Extensive stability assessment of tio/polyvinyl ether nanolubricant with physical homogenization

Proper preparation and stability evaluation of the nanolubricant shall be established when applying the nanoparticle dispersion technique in a two-phase system. The stability of the nanolubricant ensures the maximum benefit gained from the dispersion of nanoparticles in specified Polyvinyl ether (PVE). In this study, TiO2/PVE nanolubricant was prepared using two methods of physical homogenization: high-speed homogenizer (HSH) and ultrasonication bath. The HSH used a preparation time of up to 300 s in the stability assessment. Meanwhile, the ultrasonication bath had a preparation time of 1, 3, 5, and 7 h. The stability condition of the nanolubricant was evaluated using photo capturing, ultraviolet-visible (UV-Vis) spectrophotometer, zeta potential, and zeta sizer. A sample with 180 s of preparation time shows the best stability condition from HSH. The nanolubricant with ultrasonication offers excellent stability at 5 h of homogenizing time with a concentration ratio of more than 90% for up to 30 days of observation. In conclusion, ultrasonication homogenizing methods show better results than HSH with a zeta potential of more than 60 mV. In addition, HSH can be recommended as an optional method to produce nanolubricant with a low preparation time for immediate use

Stability assessment of polyvinyl-ether-based TiO2, SiO2 and their hybrid nanolubricants

Poor characterisation of nanoparticle suspensions impedes the development of nanolubricants for use in refrigeration and air-conditioning systems. Chemical treatment techniques, such as surfactants, are inappropriate for enhancing the stability of nanolubricants intended for use in vapour-compression refrigeration (VCR) systems. Prior to incorporating nanolubricants into the system, the stability of TiO2 and SiO2 nanoparticles dispersed in PVE was therefore investigated. The nanolubricants were prepared by a two-step method with the aid of an ultrasonication bath homogeniser. Visual observation and ultraviolet–visible (UV–Vis) spectrophotometric analysis were used, and zeta potential analysis was then performed to confirm the nanolubricants’ stability condition. The TiO2/PVE nanolubricant was observed to be maintained at a 95% concentration ratio for up to 30 days of evaluation. The TiO2/PVE, SiO2/PVE, and SiO2-TiO2/PVE exhibited zeta potential values of 203.1 mV, 224.2 mV, and 105.3 mV, respectively, after 7 h of sonication. A high absolute value of zeta potential indicates that the electrostatic repulsive forces between nanoparticles are exceptionally strong, indicating an excellent stable suspension. The high values of zeta potentials validated the excellent stability conditions determined by UV–Vis analysis and visual observation. It can be concluded that ultrasonication times of 7 h produced the most stable state for mono- and hybrid nanolubricants

Application Of Design Patterns And Space Concepts In The Development Of Heat Pipes

The phenomenon of condensation of vapors on a vertical fin is theoretically solved by coupling the thermal conduction in the fin to the constitutive equations of motion and energy of the condensate layer in an appropriate manner with relevant boundary conditions. The analysis accounts for the sub cooling effects of the condensate on the condensation heat transfer coefficient. A design equation that can be employed in the design of the condenser section of a flat plate heat pipe has been suggested in an earlier paper presented at the sixth international heat pipe conference held at Grenoble France. In an technical note published in the international journal of heat and mass transfer, the process of condensation on a vertical plate fin of variable thickness is analyzed to establish the effect of fin geometry on the condensation heat transfer coefficient. The results presented are of significance in the optimization of fin geometry while developing the flat plate heat pipes.In yet another paper published in the Canadian journal of chemical engineering explicit solutions are obtained for the problems of condensation of vapors on the lateral surface of a long vertical plate fin of variable cross section. The formulation yields solutions to the limiting cases so that the results can be employed in the design of the condenser section of a flat plate heat pipe in which the fin is considered to be an essential element for augmenting the condensation heat transfer.Design can be considered as an integral part along with the process know how and knowledge of fabrication/assembly of the ultimate product such as the radiation shield with embedded heat pipes as in the case of the present study within the frame workof agile manufacturing

Laminar Convective Heat Transfer And Friction Factor Of AL2O3 Nanofluid In Circular Tube Fitted With Twisted Tape Inserts

