Multi-walled Carbon Nanotube Nanofluids Research Articles

Investigation of thermo-optical properties and photothermal conversion performance of MWCNT, Fe3O4, and ATO nanofluid for volumetric absorption solar collector

For the use of volumetric absorption solar thermal collector (VASTC), the thermo-optical properties, photothermal conversion characteristics and economics of MWCNT (Multi-walled carbon nanotube) (0.0005–0.004 wt%), Fe3O4 (0.025–0.1 wt%), and antimony-doped tin oxide (ATO) (0.05–0.25 wt%) nanofluids (NFs) were comprehensively investigated. As a result, The improvement of thermal conductivity, specific heat, and viscosity of MWCNT, Fe3O4, and ATO NFs was insignificant in the concentration range where optical absorbance can improve. The photothermal conversion efficiency (ηPTC) and receiving efficiency (ηrec) were significantly improved according to the increase in the concentration. Among NFs, the 0.002 wt% MWCNT, 0.075 wt% Fe3O4, and 0.1 wt% ATO NFs had maximum ηPTC (93.3%, 90%, and 89.2%) and ηrec (83.7%, 81.4%, and 77.7%). Regarding dispersion stability, the optical transmittance of MWCNT, Fe3O4, and ATO NFs slightly increased, and long-term dispersion stability is required for the use of VASTC. Economically, the cost required per unit photothermal conversion energy (CUPTE) of 0.002 wt% MWCNT NF is 0.102–0.538 $/g, which is cheaper than 0.075 wt% Fe3O4 and 0.1 wt% ATO NFs. Overall, MWCNTs can be used as working fluid for VASTC due to their excellent optical absorption and low price once long-term dispersion stability is achieved.

A TOPSIS-based thermal performance optimization of DHCTHX using MWCNT nanofluids

Double-helically coiled tube heat exchangers are employed in many different heat transfer applications because of their better heat transfer capabilities and compact construction. The double helically coiled tube heat exchanger (DHCTHX) improves turbulence and maximizes heat transfer rate compared to straight tubes. A full factorial, orthogonal array of trials is used in this study (L27) to test various volume concentrations of nanofluids. The pressure drop, de, LMTD0C, re, and F have all been attempted to be optimized using the order preference similarity to the ideal solution technique. In this case, the mass flow rate and volume concentration are the variables for the input process, while the outputs are the heat transfer rate, pressure drop, de, LMTD0C, and F. The experimental results show that a nanofluids volume concentration is 0.6% and its mass flow is 120 with a range of 1460 Dean Numbers, which is the optimal configuration for maximizing the overall heat transmission and minimizing the pressure drop. The multiple-criteria decision-making technique was used in this study to identify the ideal cooling fluids in a DHCTHX with a significant pressure drop. The multi-walled carbon nanotube nanofluids may be used instead of conventional coolants in conjunction with the DHCTHX. According to this strategy, A3B1 is the ideal value, which aligns with the experiments’ findings.

The effects of Multiwalled Carbon Nanotube to the performance of a refrigeration system

By incorporating nanofluid technology and nanolubricants into compressors, the performance can be enhanced while also lowering worldwide fuel consumption and aiming at developing cleaner, more efficient energy sources and uses. The globe is being confronted with energy security issues and heating, cooling and HVAC systems highly contribute to it. Hence, it is critical to save energy and improve the efficiency of the refrigeration cycle. This study presents experimental and theoretical findings in order to investigate the effect of Polyester (POE)-oil based multiwalled Carbon Nanotube (MWCNT) nanolubricant on the Coefficient of Performance (COP) of a refrigeration system. The objectives of this study is to analyze the stability of MWCNT nanofluids, to obtain the COP of a refrigeration cycle run with pure POE oil and MWCNT nanofluids with different concentrations respectively. The experiment was conducted by preparing 0.55, 0.65 and 0.70 g/l MWCNT nanofluid by using the two step method. The most effective concentration used in the refrigeration system was referred to the one that resulted in the highest COP. It was determined from the experiment that 0.55 g/l MWCNT nanofluid resulted in a higher COP of 5.766 as compared to the other two concentrations. Besides, it showed an improvement of 34.6% in COP as compared to the COP of using pure POE oil in the refrigeration system, which was found to be 4.285. The 0.65 g/l and 0.70 g/l concentration of MWCNT resulted in a COP of 5.618 and 5.617, respectively. The compressor work was also analyzed and was found to be reduced noticeably after adding MWCNT nanoparticles. Hence it can be concluded that the increment of MWCNT concentration in nanofluids increases the COP of the refrigeration system but only up to a certain limit of concentration.

