MWCNT Nanofluids Research Articles

Ohmic Heating and Non-uniform Heat Source/Sink Roles on 3D Darcy–Forchheimer Flow of CNTs Nanofluids Over a Stretching Surface

The major focus of the current study was the modeling of 3D Darcy–Forchheimer flow of water–CNTs nanofluid. Impacts of non-uniform heat source/sink and Ohmic heating on 3D magneto hydrodynamic flow of water–CNTs (SWCNT and MWCNT) nanofluid were assessed. The numerical analysis method ‘Runge–Kutta–Fehlberg’ was applied for existing PDEs. It was noted that the thermal boundary layer was extended for increasing Eckert numbers along $$ x\;{\text{and}}\;y $$ direction, when the fluid showed movement away from the surface. Moreover, the gap in thermal boundary layer for H2O-SWCNT was more in comparison with H2O–MWCNT nanofluid. The numerical data of this study were validated with earlier reported outcomes and were observed to have good concord.

Heat transfer in turbulent nanofluids: Separation flow studies and development of novel correlations

Convective heat transfer plays a significant role in numerous industrial cooling and heating applications. This method of heat transfer can be passively improved by reconfiguring flow passage, fluid thermophysical properties, or boundary conditions. The broader scope of nanotechnology introduced several studies of thermal engineering and heat transfer. Nano-fluids are one of such technology which can be thought of engineered colloidal fluids with nano-sized particles. In the present study, turbulent forced convection heat transfer to nanofluids in an axisymmetric abrupt expansion heat exchanger was investigated experimentally. During heat transfer investigation, the functionalized multiwalled carbon nanotubes (MWCNT-COOH), polycarboxylate functionalized graphene nanoplatelets (F-GNP), SiO2 and ZnO water-based nanofluids were used. The convective heat transfer coefficient of fully developed turbulent flow of nanofluids flowing through an abrupt enlargement with the expansion ratio (ER) of 2 was experimentally determined at a constant wall heat flux of 12,128.56 W/m2. The experiments were conducted at the Re ranges of 4000–16,000. The observed Nusselt numbers were higher than in the case of fully developed pipe flow indicating the level of the turbulent transport is high even though the recirculating velocities were a few percentages of the bulk mean velocity. The effect of Reynolds number and nanofluid’s volume concentration on heat transfer and friction losses were studied, where all the results reveal that with the increase of weight concentration and Reynolds number, the local Nusselt number enhanced at the increment of axial ratios in all the cases showing greater heat transfer rates than those of the base fluids. Comparison between the examined four types of nanofluids, show that the carbon-based nanofluids have a greater effect on enhancing heat transfer (33.7% and 16.7% heat transfer performance improvement for F-GNP and MWCNT nanofluids respectively at 0.1 wt% concentration) at the downstream of the sudden expansion pipe. There is no reported work dealing with the prediction of the local Nusselt number at the distance equivalent to the axial ratio and flow through sudden expansion. So far, two excellent correlations for the Local Nusselt number are proposed with reasonably good accuracy. Furthermore, a new correlation is developed for the average Nusselt number.

Magnetic effect on the enhancement of photo-thermal energy conversion efficiency of MWCNT/Fe3O4 hybrid nanofluid

This study focused on the photo-thermal energy conversion performance and thermal characteristics of MWCNT/Fe3O4 hybrid nanofluid under an external magnetic field. In addition, the thermal and optimal properties of MWCNT/Fe3O4 hybrid nanofluid were compared to those of MWCNT and Fe3O4 nanofluids. The photo-thermal energy conversion efficiency of Fe3O4, MWCNT nanofluids and MWCNT/Fe3O4 hybrid nanofluid increased with the concentration and decreased with the operating time. An external magnetic field significantly enhanced the photo-thermal energy conversion efficiency at 0.2 wt% MWCNT/Fe3O4 hybrid nanofluid, the photo-thermal energy conversion efficiency was 32.8% and 45.1% with the absence and presence of an external magnetic field. Adding MWCNT nanoparticles can increase the thermal properties of the Fe3O4 nanofluid. In addition, the increase of magnetic force significantly improved the thermal conductivity of the Fe3O4 nanofluid and MWCNT/Fe3O4 hybrid nanofluid.

