Fouling, effects

The values of h, and AP, calculated by this procedure are for clean exchangers and are intended to be as accurate as possible, not conservative. A fouled exchanger will generally give lower heat-transfer rates, as reflected by the dirt resistances incorporated into Eq. (11-2), and higher pressure drops. Some estimate of fouling effects on pres-... 

Fouling Fouling affec ts MF as it affects all membrane processes. One difference is that the fouling effect caused by deposition of a foulant in the pores or on the surface of the membrane can be confounded by a rearrangement or compression of the sohds cake which may form on the membrane surface. Also, the high, open space found in tortuous-pore membranes makes them slower to foiil and harder to clean. 

To be able to check guaranteed performance without the fouling effects caused by foreign material or impurities in actual duty gas. 

Unless a manufacturer/fabricator is guaranteeing the performance of an exchanger in a specific process service, they cannot and most likely will not accept responsibility for the fouling effects on the heat transfer surface. Therefore, the owner must expect to specify a value to use in the thermal design of the equipment. This value must be determined... 

Lower chemical reactivity with non-target molecules is useful for another performance-related reason. Microorganisms prefer the protection and luxuriant environment in biofilms (the adherent microbial communities that cause detrimental surface-fouling effects in water cooling systems). Most (>99%) of the viable microorganisms in industrial systems are found in biofilms, not floating around freely in the bulk recirculating water. Compared to unstabilized chlorine or bromine, STABREX more effectively removes and disinfects biofilms as shown in Table 6. 

Tarry material was carried along with the wood hydrolyzate and deposited on cooling surfaces or in parts where flow was restricted. For that reason it was necessary to use gate or lubricated plug valves for all hydrolyzate lines. Heat exchangers for conserving heat in the liquor could not be used because of the fouling effect of the tar that precipitated on the tubes. 

TABLE 8.7. Individual Rim Resistances (1/h) Including Fouling Effects, with fi in Btu/(hr)(sqft)(°F)... 

Next, we report the anti-fouling effect.33-37) The anti-fouling effect has been confirmed only qualitatively. The time course change of surface gloss of the substrates was measured by a commercial gloss meter A self-cleaning function can also be expected with TiO -coated substrates when small amounts of organic... 

Fouling effects can be hastened by reducing the flow rate or increasing the heat-transfer rate however, this may induce different fouling mechanisms than would be experienced under actual process operating conditions. 

As a matter of fact, miniaturization inevitably results in a number of process restrictions, and completely new problems arise, too. There are, above all, the problems of blockage of microstructures by solid particles and fouling effects. Moreover, corrosion might be much more dangerous for microscopic than for macroscopic devices. 

Manttari, M., Puro, L., Nuortila-Jokinen, J., and Nystrom, M. (2000). Fouling effects of polysaccharides and humic acid in nanofiltration. J. Membr. Sci. 165,1-17. 

Because of the fouling effects, there may be a limit on the velocity of one of the fluids in a heat exchanger. For example, the velocity of cooling water in tubes of a shell-and-tube exchanger is often specified as 3 ft/s. If the velocity of one fluid is specified, the coefficient for that fluid is set, and the independent variables become At, and the film coefficient of the other fluid. 

Note that the calculation has not included various operating conditions that could alter the condensation jnocess such as fouling effects, presence of noncondensibles in the steam, subcooling of the condensate, etc. 

Membrane fouling is primarily a result of membrane-solute interaction that is generally irreversible and requires chemical cleaning to restore the original separation properties of the membrane. Fouling effects can be accenmated or minimized by proper selection of membrane material properties such as hydrophobicity/hydrophUicity or surface charge, as well as membrane pore size. A discussion on the membranes that are typically used in beer processing was included in Section... 

Jo is the initial flux at f = 0, which is an indication of the resistance to solvent transport by the membrane as well as the concentration polarization layer formed on the membrane by the proteins b is the indicator of the rate of fouling during long-term operation, or the true fouling effects, due to specific membrane-solute interactions... 

G. E. Wetterau, M. M. Clark, and C. Anselme, A dynamic model for predicting fouling effects during the ultrafiltration of a groundwater. Journal of Membrane Science 109, 185-204 (1996). 

UV lamps are usually submerged in the water, perpendicular or parallel to the water flow. Submerged lamps are inserted into a quartz sleeve to minimize the water s fouling effects. The greater the distance between the water and the lamp, the weaker the radiation... 

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