Experimental and neural network prediction of the cyclic stability and light absorption characteristics of supercritical CO2 based CNTs nanofluids

Traditional working fluids face challenges including constrained heat transfer efficiency and inadequate thermal stability, which are detrimental to the thermal efficiency of energy conversion systems. To overcome these limitations and achieve a profound breakthrough in the field of energy conversion, it is imperative to develop innovative working fluids. Consequently, this study builds a nanofluid circulation flow experimental platform and prepares a supercritical carbon dioxide/hydroxylated multi-walled carbon nanotubes nanofluid. The study conducts a series of meaningful experimental tests and performance predictions, including stability analysis, deposition characterization research, light absorption potential investigation, and artificial neural network prediction. Remarkably, the artificial neural network model exhibits excellent learning capacity in training, validation, and testing, with root mean square error of only 9.069 W/m2, 8.9996 W/m2, and 13.0143 W/m2, respectively. Test results indicate that the nanofluid reaches a steady state after 4 min, with a fluctuation amplitude of only 2.13 %. Furthermore, the deposition density of the nanofluid on nickel sheet saturates after 4 h, confirming its considerable potential for promotion and application. The light absorption capacity and power decay rate of the nanofluid are enhanced by 606–881 W/m2 and 32.3–46.99 %, compared to other typical substances. The transmittance is reduced by 8.51–22.96 % compared to other nanofluids. The nanofluid proves to be an effective alternative to conventional working fluids, providing a practical reference solution for researchers aiming to improve working fluids in the field of energy conversion.

Hydroxyl functionalized MWCNT nanofluids with excellent photothermal conversion performance in direct absorption solar collectors

Developing novel nanofluids with good stability, excellent photothermal conversion performance, and appropriate thermophysical properties is of great importance in promoting the practical utilization of nanofluids in solar collectors. In this work, hydroxyl multi-walled carbon nanotube (MWCNT-OH) nanofluids are proposed, which can achieve a high photothermal conversion of 88.2 % at a concentration of 20 ppm under 1-sun irradiation. Both the sedimentation experiment and spectrophotometer analysis prove that the prepared MWCNT-OH nanofluids have excellent stability. The influence of hydroxyl functionalization, MWCNT-OH concentrations, and temperature on the thermophysical and optical properties is analyzed. Moreover, the comparison between MWCNT-based nanofluids with different functionalization reported in the literature and our work is carried out, the results show that MWCNT-OH nanofluids in our work outperform MWCNT-based nanofluids with other types of functionalization reported in the literature. This work may promote the use of MWCNT-OH nanofluids as working fluids in solar collectors.

Experimental investigations of particle sizes effects on exergy and entropy characteristics of AL2O3 - MWCNT hybrid nanofluid along the transitional flow regime

