Particle Volumetric Concentration Research Articles

Experimentally optimized particle–polymer matrix structure for efficient daytime radiative cooling

The polymer–particle matrix structure has attracted great interest for daytime radiative cooling due to its various advantages; however, cost-effective fabrication process development and proper material selection are crucial tasks. Herein, we illustrate the selection of fabrication process and materials based on development, characterization, and experimental performance. The initial selection is based on solar radiation backscattering and isotropic thermal emission properties of polymers and particles. Among potential polymers (PMMA, PVDF, and PU), PMMA is experimentally found more suitable for radiative cooling because of negligible absorption in the solar radiation spectrum. Among the selected particles (CaCO3, BaSO4, ZnO, and SiO2), the experimental performance of BaSO4 in the polymer matrix is found to be excellent. Furthermore, the optimum particle volumetric concentration is found at 70%, with an optimum thickness of 500 μm for the substrate independent radiative cooler. Spray-coating is found to be a better option for fabrication as compared to drop casting. The performance evaluation was carried out at Varanasi, India for over two months to investigate the environmental parameters' effect on performance. For an optimized structure, the observed maximum temperature drop from the ambient is 6 °C (17 °C lower than bare roof surface) during noontime and 9 °C during the evening. At ambient temperature, the recorded cooling power is 35 W/m2 at noon (solar peak) and 78 W/m2 in the evening for the experimentally optimized structure.

Theoretical consideration of the rheological properties of aggregated suspensions

The rheological properties of particulate dispersions containing aggregate structures were theoretically investigated in this study. Under the assumption of Stokes flow, the viscosity of fluids with fine particles was derived by a theoretical method based on the multipole expansion in reciprocal space. In this method, many-body hydrodynamic interactions were considered as the multipole-expanded moment of the force density at the surface of the particles. It is possible to calculate the viscosity of particulate suspensions by considering higher-order moments. The viscosity of monodisperse particulate suspensions was calculated under various conditions. To verify the accuracy of the calculation, the viscosity of uniformly distributed particulate suspensions was calculated, and the results were compared with the experimental results of previous studies. The calculated viscosities were in good agreement with the experimental results for a wide range of particle volumetric concentrations. The viscosity of aggregated suspensions was also calculated to examine the mechanism of viscosity change. The viscosity was systematically calculated with changing the aggregate size and particle concentration. The results indicate that the hydrodynamic effect is not significant on the viscosity change by aggregation, which is contrary to the assumption of previous viscosity models. The calculation results suggest that the increase in the viscosity of aggregated suspensions is instead caused by the direct influence of inter-particle forces.

Fracture roughness effects on slickwater proppant slurry settling attenuation

This study evaluates and quantifies fracture roughness effects on proppant particle settling in fractures utilizing coupled, resolved computational fluid dynamics (i.e., simulation of carrier fluid behavior) and the discrete element method (i.e., simulation of proppant particle behavior). This work focuses specifically on “slickwater” based proppant slurries. Rough fracture geometries are generated using a spectral-based algorithm with surficial roughness varied by adjusting fractal dimension and root-mean-square asperity heights descriptive parameters. This work also considers particle volumetric concentration and influence from flowing conditions on particle settling. Results indicate that the attenuation of quiescent settling rates is more pronounced in rough fractures as the aperture narrows. The degree of quiescent slurry settling attenuation corresponds to fractal dimension and root-mean-square asperity height values. A formulation to describe the average settling rate of quiescently settling slurries in rough fractures is proposed and evaluated. Fracture roughness causes erratic settling velocities of flowing slurries, with some cases having upward proppant velocity, specifically at narrow apertures at or below two times the particle size for the condtions considered in this work. The onset of this behavior is dependent on degree of roughness, with erratic velocities occurring at narrower relative apertures for smoother fractures compared to rougher fractures. Preferential flow pathways formed in rough fractures at narrower apertures, are noted to cause these erratic settling behaviors. The overall findings provide a greater understanding of particle settling behavior in rough rock fractures, aiding in the design process for fracture enhancement projects.

