Grinding, like other abrasive processes, may generate high local temperatures along the arc of cut. These can cause various forms of surface damage in the most sensitive finishing phase of the manufacturing cycle. Traditional cooling... more
Grinding, like other abrasive processes, may generate high local temperatures along the arc of cut. These can cause various forms of surface damage in the most sensitive finishing phase of the manufacturing cycle. Traditional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. A new approach to this problem has been devised utilizing the high penetrative power of fast air jets combined with a water/soap mist to greatly improve convective cooling and lubrication along the arc of cut. The results obtained offer striking improvements compared to traditional liquid coolants especially if the relative simplicity of the method is considered.
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Simultaneous whole field velocity and heat transfer measurements were performed to characterize the interaction of a single rising ellipsoidal bubble with the free convection flow from a heated flat surface. This design note reports on... more
Simultaneous whole field velocity and heat transfer measurements were performed to characterize the interaction of a single rising ellipsoidal bubble with the free convection flow from a heated flat surface. This design note reports on the optimization of a purpose built high frame rate time-resolved digital particle image velocimetry system, which was used to map the bubble wake interaction with
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This paper describes an experimental investigation of heat transfer in two tube banks, one in-line and one staggered, located in the freeboard region of a gas fluidized bed. The objectives of this study are twofold. Firstly, examination... more
This paper describes an experimental investigation of heat transfer in two tube banks, one in-line and one staggered, located in the freeboard region of a gas fluidized bed. The objectives of this study are twofold. Firstly, examination of the local heat transfer results is used to identify the dominant heat transfer mechanisms. Secondly, the overall heat transfer performance of the two tube configurations is of relevance for the design, selection and siting of heat exchangers for fluidized bed combustors. The experimental results show that the dominant influence on heat transfer is the local concentration of particles, with the impact over the rear of tubes by particles disengaging from the flow having a significant effect on wake heat transfer. The latter mechanism is less important for tubes in the first and second rows of the in-line array, due to the shielding effect of the surrounding tubes. This difference in wake heat transfer contributes to higher mean Nusselt numbers, on average, for the tubes located in the staggered array.
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Research Interests: Engineering, Physics, Mechanics, Chemistry, Heat Transfer, and 3 morePhysical sciences, Bubble, and Wake
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The effect of solid particles in suspension on heat transfer for tubes located within a square tube bundle of pitch-diameter ratio 1.75 has been investigated. Tests conducted at a Reynolds number of 6000 with mean particle diameters of 58... more
The effect of solid particles in suspension on heat transfer for tubes located within a square tube bundle of pitch-diameter ratio 1.75 has been investigated. Tests conducted at a Reynolds number of 6000 with mean particle diameters of 58 and 127 μm at a mass loading ratio of 0.5 kg particles/kg air indicate that heat transfer is enhanced at all locations by the presence of the particles. However, at a Reynolds number of 12 000 there is a net decrease in the mean Nusselt number at all positions, with the exception of the first row. Assessment of the main mechanisms by which particles modify heat transfer in in-line tube arrays suggests that the enhancement of heat transfer is a consequence of the increased thermal capacity of the suspension, whereas the reduction in Nusselt number is considered to result from a change in the flow structure and turbulence within the array.
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... 203-204. [15] J. Woolman, RA Mottram: The mechanical and physical properties of the British Standard En steels (BS 970-1955), compiled by Steel User Section, British Iron and Steel Research Association. Oxford, Pergamon Press 1964 ... more
... 203-204. [15] J. Woolman, RA Mottram: The mechanical and physical properties of the British Standard En steels (BS 970-1955), compiled by Steel User Section, British Iron and Steel Research Association. Oxford, Pergamon Press 1964 1969.
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Grinding, like other abrasive processes, may generate high local temperatures along the arc of cut. These can cause various forms of surface damage in the most sensitive finishing phase of the manufacturing cycle. Traditional cooling... more
Grinding, like other abrasive processes, may generate high local temperatures along the arc of cut. These can cause various forms of surface damage in the most sensitive finishing phase of the manufacturing cycle. Traditional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. A new approach to this problem has been devised utilizing the high penetrative power of fast air jets combined with a water/soap mist to greatly improve convective cooling and lubrication along the arc of cut. The results obtained offer striking improvements compared to traditional liquid coolants especially if the relative simplicity of the method is considered.
