0

IN THIS ISSUE

### Guest Editorial

J. Thermal Sci. Eng. Appl. 2019;11(4):040301-040301-2. doi:10.1115/1.4044203.
FREE TO VIEW

Heat transfer enhancement in heat-exchange devices is one of the key factors affecting energy savings and compact designs in wide variety of engineering applications. Pioneering heat transfer research has been carried out leading to the development of a new innovative energy enhancement technique through the addition of nanoparticles (usually less than 100 nm) to low thermal conductivity conventional fluids. Fluids with suspended nanoparticles are called “nanofluids.” The suspended metallic or nonmetallic nanoparticles change the transport properties and heat transfer characteristics of the base fluid by a significant extent. Metallic nanofluids often refer to those containing metallic nanoparticles (such as Cu, Al, Zn, Ni, Si, Fe, Ti, Au, and Ag), while nanofluids containing nonmetallic nanoparticles such as aluminum oxide (Al2O3), copper oxide (CuO), and silicon carbide (SiC, ZnO, TiO2) are often considered as nonmetallic nanofluids. Nanofluids exhibit superior heat transfer properties compared to conventional heat transfer fluids. Recently, the idea of using hybrid nanofluids by suspending dissimilar nanoparticles has been investigated for further improvement of the heat transfer and pressure drop characteristics by employing a trade-off between the advantages and disadvantages of individual suspension (attributed to good aspect ratios), better thermal networks, and the synergistic effects of nanomaterials.

Topics: Modeling , Nanofluids
Commentary by Dr. Valentin Fuster

### Research Papers

J. Thermal Sci. Eng. Appl. 2019;11(4):041001-041001-11. doi:10.1115/1.4041877.

The oscillatory flows are often utilized in order to augment heat transfer rates in various industrial processes. It is also a well-known fact that nanofluids provide significant enhancement in heat transfer at certain conditions. In this research, heat transfer in an oscillatory pipe flow of both water and water–alumina nanofluid was studied experimentally under low frequency regime laminar flow conditions. The experimental apparatus consists of a capillary tube bundle connecting two reservoirs, which are placed at the top and the bottom ends of the capillary tube bundle. The upper reservoir is filled with the hot fluid while the lower reservoir and the capillary tube bundle are filled with the cold fluid. The oscillatory flow in the tube bundle is driven by the periodic vibrations of a surface mounted on the bottom end of the cold reservoir. The effects of the frequency and the maximum displacement amplitude of the vibrations on thermal convection were quantified based on the measured temperature and acceleration data. It is found that the instantaneous heat transfer rate between de-ionized (DI) water (or the nanofluid)-filled reservoirs is proportional to the exciter displacement. Significantly reduced maximum heat transfer rates and effective thermal diffusivities are obtained for larger capillary tubes. The nanofluid utilized oscillation control heat transport tubes achieve high heat transfer rates. However, heat transfer effectiveness of such systems is relatively lower compared to DI water filled tubes.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041002-041002-9. doi:10.1115/1.4042352.

The contribution of the current study is to investigate the mixed convection in an inclined nanofluid filled cavity saturated with a partially layered non-Darcy porous medium. Moreover, due to the advantage of the particle-based methods, we presented the improved version of an incompressible smoothed particle hydrodynamics (ISPH) method. The current ISPH method was improved in boundary conditions treatment using renormalization kernel function. In the current investigation, we assumed that the inclined cavity is filled with a Cu-water nanofluid. The upper half of the cavity is saturated with a non-Darcy porous medium. Here, one domain approach is used for coupling the nanofluid and the porous medium layer. The cooled top wall of the cavity is carrying a tangential unit velocity and the bottom wall is heated. The other two wall sides are adiabatic at zero velocity. Here, we investigated the effects of the Richardson parameter $Ri0.0001–100$, Darcy parameter Da $10−5–10−2$, an inclination angle $α0–90deg$ and a various solid volume fraction $ϕ0–0.05$ on the heat transfer of a Cu-water nanofluid. The obtained results showed that the average Nusselt number decreases as the Richardson number increases. An addition of 1–5% Cu nanoparticles slightly increased the overall heat transfer rate.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041003-041003-9. doi:10.1115/1.4041878.

