Al2O3 H2O Nanofluid Research Articles

Comparative numerical study featuring magnetized nanofluids configured by elongating sheet with thermophoresis and Brownian motion

This study investigates the heat and mass transfer characteristics of MHD rotating Fe₃O₄-Al₂O₃/H₂O hybrid nanofluid flow over a three-dimensional stretching surface. Comparative analysis was conducted among the base fluid H₂O, Al₂O₃-H₂O nanofluid, and Fe₃O₄-Al₂O₃/H₂O hybrid nanofluid, focusing on velocity, temperature, and concentration distributions influenced by thermophoresis, Brownian motion, Hall current, temperature ratio, magnetic parameter, rotation, and thermal radiation. The governing nonlinear partial differential equations were transformed into ordinary differential equations using similarity adaptations and solved numerically with the BVP-5C method in MATLAB. Results indicate that increasing the thermophoresis and Brownian motion parameters elevates the temperature profile while affecting the concentration distribution differently. The hybrid nanofluid exhibited a higher temperature distribution compared to the nanofluid and base fluid, whereas the base fluid showed a greater concentration gradient.

Artificial neural network prediction on free convection in a triangular chamber with a v-shaped corrugated bottom wall filled with nanofluid

Artificial neural network (ANN) prediction on magnetohydrodynamic (MHD) free convection for complex systems using nanofluid plays a significant role in understanding and optimizing the system’s behaviour. The current research investigates how various governing parameters affect heat transport within a v-shaped corrugated bottom triangular chamber consisting of Al2O3-H2O nanofluid. The vertical wall is kept at a uniform low temperature, the inclined wall is adiabatic, and the v-shaped corrugated bottom wall is exposed to constant high temperature. The Galerkin weighted residual approach, based on the method of finite elements, is used to solve the dimensionless PDE problems with boundary constraints. The isotherms, streamlines, and average Nusselt numbers are displayed for various Hartmann numbers (0 ≤ Ha ≤ 100), Rayleigh numbers (103 ≤ Ra ≤ 106), and nanoparticles volume fractions (0.01 ≤ ϕ ≤ 0.05). It demonstrates how the average Nu is affected by Ha, Ra, and ϕ. Furthermore, it has been discovered that the average Nu increases with Ra and ϕ but decreases with Ha. However, the Levenberg-Marquardt back propagation method is employed for the artificial neural network (ANN) approach on 120 datasets to estimate the average Nu, demonstrating an excellent correlation with simulated data and an average R2 of 0.99689. MATLAB software is used to calculate the ANN predictions.

Dynamics of nanoparticle diameter and solid–liquid interfacial layer on the Al2O3–H2O nanofluid flow over a uni-directional extending heated surface: a numerical analysis

Dynamics of nanoparticle diameter and solid–liquid interfacial layer on the Al2O3–H2O nanofluid flow over a uni-directional extending heated surface: a numerical analysis

A numerical simulation of heat transfer performance on MHD nanofluids in porous metal for enhancing CPU cooling efficiency

The main goal of this study is to enhance CPU cooling efficiency using nanofluids, and the novelty of the study lies in the investigation of heat transfer and convective flow of MHD nanofluid through porous metal structures and foam heat sink/source to improve CPU cooling efficiency. The governing equations for the flow model are solved using the BVP4C with MATLAB package through shooting techniques. The effects of various parameters on velocity, temperature fields, HT and drag force are discussed through graphical simulations. The results indicate that as the Reynolds and Darcy numbers rise, fluid flow velocity undergoes unique alterations. Higher Reynolds and Darcy numbers result in cooler temperatures, while higher heat generation lead to warmer temperatures.Boosting Prandtl number improves HT by 52% with Cu nanoparticles, whereas elevating heat generation values reduce HT by 6.43% more efficiently with Cu nanoparticles than Al2O3 nanoparticles. Raising the Hartmann number would boost drag force, but the Darcy number opposes it. An increase in Hartmann number leads to a decrease in HT by 30.16% for Al2O3-H2O nanofluids and 47.81% for Cu-H2O nanofluids. The findings contribute to the development of advanced computing devices, paving the way for more efficient and reliable electronic systems in various applications.

