Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop cha...Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop channels, besides a third mixed configuration as to achieve in-between results regarding hydraulic performance. Friction factor correlations were provided with the channel Reynolds number ranging from 1175 to 8325. Two-dimensional (2D) mean velocity field was obtained by Particle Tracking Velocimetry (PTV) with Reynolds number equal to 3450. To the best of our knowledge, this is the first experimental study that quantified the complete 2D velocity field of a typical PHE channel. This value allowed comparison with literature results of Plate and Shell Heat Exchanger (PSHE) channels with the same Reynolds number. PSHE mean velocity field is highly heterogeneous as compared to the one obtained for PHE channels. Peak velocity magnitude in the PSHE center is 50% higher than its bulk velocity, whereas this value is only 15% higher in the PHE center. Pressure drop in PHE mixed channels cannot be approximated by averaging chevron angles: furrow flow prevailed in the specified conditions. The axial velocity is asymmetric regarding the vertical plane. Smooth streamlines prevail in the channel inlet. Recirculation zones at the channel exit affect pipe flow in the manifold outlet with swirling flow structures. The necessary length to obtain fully developed pipe flow at the channel outlet was estimated. Significant velocity components occur in the distribution areas and can limit the heat exchanger performance. The results reported herein are essential to understand how the PHE channel geometry affects the velocity field and, therefore, local heat transfer and dissipation processes.展开更多
This study investigates the influence of waste characteristics,especially zeta potential,on the properties of cement pastes and solutions.The focus is to evaluate the impact of the zeta potential of cement particles a...This study investigates the influence of waste characteristics,especially zeta potential,on the properties of cement pastes and solutions.The focus is to evaluate the impact of the zeta potential of cement particles and waste materials on the sedimentation speed,rheology,and hardening time of stabilized cement pastes.Portland Cement II F 40,retarder additive,silica,and fly ash were used in the research.The pastes were prepared,and during the stabilization period,their rheological properties and pH were evaluated.The zeta potential and sedimentation speed of the cement and waste particles were measured at the pH that the pastes presented during the entire stabilization period.After the stabilization period,the pastes were subjected to the hardening time test.The zeta potential analyses revealed diverse values for the different powder types,with the cement particles exhibiting a zeta potential of−3.0 mV,the silica particles exhibiting−10.5 mV,and the fly ash particles exhibiting−20.3 mV.The influence of the high zeta potential modulus was observed on the sedimentation speed,with the solution containing fly ash exhibiting a speed of 40.01μm/s,whereas the solution containing only cement exhibited a speed of 99.38μm/s.In the pastes,the results indicate that the presence of fly ash particles with a significantly negative zeta potential led to a 16%reduction in hardening time compared to particles with a lower modulus of zeta potential.Rheometry tests showed that the inclusion of fly ash particles prevented the formation of agglomerates.Although the zeta potential influenced agglomerate formation and hardening time,it was found to have no effect on yield stress or viscosity.展开更多
Social Media have increasingly provided data about the movement of people in cities making them useful in understanding the daily life of people in different geographies.Particularly useful for travel analysis is when...Social Media have increasingly provided data about the movement of people in cities making them useful in understanding the daily life of people in different geographies.Particularly useful for travel analysis is when Social Media users allow(voluntarily or not)tracing their movement using geotagged information of their communication with these online platforms.In this paper we use geotagged tweets from 10 cities in the European Union and United States of America to extract spatiotemporal patterns,study differences and commonalities among these cities,and explore the nature of user location recurrence.The analysis here shows the distinction between residents and tourists is fundamental for the development of city-wide models.Identification of repeated rates of location(recurrence)can be used to define activity spaces.Differences and similarities across different geographies emerge from this analysis in terms of local distributions but also in terms of the worldwide reach among the cities explored here.The comparison of the temporal signature between geotagged and non-geotagged tweets also shows similar temporal distributions that capture in essence city rhythms of tweets and activity spaces.展开更多
