Hybrid PCM concentration on energy storage and thermal performance of solar thermal air heater featured with carbon nanotube and copper oxide nanofluid

This paper utilizes the experimental and numerical results obtained during quenching of stainless steel (SS) probes in carbon nanotube (CNT) nanofluids to arrive at an optimum CNT concentration and bath temperature for maximum quenching heat transfer rate. The individual effect of CNT concentration and bath temperature on the quenching heat transfer rate has recently been published by the authors. The objective of this work is to study the combined effect of CNT concentration and bath temperature on the heat transfer rate during quenching. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs in de-ionized (DI) water without any surfactant at 0.50 and 0.75 wt. % of CNTs. Cylindrical quench probes made of SS 304L with a diameter of 20 mm and an aspect ratio of 2.5 were quenched in the CNT nanofluids by maintaining at 30, 40, and 50°C using an external water bath. The recorded time-temperature data during quenching were used as input and the heat flux and temperature at the quenched surface were estimated based on the inverse heat conduction (IHC) method. The computed boiling curves during quenching were used in conjunction with the boiling curves published in literature to arrive at an optimum CNT concentration and bath temperature for maximum heat transfer rates. The computational results showed that the peak heat flux during quenching of SS probes in CNT nanofluids increased when the CNT nanofluid was maintained at 40 than at 30°C and it started decreasing with further increase in the bath temperature irrespective of the CNT concentration. The enhanced heat transfer performance of CNT nanofluid at a slightly higher temperature during quenching is attributed to the enhanced Brownian motion of CNTs in nanofluid.

This paper utilizes the experimental and numerical results obtained during quenching of stainless steel (SS) probes in carbon nanotube (CNT) nanofluids to arrive at an optimum CNT concentration and bath temperature for maximum quenching heat transfer rate. The individual effect of CNT concentration and bath temperature on the quenching heat transfer rate has recently been published by the authors. The objective of this work is to study the combined effect of CNT concentration and bath temperature on the heat transfer rate during quenching. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs in de-ionized (DI) water without any surfactant at 0.50 and 0.75 wt. % of CNTs. Cylindrical quench probes made of SS 304L with a diameter of 20 mm and an aspect ratio of 2.5 were quenched in the CNT nanofluids by maintaining at 30, 40, and 50°C using an external water bath. The recorded time-temperature data during quenching were used as input and the heat flux and temperature at the quenched surface were estimated based on the inverse heat conduction (IHC) method. The computed boiling curves during quenching were used in conjunction with the boiling curves published in literature to arrive at an optimum CNT concentration and bath temperature for maximum heat transfer rates. The computational results showed that the peak heat flux during quenching of SS probes in CNT nanofluids increased when the CNT nanofluid was maintained at 40 than at 30°C and it started decreasing with further increase in the bath temperature irrespective of the CNT concentration. The enhanced heat transfer performance of CNT nanofluid at a slightly higher temperature during quenching is attributed to the enhanced Brownian motion of CNTs in nanofluid.

In this paper, the effect of nanofluid temperature on the heat transfer rate has been studied during immersion quenching in Carbon Nanotube (CNT) nanofluid. For this purpose, CNT nanofluid was prepared by suspending 0.25wt% of chemically treated CNTs (TCNT) in de-ionized (DI) water without any surfactant. Quench probes with a diameter of 20 mm and a length of 50 mm were machined from 304L stainless steel and quenched in CNT nanofluid when maintained at 30 °C, 40 °C and 50 °C. The heat flux and temperature at the quenched surface were estimated based on the Inverse Heat Conduction (IHC) method using the measured temperature data during quenching as input. The computation results showed that the peak heat flux increased when the CNT nanofluid was maintained at 40 °C than at 30°C and decreased with further increase in the CNT nanofluid temperature. The enhanced heat transfer performance of CNT nanofluid during quenching at a slightly higher temperature is attributed to the increase in the Brownian motion of CNTs in nanofluid. The reduced heat transfer rate when the CNT nanofluid maintained at 50 °C during quenching was due to the predominant effect of quenchant temperature on quenching heat transfer rate.