Vegetable oil is considered as one among the promising alternatives for diesel fuel as it holds properties very close to diesel fuel. However, straight usage of vegetable oil in compression ignition (CI) engine resulted in inferior performance and emission behavior. This can be improved by modifying the straight vegetable oil into its esters, emulsion, and using them as a fuel in CI engine showcased an improved engine behavior. Waste cooking oil (WCO) is one such kind of vegetable oil gained a lot of attraction globally as it is generated in a large quantity locally. The present investigation aims at analyzing various parameters of single cylinder four stroke CI engine fueled with waste cooking oil biodiesel (WCOB), waste cooking oil biodiesel water emulsion (WCOBE) while the engine is operated with a constant speed of 1500 rpm. Furthermore, an attempt is made to study the impact of nanofluids in the behavior of the engine fueled with WCOB blended with nanofluids (WCOBN50). This work also explored a novel method of producing nanofluids using one-step chemical synthesis method. Copper oxide (CuO) nanofluids were prepared by the above mentioned method and blended with waste cooking oil biodiesel (WCOBN50) using ethylene glycol as a suitable emulsifier. Results revealed that brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) of WCOBN50 are significantly improved when compared to WCOB and WCOBE. Furthermore, a higher reduction in oxides of nitrogen (NOx), carbon monoxide (CO), hydrocarbon (HC), and smoke emissions were observed with WCOBN50 on comparison with all other tested fuels at different power outputs. It is also identified that one-step chemical synthesis method is a promising technique for preparing nanofluids with a high range of stability.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041004-041004-12. doi:10.1115/1.4043662.

In this paper, experimental investigations were carried out to observe the melting process of a bio-based nano-phase change materials (PCM) inside open-cell metal foams. Copper oxide nanoparticles with five different weight fractions (i.e., 0.00%, 0.08%, 0.10%, 0.12%, and 0.30%) were dispersed into bio-based PCM (i.e., coconut oil) to synthesize nano-PCMs. Open-cell aluminum foams of different porosities (i.e., 0.96, 0.92, and 0.88) and pore densities (i.e., 5, 10, and 20 pores per inch (PPI)) were considered. An experimental setup was constructed to monitor the progression of the melting process and to measure transient temperatures variations at different selected locations. Average thermal energy storage rate (TESR) was calculated, alongside the melting time was recorded. The effects of various nanoparticles concentration, metal foam pore densities, porosities, and isothermal surface temperature on the melting time, TESR, thermal energy distribution, and the melting behavior were studied. It was observed that the melting time significantly reduced by using metal foam and increasing the isothermal surface temperature. It was concluded that the effect of adding nanoparticles on the TESR depends on the characteristics of metal foam, as well as, the weight fractions of nanoparticles. The change in TESR varied from −1% to 8.6% upon addition of 0.10 wt % nanoparticles compared to pure PCM, whereas the increase in the nanoparticles concentration from 0.10% to 0.30% changed TESR by −10.6% to 4.5%. The results provide an insight into the interdependencies of parameters such as pore density and porosity of metal foam and nanoparticles concentration on the melting process of nano-PCM in metal foam.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041005-041005-11. doi:10.1115/1.4043596.

The present work aims at developing a heat transfer model for phase change material nanocomposite (PCMNC)-based finned heat sink to study its heat rejection potential. The proposed model is developed in line with the binary alloy formulation for smaller size nanoparticles. The present study gives a more insight into the nanoparticle distribution while the nanocomposite is undergoing phase change. The nanocomposite is placed in the gap between the fins in a finned heat sink where solidification occurs from the top and lateral sides of fins. The proposed numerical model is based on finite volume method. Fully implicit scheme is used to discretize the transient terms in the governing transport equations. Natural convection in the molten nanocomposite is simulated using the semi-implicit-pressure-linked–equations-revised (SIMPLER) algorithm. Nanoparticle transport is coupled with the energy equation via Brownian and thermophoretic diffusion. Enthalpy porosity approach is used to model the phase change of PCMNC. Scheil rule is used to compute the nanoparticle concentration in the mixture consisting of solid and liquid PCMNC. All the finite volume discrete algebraic equations are solved using the line-by-line tridiagonal-matrix-algorithm with multiple sweeping from all possible directions. The proposed numerical model is validated with the existing analytical and numerical models. A comparison in thermal performance is made between the heat sink with homogeneous nanocomposite and with nonhomogeneous nanocomposite. Finally, the effect of spherical nanoparticles and platelet nanoparticles to the solidification behavior is compared.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041006-041006-10. doi:10.1115/1.4043760.

