The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jan K. Spelt - One of the best experts on this subject based on the ideXlab platform.
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dust reduction in abrasive jet micro machining using liquid films
Powder Technology, 2016Co-Authors: Reza Haj Mohammad Jafar, Jan K. Spelt, M Papini, V HadaviAbstract:Abstract Abrasive jet micro-machining (AJM) uses a high-velocity particle jet to erode features in target substrates for a variety of applications, including micro-electro-mechanical and micro-fluidic device fabrication. AJM can result in a dusty environment due primarily to airborne, rebounding abrasive particles that eventually settle. This paper proposes a novel concept of covering the target with a layer of liquid in order to improve the process cleanliness. Films of water, glycerin, and a polymer solution were used to investigate the effect of liquid viscosity and film thickness on the percentage of captured particles, and also on the depth, width, erosion rate, roughness, and waviness of abrasive jet micro-machined channels. The glycerin film captured up to 61% of the rebounding particles during the machining of micro-channels. The channel depth, width, erosion rate, and roughness decreased, and the channel centreline waviness increased. Films of the long-chain polymer solution and of pure water absorbed up to 42% and 36%, respectively, of the rebounding particles, while not significantly changing the channel depth, width, roughness, and waviness. For all liquids, the percentage of trapped particles increased with increasing film thickness. The results showed that AJM with the target covered by a thin liquid film is a viable way of increasing process cleanliness by decreasing the amount of airborne particulates.
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high pressure abrasive slurry jet micro machining using slurry entrainment
The International Journal of Advanced Manufacturing Technology, 2015Co-Authors: Naser Haghbin, Jan K. Spelt, M Papini, Farbod AhmadzadehAbstract:A novel high-pressure (water pump pressure up to 250 MPa) abrasive slurry micro-machining (HASJM) system was introduced. By feeding a premixed slurry into the mixing chamber of a water jet machine with a micro-nozzle (mixing tube diameter of 254 μm), premature erosion of system components was avoided. An optimum erosion rate of 2.7 mg/g was reached when machining Al6061-T6 with a slurry of 25 μm aluminum oxide particles under conditions (slurry flow rate = 200 g/min and water pump pressure = 235 MPa) near to those which theoretically maximized momentum transfer between the inlet slurry and the water jet entering the mixing chamber from the orifice. It was found that when the standoff distance increased tenfold, the erosion rate almost doubled in glass, but decreased by 50 % in Al6061-T6, due to differences in the erosion at the jet periphery for the two materials. For aspect ratios greater than 0.9, high-quality symmetric channels with a centerline waviness below 6.9 μm and a centerline roughness below 1.1 μm could be produced using a single pass at a low traverse velocity of 40 mm/min. The use of multiple machining passes at a relatively high traverse speed (~1000 mm/min) was found to produce asymmetric channels when the aspect ratio was greater than 0.9, owing to jet deflection from steps formed on the cutting front. Channels produced by micro-milling Al6061-T6 and glass had a 50 % lower centerline waviness and 16 % lower centerline roughness than those made with the conventional abrasive water jet in which air and abrasive entered the mixing chamber.
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abrasive waterjet micro machining of channels in metals comparison between machining in air and submerged in water
International Journal of Machine Tools & Manufacture, 2015Co-Authors: Naser Haghbin, Manuela Papini, Jan K. SpeltAbstract:Abstract Abrasive water jet technology can be used for micro-milling using recently developed miniaturized nozzles. Abrasive water jet (AWJ) machining is often used with both the nozzle tip and workpiece submerged in water to reduce noise and contain debris. This paper compares the performance of submerged and unsubmerged abrasive water jet micro-milling of channels in 316L stainless steel and 6061-T6 aluminum at various nozzle angles and standoff distances. The effect of submergence on the diameter and effective footprint of AWJ erosion footprints was measured and compared. It was found that the centerline erosion rate decreased with channel depth due to the spreading of the jet as the effective standoff distance increased, and because of the growing effect of stagnation as the channel became deeper. The erosive jet spread over a larger effective footprint in air than in water, since particles on the jet periphery were slowed much more quickly in water due to increased drag. As a result, the width of a channel machined in air was wider than that in water. Moreover, it was observed that the instantaneous erosion rate decreased with channel depth, and that this decrease was a function only of the channel cross-sectional geometry, being independent of the type of metal, the jet angle, the standoff distance, and regardless of whether the jet was submerged or in air, in either the forward or backward directions. It is shown that submerged AWJM results in narrower features than those produced while machining in air, without a decrease in centerline etch rate.