MHD Slip Flow of CNT-Ethylene Glycol Nanofluid due to a Stretchable Rotating Disk with Cattaneo–Christov Heat Flux Model

This article deals with carbon nanoliquid flow due to stretchable rotating disk with the effect of Cattaneo–Christov heat flux model. Both SWCNTs and MWCNTs are considered with ethylene glycol as the base fluid. The effects of nanoparticle volume friction, normally applied magnetic field, stretching factor, velocity, and thermal slip factors are examined. The fundamental flow governing equations are transformed into dimensionless system of coupled nonlinear ordinary differential equations, and they are solved numerically using spectral quasi-linearization method (SQLM). Employing graphs and tables, the results of velocity and temperature fields as well as skin friction coefficient and local heat transfer rate are analyzed and presented via embedded parameters. The results reveal that higher velocity fields and lower temperature fields are noticed in the MWCNT nanofluids than SWCNT nanofluids. The higher incidence of magnetic field improves the thermal boundary layer thickness. A growth in velocity slip factor reduces the momentum boundary layer thickness of the nanoliquid flow. Generally, radial stretching of the disk is helpful in improving the cooling process of the rotating disk in practical applications.

Experimental hydrothermal behavior of hybrid nanofluid for various particle ratios and comparison with other fluids in minichannel heat sink

The effect of the particle mixture ratio in hybrid nanofluid on minichannel heat sink performance is analyzed experimentally. The heat sink, made of aluminium, contains nine parallel rectangular minichannels having cross section of 1 mm × 3 mm with 30 mm length. Total 0.01% volume concentration of Al2O3 and MWCNT nanoparticles for various mixing ratios (10:0, 8:2, 6:4, 4:6, 2:8 and 0:10) is used to synthesize water-based hybrid nanofluids. Different parameters as volumetric flow rate (0.17–0.5 LPM), fluid inlet temperature (20–40 °C) and heat flux (8.3 W/cm2) are considered. Present Al2O3-MWCNT hybrid nanofluid is compared as well with hybrid nanofluids available in literature based on both thermophysical-transport and hydrothermal properties. Heat transfer coefficient, Nusselt number, pressure drop and friction factor increase with an increase in MWCNT fraction in hybrid nanofluid. Maximum heat transfer coefficient and pressure drop increments are 44.1% and 68.1%, respectively, for MWCNT nanofluid. Inlet fluid temperature has a negative effect on pressure drop and positive effect on heat transfer coefficient. Nusselt number to friction factor ratio is observed maximum at 6:4 mixing ratio of Al2O3 and MWCNT. Al2O3 + MWCNT (optimum mixing ratio of 6:4) hybrid nanofluid is found better as compared to existing hybrid nanofluids at total volume concentration of 0.01%.

Experimentation on effect of particle ratio on hydrothermal performance of plate heat exchanger using hybrid nanofluid

To quantify the fostering in energetic and exergetic performances of counter flow corrugated plate heat exchanger, several experiments were conducted using Al2O3–MWCNT hybrid nanofluids as coolant. The Al2O3–MWCNT hybrid nanofluids with different nanoparticle volume ratios (5:0, 4:1, 3:2, 2:3, 1:4 and 0:5) and 0.01 v% concentration were used as a coolant for sub-ambient temperature application. Operating parameters which were varied are the coolant flow rate ranging from 2.0 to 4.0 lpm and coolant inlet temperature from 10 to 25 °C. Effects on heat transfer coefficient, heat transfer coefficient to pressure drop ratio, pump work, performance index, irreversibility and exergetic efficiency are investigated. Variation of Nusselt number with Reynolds number has also been studied for different nanoparticle volume ratios. Improvement up to 15.2% has been observed in the heat transfer coefficient for MWCNT (0:5) nanofluid with the negligible enhancement of 0.02% in the pump work and 2.96% enhancement in the performance index. Hydrothermal performance of nanofluids increases with increase in MWCNT ratio in particle mixture due to the negligible effect on pressure drop. No optimum ratio has been found within the studied mixture ratios of nanoparticles.

