Mahidzal Dahari

Investigation of rib's height effect on heat transfer and flow parameters of laminar water-Al2O3 nanofluid in a rib-microchannel

The laminar forced convection heat transfer of water-Al2O3 nanofluids through a horizontal rib-microchannel was studied. The middle section of the down wall of microchannel was at a lower temperature compared to the entrance fluid. Simulations were performed for Reynolds numbers 10 and 100 and nanoparticle volume fractions of 0.00 to 0.04, inside a two-dimensional rectangular microchannel with 2.5mm length and 25µm width. The two-dimensional governing equations were discretized using a finite volume method. The effects of ribs hight and position, nanoparticle concentration and Reynolds number on the thermal and hydraulics behavior of nanofluid flow were investigated. The results were portrayed in terms of velocity, temperature and Nusselt number profiles as well as streamlines and isotherm contours. The model predictions were found to be in good agreements with those from previous studies. The results indicate that the normal internal ribs or turbulators, can significantly enhance the convective heat transfer within a microchannel. However, the added high ribs can cause a larger friction factor, compared to that in the corresponding microchannel with a constant height of the ribs. The results also illustrate that by increasing the ribs heights and volume fraction of nanoparticles, friction coefficient, heat transfer rate and average Nusselt number of the ribbed-microchannels tend to augment. In addition, the simulation results confirm that changing the solid volume fraction and the ribs height, cause significant changes in temperature and dimensionless velocity along the centerline of the flow, through the ribbed areas.

Comparison of the Finite Volume and Lattice Boltzmann Methods for Solving Natural Convection Heat Transfer Problems inside Cavities and Enclosures

Different numerical methods have been implemented to simulate internal natural convection heat transfer and also to identify the most accurate and efficient one. A laterally heated square enclosure, filled with air, was studied. A FORTRAN code based on the lattice Boltzmann method (LBM) was developed for this purpose. The finite difference method was applied to discretize the LBM equations. Furthermore, for comparison purpose, the commercially available CFD package FLUENT, which uses finite volume Method (FVM), was also used to simulate the same problem. Different discretization schemes, being the first order upwind, second order upwind, power law, and QUICK, were used with the finite volume solver where the SIMPLE and SIMPLEC algorithms linked the velocity-pressure terms. The results were also compared with existing experimental and numerical data. It was observed that the finite volume method requires less CPU usage time and yields more accurate results compared to the LBM. It has been noted that the 1st order upwind/SIMPLEC combination converges comparatively quickly with a very high accuracy especially at the boundaries. Interestingly, all variants of FVM discretization/pressure-velocity linking methods lead to almost the same number of iterations to converge but higher-order schemes ask for longer iterations.

Performance Evaluation of Nanofluids in an Inclined Ribbed Microchannel for Electronic Cooling Applications

Nanofluids are liquid/solid suspensions with higher thermal conductivity, compared to common working fluids. In recent years, the application of these fluids in electronic cooling systems seems prospective. In the present study, the laminar mixed convection heat transfer of different water–copper nanofluids through an inclined ribbed microchannel–– as a common electronic cooling system in industry––was investigated numerically, using a finite volume method. The middle section of microchannel’s right wall was ribbed, and at a higher temperature compared to entrance fluid. The modeling was carried out for Reynolds number of 50, Richardson numbers from 0.1 to 10, inclination angles ranging from 0° to 90°, and nanoparticles’ volume fractions of 0.0–0.04. The influences of nanoparticle volume concentration, inclination angle, buoyancy and shear forces, and rib’s shape on the hydraulics and thermal behavior of nanofluid flow were studied. The results were portrayed in terms of pressure, temperature, coefficient of friction, and Nusselt number profiles as well as streamlines and isotherm contours. The model validation was found to be in excellent accords with experimental and numerical results from other previous studies. The results indicated that at low Reynolds’ flows, the gravity has effects on the heat transfer and fluid phenomena considerably; similarly, with inclination angle and nanoparticle volume fraction, the heat transfer is enhanced by increasing the Richardson number, but resulting in a less value of friction coefficient. The results also represented that for specific Reynolds (Re) and Richardson (Ri) numbers, heat transfer and pressure drop augment‐ ed by increasing the inclination angle or volume fraction of nanoparticles. With regard to the coefficient of friction, its value decreased by adding less nanoparticles to the fluid or by increasing the inclination angle of the microchannel.

