Boiling heat transfer serves as an efficient mechanism to dissipate large amounts of thermal energy due to the latent heat of phase change. In academic studies, typically ultra-pure deionized (DI) water is used to avoid contamination. However, in industrial and commercial settings, the working fluid might be contaminated with sediments, dust, salts, or organic matter. Long-term boiling processes in non-DI water cause substantial build-up of a stable layer of deposit that dramatically reduces the heat transfer coefficient. Therefore, heating applications in a contaminated medium demand strategies to prevent such fouling. Here, we studied the use of lubricant infused surfaces (LIS) and their ability to possibly minimize the deposition of calcium sulfate. Aluminum samples were infused with Krytox 102 oil and the heat transfer coefficient was investigated at a vertical and horizontal surface orientation. Fouling effects were introduced by pool boiling for 7.5 hours in a 6.97 mM calcium sulfate solution at constant heat flux. Heat flux curves for both plain aluminum and LIS were calibrated before contamination. Initially, the LIS was unable to support a nucleate phase and transitioned directly from liquid convection to film boiling heat transfer. Upon partial degradation of the lubricant layer during long-run experiments, nucleate boiling ensued. Over 7.5 hours, the heat transfer coefficient of each sample (Al and LIS) degraded between 5.4% and 7.9% with no significant correlation with either lubricant treatment or surface orientation. Post boiling profilometry was conducted on each sample to characterize the thickness and distribution of the calcium sulfate layer. In these experiments, the plain aluminum surface outperformed the LIS at both orientations in minimizing calcium layer thickness. The LIS oriented vertically outperformed the LIS oriented horizontally.
{"title":"Evolution of Heat Transfer in Pool Boiling in Contaminated Water","authors":"Jacob D. Graham, A. Hawa, Patricia B. Weisensee","doi":"10.1115/icnmm2020-1041","DOIUrl":"https://doi.org/10.1115/icnmm2020-1041","url":null,"abstract":"\u0000 Boiling heat transfer serves as an efficient mechanism to dissipate large amounts of thermal energy due to the latent heat of phase change. In academic studies, typically ultra-pure deionized (DI) water is used to avoid contamination. However, in industrial and commercial settings, the working fluid might be contaminated with sediments, dust, salts, or organic matter. Long-term boiling processes in non-DI water cause substantial build-up of a stable layer of deposit that dramatically reduces the heat transfer coefficient. Therefore, heating applications in a contaminated medium demand strategies to prevent such fouling. Here, we studied the use of lubricant infused surfaces (LIS) and their ability to possibly minimize the deposition of calcium sulfate. Aluminum samples were infused with Krytox 102 oil and the heat transfer coefficient was investigated at a vertical and horizontal surface orientation. Fouling effects were introduced by pool boiling for 7.5 hours in a 6.97 mM calcium sulfate solution at constant heat flux. Heat flux curves for both plain aluminum and LIS were calibrated before contamination. Initially, the LIS was unable to support a nucleate phase and transitioned directly from liquid convection to film boiling heat transfer. Upon partial degradation of the lubricant layer during long-run experiments, nucleate boiling ensued. Over 7.5 hours, the heat transfer coefficient of each sample (Al and LIS) degraded between 5.4% and 7.9% with no significant correlation with either lubricant treatment or surface orientation. Post boiling profilometry was conducted on each sample to characterize the thickness and distribution of the calcium sulfate layer. In these experiments, the plain aluminum surface outperformed the LIS at both orientations in minimizing calcium layer thickness. The LIS oriented vertically outperformed the LIS oriented horizontally.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123293419","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}
This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.