Experimental study of transparent oscillating heat pipes filled with solar absorptive nanofluids

Nanoparticle-based volumetric solar absorption has been shown to be a potential technique to realize efficient solar harvesting. However, most of studied systems are stationary and cannot achieve long distance solar energy transport, which limits their applications. A novel idea of using directive absorptive nanofluids in oscillating heat pipes (OHP) is investigated in this work, which would achieve efficient solar energy capture and transportation simultaneously without the use of any additional pumping power. The influence of a variety of parameters such as nanoparticle type, nanoparticle concentration, nanofluids filling ratio and solar radiation intensity on the performance of OHPs are investigated. It is found that there exists an optimal filling ratio of the nanofluid for the OHP (i.e., 83%), under which single direction circulation of the working fluid is achieved and the thermal resistance of the OHP reaches the minimum. An extremely high thermal conductivity, i.e., 6000 W/m·K, is obtained when the OHP is filled with 3.0 wt% MWCNT nanofluid. The maximum energy conversion efficiency reaches to 92% under the current experimental settings. Strong absorption of solar energy, efficient vapor generation inside the OHP and proper configuration of the OHP should be responsible for the efficient operation of such a system.

Cattaneo–Christov Heat Flux Model for Three-Dimensional Rotating Flow of SWCNT and MWCNT Nanofluid with Darcy–Forchheimer Porous Medium Induced by a Linearly Stretchable Surface

In this paper we investigated the 3-D Magnetohydrodynamic (MHD) rotational nanofluid flow through a stretching surface. Carbon nanotubes (SWCNTs and MWCNTs) were used as nano-sized constituents, and water was used as a base fluid. The Cattaneo–Christov heat flux model was used for heat transport phenomenon. This arrangement had remarkable visual and electronic properties, such as strong elasticity, high updraft stability, and natural durability. The heat interchanging phenomenon was affected by updraft emission. The effects of nanoparticles such as Brownian motion and thermophoresis were also included in the study. By considering the conservation of mass, motion quantity, heat transfer, and nanoparticles concentration the whole phenomenon was modeled. The modeled equations were highly non-linear and were solved using homotopy analysis method (HAM). The effects of different parameters are described in tables and their impact on different state variables are displayed in graphs. Physical quantities like Sherwood number, Nusselt number, and skin friction are presented through tables with the variations of different physical parameters.

Darcy–Forchheimer flow of carbon nanotubes due to a convectively heated rotating disk with homogeneous–heterogeneous reactions

Here, Darcy–Forchheimer flow of dissipating SWCNT and MWCNT nanofluids induced by rotation of disk with homogeneous–heterogeneous reactions and convective boundary condition is examined. Xue model of nanofluid is implemented in mathematical modeling. The resulting problems are computed for convergent optimal series solutions. Graphical results have been presented for physical quantities. Our findings indicate that skin friction coefficients and local Nusselt number are enhanced for larger values of nanoparticle volume fraction.

Experimental investigation on rheological properties of water based nanofluids with low MWCNT concentrations

The rheological properties of water based MWCNT nanofluids are investigated at five different low volume concentrations (0.0047%, 0.0238%, 0.0571%, 0.1428%, 0.2381%) and five low temperatures (275 K, 277 K, 279 K, 281 K, 283 K) by a novel experimental method in the present study. The present methodology combines the 3ITT test and the DSO test. Measurements show that the nanofluids are featured with clear thixotropy and shear thinning behaviors when the concentration is above 0.0571%. It is further shown that the thixotropy becomes less obvious as the concentration lowers implying a stronger Newtonian fluid characteristic. Therefore the concentration of 0.0571% can be regarded as the critical point quantifying the transition from Newtonian to non-Newtonian and this critical concentration is independent of temperature. It is also observed that relative viscosity increases slightly with temperature at medium shear rate. Moreover, temperature sweep measurement suggests that the viscosity decreases with temperature firstly and it increases beyond a critical temperature, which can be curbed by raising the shear rate for solutions with concentration lower than 0.0571%. The dependency of the relative viscosity of the MWCNT nanofluids on shear rate, temperature and concentration is obtained and a new and accurate correlation is developed for engineering application.

