Semi-Theoretical Modeling Oscillatory Fouling in Enhanced Tubes in Cooling Tower Systems

2007 ◽  
Author(s):  
Wei Li
Keyword(s):  
Cooling Tower ◽  
Oscillatory Behavior ◽  
Linear Range ◽  
Specific Interest ◽  
Particulate Fouling ◽  
Internal Parameters ◽  
Enhanced Tubes ◽  
Adequate Accuracy ◽  
Oscillatory Model

The fluctuation of fouling data, a well-known fouling phenomenon, was recognized in applications three decades ago, but it had not yet been well understood. Of specific interest is long term, combined precipitation and particulate fouling in cooling tower systems. Fouling data collected in seven 15.54 mm I.D. copper, helically ribbed tubes at water velocity (1.07 m/s) at practical conditions shows an oscillatory behavior. In order to observe it, a water temperature difference of 3.0°C, or greater, was needed for adequate accuracy based on an uncertainty analysis. Oscillatory model was used to analyze the data. The frequencies of the fluctuation are the same for the seven tested tube geometries. A series of semi-theoretical correlations of fluctuation of the long-term cooling tower water fouling data were developed. It was found that there are two ranges of amplitudes of the fluctuation based on internal parameters: linear range and non-linear range.

Experimental Studies of Shell and Tube Condenser Fouling and Accelerated Particulate Fouling in Internal Helical-Rib Roughness Tubes

2003 ◽  
Author(s):  
Wei Li
Keyword(s):  
Cooling Tower ◽  
Experimental Studies ◽  
Cooling Water ◽  
Particulate Fouling ◽  
Enhanced Tubes ◽  
Shell And Tube ◽  
Condenser Fouling ◽  
Tube Condenser

This paper addresses fouling in a family of seven 15.54 mm I.D. copper, helically ribbed tubes, which have different ridge heights, helix angles, and number of ridge starts. A series of semi-theoretical linear fouling correlations as a function of the product of area indexes and efficiency indexes for long term combined precipitation and particulate fouling (PPF) in cooling tower systems and a series of semi-theoretical linear fouling correlations as a function of the efficiency indexes for particulate fouling were developed. The correlations can be directly used to assess the fouling potential of enhanced tubes in actual cooling water situations.

Oscillatory Fouling in Condensers in Cooling Tower Systems

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Wei Li
Keyword(s):  
Theoretical Analysis ◽  
Cooling Tower ◽  
Oscillatory Behavior ◽  
Water Velocity ◽  
Experimental Uncertainty ◽  
Physical Mechanisms ◽  
The Mean ◽  
Relationship Of ◽  
The Relationship

Abstract Oscillatory fouling in condensers using cooling tower water was recognized in 1980s, but it had not yet been theoretically analyzed. Without careful theoretical analysis, it is easy to think that oscillatory fouling phenomenon is generated from experimental uncertainty. The new analysis is to split the fouling rate into a mean variable and a fluctuating variable. The mean variable exhibits an asymptotic behavior, and the fluctuating variable exhibits an oscillatory behavior. A theoretical analysis based on the relationship of continuity is used to present fouling oscillatory behavior along the space and time dimensions simultaneously to provide the intuitive understanding in physical mechanisms driving the phenomenon. A series of long-term cooling tower water fouling tests were conducted: fouling data collected in two copper helically ribbed tubes with the same internal and external diameters and different inside geometric parameters at the same water velocity in condenser in practical cooling tower conditions present oscillatory behavior. The frequencies of the fluctuation are the same for the two tested tube geometries. The spatial and the temporal oscillatory fouling behaviors presented in the experimental results are predicted by the theoretical analysis.

The Performances of Internal Helical-Rib Roughness Tubes Under Fouling Conditions: Practical Cooling Tower Water Fouling and Accelerated Particulate Fouling

2003 ◽  
Vol 125 (4) ◽  
pp. 746-748 ◽  
Author(s):  
Wei Li
Keyword(s):  
Cooling Tower ◽  
Particulate Fouling

This paper addresses fouling in a family of seven copper helically ribbed tubes. Series of semi-theoretical linear fouling correlations for long term combined precipitation and particulate fouling (PPF) in cooling tower systems and for accelerated particulate fouling were developed.