Numerical study of the optimization of the thermal and flow characteristics of a collector design of microchannels with two inlets and outlets, containing a nanofluid and a water-based fluid

The effect of aluminum microchannel geometry on the flow properties of water and Al2O3–H2O nanofluid was studied numerically using CFD. For this purpose, we studied three cases of three different shapes of microchannels, the first case is rectangular micro channels, and in the second case, we added obstacles to the bottom and top walls of the microchannels. In the last case, we gradually decreased the hydraulic diameter of the channels at a distance of 2L/3 from the outlet of the microchannel. The channels have two inlets and one outlet. There is also a continuous flow heat source at the bottom of the channels. In this study, the Reynolds number varied from 300 to 600 for the two inlets. We also used water and a nanofluid with a low volume concentration of nanoparticles (2%). We considered that the fluid temperature at the inlet of the microchannels changes from 293 K to 300 K. We relied on the finite volume method with the SIMPLE algorithm in the calculation method. According to the results obtained from this study, the effect of changing the value of the Rayleigh number at the two entrances of the channel was observed on the temperature and velocity of the fluid and on the heat exchange inside the channels in the three cases. We also found that difference of the average of the Nusselt number between the nanofluid and the basic one in the three cases at Re =600 is 1.15, 1.74, and 1.57, respectively. In addition, we found that the shape of the studied micro channels has an effect on the friction factor and thermal resistance.

Numerical analysis of unsteady free convection under the combined influence of inclined magnetohydrodynamic and exothermic chemical reaction in an enclosure filled with nanofluid

Unsteady study of the natural convection of aluminum oxide-water nanofluid within a trapezoidal geometry containing a circular cylinder located at its center. Finite Element method has been considered for the numerical analysis. The proposed investigation handled the impact of Rayleigh number (103–105), chemical reaction parameter (0–4), aluminum oxide nanoparticles volume fraction (0–0.06), magnetic field (0–63) and its inclination angle (0°–90°), and circular obstacle diameter (0.3–0.7) effects on time-dependent natural convection of Al2O3–H2O nanofluid. On the other hand, the value of Prandtl number has kept constant at (Pr = 6.2). Since the nanofluid mobility at φ = 0.02, Ha = 3, and Fk = 1 significantly improved, the heat transfer rate achieved its maximum intensity at Ra = 105. Research also reveals a little effect on heat transfer by increasing the fraction of nanoparticles. Additionally, as Ha intensifies from 0 to 63, a final change in the mean Nusselt number of 28.65 % is displayed. Finally, as the magnetic field angle of rotation is diminished, more enhancement in heat transmission is achieved. This research provides insights into the intricate relationship between natural convection and exothermic reaction under the influences of various conditions. This can illustrate the flow and thermal behaviors of nanofluid in such non-uniform shapes in many engineering applications.

Direct Absorption Solar Collector: An Experimental Investigation of Al2O3-H2O Nanofluid over the Flat Plate at Different Tilt Angles, and Mass-Flow Rates

The escalating demand for solar thermal energy, coupled with the current inefficiencies in existing systems, underscores the critical need for innovative advancements in thermal storage solar collectors. The efficiency of solar collectors relies not solely on design effectiveness but also on the thermophysical properties, such as heat capacity and thermal conductivity, inherent in the working fluid. This study investigates a novel solar collector with a gross area of 0.36 m2, operating on the principle of direct absorption. Experimental investigations were done at various tilt angles (15°, 20°, and 30°) with respect to the horizontal, considering different flow rates and nanofluid settlement within the base fluids. The use of Al2O3 nanoparticles into the base fluid as water, exhibits significant positive effects on the thermophysical properties of the nanofluids, with a volume concentration of 0.003%. The efficiency of the solar collector was calculated across three mass flow rates (0.5, 1, and 1.33 L/min) at each tilt angle. Notably, the study reveals that the efficiency peaks at a 15° tilt due to an optimal flow configuration for maximum energy harvest across all three mass flow rates. Increasing the mass flow rate yields efficiency increments for all tilt angles (15°, 20°, and 30°), with 1 L/min emerging as the optimal mass-flow rate in most cases. This research not only addresses the immediate need for improved solar thermal technologies but also aligns with global sustainability goals, contributing to the IEA Net Zero Emissions initiative and supporting UN Sustainable Development Goals 7, 9, and 11. The paper also includes a critical literature review on the use of nanofluids in solar thermal collectors to improve thermo-physical properties and enhance solar efficiency. Additionally, the key findings regarding the influence and tilt angle on solar efficiency are discussed.

