Numerical study of a confined slot impinging jet with nanofluids

Abstract

BackgroundHeat transfer enhancement technology concerns with the aim of developing more efficient systems to satisfy the increasing demands of many applications in the fields of automotive, aerospace, electronic and process industry. A solution for obtaining efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the possibility of increasing the thermal performances of the working fluids can be taken into account, and the introduction of nanoparticles in a base fluid can be considered.ResultsIn this article, a numerical investigation on confined impinging slot jet working with a mixture of water and Al2O3 nanoparticles is described. The flow is turbulent and a constant temperature is applied on the impinging. A single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations and Reynolds number have been considered to study the behavior of the system in terms of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours.ConclusionsThe dimensionless stream function contours show that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Reynolds number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point, and the lowest at the end of the heated plate. The average Nusselt number increases for increasing particle concentrations and Reynolds numbers; moreover, the highest values are observed for H/W = 10, and a maximum increase of 18% is detected at a concentration equal to 6%. The required pumping power as well as Reynolds number increases and particle concentrations grow, which is almost 4.8 times greater than the values calculated in the case of base fluid.List of symbols

Thermal performance and entropy generation analysis of a high concentration ratio parabolic trough solar collector with Cu-Therminol®VP-1 nanofluid

“…The nanofluid specific heat capacity is given by [51][52][53] (1 ) (25) The Bruggeman model [52,56], which considers interaction among spherical particles with various concentrations of inclusion, was used for modelling thermal conductivity of the nanofluid. The thermal conductivity obtained with the Bruggeman model compares very well with Maxwell's model of the classic effective medium theory which was shown to be accurate for well-dispersed particles in a benchmark study of thermal conductivities of nanofluids [57].…”

“…Whereas, the specific heat capacity was determined from the commonly used expression that assumes thermal equilibrium between particles and the surrounding liquid [51,52].…”

Numerical Study of Laminar Confined Impinging Slot Jets with Nanofluids

“…The investigation on nanofluid behaviour is becoming more and more popular, as testified by recent reviews and papers on this issue [35][36][37][38][39][40][41][42][43][44] but inconsistencies in published data and disagreements on the heat transfer mechanisms have been underlined by Keblinski et al [45] and recently by Gherasim et al [46]. However, a few examples of studies on nanofluids in impinging jets have been investigated experimentally and numerically and, according to the best knowledge of the present authors, their investigations have been reported in [46][47][48][49][50][51][52][53][54][55][56][57][58][59]. Roy et al [50] provided the first numerical results on the hydrodynamic and thermal fields of Al 2 O 3 /water nanofluid in a radial laminar flow cooling system, underlining a heat transfer enhancement up to 200% in the case of a nanofluid with 10% in nanoparticle volume concentration at a Reynolds number equal to 1200.…”

“…Furthermore, temperature-dependent thermophysical properties of nanofluids were found to have a marked bearing on the simulation results. Manca et al [57] numerically investigated the confining effects on impinging slot jets in the turbulent regime, such as for Reynolds numbers, ranging from 5000 to 20000. They adopted the single-phase approach in order to describe the Al 2 O 3 /water nanofluid behaviour for particle concentrations up to 5%.…”

Heat Transfer Enhancement and Entropy Generation of Nanofluids Laminar Convection in Microchannels with Flow Control Devices

“…Al 2 O 3 -water nanofluids are selected as working substances in this study [29,30], which are assumed as the mixtures of base fluid (water) and Al 2 O 3 nanoparticle with 30 nm diameter. The physical properties of the base fluid and Al 2 O 3 nanoparticle [31,32] are shown in Table 1, in which the reference temperature is 293 K. A single-phase model [33] is used to evaluate the physical properties of Al 2 O 3 -water nanofluids, and based on the assumptions that the aluminium oxide nanoparticle is spherical and homogeneously suspended in the base fluid, the following models are used to compute density, specific heat, dynamic viscosity, and thermal conductivity, respectively. Obtained from the above data and models, the physical properties of Al 2 O 3 -water nanofluids are shown in Table 2.…”