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A novel hybrid nanofluid was explored in order to find an efficient heat-transmitting fluid to replace standard fluids and revolutionary nanofluids. By using tangent hyperbolic hybrid combination nanoliquid with non-Newtonian ethylene glycol (EG) as a basis fluid and a copper (Cu) and titanium dioxide (TiO2) mixture, this work aims to investigate the viscoelastic elements of the thermal transferring process. Flow and thermal facts, such as a slippery extended surface with magnetohydrodynamic (MHD), suction/injection, form factor, Joule heating, and thermal radiation effects, including changing thermal conductivity, were also integrated. The Keller–Box method was used to perform collective numerical computations of parametric analysis using governing equivalences. In the form of graphs and tables, the results of TiO2–Cu/EG hybrid nanofluid were compared to those of standard Cu/EG nanofluid in important critical physical circumstances. The entropy generation study was used to examine energy balance and usefulness for important physically impacting parameters. Detailed scrutiny on entropy development get assisted with Weissenberg number, magnetic parameter, fractional volumes, injection parameter, thermal radiation, variable thermal conductivity, Biot number, shape variation parameter, Reynolds and Brinkman number. Whereas the entropy gets resisted for slip and suction parameter. In this case, spotted entropy buildup with important parametric ranges could aid future optimization. [ABSTRACT FROM AUTHOR]

This paper aims to examine the effects of singleand multi‐walled carbon nanotubes (CNTs) nanoparticles on heat transfer enhancement and inherent irreversibility in the boundary layer of water base nanoliquid flow over a convectively heated moving wedge with thermal radiation. Manipulation of the angle positioning towards the flow stream provides the opportunity for comparing physical aspects in the flow states, where three main geometries of the well‐known Falkner–Skan problem include: (i) the flat plat (named Blasius flow), (ii) the wedge, and (iii) the vertical plate (named Hiemenz stagnation flow) have been considered to present a comprehensive development of this significant problem. Applying suitable similarity constraints, the model partial differential equations are transformed into a set of nonlinear ordinary differential equations. Solutions are obtained analytically via optimal homotopy asymptotic method and numerically via shooting technique coupled with the Runge–Kutta–Fehlberg fourth–fifth scheme. The impacts of solid volume fraction of carbon nanoparticles along with other germane factors, such as wedge angle, velocity ratio parameter, Biot number, thermal radiation, and so forth on velocity and thermal profiles, Nusselt number, heat transfer enhancement, rate of entropy generation, and irreversibility ratio, are scrutinized via graphical simulations and discussed. Optimization of such entropy developments in the system was found to depend on geometrical (β), dynamical (λ), and thermophysical (Bi, NR, Ec, φ) parameters. The ultimate objective of reducing the energy loss and enhancing heat transference was obtained with the geometrical manipulation of a flat plate case (β = 0). Dynamically (λ = 1) were spotted to exert the best fluidity irrespective of obstacle shapes (wedge or plate) in its way. In thermophysical aspects, reducing the convective heating develops a favorable situation for attaining the optimal balance between energy loss and heat transfer. SWCNT/water could be the better choice with enhanced thermal transference ability and exerts minimal irreversibility to overshadow the influences of all the above‐mentioned factors. The SWCNT suspended nanofluid can provide 12%–64% heat transfer enhancement when compared with the multiwalled CNT nanofluid which ranges from over 11% to 58% heat transference rate. [ABSTRACT FROM AUTHOR]

Abstract: The convective heat loss mechanism in a solar cavity receiver is influenced by the presence of the stagnation and convective zone within the receiver. This paper focuses on the experimental and numerical studies carried out to identify these zones in a downward facing cylindrical cavity receiver of length 0.5 m, internal diameter 0.3 m and having a wind skirt of 0.5 m in diameter. This design is different from the receiver used normally for dish-Stirling systems. It is meant for providing low and medium temperature process heat and does not have stringent constraints on tube volume and pressure drop. The experiments are conducted for low and medium fluid inlet temperatures between 50 °C and 150 °C for receiver inclination angles of 0 (side ways facing cavity), 30, 45, 60 and 90° (vertically downward facing receiver). Water is used as the working fluid within the receiver tubes during the low temperature tests (50–75 °C) while compressed air is the working fluid for the medium temperature tests (130 and 150 °C). The numerical investigations have also been carried out for various conditions. The air velocity and temperature profiles obtained from the numerical and experimental studies are analysed to determine the zone boundary, which is found to be nearly a horizontal plane passing through the topmost point of the cavity aperture. This validates the results reported in the literature. This paper proposes a quantitative estimate for identifying the zone boundary and a term called “critical air temperature gradient” is defined for this purpose. The locations within the cavity having the air temperature gradient less than the critical air temperature gradient represent the stagnation zone. The locations having air temperature gradient more than the critical air temperature gradient represent the convective zone. A non-dimensional parameter ψ is defined to represent the values of the air temperature gradient. It is observed that a value of about 0.3 for ψ corresponds to the critical air temperature gradient for all the tests carried out. The stagnation zone is observed at regions having ψ ≤ 0.3 and convective zone having ψ > 0.3. [Copyright &y& Elsevier]

