Applied Mechanics and Materials Vol. 819

Abstract: Microfluidics platform offers a great advantage in bio-sensing and clinical diagnostics miniaturization. The requirement of inexpensive and rapid-prototyping materials are essential in microfluidics device commercialization. This paper presents rapid prototyping of UV-curing Polyurethane Methacrylate (PUMA) microchannel from the Polydimethlsiloxane (PDMS) mold. Two techniques in PUMA microchannel UV-curing rapid prototyping have successfully demonstrated in this work. The first technique utilized thin film transparency sheet as PUMA resin top surface cover in facilitating PUMA UV-curing. The second method exploited confined nitrogen gas environment in Pyrex dish chamber in expediting PUMA curing under UV light exposure. In this work, two different approaches of fluidic interconnect tubings for PUMA microchannel inlet and outlet are also presented. Reversible bonding techniques using corona discharge treatment are utilized for bonding of PUMA microchannel and fluidic interconnect with PUMA, silicon, glass and PDMS substrate. Accomplishment of preliminary fluid flow testing using PUMA microchannel proved its capability for microfluidics applications.

Abstract: In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-k_L- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-k_L-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

Abstract: In this paper, an experimental study of a laminar flow solid desiccant dehumidifier has been presented. The cyclic steady state performance of adsorption-desorption processes was analyzed at various heat source temperatures and typical ambient humidity conditions in tropics. The desiccant dehumidification system consists of two beds filled with silica gel, two heat exchangers operating at 30 ^oC and 80 ^oC respectively, three humidity stations for measurement of the temperature and humidity conditions of the system and a blower to make airflow throughout the system. Type-RD silica gel of 0.3 mm average diameter was used as the working desiccant in the dehumidification system. This system has no moving parts rendering less maintenance compared with a rotary type. It is also energy-efficient means of dehumidification by adsorption process with low temperature heat source as compared to the conventional methods. As a result, it was observed the humidity ratio of inlet air is reduced from 24 g/kg of dry air to about 17 g/kg of dry air. Concomitantly, hot water at 80 ^oC is used to regenerate the adsorbent.

Abstract: The purpose of this study is to present a comparative study between Newtonian and non-Newtonian blood viscosity models for simulating the hemodynamic wall shear stress (WSS) of cerebral aneurysms. The non-Newtonian blood viscosity was modeled using the Carreau-Yasuda nonlinear model. Two realistic cerebral aneurysm models, derived from 3D angiography imaging, were studied and simulated via computational fluid dynamics solver based on finite volume method, with a pulsating sinusoidal waveform boundary conditions. The maximum wall shear stresses were found at the aneurysm’s neck and apex, the inlet arteriole recorded an average wall shear stress and as for the blebs and tips the wall shear stress values were remarkably low. The comparison indicated that non-Newtonian blood viscosity model predicted a lower range of WSS than of the Newtonian model, which provides more accuracy for simulating aneurysm hemodynamics.

Abstract: This study experimentally investigated two-phase flow pressure drop of propane as refrigerant in horizontal small tube. Inner diameter and length of the tube were 7.6 mm and 1.07 m, respectively. In order to get pressure drop data, the experiment was conducted in various conditions of 10 to 25 kW m^-2 heat flux, 200 to 628 kg m^-2 s^-1 mass flux, and 4.0 to 11.7°C saturation temperature. This study clearly showed the effect of heat flux, mass flux, and saturation temperature on the pressure drop of propane. This study also investigated which fluid properties gave higher effect on the frictional pressure drop due to its change over the process based on the recent experiment data. The existing pressure drop correlations were evaluated against the experimental result.

Abstract: During oil wellbore drilling processes, filter cake is formed on the sidewalls of the well hole due to filtration of drilling fluid particles. The filter cake is crucial to the drilling process, since it helps to maintain the wellbore hole, protects the drilling bit from jamming and facilitates the subsequent phases of the well development. The most important parameter for filter cake formation is its thickness and its variation due to drilling conditions. In this paper, the drilling fluid particles filtration process was simulated at conditions mimicking deep wellbore drilling. The drilling fluid was simulated as a non-Newtonian two-phase fluid of liquid and particles, utilizing an Eulerian-Eulerian approach. The model successfully predicted a filter cake thickness which agrees well with measurements and previous CFD work.