Heat transfer enhancement of nanofluids in a four-blade LPD static mixer

The heat transfer performance of nanofluids within a four-bladed LPD static mixer was investigated using a combination of experiments and simulations under constant heat flow boundary conditions with Re ranging from 3519 to 16719. Al2O3-H2O nanofluid with volume fraction φ = 0.3 % was prepared experimentally and the stability of the nanofluid was analyzed by settling observation method and Dynamic light scattering (DLS). Numerical simulations were adopted to analyze the effects of nanoparticle types, volume fractions and types of mixing nanofluids on the heat transfer enhancement inside the four-bladed LPD static mixer. The results show that the maximum error of Nusselt number (Nu) between the predicted values of Mixture model and experimental values was 7.39 %. Because of the combined heat transfer performance coefficient PEC more than 1 with the increasing of Re, the mixers with α = 30° and β = 45° instead of KSM could be recommended when Re > 5279. The PEC of Al2O3-H2O nanofluids gradually increases with the increasing φ. At the same Re and φ, the flied synergy number Fc and PEC of the mixed nanofluids are 1.01–1.47 times and 1.15–3.35 times higher than those of the single nanofluids.

Numerical simulation on nanofluid enhancement of downward facing surface’s critical heat flux

In this work, an improved wall boiling model for nanofluids was proposed, taking into account the effect of bubble slip on the wall heat flux density, as well as the effects of nanofluid thermophysical properties and nanoparticle deposition on the density of nucleation sites and bubble departure diameter. The nucleation site density and bubble departure diameter were calculated and compared with the experimental data, the deviations were not more than 7.80% and 9.81%, respectively. The downward-facing surface’s critical heat flux (CHF) was numerically simulated using Al2O3-H2O nanofluids. The simulation results of CHF were compared with the experimental data, and the maximum deviation did not exceed ±16.9%. Compared to pure water, the average CHF enhancement of 0.001–0.01vol% Al2O3-H2O nanofluid was 65.4%. The impacts of thermophysical properties, contact angle, and surface roughness were analyzed separately using the control variable method. The results showed that the wall temperature and void fraction were mostly not affected by thermophysical properties, and the variation in contact angle and surface roughness had a substantial impact. For the CHF improvement of 0.001vol% Al2O3–H2O nanofluids, the proportions of contact angle, surface roughness, and thermophysical properties on the CHF enhancement are 57%, 8%, and 1%. CHF enhancement with nanofluid was strongly related to the changes in contact angle and surface roughness.

Effects of self-cleaning technique and nanofluid cooling on performance of photovoltaic solar unit employing sinusoidal surfaces

