Tun Ping Teng

Effects of nanolubricant on performance of hydrocarbon refrigerant system

This work discusses the replacement of the R-134a refrigerant and polyester lubricant with a hydrocarbon refrigerant and mineral lubricant. The mineral lubricant included added Al2O3 nanoparticles (0.05, 0.1, and 0.2wt% ) to improve the lubrication and heat-transfer performance. Experimental results indicated that the 60% R-134a and 0.1wt% Al2O3 nanoparticles were optimal. Under these conditions, the power consumption was reduced by about 2.4%, and the coefficient of performance was increased by 4.4%. These results show that replacing R-134a refrigerant with hydrocarbon refrigerant and adding Al2O3 nanoparticles to the lubricant effectively reduced power consumption.

Characteristics of phase-change materials containing oxide nano-additives for thermal storage

In this study, the authors report the production of nanocomposite-enhanced phase-change materials (NEPCMs) using the direct-synthesis method by mixing paraffin with alumina (Al2O3), titania (TiO2), silica (SiO2), and zinc oxide (ZnO) as the experimental samples. Al2O3, TiO2, SiO2, and ZnO were dispersed into three concentrations of 1.0, 2.0, and 3.0 wt.%. Through heat conduction and differential scanning calorimeter experiments to evaluate the effects of varying concentrations of the nano-additives on the heat conduction performance and thermal storage characteristics of NEPCMs, their feasibility for use in thermal storage was determined. The experimental results demonstrate that TiO2 is more effective than the other additives in enhancing both the heat conduction and thermal storage performance of paraffin for most of the experimental parameters. Furthermore, TiO2 reduces the melting onset temperature and increases the solidification onset temperature of paraffin. This allows the phase-change heat to be applicable to a wider temperature range, and the highest decreased ratio of phase-change heat is only 0.46%, compared to that of paraffin. Therefore, this study demonstrates that TiO2, added to paraffin to form NEPCMs, has significant potential for enhancing the thermal storage characteristics of paraffin.

Estimation and experimental study of the density and specific heat for alumina nanofluid

This study analyses the density and specific heat of alumina (Al2O3)/water nanofluid to determine the feasibility of relative calculations. The Al2O3/water nanofluid was produced by the direct-synthesis method with cationic chitosan dispersant served as the experimental sample, and was dispersed into three concentrations of 0.5, 1.0 and 1.5 wt.%. This experiment measures the density and specific heat of nanofluid with weight fractions and sample temperatures with a liquid density meter and a differential scanning calorimeter (DSC). To assess the availability of these equations, it then compares the experimental data with the calculated results according to the concepts of mixing theory and statistical mechanism. Comparing the calculated results of density and specific heat with the experimental data, the deviation of density fell within the range of −1.50% to 0.06% and 0.25% to 2.53%, whereas the deviation of specific heat fell within the range of −0.07% to 5.88% and −0.35% to 4.94%, respectively. Calculated results of density and specific heat show a trend of greater deviation with an increased concentration of nanofluid. However, two kinds of density and specific heat of the calculated results fall within an acceptable deviation range in this study.

Performance evaluation on an air-cooled heat exchanger for alumina nanofluid under laminar flow

This study analyzes the characteristics of alumina (Al2O3)/water nanofluid to determine the feasibility of its application in an air-cooled heat exchanger for heat dissipation for PEMFC or electronic chip cooling. The experimental sample was Al2O3/water nanofluid produced by the direct synthesis method at three different concentrations (0.5, 1.0, and 1.5 wt.%). The experiments in this study measured the thermal conductivity and viscosity of nanofluid with weight fractions and sample temperatures (20-60°C), and then used the nanofluid in an actual air-cooled heat exchanger to assess its heat exchange capacity and pressure drop under laminar flow. Experimental results show that the nanofluid has a higher heat exchange capacity than water, and a higher concentration of nanoparticles provides an even better ratio of the heat exchange. The maximum enhanced ratio of heat exchange and pressure drop for all the experimental parameters in this study was about 39% and 5.6%, respectively. In addition to nanoparticle concentration, the temperature and mass flow rates of the working fluid can affect the enhanced ratio of heat exchange and pressure drop of nanofluid. The cross-section aspect ratio of tube in the heat exchanger is another important factor to be taken into consideration.

Evaluating stability of aqueous multiwalled carbon nanotube nanofluids by using different stabilizers

The 0.5 wt.% multiwalled carbon nanotubes/water nanofluids (MWNFs) were produced by using a two-step synthetic method with different types and concentrations of stabilizers. The static position method, centrifugal sedimentation method, zeta potential measurements, and rheological experiments were used to assess the stability of the MWNFs and to determine the optimal type and fixed MWCNTs-stabilizer concentration of stabilizer. Finally, MWNFs with different concentrations of MWCNTs were produced using the optimal type and fixed concentration ratio of stabilizer, and their stability, thermal conductivity, and pH were measured to assess the feasibility of using them in heat transfer applications. MWNFs containing SDS and SDBS with MWCNTs-stabilizer concentration ratio were 5 : 2 and 5 : 4, respectively, showed excellent stability when they were evaluated by static position, centrifugal sedimentation, zeta potential, and rheological experiments at the same time. The thermal conductivity of the MWNFs indicated that the most suitable dispersing MWNF contained SDBS. MWNFs with MWCNTs concentrations of 0.25, 0.5, and 1.0wt.% were fabricated using an aqueous SDBS solution. In addition, the thermal conductivity of the MWNFs was found to have increased, and the thermal conductivity values were greater than that of water at 25°C by 3.20%, 8.46%, and 12.49%.