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abrasive enhanced electrochemical slurry jet micro machining comparative experiments and synergistic effects
Journal of Materials Processing Technology, 2014Co-Authors: H Nouraei, Jan K. Spelt, M PapiniAbstract:Abstract Abrasive enhanced electrochemical slurry-jet machining (ESJM) is presented as a new approach to the micro-machining of metals using a combination of abrasive slurry-jet machining (ASJM) and electrochemical jet machining (ECJM). A novel ESJM prototype was developed to generate a charged slurry jet consisting of a mixture of Al2O3 abrasive particles and an electrolytic solution of NaCl and NaNO3. A DC potential of 30 V was applied between the nozzle and specimen. A series of micro-channels were machined in Stellite 12 using ASJM, ECJM and ESJM processes to investigate the relative effects of erosion and anodic dissolution on the material removal rate and surface finish in the combined process of ESJM. The results illustrated that the ESJM process results in significantly greater target mass loss rate than the separate erosion and corrosion processes. The magnitude of the synergistic effect on the rate of mass loss was found to vary from positive to negative as the erosion component increased with increasing particle kinetic energy (jet pressure) and particle concentration. The roughness of the channels machined using ESJM was between that obtained with ASJM and ECJM. The roughness decreased as the erosion component of the total mass loss increased.
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surface evolution models for abrasive slurry jet micro machining of channels and holes in glass
Wear, 2014Co-Authors: H Nouraei, Kamran Kowsari, Marcello Papini, Jan K. SpeltAbstract:Abstract Abrasive slurry jet micro-machining (ASJM) uses a jet of abrasive slurry to erode features with relatively high resolution without the need for a patterned mask. The present study investigated the ability of a surface evolution model to predict the profiles of micro-channels and holes machined in borosilicate glass with a newly developed ASJM system. The system could produce micro-channels with depth and width variations along their length of less than 3%, and a channel-to-channel repeatability within 5%. The fundamental erosion rate of the borosilicate glass was measured as a function of impact angle using a slurry of water mixed with a low concentration of 10 and 25 µm nominal diameter aluminum oxide particles. This erosion rate-impact angle relationship was used in an existing model developed previously for the abrasive air jet micro-machining of brittle materials. The results demonstrated that, despite the differences in abrasive flow patterns between air and slurry based systems, the surface evolution model accurately predicted the profiles of micro-channels with a maximum error of 7% for aspect ratios (depth/width) of up to 5. The predicted profiles of holes were also in reasonable agreement with a maximum error of 14% for aspect ratios close to 1.
M Papini - One of the best experts on this subject based on the ideXlab platform.
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dust reduction in abrasive jet micro machining using liquid films
Powder Technology, 2016Co-Authors: Reza Haj Mohammad Jafar, Jan K. Spelt, M Papini, V HadaviAbstract:Abstract Abrasive jet micro-machining (AJM) uses a high-velocity particle jet to erode features in target substrates for a variety of applications, including micro-electro-mechanical and micro-fluidic device fabrication. AJM can result in a dusty environment due primarily to airborne, rebounding abrasive particles that eventually settle. This paper proposes a novel concept of covering the target with a layer of liquid in order to improve the process cleanliness. Films of water, glycerin, and a polymer solution were used to investigate the effect of liquid viscosity and film thickness on the percentage of captured particles, and also on the depth, width, erosion rate, roughness, and waviness of abrasive jet micro-machined channels. The glycerin film captured up to 61% of the rebounding particles during the machining of micro-channels. The channel depth, width, erosion rate, and roughness decreased, and the channel centreline waviness increased. Films of the long-chain polymer solution and of pure water absorbed up to 42% and 36%, respectively, of the rebounding particles, while not significantly changing the channel depth, width, roughness, and waviness. For all liquids, the percentage of trapped particles increased with increasing film thickness. The results showed that AJM with the target covered by a thin liquid film is a viable way of increasing process cleanliness by decreasing the amount of airborne particulates.
