The relationship between size-segregated particles migration phenomenon and combined membrane fouling in ultrafiltration processes: The significance of shear stress

Author(s):  
Xing Du ◽  
Kaiming Zhang ◽  
Haiyang Yang ◽  
Kai Li ◽  
Xuefei Liu ◽  
...  
2000 ◽  
Vol 41 (10-11) ◽  
pp. 173-180 ◽  
Author(s):  
L. Vera ◽  
S. Delgado ◽  
S. Elmaleh

A novel technique was tested for reducing tubular mineral membrane fouling by injecting gas into a cross-flow stream. The injected gas is thought to form complex hydrodynamic conditions inside the microfiltration module, which increase the wall shear stress, preventing the membrane fouling and enhancing the microfiltration mass transfer. The experimental study was carried out with biologically treated wastewater filtered through a tubular inorganic membrane (Carbosep M14). The flux, monotonously increasing with gas velocity, was more than tripled. New dimensionless quantities of shear stress number and resistance number were developed by generalisation of the dimensional analysis already carried out for the steady state flux of classical unsparged cross-flow filtration. A unique formalism allowed then interpreting the experimental results of both classical diphasic filtration and sparged filtration. The main limiting mass transport process was due to the solid content.


2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Lifeng Li ◽  
Weili Gong ◽  
Huilin Deng ◽  
Xiaohu Zhang ◽  
Gan Li

Red clay is a special soil layer with complex engineering properties distributed in tropical and subtropical regions. An anchor cable support is a common form of red clay slope support. The effectiveness of the anchor cable support is mainly determined by the anchoring force provided by the red clay stratum. Increase of the water content will lead to the rapid deterioration of the mechanical properties of red clay, which will lead to the reduction of the anchoring force of the slope anchor cable and lead to the failure of the support. Based on the classical Phillips and uniform anchorage shear stress distribution theory, this paper puts forward a uniform-exponential distribution pattern of anchorage shear stress according to the specific characteristics of red clay by using the characteristics of the peak shear strength and residual shear strength of the rock and soil mass. With increasing anchorage force, the dynamic evolution (single exponential distribution ⟶ double single exponential distribution ⟶ uniform index exponential complex distribution ⟶ uniform distribution) of the anchorage shear stress is analysed. Based on the peak and residual test of the cohesive force and internal friction angle, the relationship between the anchoring force and buried depth and water content is established by analysing the factors influencing the anchoring force. It can be found from the field test that, according to the relationship established, the limit anchorage force of the anchor cable in the red clay stratum can be calculated and the water sensitivity of the anchor cable’s limit anchorage force can be quantitatively analysed.


Several experiments were devised to find out whether it is possible to measure the internal shearing stresses in a compressed disc, and the conditions under which it is possible to do so. Equations are developed for analysing shear stresses parallel to planes of slip and distortion due to double and single slipping. The relationship between shear stress and amount of shear is found for tensile and for compression specimens, when slipping is confined to one plane. The experimental results in the two cases are identical. The fact that the component of force normal to plane of slip is a pressure in one case and a tension in the other makes no measurable difference to resistance to slipping for given amount of slip. During double slipping resistance to shear increases more rapidly for a given total amount of slipping than when all slip is confined to one plane. The experiments cover a large range and show that resistance to shear goes on increasing up to greatest amounts of distortion used.


Author(s):  
Daniel R. Robichaud ◽  
Peter Grigg ◽  
Allen H. Hoffman

Mechanoreceptor neurons were studied in an isolated rat skin preparation subjected to dynamic biaxial stretch. The strength of the relationship between neuronal responses and mechanical variables was determined using multiple logistic regression. The experimental protocol allowed the normal stresses as well as the maximum shear stress to be manipulated. In n=4 neurons, response was associated with the time rate of change of normal stress and this response was affected by the direction of loading. There was no relationship between response and the value of maximum shear stress. There was a strong association with the rate of change of maximum shear stress.


Author(s):  
Frank Gijsen ◽  
Jolanda Wentzel ◽  
Johan Schuurbiers ◽  
Frits Mastik ◽  
Johannes Schaar ◽  
...  

It is well established that atherosclerotic plaques generally develop in low shear stress regions, including curved arterial segments and bifurcations1. Once these plaques intrude into the lumen, the shear stress they are exposed to alters with hitherto unknown consequences. We hypothesize that in the more advanced stages of the disease, shear stress has an important impact on plaque composition in such a way that high shear stress enhances plaque vulnerability through its biological impact on the endothelium2. We investigated this hypothesis previously by studying the relationship between shear stress and strain, a marker for plaque composition, in human coronary arteries3. In this study, we will extend that study by investigating how shear stress influences changes of strain, and thus plaque composition, over a period of 6 months.