The urgent need for electricity generation for both commercial and residential uses can be satisfied by photovoltaic units, but the serious flaws of these units arise from the negative effects of environmental factors like dust, shadow, radiation, and wind on their performance. The present study examines how PV panels operate under dusty conditions, using ANSYS FLUENT software and focusing on steady-state and laminar conditions. This study aims to numerically examine a three-dimensional (3-D) photovoltaic thermal (PV-T) unit with sinusoidal walls (PV-T-SW). The testing fluids examined in current paper are Al2O3-H2O nanofluid and H2O. Under the same initial and boundary conditions, three configurations were tested: a PV module, a straight channel PV-T unit, and the PV-T-SW, which are numerically compared and examined. An important element that declines the power generation efficiency is the deposition of dust on photovoltaic panels. The key novelty of the current study is that it provides a numerical modeling of the impact of dust in the presence and absence of a self-cleaning coating on a photovoltaic thermal system, as well as the optimal cooling mode and configuration. First, suitable temperature management systems are critical for achieving high-efficiency solar photovoltaics, and in heat exchange devices, the employment of corrugated structures has proven to be a helpful strategy because of the benefits of extended surface area. Finally, the electrical (ηele) and thermal (ηth) efficiency are assessed by taking into account the optical properties of dust deposition and hydrophobic coating. The factors evaluated are the impacts of varying nanofluid concentration, inlet flow Reynolds number (ranging from 500 to 1500), wavy channel amplitude, and wavelengths on cooling performance. The findings revealed that using 4 % water-aluminum oxide as an operating fluid instead of H2O improved the coefficients of heat transfer in the channel by 15.7 %. In addition, at the next step, when water-aluminum oxide was used as a coolant and the sinusoidal channel was examined with different geometrical characteristics, it was discovered that the 9 mm wavelength and 0.8 mm amplitude channel, in comparison to the simple form of the system, had superior heat transfer performance. Furthermore, the obtained data indicate that the ηele decreased by 40 % as the dust deposition happens, and it was discovered that the coating reduced that negative effect on the glass used to cover solar cells. Because of rising environmental issues and the expense of energy, thermal control of sources of energy that are renewable is becoming more and more important. The findings of this investigation can be used for future PV cooling innovation unit development and optimization.

A sensitivity analysis on thermal conductivity of Al2O3-H2O nanofluid: A case based on molecular dynamics and support vector regression method

The current study examines the sensitivity study of the thermal conductivity of water-based alumina nanofluids with variations in concentration, sphericity, and temperature. Thermal conductivity data of alumina nanofluids were obtained by simulation using the non-equilibrium molecular dynamics method with the parameters of nanoparticle volume fraction (1.24–6.2%), particle sphericity (0.6975–1.0), and temperature (290–360 K). Volume fraction and temperature have been discovered to have a major effect on the thermal conductivity of nanofluids, but sphericity should also be taken into consideration. Further, for parameter sensitivity analysis, a support vector machine regression model of thermal conductivity versus parameters was created with a coefficient of determination up to 0.98. The findings show that an Al2O3-H2O nanofluid's thermal conductivity increases with temperature and volume fraction while decreasing with sphericity. Temperature, sphericity, and volume fraction are the variables that are most sensitive to modification, according to a sensitivity analysis. A change in thermal conductivity of up to 4 % can occasionally be brought on by temperature differences of merely 1 %. The use of spherical particles makes it possible for the thermal conductivity of the nanofluid to be more stable, and the sensitive volume fraction region that can cause thermal conductivity to fluctuate across a large range is between 2.5 % and 5.5 %.

Comparison of the use of different nanofluids for heat transfer from the outer surface of spiral tubes: Energy, exergy, and exergoeconomic (3E) analysis

Heat exchangers play a crucial role in industrial processes by facilitating the efficient transfer of thermal energy. The thermophysical properties of nanofluids, which consist of nanoparticles dispersed in conventional heat transfer fluids, are enhanced. Their remarkable thermal conductivity and convective heat transfer characteristics have the potential to significantly improve heat transfer processes. In the present investigation, a numerical study has been carried out to investigate the effect of different nanofluids on heat transfer from outer surface of a spiral coil based on the first and second laws of thermodynamics. The numerical solutions are checked against previous experimental and numerical research in the field. Nusselt number, Euler number, exergy efficiency, irreversibility, and equipment cost are studied with respect to concentration, mass flow ratio (Rm), and shell and tube inlet temperature for a variety of nanofluids, including Al2O3/H2O, CuO/H2O, Fe2O3/H2O, and TiO2/H2O. Compared to water, the exergy efficiency is lower while using nanofluids, as shown by the results, especially in higher nanofluid concentrations, and among the different nanofluids, Al2O3–H2O nanofluid was found to have the highest thermodynamics second law efficiency. The exergy destruction rate experiences linear growth by increasing the nanofluid concentration. A higher pressure drop based on the Euler number is expected for nanofluids. In addition, the consumption of nanofluids on the shell side results in a considerable reduction of the purchased equipment cost (PEC) value compared to water. As opposed to the tube-side input temperature, variations in the shell-side inlet temperature found to have a greater impact on the heat exchanger's exergetic performance.

