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Assessment of Silt Density Index (SDI) as Fouling Propensity Parameter in Reverse Osmosis DesalinationRachman, Rinaldi 07 1900 (has links)
Reverse osmosis operations are facing persistent fouling phenomenon that has challenged
the integrity of these processes. Prediction of fouling potential by measuring a fouling index
toward feed water is essential to ensure robust operation. Moreover, employing a reliable
fouling index with good reproducibility and precision is necessary. Silt density index (SDI)
is considered insufficient in terms of reliability and empirical theory, among other
limitations. Nevertheless due its simplicity, SDI measurement is utilized extensively in RO
desalination systems. The aim of this research is to assess the reliability of SDI. Methods
include the investigation of different SDI membranes and study of the nature of the SDI
filtration. Results demonstrate the existence of the membrane properties' variation within
manufacturers, which then causes a lack of accuracy in fouling risk estimation. The nature
of particles during SDI filtration provides information that particle concentration and size
play a significant role on SDI quantification with substantial representation given by particles
with size close to membrane nominal pore size. Moreover, turbidity assisted SDI
measurements along with determination of UF pretreated and clean water fouling potential,
establishes the indication of non-fouling related phenomena involved on SDI measurement
such as a natural organic matter adsorption and hydrodynamic condition that alters during
filtration. Additionally, it was found that the latter affects the sensitivity of SDI by being
represented by some portions of SDI value.
Keywords: Reverse Osmosis, Fouling index, Particulate Fouling, Silt Density Index (SDI),
and Assessment of SDI.
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Polymeric Hollow Fiber Heat Exchanger Design / Polymeric Hollow Fiber Heat Exchanger DesignAstrouski, Ilya January 2016 (has links)
This Ph.D. thesis is focused on theory and experimental investigations developing of new knowledge about polymeric hollow fiber heat exchanger (PHFHE). The state-of-the-art study of plastic heat exchangers shows that their usage is limited by several niches where their advantages significantly dominates, or where the use of non-plastic competitors is not impossible. On the other hand, plastic heat exchangers (and PHFHEs in particular) are devices of increasing interest. It is shown that use of small tubes (fibers) allows PHFHEs to be more competitive than conventional plastic heat exchangers. Small hydraulic diameter of a fiber causes high heat transfer coefficients, reduces thermal resistance of plastic wall and allows it to create light and compact design. Detailed study of fluid flow and heat transfer inside the hollow fiber showed that conventional approaches for single-phase laminar flow can be utilized. Poiseuille number equal to 64 and Nussel number about 4 are recommended to be used to predict pressure drops and heat transfer coefficient, respectively. Additional attention should be paid to careful determination of fiber diameter and liquid properties (viscosity). Scaling effects, such as axial heat conduction, thermal entrance region and viscous dissipation can be neglected. The study of outside heat transfer showed that heat transfer on fiber bunches are intense and are competitive to contemporary compact finned-tube heat exchangers. The Grimson approach showed clear correlation with experimental results and, thus is recommended to predict heat transfer coefficients on fiber bunches. Two types of fouling (particulate- and biofouling) of outer fiber surface were experimentally studied. It was found that particulate fouling by titanium oxide particles is not intense and deposits can be removed relatively easy. However, fouling is much more intense when it is associated with biofouling caused by wastewater. In this case, smooth and low-adhesive surface of plastic is not sufficient precaution to prevent deposit formation.
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