• Heat transfer and flow characteristics of the heat exchanger is analyzed. • The inner Nusselt number is influenced by the inner and outer Dean numbers. • Heat transfer coefficient is higher in this heat exchanger. • From heat transfer point of view there exists an optimum cone angle. • A correlation is proposed to predict Nusselt number. The present study deals with the experimental and numerical investigations on the heat transfer and fluid flow characteristics of a conical coil double pipe heat exchanger. The effects of Dean number, curvature and torsion on the Nusselt number and overall heat transfer coefficient are discussed. The numerical scheme is validated with the experimental results. Overall heat transfer coefficient is calculated and the heat transfer coefficient is determined using Wilson plot. The results showed that the Dean number in the annulus and inner tube have significant effect on the inner Nusselt number. Also the inner Nusselt number is influenced by the ratio of mass flow rates of hot and cold fluids. Use of conical exchanger instead of helical type leads to an enhancement in the overall heat transfer coefficient. However the friction factor is slightly higher in conical coil heat exchangers. The overall heat transfer coefficient varies with cone angle and there exists an optimum value of cone angle. A correlation is proposed to estimate Nusselt number in terms of Dean number, Prandtl number. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer and flow characteristics of the heat exchanger is analyzed. • Numerical results are validated with experimental results. • Heat transfer coefficient is higher in this heat exchanger. • From heat transfer point of view there exists an optimum value of pitch. • A correlation is proposed to predict Nusselt number. Abstract Experimental and numerical investigations have been carried out on a helical coil double pipe heat exchanger to study its heat transfer and flow characteristics. Two major parameters are identified to affect convective heat transfer, namely the Dean number and torsion. Overall heat transfer coefficients are calculated and the heat transfer coefficients are determined using Wilson plot. The numerical scheme is validated with the experimental results obtained from present study also with that reported in literature. The results showed that use of helical coil heat exchanger instead of straight tube type leads to an enhancement in the Nusselt number. However the friction factor is high in helical coil. The Nusselt number in the inner tube and annulus increase with Dean number and the effect of Dean number on Nusselt number is more significant in the annulus. The overall heat transfer coefficient varies with pitch and there exists an optimum value of pitch. A correlation is proposed to estimate Nusselt number in terms of Dean number, Prandtl number and dimensionless pitch. [ABSTRACT FROM AUTHOR]

Emergence of nanotechnology opens up new avenues in diverse research frontiers. Nanorefrigerants are nanotechnology based refrigerants, which are stable mixture of nanoparticles of metal, oxide, carbon and its allotropes and refrigerants. Development of nanorefrigerants provides a new research frontier in the heat transfer perspective. The studies on nanorefrigerants are still in its budding stage. The intention of the present paper is to provide a comprehensive overview of experimental studies on thermophysical and rehological properties, boiling and condensation phenomena, pressure drop characteristics, aggregation behaviour, migration and degradation characteristics of different nanorefrigerants and application of nanorefrigerants in HVAC systems. Various outlooks of future scope associated with the studies of nanorefrigerants have also been suggested. It has been recognized that addition of nanoparticles in refrigerants contributes noteworthy augment in the thermal physical and heat transfer characteristics of refrigerants. Furthermore, application of nanorefrigerants in heating, ventilation, and air conditioning systems enhance the overall performance in terms of coefficients of performance (COP) and energy efficiency. [ABSTRACT FROM AUTHOR]

It is well known that solar energy is the main source of thermal energy coming from the sun responsible for huge operations in engineering studies. It can be seen in the technology of photovoltaic cells, solar streetlights, solar energy plates, and solar water pumping. This study is for investigating solar radiation as well as a method to improve the performance of the solar water pump (SWP) with the use of solar radiation along with nanotechnology. The thermal transfer performance of the pump is checked for the case of many impacts including heat radiations and variable thermal conductivity. An Oldroyd‐B nanofluid with entropy production analysis has been scrutinized as a working coolant liquid in the system. Graphene oxide (GO) and Cu nanoparticles have been employed in engine oil (EO) as the base liquid. It is noticed that the heat transfer performance of SWP increases in the case of amplification in thermal radiation and temperature‐dependent thermal conductivity characteristics. In comparison to low thermal conductivity nanofluid, high thermal conductivity nanofluid provides the best capability for heat transmission. The thermal efficiency of the used (GO/EG) nanofluid has been enhanced by between 7.70% and 26.68% than (Cu/EO) nanofluid. [ABSTRACT FROM AUTHOR]

