Forced convection heat transfer characteristics of Al2O3 nanofluids in a minichannel - an experimental study

In this study, an experimental investigation on the convective heat transfer characteristics of Al2O3 nanofluids flowing through an horizontal minichannel under the laminar and turbulent flow and constant heat flux conditions is performed. Several sample nanofluids were prepared using two base fluids (water and the mixture 80/20 DW/EG vol.%) and several low concentrations of Al2O3 nanoparticles ranging from 0.01 to 0.1 vol%. An existing experimental setup was modified for this study. The measurements were taken for the base fluid and nanofluids at each flow and heating conditions. The results are analyzed in terms of Nu and friction factor (f) in comparison with those of the base fluid. The results demonstrate that the used low concentrations of Al2O3 nanoparticles are not enough to yield any noticeable enhancement in heat transfer of the nanofluid samples. The deviations between the results of the nanofluids and the base fluid are small and within the uncertainty range of the experimental setup.

Effect of Physical Characteristics and Hydrodynamic Conditions on Transport and Deposition of Microplastics in Riverine Ecosystem

Microplastic disposal into riverine ecosystems is an emergent ecological hazard that mainly originated from land-based sources. This paper presents a comprehensive review on physical processes involved in microplastics transport in riverine ecosystems. Microplastic transport is governed by physical characteristics (e.g., plastic particle density, shape, and size) and hydrodynamics (e.g., laminar and turbulent flow conditions). High-density microplastics are likely to prevail near riverbeds, whereas low-density particles float over river surfaces. Microplastic transport occurs either due to gravity-driven (vertical transport) or settling (horizontal transport) in river ecosystems. Microplastics are subjected to various natural phenomena such as suspension, deposition, detachment, resuspension, and translocation during transport processes. Limited information is available on settling and rising velocities for various polymeric plastic particles. Therefore, this paper highlights how appropriately empirical transport models explain vertical and horizontal distribution of microplastic in riverine ecosystems. Microplastics interact, and thus feedback loops within the environment govern their fate, particularly as these ecosystems are under increasing biodiversity loss and climate change threat. This review provides outlines for fate and transport of microplastics in riverine ecosystems, which will help scientists, policymakers, and stakeholders in better monitoring and mitigating microplastics pollution.

Reduction of HC and CO in the Exhaust Gas of Minibus Vehicles by Natural Zeolite

Air pollution due to burning fossil fuels is still an environmental problem today. This paper presents the research results; method of reducing HC and CO in the exhaust gas of minibus vehicles. This method uses a pollutant gas trap (PGT) device, which functions as an adsorption medium, and natural zeolite as an absorbent material. The PGT device is designed in such a way that the zeolite can adsorb HC and CO gases flowing in it. The PGT device consists of a hollow body and supporting equipment arranged in it. The cavity of the PGT device is filled with zeolite granules and can be passed through vehicle exhaust gases. The PGT device consists of laminar and turbulent flow types, while the zeolite grains used are 2.54 mm and 1.27 mm. The PGT-zeolite device is installed at the exhaust end of the vehicle, so that polluting gases are absorbed by the zeolite. The adsorption capability of the PGT-zeolite device was measured with an Automotive-Emission-Analyzer, type NHA-406EN. Turbulence type PGT device, capable of reducing pollutant gases HC ≈ 40% and CO ≈ 42% respectively for the zeolite grain size of 2.54 mm. Meanwhile, the laminar flow type PGT device was able to reduce HC ≈ 36% and CO ≈ 42% gas, respectively for the zeolite grain size of 2.54 mm. The results of this study indicate that the PGT-zeolite device has a very good ability to reduce pollutant gases in the exhaust gas of minibus vehicles. Therefore, it is necessary to continue research on the feasibility of using natural zeolite, as an absorber of polluting gases in other types of vehicles.

On the Hierarchy of Models for Pipe Transients: From Quasi-2D Water Hammer Models to Full 3D CFD Models

A hierarchy of models exists in the literature for the simulation of pipe transients. One-dimensional water hammer models are readily available and provide a cost-effective tool for the analysis of such transients. The main shortcoming of 1D models is the quasi-steady approximation of the frictional term, which results in poor modelling of the attenuation of the transient. To overcome this drawback, quasi-2D water hammer models were introduced, which allow the computation of the unsteady velocity profile and hence provide improved modelling of the attenuation phenomenon. Recently, interest has developed in the use of CFD models based on the Navier-Stokes equations in the simulation of fluid transients. Both axisymmetric CFD models and full 3D CFD models are used in this regard. The aim of the current paper is to carry out a comparative study between the performance of quasi-2D water hammer models, axisymmetric CFD models and full 3D CFD models. Numerical computations using the three models are performed for both laminar and turbulent flow cases. Present results show that the quasi-2D water hammer model and the axisymmetric CFD model provide near identical results in terms of computing the magnitude, phase and attenuation of the transient. Reported results also demonstrate the computational efficiency of the quasi-2D model, which provides results that agree reasonably well with the full 3D CFD model results while using a grid density which is an order of magnitude lower than the grid requirements for the full 3D CFD model.