A numerical study of neutrally buoyant slickwater proppant flow and transport in rough fractures

Influence of rough rock surface geometry on flow behavior for single and multiple neutrally buoyant particles in fractures is explored. Degree of roughness is evaluated by varying synthetic surfaces’ root-mean-square asperity height and fractal dimension. Influences of flow Reynolds number and multiparticle volumetric concentration are also considered. Simulated behavior of particles within fluid is performed utilizing resolved computational fluid dynamics with the Discrete Element Method. Behavior within rough fracture apertures is contrasted against behavior within smooth wall fractures. Findings show accentuation in particle transport rate for some rough fractures at intermediate particle diameter to mechanical aperture ratio values. Further narrowing of fracture mechanical aperture past these intermediate values leads to increased particle–wall collision interactions, causing attenuation of particle transport rate and eventual particle arrest. Mechanical aperture in rough fractures where particle arrest occurs is appreciably larger than particle diameter and largely depend on surface fractal dimension and asperity height root-mean-square. Multiparticle flow and transport evaluations also reveal that increased particle interactions lead to varied hydraulic aperture values. Hydraulic aperture is found to be dependent on combined effects from injection particle volumetric concentration and surface roughness at moderate mechanical aperture, with increasing importance of surface roughness as mechanical aperture narrows. Further, it is found that particle jamming depends more on fracture geometry than injected particle volumetric concentration. This work provides a unique micro-level perspective of particle slurry behavior within rough rock fracture interfaces, pointing to the shortcomings of assumed analogous smooth-walled fracture face behavioral characterizations utilized in past investigations.

Simultaneous improvement of microgeometry and surface quality of spur and straight bevel gears by abrasive flow finishing process

This article reports on influence of extrusion pressure, abrasive particle size and volumetric concentration on simultaneous reduction of surface roughness and microgeometry errors of spur and straight bevel gear by abrasive flow finishing (AFF) process. A vertical configured experimental apparatus was developed for two-way AFF and developed fixtures for finishing gears. Experimental investigations were conducted to identify optimum parametric combination, using response surface methodology, based on Box–Behnken design approach. Results revealed that higher values of abrasive particle size and volumetric concentration yield more percentage decrease in surface roughness and microgeometry error. Roughness profile, bearing area curve, microhardness, surface morphology, and wear resistance of the gear having best quality finishing were studied. Surface morphology analysis of the flank regions of the best finished spur and straight bevel gears found them to be smooth and free from cracks and burrs. Reciprocating wear test results revealed higher wear resistance of the AFF finished gears as compared to the unfinished gears. AFF also enhanced microhardness of the finished gears, which would enhance their operating performance and service life. This study shows that AFF is a flexible, economical, productive, easy to operate, and sustainable nontraditional process for precision finishing of gear that can simultaneously improve microgeometry, surface finish, microhardness, surface morphology, wear resistance, and residual stresses of the finished gears. Gear manufacturers and users will be benefited by the outcome of this study. JEL codes: C00, C20

Particle clustering dynamics in dense-phase particle-fluid slurries

This study investigates clustering mechanisms during flow and transport of dense-phase particle–fluid slurry, evaluating the slurry’s complex internal composition effects on particle conveyance. Dense-phase particle–fluid flow and transport are affected by frequent particle–particle collisions, leading to development of particle clusters. Particle conveyance and irregularities of particle placement in fractures due to clustering influence is a topic of interest for proppant injection used during hydraulic fracturing for enhancement of geothermal and hydrocarbon reservoirs. A micromechanical (particle-level) approach using the Discrete Element Method coupled with computational fluid mechanics (DEM-CFD) reveals interesting underlying mechanisms which govern overall slurry conveyance. In this study, qualitative clustering shapes and quantitative clustering characteristics are related to variances in the Durand-Froude number and injected particle volumetric concentrations. Furthermore, this study compares coupled DEM-CFD model results with simplified particle transport evaluations used in some hydraulic fracture simulation software. Results show that particle deposition dynamics do not fully follow predictions based on simplified evaluations at higher injection volumetric concentrations. In most of these cases, conveying particle suspension concentration is non-linear in behavior that differs from the anticipated particle behavior described by simplified evaluations. Overall, this work improves understanding of flowing particle slurry structure and slurry clustering influence on flow and transport.