Controlling the wetting behaviour of liquids on surfaces is important for a variety of industrial applications such as water-repellent coatings and lubrication. Liquid behaviour on a surface can range from complete spreading, as in the 'tears of wine' effect, to minimal wetting as observed on a superhydrophobic lotus leaf. Controlling droplet movement is important in microfluidic liquid handling, on self-cleaning surfaces and in heat transfer. Droplet motion can be achieved by gradients of surface energy. However, existing techniques require either a large gradient or a carefully prepared surface to overcome the effects of contact line pinning, which usually limit droplet motion. Here we show that two-component droplets of well-chosen miscible liquids such as propylene glycol and water deposited on clean glass are not subject to pinning and cause the motion of neighbouring droplets over a distance. Unlike the canonical predictions for these liquids on a high-energy surface, these droplets do not spread completely but exhibit an apparent contact angle. We demonstrate experimentally and analytically that these droplets are stabilized by evaporation-induced surface tension gradients and that they move in response to the vapour emitted by neighbouring droplets. Our fundamental understanding of this robust system enabled us to construct a wide variety of autonomous fluidic machines out of everyday materials. [ABSTRACT FROM AUTHOR]

MHD Natural convection, which is one of the principal types of convective heat transfer in numerous research of heat exchangers and geothermal energy systems, as well as nanofluids and hybrid nanofluids. This work focuses on the investigation of Natural convective heat transfer evaluation inside a porous triangular cavity filled with silver-magnesium oxide/water hybrid nanofluid [H2O/Ag-MgO]hnf under a consistent magnetic field. The laminar and incompressible nanofluid flow is taken to account while Darcy–Forchheimer model takes account of the advection inertia effect in the porous sheet. Controlled equations of the work have been approached nondimensional and resolved by Galerkin finite element technique. The numerical analyses were carried out by varying the Darcy, Hartmann, and Rayleigh numbers, porosity, and characteristics of solid volume fraction and flow fields. Further, the findings are reported in streamlines, isotherms and Nusselt numbers. For this work, the parametric impact may be categorized into two groups. One of them has an effect on the structural factors such as triangular form and scale on the physical characteristics of the important outputs such as fluidity and thermal transfer rates. The significant findings are the parameters like Rayleigh and slightly supported by Hartmann along with Darcy number, minimally assists by solid-particle size and rotating factor as clockwise assists the cooler flow at the center and anticlockwise direction assists the warmer flow. Clear raise in heat transporting rate can be obtained for increasing solid-particle size. [ABSTRACT FROM AUTHOR]

Scientists and researchers are enthusiastically utilizing novel technologies that can substantially reduce energy consumption in diverse thermal systems. The foremost aim of the present investigation is to exploit the potential of nanoparticles on the enhancement of heat transfer characteristics of refrigerant and tribological capabilities of lubricant. Experimental investigations on the forced convection heat transfer characteristics of R134a/SiO 2 nanorefrigerant (R134a + SiO 2 -polyalkylene glycol nanolubricant) are carried out. The effect of particle concentration, heat flux, mass flux, and vapour quality are investigated. The friction reduction and anti-wear properties of the nanolubricant are evaluated using four-ball tribo-tester. The results reveal that the presence of nanoparticles in the refrigerant significantly enhances the heat transfer coefficient of refrigerant and the tribological behaviour of lubricant. The maximum increase in heat transfer coefficient is 163.2% corresponding to a particle concentration of 0.4%. The presence of nanoparticles in refrigerant results in a marginal increase in pressure drop. However, the penalty in pressure drop is insignificant compared to the enhancement in heat transfer. Excellent friction reduction and anti-wear performance are also manifested by the nanolubricant. The maximum reduction in the friction coefficient is 37.76% and that of wear scar diameter is 40.83%. Considering the heat transfer and tribological characteristics, the optimum value of the particle volume fraction is 0.4%. SiO 2 -PAG nanolubricant can be considered as a potential energy-saving alternative to refrigerant compressor oils. Unlabelled Image • Heat transfer characteristics of R134a /SiO 2 nanorefrigerant are studied. • Heat transfer coefficient increases up to 163.2%. • Tribological properties of nanolubricant are evaluated. • Better friction reduction and anti-wear properties are evidenced. • Optimum value of particle concentration is suggested as 0.4%. [ABSTRACT FROM AUTHOR]

An experimental investigation has been carried out to study the heat transfer characteristics of ethylene glycol/water mixture(60:40) appended with TiO 2 nanoparticles. The effect of volume fraction and Reynolds number are studied. Stable nanofluid is prepared using two-step method. Thermal conductivity and viscosity data required for the calculation of various heat transfer parameters are measured. The maximum enhancement in thermal conductivity is 24%(at volume fraction 0.8% and temperature 50°C) and the corresponding increase in viscosity is 16%. An experimental set up was designed and fabricated to conduct forced convection studies. For convection studies the volume fraction is varied from 0.2 to 0.5% and Reynolds number from 850 to 2050. The nanofluid has better heat transfer characteristic compared to base fluid. The heat transfer enhancement is influenced by thermal properties of the nanofluid, particle concentration and Reynolds number. The maximum enhancement in heat transfer coefficient is 116% with Reynolds number of 2050 and 0.5% volume fraction. [ABSTRACT FROM AUTHOR]