Numerical Study of Entropy Generation in a Flowing Nanofluid Used in Micro- and Minichannels

This article mainly concerns theoretical research on entropy generation influences due to heat transfer and flow in nanofluid suspensions. A conventional nanofluid of alumina-water (Al2O3-H2O) was considered as the fluid model. Due to the sensitivity of entropy to duct diameter, mini- and microchannels with diameters of 3 mm and 0.05 mm were considered, and a laminar flow regime was assumed. The conductivity and viscosity of two different nanofluid models were examined with the help of theoretical and experimentally determined parameter values. It was shown that order of the magnitude analysis can be used for estimating entropy generation characteristics of nanofluids in mini- and microchannels. It was found that using highly viscous alumina-water nanofluid under laminar flow regime in microchannels was not desirable. Thus, there is a need for the development of low viscosity alumina-water (Al2O3-H2O) nanofluids for use in microchannels under laminar flow condition. On the other hand, Al2O3-H2O nanofluid was a superior coolant under laminar flow regime in minichannels. The presented results also indicate that flow friction and thermal irreversibility are, respectively, more significant at lower and higher tube diameters.

Numerical Study of Entropy Generation due to Coupled Laminar and Turbulent Mixed Convection and Thermal Radiation in an Enclosure Filled with a Semitransparent Medium

The effect of radiation on laminar and turbulent mixed convection heat transfer of a semitransparent medium in a square enclosure was studied numerically using the Finite Volume Method. A structured mesh and the SIMPLE algorithm were utilized to model the governing equations. Turbulence and radiation were modeled with the RNG k-ε model and Discrete Ordinates (DO) model, respectively. For Richardson numbers ranging from 0.1 to 10, simulations were performed for Rayleigh numbers in laminar flow (104) and turbulent flow (108). The model predictions were validated against previous numerical studies and good agreement was observed. The simulated results indicate that for laminar and turbulent motion states, computing the radiation heat transfer significantly enhanced the Nusselt number (Nu) as well as the heat transfer coefficient. Higher Richardson numbers did not noticeably affect the average Nusselt number and corresponding heat transfer rate. Besides, as expected, the heat transfer rate for the turbulent flow regime surpassed that in the laminar regime. The simulations additionally demonstrated that for a constant Richardson number, computing the radiation heat transfer majorly affected the heat transfer structure in the enclosure; however, its impact on the fluid flow structure was negligible.

Mathematical Modeling for Nanofluids Simulation: A Review of the Latest Works

Exploiting nanofluids in thermal systems is growing day by day. Nanofluids having ultrafine solid particles promise new working fluids for application in energy devices. Many studies have been conducted on thermophysical properties as well as heat and fluid flow characteristics of nanofluids in various systems to discover their advantag‐ es compared to conventional working fluids. The main aim of this study is to present the latest developments and progress in the mathematical modeling of nanofluids flow. For this purpose, a comprehensive review of different nanofluid computational fluid dynamics (CFD) approaches is carried out. This study provides detailed information about the commonly used formulations as well as techniques for mathematical modeling of nanofluids. In addition, advantages and disadvantages of each method are rendered to find the most appropriate approach, which can give valid results.

