Cavitation Induced Accelerated Erosion In Large Slurry Pumps

Centrifugal slurry plumps experience accelerated erosion. Research to understand and to control has been inconclusive. This investigation is being conducted to qualitatively examine the patterns of accelerated erosion in the samples photographed or collected from slurry pumps in the field, and to compare with the patterns on an aluminium specimen eroded by a submerged fast moving cavitating water jet in abrasives. The selected field samples are a front liner, and the front shroud of an impeller. The examination has resulted in: (1) Identification of three areas in slurry pumps which experience accelerated erosion the front liner, the front shroud and the impellerâs vanes. (2) Identification of the three common features both in the samples and in the aluminium specimen; namely: directional groves along the direction of the main slurry-flow, cavities and pitting, and the embedding of abrasive in the surfaces. The paper concludes the common features of localised cavitation and corresponding accelerated erosion in slurry pumps which are observed in the lowest local pressure areas. The current definition of cavitation is based on the lowest mean-pressure in the cross section area is replaced with a lowest-localpressure based definition which is followed with redefinition of the Cavitation Number based on local parameters, the flow mapping of vortexes, vortices, flow separation behind obstacles, and tensile forces within a velocity boundary layer, and prediction of localised cavitation at the design stage, and adopting cavitation erosion preventative measures such as air entrainment in erosion areas

Thermal Modeling and Design Optimisation of Compact Building Integrated Photovoltaic (BIPV) Facades for Application at the University of Technology Sydney (UTS)

Thermal models and correlations for the convection heat transfer coefficients are mainly for isothermal or constant heat flux surfaces and can result in discrepancies of up to 50% in the prediction of surface temperatures or heat fluxes on Photovoltaic (PV) panels. An experimental investigation was conducted to develop the thermal models and correlations for natural convection on a vertical PV module with nonisothermal surfaces. The paper also reports on the PV configuration with the maximum electric efficiency and natural convection cooling. A proximity mobile probe with two K-type thermocouples was developed to measure simultaneously local surface and air temperatures on the PV surface at a fixed distance. Thermocouples, anemometers, voltmeter, ampere-meter and Lux-meter were interfaced to a computer and sampled at a rate of 6 samples per minute (one every 10 second). The electric energy conversion efficiency and the natural convection cooling were quantified for the dimensionless channel spacing of s/h=0.015, 0.0.3, 0.045, 0.06 and 0.075 on a PV with a single glazing. An optimum configuration for a PV with single-glazing and the channel spacing of s/h=0.06 was selected for its maximum efficiency and natural convection cooling and proposed to be retrofitted on the existing UTS buildings

Experimental Study Of Wind Effects On The Airflow Of Natural Draft Wet Cooling Towers

Natural draft cooling towers may enhance the overall performance of a thermal or a nuclear power station by providing coolant water to the condenser at a reduced temperature. The cooling tower thermal performance and its air flow inside the tower are influenced by the prevailing cross winds which in turn are amplified or damped by the flowconditioning characteristics of surrounding structures, building and terrains in the relative proximity and orientation to the tower. These characteristics were investigated in the No-1 cooling tower at the Mount Piper Power Station near Sydney in Australia. The tower was instrumented using thermocouples and directional anemometers to measure air velocities and temperatures both inside and outside of the tower over three months period. The test results have indicated that surrounding structures and their relative orientations to the tower and wind directions affect on the air flow rate inside a tower and should be considered at the design stage

Electrohydrodynamic effects on characteristic of isolated bubbles in the nucleate pool boiling regime

Application of electric fields demonstrates great promise as an active heat transfer enhancement technique. Here, we study experimentally some characteristics of isolated bubbles such as bubble departure diameter, nucleation rate (frequency), and density of nucleation sites under the influence of an electric field In the nucleate pool boiling regime, isolated bubbles were recorded with a high-speed video camera at a rate of 1000 frames/s. The quantitative and qualitative analyses of bubble characteristics, and latent heat transfer concluded that at a constant heat flux condition in the isolated bubble regime, the density of nucleation sites was a very sensitive boiling parameter when electric field varied. The latent heat contribution varied proportional with the density of nucleation sites when heat flux and/or electrode voltage varied. This further simplifies the complex task of modeling of the electrohydrodynamic enhanced pool boiling heat transfer in the isolated bubble regime. © 2003 Elsevier Science Inc. All rights reserved