Experimental investigation into a parabolic solar collector with direct flow evacuated tube

Solar energy is among the cleanest and most adaptable in comparison with other renewable energy sources. Considering the request for long-term using of solar collectors, developing and enhancing the performance of these systems has become one of the main subjects. Parabolic trough solar collector (PTSC) is one of the best usual solar collectors. improving the thermal performance of PTSC concentrates several attention and different approaches are evaluated to maximize the collector thermal efficiency with a reasonable penalty in the pressure drop and energy losses. For this reason, the use of different nanofluids as working fluids, as well as the use of various absorbers (receivers) are the major challenges and techniques which are examined. Therefore, in this study, a novel parabolic trough solar collector (PTSC) using U type tube is designed and manufactured. To increase the operational temperature, evacuated tube is used and performance of the mentioned system is experimentally examined using both distilled water and CuO nanofluid as working fluids. It should be noted that, CuO is selected as nanoparticle and water as base fluid. CuO/nanofluid. Absorption spectrum results of CuO/nanofluid at different resting times by using Ultraviolet–Visible (UV–Vis) spectroscopy examined. Experimental results for the changes in three important parameters including, performance index (PI), thermal efficiency as well as pressure drop are obtained for different mass flow rates including, 1, 3 and 5 L/min and also three particle volumetric concentrations including 0.01%, 0.05% and 0.08%. The results showed that, thermal efficiency, pressure drop and PI is mostly affected and increased by mass flow rate and nanofluid volume fraction. In addition, based on the experimental results, maximum thermal efficiency and performance index are obtained respectively 71% and 1.74, corresponding in the case of nanofluid with 0.08% volume fraction and mass flow rate of 5 L/min.

Heat transfer and entropy generation analysis of internal flow of nanorefrigerant with slip condition at wall

Heat transfer enhancement has always been the main purpose in designing the heat exchangers in various industrial applications. In addition, nanofluids have shown potential as industrial cooling fluids due to the enhanced heat transfer characteristics particularly in heat exchanger applications. Whilst enhancing heat transfer using nanofluids, there is a trade-off of causing higher irreversibility and pressure drop. Therefore, in order to have a better view of thermal performances, it is necessary to consider other aspects of the thermal system in addition to heat transfer factors such as pressure drop and entropy generation. In the present study, the heat transfer characteristics and entropy generation analysis of a laminar nanofluid flow in a 3 mm horizontal circular tube subjected to a uniform heat flux and slip boundary condition is evaluated numerically using ANSYS Fluent software. Two types of nanofluids that are obtained from dispersing of Al2O3 and SiO2 nanoparticles in pure HFE7000 are considered with particle volumetric concentrations of 0, 1, 4 and 6% and Reynolds numbers of 400, 800, 1200 and 1600. Results indicate that mean pressure drop reduces about 25% by using the slip boundary condition at the wall. In addition, while using a slipping wall pipe with slip length of 100 µm and 6% volume concentration of Al2O3 dispersed in HFE7000, total entropy generation decreases about 20% in comparison to pure HFE7000 flowing in a no-slip pipe.

Multi-objective optimization of solar collector using water-based nanofluids with different types of nanoparticles

This study looks at the effects of different kinds of nanoparticles including AL2O3, SiO2, and CuO on the design of a solar flat plate collector in different volumetric concentrations. Water was used as the base fluid, and optimal SFPC parameters were obtained for each of the nanofluids. Both the efficiency and total annual cost were selected as objective functions, and the optimum Pareto fronts were compared with those of the base fluid. The results show a significant enhancement in both the efficiency and TAC for all the studied nanofluids compared with the pure water as the working fluid. The efficiency improved by 4.47%, 4.65%, and 5.22% in the cases of AL2O3, SiO2, and CuO compared with base fluid with a fixed TAC of 67 $ year−1. With a fixed efficiency of 0.564, TAC decreased by 25.45%, 25.87%, and 27.88%, respectively. The optimum design parameters show that lower heat transfer surface area and insulator thickness are needed for CuO compared with the other cases, followed by SiO2, AL2O3, and the base fluid. In the optimum conditions, a lower particle volumetric concentration is required for CuO, followed by Al2O3 and SiO2.