The main objective of the present study is to carry out experimental investigation on thermal performance of the nanofluid-based rectangular natural circulation loop (NCL). For this study, an experimental test rig is fabricated with heater as heat source, and tube in tube heat exchanger as heat sink. For the experimentation, three different nanofluids are used as working fluids. The nanometer-sized particles of silicon dioxide (SiO2), copper oxide (CuO), and alumina (Al2O3) are dispersed in distilled water to produce the nanofluids at different volume concentrations ranging from 0.5% to 1.5%. Experiments are carried out at different power inputs and different cold fluid inlet temperatures. The results indicate that NCL operating with nanofluid reaches steady-state condition quickly, when compared to water due to its increased thermal conductivity. The steady-state reaching time is reduced by 12–27% by using different nanofluids as working fluids in the loop when compared to water. The thermal performance parameters like mass flow rate, Rayleigh number, and average Nusselt number of the nanofluid-based NCL are improved by 10.95%, 16.64%, and 8.10%, respectively, when compared with water-based NCL. At a given power input, CuO–water nanofluid possess higher mass flow rate, Rayleigh number and Nusselt number than SiO2–water and Al2O3–water nanofluids due to better thermo-rheological properties.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041007-041007-9. doi:10.1115/1.4043758.

The mixed convection in a cubical cavity with active lateral walls and filled with a graphene–platinum hybrid nanofluid was investigated numerically and exclusively in the present paper. The lateral left and back sidewalls were kept at a hot temperature (Th), while the lateral right and front sidewalls were kept at a cold temperature (Tc). Both the top and bottom walls were assumed thermally insulated. The top wall of the cavity was considered moving with two different directions. The first one is in the x-direction (case I), while the second case is in the z-direction (case II). Also, the case of the fixed top wall was studied just for comparison. The solid volume fractions have been varied as 0 ≤ $φ$ ≤ 0.1%, while the Richardson number is varied in the range of 0.01 ≤Ri ≤ 10. It was found that the maximum average Nusselt number corresponds to the case when the top wall moving in the negative x-direction. Also, the results indicated that the average Nusselt number increases with the increase in the Richardson number and the solid volume fraction.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041008-041008-12. doi:10.1115/1.4043849.

In this study, the thermofluid characteristics of double spirally coiled tube heat exchanger (DSCTHE) were investigated numerically. A three-dimensional (3D) computational fluid dynamic (CFD) model was developed using ansys 14.5 software package. To investigate the heat transfer and pressure drop characteristics of DSCTHE, the Realize k–ε turbulence viscous model had been applied with enhanced wall treatment for simulating the turbulent thermofluid characteristics. The governing equations were solved by a finite volume discretization method. The effect of coil curvature ratio on DSCTHE was investigated with three various curvature ratios of 0.023–0.031 and 0.045 for inner tube side and 0.024–0.032–0.047 for annular side. The effects of addition of Al2O3 nanoparticle on water flows inside inner tube side or annular side with different volume concentrations of 0.5%, 1%, and 2% were also presented. The numerical results were carried out for Reynolds number with a range from 3500 to 21,500 for inner tube side and from 5000 to 24,000 for annular side, respectively. The obtained results showed that with increasing coil curvature ratio, a significant effect was discovered on enhancing heat transfer in DSCTHE at the expense of increasing pressure drop. The results also showed that the heat transfer enhancement was increased with increasing Al2O3 nanofluid concentration, and the penalty of pressure drop was approximately negligible.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041009-041009-13. doi:10.1115/1.4043820.

This study presents a novel performance evaluation of the commercially available LS-2 collector operating with an oil-based olive leaf-synthesized nanofluid. The nanoparticles were synthesized experimentally from olive leaf extracts (OLEs): OLE-ZVI and OLE-TiO2. The thermophysical properties of the nanoparticles were then added to Syltherm-800 thermal oil, and its performance on the parabolic trough solar collector (PTC) was evaluated numerically. The PTC under study was modeled on the engineering equation solver (EES) and validated thermally with results found in the literature. The synthesized nanoparticles were also found to possess anticorrosion properties, nontoxic, and less expensive to produce when compared to commercially available ones. The use of the nanofluids (Syltherm-800/OLE-ZVI and Syltherm-800/OLE-TiO2) was evaluated against the parameters of thermal and exergetic efficiencies, heat transfer coefficient, thermal losses, and pressure drop. The study shows that an enhancement in thermal performance of 0.51% and 0.48% was achieved by using Syltherm-800/OLE-ZVI and Syltherm-800/OLE-TiO2 nanofluids, respectively. A heat transfer coefficient enhancement of 42.9% and 51.2% was also observed for Syltherm-800/OLE-TiO2 and Syltherm-800/OLE-ZVI nanofluids, respectively. Also, a mean variation in pressure drop of 11.5% was observed by using the nanofluids at a nanoparticle volumetric concentration of 3%. A comparison of the results of this study with related literature shows that the proposed nanofluids outperform those found in literature.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041010-041010-12. doi:10.1115/1.4043967.

