An Experimental Approach to Show that High Cutting Speeds Can Reduce the CO2 Emissions during Machining

It is essential that the CO2 emissions produced by metal cutting manufacturing are reduced due to global warming. Metal cutting is an essential aspect of modern manufacturing, and accounts for approximately 70 percent of world metal manufacturing. Reductions of CO2 can be shown to be possible when machining at high cutting speed, when using tungsten coated tool tips. The addition of air-cooled with the addition of a small amount of vegetable oil, also allows high cutting speeds to be used. In addition to the cutting speed the tool paths and depth of cut are examined to determine their effect in reducing the CO2 emissions. A machining conditions model, reducing the environmental burden for machining operation is proposed based on this research. Two Numerical Control (NC) programs that produce a simple shape are evaluated, to show the feasibility of the proposed operating conditions model

Heat transfer enhancement due to cavities in impinging jets

This paper presents results from a study into the effectiveness of surface cavities in achieving increased heat transfer rates in impinging fluid jets. In this work a cylindrical cavity with an isothermally heated base was introduced beneath a steady fluid jet. The effects on the total heat transfer rate from the cavity were evaluated in a parametric study. Cavity depths up to 6 times the jet diameter were investigated at a range of Reynolds numbers and jet to surface distances. The key parameters affecting the heat transfer were found to be the Reynolds number and the distance between the jet nozzle exit and the cavity base. The effects of these parameters are discussed, and a useful range for each is identified with respect to heat transfer enhancement. The cavity arrangement was found to significantly enhance the heat transfer with the maximum heat transfer from the cavity found to be 33% higher than the heat transfer from a similarly heated flat plate

Air-Cooling Used For Metal Cutting

Air-cooling and dry machining are both being trialled as possible solutions to the metal cutting industry’s long running problems of extending tool life, reducing tool failure and minimising the heat generation at the tool tip. To date, large amounts of expensive coolant which cause both environmental damage and health hazards have had to be used. The introduction of dry machining is the goal of today’s metal cutting industry that tirelessly endeavours to reduce machining costs and impact from chemicals in the environment. Modern tool tips are already capable of maintaining their cutting edge at higher temperatures, but even with these improvements in tool materials, the cutting edge will eventually break down. Applying cold air to the tool interface of these modern tool tips will also help prolong their tool life reducing the cost of metal cutting. Dry machining incorporating air being directed on to the tool interface is considered in this paper as a possible alternative for harmful liquid-based cooling. However, low convective heat removal rates associated with conventional air-cooling methods are generally inadequate for dissipating intense heat generation in the cutting processes, and suitable improved cooling methodologies have yet to be established

Forced Convective Heat Transfer and Fluid Flow Characteristics in Curved Ducts

Fluid flow through curved ducts is influenced by the centrifugal action arising from duct curvature and has behaviour uniquely different to flow within straight ducts. In such flows, centrifugal forces induce secondary flow vortices and produce spiralling fluid motion within curved ducts. Secondary flow promotes fluid mixing with intrinsic potential for thermal enhancement and, exhibits possibility of fluid instability and additional secondary vortices under certain flow conditions. Reviewing the published work on numerical and experimental studies, this chapter discusses the current knowledge-base on secondary flow in curved ducts and, identifies the deficiencies in analyses and fundamental understanding. The chapter then presents an extensive research study capturing advanced aspects of secondary flow behaviour and associated wall heat transfer processes for both rectangular and elliptical curved ducts.This study develops a new three-dimensional numerical model incorporating helicity approach and curvilinear mesh that is validated against published data to overcome current modelling limitations. Flow patterns and thermal characteristics are obtained for a range of duct aspect ratios, flow rates and wall heat fluxes. Results are analysed for parametric influences and construed for clearer physical understanding of the flow mechanics involved. The study formulates two analytical techniques whereby secondary vortex detection is integrated into the computational process with unprecedented accuracy and reliability. The vortex inception at flow instability is carefully examined with respect to the duct aspect ratio, duct geometry and flow rate. An entropy-based thermal optimisation technique is developed and tested for fluid flow through curved rectangular and elliptical ducts

Parametric investigation of a synthetic jet heat sink for enhanced micro-scale heat transfer

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.This paper examines the characteristics of a pulsating fluid jet known as synthetic jet and its cooling effectiveness for heated micro fluid passages. The jet mechanism uses an oscillating diaphragm to inject a high-frequency fluid jet with a zero net mass flow through the jet orifice. The pulsed jet and the micro passage flow interaction is modelled as a 2- dimensional finite volume simulation with unsteady Reynolds­ averaged Navier-Stokes equations. For a range of conditions, the special characteristics of this periodically interrupted flow are identified while predicting the associated convective heat transfer rates. The results indicate that the pulsating jet leads to outstanding thermal performance in the micro passage increasing its heat dissipation by about 4.3 times compared to a micro passage without jet interaction within the tested parametric range. The degree of enhancement is first seen to grow gently and then rather rapidly beyond a certain flow condition to reach a steady value. The study also identifies the operational limits imposed by the fluid compressibility on the heat transfer characteristics. The proposed strategy has the unique intrinsic ability to generate outstanding degree of thermal enhancement in a micro passage without increasing its flow pressure drop. The technique is envisaged to have application potential in miniature electronic devices where localised cooling is desired over a base heat dissipation load.ksb201

Analysis of secondary flow characteristics and hydrodynamic instability in fluid flow through curved ducts

This paper presents an investigation on the unique flow characteristics associated with fluid flow through curved ducts, which are fundamentally different to those in straight fluid passages. In curved ducts, the flow is subjected to centrifugal forces that induce counter-rotating vortices in the main axial fluid stream and give rise to spiralling fluid motion, commonly known as secondary flow. The study develops a novel three-dimensional computational fluid dynamics analysis whereby the laminar developing fluid flow in a curved rectangular duct is modelled. The flow characteristics are identified for a range of flow rates and duct aspect ratios at several duct curvatures. The contours of secondary flow and axial velocities are obtained to recognise the influence of flow/geometrical parameters on the secondary flow. Comparisons are made between the numerical predictions and the available experimental data. It is observed that, with increased duct flow rate, the secondary flow intensifies and beyond a certain critical flow condition, leads to hydrodynamic instability. The fluid flow structure is then significantly altered with the appearance of additional pair (or pairs) of vortices, termed as Dean Vortices, at the outer wall of the curved duct. This flow behaviour is also highly influenced by the duct aspect (height to width) ratio. The paper develops and presents a new approach for predicting the onset of Dean vortex generation

Heat transfer enhancement in single impinging jets due to surface cavities

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This paper presents an assessment of a novel technique that further enhances the heat transfer potential of a single impinging jet. The method entails a geometrical modification to the jet impingement surface wherein the jet is directed into a cylindrical cavity located coaxially beneath the jet orifice. A numerical study is performed to examine the parametric influence on heat dissipation and flow characteristics of this modified jet impingement process. The results indicate a very significant increase in heat transfer, which is primarily dependent on cavity depth and jet Reynolds number.cs201