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high pressure abrasive slurry jet micro machining using slurry entrainment
The International Journal of Advanced Manufacturing Technology, 2015Co-Authors: Naser Haghbin, Jan K. Spelt, M Papini, Farbod AhmadzadehAbstract:A novel high-pressure (water pump pressure up to 250 MPa) abrasive slurry micro-machining (HASJM) system was introduced. By feeding a premixed slurry into the mixing chamber of a water jet machine with a micro-nozzle (mixing tube diameter of 254 μm), premature erosion of system components was avoided. An optimum erosion rate of 2.7 mg/g was reached when machining Al6061-T6 with a slurry of 25 μm aluminum oxide particles under conditions (slurry flow rate = 200 g/min and water pump pressure = 235 MPa) near to those which theoretically maximized momentum transfer between the inlet slurry and the water jet entering the mixing chamber from the orifice. It was found that when the standoff distance increased tenfold, the erosion rate almost doubled in glass, but decreased by 50 % in Al6061-T6, due to differences in the erosion at the jet periphery for the two materials. For aspect ratios greater than 0.9, high-quality symmetric channels with a centerline waviness below 6.9 μm and a centerline roughness below 1.1 μm could be produced using a single pass at a low traverse velocity of 40 mm/min. The use of multiple machining passes at a relatively high traverse speed (~1000 mm/min) was found to produce asymmetric channels when the aspect ratio was greater than 0.9, owing to jet deflection from steps formed on the cutting front. Channels produced by micro-milling Al6061-T6 and glass had a 50 % lower centerline waviness and 16 % lower centerline roughness than those made with the conventional abrasive water jet in which air and abrasive entered the mixing chamber.
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abrasive enhanced electrochemical slurry jet micro machining comparative experiments and synergistic effects
Journal of Materials Processing Technology, 2014Co-Authors: H Nouraei, Jan K. Spelt, M PapiniAbstract:Abstract Abrasive enhanced electrochemical slurry-jet machining (ESJM) is presented as a new approach to the micro-machining of metals using a combination of abrasive slurry-jet machining (ASJM) and electrochemical jet machining (ECJM). A novel ESJM prototype was developed to generate a charged slurry jet consisting of a mixture of Al2O3 abrasive particles and an electrolytic solution of NaCl and NaNO3. A DC potential of 30 V was applied between the nozzle and specimen. A series of micro-channels were machined in Stellite 12 using ASJM, ECJM and ESJM processes to investigate the relative effects of erosion and anodic dissolution on the material removal rate and surface finish in the combined process of ESJM. The results illustrated that the ESJM process results in significantly greater target mass loss rate than the separate erosion and corrosion processes. The magnitude of the synergistic effect on the rate of mass loss was found to vary from positive to negative as the erosion component increased with increasing particle kinetic energy (jet pressure) and particle concentration. The roughness of the channels machined using ESJM was between that obtained with ASJM and ECJM. The roughness decreased as the erosion component of the total mass loss increased.