We experimentally investigated the fully developed laminar convective heat transfer and friction factor characteristics of different volume concentrations of Al2O3 nanofluid in a plain tube and fitted with different twist ratios of twisted tape inserts. Experiments were conducted with water and nanofluid in the range of 700 Re2200, particle volume concentration of 0.5%, and twisted tape twist ratios of 0H / D15. The nanofluid heat transfer coefficient is high compared to water and further heat transfer enhancement is observed with twisted tape inserts. The pressure drop increases slightly with the inserts, but is comparatively negligible. A generalized regression equation is developed based on the experimental data for the estimation of the Nusselt number and friction factor for water and nanofluid in a plain tube and with twisted tape inserts

Turbulent Film Condensation of Pure Vapors Flowing Normal to a Horizontal Condenser Tube - Constant Heat Flux at the Tube Wall

A mathematical model is developed for the study of external turbulent film condensation of pure vapors flowing downward and normal to the axis of the condenser tube with constant heat flux condition maintained at the tube wall. The magnitude of interfacial shear is estimated for a given external flow condition of the vapor with the help of Colburn’s analogy. The average condensation heat transfer coefficients for different system conditions are evaluated. The present theory is compared with the available experimental and theoretical data in the literature and is found to be satisfactory

Natural Convection-Radiation from a Vertical Base-Fin Array with Emissivity Determination

Experiments have been conducted to determine the emissivity for black chrome coated and uncoated aluminum surfaces. The emissivity of the surfaces is estimated considering combined convection radiation heat transfer and observed to be a constant in the range of 60 to 110°C. The combined heat transfer coefficients from black chrome coated vertical base vertical fin array of size 70 x 70 mm consisting of 22 aluminum fins with a fin spacing of 10 mm by natural convection and radiation has been determined at different heat inputs. Theoretical analysis of single fin geometry of constant thickness considering both convection and radiation has been used to predict the temperature distribution and heat flow. The theoretical values of heat flow estimated for a fin array is in good agreement with the experimental observations validating the emissivity of the surface. The experimental data is further validated with the equations of Nusselt presented by Churchill and Chu

Natural Convection-Radiation from a Vertical Base-Fin Array with Emissivity Determination

Experiments have been conducted to determine the emissivity for black chrome coated and uncoated aluminum surfaces. The emissivity of the surfaces is estimated considering combined convection radiation heat transfer and observed to be a constant in the range of 60 to 110°C. The combined heat transfer coefficients from black chrome coated vertical base vertical fin array of size 70 x 70 mm consisting of 22 aluminum fins with a fin spacing of 10 mm by natural convection and radiation has been determined at different heat inputs. Theoretical analysis of single fin geometry of constant thickness considering both convection and radiation has been used to predict the temperature distribution and heat flow. The theoretical values of heat flow estimated for a fin array is in good agreement with the experimental observations validating the emissivity of the surface. The experimental data is further validated with the equations of Nusselt presented by Churchill and Chu

Influence of aluminum oxide nanoparticles on the physical and mechanical properties of wood composites

Aluminum oxide nanoparticles were used as nanofillers in urea-formaldehyde (UF) resin and prepared for medium density fiberboards (MDF). The nanofillers composed weight percentage of the UF resin. The thermal and viscoelastic properties were studied using differential scanning calorimetry and dynamic mechanical analysis. The H value of the UF resin showed an increase with increasing nanoparticle concentration. The core temperature during hot pressing increased with the addition of nanofillers. The formaldehyde emissions from MDF decreased with an increase in the concentration of nanofillers. The internal bonding strength and the modulus of rupture of boards were improved significantly after nanoparticle loading

Heat Transfer Enhancement Using Nanofluids in an Automotive Cooling System

The increasing demand of nanofluids in industrial applications has led to increased attention from many researchers. In this paper, heat transfer enhancement using TiO2 and SiO2 nanopowders suspended in purewater is presented. The test setup includes a car radiator, and the effects on heat transfer enhancement under the operating conditions are analyzed under laminar flow conditions. The volume flow rate, inlet temperature and nanofluid volume concentration are in the range of 2–8 LPM, 60–80 °C and 1–2% respectively. The results showed that the Nusselt number increased with volume flow rate and slightly increased with inlet temperature and nanofluid volume concentration. The regression equation for input (volume flow rate, inlet temperature and nanofluid volume concentration) and response (Nusselt number) was found. The results of the analysis indicated that significant input parameters to enhance heat transfer with car radiator. These experimental results were found to be in good agreement with other researchers' data, with a deviation of only approximately 4%