Performance analysis for hybrid PV/T system using low concentration MWCNT (water-based) nanofluid

This paper presents experimental work on utilising Nanofluid as a working agent for Photovoltaic Thermal Systems (PV/T). PV/T systems are one kind of hybrid systems in energy utilisation. They convert the incident solar radiation into two energy types; electricity and heat. In this research, experimental outdoor tests were directed to assess the execution of PV/T system that utilises water-based Multi Walls Carbon Nano Tubes “MWCNT” as a heat storage/heat absorption agent. The effect of varying Nanofluid volume concentration ratio was studied within the range (0%:0.3%) while fixing the circulation rate at 1.2 l/min. By analysing the experimental results, it can be noted that adding Nano Particles to the base fluid caused the thermal properties to have a significant increment leading the PV/T system to have a better thermal and electrical efficiency. The best system efficiencies were obtained at 0.075% V of MWCNTs – water based Nanofluid. At this concentration, a temperature reduction of 12 °C for the PV panel was attained at maximum incident radiation leading to an overall system efficiency of 83.26%. Also, an average temperature reduction of 10.3 °C was achieved over the daytime leading to an overall efficiency of 61.23%.

Improving the performance of heat pipe embedded evacuated tube collector with nanofluids and auxiliary gas system

An attempt was made to design an evacuated tube heat pipe solar collector (ETHPSC) with a gas package for a four-member family to supply the required energy and to evaluate the effect of different nanofluids on its performance. CuO, TiO2 and MWCNT nanofluids were used, whose performance was compared with water as the working fluid. The given system was tested in the weather conditions of Sanandaj city, Iran. The results showed the maximum temperature of output working fluid from collector was recorded in second half of august 2016 between 13:00 and 15:00 p.m. and in second half of October 2016 between 12:00 and 14:30, at which time solar radiation intensity and air temperature were at their maximum level. MWCNT, CuO and TiO2 nanofluids, owing to high thermophysical properties, had a better performance than water. The fuel consumption saving of the designed solar system, compared to the common package system, during the testing period was found to be 67.7% in August and 42.2% in October. With nanoparticles MWCNT, CuO and TiO2, compared to water, the efficiency of collector increased by 25%, 12% and 5%, respectively in August and by 25%, 15% and 7%, respectively in October.

Experimental investigation on HSFP using MWCNT based nanofluids for high power light emitting diodes

LEDs, of late, have received attention as the next generation lighting system for enhanced luminous efficiency and higher lifespan. However, the thermal management of the LEDs is the crucial parameter to be countered for global acceptance as a revolutionary illumination source. This paper reports the experimental investigation of natural convective heat transfer of high power LED COBs using MWCNT and MWCNT-CuO nanofluids mixed with de-ionized water. The study uses MWCNT based nanofluids as a route to enhance the heat transfer of high power LEDs by the passive cooling technique. This study presents an innovative cooling device integrated with numerous fluid pockets, called the HSFP, to achieve the enhanced thermal performance of heat sinks for applications in high intensity LED lights. Nanofluids of various concentrations were formulated and their heat transfer performance evaluated using a series of experiments and compared with liquid cooling and a conventional heat sink. The experimental finding reveals 20–30% lowered thermal resistance using the new HSFP (nanofluids). Thus, the HSFP found to effectively dissipates the heat in high-power LED COBs using nanofluids as the cooling medium compared to the conventional heat sink.