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characteristics of abrasive slurry jet micro machining a comparison with abrasive air jet micro machining
Journal of Materials Processing Technology, 2013Co-Authors: H Nouraei, Jan K. Spelt, M Papini, A WodoslawskyAbstract:Abstract Abrasive slurry jet micro-machining (ASJM) uses a well-defined jet of abrasive slurry to erode features in a solid target. Compared with abrasive water jet machining (AWJM), the present ASJM system operates at pressures that are roughly two orders of magnitude lower and uses a premixed slurry of relatively low concentration. The objective of the present study was to gain a better understanding of the mechanics of erosion in ASJM by comparing its performance in the micro-machining of holes and channels in borosilicate glass with that of abrasive air jet micro-machining (AJM), a process that is simpler and relatively well understood. A new ASJM system was developed and used to machine blind holes and smooth channels of relatively uniform depth that did not suffer from the significant waviness previously reported in the literature. The effect of particle velocity, particle concentration, jet traverse speed and jet impact angle were examined. A direct comparison of ASJM and AJM results was possible since novel measurements of the crushing strength of the aluminum oxide abrasive particles used in both experiments proved to be unaffected by water. Brittle erosion was shown to be the dominant material removal mechanism in both ASJM and AJM in spite of the significant flow-induced decrease in the local impact angles of many of the particles in ASJM. A new model of the rapid particle deceleration near the target surface helped explain the much smaller erosion rates of ASJM compared with those in AJM. The modeling of the erosion process during the micro-machining of channels showed that the effect of the local impact angle at the leading edge of the advancing jet was much more significant in ASJM than in AJM, primarily due to the narrower focus of the jet impact zone in ASJM. The differences in the water and air flow fields and associated particle trajectories were used to explain the steeper side walls and flatter bottoms of the holes and channels machined with unmasked ASJM compared to those with masked AJM. The respective structures of the water and air jets also explained the much sharper definition of the edges of these features using ASJM compared with maskless AJM. The results of the study show that ASJM can be used to accurately micro-machine channels and holes with a width of 350–500 μm and an aspect ratio of 0.5–1.3 without the use of masks.
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surface roughness and erosion rate of abrasive jet micro machined channels experiments and analytical model
Wear, 2013Co-Authors: Haj Mohammad R Jafar, Jan K. Spelt, M PapiniAbstract:Abstract Abrasive jet micro-machining (AJM) uses a high velocity particle jet to erode features in target substrates for a variety of applications, including micro-electro-mechanical and micro-fluidic device fabrication. The roughness of micro-channels for micro-fluidic applications made using AJM can affect fluid flow phenomena such as separation efficiency, electro-osmotic mobility and solute dispersion. Moreover, surface roughness plays a major role in micro-scale adhesion contact in MEMS and light scattering in optoelectronics devices. This paper presents experimental data on the effect of particle size, velocity, and angle of attack on the roughness of unmasked channels machined in borosilicate glass using AJM. Single impact experiments were conducted to quantify the damage due to the individual alumina particles. Based on these observations, the assumed location of lateral crack initiation in a relatively simple analytical model from the literature was modified, and used to predict the roughness and erosion rate. The previous model, which calculated an areal roughness, was also modified to yield a 2D linear value of R a so that it could be compared with linear profilometer scans. This modified model predicted the steady-state roughness and erosion rate of unmasked channels with average errors of 36% and 73%, respectively.
H Nouraei - One of the best experts on this subject based on the ideXlab platform.
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abrasive enhanced electrochemical slurry jet micro machining comparative experiments and synergistic effects
Journal of Materials Processing Technology, 2014Co-Authors: H Nouraei, Jan K. Spelt, M PapiniAbstract:Abstract Abrasive enhanced electrochemical slurry-jet machining (ESJM) is presented as a new approach to the micro-machining of metals using a combination of abrasive slurry-jet machining (ASJM) and electrochemical jet machining (ECJM). A novel ESJM prototype was developed to generate a charged slurry jet consisting of a mixture of Al2O3 abrasive particles and an electrolytic solution of NaCl and NaNO3. A DC potential of 30 V was applied between the nozzle and specimen. A series of micro-channels were machined in Stellite 12 using ASJM, ECJM and ESJM processes to investigate the relative effects of erosion and anodic dissolution on the material removal rate and surface finish in the combined process of ESJM. The results illustrated that the ESJM process results in significantly greater target mass loss rate than the separate erosion and corrosion processes. The magnitude of the synergistic effect on the rate of mass loss was found to vary from positive to negative as the erosion component increased with increasing particle kinetic energy (jet pressure) and particle concentration. The roughness of the channels machined using ESJM was between that obtained with ASJM and ECJM. The roughness decreased as the erosion component of the total mass loss increased.
