A Comparative Study of the Spray Characteristics of Nanofluids and Spray Cooling Performance

Nanofluids are promising candidates for improving combustion performance through reducing emissions (as a fuel spray additive) or as spray coolants in various thermal management systems (by enhancing the surface heat transfer rate). In this study, experiments were conducted to compare the viscosity, free spray properties and the cooling performance of a water spray with an Alumina nanofluid spray prepared using an ultrasonic bath. A commercial, gasoline, port-fuel injector was used to spray Aluminum oxide nanoparticle solutions at a pressure of 3 bar (40-50 nm, 0, 0.01 and 0.07% by mass) onto a heated, smooth Aluminum surface, mimicking the geometry of a bowled engine piston. The temperature of the piston surface was varied in the range of 25-180 °C (above the Leidenfrost temperature). A Phase Doppler Anemometer was used to measure the droplet size and axial and radial velocity distributions at a series of points, with and without spray impingement. Incident and rebounding axial droplet velocities were recorded in the ranges of 4 to 7 ms-1 and -0.8 to 0.8 ms-1 respectively for all sprays. High-speed video observations showed that the approximate spray cone envelope angle was reduced from 26° to 19° with the addition of nanoparticles. The mean droplet diameter in the case of the nanofluids was consistently greater (generally between 10 and 30% for the 0.07% case) when compared to the water spray and evidenced by pooling and splashing on the piston surface. For the heated piston cases, the heat transfer effect was only enhanced in the case of the 0.07% mass concentration, resulting in a 15 °C reduction in surface temperature after 35 seconds when compared to the water case, decreasing from 165 to 110 °C at an injection frequency of 25 Hz and duration of 8 ms. A much smaller effect was observed in the central bowl location; approximately 3-5 °C after 20 seconds. The main boiling regimes were observed as the surface cooled. The transition to single-phase cooling occurred approximately 10 seconds earlier in the water case for the location directly under the impinging spray jet. The heat transfer rate showed a stronger correlation between droplet number count and droplet diameter at the surface in the case of the nanofluid compared to water. The deposition of a rough, solid film of Aluminum oxide on the piston surface at the point of spray impact was observed and considered to contribute to the enhanced heat transfer effect

A Comparative Study of the Spray Characteristics of Nanofluids and Spray Cooling Performance

Nanofluids are promising candidates for improving combustion performance through reducing emissions (as a fuel spray additive) or as spray coolants in various thermal management systems (by enhancing the surface heat transfer rate). In this study, experiments were conducted to compare the viscosity, free spray properties and the cooling performance of a water spray with an Alumina nanofluid spray prepared using an ultrasonic bath. A commercial, gasoline, port-fuel injector was used to spray Aluminum oxide nanoparticle solutions at a pressure of 3 bar (40-50 nm, 0, 0.01 and 0.07% by mass) onto a heated, smooth Aluminum surface, mimicking the geometry of a bowled engine piston. The temperature of the piston surface was varied in the range of 25-180 °C (above the Leidenfrost temperature). A Phase Doppler Anemometer was used to measure the droplet size and axial and radial velocity distributions at a series of points, with and without spray impingement. Incident and rebounding axial droplet velocities were recorded in the ranges of 4 to 7 ms-1 and -0.8 to 0.8 ms-1 respectively for all sprays. High-speed video observations showed that the approximate spray cone envelope angle was reduced from 26° to 19° with the addition of nanoparticles. The mean droplet diameter in the case of the nanofluids was consistently greater (generally between 10 and 30% for the 0.07% case) when compared to the water spray and evidenced by pooling and splashing on the piston surface. For the heated piston cases, the heat transfer effect was only enhanced in the case of the 0.07% mass concentration, resulting in a 15 °C reduction in surface temperature after 35 seconds when compared to the water case, decreasing from 165 to 110 °C at an injection frequency of 25 Hz and duration of 8 ms. A much smaller effect was observed in the central bowl location; approximately 3-5 °C after 20 seconds. The main boiling regimes were observed as the surface cooled. The transition to single-phase cooling occurred approximately 10 seconds earlier in the water case for the location directly under the impinging spray jet. The heat transfer rate showed a stronger correlation between droplet number count and droplet diameter at the surface in the case of the nanofluid compared to water. The deposition of a rough, solid film of Aluminum oxide on the piston surface at the point of spray impact was observed and considered to contribute to the enhanced heat transfer effect

A new approach to modelling the two way coupling for momentum transfer in a hollow-cone spray

[EN] A new approach to modelling the interaction between droplets and the carrier phase is suggested. The new model is applied to the analysis of a spray injected into a chamber of quiescent air, using an Eulerian-Lagrangian approach. The conservative formulation of the equations for mass, momentum and energy transport is used for the analysis of the carrier phase. The dispersed phase is modelled using the Lagrangian approach with droplets represented by individual parcels. The implementation of the Discontinuous Galerkin method (ForestDG), based on a topological representation of the computational mesh by a hierarchical structure consisting of oct- quad- and binary trees, is used in our analysis. Adaptive mesh refinement (h-refinement) enables us to increase the spatial resolution for the computational mesh in the vicinity of the points of interest such as interfaces, geometrical features, or flow discontinuities. The local increase in the expansion order (p-refinement) at areas of high strain rates or vorticity magnitude results in an increase of the order of the accuracy of discretisation of shear layers and vortices. The initial domain consists of a graph of unitarian-trees representing hexahedral, prismatic and tetrahedral elements. The ancestral elements of the mesh can be split into self-similar elements allowing each tree to grow branches to an arbitrary level of refinement. The connectivity of the elements, their genealogy and their partitioning are described by linked lists of pointers. These are attached to the tree data structure which facilitates the on-the-fly splitting, merging and repartitioning of the computational mesh by rearranging the links of each node of the tree. This enables us to refine the computational mesh in the vicinity of the droplet parcels aiming to accurately resolve the coupling between the two phases.The authors are grateful to EPSRC (grants EP/K005758/1 and EP/M002608/1) for financial supportPapoutsakis, A.; Sazhin, S.; Begg, S.; Danaila, I.; Luddens, F. (2017). A new approach to modelling the two way coupling for momentum transfer in a hollow-cone spray. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 448-455. https://doi.org/10.4995/ILASS2017.2017.4671OCS44845

The fully Lagrangian approach to the analysis of particle/droplet dynamics:implementation into ANSYS Fluent and application to gasoline sprays

The fully Lagrangian approach (FLA) to the calculation of teh number density of inertial partucles in dilute gas-particles flows was incorporated into teh CFD code ANSYS Flunet. The new verion of ANSYS Fluent was applied to moedling dilute gas-particle flow around a cylinder and liquid droplets in a gasoline fuel spray. In a steady-state case, thre predictions of the FLA for the flow around a cylinder and those based on teh equilibrium Eulerian method (EE) are almost the same for small Stokes number (Stk) and small Reynolds number (Re). FLA predicts higher values of the gradients of particle number densities in front of the cylinder compared with the ones predicted by the EE for larger values of Stk and Re. Application of FLA to a direct injection gasoline fuel spray has concentrated on the computation of the number densities of droplets. Results revelaed good agreement between the numerical simulation and exeperimental data

Continuous–Discrete Time-Observer Design for State and Disturbance Estimation of Electro-Hydraulic Actuator Systems

International audienc