Fouling external

Design to allow for internal and external fouling resulting in reduction of heat transfer capacity... 

External fouling is caused by the formation of a cake layer of cells or other materials on the membrane surface, leading to a reduction in permeate flux (defined as the volume of permeate produced per time and membrane area). Internal fouling is caused mainly by proteins and particles smaller than membrane pores. Proteins and protein aggregates can adsorb or deposit at the pore entrance or inside the pores and cause pore blockage or narrowing, leading to increased hydraulic resistance (2). 

Parametric studies of the effects of TMP, temperature and crossflow velocity on the permeate flux and protein retention rate have been conducted using 0.8 pm alumina membranes at a pH of 4.4. The maximum steady state flux is observed at a TMP of 3 bars. As expected, a higher crossflow velocity increases the steady state permeate flux, as illustrated in Figure 6.3 under the condition of 50 C, TMP of 5 bars and pH of 4.40 [Attia et al., 1991b]. The protein retention rate also improves with the inciease in the crossflow velocity. The permeate flux reaches 175 L/hr-m, accompanied by a protein retention rate of 97.5% when the crossflow velocity is at 3.8 m/s. This improvement in the flux corresponds to a reduction in the thickness of the external fouling layer. 

Commonly used heat-transfer surfaces are internal coils and external jackets. Coils are particularly suitable for low viscosity Hquids in combination with turbine impellers, but are unsuitable with process Hquids that foul. Jackets are more effective when using close-clearance impellers for high viscosity fluids. For jacketed vessels, wall baffles should be used with turbines if the fluid viscosity is less than 5 Pa-s (50 P). For vessels equipped with cods, wall baffles should be used if the clear space between turns is at least twice the outside diameter of the cod tubing and the fluid viscosity is less than 1 Pa-s (10... 

Circffiation and heat transfer in this type of evaporator are strongly affected by the liquid level. Highest heat-transfer coefficients are achieved when the level, as indicated by an external gauge glass, is only about halfway up the tubes. Shght reductions in level below the optimum result in incomplete wetting of the tube walls with a consequent increased tendency to foul and a rapid reduction in capacity. When this type of evaporator is used with a liquid that can deposit salt or scale, it is customary to operate with the liquid level appreciably higher than the optimum and usually appreciably above the top tube sheet. 

Bath level loss can be the result of too high a bath temperature. This is often caused by the temperature controller on the process stream. Fouling of the process coil, internal and/or external, means a hotter bath is needed to accomplish the same heat transfer. The coil should be removed and cleaned. 

The usual applications for finned tubes are in heat transfer involving gases on the outside of the tube. Other applications also exist, such as condensers, and in fouling service where the finned tube has been shown to be beneficial. The total gross external surface in a finned exchanger is many times that of the same number of plain or bare tubes. 

External treatment carryover, and after-precipitation Fouling and blocked check valves Erosion/corrosion... 

The present state of the art in blood pH measurements allows for rapid (1 minute) determination of pH between 6.4 and 8.0 to within at least 0.005 units for whole blood sample volumes < 100 microliters. The temperature of the electrodes and sample is generally controlled to within 0.1 °C for this level of precision and frequent calibration is carried out (in some cases a one point calibration for each sample). The electrodes require (both the glass and external reference) some maintenance due to protein fouling, however this procedure is largely automated. The useful life of an electrode is one year or less and the cost is well over 100 (U.S.) each. New technologies, both electrochemical and non-electrochemical, must compete with this attractive performance and provide for lower operating costs in order to be successful. 

If Heart-fire influences its external related organ, the Small Intestine, patients may have dark urine with a foul smell which may be accompanied by urgent and painful sensations. 

If damp-heat accumulates in the Liver meridian, it may bring about symptoms such as swelling of the external genital region or itch in the vagina, eczema, and turbid and foul-smelling leukorrhea and urine. 

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