Modeling oscillatory fouling in enhanced tubes in cooling tower systems

2010 ◽  
Vol 47 (5) ◽  
pp. 563-569
Author(s):  
Jie Wu ◽  
Zhengjiang Zhang ◽  
Lin Cheng ◽  
Wei Li ◽  
Zhiming Xu
Keyword(s):  
Cooling Tower ◽  
Enhanced Tubes

Analysis of Fouling Characteristic in Enhanced Tubes Using Multiple Analogies

2010 ◽  
Author(s):  
Wei Li ◽  
Guanqiu Li ◽  
Zhengjiang Zhang ◽  
Zhiming Xu ◽  
Shanrang Yang
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
Transfer Coefficient ◽  
Cooling Tower ◽  
Comprehensive Analysis ◽  
Von Karman ◽  
Enhanced Tubes ◽  
Plain Tube ◽  
Von Kármán

This paper provides a comprehensive analysis on cooling tower fouling data taken from seven 15.54 mm I.D. helically ribbed, copper tubes and a plain tube at Re = 16000. A new mathematical model has been developed. The mass transfer coefficient Km is calculated through three analogies, which are Prandtl analogy, Von-Karman analogy, and j factor analogy. Fouling deposition is assumed to be determined by two processes, which are corresponding to heat flux and fluid friction. Von-Karman analogy is proved the best analogy among the three. Series of semi-theoretical fouling correlations as a function of the product of area indexes and efficiency indexes were developed. They were applicable to different internally ribbed geometries. The correlations can be directly used to assess the fouling potential of enhanced tubes in actual cooling tower water situations.

scholarly journals Why are our Jar Lids Crumbling?

2018 ◽  
Vol 2 ◽  
pp. e25928
Author(s):  
Jennifer Trimble
Keyword(s):  
Natural History ◽  
Specific Interest ◽  
Natural History Museums ◽  
Factors Affecting ◽  
The Public ◽  
History Museums ◽  
Comparative Zoology ◽  
Potential Impact ◽  
Public Exhibition

Glass jars and lids used to house fluid preserved specimens in Natural History Museums are arguably one of the most important factors needed to ensure the long term conservation of the specimens in their collections. Additionally these jars are used to display specimens in exhibits, and are the first, and often the only line of defense against damage caused by evaporation of the fluids used to preserve specimens. The Harvard Museum of Natural History (HMNH) was established as the public face of the Museum of Comparative Zoology (MCZ) which opened its doors in 1859. Often, the Museum of Comparative Zoology loans fluid preserved invertebrates to the Museum of Natural History at Harvard for display. Of specific interest to this project is a permanent arthropod exhibit displaying a variety of specimens in jars ranging from 4 oz to 1 gallon in size. During a 7-year public exhibition loan, lids began to deteriorate while on display. Visually, these lids became cracked and webbed, and upon physical manipulation the plastic crumpled into pieces. Notably, this problem has not been observed in research collections where the specimens are permanently stored. Possible factors affecting lid stability include temperature and light, and other unknowns. Given the potential impact of this issue on all collections we investigated the possible causes of lid degradation and wish to bring attention to this issue. Photography was used to document the physical problem and MicroCT was used to investigate both cracked and new lids. The resulting images are displayed here. Although the composition of lids are explored, and other jar methods outlined, flint jars remain the most consistent, and sturdy option for a student oriented museum.

scholarly journals Spatiotemporal Patterns of High-Frequency Activity (80-170 Hz) in Long-term Intracranial EEG

Neurology ◽  
2020 ◽  
pp. 10.1212/WNL.0000000000011408
Author(s):  
Zhuying Chen ◽  
David B. Grayden ◽  
Anthony N. Burkitt ◽  
Udaya Seneviratne ◽  
Wendyl J. D'Souza ◽  
...  
Keyword(s):  
Circadian Rhythms ◽  
High Frequency ◽  
Focal Epilepsy ◽  
High Amplitude ◽  
Oscillatory Behavior ◽  
Patient Specific ◽  
Intracranial Eeg ◽  
Large Variability ◽  
High Frequency Activity

Objective:To determine the utility of high-frequency activity (HFA) and epileptiform spikes as biomarkers for epilepsy, we examined the variability in their rates and locations using long-term ambulatory intracranial EEG (iEEG) recordings.Methods:This study used continuous iEEG recordings obtained over an average of 1.4 years from 15 patients with drug-resistant focal epilepsy. HFA was defined as 80-170 Hz events with amplitudes clearly larger than the background, which was automatically detected using a custom algorithm. The automatically detected HFA was compared with visually annotated high-frequency oscillations (HFOs). The variations of HFA rates were compared with spikes and seizures on patient-specific and electrode-specific bases.Results:HFA included manually annotated HFOs and high-amplitude events occurring in the 80-170 Hz range without observable oscillatory behavior. HFA and spike rates had high amounts of intra- and inter-patient variability. Rates of HFA and spikes had large variability after electrode implantation in most of the patients. Locations of HFA and/or spikes varied up to weeks in more than one-third of the patients. Both HFA and spike rates showed strong circadian rhythms in all patients and some also showed multiday cycles. Furthermore, the circadian patterns of HFA and spike rates had patient-specific correlations with seizures, which tended to vary across electrodes.Conclusions:Analysis of HFA and epileptiform spikes should consider post-implantation variability. HFA and epileptiform spikes, like seizures, show circadian rhythms. However, the circadian profiles can vary spatially within patients and their correlations to seizures are patient-specific.

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