Author(s):  
K. Van der Heiden ◽  
H. C. Groen ◽  
P. C. Evans ◽  
L. Speelman ◽  
F. Gijsen ◽  
...  

Atherosclerosis is a lipid- and inflammation driven disease of the larger arteries and is found at specific locations in the arterial tree, i.e. at branches and bends where endothelial cells are exposed to low and low, oscillatory shear stress. Shear stress, the frictional force acting on the endothelial cells as a result of the blood flow, affects endothelial physiology. It determines the location of atherosclerotic lesion development as low and low, oscillatory shear stress induce pro-inflammatory transcription factors but reduce expression and/or activity of anti-inflammatory transcription factors in endothelial cells, rendering the vascular wall vulnerable for inflammation. Consequently, in the presence of atherosclerotic risk factors, such as hypercholesterolemia and diabetes, atherosclerotic lesion development can occur. Although the relationship between low and low, oscillatory shear stress and the prevalence of atherosclerosis has been recognized for several decades, insight into the mechanisms underlying this relationship is still incomplete. The correlation between shear stress and endothelial inflammation was demonstrated by in vitro experiments, in which cultured endothelial cells were exposed to specific flow profiles, and confirmed in vivo by gene expression pattern studies at atherosclerosis-susceptible sites. However, the relationship was not substantiated by direct causal in vivo evidence. Therefore, we developed a method to change the local shear stress field in mice in vivo and studied its effect on the endothelial molecular pathways and resulting atherosclerotic plaque formation. Moreover it allowed us to develop non-invasive molecular imaging strategies to detect vulnerable plaques.


2008 ◽  
Vol 57 (4) ◽  
pp. 601-605 ◽  
Author(s):  
Y. C. Su ◽  
C. P. Huang ◽  
H. C. Lee ◽  
Jill R. Pan

Recently, the membrane bioreactor (MBR) process has become one of the novel technologies to enhance the performance of biological treatment of wastewater. Membrane bioreactor process uses the membrane unit to replace a sediment tank, and this can greatly enhance treatment performance. However, membrane fouling in MBR restricts its widespread application because it leads to permeate flux decline, making more frequent membrane cleaning and replacement necessary, which then increases operating and maintenance costs. This study investigated the sludge characteristics in membrane fouling under sub-critical flux operation and also assessed the effect of shear stress on membrane fouling. Membrane fouling was slow under sub-critical flux operation. However, as filamentous microbes became dominant in the reactor, membrane fouling increased dramatically due to the increased viscosity and polysaccharides. A close link was found between membrane fouling and the amount of polysaccharides in soluble EPS. The predominant resistance was the cake resistance which could be minimized by increasing the shear stress. However, the resistance of colloids and solutes was not apparently reduced by increasing shear stress. Therefore, smaller particles such as macromolecules (e.g. polysaccharides) may play an important role in membrane fouling under sub-critical flux operation.


2012 ◽  
Vol 549 ◽  
pp. 491-495
Author(s):  
Wan You Zhang ◽  
Xin Yan Wang ◽  
Li Juan Xi

In order to study the relationship between extracellular polymeric substances (EPS) and membrane fouling, the effect of extracellular polymeric substances (EPS) on the operation of membrane bioreactor (MBR) was investigated in this paper. The operation of membrane was analyzed by evaluating sludge volume index (SVI), modified fouling index (MFI), and membrane resistance (Rt), respectively. The results showed that SVI, MFI, and Rt increased with the accumulation of EPS, and membrane fouling aggravated with the increase of EPS, this illustrated that the content of EPS had a direct influence on SVI, MFI, Rt and membrane fouling. The consequences could offer a simple method to monitor the concentration of EPS by analyzing SVI, MFI, or Rt.


2013 ◽  
Vol 9 (8) ◽  
pp. 989-995 ◽  
Author(s):  
Jolanda J. Wentzel ◽  
Johan C.H. Schuurbiers ◽  
Nieves Gonzalo Lopez ◽  
Frank J.H. Gijsen ◽  
Alina G. van der Giessen ◽  
...  

2012 ◽  
Vol 476-478 ◽  
pp. 1749-1752
Author(s):  
Suo Kui Tan ◽  
Xiao Ping Song ◽  
Song Ji ◽  
Hong Zhao ◽  
Min Wu ◽  
...  

This paper emphasis has researched the ER properties of Ni group core-shell nano particles modifier with Urea,SDBS and other polar molecule,analysis the relationship among ER properties and polar molecule type ,compound modifier under different electric field or magnetic field. It is found that the shear stress increasing with adding polar molecule, compound polar molecule modify can marked advance the properties of Ni group core-shell particles ER fluid.


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