Particle image and tracking velocimetry of solid-liquid turbulence in a horizontal channel flow

The turbulence statistics of the solid and liquid phases in a horizontal turbulent channel flow are experimentally investigated to identify the effect of particle size, flow Reynolds number (Re) and the volumetric concentration of particles. Glass beads with diameters of 285, 340, 530 and 700 µm are used to produce suspensions at particle volumetric concentrations between 0.05 and 0.18%. Measurements are made at Re of 50,000, 75,000, 100,000, and 125,000 based on channel height and average velocity. The instantaneous velocity of the glass beads is obtained using a correlation-based particle tracking velocimetry (PTV) while particle image velocimetry (PIV) using smaller tracers is applied simultaneously to obtain the liquid phase velocity. It is observed that the solid phase velocity is larger than the liquid phase in the near-wall region for the larger particles and higher flow Re. The particle Re number, Rep, defined based on the particle diameter and the slip velocity (mean relative velocity between the liquid and solid phases), and the Stokes number (St) are used to evaluate the turbulence modulation of the liquid phase. Particle Re numbers as large as 225 are calculated for the 700 µm particles at Re = 125,000, which leads to vortex shedding and, consequently, increases turbulence intensity of the liquid phase relative to the unladen flow. The PTV results indicate that the turbulence intensity of the solid phase decreases with increase of St (i.e. larger particles and higher flow Re). The solid phase volumetric concentration has negligible effect on the solid phase turbulence, while the wall-normal turbulence intensity of the liquid phase increases with the volumetric concentration. This observation reveals the two-way coupling of the solid and liquid phases at the range of concentrations investigated in the current study.

Numerical investigation of heat transfer by an impinging jet using alumina–water nanofluid

This article reports numerical investigations of turbulent flow field and heat transfer performance of water-alumina nanofluid jet impingement. The jet impinges over a flat, circular heated surface from a circular pipe of diameter . The influence of jet Reynolds number (1,200 ≤ ≤ 40,000), jet-outlet-to-target wall distance (2 ≤ ≤ 12.8), and particle volumetric concentration (0 ≤ φ ≤ 10%) on the fluid flow and heat transfer are examined. The results of fluid flow and heat transfer are compared with the published experimental data. It is found that the heat transfer increases with increasing values of the particle volumetric concentration while the flow field and turbulent kinetic energy distribution remain unchanged with the inclusion of nanoparticles. About 28% enhancement in stagnation Nusselt number is observed at low values of nanoparticle volumetric concentration (φ = 0.1%) and in the Reynolds number range of 29,000–40,000. For jet-outlet-to-target wall spacing values used in the current study, the local Nusselt number distributions vary according to Nu ∝ . Numerical simulations are performed using Reynolds-averaged Navier–Stokes method with the shear stress transport k-ω model in commercial CFD code ANSYS-CFX.

A Critical Review of Heat Transfer Characteristic Using Nanofluid Flow Around a Set of 2D Cylinder Arrangements?

