ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels最新文献

{"title":"Atmospheric Condensation Performance of Plain Copper and Graphene Oxide Coated Copper Surfaces","authors":"M. R. Haque, A. Betz","doi":"10.1115/ICNMM2018-7610","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7610","url":null,"abstract":"Atmospheric condensation is important for multiple practical applications such as distillation/desalination of water, aerospace, dehumidification, and water harvesting etc. Graphene, an allotrope of carbon with two dimensional structure, has excellent thermal and electrical properties. Here we present condensation studies of water on plain copper and graphene oxide (GO) coated copper surface with different environmental conditions to explore the size distribution of the generated droplets and area coverage in order to characterize the surfaces for larger condensate harvesting. Later, droplet growth and size distributions were recorded for 41 minutes 20 seconds on the surfaces at 40% and 60% relative humidities with a surface temperature of 278 ± 0.5 K. The chamber was maintained at atmospheric pressure and 295 ± 0.5 K. The samples were observed via optical microscopy and videos of the condensation dynamics were captured. The droplet grew mainly by direct condensation and coalescence event. At later stages of condensation, surface coverage increased significantly compared to early stages for all the considered cases. Approximate 95% surface coverage was observed for GO coated copper surface which provides a great insight of this substrates for implementing it in the desired water harvesting applications. The pinning of droplets into the micro/nanostructures of the coated surfaces leads enough time for the first generation droplets to grow in larger size and made more preferential for subsequent coalescence events. Within the initial period of condensation, the number of droplets reduced according to power law decay. The contribution of coalescence mechanism in droplet growth was found larger for 60% RH than 40% RH. As droplet grew larger, direct growth became less significant compared to coalescence phenomenon.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134603440","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes","authors":"Jensen Hoke, T. Bandhauer, J. Kotovsky, J. Hamilton, Paul Fontejon","doi":"10.1115/ICNMM2018-7664","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7664","url":null,"abstract":"Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128784129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Frost Formation on Aluminum and Hydrophobic Surfaces","authors":"M. R. Haque, A. Betz","doi":"10.1115/ICNMM2018-7609","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7609","url":null,"abstract":"Ice and frost formation on the surfaces of car windshield, airplanes, air-conditioning duct, transportation, refrigeration and other structures is of great interest due to its negative impact in the efficiency and reliability of the system. Frost formation is a complex and fascinating phenomenon. Frequent defrosting are required to remove the ice that causes economic losses. In order to delay the freezing phenomenon, hydrophobic surfaces (Al-H) were prepared using a very simple and low cost method by dip coating of Aluminum in Teflon© and FC - 40 solution at a ratio of 2:10. Later, the samples were placed on a freezing stage in a computer controlled environmental chamber. The freezing stage was held at a constant temperature of 265 ± 0.5 K. The environmental temperature was set to 295 ± 0.5 K and the relative humidity (RH) was set to 40% and 60% respectively. The samples were observed via optical microscopy from the top and videos of the freezing dynamics were captured. The time required for the whole surface to freeze was named as ‘Freezing time’ and is determined by investigating the consecutive images. The inter-droplet freezing wave propagation was accelerated via a frozen droplet/area and then propagates through the surface very quickly. Ice bridging was also seen for the frost propagation. However, the maximum freezing front propagation velocity was found for Al surfaces at 60% RH. At 40% RH, the Al surface required approximately 10 ± 1 minutes to freeze while the Al-H surface delay freezing until 15 ± 1 minutes. This is due to a slow rate of nucleation and also increased rate of coalescence. At 60% RH, both surface froze faster than 40% RH. The Al surface required 6.5 ± 1 minutes and the Al-H surface froze after 10 ± 1 minutes. The change in freezing kinetics, freezing time, the size of droplets at freezing, and the surface area covered at freezing are all related to the rate of coalescence of droplets. Again, the added thermal resistance of the coating and less water-surface contact area of the droplet to the cooled hydrophobic surface inhibited the growth rate resulting the freezing delay.