Search

Transient and steady‐state characteristics of the natural circulation loop are studied using various water‐based tri‐hybrid (different nature and shaped nanoparticles) nanofluids. Effects of input power, loop inclination and loop aspect ratio on the mass flow rate, effectiveness, and entropy generation rate are studied. Results disclose that tri‐hybrid nanofluids reduce the oscillation and attain steady state faster than water. Effectiveness increases and entropy generation rate decreases by using tri‐hybrid nanofluids. Nanoparticle shape has found a significant impact. Al2O3 + Cu + CNT/water shows the best performance. The mass flow rate increases with input power, loop aspect ratio, whereas, reduces with loop inclination. Effectiveness decreases and then increases with input power, whereas increases with loop inclination and decreases with loop aspect ratio. Entropy generation upsurges with input power and loop inclination, whereas decreases with loop aspect ratio. Loop aspect ratio of 1.5 to 3 is found suitable for better performance. [ABSTRACT FROM AUTHOR]

Energy and exergy performances of natural circulation loop (NCL) with various water-based hybrid nanofluids (Al2O3+TiO2, Al2O3+CNT, Al2O3+Ag, Al2O3+Cu, Al2O3+CuO, Al2O3+graphene) with 1% volumetric concentration are compared in this study. New thermophysical property models have been proposed for hybrid nanofluids with different particle shapes and mixture ratio. Effects of power input, loop diameter, loop height, loop inclination and heater/cooler inclination on steady-state mass flow rate, effectiveness, and entropy generation are discussed as well. Results show that both the steady-state mass flow rate and energy-exergy performance are enhanced by using the hybrid nanofluids, except Al2O3+graphene, which shows the performance decrement within the studied power range. Al2O3+Ag hybrid nanofluid shows highest enhancement in mass flow rate of 4.8% compared to water. The shape of nanoparticle has shown a significant effect on steady-state performance; hybrid nanofluid having cylindrical and platelet shape nanoparticles yields lower mass flow rate than that of spherical shape. Mass flow rate increases with the increasing loop diameter and height, whereas decreases with the increasing loop and heater/cooler inclinations. Both effectiveness and entropy generation increase with the decreasing loop diameter and height, whereas increasing the loop and heater/cooler inclinations. This study reveals that the particle shape has a significant effect on the performance of hybrid nanofluids in NCL, and the use of hybrid nanofluid is more effective for higher power. [ABSTRACT FROM AUTHOR]

It is necessary to investigate the relative effect of various phenomena before neglecting the same for simulating the single-phase natural circulation loop to obtain an acceptable prediction. Hence, the present study focuses on the validation and effect of different assumptions related to Boussinesq approximation, property variation, bend effect, heat loss, axial fluid and wall conduction on the transient and steady-state characteristics. Effect of assumptions for different working fluids (water, brines and hybrid nanofluids), and assess the effect of different heat flux distributions, like uniform, linear, non-linear, sinusoidal and Gaussian, applied to heater are also explored. Mass flow rate (predicts heat transport capability), effectiveness (predicts heat transfer ability) and entropy generation rate (predicts irreversibility) are evaluated. The results disclose that the Boussinesq approximation with constant other properties under-predicts the steady-state mass flow rate and effectiveness and over-predicts the entropy generation rate. This assumption cannot be applied for all working fluids. The fluid and solid conduction is the crucial parameter for simulating transient characteristics. Gaussian heat flux distribution shows the highest mass flow rate and non-linear increasing heat flux shows the highest effectiveness and entropy generation rate. This study will help to consider reasonable assumptions for the numerical simulation. [ABSTRACT FROM AUTHOR]

Transient analysis of vertical heating and horizontal cooling rectangular single-phase natural circulation loop with various water-based hybrid nanofluids (Al 2 O 3 + Ag, Al 2 O 3 + Cu, Al 2 O 3 + TiO 2 , Al 2 O 3 + CNT, Al 2 O 3 + Graphene) with 1% volumetric concentration is studied numerically. Temporal fluctuation and time required to attain the steady-state, transient mass flow rate and energy-exergy performance parameters (effectiveness and total entropy generation) using hybrid nanofluids are compared with water. The effect of power input and geometry parameter (diameter and height) of the loop on transient performances is studied as well. The result reveals that the fluctuation of mass flow rate and time required to attain the steady-state are less for hybrid nanofluids as compared to water. However, platelet and cylindrical shaped nanoparticles yield a lower stability as compared to spherical shaped. The mass flow rate is enhanced with hybrid nanofluids, except Al 2 O 3 + CNT and Al 2 O 3 + Graphene, as compared to water. The energy-exergy performance of hybrid nanofluids is higher than water. The maximum increment in mass flow rate is shown by Al 2 O 3 + Ag hybrid nanofluid (3%), whereas Al 2 O 3 + Graphene shows the highest increment in effectiveness (25.4%) and highest decrement in total entropy generation (14.3%) as compared to water. Smaller diameter and lower height of loop are found preferable for the flow stability. [ABSTRACT FROM AUTHOR]