Our paper includes the results of a numerical simulation performed to study the nanofluid flow around a set of 2D cylinder arrangements. Two types of nanofluids involving Al2O3 and CuO nanoparticles dispersed separately in base fluids of water and ethylene glycol mixture 60:40; those nanofluids were taken to evaluate their effect on the flow around different equilateral-triangular arrangements of cylinders. The continuity and the momentum equations have been numerically solved by using a special technic named “SIMPLE algorithm.” Besides, the thermo-physical parameters of nanofluids have been evaluated using the theory of one fluid phase; thus, contemporary correlations of thermal conductivity and viscosity of nanofluids have been used in this paper as well as our previous work (Int J Adv Technol 7(4)0976–4860, 2016). The correlations are functions of particle volumetric concentration as well as temperature. The results of heat transfer characteristics of nanofluid flow around 2D cylinder arrangement revealed clear improvement compared with the base fluids. This enhancement is very interesting in engineering of flows with different equilateral-triangular arrangement characteristics of cylinders, while the gap ratios (G/D) of the three cylinders and incidence angle exert an enhancement efficiency influence on the heat transfer characteristics. The achieved results indicate that the use of aspect ratio 2.26 and incidence angle 1.98° leads to the high amounts of heat transfer inside the tube. In this study, the results obtained can be a fruitful source for developing and validating of new codes both in a scientific and commercial manner.

Freeze-Thaw Characteristics of Water-Based Copper Oxide Nanofluid

This research examined the freeze-thaw characteristics of a water-based copper oxide (CuO) nanofluid for its successful application in cold regions, where freezing of heat transfer fluids can occur. The enhanced thermal conductivity (k) of nanofluid makes it valuable as a heat transfer fluid, but k diminishes as the average particle size (APS) of the dispersed nanoparticles grows. Therefore, experiments were conducted to determine the effect of freezing on the APS of nanofluid suspensions due to agglomeration. Additionally, it was studied, if the freezing point of the nanofluid was elevated or depressed as the volumetric concentration of nanoparticles in the suspension was increased from 1 % to 5%. Another objective of this experimental study was to compare the time required for precooling, freezing and subcooling of different concentrations of nanofluids and the base fluid. The results showed that the APS grew by as much as 51.2% larger due to the phenomenon of freezing, which would reduce the heat transfer performance. The addition of nanoparticles did not affect the freezing point of the nanofluids, tested for two particle volumetric concentrations of 1 and 5 %. It was observed that the precooling time of 5% CuO concentration was the longest. For the complete solidification process, the water and 1% CuO had comparable freezing times, while the 5% nanofluid had the shortest freezing time. The subcooling time was increased with particle volumetric concentration.

Numerical study on impact behavior of nanoparticle shapes on the performance improvement of shell and tube heat exchanger

Using nanoparticle in the fluid is a novel engineering issue which could improve the performance of heat exchanger. The main goal of this study is determining the effect of different nanoparticle shapes on the thermoeconomic improvement of a shell and tube heat exchanger (STHE). For this purpose, Boehmite alumina is selected as a nanoparticle with the four different shapes including platelets, blades, cylindrical and bricks. Then the heat exchanger annual cost and effectiveness are optimized by considering the mentioned nanoparticle shapes additive and the results are compared with each other and with the absence of nanoparticle additive. Nine design parameters such as particle volumetric concentration and flow allocation are selected and optimization is performed for the different sets of hot and cold side mass flow rates. The optimum results reveal that heat exchanger thermoeconomic parameters are improved higher in the case of bricks as nanoparticle shape and generally followed by blades, cylindrical and platelets shapes. For example, 1.24% grown in the effectiveness and 3.75% reduction in the annual cost are observed in the case of blades shape nanoparticle compared with the case of without nanoparticle. In addition it is observed that, higher particle concentration is needed in the case of blades and bricks nanoparticle shapes as compared with the other studied shapes.

Experimental investigation of thermal conductivity and specific heat of nanoparticles mixed cutting fluids

Excessive use of conventional cutting fluids during conventional machining in wet condition (flood mode) and use of wrong and inefficient methods of its disposal can affect the operator’s health and environment. This has led to the development of a new type of cutting fluid, which can overcome the problems of use of conventional cutting fluids and have better thermal properties and tribological properties. In the present work, different nano fluids are prepared by suspension of Titanium dioxide (TiO2), Siliconoxide (SiO2) and Aluminumoxide (Al2O3) nano particles in vegetable oil water mulsion at room temperature. The Nano particles are mixed in oil water emulsion in different volumetric concentrations. Then thermal conductivity and specific heat of the nano fluids are measured at different temperatures for different Nano particle volumetric concentrations. From the experimental results, it has been found that increase of Nano particles concentration in base fluid enhanced its thermal conductivity and decreases its specific heat. Furthermore, thermal conductivity andspecificheatofthreedifferentnanofluidsarecomparedwitheachother and recorded that suspension of Nano particles into oil water based fluid increases its cooling capacity. It is also found the Al2O3 exhibits excellent thermal properties than TiO2 and SiO2 based nano fluids.