A study of cavitation induced surface erosion in abrasive waterjet cutting systems

Current jet cutting systems experience severe nozzle erosion and associated maintenance and downtime costs. An experimental investigation was conducted to qualitatively and quantitatively analyse the generation of cavitation in a high pressure water jet cutting system, and to characterise cavitation induced accelerated surface erosion by slurries. The analysis of surface morphology indicates that the shearing induced by cavitation played a major role in the erosion process. The results promise a feasible solution to reduce nozzle wear, and to enhance material removal in the jet cutting process

Thermal Conductivity of Graphite Felt at High Temperatures

Thermal conductivity measurements in vacuum, helium and air of WDF graphite felt were conducted at room temperature. It was found that conduction along the solid paths, gas conduction and radiation between fibres are the dominant heat transfer mechanisms. All heat transfer models reviewed indicated that there are geometrical parameters to be determined experimentally in order to be able to quantify the conduction and radiative mechanisms. Experimental results obtained at room temperature were used to calculate the conduction tortuosity, Ï. Results from the literature were used to determine the radiation constant, Cfr. Using these parameters, an equation for the felt thermal conductivity as a function of the absolute temperature was obtained

Design of a mobile probe to predict convection heat transfer on building integrated photovoltaic (BIPV) at University of Technology Sydney (UTS)

Copyright © 2015 by ASME. In the absence of a simple technique to predict convection heat transfer on building integrated photovoltaic (BIPV) surfaces, a mobile probe with two thermocouples was designed. Thermal boundary layers on vertical flat surfaces of a photovoltaic (PV) and a metallic plate were traversed. The plate consisted of twelve heaters where heat flux and surface temperature were controlled and measured. Uniform heat flux condition was developed on the heaters to closely simulate non-uniform temperature distribution on vertical PV modules. The two thermocouples on the probe measured local air temperature and contact temperature with the wall surface. Experimental results were presented in the forms of local Nusselt numbers versus Rayleigh numbers "Nu=a ∗ (Ra)b", and surface temperature versus dimensionless height [Ts -T∞ = c∗(z/h)d]. The constant values for "a", "b", "c" and "d" were determined from the best curve-fitting to the power-law relation. The convection heat transfer predictions from the empirical correlations were found to be in consistent with those predictions made by a number of correlations published in the open literature. A simple technique is then proposed to employ two experimental data from the probe to refine empirical correlations as the operational conditions change. A flexible technique to update correlations is of prime significance requirement in thermal design and operation of BIPV modules. The work is in progress to further extend the correlation to predict the combined radiation and convection on inclined PVs and channels

Design of compact BIPV façades for the buildings at the University of Technology Sydney (UTS)

Ecologically Sustainable buildings are being designed for the University of Technology, Sydney (UTS) where the building façade and equipment may serve as a project-based environment for engineering students learning about energy efficiency. Building Integrated Photovoltaic (BIPV) panels with poly-crystalline Photovoltaic (PV) module were designed and experimentally tested. The power input, and power output, surface temperatures, and channel spacing(s) between the PV module and glazed layer(s) were measured at cooling conditions with both fan-on and fan-off conditions. The electric energy conversion efficiency and the heat transfer ratios of conduction, natural convection, forced convection, and radiation reflection were determined for BIPV panels and optimized against the surface temperature and the channel spacing(s). An optimum BIPV with compact spacing for the single glazed (double-skinned) facade was suggested to be retrofitted to existing buildings, while an optimum BIPV with compact spacing for the double glazed (triple-skinned) façade was suggested for the building development at UTS. The project is ongoing and serves as a collaborative educational platform for students and staff. Copyright © 2009 by ASME