Journal of Heat and Mass Transfer Research
Volume:9 Issue: 1, Winter-Spring 2022

In this study, the design of a nanofluid driven shell and tube heat exchanger is optimized, for the first time, by use of three multi objective algorithms. Two different operating conditions are investigated to compare the performance of the algorithms based on an economic model (cost function). Based on the obtained results, the Genetic, Particle Swarm and Jaya optimization algorithms can all improve the design. The amount of design improvement by each method is 9.66%, 10.63% and 10.9% respectively. Also from the view point of optimization time, Jaya optimization algorithm has relatively less CPU time than the other two algorithms, which in fact, reduces computational costs in complicated computations. Finally, due to the good performance of Jaya optimization algorithm in comparison with other considered algorithms, the performance of the heat exchangers is evaluated for using Ag, TiO2 and Al2O3 nanofluids of 0.5% to 5 vol.% by this algorithm. A performance evaluation factor (PE) is introduced as the criterion for simultaneous investigation of thermal and hydraulic performance of nanofluids. The results show that silver nanofluid, among other ones has better performance.

An investigation is carried out to study MHD boundary layer flow, heat and mass transfer of an incompressible viscous fluid past a continuously moving nonlinear stretching porous sheet in porous medium with temperature dependent fluid properties subject to heat source, viscous dissipation, chemical reaction and suction. The fluid viscosity and the thermal conductivity are assumed to vary as an inverse function and linear function of temperature respectively. The governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations by using similarity transformations and solved numerically by the Matlab’s built in solver bvp4c. The numerical results are presented graphically for velocity, temperature and concentration distributions. The skin friction, wall temperature and wall concentration gradients are tabulated for emerging parameters. It is arrived at a good agreement on comparing the present numerical results with previously published results. It is found that skin friction rises but wall temperature and wall concentration gradients fall with growing viscosity, magnetic field, stretching parameter and Darcy parameter respectively. The thermal conductivity parameter diminishes wall temperature gradient while the Schmidt number and chemical reaction parameter enhance wall concentration gradient.

In this paper, an analytical solution is presented for the stagnation-point flow of MHD Walters’ B fluid towards a vertical stretching surface with elastic-deformation and chemical reaction. The higher non-linear ordinary differential equations for the heat and mass transfer are obtained from partial differential equations via similarity transformation techniques and solved by the modern analytical method. The behaviors of the various embedded parameter are addressed and the result justifies among others that the fluid exhibits Newtonian properties in the absence of local Weissenberg number. On the other hand, the presence of local Weissenberg number makes the model possess the Non-Newtonian properties with great industrial application such as plastic film, artificial fibers, and higher molecular-weight liquid used in industries and engineering field, while greater cooling problems commonly encountered in industries and engineering discipline for the cooling of the system or electronics components is observed with higher values of thermal buoyancy effect.

Condensation is an important heat transfer regime, with vast applications in industries such as power generation and cooling systems. In the present study, the changes in the coating thickness and geometry of hydrophobic areas were investigated on hydrophobic-hydrophilic plates and totally hydrophobic ones, and a no-coating plate was also studied experimentally for the condensation phenomenon. Considering the use of aluminium as the base material, tests such as lithography with positive photoresist was conducted to study the photoresist adhesion to the aluminium surface and its impact on heat transfer, as well as testing the lift-off process to remove the remaining photoresist at the final stage of producing the plates, to improve their surfaces and optimize the major parameters in the production stage. For this study, one type of totally hydrophobic surface and two types of hybrid hydrophobic-hydrophilic surfaces with different widths of hydrophobic and hydrophilic areas were produced, each type in three thicknesses of 200, 450 and 900 nm. Considering the different values of coating thicknesses, the width of the hydrophobic and hydrophilic areas, the heat transfer coefficient and heat flux were calculated for each plate, and the optimal conditions for each plate were determined. Compared to the uncoated plates, the heat transfer coefficient and heat flux for each plate with hybrid hydrophobic-hydrophilic surfaces (width of 860 μm for hydrophilic area and 970 μm for the hydrophobic, and thickness of 450 nm) registered increase by 1.44-2.01 and 1.43-1.81 times, respectively, which were the highest among the plates in the present study.