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surface evolution models for abrasive slurry jet micro machining of channels and holes in glass
Wear, 2014Co-Authors: H Nouraei, Kamran Kowsari, Marcello Papini, Jan K. SpeltAbstract:Abstract Abrasive slurry jet micro-machining (ASJM) uses a jet of abrasive slurry to erode features with relatively high resolution without the need for a patterned mask. The present study investigated the ability of a surface evolution model to predict the profiles of micro-channels and holes machined in borosilicate glass with a newly developed ASJM system. The system could produce micro-channels with depth and width variations along their length of less than 3%, and a channel-to-channel repeatability within 5%. The fundamental erosion rate of the borosilicate glass was measured as a function of impact angle using a slurry of water mixed with a low concentration of 10 and 25 µm nominal diameter aluminum oxide particles. This erosion rate-impact angle relationship was used in an existing model developed previously for the abrasive air jet micro-machining of brittle materials. The results demonstrated that, despite the differences in abrasive flow patterns between air and slurry based systems, the surface evolution model accurately predicted the profiles of micro-channels with a maximum error of 7% for aspect ratios (depth/width) of up to 5. The predicted profiles of holes were also in reasonable agreement with a maximum error of 14% for aspect ratios close to 1.
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characteristics of abrasive slurry jet micro machining a comparison with abrasive air jet micro machining
Journal of Materials Processing Technology, 2013Co-Authors: H Nouraei, Jan K. Spelt, M Papini, A WodoslawskyAbstract:Abstract Abrasive slurry jet micro-machining (ASJM) uses a well-defined jet of abrasive slurry to erode features in a solid target. Compared with abrasive water jet machining (AWJM), the present ASJM system operates at pressures that are roughly two orders of magnitude lower and uses a premixed slurry of relatively low concentration. The objective of the present study was to gain a better understanding of the mechanics of erosion in ASJM by comparing its performance in the micro-machining of holes and channels in borosilicate glass with that of abrasive air jet micro-machining (AJM), a process that is simpler and relatively well understood. A new ASJM system was developed and used to machine blind holes and smooth channels of relatively uniform depth that did not suffer from the significant waviness previously reported in the literature. The effect of particle velocity, particle concentration, jet traverse speed and jet impact angle were examined. A direct comparison of ASJM and AJM results was possible since novel measurements of the crushing strength of the aluminum oxide abrasive particles used in both experiments proved to be unaffected by water. Brittle erosion was shown to be the dominant material removal mechanism in both ASJM and AJM in spite of the significant flow-induced decrease in the local impact angles of many of the particles in ASJM. A new model of the rapid particle deceleration near the target surface helped explain the much smaller erosion rates of ASJM compared with those in AJM. The modeling of the erosion process during the micro-machining of channels showed that the effect of the local impact angle at the leading edge of the advancing jet was much more significant in ASJM than in AJM, primarily due to the narrower focus of the jet impact zone in ASJM. The differences in the water and air flow fields and associated particle trajectories were used to explain the steeper side walls and flatter bottoms of the holes and channels machined with unmasked ASJM compared to those with masked AJM. The respective structures of the water and air jets also explained the much sharper definition of the edges of these features using ASJM compared with maskless AJM. The results of the study show that ASJM can be used to accurately micro-machine channels and holes with a width of 350–500 μm and an aspect ratio of 0.5–1.3 without the use of masks.
Issam Mudawar - One of the best experts on this subject based on the ideXlab platform.