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"121 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123157075","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Electrode Configurations on the Performance of Electro-Hydrodynamic Micromixer","authors":"Hak-Sun Kim, Hyun-Oh Kim, Youn-J. Kim","doi":"10.1115/ICNMM2018-7654","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7654","url":null,"abstract":"Micromixers are widely used in chemical engineering and bioengineering industries. In this study, geometrical effects of electrodes were investigated to mix fine particles affected by external electric field. In order to improve the particle mixing performance of micromixer, the electroosmosis effect could be utilized with configuration of electrodes at the top and bottom of microchannel. Numerical analysis was performed to derive the pattern of electrodes with superior mixing efficiency by changing voltages and zeta potentials applied to the micromixer channel, by using COMSOL Multiphysics 5.2. The results of mixing performance were graphically depicted with various arrangements of electrode and flow conditions.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132825626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spontaneous Displacement of Resident Fluid in Heterogeneous Porous Medium","authors":"Shabina Ashraf, J. Phirani","doi":"10.1115/ICNMM2018-7737","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7737","url":null,"abstract":"Surface tension driven flow in which one fluid displaces another is of importance in microfluidic devices for diagnostics, lab on chip devices and flow in oil reservoirs. Spontaneous impregnation of a preferentially wetting phase displacing an existing non-wetting phase in a homogeneous porous medium is known to follow diffusive dynamics. However, in a heterogeneous porous medium the hydrodynamic interaction between the narrow and the wide pores significantly alters the impregnation behavior. Previous studies have shown that the imbibing fluid interface leads in the narrow pores contrary to the predictions from the diffusive dynamics of homogeneous porous medium. This is due to the higher suction pressure in the narrow pores which draw fluid from the wide pores. The effect of fluid properties and relative flow properties of the pores with respect to other pores on the non-wetting fluid displacement in the heterogeneous porous medium is still unknown. In the current work, we develop a quasi one-dimensional, lubrication approximation model, which predicts the spontaneous imbibition in a heterogeneous porous medium. We explore all the possible relative fluid properties and flow properties of the layers in the heterogeneous porous medium and show that our model is able to predict the flow behavior in all the cases. We also present the results of the spontaneous imbibition experiments, which agree with our model. The experiments show that the two phase interface progresses faster in the narrow pores as predicted by the one-dimensional model. The result is important for predicting and controlling the flow behavior in a heterogeneous porous medium.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114745378","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Theoretical and Experimental Analysis of Increasing Pressure During Pool-Boiling","authors":"Smreeti Dahariya, A. Betz","doi":"10.1115/ICNMM2018-7673","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7673","url":null,"abstract":"The thermo-fluid properties of water change at high pressure. The performance of high pressure pool boiling greater than 50 Psi has not been studied widely. The aim of this paper is to analyze the experimental data to describe the effect of increasing pressure during pool boiling. Hsu’s correlation was used to predict the active nucleation sites. The maximum and minimum radii of the active nucleation sites were determined as a function of heat flux or degree of wall superheats over a wide range of pressures. The bubble dynamics are discussed using the predicted values of fundamental boiling quantities such as bubble departure diameter, active nucleation site density and bubble release frequency. The thickness of the boundary layer was assumed to be 30 microns. Rohsenow’s and Forster’s correlations were used to predict the pool boiling curve for different pressures. The comparison was made with the experimental data for water of a plain copper surface of increasing pressure. The parametric trend provides fundamental insight and explains how the system pressure can maximize the boiling efficiency of new generation boilers.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122699024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental Study of Nucleate Flow Boiling to Convective Flow Boiling Transition in a Horizontal Heated Pipe","authors":"C. Dorao, F. Morin, M. Fernandino","doi":"10.1115/ICNMM2018-7682","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7682","url":null,"abstract":"In flow boiling, two different mechanisms, namely nucleate boiling and convective boiling, are considered to be dominant at different working conditions while superimposing in a transition regime. The transition between these two regimes has been considered in different ways in available correlations in the literature. However, few experimental studies have focused on the characteristics of such transition. In this work the nucleate flow boiling-convective flow boiling transition is studied experimentally in a horizontal heated pipe of 5mm ID using R134a as working fluid. The study consist on varying the local hat flux while maintaining the mass flux, pressure and local quality fixed. It is shown that the transition is quite sharp indicating that the superimposing of both mechanism is rather limited.