Two-phase closed thermosyphon (TPCT) is a cost-effective heat transfer device with high thermal efficiency owing to extensive interphase heat and mass transfer. Thus, TPCT has found many industrial applications. Proper selection of the working fluid could further improve efficiency of TPCT, and nanofluids with superior thermal properties are suitable choices. Numerical simulation of boiling and condensation, natural circulation, and hybrid nanofluid modeling in a closed space is a notable challenge and current study is devoted to this subject. In this study, a novel methodology for incorporating the effects of compressibility and thermal expansion into all thermophysical properties of both phases is developed and programmed into a validated computational fluid dynamics (CFD) code. Distilled water, a regular nanofluid, Al2O3/water, and a hybrid nanofluid, TiSiO4/water are selected as the working fluids. Experimental data for wall thermal profile are employed to validate the numerical simulation. Then, overall thermal resistance is evaluated in terms of nanoparticles concentration and input power variations. Results indicate that the numerical methodology developed in this study could evaluate the optimum state of TPCT in an efficient and accurate manner and the optimum state for regular and hybrid nanofluid demonstrates 48% and 54% improvement over distilled water, respectively. Furthermore, a subtle relation between the thermal resistance and the height to which fluid column rises in TPCT has been discerned and quantified, which is used as a supplement to the conventional qualitative method of reasoning to justify the somewhat controversial behaviors of nanofluid application in TPCT.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041011-041011-7. doi:10.1115/1.4043991.

Based on Buongiorno's theory and Cauchy equations of motion, a model is developed to examine homogeneous–heterogeneous reactions in boundary layer flow of a nanofluid over a stretching sheet in which a uniform magnetic field is added perpendicular to the flow direction. We apply the shooting method and the fourth-order Runge–Kutta integration to obtain multiple solutions of nonlinear ordinary differential equations with various physical parameters. Results show that nanofluids play significant roles in the procedures of homogeneous and heterogeneous reactions, which may help maintain the stability of chemical reactions. In addition, the terms related to Maxwell fluid either have effect on stability of the system; furthermore, the increasing elastic and magnetic parameters delay the appearance of bifurcation points.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041012-041012-14. doi:10.1115/1.4044136.

The mixed convective heat transfer of a micropolar nanofluid in a square lid-driven cavity has been numerically studied. The lid is thermally insulated, the side walls are kept cold, and the bottom wall is kept hot with sinusoidally thermal boundary condition. The governing equations were solved by finite volume method using the SIMPLE algorithm. The effect of Grashof number (102–105), the volume fraction of nanoparticles (0.0–0.1), and micropolarity (0.0–2.0) has been investigated on the heat transfer of Al2O3–water nanofluid. Also, the variable model was used to calculate fluid viscosity and thermal conductivity coefficient of the nanofluid. The results showed that an increase in Grashof amplifies the buoyancy force and enhances the Nusselt number. Also, an increase in vortex viscosity at low Grashof numbers strengthens the forced convection and increases the Nusselt number over the bottom wall. However, at Gr = 105, the increase in vortex viscosity up to K = 1.0 leads to a decrease in the amount of heat transfer, but its further increase entails the increase in heat transfer. Although the addition of nanoparticles to the fluid improves heat transfer rate, the extent of improvement at nonzero K values is lower than that in the Newtonian fluid. The comparison of the average Nusselt number computed on the hot wall under two different states of temperature-depended thermo-physical properties and constant thermo-physical properties reveals that their difference is more significant for the Newtonian fluid especially at higher volume fraction.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041013-041013-19. doi:10.1115/1.4044120.