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effects of jet pattern on two phase performance of hybrid micro channel micro circular jet impingement thermal management scheme
International Journal of Heat and Mass Transfer, 2009Co-Authors: Myung Ki Sung, Issam MudawarAbstract:This paper explores the two-phase cooling performance of a hybrid cooling scheme in which a linear array of Micro-Jets deposits liquid gradually along each channel of a micro-channel heat sink. The study also examines the benefits of utilizing differently sized jets along the micro-channel. Three Micro-Jet patterns, decreasing-jet-size (relative to center of channel), equal-jet-size and increasing-jet-size, were tested using HFE 7100 as working fluid. It is shown feeding subcooled coolant into the micro-channel in a gradual manner greatly reduces vapor growth along the micro-channel. Void fraction increased between jets but decreased sharply beneath each jet, creating a repeated pattern of growth followed by coalesce, and netting only a mild overall increase in void fraction along the flow direction with predominantly liquid flow at outlet. Unlike most flow boiling situations, where pressure drop increases with increasing heat flux, pressure drop in the hybrid configurations actually decreased and reached a minimum just before CHF. This behavior is closely related to the low void fraction and predominantly liquid flow. Pressure drop in the two-phase region is highest for the equal-jet-size pattern, followed by the decreasing-jet-size and increasing-jet-size patterns, respectively. Low void fraction increased the effectiveness of the hybrid cooling schemes in utilizing bulk liquid subcooling and therefore helped achieve high CHF values. The decreasing-jet-size pattern, which had the highest outlet subcooling, achieved the highest CHF. A single correlation was constructed for the three jet patterns, which relates the two-phase heat transfer coefficient to heat flux and wall superheat.
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effects of jet pattern on single phase cooling performance of hybrid micro channel micro circular jet impingement thermal management scheme
International Journal of Heat and Mass Transfer, 2008Co-Authors: Myung Ki Sung, Issam MudawarAbstract:Abstract This study explores the single-phase cooling performance of a hybrid cooling module in which a series of Micro-Jets deposit coolant into each channel of a micro-channel heat sink. This creates symmetrical flow in each micro-channel, and the coolant is expelled through both ends of the micro-channel. Three Micro-Jet patterns are examined, decreasing-jet-size (relative to center of channel), equal-jet-size and increasing-jet-size. The performance of each pattern is examined experimentally and numerically using HFE 7100 as working fluid. Indirect refrigeration cooling is used to reduce the coolant’s temperature in order to produce low wall temperatures during high-flux heat dissipation. A single heat transfer coefficient correlation is found equally effective at correlating experimental data for all three jet patterns. Three-dimensional numerical simulation using the standard k–e model shows excellent accuracy in predicting wall temperatures. Numerical results show the hybrid cooling module involves complex interactions of impinging jets and micro-channel flow. Increasing the coolant’s flow rate strengthens the contribution of jet impingement to the overall cooling performance, and decreases wall temperature. However, this advantage is realized at the expense of greater wall temperature gradients. The decreasing-jet-size pattern yields the highest convective heat transfer coefficients and lowest wall temperatures, while the equal-jet-size pattern provides the greatest uniformity in wall temperature. The increasing-jet-size pattern produces complex flow patterns and greater wall temperature gradients, which are caused by blockage of spent fluid flow due to the impingement from larger jets near the channel outlets.