Experimental analysis of heat transfer in spiral coils using nanofluids and coil geometry change in a solar system

Thermal coils have been extensively used as heat exchanger in many industrial and air-conditioning systems. The present study experimentally investigated three different geometries of thermal coils, including cylindrical spiral, conical spiral and conical-cylindrical spiral coils as well as working fluids water and MWCNT, CuO and TiO2 nanoparticles. The effects of coil geometry and working fluid on the coil performance were evaluated. The working fluid in nanoparticles was 70:30 volumetric mixture of water and propylene glycol. Surfactant was used for more dispersion of nanoparticles in solution, and concentration of nanoparticles in all states was stable and equal to 0.1% of volume and that of surfactant was 0.1% of mass. To evaluate the performance of thermal coils, an evacuated heat pipe solar cycle was used, and the effect of thermal coil on the performance of collector was investigated. Validation of the obtained results showed a good match between experimental findings and empirical relations of other researchers. Results showed a better performance for the working fluids with higher thermal conductivity during the day; and use of CuO, TiO2 and MWCNT nanofluids in the base fluid, compared to water, increased the coil heat transfer by 39%, 25% and 53%, respectively. Considering the Nusselt number, conical-cylindrical spiral coil was thermally superior to the other two geometries, and use of conical-cylindrical spiral coil and conical spiral coil enhanced the efficiency of system by 17.1% and 5.7%, respectively in comparison with cylindrical spiral coil.

Numerical study of turbulent heat transfer of nanofluids containing eco-friendly treated carbon nanotubes through a concentric annular heat exchanger

In this study, we conducted numerical simulations using finite volume method to examine thermal and hydrodynamic characteristics of clove-treated multi-walled carbon nanotube (C-MWCNT)/distilled water nanofluids in a concentric annular heat exchanger exposed to uniform and constant heat flux boundary conditions. We devised an environmentally friendly functionalization method to synthesize the MWCNTs where the MWCNTs were covalently treated with clove buds in one pot using free radical grafting reaction for preparation of homogeneous MWCNT nanofluid without involving existing corrosive, hazardous acid based conventional functionalization methods of carbon nanomaterials. We analysed the C-MWCNTs using Fourier transform infrared spectroscopy in order to assess the surface modification of MWCNTs. Next, we performed numerical simulations in order to predict the convective heat transfer and hydrodynamic characteristics of the nanofluids considering three concentrations of C-MWCNTs: 0.075, 0.125, and 0.175 wt.%. The effective thermo-physical properties of the nanofluids, which we obtained experimentally, were used in our three-dimensional simulations in order to solve the governing equations of fluid dynamics (continuity, momentum and energy), along with the k-ω turbulence model. We found that there is a good agreement between the simulation and experimental results. We also noticed that the addition of a small fraction of C-MWCNTs into distilled water significantly enhances the convective heat transfer coefficient relative to distilled water. Our results are also encouraging because we observed that the friction factor does not vary significantly for the nanofluids at their concentration range. In general, we conclude that our simulation model can be used to predict the convective heat transfer and hydrodynamic characteristics of C-MWCNT/distilled water nanofluids in a concentric annular heat exchanger with reasonable accuracy and the results show the promising capabilities of these nanofluids as coolants.

Effects of Nano Particles Attached onto a Heat Transfer Surface in the Thermal-Hydraulic System

This work experimentally explored the influence of nano-fouling, and it was also compared and analyzed CHF, flow boiling heat transfer coefficient, contact angle, and surface roughness. The working fluids in this study were used as purewater and a 0.01 vol% oxidized MWCNT nanofluid. The flow velocity conditions are established at 0.5, 1.0, and 1.5 m/s. Also, the nanoparticles of oxidized graphene were deposited on a heat transfer surface, and artificial spray coating times for nano-fouling are established at 0, 120, 180, and 240 sec. As the results, it was found that the superheated temperature to the CHF extremely increased in case of nano-fouling, it is caused by physical damage of heat transfer system. The flow boiling heat transfer coefficient in an oxidized graphene nanofluid increased up to 24.29% without any treatment on the heat transfer surface, but the coefficient in case of nano-fouling decreased down to 16.26% more than in the purewater.

