Pure crossflow

Pure crossflow is found in flat plate heat exchangers, as indicated by Fig. 1.22. The temperatures of both fluids also change perpendicular to the flow direction. This is schematically shown in Fig. 1.23. Each fluid element that flows in a crossflow heat exchanger experiences its own temperature change, from the entry temperature which is the same for all particles to its individual exit temperature. Crossflow is often applied in a shell-and-tube heat exchanger when one of the fluids is gaseous. The gas flows around the rows of tubes crosswise to the tube axis. The other fluid, normally a liquid, flows inside the tubes. The addition of... 

An increase in the number n of tube rows in series approaches the case of pure crossflow, in which the temperatures of both fluids change in x and y or rather the dimensionless coordinates x+ and y+, from (1.121), cf. Fig. 1.23. The heat transferred, through a surface element of dimensions... 

For pure crossflow to a bank of tubes, or for a mixture of crossflow and counter-current flow, the factor is less than unity ... 

Heat Transfer Coefficients. In this method, an actual heat transfer coefficient on the shellside hs is determined, correcting the ideal heat transfer coefficient /r.dcai for various leakage and bypass flow streams. The /tldeai is determined for pure crossflow in an ideal tubebank, assuming the entire shellside stream flows across the tubebank at or near the centerline of the shell. The correction factor is defined as a product of five correction factors JUJ2, - J that take into account, respectively, the effects of ... 

The ideal pressure drop in the central section Apbi assumes pure crossflow of the fluid across the ideal tube bundle. This pressure drop should be corrected for (a) leakage streams (A and E, Fig. 17.30 correction factor Re), and (b) bypass flow (streams C and F, Fig. 17.30 ... 

Solution Since there is no pressure drop in either stream along the module length, and we have pure crossflow, we can use the Pan and Habgood (1978a) analysis for nonconstant ab> i e. ab can change with composition. 

To remove the acid gas CO2 from natural gas at SOOpsia, a polymeric membrane module is being used. The permeate side pressure may be assumed to be quite low. The feed gas has 10% CO2. The purified natural gas should have only 2% CO2. The permeability values (in barter) for CO2 and the dominant consitutent of natural gas CH4, are 200 and 5 units, respectively. Calculate the highest and lowest values of the CO2 mole fraction in the permeate side if you can assume pure crossflow in the module. Identify the locations. What will be the values of CH4 in the permeate at these locations Assume a binary CO2-CH4 system. 

P. Zumbusch, W. Kulcke, G. Brunner. Use of alternating electric fields as antifouling strategy in ultrafiltration of biological suspensions. Introduction of a new experimental procedure for crossflow filtration. J Memb Sci 142-.15 (1998). R. L. Rowley, T. D. Shupe, M. W. Schuck. A direct method for determination of chemical potential with molecular dynamics simulations. 1. Pure components. Mol Phys 52 841, 1994. 

Both crossflow and deadend systems can be used in premix and direct membrane emulsification. In the crossflow premix system the coarse emulsion is diluted by permeation into pure continuous phase/diluted emulsion recirculating at the low-pressure side of the membrane. In the deadend system the fine emulsion is withdrawn as a product after passing through the membrane, without any recirculation and/or dilution with the continuous phase. In this process, the fine emulsion can... 

After formation, we utilized pure water to measure the tydraulic permeability, Lp (cm/atm-mln) of the dynamic layer. For a constant crossflow velocity, Lp is seen to decrease with an increase in the pressure of formation, as seen from Trials 1-4 in Table 1. This could be interpreted either as due to an increase in the thickness of the dynamic layer or a "tightening" of... 

There is available a sieve-tray tower 0.75 m in diameter, containing 6 crossflow trays at 0.5-m tray spacing. The perforations are 4.75 mm in diameter, arranged in a triangular pitch on 12.5-mm centers, punched in sheet metal 2 mm thick. The weir height is 40 mm. Assume isothermal scrubbing with pure water at 303 K. The water flow rate to be used should not exceed 50% of the maximum recommended for crossflow sieve trays, which is 0.015 m3/s-m of tower diameter (Treybal, 1980). The gas flow rate should not exceed 80% of the flooding value. 

RO is used to treat 1.31 m3/s of seawater at 293 K containing 3.5 wt% dissolved solids to produce 0.44 m3/s of potable water with 500 ppm of dissolved solids. The feed-side pressure is 138 bar, while the permeate pressure is 3.4 bar. A single stage of spiral-wound membrane is used that approximates crossflow. If the total membrane area is 0.10 km2, estimate the permeance for water and the salt rejection. Assume that the densities of the seawater and of the brine are approximately equal to the density of pure water. 

As can be seen from the graphical constmction the concentration of the transfer component B in the raffinate is reduced step by step to very low values. However, the coneentration in the extract also falls down making the recoveiy of a pure flac-tion of 5 by further separation processes more difBcult. The analogous process of multiple crossflow leaching is shown in Fig. 6.2-4. The thermodynamics of both types of extraction are completely equivalent. 

The membranes and module sales in 1998 were estimated at more than US 4.4 billion worldwide [1], shared by different applications (Fig. 1.1). If equipment and total membrane systems are also considered, the estimate would be double. At least 40% of the market is in the United States [2, 3], 29% of the market is shared by Europe and the Middle East. The markets in Asia and South America are growing fast A more recently published study [3] estimates the combined market for membranes used in separation and nonseparation applications to be worth 5 billion only in the US, with an aimual growth rate of 6.6%. According to another recent study [4], the demand for pure water will drive the market for crossflow membrane equipment and membranes worldwide from 6.8 billion in 2005 to 9 biUion in 2008. 

The system is charged with buffer, the TMP and crossflow velocity for the run are set and the buffer (pure water) flux taken at experimental conditions. 

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