Two-way fluid-structure interaction study of twisted tape insert in a circular tube having integral fins with nanofluid

This work deals with fluid-structure interaction (FSI), one of the emerging areas of numerical simulation and calculation. This research shows a numerical study investigating heat transfer enhancement and fluid-structure interaction in a circular finned tube by using alumina nanofluid as a working fluid with a typical twisted tape that has a twisting ratio of 1.85. The studied nanofluid volumes of fraction are φ=0, 3, 5 % under conditions of laminar and turbulent flow. The solution for such problems is based on the relations of continuum mechanics and is mostly done with numerical methods. FSI occurs when the flow of fluid influences the properties of a structure or vice versa. It is a computational challenge to deal with such problems due to complexity in defining the geometries, nature of the interaction between a fluid and solid, intricate physics of fluids and requirements of computational resources. CFD investigations were made based on the numerical finite volume techniques to solve the governing three-dimensional partial differential equations to get the influence of inserted twisted tape and concentration of nanofluid on heat transfer enhancement, friction loss, average Nusselt number, velocity profile, thermal performance factor characteristics, and two-way interaction in a circular tube at laminar and turbulent flow. The governing continuity, momentum and energy transfer equations are solved using Ansys Fluent and Transient Structural. The simulation results show that the deformations of two-way coupling fluctuate from side to side, with 0.004 mm, as maximum amplitude, located at the typical twisted tape center. Heat transfer dissipation improved by adding fins and as Reynolds numbers increase the heat transfer behavior increases.

Laminar-Turbulent Transition Localization in Thermographic Flow Visualization by Means of Principal Component Analysis

Thermographic flow visualization is a contactless, non-invasive technique to visualize the boundary layer flow on wind turbine rotor blades, to assess the aerodynamic condition and consequently the efficiency of the entire wind turbine. In applications on wind turbines in operation, the distinguishability between the laminar and turbulent flow regime cannot be easily increased artificially and solely depends on the energy input from the sun. State-of-the-art image processing methods are able to increase the contrast slightly but are not able to reduce systematic gradients in the image or need excessive a priori knowledge. In order to cope with a low-contrast measurement condition and to increase the distinguishability between the flow regimes, an enhanced image processing by means of the feature extraction method, principal component analysis, is introduced. The image processing is applied to an image series of thermographic flow visualizations of a steady flow situation in a wind tunnel experiment on a cylinder and DU96W180 airfoil measurement object without artificially increasing the thermal contrast between the flow regimes. The resulting feature images, based on the temporal temperature fluctuations in the images, are evaluated with regard to the global distinguishability between the laminar and turbulent flow regime as well as the achievable measurement error of an automatic localization of the local flow transition between the flow regimes. By applying the principal component analysis, systematic temperature gradients within the flow regimes as well as image artefacts such as reflections are reduced, leading to an increased contrast-to-noise ratio by a factor of 7.5. Additionally, the gradient between the laminar and turbulent flow regime is increased, leading to a minimal measurement error of the laminar-turbulent transition localization. The systematic error was reduced by 4% and the random error by 5.3% of the chord length. As a result, the principal component analysis is proven to be a valuable complementary tool to the classical image processing method in flow visualizations. After noise-reducing methods such as the temporal averaging and subsequent assessment of the spatial expansion of the boundary layer flow surface, the PCA is able to increase the laminar-turbulent flow regime distinguishability and reduce the systematic and random error of the flow transition localization in applications where no artificial increase in the contrast is possible. The enhancement of contrast increases the independence from the amount of solar energy input required for a flow evaluation, and the reduced errors of the flow transition localization enables a more precise assessment of the aerodynamic condition of the rotor blade.

Combined Electrochemical & Biological Treatment of Industrial Wastewater Using Porous Electrodes and a Packed Bed Aerator

Zinc, nickel and propylene glycol methyl ether were simultaneously removed from simulated wastewater in a column containing a counter-current packed bed and an electrochemical cell. Rectangular porous aluminum foam cathode and porous stainless steel anode were used in a plate-in-tank configuration. During combined biological and electrochemical treatment the wastewater flux was 0.00183 and 0.00915 m³.m̈².s̈¹ at a constant volumetric air flux of 0.0518 m³.m̈².s̈¹. Over a 72 hour treatment period the BOD5 was reduced by 32% and 55% for each volumetric liquid flux, respectively; zinc was reduced by 98% for both fluxes, and nickel was reduced by 95% and 82%, respectively. For sole electrochemical treatment of 48 hours, laminar and turbulent flow conditions were studied. Operating in the laminar flow region of 0.00183 and 0.00915 m³.m̈².s̈¹; zinc was reduced by 95% for both fluxes; nickel was reduced by 80% and 60%, respectively. For the turbulent region in the electrochemical cell, the volumetric liquid fluxes were 0.0137, 0.0229, 0.0321 and 0.0366 m³.m̈².s̈¹. Per cent reduction of both zinc and nickel in this region was less than that encountered in laminar flow. For all the fluxes in the turbulent region zinc was reduced by 82%; nickel was reduced by 55% at a flux of 0.0137 m³.m̈².s̈¹ and 60% at a flux of 0.0366 m³.m̈².s̈¹. Increasing electrode surface area as a means of improving heavy metal reduction by using rectangular porous material in a plate-in-tank configuration is not a viable option at higher volumetric liquid fluxes.