Experimental investigation on particle size effect on entropy and exergy characteristics of AL2O3 - MWCNT hybrid nanofluid in transitional flow Regime was carried out with four different particle sizes (i.e., for Aluminum oxide (AL2O3), 20 nm, and 5 nm used while Multiwalled Carbon Nanotubes (MWCNT) <7 nm and 30–50 nm particles). 0.3 vol concentrations of three hybrid nanofluids with different particle size combinations (i.e., Al2O3(20 nm) – MWCNT(20–30 nm), Al2O3(20 nm) – MWCNT(<7 nm), and then Al2O3(5 nm) – MWCNT(<7 nm)) are prepared using a two-step method, at a percentage weight composition (PWC) of 60:40. Results shows that Nanofluid with Al2O3 (20 nm) and MWCNT (<7 nm) have shown the best performance. It has an exergy efficiency of 54.12% at turbulent Reynold number of 4500, while in the transitional flow regime, it records an exergy efficiency of 47.85%. Frictional entropy and thermal entropy in the transitional regime were reduced with hybrid nanofluid of Al2O3 (20 nm) and MWCNT (<7 nm) by 6.78% and 13.53%, respectively, as compared to Al2O3 (5)- MWCNT (<7) nanofluid. Both thermal and frictional entropy effects were better minimized in the turbulent regime than in the lamina and transitional regime, as they were reduced by 16.66 and 24.7%, respectively. The study also recommends that for further investigations, more samples need to be taken to reach a clearer conclusion the effect of particle size, and since this is a hybrid nanofluid the samples should be of different sizes from both nanoparticles.

Experimental analysis of thermal performance of direct absorption parabolic trough collector integrating water based nanofluids for sustainable environment applications

Integration of nanofluids with solar collectors to enhance collector's thermal performance stands out as one of the most effective techniques owning to nanofluids favorable thermo-physical properties. By improving the thermo-physical properties of heat transfer fluids, nanofluids enhance the efficiency of thermal systems by improving the thermal energy storage capacity. This experimental study serves as a novel comparison between water-based Al2O3 (Alumina) and Multi-walled Carbon Nanotubes (MWCNTs) nanofluids in such mass concentrations (0.1%, 0.2%, and 0.3%) at fixed mass flow rates of 0.012 kg/s and 0.024 kg/s to investigate the impact on the performance of Direct Absorption Parabolic Trough Collectors (DAPTC) under the arid climatic conditions of Pakistan. The peak thermal efficiencies were found to be 40%, 56% and 58% for distilled water (DW), Al2O3-water and CNTs-water nanofluids, respectively. Thermal efficiency of DAPTC was improved by 18% in comparison with the basefluid alone on account of increased surface area, thermal conductivity and overall heat transfer capabilities. The CNTs-water nanofluids were observed to be more thermal efficient Heat Transfer Fluids (HTFs) owing to the black color and comparatively lower specific heat capacity. These thermal efficient fluids are of great use in the thermal energy storage systems. In addition, the use of nanofluids for heating and cooling purposes in industries is preferable as operational and manufacturing costs can also be lowered by reducing the systems size.

Investigation of turbulent heat transfer performance of aviation turbine fuel multi-wall carbon nanotube nanofluid

Nanofluid is a novel heat transfer fluid prepared by suspending high thermal conductivity nano-sized particles in conventional fluids (water, engine oil and ethylene glycol). Thermo-physical properties (Thermal conductivity, dynamic viscosity and specific heat) and turbulent heat transfer performanceof Aviation Turbine Fuel (ATF) based Multiwall Carbon Nanotube (MWCNT) nanofluid are investigated experimentally for particle volume concentrations of 0–1% and at mean fluid temperatures of 30οC and 50οC for a potential regenerative heat transfer application in semi-cryogenic liquid propellant rocket engine. The experimental results show that the heat transfer coefficient of the nanofluid increases with particle volume concentration, with a maximum enhancement at 1% particle volume concentration of approximately 23% and 50% observed at 30οC and 50οC respectively. Two different numerical modelling approaches (a single phase fluid model with enhanced thermo-physical properties and an Eulerian-Lagrangian model called the “discrete phase model”) are employed to simulate the experimental conditions. The predictions from both numerical modelling approaches are found to compare reasonably well with the experimental data. The enhanced heat transfer performance is expressed on an equal power penalty basis to clearely show the advantage of the nanofluid.