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single phase hybrid micro channel micro jet impingement cooling
International Journal of Heat and Mass Transfer, 2008Co-Authors: Myung Ki Sung, Issam MudawarAbstract:Abstract A new hybrid cooling scheme is proposed for high-flux thermal management of electronic and power devices. This scheme combines the cooling benefits of micro-channel flow and Micro-Jet impingement with those of indirect refrigeration cooling. Experiments were performed to assess single-phase cooling performance using HFE 7100 as working fluid. Excellent predictions were achieved using the standard k–e model. The proposed cooling scheme is shown to involve complex interactions of impinging jets with micro-channel flow. Increasing jet velocity allows jets to penetrate the micro-channel flow toward the heated surface, especially in shallow micro-channels, greatly decreasing wall temperature. Despite the relatively poor thermophysical properties of HFE 7100, the proposed cooling scheme facilitated the dissipation of 304.9 W/cm2 without phase change; further improvement is possible by increasing jet velocity and/or decreasing coolant temperature. In addition to the numerical predictions, a superpositioning technique is introduced that partitions the heat transfer surface into zones that are each dominated by a different heat transfer mechanism, and assigning a different heat transfer coefficient value to each zone. Using this technique, a new correlation is developed that fits the data with a mean absolute error of 6.04%.
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single phase and two phase heat transfer characteristics of low temperature hybrid micro channel micro jet impingement cooling module
International Journal of Heat and Mass Transfer, 2008Co-Authors: Myung Ki Sung, Issam MudawarAbstract:Abstract This study examines the single-phase and two-phase cooling performance of a hybrid micro-channel/Micro-Jet impingement cooling scheme using HFE 7100 as working fluid. This scheme consists of supplying coolant from a series of jets that deposit liquid into the micro-channels. A single-phase numerical scheme that utilizes the k–e turbulent model and a method for determining the extent of the laminarized wall layer shows very good predictions of measured wall temperatures. It is shown jet velocity has a profound influence on single-phase cooling performance. High jet velocities enable jet fluid to penetrate the axial micro-channel flow and produce a strong impingement effect at the wall. On the other hand, the influence of jets at low jet velocities is greatly compromised compared to the micro-channel flow. During nucleate boiling, vapor layer development along the micro-channel in the hybrid module is fundamentally different from that encountered in conventional micro-channels. Here, subcooled jet fluid produces repeated regions of bubble growth followed by bubble collapse, rather than the continuous growth common to conventional micro-channel flow. By reducing void fraction along the micro-channel, the hybrid scheme contributes greater wall temperature uniformity. Increasing subcooling and/or flow rate delay the onset of boiling to higher heat fluxes and higher wall temperatures, and also increase critical heat flux considerably. A nucleate boiling heat transfer coefficient correlation is developed that fits the present data with a mean absolute error of 6.10%.
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experimental and numerical investigation of single phase heat transfer using a hybrid jet impingement micro channel cooling scheme
International Journal of Heat and Mass Transfer, 2006Co-Authors: Myung Ki Sung, Issam MudawarAbstract:Abstract Experimental and numerical methods were used to explore the cooling performance of a new hybrid device consisting of a slot jet impinging into a micro-channel, thus capitalizing upon the merits of both cooling configurations. The three-dimensional heat transfer characteristics of this device were analyzed using the standard k–e turbulent model. Numerical predictions for liquid PF-5052 show excellent agreement with experimental measurements. Vorticity effects are shown to greatly influence cooling performance outside the impingement zone. Higher jet Reynolds numbers yielded stronger attachment to the heated surface and lower surface temperatures. The model was also used to optimize the cooling performance for a water-cooled device. Lower surface temperatures were achieved by decreasing jet width and micro-channel height. These findings are used to recommend a simplified hybrid cooling geometry in pursuit of both lower surface temperatures and smaller temperature gradients across the heated surface.
Jun Wang - One of the best experts on this subject based on the ideXlab platform.
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an experimental study of the abrasive water jet micro machining process for quartz crystals
Advanced Materials Research, 2012Co-Authors: Jing Ming Fan, Jun WangAbstract:An experimental study of the machining process for micro-channels on a brittle quartz crystal material by an abrasive slurry jet (ASJ) is presented. A statistical experiment design considering the major process variables is conducted, and the machined surface morphology and channelling performance are analysed to understand the micro-machining process. It is found that a good channel top edge appearance and bottom surface quality without wavy patterns can be achieved by employing relatively small particles at shallow jet impact angles. The major channel performance measures, i.e. material removal rate (MRR) and channel depth, are then discussed with respect to the process parameters. It shows that with a proper control of the process variables, the abrasive water jet (AWJ) technology can be used for the micro-machining of brittle materials with high quality and productivity.