Forward and inverse kinematics model for robotic welding process using KR-16KS KUKA robot

This paper aims to model the forward and inverse kinematics of a KUKA KR-16KS robotic arm in the application of a simple welding process. A simple welding task to weld a block onto a metal sheet is carried out in order to investigate the forward and inverse kinematics models of KR-16KS. A movement flow planning is designed and further developed into the KR-16KS programming. Eleven points of movement are studied for the forward kinematic modeling. A summary of calculation is obtained. A general D-H representation of forward and inverse matrix is obtained. This can be used in each of the welding operation movement based on KUKA KR-16KS robotic arm. A forward kinematic and an inverse kinematic aspect of KUKA KR-16KS is successfully modeled based on a simple welding task.

Experimental study on thermo-physical and rheological properties of stable and green reduced graphene oxide nanofluids: Hydrothermal assisted technique

ABSTRACT In this study a dehydration hydrothermal technique has been used to introduce a simple, environmentally friendly and facile method for manufacturing highly dispersed reduced graphene oxide for improving the thermo-physical and rheological properties of heat transfer liquids. The hydrothermal reduction of graphene oxide was verified by various characterizations methods such as UV–visible absorption spectroscopy, Zeta potential, Raman spectroscopy, X-ray photoemission spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. A thorough investigation was conducted on the thermo-physical properties of reduced graphene oxide at concentrations of 0.02, 0.04, 0.06, and 0.08 wt% under different temperatures. Significant improvements in electrical and thermal conductivity were obtained by adding a small amount of hydrothermal-assisted reduced graphene oxide (h-rGO) in the suspension. The viscosity and density remained relatively unchanged with the increase of concentrations where the pH was maintained within the desirable value, despite the fact that no additive was used during the reduction process. It is noteworthy to highlight that the h-rGO aqueous suspensions have shown Newtonian behavior. Results indicated that the h-rGO could be employed as a promising additive for conventional heat transfer liquids for different thermal applications. GRAPHICAL ABSTRACT

A Hybrid Finite-Element/Finite-Difference Scheme for Solving the 3-D Energy Equation in Transient Nonisothermal Fluid Flow over a Staggered Tube Bank

This article presents a hybrid finite-element/finite-difference approach. The approach solves the 3-D unsteady energy equation in nonisothermal fluid flow over a staggered tube bank with five tubes in the flow direction. The investigation used Reynolds numbers of 100 and 300, Prandtl number of 0.7, and pitch-to-diameter ratio of 1.5. An equilateral triangle (ET) tube pattern is considered for the staggered tube bank. The proposed hybrid method employs a 2-D Taylor-Galerkin finite-element method, and the energy equation perpendicular to the tube axis is discretized. On the other hand, the finite-difference technique discretizes the derivatives toward the tube axis. Weighting the 3-D, transient, convection-diffusion equation for a cube verifies the numerical results. The L2 norm of the error between numerical and exact solutions is also presented for three different hybrid meshes. A grid independence study for the energy equation preceded the final mesh. The outcome is found to be in acceptable concurrence with those from the previous studies. After the temperature field is attained, the local Nusselt number is computed for the tubes in the bundle at different times. The isotherms are also obtained at different times until a steady-state solution is reached. The numerical results converge to the exact results through refining the mesh. The implemented hybrid scheme requires less computation time compared with the conventional 3-D finite-element method, requiring less program coding.

A Comprehensive Review of Milk Fouling on Heated Surfaces

Heat exchanger performance degrades rapidly during operation due to formation of deposits on heat transfer surfaces which ultimately reduces service life of the equipment. Due to scaling, product deteriorates which causes lack of proper heating. Chemistry of milk scaling is qualitatively understood and the mathematical models for fouling at low temperatures have been produced but the behavior of systems at ultra high temperature processing has to be studied further to understand in depth. In diversified field, the effect of whey protein fouling along with pressure drop in heat exchangers were conducted by many researchers. Adding additives, treatment of heat exchanger surfaces and changing of heat exchanger configurations are notable areas of investigation in milk fouling. The present review highlighted information about previous work on fouling, influencing parameters of fouling and its mitigation approach and ends up with recommendations for retardation of milk fouling and necessary measures to perform the task.