Numerical solution of entropy generation in nanofluid flow through a surface with thermal radiation applications

<div class="section abstract"><div class="htmlview paragraph">Inconel 625, nickel based alloy, is found in gas turbine blades, seals, rings, shafts, and turbine disks. On the other hand, the manufacturing of this alloy is challenging, mainly when machining processes are used due to excellent mechanical properties. Application of nanofluids in minimum quantity lubrication (MQL) shows gaining importance in the machining process, which is economical and eco-friendly. The principal objective of this investigational work is to study the influence of three types of nanofluids in the MQL turning of Inconel 625 nickel based alloys. The used nanofluids are multi-walled carbon nanotubes (CNT), alumina (Al<sub>2</sub>O<sub>3</sub>) and copper oxide (CUO) dispersed in vegetable oil. Taguchi-based L<sub>27</sub> orthogonal array is used for the experimental design. The parameter optimization of design variables over response is carried out by the use of Taguchi-based derringer's desirability function. The design variables are machining parameters (speed, feed), nanofluids (Al<sub>2</sub>O<sub>3</sub>, CNT, CUO), and three different weight percentage (0.1, 0.25, and 0.5 wt. %). The results showed that minimum values of surface roughness could be achieved at 0.10 wt. % of nanoparticles, CNT nanofluids, a cutting speed of 40 m/min and a feed rate of 0.17 mm/rev. In the interim, minimal tool wear can be achieved by the application of 0.50 wt% nanoparticle concentration, Al<sub>2</sub>O<sub>3</sub> nanofluids, 40 m/min speed and 0.14 mm/rev feed rate. Further statistical analysis emphasized that cutting velocity and nanofluids have a significant effect on Ra and Vba. Abrasion and small adhesion are the dominant wear types. Desirability analysis revealed 0.5 wt.%, Al<sub>2</sub>O<sub>3</sub> nanofluids, 40 m/min and 0.20 mm/rev are found as optimized parameter levels which simultaneously optimize the surface roughness and flank wear. At the optimized cutting conditions, Al<sub>2</sub>O<sub>3</sub> nanofluids exhibit the improvement of Ra and Vba by 9.0% 4.26%, and 5.4%, 65% as compared to CNT and CUO nanofluids. Thus the Al<sub>2</sub>O<sub>3</sub> nanofluids show the overall performance on machinability characteristics that of CNT and CUO nanofluids. This finding is a step towards sustainable machining of difficult-to-process material such as nickel based alloy.</div></div>

In this article, water based carbon nanotube (CNT) nanofluids have been used as quenchants to study their effects on the heat transfer rate during immersion quenching. For this purpose, water based CNT nanofluids were prepared by dispersing CNTs with and without the use of surfactant. Quench probes with a diameter of 20 mm and a length of 50 mm were prepared from 304L stainless steel. Thermocouples were fixed at the selected location inside the quench probes and the probes were quenched in distilled water and CNT nanofluids. During quenching, time-temperature data were recorded using a data acquisition system. The heat flux and temperature at the quenched surface were estimated through the inverse heat conduction method. The computation results showed that the peak heat flux was higher by 37.5% during quenching in CNT nanofluid prepared without surfactant than that in water. However, surfactant assisted CNT nanofluid promoted a prolonged vapor phase during quenching and hindered the heat transfer rates significantly. The peak heat flux was dropped by 24.9% during quenching in CNT nanofluid prepared with surfactant as compared with its base fluid of water.

A comprehensive thermal-hydraulic assessment of solar flat-plate air heaters

Performance improvement of a single slope solar still by employing thermoelectric cooling channel and copper oxide nanofluid: An experimental study

Performance evaluation and optimization of solar assisted air heater with discrete multiple arc shaped ribs

Nanofluids with their enhanced thermal conductivity are believed to be a promising coolant in heat transfer applications. In this study, carbon nanotube (CNT) nanofluids of 0.01 wt%, stabilised by 1.0 wt% gum arabic were used as a cooling liquid in a concentric tube laminar flow heat exchanger. The flow rate of cold fluid varied from 10 to 50 g/s. Both experimental and numerical simulations were carried out to determine the heat transfer enhancement using CNT nanofluids. Computational fluid dynamics (CFD) simulations were carried out using Fluent v 6.3 by assuming single-phase approximation. Thermal conductivity, density and rheology of the nanofluid were also measured as a function of temperature. The results showed thermal conductivity enhancement from 4% to 125% and nearly 70% enhancement in heat transfer with increase in flow rate. Numerical results exhibited good agreement with the experimental results with a deviation of . CNT nanofluids at 0.01 wt% CNTs showed Newtonian behaviour with no significant increase in the density.