A theoretical analysis of SWCNT–MWCNT and H2O nanofluids considering Darcy–Forchheimer relation

The remarkable features of carbon nanotubes (CNTs) such as physicochemical compatibility, high conductivity, effective electrical conductivity, light weight and stability (chemical, mechanical) form them a superlative substance to be manipulated in electrochemical mechanisms. Having such effectiveness of CNTs in view our intention in this investigation is to elaborate the significance of non-Darcian relation in flow of CNTs based on water by rotating disk. Outcomes for both CNTs (single walled, multi walled) are presented and elaborated. Thermal radiation and Partial slip aspects are further a part of this research. The process of non-dimensionalization is performed utilizing Von Karman approach. Optimal homotopic scheme is employed for analysis. Velocity, Nusselt numbers, temperature and skin friction have been computed and addressed.

Numerically investigation on heat transfer and Pressure drop behavior of MWCNT nanofluid in MCHS

Background/Objectives: To find the best method for nanofluid stability or increment in heat transfer enhancement and terminating pressure drop. Methods/Statistical analysis: Nanofluids have big problem regarding its own preparation or stability. Here is details which can prevent both of problem. This paper based on a work which is able to prevent nanofluids stability problem or pressure drop problem in MCHS. Findings: MCHS vary from 2 cm to several feet or meter because its depends on the requirement of work. The design procedure is complex because of its diameter vary in micro-meter, but it can be designed for our requirement easily. Traditionally we utilized water, ethylene-glycol & some special kind of oils. But, with the large demand in obligation of working efficiency nanofluids were produced which are colloidal mixture of base fluid with nanoparticles. Nanofluids have truly developed the heat transfer characteristics of base fluids & hence are great base to overall working efficiency of the system. But along with advantages it also has quite a few disadvantages to which are stability, limitation to the volumetric concentration addition process of manufacturing and most of all economics of production. Improvements/Applications: They can also be used for wide range of applications such as in the chemical industry, food processing industry, refrigeration industry, computer technology industry, automobile industry, aerospace industry, power plant, mechanical industry etc. Keywords: Heat Transfer, Micro Channel Heat Sink, Pressure Drop, MWCNT’S

Heat transfer characteristics of MWCNT nanofluid in rectangular mini channels

Heat transfer characteristics of MWCNT nanofluid in rectangular mini channels

Development of a New Correlation and Post Processing of Heat Transfer Coefficient and Pressure Drop of Functionalized COOH MWCNT Nanofluid by Artificial Neural Network

Background: Because of nanofluids applications in improvement of heat transfer rate in heating and cooling systems, many researchers have conducted various experiments to investigate nanofluid's characteristics more accurate. Thermal conductivity, electrical conductivity, and heat transfer are examples of these characteristics. Method: This paper presents a modeling and validation method of heat transfer coefficient and pressure drop of functionalized aqueous COOH MWCNT nanofluids by artificial neural network and proposing a new correlation. In the current experiment, the ANN input data has included the volume fraction and the Reynolds number and heat transfer coefficient and pressure drop considered as ANN outputs. Results: Comparing modeling results with proposed correlation proves that the empirical correlation is not able to accurately predict the experimental output results, and this is performed with a lot more accuracy by the neural network. The regression coefficient of neural network outputs was equal to 99.94% and 99.84%, respectively, for the data of relative heat transfer coefficient and relative pressure drop. The regression coefficient for the provided equation was also equal to 97.02% and 77.90%, respectively, for these two parameters, which indicates this equation operates much less precisely than the neural network. Conclusion: So, relative heat transfer coefficient and pressure drop of nanofluids can also be modeled and estimated by the neural network, in addition to the modeling of nanofluid’s thermal conductivity and viscosity executed by different scholars via neural networks.