Second law and thermal analyses of non-Newtonian nanofluid double-diffusive natural convection within a two-hot-baffles-equipped C-shaped domain impacted by magnetic field

PurposeThe entropy and thermal behavior analyses of non-Newtonian nanofluid double-diffusive natural convection inside complex domains may captivate a bunch of scholars’ attention because of the potential utilizations that they possess in modern industries, for example, heat exchangers, solar energy collectors and cooling of electronic apparatuses. This study aims to investigate the second law and thermal behavior of non-Newtonian double-diffusive natural convection (DDNC) of Al2O3-H2O nanofluid within a C-shaped cavity emplacing two hot baffles and impacted by a magnetic field.Design/methodology/approachFor the governing equations of the complicated and practical system with all considered parameters to be solved via a formidable numerical approach, the finite element method acts as an approach to achieving the desired solution. This method allows us to gain a detailed solution to the studied geometry.FindingsThis investigation has been executed for the considered parameters of range, such as power-law index, baffle length, Lewis number, buoyancy ratio, Hartmann number and Rayleigh number. The main results reveal that isothermal and concentration lines are significantly more distorted, indicating intensified concentration and temperature distributions because of the growth of baffle length (L). Nuave decreases by 8.4% and 0.8% while it enhances by 49.86% and 33.87%, respectively, because of growth in the L from 0.1 to 0.2 and 0.2 to 0.3.Originality/valueSuch a comprehensive study on the second law and thermal behavior of DDNC of Al2O3-H2O nanofluid within a C-shaped cavity emplacing two hot baffles and impacted by magnetic field has not yet been carried out.

Dual solutions of mixed convective hybrid nanofluid flow over a shrinking cylinder placed in a porous medium

Mixed convective hybrid nanofluid flow over a shrinking cylinder saturated in a porous medium is analyzed in the presence of magnetic field. The mathematical model of the present problem is formulated with constant thermophysical properties. The system of governing equations is reduced to ordinary differential equations utilizing appropriate similarity transformations. The resulting equations are solved by the implicit Runge-Kutta-Butcher procedure together with Nachtsheim-Swigert iteration scheme. The key findings are that the skin friction coefficient and the Nusselt number are substantially augmented with the increase in mixed convection parameter, Ri, magnetic field parameter, M, and porosity parameter, K. However, the boundary layer separation is delayed owing to the higher value of M, Ri, K, curvature parameter, γ, volume fractions of Al2O3 (φ1) and Cu (φ2). Moreover, the thermal boundary layer for the Cu–Al2O3/H2O hybrid nanofluid is wider in comparison with that for Cu–H2O and Al2O3–H2O nanofluid. On the other hand, the momentum boundary layer is thicker for 10 % of Al2O3 nanoparticle volume fraction and the reverse is seen for 10 % volume fraction of Cu nanoparticle.

Multiple-Relaxation-Time Lattice Boltzmann Simulation of Soret and Dufour Effects on the Thermosolutal Natural Convection of a Nanofluid in a U-Shaped Porous Enclosure