Comparison and evaluation of energetic and exergetic performance of an evacuated tube solar collector using various nanofluid

There is a growing interest in renewable energy sources cause the worsening impact of fossil fuel development and abuse on the ecological environment. Solar collectors are major facilities that utilize solar energy, many studies and techniques have been employed to increase the efficiency of the collectors. This paper aims to evaluate the thermal performance of an evacuated tube solar collector(ETSC) in the solar thermal system by using Al2O3, CuO, Fe3O4 and Multi-walled carbon nanotube(MWCNT) nanofluid as working fluids. An evaluation approach for the energy, exergy and entropy of ETSC were proposed. Furthermore, the energy gained and stored by nanofluid in the solar collector was also been studied. The ETSC shown highest energy and exergy efficiency when the 0.01 vol%-MWCNT nanofluid was used which was 33.1% higher than that of water, and it was the same situation of exergy efficiency while the highest was 3.17 under the optimum situation. In addition, the energy gained by 0.01 vol%-MWCNT nanofluid showed the highest potential of energy absorption than other nanofluid, the maximum exergy destruction and entropy generation were achieved when water was used as working fluid of solar collector while the lowest were observed when MWCNT nanofluid with 0.01 vol% was used. Compared to normal working fluid in the ETSC, the use of nanofluid with high thermal conductivity can save more fossil fuels and coals which have a positive effect on protecting the environment.

The dynamic stability of silicone oil-based MWCNT nanofluids under high-temperature, high-flux irradiation, and shear-flow conditions

Nanofluid-based volumetric-type solar collectors have emerged as a promising technique for solar thermal applications. However, achieving the long-term stability of nanofluids under high-temperature, high-flux irradiation, and shear-flow conditions is still challenging. Herein, we propose a facile method to stabilize silicon oil-based multi-walled carbon nanotube (MWCNT) nanofluids via shear flow. The effects of shear flow on the stability of nanofluids are experimentally evaluated. Results indicate that the shearing force can break up the clusters. Once achieving a dynamic equilibrium between cluster formation and cluster breakage, the instability of nanofluids can be controlled within 7.3% for the heating temperature range 140 °C–180 °C. Besides, the shear-flow stabilized nanofluids can keep dynamic stability and maintain high solar thermal conversion performance with an efficiency reduction of within 7% after cyclic tests under irradiation of 19 Sun for 24 h. The proposed method offers a practical path for stabilizing nanofluids under harsh conditions.

Effect of thermal radiation on nonDarcy hydromagnetic convective heat and mass transfer flow of a water–SWCNT’s and MWCNT’s nanofluids in a cylindrical annulus with thermo-diffusion and chemical reaction

The examined through analysis of the movement of water-based single wall carbon nanotube (SWCNT) and multiwall carbon nanotube (MWCNT) nanofluids in a coordinate annulated zone under influence of non-uniform heat source/sink. By imposing the appropriate nondimensional variables, the governing partial differential equations are converted into a system of coupled nondimensional partial differential equations. By means of the usage of quadratic polynomials and the Galerkin finite element detail approach, the nonlinear equations have been executed. The expressions representing fluid velocity, temperature and concentration are discussed graphically. While skin friction, heat transfer and mass transfer are revealed in tabular structure. The proposed scheme is shown to have faster convergence than the existing scheme with excellent accuracy. Various parametric values have been analyzed and observed that higher temperatures and concentrations are produced with lower velocities with and bigger velocities with higher radiative heat flux or nanoparticle volume fraction.

Improving the solidification performance of deionized water using magnetically oriented CNT by Fe3O4 nanoparticles as magnetic agents

In this work, directionally distributed Multi-walled Carbon Nanotube (MWCNT) were applied for supercooling suppression and improving the thermal conductivity of deionized water during the solidification. Specifically, Fe3O4 nanoparticles coated MWCNT are magnetized which would be directionally arranged along with the direction of extra magnetic field. A comparative study of solidification characteristics of the water based MWCNT nanofluids was carried out. The results indicated that 0.1% magnetic MWCNT nanofluid shows 31% enhancement in the thermal conductivity under the magnetic field intensity of 150 mT for fully display their axial thermal conductivity, and it exhibits ignorable reduction in the latent heat compared to the pure water. As a result, the magnetic MWCNT nanofluid has the optimal solidification characteristics under the magnetic field with 68% reduction in supercooling and 36% advance in the total solidification time. Moreover, the dynamic characteristics of solid/liquid interface were discussed, and then the growing velocity of ice crystal is obtained.