{"title":"Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps","authors":"D. Moreira, G. Ribatski, S. Kandlikar","doi":"10.1115/icnmm2020-1012","DOIUrl":"https://doi.org/10.1115/icnmm2020-1012","url":null,"abstract":"\u0000 This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122059796","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}
P. Raghupathi, A. Owens, M. Steinke, T. Lin, Ankit Kalani, D. C. Moreira, J. Gonzalez-Hernandez, Zujie Lu, R. Banerjee, Michael M. Daino, Arvind Jaikumar, A. Chauhan, A. Rishi, I. Perez-Raya, Travis S. Emery, Fernando Guimarães Aguilar
Professor Satish G. Kandlikar has been an outstanding researcher in the field of heat transfer having published some of the most widely cited publications over the last 30 years. Through the years he has co-authored 212 journal paper in various areas of heat transfer. The present paper provides a compressive look at Professor Kandlikar’s research work over the years. The research work has been broadly categorized into 1) flow boiling correlations, 2) fluid flow and heat transfer in microchannels, 3) roughness effect at microscale, 4) pool boiling heat transfer and CHF modeling, 5) surface enhancements for pool boiling, 6) numerical modeling of bubble growth in boiling, 7) modeling liquid-vapor and liquid-liquid interfaces, 8) water transport in PEM fuel cells and 9) infrared imaging to detect breast cancer. The research conducted in each of these areas has produced some landmark findings, some of the most widely used theoretical models and an abundance of high quality experimental data. The focus of this paper is to collate major finding and highlights some of the common themes that guided the research in Professor Kandlikar’s group. This will help the readers gain a comprehensive understanding of each of the areas of study in Professor Kandlikar’s group and place the findings of the paper in a larger context.
教授Satish G. Kandlikar一直是一个杰出的研究人员在传热领域发表了一些最广泛引用的出版物在过去的30年。多年来，他在传热的各个领域共同撰写了212篇期刊论文。本文简要介绍了坎德利卡教授多年来的研究工作。研究工作大致分为:1)流动沸腾的相关性，2)微通道内的流体流动和传热，3)微尺度下的粗糙度效应，4)池沸腾传热和CHF建模，5)池沸腾的表面增强，6)沸腾中气泡生长的数值模拟，7)液体-蒸汽和液体-液体界面的模拟，8)PEM燃料电池中的水传输，9)红外成像检测乳腺癌。在这些领域进行的研究产生了一些具有里程碑意义的发现，一些最广泛使用的理论模型和大量高质量的实验数据。本文的重点是整理主要发现，并突出一些共同的主题，指导研究在Kandlikar教授的小组。这将有助于读者对Kandlikar教授小组的每个研究领域有一个全面的了解，并将论文的发现置于更大的背景下。
{"title":"Insight to Innovation: An Overview of Research Journey of Dr. Satish Kandlikar","authors":"P. Raghupathi, A. Owens, M. Steinke, T. Lin, Ankit Kalani, D. C. Moreira, J. Gonzalez-Hernandez, Zujie Lu, R. Banerjee, Michael M. Daino, Arvind Jaikumar, A. Chauhan, A. Rishi, I. Perez-Raya, Travis S. Emery, Fernando Guimarães Aguilar","doi":"10.1115/icnmm2020-1071","DOIUrl":"https://doi.org/10.1115/icnmm2020-1071","url":null,"abstract":"\u0000 Professor Satish G. Kandlikar has been an outstanding researcher in the field of heat transfer having published some of the most widely cited publications over the last 30 years. Through the years he has co-authored 212 journal paper in various areas of heat transfer. The present paper provides a compressive look at Professor Kandlikar’s research work over the years. The research work has been broadly categorized into 1) flow boiling correlations, 2) fluid flow and heat transfer in microchannels, 3) roughness effect at microscale, 4) pool boiling heat transfer and CHF modeling, 5) surface enhancements for pool boiling, 6) numerical modeling of bubble growth in boiling, 7) modeling liquid-vapor and liquid-liquid interfaces, 8) water transport in PEM fuel cells and 9) infrared imaging to detect breast cancer. The research conducted in each of these areas has produced some landmark findings, some of the most widely used theoretical models and an abundance of high quality experimental data. The focus of this paper is to collate major finding and highlights some of the common themes that guided the research in Professor Kandlikar’s group. This will help the readers gain a comprehensive understanding of each of the areas of study in Professor Kandlikar’s group and place the findings of the paper in a larger context.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125305531","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}
L. Christensen, Stefan Holebæk, Nisanthan Thanabalasingham, J. Hærvig, H. Sørensen
The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry. The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3). It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.