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131509620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Miniaturized Tubular Cooling Crystallizer With Solid-Liquid Flow for Process Development","authors":"Mira Schmalenberg, L. Hohmann, N. Kockmann","doi":"10.1115/ICNMM2018-7660","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7660","url":null,"abstract":"Production of fine chemicals and pharmaceuticals often includes solid-liquid suspension flow. For continuous cooling a tubular crystallizer was designed based on the coiled flow inverter (CFI) concept, providing a narrow residence time distribution (RTD) of the liquid phase. Counter-current cooling allows for a smooth adjustment of the axial temperature profile. Successful operation of up to 50 g min−1 in a prototype with 4 mm inner diameter was scaled down to a tube-in-tube CFI crystallizer (CFIC) with an inner diameter of 1.6 mm and varying length from 7.8 to 54.6 m. This leads to a significantly lower consumption of chemicals in process development with lower total mass flow rates of 15–20 g min−1. Due to modular design, mean residence time (3.8 to 6.9 min) and mean cooling rate (0.6 to 1.4 K·min−1) were varied at constant mass flow rate. Crystallization growth rate and yield are analyzed with the L-alanine/water test system and seed crystals of 125–180 μm.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125341045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transient Thermal Characteristics for a Liquid Drop Impacting a Hot PCM Substrate","authors":"A. A. Khan, Dilip Choudhary, Abhishek Basavanna, S. Najmee, Jessica Crisantes, N. Dhillon","doi":"10.1115/ICNMM2018-7694","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7694","url":null,"abstract":"The physics of the transient behavior of liquid drops impacting hot or cold surfaces are of significance in many different applications such as spray cooling, aircraft icing, etc. Further, the transient heating and cooling of vapor spots and liquid patches is of significance in determining the heat transfer performance parameters in phase change processes such as boiling and condensation. The thermal transients in all these processes are primarily dictated by the passive thermal properties of the solid substrate (e.g. thermal conductivity, specific heat) and by the flow conditions. An active control (or manipulation) of these thermal transients could provide a means to enhance the performance parameters in various phase change-based heat transfer processes. In this study, we experimentally explore the effect of a solid-liquid phase change material (PCM) coating on the thermal characteristics of a liquid drop impacting a hot surface. High-speed optical and infrared imaging techniques are employed for visualizing the flow and measuring the temperatures, respectively. The PCM, depending on its melting temperature and due to its latent heat of fusion, disrupts the normal process of the heating of the drop and cooling of the substrate. The insights obtained from these findings can have a significant impact on several technologies in the areas of phase change-based heat transfer and thermal management.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"39 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126968449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Saturated Nucleate Pool Boiling of Ethanol-Water Binary Mixtures on Smooth and Enhanced Laser Processed Metal Surfaces","authors":"M. Zupančič, J. Voglar, P. Gregorčič, I. Golobič, Peter Zakšek","doi":"10.1115/ICNMM2018-7755","DOIUrl":"https://doi.org/10.1115/ICNMM2018-7755","url":null,"abstract":"Pool boiling experiments of water and ethanol-water binary mixtures were conducted on smooth and laser textured stainless steel foils. High-speed IR thermography was used to measure transient temperature field during boiling in order to determine nucleation frequencies, nucleation site densities, bubble activation temperatures, wall-temperature distributions and average superheats as well as heat transfer coefficients. Saturated pool boiling experiments were conducted at atmospheric pressure over a heat flux range of 5–250 kW m−2 for pure water and ethanol-water mixtures (1% and 10% m/m). For both mixtures and both types of surfaces we measured significant decrease in average heat transfer coefficient and increase in bubble activation temperatures in comparison to pure water. However, laser textured surface in average provided around 60% higher nucleation frequency and more than 100% higher nucleation site density compared to smooth surface for both of the tested binary mixtures. Consequentially, heat transfer coefficient was enhanced for more than 30%. Our results show that laser textured surfaces can improve boiling performance for water and ethanol-water mixtures, but at the same time the addition of ethanol reduces heat transfer coefficient despite the enhancement of nucleation site density and nucleation frequency. This is also in agreement with available experimental data and existing theoretical models.","PeriodicalId":137208,"journal":{"name":"ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115099692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}