidized beds [3]. Many researchers have used commercial CFD codes for simulating multiphase problems and similar simulations were performed by Taghipour [4] in fluidized bed with the presence of air and sand using FLUENT 4.56. The research was carried out at various velocities. The performance of the code was better at higher gas velocities. Many researchers have simulated three-dimensional two fluids CFD model of gas particle flow in the CFB using the code CFX4.3. The turbulence was modeled by k-e turbulence model in the gas phase and a fixed particle viscosity model in the solid phase. This CFD model showed good agreement with the experiments [5]. A similar study of gas/particle flow behavior in the riser section of a circulating fluidized bed (CFB) was done using FLUENT 4.4. Fluid Catalytic Cracking (FCC) particles and air were used as the solid and gas phases, respectively. The computational results showed that the inlet and outlet design have significant effects on the overall gas and solid flow patterns and cluster formations in the riser [6].

A swarm intelligent approach for multi-objective optimization of compact heat exchangers

Design optimization of heat exchangers is a very complicated task that has been traditionally carried out based on a trial-and-error procedure. To overcome the difficulties of the conventional design approaches especially when a large number of variables, constraints and objectives are involved, a new method based on a well-established evolutionary algorithm, particle swarm optimization, weighted sum approach and a novel constraint handling strategy is presented in this study. Since the conventional constraint handling strategies are not effective and easy-to-implement in multi-objective algorithms, a novel feasibility-based ranking strategy is introduced which is both extremely user-friendly and effective. A case study from industry has been investigated to illustrate the performance of the presented approach. The results show that the proposed algorithm can find the near pareto-optimal with higher accuracy when it is compared to conventional non-dominated sorting genetic algorithm II. Moreover, the difficulties of a trial-and-error process for setting the penalty parameters are solved in this algorithm.

Numerical Analysis on Natural Convection Heat Transfer of a Heat Sink with Cylindrical Pin Fin

As technology advancement progressed in this information age or commonly known as digital age, thermal management has equally improved to keep up with demands from the electronic sector. Hence, heat sink study has become more and more prominent. Natural convection holds advantages since it is maintenance free and has zero power consumption. The purpose of this research is to study the heat transfer performance of heat sink with parametric variations of number and height of pin fin at temperature 308K, 323K, 338K, 353K and 368K. In addition, effect of porosity ranges from 0.524 to 0.960 on thermal resistance was investigated as well. Study found that heat transfer coefficient increases as temperature difference between heat sink and ambient increases. Thermal resistance decreases when porosity increases until it reaches the minimum and subsequently increases. The optimum porosity shown in this study is around 88%.

Review of Numerical Studies on NOx Emission in the Flameless Combustion

Today one source of pollution emission in the combustion of fossil fuels is the formation of nitrogen oxides. To solve this problem many technologies have been introduced such as flameless combustion. Flameless combustion is of a great interest since it simultaneously provides higher thermal efficiency together with controlling the pollutant emission such as NOX. In this technology, the preheat temperature of the combustion air must be higher than the auto-ignition temperature of the reactant mixture. In this study, papers showing the numerical studies on the flameless combustion to reduce NOX emission are presented.

New empirical correlations for sizing adiabatic capillary tubes in refrigeration systems

This paper presents new empirical correlations that have been developed for sizing adiabatic capillary tubes used in small vapor compression refrigeration and air-conditioning systems. A numerical model which is based on the basic equations of conservation of mass, momentum and energy was developed. Colebrooks formulation was used to determine the single phase friction factor. The two-phase viscosity models - Cicchitti et al., Dukler et al. and McAdam et al. were used based on the recommendation from literature to determine the two-phase viscosity factor. The developed numerical model was validated using the experimental data from literature. The numerical model was used to study the effects of relevant parameters on capillary tube length and the results showed that the length of capillary tube increase with increase in condensing temperature, subcooling, and inner diameter of tube but decrease with increase in surface roughness and mass flow rate. Thereafter, empirical correlation of the capillary tube length with the five dependent variables was presented. The empirical models are validated using experimental data from literature. Different from the previous studies, the empirical models have a large set of refrigerants and wide operating conditions. The developed correlation can be used as an effective tool for sizing adiabatic capillary tube with system models working with alternative refrigerants.

Gas-solid flow modelling in a circulating fluidized bed

Abstract A numerical parametric study was performed to understand the influence of various riser exit geometries on the hydrodynamics of gas—solid flow in the riser of a circulating fluidized bed (CFB) . An Eulerian continuum formulation was applied to both phases. A gas—particle computational fluid dynamics (CFD) model of flow has been investigated using CFD software FLUENT . The turbulence was modelled by the k-ε turbulence model in the gas phase. The simulations were done using the geometrical configuration of a CFB test rig available at the Universiti Teknologi Malaysia (UTM) . The computational model was used to simulate the flow behaviour in the riser and exit geometries under same operating conditions. In addition, several numerical experiments were carried out to understand the influence of riser end effects, particle size, gas solid velocity and solids volume fraction on the simulated flow characteristics. It was found that the k-ε turbulence model predicted good mixing behaviour. The results were found to be useful in interpreting the flows in commercial riser exits. Simulation results has added valuable knowledge to model gas—solid flow in the risers and their exits.