这个项目的范围是研究挡板的几何形状如何影响Re = 1000时流过方形管道的流体的传热和压力损失。为此，进行了大涡模拟，研究了挡板高度和挡板宽度的影响。重点是完全发展的流动，在流向站重复自己。利用粒子图像测速技术对计算流体动力学模拟预测的流场进行了验证。根据努塞尔数Nu和损耗系数f对不同的设计进行评估，这些系数使用由无挡板的方形管道组成的参考几何形状进行归一化。将这两个参数合并为一个性能参数eta η = (Nu/Nu0)/(f / f0)(1/3)。结果表明，添加挡板可使η增大四倍。减小折流板的高度可以减少传热，同时显著降低压力损失，最终得到更高的η值。减小挡板高度也会增大上壁面的温度梯度，减小下壁面的温度梯度。减小挡板宽度导致最大的温度梯度，但导致流体内部传热不良。
{"title":"Fully-Developed Convective Heat Transfer and Pressure Drop in a Square Duct With Baffle Inserts Using CFD Analysis","authors":"L. Christensen, Stefan Holebæk, Nisanthan Thanabalasingham, J. Hærvig, H. Sørensen","doi":"10.1115/icnmm2020-1066","DOIUrl":"https://doi.org/10.1115/icnmm2020-1066","url":null,"abstract":"\u0000 The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry.\u0000 The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3).\u0000 It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125418192","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}
Flow boiling heat transfer in microchannels can remove high heat loads from restricted spaces with high heat transfer coefficients and minimum temperature gradients. However, many works still report problems with instabilities, high pressure drop and early critical heat flux, which hinder its possible applications as thermal management solutions. Much comprehension on the phenomena concerning flow boiling heat transfer is still missing, therefore many investigations rely on empirical methods and parametric studies to develop novel configurations of more efficient heat sinks. Nevertheless, investigations involving vapor extraction have successfully addressed all these previously reported issues while also increasing the heat transfer of heat sinks employing flow boiling in microchannels. In this sense, the objective of this review is to identify the main techniques employed for vapor extraction in microchannels-based heat sinks and analyze the physical mechanisms underneath the observed improvements during flow boiling, such that some design guidelines can be drawn. Three main strategies can be identified: passive vapor extraction, active vapor extraction, and membrane-based vapor extraction. All these strategies were able to dissipate heatfluxes higher than 1 kW/cm2, with the best performance achieved by a membrane-based heat sink, followed by active and passive designs. According to the present experimental and numerical data available in the literature, there is still room for improvement.
{"title":"Review of Enhancement Techniques With Vapor Extraction During Flow Boiling in Microchannels","authors":"D. Moreira, G. Ribatski, S. Kandlikar","doi":"10.1115/icnmm2020-1068","DOIUrl":"https://doi.org/10.1115/icnmm2020-1068","url":null,"abstract":"\u0000 Flow boiling heat transfer in microchannels can remove high heat loads from restricted spaces with high heat transfer coefficients and minimum temperature gradients. However, many works still report problems with instabilities, high pressure drop and early critical heat flux, which hinder its possible applications as thermal management solutions. Much comprehension on the phenomena concerning flow boiling heat transfer is still missing, therefore many investigations rely on empirical methods and parametric studies to develop novel configurations of more efficient heat sinks. Nevertheless, investigations involving vapor extraction have successfully addressed all these previously reported issues while also increasing the heat transfer of heat sinks employing flow boiling in microchannels. In this sense, the objective of this review is to identify the main techniques employed for vapor extraction in microchannels-based heat sinks and analyze the physical mechanisms underneath the observed improvements during flow boiling, such that some design guidelines can be drawn. Three main strategies can be identified: passive vapor extraction, active vapor extraction, and membrane-based vapor extraction. All these strategies were able to dissipate heatfluxes higher than 1 kW/cm2, with the best performance achieved by a membrane-based heat sink, followed by active and passive designs. According to the present experimental and numerical data available in the literature, there is still room for improvement.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116403732","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}
Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties in applications such as electronics cooling and lab-on-chip. Here, an expression is developed to characterize the hydrodynamic slip in a laminar flow which occurs near the surface for the case when positive meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered shear free. The no slip condition exists at the tips of the ridges. Conformal maps from the literature are used to derive an expression which is a function of cavity fraction of the surface. The positive protrusion angle is 90 degrees. Cavity fractions range from 0 to 75%.