文摘Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop channels, besides a third mixed configuration as to achieve in-between results regarding hydraulic performance. Friction factor correlations were provided with the channel Reynolds number ranging from 1175 to 8325. Two-dimensional (2D) mean velocity field was obtained by Particle Tracking Velocimetry (PTV) with Reynolds number equal to 3450. To the best of our knowledge, this is the first experimental study that quantified the complete 2D velocity field of a typical PHE channel. This value allowed comparison with literature results of Plate and Shell Heat Exchanger (PSHE) channels with the same Reynolds number. PSHE mean velocity field is highly heterogeneous as compared to the one obtained for PHE channels. Peak velocity magnitude in the PSHE center is 50% higher than its bulk velocity, whereas this value is only 15% higher in the PHE center. Pressure drop in PHE mixed channels cannot be approximated by averaging chevron angles: furrow flow prevailed in the specified conditions. The axial velocity is asymmetric regarding the vertical plane. Smooth streamlines prevail in the channel inlet. Recirculation zones at the channel exit affect pipe flow in the manifold outlet with swirling flow structures. The necessary length to obtain fully developed pipe flow at the channel outlet was estimated. Significant velocity components occur in the distribution areas and can limit the heat exchanger performance. The results reported herein are essential to understand how the PHE channel geometry affects the velocity field and, therefore, local heat transfer and dissipation processes.
文摘This study investigates the influence of waste characteristics,especially zeta potential,on the properties of cement pastes and solutions.The focus is to evaluate the impact of the zeta potential of cement particles and waste materials on the sedimentation speed,rheology,and hardening time of stabilized cement pastes.Portland Cement II F 40,retarder additive,silica,and fly ash were used in the research.The pastes were prepared,and during the stabilization period,their rheological properties and pH were evaluated.The zeta potential and sedimentation speed of the cement and waste particles were measured at the pH that the pastes presented during the entire stabilization period.After the stabilization period,the pastes were subjected to the hardening time test.The zeta potential analyses revealed diverse values for the different powder types,with the cement particles exhibiting a zeta potential of−3.0 mV,the silica particles exhibiting−10.5 mV,and the fly ash particles exhibiting−20.3 mV.The influence of the high zeta potential modulus was observed on the sedimentation speed,with the solution containing fly ash exhibiting a speed of 40.01μm/s,whereas the solution containing only cement exhibited a speed of 99.38μm/s.In the pastes,the results indicate that the presence of fly ash particles with a significantly negative zeta potential led to a 16%reduction in hardening time compared to particles with a lower modulus of zeta potential.Rheometry tests showed that the inclusion of fly ash particles prevented the formation of agglomerates.Although the zeta potential influenced agglomerate formation and hardening time,it was found to have no effect on yield stress or viscosity.
基金partially funded by the DAAD Project(No.57474280)Verkehr-SuTra:Technologies for Sustainable Transportation,within the Programme:A New Passage to India—Deutsch-Indische Hochschulkooperationen ab 2019the German Federal Ministry of Education and Research,Bundesministerium für Bildung und Forschung(BMBF),project FuturTrans:Indo-German Collaborative Research Center on Intelligent Transportation Systemsby the European Union's Horizon 2020 research and innovation programme under grant agreement No.815069(project MOMENTUM(Modelling Emerging Transport Solutions for Urban Mobility)).
文摘Social Media have increasingly provided data about the movement of people in cities making them useful in understanding the daily life of people in different geographies.Particularly useful for travel analysis is when Social Media users allow(voluntarily or not)tracing their movement using geotagged information of their communication with these online platforms.In this paper we use geotagged tweets from 10 cities in the European Union and United States of America to extract spatiotemporal patterns,study differences and commonalities among these cities,and explore the nature of user location recurrence.The analysis here shows the distinction between residents and tourists is fundamental for the development of city-wide models.Identification of repeated rates of location(recurrence)can be used to define activity spaces.Differences and similarities across different geographies emerge from this analysis in terms of local distributions but also in terms of the worldwide reach among the cities explored here.The comparison of the temporal signature between geotagged and non-geotagged tweets also shows similar temporal distributions that capture in essence city rhythms of tweets and activity spaces.