This article reports an investigation of the Soret and Dufour effects on the double-diffusive natural convection of Al2O3-H2O nanofluids in a U-shaped porous enclosure. Numerical problems were resolved using the multiple-relaxation-time (MRT) lattice Boltzmann method (LBM). The indented part of the U-shape was cold, and the right and left walls were heated, while the bottom and upper walls were adiabatic. The experimental data-based temperature and nanoparticle size-dependent correlations for the Al2O3-water nanofluids are used here. The benchmark results thoroughly validate the graphics process unit (GPU) based in-house compute unified device architecture (CUDA) C/C++ code. Numeral simulations were performed for a variety of dimensionless variables, including the Rayleigh number, (Ra = 104,105,106), the Darcy number, (Da = 10−2,10−3,10−4), the Soret number, (Sr = 0.0,0.1,0.2), the Dufour number, (Df = 0.0,0.1,0.2), the buoyancy ratio, (−2≤Br≤2), the Lewis number, (Le = 1,3,5), the volume fraction, (0≤ϕ≤0.04), and the porosity, ϵ = (0.2−0.8), and the Prandtl number, Pr = 6.2 (water) is fixed to represent the base fluid. The numerical results are presented in terms of streamlines, isotherms, isoconcentrations, temperature, velocity, mean Nusselt number, mean Sherwood number, entropy generation, and statistical analysis using a response surface methodology (RSM). The investigation found that fluid mobility was enhanced as the Ra number and buoyancy force increased. The isoconcentrations and isotherm density close to the heated wall increased when the buoyancy force shifted from a negative magnitude to a positive one. The local Nu increased as the Rayleigh number increased but reduced as the volume fraction augmented. Furthermore, the mean Nu (Nu¯) decreased by 3.12% and 6.81% and the Sh¯ increased by 83.17% and 117.91% with rising Lewis number for (Ra=105 and Da=10−3) and (Ra=106 and Da=10−4), respectively. Finally, the Br and Sr demonstrated positive sensitivity, and the Ra and ϕ showed negative sensitivity only for higher values of ϕ based on the RSM.

On Entropy Generation and Heat Transfer Due to Magneto-Marangoni Convective γ Al2O3-H2O/C2H6O2 Nanofluid Flow Over a Porous Surface

A numerical analysis is carried out for water/Ethylene Glycol based γ Al2O3 nanofluid movement over a horizontal permeable sheet placed within a porous medium using MATLAB package Bvp4c solver. Other flow controlling conditions like Non-linear thermal radiation and uniform Magnetic field are also considered for this study. The present study is novel in terms of entropy generation and heat transfer rate investigation for mentioned fluid system in the existence of dissipation (an irreversible process) and heat generation/absorption impact. First, a mathematical pattern is prepared in the form of partial differential equations to represent the Marangoni convection flow and temperature, considering suitable boundary conditions. Using similarity parameters, we convert our mathematical model in dimensionless form and then solved it. Accuracy of obtained data is also cross-checked with another numerical technique “Runge-Kutta fourth order” along with shooting process. Using velocity and temperature fields, entropy is measured for present system. From the plots, it is noted that entropy as well as Bejan number is qualitatively changed for parameters namely, volume fraction parameter, radiation parameter, Brinkmann number and heat generation/absorption parameter. It is noticed that heat transfer rate and entropy generation number is higher for γ Al2O3-C2H6O2 nano fluid then γ Al2O3-H2O nano fluid.

Multi-objective optimization of a combined heat sink with triangular protrusion and corrugated surface impinged by a nanofluid slit-confined jet

Improving temperature uniformity and heat transfer capacity is crucial for the application of a jet-impingement heat sink in dissipating heat from high-power electronic devices. Therefore, a combined heat sink with a triangular protrusion in the stagnation zone, a corrugated surface in the wall-jet zone, and an oblique angle of the upper plate impinged by a nanofluid jet is proposed. A two-dimensional model is established, using Al2O3-H2O nanofluid as coolant. The effects of the structural parameters of the heat sink, the volume fraction of the nanofluid on the temperature uniformity of the heat sink and the jet-impingement heat transfer were studied numerically. Meanwhile, the structure of the heat sink is optimized by the NSGA-II genetic algorithm. The results indicate that the three structures can enhance both the temperature uniformity and the heat-transfer capacity. Using nanofluids with a 3%volume fraction and a Reynolds number of 8,000, the average Nusselt number of the optimal structure is 26 % greater than that of a jet impingement flat heat sink, the temperature standard deviation is 67 % less, and the friction coefficient and thermal-hydraulic performance factor are greater by 55 % and 9 %, respectively. Meanwhile, the optimized structure exhibits excellent heat dissipation and temperature uniformity at higher heat flux. The allowable maximum heat flux reaches 341 W/cm2 when the junction temperature of the hot spot does not exceed 348 K, and the temperature standard deviation is 2.926, which are increase by 83 % and decrease by 36 % compared with that of jet-impingement plate heat sink, respectively.