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

Heat dissipation from electrical appliances is a significant issue with contemporary electrical devices. One factor in the improvement of heat dissipation is the heat transfer performance of the working fluid. In this study, we used plasma arc technology to produce a nanofluid of carbon nanoparticles dispersed in distilled water. In a one-step synthesis, carbon was simultaneously heated and vaporized in the chamber, the carbon vapor and particles were then carried to a collector, where cooling furnished the desired carbon/water nanofluid. The particle size and shape were determined using the light-scattering size analyzer, SEM, and TEM. Crystal morphology was examined by XRD. Finally, the characterization include thermal conductivity, viscosity, density and electric conductivity were evaluated by suitable instruments under different temperatures. The thermal conductivity of carbon/water nanofluid increased by about 25% at 50°C compared to distilled water. The experimental results demonstrated excellent thermal conductivity and feasibility for manufacturing of carbon/water nanofluids.

Research and development of measurement device for thermal conductivity of nanofluids

This research aims to develop a device for measuring thermal conductivity of nanofluid using transient hot-wire methodology. The proposed measurement system comprises of sensing wires coupled with an electrical measurement unit kept in a constant-temperature environment. The wires are made of nickel-chromium alloy a coating with Teflon for insulation. Enhanced ratio of thermal conductivity in a nanofluid is calculated from the difference in electrical parameters with and without CuO nanoparticles added. The results show that thermal conductivities are enhanced by 5.8% and 9.6% when CuO nanoparticles of 1.1%wt and 2.2%wt are added, respectively. Resultant data was then compared with that obtained by two other measurement devices. The difference in measurements was within 5%. This proves that the system developed in this study can perform effective measurement of thermal conductivity of nanofluids.

Feasibility assessment of thermal management system for green power sources using nanofluid

A thermal management system using alumina (Al2O3)/water as the nanofluid for green power sources was experimentally assessed in this paper. Basic thermal principles and formulas were utilized to evaluate the performance of an air-cooled heat exchanger. The Al2O3/water nanofluid was produced at the concentrations of 0.5, 1.0, and 1.5 wt.%. The testing conditions of this experiments were above three concentrations, five coolant flow rates (0.8, 1.2, 1.6, 2.0, and 2.4 L/min.), and three heating powers (50, 100, and 150W). Firstly, basic properties of nanoparticles were analyzed. Fundamental relationships of the Al2O3/water nanofluid with respect to temperatures and concentrations were measured such as: viscosity, density, and specific heat. Next, an innovative concept named efficiency factor (EF) was proposed to quantitatively evaluate the thermal system performance. Theenhancement of thermal system performance compared with distilled water was then defined as an efficiency factor ratio (REF). The experimental results demonstrated that the efficiency factor ratios were optimal at low flow rate (0.8 L/min.) and low concentration (0.5%). Values of REF were all below 1.0 at high flow rates (1.2-2.4 L/min.). This research points out the direction of optimizing a thermal management system for green energy sources in the near future.

Characterization of Heat Storage by Nanocomposite-Enhanced Phase Change Materials

This study involved a two-step method of adding multi-walled carbon nanotube (MWCNTs) and alumina (Al2O3) nanoparticles to paraffin wax, forming nanocomposite-enhanced phase change materials (NEPCMs). The NEPCMs in a phase change experiment were influenced by the concentrations of the nano-materials and the heating temperature of water. The objective of this paper is to investigate the optimal parameters of added nano-materials. The experimental results show that the phase change temperature of the paraffin wax slightly increases after adding the nano-materials to the paraffin wax. In addition, the nano-materials in the paraffin wax will reduce the temperature difference between test samples and heating water, indicating that adding the nano-materials can effectively reduce the thermal resistance of the experimental samples and improve the efficiency of thermal energy storage.

Preparation and characterization of carbon nanofluids by using a revised water-assisted synthesis method

A revised water-assisted synthesis system (RWAS) was used to fabricate carbon/water nanofluids (CWNFs). The CWNFs were manufactured by heating graphite rods at different temperatures (700, 800, 900, and 1000°C). Aspects of the CWNFs and suspended nanocarbon, such as the morphology, structure, optical characteristics, and production rate, were fully characterized. Furthermore, the suspension performance of the CWNFs was controlled by adding a dispersant (water-soluble chitosan) at different concentrations. Finally, the CWNFs were determined to assess the influence of both the heating temperature of the graphite rod module (process temperature) and the dispersant concentration on the fundamental characteristics of the CWNFs. The results showed that the nanocarbon was a mixture of nanocrystalline graphite and amorphous carbon. Heating the graphite rod module at higher process temperatures resulted in a higher production rate and a greater nanocarbon particle size. Furthermore, adding dispersant could improve the suspension performance; increase the viscosity, density, and specific heat; and reduce the thermal conductivity of the CWNFs. The optimal combination of the process temperature range and dispersant concentration was 800 to 900°C and 0.2wt.%, respectively, based on the production rate, suspension performance, and other fundamental properties of the CWNFs.