Investigation of the thermal conductivity of propylene glycol nanofluids and comparison with correlations

Experimental study has been carried out to determine the thermal conductivity of five different nanofluids containing aluminum oxide, copper oxide, zinc oxide, silicon dioxide and titanium dioxide nanoparticles dispersed in a base fluid of 60:40 (by mass) propylene glycol and water mixture. The effect of particle volumetric concentration up to 6% was studied with temperatures ranging from −30° to 90°C. Experiments showed an increase in thermal conductivity of nanofluids with increasing concentration and temperature. The thermal conductivity of nanofluids showed a strong dependence on particle volumetric concentration, particle size, properties of particles and the base fluid and temperature. Several existing theoretical models for thermal conductivity of nanofluids were compared with the experimental data, but they all showed disagreement. From comparisons, the most agreeable model was selected and a curve-fit constant was derived to match the data of propylene glycol nanofluids. This model expresses the thermal conductivity of nanofluids as a function of Brownian motion, Biot number, fluid temperature, particle volumetric concentration, and the properties of the nanoparticles and the base fluid. This model provided good agreement with 600 experimental data points obtained from five different nanofluids with an average absolute deviation of 1.79 percent. Because of the enhanced thermal conductivity with increasing temperature, nanofluids should be more beneficial at higher temperature applications.

Heat transfer and entropy generation analysis of HFE 7000 based nanorefrigerants

In this study, two dimensional numerical simulations of forced convection flow of HFE 7000 based nanofluids in a horizontal circular tube subjected to a constant and uniform heat flux in laminar flow were performed by using single phase homogeneous model. Four different nanofluids considered in the present study are Al2O3, CuO, SiO2 and MgO nanoparticles dispersed in pure HFE 7000. The simulations were performed with particle volumetric concentrations of 0, 1, 4 and 6% and Reynolds number of 400, 800, 1200 and 1600. Most of the previous studies on the forced convective flow of nanofluids have been investigated through hydrodynamic and heat transfer analysis. Therefore, there is limited number of numerical studies which include both heat transfer and entropy generation investigations of the convective flow of nanofluids. The objective of the present work is to study the influence of each dispersed particles, their volume concentrations and Reynolds number on the hydrodynamic and thermal characteristics as well as the entropy generation of the flow. In addition, experimental data for Al2O3–water nanofluid was compared with the simulation model and high level agreement was found between the simulation and experimental results. The numerical results reveal that the average heat transfer coefficient augments with an increase in Reynolds number and the volume concentration for all the above considered nanofluids. It is found that the highest increase in the average heat transfer coefficient is obtained at the highest volume concentration ratio (6%) for each nanofluids. The increase in the average heat transfer coefficient is found to be 17.5% for MgO-HFE 7000 nanofluid, followed by Al2O3-HFE 7000 (16.9%), CuO-HFE 7000 (15.1%) and SiO2-HFE 7000 (14.6%). However, the results show that the enhancement in heat transfer coefficient is accompanied by the increase in pressure drop, which is about (9.3–28.2%). Furthermore, the results demonstrate that total entropy generation reduces with the rising Reynolds number and particle volume concentration for each nanofluid. Therefore, the use of HFE 7000 based MgO, Al2O3, CuO and SiO2 nanofluids in the laminar flow regime is beneficial and enhances the thermal performance.