{"title":"Slip in the Presence of Semi-Circular Menisci Between Parallel Ridges","authors":"L. Lam, Y. Muzychka","doi":"10.1115/icnmm2020-1074","DOIUrl":"https://doi.org/10.1115/icnmm2020-1074","url":null,"abstract":"\u0000 Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties in applications such as electronics cooling and lab-on-chip. Here, an expression is developed to characterize the hydrodynamic slip in a laminar flow which occurs near the surface for the case when positive meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered shear free. The no slip condition exists at the tips of the ridges. Conformal maps from the literature are used to derive an expression which is a function of cavity fraction of the surface. The positive protrusion angle is 90 degrees. Cavity fractions range from 0 to 75%.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133144081","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}
Rohan Sharma, Scott Shirley, Tahir Farrukh, M. Kavosi, Myeongsub Kim
Biofuel is one of the renewable energy resources alternatives to fossil fuels [1]. Among various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting performance, making such a fuel less competitive. To increase the separation performance of microalgae from cultivation solution, we used a spiral microchannel that enables the isolation of biofuel-algae particles from water and contaminants contained in the culturing solution. Our preliminary data show that separation performance in the microfluidic centrifugal separator is as high as 88% within a quick separation time of 30 seconds. To optimize separation performance, multiple parameters of algae behaviors and separation techniques were studied and were manipulated to achieve better performance. We found that changing these factors altered the separation performance by increasing or decreasing flocculation, or “clumping” of the microalgae within the microchannels. The important characteristics of the separator geometry, fluid properties, and environmental conditions on algae separation was found and will be further studied in the forthcoming tests. This introductory study reveals that there is an opportunity to improve the currently low performance of algae separation in centrifugal systems using much smaller designs in size, ensuring a much more efficient algae harvesting.
{"title":"Microalgae Harvesting in a Microfluidic Centrifugal Separator for Enhanced Biofuel Production","authors":"Rohan Sharma, Scott Shirley, Tahir Farrukh, M. Kavosi, Myeongsub Kim","doi":"10.1115/icnmm2020-1078","DOIUrl":"https://doi.org/10.1115/icnmm2020-1078","url":null,"abstract":"\u0000 Biofuel is one of the renewable energy resources alternatives to fossil fuels [1]. Among various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting performance, making such a fuel less competitive. To increase the separation performance of microalgae from cultivation solution, we used a spiral microchannel that enables the isolation of biofuel-algae particles from water and contaminants contained in the culturing solution. Our preliminary data show that separation performance in the microfluidic centrifugal separator is as high as 88% within a quick separation time of 30 seconds. To optimize separation performance, multiple parameters of algae behaviors and separation techniques were studied and were manipulated to achieve better performance. We found that changing these factors altered the separation performance by increasing or decreasing flocculation, or “clumping” of the microalgae within the microchannels. The important characteristics of the separator geometry, fluid properties, and environmental conditions on algae separation was found and will be further studied in the forthcoming tests. This introductory study reveals that there is an opportunity to improve the currently low performance of algae separation in centrifugal systems using much smaller designs in size, ensuring a much more efficient algae harvesting.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117294986","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}
Particle laden polymeric flows are of interest to the fluid mechanics community due to the possibility of flow induced aggregation and structure formation. Here, we show that when particle laden polymeric suspensions flow through an annular area at moderate Reynolds numbers (∼ 10) and Weissenberg numbers (∼ 10−2–10−1), it can result in formation of flow induced structures. Specifically, the particle can aggregate in the form of thin slender, flexible structures called streamers. The name ‘streamer’ is inspired by their slender morphology which is similar to bacterial streamers formed in bacterial aggregation subjected to continuous hydrodynamic flow. In the present work, polyethylene oxide (PEO) and dry gram flour has been used to create particle laden polymeric fluid suspension. The Taylor-Couette geometry has been modified by employing a stationary needle in the annular space to study the effect of varying hydrodynamic conditions on streamer formation and their morphology. Experimental observations show that depending on the polymer to particle concentration ratio (Cpolymer/Cparticle) and the hydrodynamic condition, different morphologies of streamers can be obtained. This is collated in the form of a state diagram. Surprisingly, it is observed that aged polymeric suspensions enhance streamer formation when employed in conjunction with gram flour powder that function as colloidal particles. Zeta potential and rheological measurements have been performed to gain further insights on the change in properties of polymer on account of ageing.