Solid‐Volume‐Fraction Retained Tailoring of Thermal Diffusivity of Multiwalled Carbon Nanotube Nanofluid: A Photothermal Investigation

The diversified forms of heat engines necessitate developing energy‐efficient engine oils and coolants. The article proposes a method of thermal diffusivity tuning of the base fluid (ethylene glycol) using multiwalled carbon nanotubes (MWCNTs), annealed at different temperatures, without altering the solid volume fraction. Having studied the annealing‐induced structure modifications of MWCNTs through thermogravimetric and spectroscopic studies, the thermal diffusivity variations are investigated through the sensitive photothermal mode‐mismatched dual‐beam thermal lens technique. The study reveals that the annealing‐induced structure modifications lower the nanofluid's thermal diffusivity and unveils the existence of transition annealing temperature of MWCNTs above which the nanoparticles can make the nanofluid a heat trapper. The study also proposes the importance of making more energy‐efficient engine oils by keeping the temperature of the engine oil below the transition temperature.

Stability and Thermal Property Optimization of Propylene Glycol-Based MWCNT Nanofluids

Propylene glycol-based MWCNT (multi-walled carbon nanotubes) nanofluids were prepared in the framework of a two-step method and by using a suitable PVP (polyvinyl pyrrolidone) dispersant. The BBD (Box-Behnken design) model was exploited to analyze 17 sets of experiments and examine the sensitivity of the absorbance to three parameters, namely the concentration of MWCNT, the SN ratio (mass ratio of carbon nanotubes to surfactants) and the sonication time. The results have revealed that, while the SN ratio and concentration of MWCNT have a strong effect on the absorbance, the influence of the sonication time is less important. The statistical method of analysis of variance (ANOVA) was further used to determine the F- and <i>p</i>-values of the model. Five experiments were run to validate this approach. Since sample 2 was found to display the greatest absorbance, it was selected for stability monitoring as well as thermal conductivity and viscosity measurements. This sample has been found to be stable; the viscosity decreased with increasing temperature; the addition of MWCNT nanoparticles was more effective in improving the thermal conductivity of propylene glycol than other methods in the literature. Moreover, the MWCNT nanofluid based on propylene glycol exhibited higher thermal conductivity at low temperatures.

Investigating the thermal effect of channel heatsink using MWCNTs nanofluids

The utilisation of Multi-walled carbon nanotubes (MWCNTs) nanofluids is considered to be a highly efficient approach in the field of thermal engineering, specifically for the purpose of cooling electronic processors. The usage of a microchannel along with an electronic chip for liquid cooling of electronics presents a compelling substitute to the conventional bulky aluminium heat sinks. A minichannel heat sink employing MWCNTs nanofluid as a coolant is further enhanced in thermal and hydraulic performance. In order to analyze the performance of the minichannel heat sinks, a conjugate heat transfer model has been solved using the commercial software ANSYS-CFD. Theoretically, it showed that the presence of MWCNTs reduced thermal resistance and increased the thermal conductivity of liquid cooling system. The results reveal a maximum enhancement of in average heat transfer coefficient ( h ) for minichannel heat sink using MWCNTs as a coolant at volume 40%, 46%, and 52% concentrations of 0.25%, 0.5% and 0.75%. The performance evaluation shows that the overall performance of the minichannel heat sink using MWCNTs cooled minichannel heat sink at 0.75% volume concentration is roughly enhanced more as compared to water.