Confined jet array impingement cooling with spent flow distraction using NEPCM slurry

The confined jet array impingement cooling with spent flow distraction using nano-encapsulated phase change material (NEPCM) slurry (or nanofluids) is investigated numerically using a homogeneous model, based on effective thermophysical properties of the slurry. The NEPCM slurry consists of the carrier fluid of polyalphaolefin (PAO) and the NEPCM particles with Polystyrene shell and paraffin core. The jet impingement cooling of a slot jet array with jet width of 100μm, confinement height of 300μm, and jet-to-jet distance of 400μm is investigated numerically under conditions of different jet velocities, inlet temperatures, particle volumetric concentrations, as well as heat fluxes. Unlike MEPCM (micro-encapsulated phase change material) where micro-convection effect plays an important role in heat transfer enhancement, it is found that this effect has little impact on heat transfer of NEPCM because of much smaller particles of NEPCM. There exists an optimal volumetric concentration to achieve the best heat transfer performance for a given jet velocity, and this optimal volumetric concentration at first increases and then becomes saturated with increasing jet velocity in the range of the present study. An optimal inlet temperature, close to (but lower than) the peak of melting curve of PCM, is determined for the maximum heat transfer enhancement; it is found that the higher the jet velocity (when heat flux is fixed) or the lower the heat flux (when jet velocity is fixed), the closer the optimal inlet temperature to the peak of melting curve. The local heat transfer under the exit slot is the lowest because of the formation of a stagnant zone by the head-to-head collision of the two adjacent wall jets, and adding of NEPCM does not change the basic characteristics of local heat transfer, but a little bit extends the low heat transfer region.

Investigating the effect of nanoparticle on thermo-economic optimization of fin and tube heat exchanger

In this paper, the effects of Al2O3 nanoparticles suspended in the water-based fluid on the thermo-economic properties of a fin and tube heat exchanger are studied using fast and elitism nondominated sorting genetic algorithm. Nine design parameters are selected as design parameters, and the total annual cost and effectiveness are considered as the two objective functions. First, the effect of nanoparticle on the total annual cost versus effectiveness is obtained at different cold side mass flow rates, and the results are compared with the base fluid. The results show that nanoparticles have a significant influence on the total annual cost and effectiveness in a lower cold side mass flow rates. Next, the heat exchanger volume versus effectiveness for the optimum points is measured at different cold side mass flow rates. It is demonstrated that, adding Al2O3 nanoparticle to the base fluid for the fixed value of effectiveness, decreases the heat exchanger volume, and this reduction is more significant in the lower mass flow rates. The pressure drop and total heat transfer surface area versus effectiveness for the optimum points are also obtained with and without nanoparticle. An increase in the tube side pressure drop is revealed in the nanofluid. In addition, due to the increase in the overall heat transfer coefficient, the lower heat transfer surface area is required for the fixed value of effectiveness. Finally, variations of objective functions versus particle volumetric concentration for five typical optimum points are estimated. It is concluded that an optimal value for the volumetric concentration can be obtained, in which the effectiveness is highest.

Heat transfer coefficient and critical heat flux during nucleate pool boiling of water in the presence of nanoparticles of alumina, maghemite and CNTs

The characteristics of nucleate pool boiling were investigated with nanofluids in a chamber. Nanoparticles of alumina, maghemite and carbon nanotubes were added separately to distilled water. Particle volumetric concentrations of 0.02% and 0.10% were applied. Experiments with water on the heater copper surface covered with nanoparticles were conducted to evaluate the effect of deposition. Boiling curves, critical heat fluxes and heat transfer coefficients were obtained and compared to reference data for water. The wettability was determined from contact angle measurements. In the experiments with the nanofluids, the nanoparticles were deposited on the test surface. The static contact angle for the water on the copper oxide surface decreased from around 85° to 0° following the deposition of the nanoparticles. Values for the critical heat flux increased from around 26–37% for all test cases. These results are attributed to the complete wetting behavior presented by the nanoparticles deposited on the test surface. Estimates obtained using the Kandlikar (2001) correlation deviated from the experimental values by less than 9%. The heat transfer coefficients were the same or lower in comparison with the reference case.