{"title":"Streamer Formation in Particle Laden Polymeric Flows","authors":"N. Chandra, Aloke Kumar, Hossein Ebrahimi","doi":"10.1115/icnmm2020-1069","DOIUrl":"https://doi.org/10.1115/icnmm2020-1069","url":null,"abstract":"\u0000 Particle laden polymeric flows are of interest to the fluid mechanics community due to the possibility of flow induced aggregation and structure formation. Here, we show that when particle laden polymeric suspensions flow through an annular area at moderate Reynolds numbers (∼ 10) and Weissenberg numbers (∼ 10−2–10−1), it can result in formation of flow induced structures. Specifically, the particle can aggregate in the form of thin slender, flexible structures called streamers. The name ‘streamer’ is inspired by their slender morphology which is similar to bacterial streamers formed in bacterial aggregation subjected to continuous hydrodynamic flow. In the present work, polyethylene oxide (PEO) and dry gram flour has been used to create particle laden polymeric fluid suspension. The Taylor-Couette geometry has been modified by employing a stationary needle in the annular space to study the effect of varying hydrodynamic conditions on streamer formation and their morphology. Experimental observations show that depending on the polymer to particle concentration ratio (Cpolymer/Cparticle) and the hydrodynamic condition, different morphologies of streamers can be obtained. This is collated in the form of a state diagram. Surprisingly, it is observed that aged polymeric suspensions enhance streamer formation when employed in conjunction with gram flour powder that function as colloidal particles. Zeta potential and rheological measurements have been performed to gain further insights on the change in properties of polymer on account of ageing.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116292665","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}
The current industrial trend requires development of efficient heat dissipation systems. A tapered microgap on the heater surface provides an efficient pool boiling heat transfer technique in dissipating large heat fluxes. This study is focused on capturing the high-speed images of bubble nucleation, growth and expansion processes. The interface velocities are estimated by tracking the interface of the growing bubble. The insight into interface motion will help in estimating the magnitude of the expanding force and predicting the pressure recovery effect during two-phase flow in the gap. The expansion force helps in establishing high flow rates resulting in high heat transfer coefficient (HTC) and critical heat flux (CHF) values. The effect of design parameters such as taper angle and height of the microgap on the bubble growth patterns are evaluated. The results show that the bubbles are nucleated and are then confined in the narrow gap. The tapered configuration propels the leading bubble interface in the flow direction and eventually the entire bubble in that direction. The bubble motion causes liquid to enter from the narrow region of the microgap. This effect, combined with the pressure recovery resulting from the two-phase flow in the expanding section of the microgap provides a bubble pumping mechanism. This configuration results in improving both the critical heat flux and heat transfer coefficient during pool boiling.