Experimental Evaluation of Thermal Conductivity and Other Thermophysical Properties of Nanofluids Based on Functionalized (-OH) Mwcnt Nanoparticles Dispersed in Distilled Water

A possible way to increase thermal conductivity of working fluids, while keeping pressure drop at acceptable levels, is through nanofluids. Nanofluids are nano-sized particles dispersed in conventional working fluids. A great number of materials have potential to be used in nanoparticles production and then in nanofluids; one of them is Multi-Walled Carbon Nano Tubes (MWCNT). They have thermal conductivity around 3000 W/mK while other materials used as nanoparticles like CuO have thermal conductivity of 76.5 W/mK. Due to this fact, MWCNT nanoparticles have potential to be used in nanofluids production, aiming to increase heat transfer rate in energy systems. In this context, the main goal of this paper is to evaluate from the synthesis to the experimental measurement of thermal conductivity of nanofluid samples based on functionalized (-OH) MWCNT nanoparticles. They will be analyzed nanoparticles with different functionalization degrees (4% wt, 6% wt, and 9% wt). In addition, it will be quantified other thermophysical properties (dynamic viscosity, specific heat and specific mass) of the synthetized nanofluids. So, the present work can contribute with experimental data that will help researches in the study and development of MWCNT nanofluids. According to the results, the maximum increment obtained in thermal conductivity was 10.65% in relation to the base fluid (water).

Computation of Stagnation Point Convection Flow of Carbon Nanotube Nanofluids From a Stretching Sheet With Melting: Dual Solutions

Abstract A theoretical study in stagnation point flow is presented where melting heat transfer effects of carbon nanotube (CNT) from a stretching surface is appeared. Both carbon nanotubes like single-wall CNT (SWCNT) and multiwall CNT (MWCNT) are homogeneously dispersed in the base fluid. As the ordinary (or base) fluids, water and kerosene oil are employed. A set of nonlinear ordinary differential equations with appropriate boundary conditions is formed by transforming the governing equations via similarity transformations. The transformed nonlinear ordinary differential equations are then solved numerically using the bvp4c solver in matlab, an efficient numerical finite difference method. The impact of nanoparticle volume fraction, velocity, melting, stretching parameter, and CNT type on transport characteristics are explored and visualized graphically and in tabular forms. Verification of the matlab computations with available data in certain limiting cases is included showing excellent agreement. Existence of dual (upper and lower branch) solution is shown for a certain range of stretching sheet parameter. The obtained dual solutions are examined for velocity and temperature in detail. A stability analysis demonstrates that the first solution is a stable solution, and the second solution is an unstable solution. Local skin friction and local Nusselt number are also computed in order to determine critical values that can permit dual solutions. It is observed that when a dimensionless melting parameter is greater than 1, SWCNT nanofluids attain greater velocities than MWCNT nanofluids for water as well as kerosene oil base fluids. Moreover, the flow is accelerated for SWCNT compared with MWCNT for both water and kerosene oil. With increasing stretching parameter, the heat transfer rate (Nusselt number) increases, whereas skin friction coefficients decrease. Higher skin friction and Nusselt number are obtained for SWCNTs compared to MWCNTs due to their greater density and thermal conductivity. The study is relevant to phase change manufacturing fluid dynamics of nanomaterials.

ANFIS based effectiveness and number of transfer units predictions of MWCNT/water nanofluids flow in a double pipe U-bend heat exchanger

In this study, the heat transfer coefficient, Nusselt number, effectiveness and number of transfer units of water mixed multi-walled carbon nanotubes nanofluids passes through a tube-in-tube heat exchanger was experimentally investigated. Investigations were performed in the operating conditions of Reynolds number ranging from 3500 to 12000 and volume concentrations ranging from 0% to 0.3%, respectively. The obtained four parameters were predicted using adaptive neuro fuzzy inference system (ANFIS). The Reynolds number and particle volume loadings are the input data in artificial neural network analysis and heat transfer coefficient, Nusselt number, effectiveness and number of transfer units is output or target. The Nusselt number, heat transfer coefficient, effectiveness, and number of transfer units was enhanced to 31.3%, 44.17%, 2.51% and 2.76% at φ = 0.3% and at a Re of 10005, against base fluid. Implementation of ANFIS with various quantities of neurons in the mid layer provides 1–10−6 with the correlation coefficient (R2) of 0.9978, and 0.9998 and root mean square error of 0.0018581, and 0.0014159 for heat transfer coefficient and Nusselt number, respectively. The above developed structure has been successful in predicting 96% of variation in all the parameters.