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modeling the material removal rate in micro abrasive water jet machining of glasses
Advanced Materials Research, 2010Co-Authors: Jing Ming Fan, Chang Ming Fan, Jun WangAbstract:Micro abrasive water jet (MAWJ) machining is a new promising micro machining technology for brittle material. The rate of material removal is one of the most important parameter for abrasive processes. Predictive mathematical model for the material removal rate is presented for micro channel machining by micro abrasive water jet (MAWJ). A dimensional analysis technique is used to formulate the model. The validity and predictive capability of the models are assessed and verified by an experimental investigation when machining glasses. It shows that the predictions of the models are in good agreement with the experimental data.
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machining of micro channels on brittle glass using an abrasive slurry jet
Key Engineering Materials, 2010Co-Authors: King Lun Pang, Thai Nguyen, Jun WangAbstract:This paper presents a study of using an abrasive slurry jet for the machining of micro channels on brittle glasses. The machined surface morphology and channel dimensions are used to assess the technology. Surface morphology was found featuring with two types of wave patterns; one was along the channels with large wave lengths as a result of the jet deflection during the motion of nozzle, and the other was due to viscous flow that resulted in smooth surface eroded predominantly by ductile mode. The investigation showed that using higher jet pressure and higher particle concentration enables to create channels with higher depth, although these widened the channels and degraded the surface quality in some cases by inducing a larger number of pit fragments on the surface. With proper control of the operating parameters, this technology can be used for machining micro channels on brittle materials with high quality of surface finish.
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analysis and modelling of particle velocities in micro abrasive air jet
International Journal of Machine Tools & Manufacture, 2009Co-Authors: Jun Wang, Jing Ming FanAbstract:Abrasive jet micromachining (AJM) is a non-traditional technology that can effectively remove hard and brittle materials at high cut quality. A key requisite in modelling the AJM process is to determine the velocities of abrasive particles. In this paper, a theoretical analysis for particle velocities within a micro-abrasive air jet is presented and the associated particle velocity models are developed. The particle velocities at the nozzle exit are determined based on the nozzle length, particle mean diameter, particle density, air density and air flow velocity. The distribution of particle velocities along the jet centerline downstream from the nozzle and the particle velocity profile at a jet cross-section are also modelled considering surrounding air entrainment and air-particle interaction. A numerical solution to the models is developed to determine the particle velocities by dividing the nozzle and the jet flow in air into small segments along the jet axial direction. The developed models are finally verified by comparing the calculated particle velocities with those from a particle image velocimetry (PIV) measurement of the velocity distribution in micro-abrasive air jets. It is shown that the model calculations and the corresponding experimental results are in good agreement with less than 4% average errors.
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modelling the erosion rate in micro abrasive air jet machining of glasses
Wear, 2009Co-Authors: Jing Ming Fan, Cheng Yong Wang, Jun WangAbstract:Micro abrasive jet machining (MAJM) is an economical and efficient technology for micro-machining of brittle material like glasses. The erosion of brittle materials by solid micro-particles is a complex process in which material is removed from the target surface by brittle fractures. The rate of material removal is one of the most important quantities for a machining process. Predictive mathematical models for the erosion rates in micro-hole drilling and micro-channel cutting on glasses with an abrasive air jet are developed. A dimensional analysis technique is used to formulate the models as functions of the particle impact parameters, target material properties and the major process parameters that are known to affect the erosion process of brittle materials. The predictive capability of the models is assessed and verified by an experimental investigation covering a range of the common process parameters such as air pressure, abrasive mass flow rate, stand-off distance and machining time (for hole machining) or traverse speed (for channel machining). It shows that model predictions are in good agreement with the experimental results.