Unsteady natural convection flow and heat transfer utilizing magnetic nanoparticles in the presence of a sloping magnetic field inside a square enclosure are simulated numerically following nonhomogeneous dynamic model. Four different thermal boundary conditions: constant, parabolic in space, sinusoidally in space, and time for the bottom hot wall are considered. The top wall of the enclosure is cold while the vertical walls are thermally insulated. Galerkin weighted residual finite element method is used to solve the governing nondimensional partial differential equations. For simulations, 12 types of nanofluids consisting magnetite (Fe3O4), cobalt ferrite (CoFe2O4), Mn–Zn ferrite (Mn–ZnFe2O4), and silicon dioxide (SiO2) nanoparticles along with water, engine oil, and kerosene as base fluids are used. The effects of the important model parameters such as Hartmann number, magnetic field sloping angle, and thermal Rayleigh number on the flow fields are investigated. The results show that the average Nusselt number, shear rate, as well as the nanofluid velocity decreases as the Hartmann number intensifies. Moreover, the rate of heat transfer in nanofluid exaggerates with the increase of the thermal Rayleigh number and the magnetic field sloping angle. Sinusoidally varied in space thermal boundary condition at the bottom wall provides the highest average Nusselt number and the shear rate compared to the other types of thermal boundary conditions studied here. For this case, the highest average Nusselt number is obtained for the Mn–ZnFe2O4–Ke nanofluid. On the other hand, Fe3O4–H2O nanofluid delivers the highest shear rate compared to the other premeditated nanofluids.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041014-041014-16. doi:10.1115/1.4044078.

Stability analysis for the Walters-B model saturated with permeable nanofluid is taken under study including cross diffusion effects. The porous medium is defined using modified Darcy model, and the nanofluid is considered to have the impact of thermophoresis and Brownian motion. The thermal energy equation includes the effects of diffusion and also cross diffusion. For the study of linear theory, normal mode procedure is applied and to understand the nonlinear theory, the method of minimal representation of double Fourier series is utilized. The effects of nondimensional parameters such as concentration Rayleigh number, Lewis number, Soret and Dufour parameters, Solutal Rayleigh number, elastic parameter, Prandtl number, viscosity ratio, and conductivity ratio on the stationary and oscillatory convections are represented graphically. The effect of time on transient Nusselt numbers is also taken under investigation. It is concluded that when time is small, the three Nusselt numbers oscillate for all the governing parameters and approach to steady-state as time increases.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041015-041015-7. doi:10.1115/1.4044137.

In this paper, experimental investigation has been performed to characterize the heat transfer behavior of CuO–water and ZnO–water nanofluids. Nanofluids containing different volume percent (vol %) of nanoparticle concentrations flowed over a flat copper plate under a constant heat load. The constant heat flux was maintained using evenly placed cartridge heaters. The heat transfer coefficients of nanofluids were measured and compared with the results obtained from identical experiments performed with de-ionized (DI) water. In order to thoroughly characterize the nanofluids, nanoparticle size was investigated to inspect for possible agglomeration. The particle size was measured by using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS). Enhancement of convective heat transfer of nanofluids was 2.5–16% depending on the nanoparticle concentrations and Reynolds number. The plausible mechanisms of the enhanced thermal performance of CuO and ZnO nanofluids will be discussed in the following paper.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041016-041016-8. doi:10.1115/1.4044184.

Different-radius of curvature pipes are experimentally investigated using distilled water and Fe3O4–water nanofluid with two different values of the nanoparticle volume fraction as the working fluids. The mass flow rate is approximately varied from 0.2 to 0.7 kg/min (in the range of laminar flow); the wall heat flux is nearly kept constant. The experimental results reveal that utilizing the nanofluid increases the convection heat transfer coefficient and Nusselt number in comparison to water; these outcomes are also observed when the radius of curvature is decreased and/or the mass flow rate is increased (equivalently, a rise in Dean number). The resultant pressure gradient is, however, intensified by an increase in the volume concentration of nanoparticles and/or by a rise in Dean number. For any particular working fluid, there is an optimum mass flow rate, which maximizes the system efficiency. The overall efficiency can be introduced to include hydrodynamic as well as thermal characteristics of nanofluids in various geometrical conditions. For each radius of curvature, the same overall efficiency may be achieved for two magnitudes of nanofluid volume concentration.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041017-041017-10. doi:10.1115/1.4044188.