Plate heat exchangers (PHEs) can benefit from the application of carbon nanotube (CNT) nanofluids as a promising approach to improving heat transfer performance. The production of CNT nanofluids can be made by dispersing CNTs in common fluids. The higher thermal conductivity of CNTs leads to an increase in the heat transfer rate. Moreover, CNTs contribute to a greater functional surface area of the heat exchanger, which enables more effective contact between the heat transfer surfaces and the fluids. In addition, CNT nanofluids offer advantages such as reduced pressure drop and enhanced stability. Furthermore, the stability of CNT nanofluids is crucial for long-term operation, and efforts have been made to improve their dispersion stability and prevent particle agglomeration. In summary, applying CNT nanofluids in PHEs provides an opportunity to enhance heat transfer efficiency, reduce pressure drop, and improve stability, ultimately leading to more efficient and effective heat exchanger systems.

A solvent-free ionic carbon nanotube (CNT) nanofluid with about 80 wt.% organic content was synthesized by oxidation of CNTs with mixed acid followed by a surface reaction with PEG-substituted tertiary amine. The CNT nanofluid and the pristine CNTs were introduced to polyurethane (PU) by melt-blending. The structures and properties of the nanofluid and the nanocomposites were investigated. The results show that the CNT nanofluid is in a viscous liquid state at room temperature and is stable and soluble in both aqueous and organic solvents. The CNT nanofluid distributes homogenously in the PU matrix. Due to the high content organic chains on the CNT surfaces, the breaking strength and elastic modulus of the nanocomposite decrease slightly but with about 100 % increase of breaking elongation and 50 % increase of toughness. Better dispersion of the nanofluid leads to more improvement of electrical conductivities of the composite. The solvent-free ionic nanofluid will be an excellent nanofiller in the nanocomposites.

Effect of CNT concentration and agitation on surface heat flux during quenching in CNT nanofluids

Carbon nanotube (CNT) nanofluids, with three sizes of CNTs (L-MWNT-1030, L-MWNT-4060, L-MWNT-60100) and different mass concentration (MC) of surfactant, were prepared to investigate the effects of CNTs and surfactant on the solidification behavior of deionized water (DI water). The thermal responses of the samples were tested in a constant temperature trough. It’s found that the MC of the surfactant and the size of the CNTs influence the supercooling degree (SCD) and freezing time (FT). For the L-MWNT-1030, the CNT nanofluids had lower SCD and shorter beginning FT than the DI water. But when the MC of surfactant was 0.10 %, the finishing FT was equal to that of the DI water. For the L-MWNT-4060 and L-MWNT-60100 CNT nanofluids, the SCD and FT were comparable with those of the DI water. The unusual results imply that the mechanism of nucleation and stability of the CNT nanofluids also influence the solidification behavior.

There have been numerous research studies regarding nanofluid for last two decades. The major topic was mostly focused on the thermal conductivity increase with small particle concentration. However, a conclusion regarding thermal conductivity increase and heat transfer mechanism was not achieved yet due to large discrepancies among the experimental results. In parallel with the thermal conductivity, the specific heat is a crucial thermal property in the application of the nanofluid but wide research has not been conducted. In this study, the specific heat of carbon nanotube (CNT) nanofluids were experimentally measured and the experimental results were compared with possible models to explain the results. The CNT nanofluids were produced with DI water and ethylene glycol (EG) as base fluids. Since CNTs are not mixed with DI water, gum Arabic was used as a surfactant. On the other hand, CNTs were mixed with EG without any surfactant. The specific heat was measured with Calvet calorimeter. Temperature and heat flow sensors of Calvet calorimeter were calibrated with reference materials. The experiment method was validated by comparing the base fluids with reference values showing very good agreement. The measured specific heat of CNT nanofluids decreased with particle concentration due to the lower specific heat of CNT than that of base fluids. It is found that the thermal equilibrium model of nanofluid specific heat successfully predicts the experimental results. This result can be very useful in generating desired working fluids in the diverse thermal systems because the control of the specific heat of nanofluid can be achieved.