Papers by Keyword: Laminar Flow

Abstract: To improve the heat transfer performance of laminar tubular flow, a center-cleared twisted tape of alternate axes was developed as inserts. Numerical simulation was conducted to investigate the effect of dislocation angle of twisted tapes on the thermo-hydraulic performances. The numerical results show that, the largest Nusselt number occurs at a dislocation angle of 60°. The friction factor f is relatively larger than that when the dislocation angle is 0°, and it exhibits an obvious increment with the dislocation angle. From the value of performance evaluation criterion (PEC), the best thermo-hydraulic performance is achieved at a 60° dislocation angle. The underlying mechanisms are analyzed in terms of flow field and temperature field.

Abstract: Micromixer can be divided into two categories which are active micromixer and passive micromixer. Due to the simple fabrication technology and ease of implementation in a complex microfluidic system, obstacle-based passive micromixers will be the focus in this work. A passive micromixer is depends on low Reynolds number and the channel geometry for mixing effectiveness. In this work, three designs of obstacle based micromixer were designed and evaluated. These micromixers has 237μm channel length, 30μm inlet length, 900 between inlets ports, width and depth are 30μm each. The fluids used for mixing were blood which has 3.0 × 10-3 kg/μms of viscosity and glycerin which has high viscosity than blood (1.49 × 10-3 kg/μms). The fluids used to evaluate the differences in term of their visual performance based image’s standard deviation by plotting the graph and mixing efficiency by calculation. Based on these evaluations, the Y shape with meander structure obstacle design has the best mixing efficiency at the outlet of the channel.

Abstract: Flow of viscous fluid in automation and control hydraulic systems usually is nonstationary. In such conditions research of viscous fluid unstable flow are important first of all for obtaining hydraudynamic parameters of flow and secondly, they will enable to design the system accurately and provide efficient performance of an actuator. Study of nonstationary flow of viscous fluid in cylindrical canals of circular cross-section was carried out when pressure gradiend of stationary moving flow suddenly decreases resulting in slow down of motion of fluid particles. As a result quadrically parabolic pattern of velocities is changed and their rearrangement occurs leading to a change of the flow hydraudynamic parameters. A boundary problem has been defined for the above conditions, preliminary and initial conditions have been determined and respective hydraudynamic parameters of the flow obtained. These parameters enable to reveal energy losses formation mechanism and evaluate their measure.

Abstract: Often due to the pressure gradient change in pressure systems the stationary flow pattern is disturbed initiating respective time-dependent change of hydraumechanical parameters at the cross-section. As a consequence of the pressure gradient change under the influence of varying friction and inertia forces unstable flow of fluid occurs. The study of this phenomenon presents important practical and theoretical interest.

Abstract: Mathematical background for static analysis of impulse gas seal is created in current paper. It includes evaluation of gap and flow rates of gas in turbocompressors. This paper consists of two parts. In the first one all logical steps of creation of the theoretical model for impulse gas seals are given. It should be mentioned, that they are valid for isothermal steady process which is observed here. The verification of derived theory is shown in the second part on a calculation example.

Abstract: The static mixers are widely used in many industries to obtain the desired type of mixing. In the context of mixing process, two different fluids and have a different properties will mix in a single equipment to produce an another fluid with a new property. In this research, a new approach of static mixers was proposed for pipeline mixing. The flow pattern, pressure drop and mixing characteristics (coefficient of variation) were carried out by means of computer simulations. The static mixers introduced here consists of a series of perforated plate with circle grids fractal pattern elements. The simulations work were carried out by using a commercial package of Computational Fluid Dynamic (CFD), ANSYS CFX 14.0 software. Three levels of laminar flow with Reynolds numbers (Re) of 100, 200 and 400 respectively had been used to investigate the performance of the static mixers introduced here. The effectiveness of circle grid perforated plate static mixer had been evaluated by comparing the homogeneity level of mixing fluids for each flow simulated. The simulations gave a new insights in the flow pattern in circle grids fractal perforated plate elements. The pressure drop predictions compare favorably with literature data and the coefficient of variation (COV) value for circle grid perforated plate with 50% porosity at Reynolds number 100 was 0.0744 which is out of the range meanwhile at Reynolds number 200 and 400 was 0.0483 and 0.0247 respectively which are in the range of reasonable target for many applications. Mixing in the elements occurs through a combination of flow splitting and shearing at the junctions of successive elements. Besides that, simple installation and manufacturing of this type of static mixers makes the fractal perforated plate’s element an excellent static mixing device.