Abstract: A numerical study using computational fluid dynamics method with an approach of single phase has been presented in order to determine the effects of the concentration of the nanoparticles and flow rate on the convective heat transfer and friction factor in turbulent regime flowing through three different straight channels (straight, circular and triangular) with different Reynolds number (5000 ≤ Re ≤ 20000) using constant applied heat flux. The nanofluid was used consist of Fe3O4 magnetic nanoparticles with average diameter of (13nm) dispersed in water with four volume fraction (0, 0.2, 0.4, 0.6%). The results revealed that as volume fraction and Reynolds number increase Nusselt number increase and the heat transfer rate in circular cross section tube is better than that in square and triangular cross section channels.

Abstract: Inverse-Turbulent Prandtl number (α) is an important parameter in RNG k-ε turbulence models since it affects the ratio of molecular viscosity and turbulent viscosity. In curved pipe, this highly affects the model prediction to a large range eddy-scale flow. According to Yakhot & Orzag, the α range from 1-1.3929 has not been investigated in detail in curved pipe flow (Yakhot & Orszag, 1986) and specific Re. This paper varied inverse-turbulent Prandtl number α to 1-1.3 in RNG k-ε turbulence model on cylindrical curved pipe in order to obtain the optimum value of α to predict unfully-developed flow in the curve with curve ratio R/D of 1.607. Analysis was conducted numericaly with inlet specified Re of 40900 which was generated from the experiment at α 1, 1.1, 1.2, 1.3. Wall surface roughness is not considered in this paper. With assumption that thermal diffusivity is always dominant to turbulent viscosity, higher Inverse-turbulent Prandtl number represent domination of turbulent viscosity to molecular viscosity of the flow and predict to have more interaction between large scale eddy to small scale eddy as well. The results show the use of α = 1.3 has increased the turbulent kinetic energy by 7% and the turbulent dissipation by 5% compared to general inverse-turbulent Prandtl number of 1. The value difference shows that the use of higher α on RNG turbulence model described more interaction between eddies in secondary and swirling flow at pipe curve at Re = 40900.

Abstract: The requirement to reduce 40% carbon emission in 2020 has lead Malaysia to adopt the carbon capture and storage (CCS) technology in 2009. In this research, the pressure and transport differential equation for CO₂ – brine phases flow is discretized using mixed and hybrid finite element method (MHFEM) which ensures the local continuity of the finite elements. Result shows that CO₂ flow radially outward from the injection well. Three relative permeability models are investigated and it was find out that the simplified relative permeability model (SRM) has reduced the computational time by 8.3 times (when compare to Brooks and Corey model) but it is accurate for 1 year preliminary prediction. For longer period of prediction, classical Brooks and Corey and van Genuchten models shall be used.

Abstract: The purpose of this research work is to study the hydrodynamic characteristics of a new type of artificial reef structure, in order to provide a structure with low flow resistance, which will be a more suitable shelter for fishes and marine organisms. The idea of the new artificial reef is based on the streamlined bicycle helmet design concept. The hydrodynamic characteristics of the helmet and hollow cube artificial reefs (ARs) of the same volume have been studied at different water depths and wave frequencies of Malaysia seas using Computational Fluid Dynamics (CFD) method. The finite volume RANSE (Reynolds-Averaged Navier-Stokes Eqs.) code Ansys CFX was used for calculating the reefs drag force (F_D) and flow characteristics, while the potential flow code Ansys Aqwa was used for calculating the reefs inertia force (F_I). The Shear Stress Transport (SST) turbulence model was used in the RANSE code. The results of the two ARs were then compared for studying the hydrodynamic improvement due to the use of streamlined helmet artificial reef on the flow pattern around it. The streamlined body of the helmet artificial reef enhances the flow pattern at the aft region of the reef and provides flow zones with moderate flow speed at this area, which can help fishes and marine organisms from finding good shelter. The special shape of the different openings in the body of the helmet artificial reef improves the condition of the flow velocity distribution inside the unit than that of the hollow cube unit, which can increase the amount of the nutrient to the living fishes and organisms inside the reef.