Thermal and exergy analysis of Pin-finned heatsinks for nanofluid cooled high concentrated photovoltaic thermal (HCPV/T) hybrid systems

• Cooling performance of HCPV/T is systematically investigated. • Different shaped pin-finned heat sinks (inline and staggered) are examined. • Thermal performance is determined for MWCNT nanofluids. • Exergy efficiencies of pin-fin heat sinks in HCPV/T are evaluated. • 2% MWCNT nanoparticle concentration is found to be the optimum. Cooling of High Concentrated Photovoltaic (HCPV) cells is a major concern among researchers due to higher heat generation in the cells from highly concentrated solar radiation. In the present investigation, a numerical study of the High Concentrated Photovoltaic Thermal (HCPV/T) system is conducted for the combined effect of nanofluids and pin-finned heatsinks on the cooling performance. The investigation is carried out for AZUR SPACE solar cell (Model: 3C44C) for 1000 Concentration Ratio (CR) and the Reynolds number ( Re ) varies within the laminar range (600 ≤ R e ≤ 2200). Different shapes of pin-fins and their orientations are systematically investigated for the effect of Multi-walled Carbon Nanotube (MWCNT) nanoparticles in a base fluid. The results show a significant reduction in the temperature (up to 18K) of the solar cells for the MWCNT nanofluid compared to its base fluid counterpart. A higher heat transfer characteristics (Nusselt numbers) and lower average temperature of top surface of HCPV cells are found to occur for the staggered arrangements of pin-fins. It is also noticed that the volume concentration of MWCNT in water affects heat transfer characteristics and reduction in temperature takes place up to the volume concentration of 2%. About 1.3% reduction in temperature is predicted for adding MWCNT nanoparticle concentration from 0.5% to 2%. However, in terms of exergy efficiency, maximum overall exergy (about 67% for water flow rate of 0.00167 kg/s) is found for square pin-fins with inline arrangements. The average increase in Nusselt number from inline to staggered arrangement are around 11%, 74%, and 22% respectively for circular, square and triangular fins. The maximum electrical efficiency reaches to 42.2% for both 2% and 4% MWCNT with staggered circular pin-fins for a mass flow rate of 0.0058kg/s. Finally, it appears that a combination of nanofluids and pin-finned heatsinks gives a better cooling rate in the HCPV/T system and could be a promising alternative along with other cooling techniques.

Comparisons of thermal performances in a pulsating heat pipe by using a nanofluid and a self-rewetting nanofluid with carbon nanotubes

Heat transfer performances of the ultrapure water, n-butanol self-rewetting fluid (SRF), multi-walled carbon nanotubes (MWCNTs) nanofluid (NF), and n-butanol self-rewetting MWCNTs nanofluid (SRNF) were investigated in a pulsating heat pipe (PHP). The highlight of this study was to analyze their thermal performances under different heating powers, inclination angles, and ambient temperatures. Experimental results indicated that all functional working fluids generally gave advantages in thermal transport performances relative to the ultrapure water in most cases. Furthermore, advantage of the SRF gradually emerged with increasing thermal input when compared with the ultrapure water and its enhancement ratio reached a maximum of 22%. In contrary, advantage of NF was demonstrated only when the thermal input exceeded 20W, and its enhancement percentage reached 16% at 35W. The SRNF exhibited an outstanding increase of the thermal transfer performance at a low heating power range. The augmented percentage of the SRNF was around 7–17% with the maximum value obtained at 35 W. The inclination angle also had a non-negligible impact on thermal performances of different working fluids, particularly, their thermal transfer limits in the PHP. In addition, a lower ambient temperature could generally raise the heat transmission performance of the PHP with operating fluids.