{"title":"High Speed Imaging of Bubble Interface Motion in a Tapered Microgap","authors":"A. Chauhan, S. Kandlikar","doi":"10.1115/icnmm2020-1020","DOIUrl":"https://doi.org/10.1115/icnmm2020-1020","url":null,"abstract":"\u0000 The current industrial trend requires development of efficient heat dissipation systems. A tapered microgap on the heater surface provides an efficient pool boiling heat transfer technique in dissipating large heat fluxes. This study is focused on capturing the high-speed images of bubble nucleation, growth and expansion processes. The interface velocities are estimated by tracking the interface of the growing bubble. The insight into interface motion will help in estimating the magnitude of the expanding force and predicting the pressure recovery effect during two-phase flow in the gap. The expansion force helps in establishing high flow rates resulting in high heat transfer coefficient (HTC) and critical heat flux (CHF) values. The effect of design parameters such as taper angle and height of the microgap on the bubble growth patterns are evaluated. The results show that the bubbles are nucleated and are then confined in the narrow gap. The tapered configuration propels the leading bubble interface in the flow direction and eventually the entire bubble in that direction. The bubble motion causes liquid to enter from the narrow region of the microgap. This effect, combined with the pressure recovery resulting from the two-phase flow in the expanding section of the microgap provides a bubble pumping mechanism. This configuration results in improving both the critical heat flux and heat transfer coefficient during pool boiling.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114764962","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}
Heat pipes are valuable heat transfer devices that can be used in space; however, when exposed to the extremely low temperature of space, the working fluid can freeze. Currently, there are different methods to help mitigate freezing effects, including non-condensable gas-charged heat pipes and understanding ice formation on surfaces (e.g., typically surfaces with hydrophobic coatings). However, there is limited research about ice formation on wicks. Different wicking structures may delay freezing or mitigate freezing effects. This paper will investigate ice formation on two surfaces — commercial sintered and grooved wicks. An indoor environmental chamber was used to control ambient air temperature (i.e., 22°C) and relative humidity (i.e., 60% RH) and a Peltier cooler was used to control the surface temperature (i.e., −5°C). The resulting condensation of water onto the surface and then freezing was recorded for an hour and analyzed for the time freezing began on the surface (i.e., ice is initially visible) and the time freezing was complete on the surface. Initial results indicate that the sintered wick begins to freeze first (on average at 10.73 minutes versus 13.66 for the grooved wick) and the freezing front propagates faster (taking on average 10.83 minutes versus 12.44 minutes for the grooved wick). From the analysis, it is seen that the wicking surface structure influences the initial freezing time and the rate the freezing front propagates across the surface. These differences and the causes are investigated in this paper. These differences can, in the future, be exploited to design an optimal freeze-tolerant heat pipe and heat pipe freezing models.
{"title":"Ice Formation due to Condensation of Moist Air on Commercial Wicks","authors":"Emily Stallbaumer, Adan Cernas, A. Betz, M. Derby","doi":"10.1115/icnmm2020-1088","DOIUrl":"https://doi.org/10.1115/icnmm2020-1088","url":null,"abstract":"\u0000 Heat pipes are valuable heat transfer devices that can be used in space; however, when exposed to the extremely low temperature of space, the working fluid can freeze. Currently, there are different methods to help mitigate freezing effects, including non-condensable gas-charged heat pipes and understanding ice formation on surfaces (e.g., typically surfaces with hydrophobic coatings). However, there is limited research about ice formation on wicks. Different wicking structures may delay freezing or mitigate freezing effects. This paper will investigate ice formation on two surfaces — commercial sintered and grooved wicks. An indoor environmental chamber was used to control ambient air temperature (i.e., 22°C) and relative humidity (i.e., 60% RH) and a Peltier cooler was used to control the surface temperature (i.e., −5°C). The resulting condensation of water onto the surface and then freezing was recorded for an hour and analyzed for the time freezing began on the surface (i.e., ice is initially visible) and the time freezing was complete on the surface. Initial results indicate that the sintered wick begins to freeze first (on average at 10.73 minutes versus 13.66 for the grooved wick) and the freezing front propagates faster (taking on average 10.83 minutes versus 12.44 minutes for the grooved wick). From the analysis, it is seen that the wicking surface structure influences the initial freezing time and the rate the freezing front propagates across the surface. These differences and the causes are investigated in this paper. These differences can, in the future, be exploited to design an optimal freeze-tolerant heat pipe and heat pipe freezing models.","PeriodicalId":198176,"journal":{"name":"ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133633518","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}
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