In this paper, a ferrofluid-based cooling technique is proposed for solar photovoltaic (PV) systems, where ferrofluid flow can be easily altered by the application of an external magnetic field leading to enhanced heat transfer from the hot surface of PV systems. The effect of both constant and alternating magnetic field on ferrofluid flow through a minichannel is explored numerically in the present work. A detailed parametric study is performed to investigate the effect of actuation frequencies of alternating magnetic field (0.5–20 Hz) and Reynolds numbers (Re = 24, 60, and 100) on heat transfer characteristics of ferrofluid. An overall enhancement of 17.41% is observed for heat transfer of ferrofluid in the presence of magnetic field compared to the base case of no magnetic field. For the case of alternating magnetic field, a critical actuation frequency is observed for each Reynolds number above which heat transfer is observed to decrease. The enhancement or decrease in heat transfer of ferrofluid is found to depend on several factors such as actuation frequency of alternating magnetic field, Reynolds numbers of ferrofluid flow, and formation/dispersion of stagnant layers of ferrofluid at the magnet location. Preliminary visualization of ferrofluid flow is also carried out to provide a qualitative insight to the nature of transportation of ferrofluid in the presence of an alternating magnetic field.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041018-041018-11. doi:10.1115/1.4044185.

The transient mixed convection boundary layer analysis of incompressible flow over an isothermal vertical cylinder is embedded in a saturated porous medium in the vicinity for Gyrotactic microorganism effects. The mathematical model used for the bioconvective nanofluid incorporates the effects of Brownian motion, thermophoresis, and gyrotactic microorganisms. Moreover, the resulting governing nonsimilarity equations are changed into partial differential equations and solved numerically. The results are explained graphically for various physical parameters. It is determined that bioconvection parameter boosts the heat transfer rates and the thickness of the motile microorganism reduces the mass transfer rates. Expanding bioconvection Lewis number leads to decrease in heat transfer rates and the density of the motile microorganism, whereas the mass transfer rates decelerate the flow field. The investigation is pertinent to the nanobiopolymer manufacturing processes.

Commentary by Dr. Valentin Fuster
J. Thermal Sci. Eng. Appl. 2019;11(4):041019-041019-8. doi:10.1115/1.4044201.

This article presents the generalization of the unsteady MHD free convection flow of non-Newtonian sodium alginate-ferrimagnetic nanofluid in two infinite vertical parallel plates. The different shape (blade, brick, cylinder, and platelet) ferrimagnetic nanoparticles are dissolved in the non-Newtonian sodium alginate (SA) as base fluid to form non-Newtonian nanofluids. The Jeffrey fluid model together with energy equation is considered to demonstrate the flow. The Atangana–Baleanu fractional operator is utilized for the generalization of mathematical model. The Laplace transform technique and Zakian's numerical algorithm are used to developed general solutions with a fractional order for the proposed model. The obtained results are computed numerically and presented graphically to understand the physics of pertinent flow parameters. It is noticed that the velocity and temperature profiles are significantly increased with the increasing values of the fractional parameter due to the variation in thermal and momentum boundary layers. In the case of the effect of different shapes of nanoparticles, density is a dominant factor as compared to thermal conductivity, which significantly affects the flow of non-Newtonian nanofluid.

Commentary by Dr. Valentin Fuster

### Technical Brief

J. Thermal Sci. Eng. Appl. 2019;11(4):044501-044501-9. doi:10.1115/1.4044138.

An attempt is made here to characterize thermal conductivity of water-based Al2O3 nanofluid and then use the same in a circular finned thermosyphon (TPCT) to measure its thermal performance. The concentration of Al2O3 nanofluid is varied within 0.05–0.25% by volume. The thermal conductivity of nanofluid is increased with concentration of Al2O3 nanoparticles as well as with temperature. A maximum of 26.7% enhancement of thermal conductivity is observed at 45 °C for 0.25% concentration by volume of nanofluid in comparison to that of de-ionized (DI) water. Variations of surface tension and contact angle of Al2O3 nanofluid are also compared with DI water. One of the smallest TPCT with different heat inputs (4 W, 8 W, and 12 W) and different inclinations (30 deg, 45 deg, 60 deg, and 90 deg) is tested for different concentration of Al2O3 nanofluid, which will find application in smaller electronic units. It is found that use of nanofluid decreases the wall temperature distribution of TPCT. Thermal resistance of TPCT decreases whenever TPCT is filled with nanofluid and a maximum of 36.4% reduction in thermal resistance is noted for 0.25% volume of nanoparticles at 4 W with an inclination of 60 deg. It is also found that performance of TPCT is higher at 60 deg inclination compared to other inclinations, especially for lower heat input.

Commentary by Dr. Valentin Fuster

### Errata

J. Thermal Sci. Eng. Appl. 2019;11(4):047001-047001-1. doi:10.1115/1.4032332.

The first author’s affiliation and corresponding author should be listed as follows:

Topics: Exergy , Optimization , Wheels
Commentary by Dr. Valentin Fuster