Population balance models mathematically describe the particle size distribution based on modeling physical phenomena that influence the distribution, such as aggregation, growth, and breakage. Due to the wide range of mechanisms present, several models are presented in the literature since several hypotheses are considered. In the current work, the Approximate Bayesian Computational statistical technique was used to select four different models of population balance and estimate their parameters. Three strategies were applied to the drawing of parameters, evaluating the correlation between the parameters of the models. An adaptive tolerance in each population and a stopping criterion, based on Morozov's uncertainty principle, were used for the algorithm. The technique obtained reasonable estimates for the phenomenological rates of the models. The algorithm correctly selected the model used for generating measurements, and the three draw strategies demonstrated good applicability. The results obtained showed that the algorithm presented accuracy and precision in estimating the parameters and properly selected the models analyzed.

In this paper, an electrokinetic micromixing system with conductive mixing-enclosure is proposed. The simulated micromixer can be fabricated easily and accordingly, it can be used in the microfluidic systems effectively. The mixing process is intensified by controlling the geometry of the mixing-enclosure and electric field strength. The effects of different parameters including existence of mixing-enclosure, horizontal and vertical sizes of mixing-enclosure, orientation angle of mixing-enclosure, and electric field strength on the mixing index are studied. The mixing efficiencies and mixing lengths of current electrokinetic micromixer and those previously proposed by other researchers are compared. The results showed that the mixing efficiency can be enhanced significantly as a micromixer with conductive mixing-enclosure is employed. As an advantage of the proposed micromixer, the maximum mixing efficiency does not change by boosting the electric field strength in the range of 100 V.cm-1 to 200 V.cm-1, while the mixing time diminishes as the electric field strength increases in this range. For the conductive mixing-enclosure with the orientation angle of 45°, maximum mixing efficiency of 96.6% is achieved by exerting electric field with strength of 75 V.cm-1. The current electrokinetic micromixer has superior mixing efficiency and mixing length as compared with other electrokinetic micromixers.

To analyze the possibility of heat transfer enhancement of micro-scale heat exchangers, the transport phenomena of water (H2O) - Aluminum oxide (Al2O3) nanofluid in a three-dimensional microchannel with converging flow passages in the presence of a magnetic field are numerically investigated. All simulations are performed for the Harman number (Ha) of 0-20 and the volume fraction of ∅ = 0 and 0.02 in the laminar regime (Reynolds number, Re, < 100). The magnetic field is applied in the normal direction (with respect to the flow direction). The results show that the convection heat transfer coefficient, as well as the friction factor, increases with the increase of the Hartman number. The increase in the friction factor is noticeable up to being doubled while the increase of the convection heat transfer coefficient is up to 20 %. The uniform velocity arising from the magnetic field presence gives almost uniform temperature distributions in the fluid and solid parts of the micro-channel, which makes removing higher heat fluxes within the safe temperature limit possible. Although the heat transfer performance enhances with the increase of the magnetic field, the rate of heat transfer enhancement decreases with the increasing magnetic field. In other words, the magnetic field has a maximum effective value and there is no justification for a further increase according to the energy efficiency perspectives. It should be noted that the mentioned limits for magnetic field (here, presented with Ha) are very high and almost impossible to be applied at micro-scales. In addition, the effect of the magnetic field on the velocity profile decreases with the increase of the passage convergence. In other words, the flow convergence eliminates the need for a high magnetic field to have a uniform velocity profile and as well a uniform temperature distribution.

In the present paper, heat transfer, fluid flow characteristics and entropy generation of boehmite alumina nanofluid flowing through a cylindrical helical minichannels heat sink are examined numerically. The evaluated boehmite alumina nanofluid contain dispersed platelets, cylindrical, bricks and blades nanoparticles in a water. This evaluation is performed at two Reynolds number (i.e. Re=114.5 and Re=481.5) and four nanoparticle volume fraction (i.e.,φ= 0, 1%, 2% and 4%). The numerical Results reveal that the heat transfer, friction factor, pumping power, thermal performance factor an friction entropy generation are augmented and overall thermal resistance, heat transfer entropy generation, total entropy generation and augmentation entropy generation number are diminished by increasing Reynolds number and nanoparticle volume fraction for all studied shapes of nanoparticle. The highest and lowest heat transfer, friction factor, pumping power, thermal performance factor and friction entropy generation relate to the nanofluid containing platelets and bricks shapes nanoparticle, while the maximum and minimum overall thermal resistance, heat transfer entropy generation and total entropy generation belong to the nanofluid with the bricks and platelets shapes nanoparticle. The highest performance factor was achieved for φ= 4%, Re=114.5 by using platelets shape nanoparticles and this value is about 1.477.