Abstract: The phenomenon of laminar flow in the micro-channel is demonstrated by the software simulation. It shows different velocity produces different flow layer. Water-in-oil droplets are obtained by the experiments. These experiments take water as the dispersed phase and take the oil as the continuous phase. Analyze forming process and forming factors of the droplets and the column flow. The main factors of forming droplets are surface tension, viscosity shear force and the liquid velocity. The size of droplet is associated with the flow and channel width of two liquids. Changing the pressure of the inlet can obtain droplets in different size.

Abstract: This paper presents a numerical study on laminar flow and convective heat transfer of nanofluids in a circular tube under constant wall heat flux boundary condition. Single phase model is used for simulating the heat transfer and flow behaviors of three different nanofluids. The effects of nanoparticle concentrations, nanoparticle diameter, nanoparticle material and Reynolds number on the Nusselt number and wall shear stress of nanofluids are determined and discussed in details. The comparison of Nusselt number of CuO-EG/water, SiO₂-EG/water and Al₂O₃-EG/water nanofluids are presented. The results show that Nusselt number clearly increases with an increase in the nanoparticle concentration and flow Reynolds number, while the nanoparticle diameter has an opposite effect on the Nusselt number. Compared to SiO₂-EG/water and Al₂O₃-EG/water nanofluids, CuO-EG/water nanofluids give higher Nusselt number with the same nanoparticle concentrations. The results also show that wall shear stress increases with increasing nanoparticle volume concentration.

Abstract: This work presents a numerical investigation of laminar periodic flow and heat transfer in a constant heat flux-surfaced square-channel fitted diagonally with 45° V-discrete baffles. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 200 to 1,200. Effects of different blockage ratios (BR=b/H), BR in range from 0.05-0.2 with pitch ratio of 1.0 on heat transfer and pressure loss in the channel are studied. It is apparent that vortex flows created by the 45° diagonal V-discrete baffle exist and help to induce impinging flows on wall leading to drastic increase in heat transfer rate over the smooth channel. In addition, the increase in the BR results in the rise of Nusselt number and friction factor values. The computational results reveal that the optimum thermal enhancement factor of the 45° V-discrete baffle is about 2.24 at BR=0.2.

Abstract: The applications of the static mixers are widely applied in many industries to obtain the desired type of mixing. In this context, to perform the mixing process should have two different fluids that also have different properties which will combines it in a single equipment to make an another fluid. The main objective of this research study is to propose a new approach of fractal concept (circle grid perforated plate) for internal rapid mixing by determining the coefficient of variation (COV). This study was implemented by fully numerical simulations. The simulations of mixing fluid were carried out with the help of commercial computational fluid dynamic (CFD) package ANSYS CFX 14.0 software. The simulation was done primarily in cylindrical pipe with insertions of circle grid perforated plate with porosity of 50%. Three levels of laminar flow have been chosen to result in Reynolds numbers (Re) equal to 100, 200 and 400. The effectiveness of circle grid perforated plate static mixer has been evaluated by comparing the homogeneity level of mixing fluids to the Kenics static mixer that readily available in industries applications. Based on the research findings, the COV value for circle grid perforated plate with 50% porosity at Re 100 was 0.0744 which is out of the range while Reynolds number at 200 and 400 were 0.0483 and 0.0247 respectively which are in the range in term of reasonable target of mixing homogeneity. The values of COV between 0.01 and 0.05 are the reasonable target for many applications. In term of manufacturing cost and energy loss due to static mixer, definitely this new approach of 50% porosity circle grid perforated plate is better design compared to the Kenics static mixer because of lower number of inserts and simpler design of static mixer to produce.