MOLECULAR DYNAMICS SIMULATION OF THE VISCOSITY AND THERMAL CONDUCTIVITY OF AL2O3-H2O NANOFLUIDS

This research investigated Al2O3-H2O nanofluids’ conduction of heat and viscosity using molecular dynamics method. For nanofluids, consequences of the nanoparticles’ volume fraction, temperature, size, and shape were studied. EMD computed the Al2O3-H2O nanofluid viscosity, while NEMD calculated the thermal conductivity. The findings indicated the sensitivity of the nanofluid to temperature and volume fraction variations. Alongside rising volume fraction, viscosity and conduction of heat likewise rise. When the temperature rises, the viscosity will decrease, and the thermal conductivity will increase. And the variation trend is the same as the experimental value. At the same temperature, the particle size of the nanoparticles becomes smaller, the specific surface area of the particles becomes larger, and the viscosity and thermal conductivity of the nanofluids become larger. And get the shape of the nanoparticles at the time of low volume fraction of greater effects on the viscosity and thermal conductivity of nanofluids, but in the case of high-volume fraction, volume fraction increases nano fluid viscosity and thermal conductivity coefficient is bigger.

Conditions of enhanced evaporation for nanofluids droplet and inhibition of coffee-ring effect under buoyancy and Marangoni convection

Evaporation of nanofluid droplets whose size is larger than capillary length is common in industrial processes, but there is currently a lack of research on the evaporation kinetics and more complex deposition patterns under the combined effects of buoyancy and Marangoni convection of large evaporating droplet. Experimental investigations on evaporation of Al2O3H2O nanofluid sessile droplet with initial contact line diameter of 4 mm on heating PTFE coating substrate are reported. The variation in contact angle, contact radius, and droplet volume over time under different conditions were obtained through experiments. The average evaporation rate is calculated. Internal flow characteristics are inferred through the surface temperature distribution detected by the top view infrared camera. The constant contact radius mode takes place at the beginning of evaporation. Then mixed evaporation mode and stick slip mode may occur for different substrate temperature, nanoparticle mass concentration and nanoparticle size. Increasing nanoparticle size causes a decrease in average evaporation rate. Whether the use of nanofluids can improve evaporation rate and heat transfer or not depends on multiple factors. Convection cells exist, and three kinds of deposition patterns are formed due to the underlying coupled transport phenomena. Under the combined effect of buoyancy and Marangoni convection in this article, the most common coffee-ring pattern does not appear. The deposition patterns are directly affected by the pinning stability, which decrease at higher temperature.

Thermal performance of dual flow slotted fin mini channel heat sink using Al2O3-H2O and TiO2-H2O: a numerical and experimental approach

To overcome the extensive heat generation inside the microprocessors nanofluids have gained importance because of their better thermophysical properties as compared with air and water. This work proposes a two-pronged strategy for thermal performance enhancement of mini channel heat sinks. Firstly, a novel dual flow slotted fin mini channel heat sink flow configuration is proposed. Secondly, a detailed numerical investigation is performed to assess heat transfer enhancement property of Al2O3-H2O and TiO2-H2O nanofluids. Considering the first step, fin spacing, number of slots, slot thickness and slot angle are investigated in detail yielding to the selection of best structural parameters. Two slots per fin of 0.5 mm thickness at an angle of 45° is selected because it provides better thermal performance as compared with water. Further, numerical assessment of nano fluid behavior was carried out at volumetric concentrations of 0.005% and 0.01%. For the case of novel dual flow slotted fin mini channel heat sink, maximum numerical and experimental advantages in all targeted system properties is observed for Al2O3-H2O nano fluid at volumetric concentration of 0.01%, as compared with water. Al2O3-H2O nano fluid provides better thermal performance both numerically and experimentally as compared with TiO2-H2O nanofluids. Increment in the pressure drop is noted with increasing volumetric concentrations.