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While numerous applied studies have successfully demonstrated the feasibility of unsteady cooling solutions, a consensus has yet to be reached on the local instantaneous conditions that result in heat transfer enhancement. This work aims... more
While numerous applied studies have successfully demonstrated the feasibility of unsteady cooling solutions, a consensus has yet to be reached on the local instantaneous conditions that result in heat transfer enhancement. This work aims to experimentally validate a recent analytical solution (on a local time-dependent basis) for the common flow condition of a fully developed incompressible pulsating flow in a uniformly heated vessel. The experimental setup is found to approximate the ideal constant heat flux boundary condition well, especially for the decoupled unsteady scenario where the amplitude of the most significant secondary contributions (capacitance and lateral conduction) amounts to 1.2% and 0.2% of the generated heat flux, respectively. Overall, the experimental measurements for temperature and heat flux oscillations are found to coincide well with a recent analytical solution to the energy equation by the authors. Furthermore, local time-dependent heat flux enhancements and degradations are observed to be qualitatively similar to those of wall shear stress from a previous study, suggesting that the thermal performance is indeed influenced by hydrodynamic behavior.
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An impinging synthetic jet can attain heat transfer rates comparable to a continuous jet, without net mass input. However it needs a forced cross-flow to supply fresh cooling medium. The vectoring effect of adjacent synthetic jets allows... more
An impinging synthetic jet can attain heat transfer rates comparable to a continuous jet, without net mass input. However it needs a forced cross-flow to supply fresh cooling medium. The vectoring effect of adjacent synthetic jets allows directing the flow by changing the phase between the jets. This study uses the vectoring effect of two adjacent synthetic jets to draw in fresh air, while maintaining high impingement cooling performance. The experimental approach applies infrared thermography and particle image velocimetry to quantify the local convective heat transfer and flow field, respectively. The heat transfer profiles for various phase differences have been compared to the mean flow field and wall-normal velocity fluctuation intensity. For a fixed operating point (stroke length and Reynolds number) and geometry, the cooling performance has been optimised for phase and jet-to-surface spacing, resulting in about 90% enhancement of the maximum and overall cooling rate compared ...
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In the area of heat dissipation, impinging jets have been researched over many years and are a well defined method of attaining high heat transfer coefficients. Many different techniques have been looked at over past years in an attempt... more
In the area of heat dissipation, impinging jets have been researched over many years and are a well defined method of attaining high heat transfer coefficients. Many different techniques have been looked at over past years in an attempt to discover a way to enhance this heat transfer further. This study investigates the effect of introducing a swirling motion into the fluid flow before exiting a jet nozzle. The final objective is to discover an optimal swirl geometry which will increase the heat transfer within a system compared to what would be achieved from a non-swirling jet with the same external nozzle geometry. The impinging jets? performance is determined through experimental testing using thermal imaging techniques and hot film sensors with high response times. Results from comparing the heat transfer distributions of the non-swirling jet to four swirling jet geometries have shown both enhanced and diminished performance. The changes in the Nusselt number distributions are f...
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The aim of this investigation is to optimise the data post-processing techniques associated with hot film sensors when intended to be used as a means of accurate, high-resolution heat flux measurement. More specifically, this project... more
The aim of this investigation is to optimise the data post-processing techniques associated with hot film sensors when intended to be used as a means of accurate, high-resolution heat flux measurement. More specifically, this project focuses on the performance of hot film sensors operated in a constant temperature anemometer bridge, used in conjunction with impinging jet air flows. The characteristic heat transfer behaviour in this impinging jet flow provides the reference against which the heat flux data attained using the hot film sensor is compared. As part of this investigation, three hot film calibration methods are examined for a range of sensor overheat values: (A) a wall shear correction method, (B) a physical quasi 1-D conduction model and (C) a physical quasi 2-D fin conduction model. The results show that the method C, when used in conjunction with a 5 K sensor overheat, best replicated that of the reference heat flux sensor for the jet configurations investigated.
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The development and optimization of two phase electrospray cooling is currently restricted,in part due to the insufficient knowledge of how the various parameters that define an electrospray interact and their subsequent effect on the... more
The development and optimization of two phase electrospray cooling is currently restricted,in part due to the insufficient knowledge of how the various parameters that define an electrospray interact and their subsequent effect on the heat transfer coefficients and profiles.This research aims to characterise the heat transfer to impinging electrosprays for different nozzle sizes, separation heights and flow rates.The results show that electrospray coolingis dependent on separation height and cooling fluid flow rate,and partially on nozzle size. At lower separation heights and greater flow rates a saturation point was observed where a subsequent increase in the flow rate yields no increase in the peak heat transfer coefficient. In the case of greater separation heights and lower flow rates a dispersion threshold was noted where the working fluid becomes too dispersed causing reduced heat transfer coefficients. The radial enhancement region was shown to be slightly sensitive to varying flow rate and separation height though independent of nozzle size. Nozzle size was found to be important for moderate separation heights and high flow rates. Importantly, the results show that very high peak heat transfer enhancement over natural convection can be achieved with electrosprays with exceptionally low flow rates