Tubeside Velocities

Cooling Wa.ter. The primary rehabihty concern is that water chemistry must be maintained in a low fouling, noncorroding regime. In addition, water flow velocity must be maintained above a certain threshold (ca 0.5 m/s in tubeside flow) to avoid fouling and corrosion. 

In the case of particulate fouling, one of the more common types, insuring a sufficient flow velocity and minimizing areas of lower velocities and stagnant flows to help keep particles in suspension is the most common means of deahng with the problem. For water, the recommended tubeside minimum velocity is about 0.9 to 1.0 m/s. This may not always be possible for moderate to high-viscosity fluids where the resulting pressure drop can be prohibitive. 

Tube velocity >1 m/s for crude preheat exchangers, tube velocity is 1 to 2 m/s for overhead water condensers, tube velocity is 1 to 3.5 m/s. To minimize fouling, keep tubeside velocities 3 to... 

Selecting Tube Passes. The number of tube passes is kept as low as possible in order to get simple head and tubesheet designs. For even numbers of multiple pass designs, no off-center nozzle on the floating head is required. The flow quantity and the desired minimum tubeside velocity determine the number of tubes per pass and the total area and tube length then fix the number of passes for the desired performance. However, the number of tube passes must be an even integer hence, the tube length is variable. 

Engine jacket water 1.75 For tubeside flow, the velocity for the... 

Heat transfer to tubeside < design and uneven (and uneven tube-end erosion at inlet) maldistribution to the tubes (axial nozzle entry velocity > tube velocity, for radial nozzle entry velocity >1.9 tube velocity). 

For horizontal tubeside condensers, no good methods are available for predicting heat transfer coefficients when appreciable subcooling of the condensate is required. A conservative approach is to calculate a superficial mass velocity assuming the condensate filis the entire tube and use the equations presented previousiy for a singie phase sensible heat transfer inside tubes... 

Tubeside velocities should be sufficient to provide reasonable distribution and to reduce fouling. When a minimum velocity has not been established, tubeside velocities should be as high as pressure drop will permit but should not be so high as to result in tube erosion. In general, increased velocities decrease the rate of fouling. 

Multipass exchangers with straight tubes preferrably should not be installed vertically unless tubeside velocities are relatively high and provisions are made to ensure that the tubes operated completely flooded. 

Figures also generally apply to heal exchanger tubing. However, Manning and Thompson (1991) recommend a maximum tubeside velocity of 2 to 4 ji/sec for lean/rich exchangers where rich amine is on the tubeside. 

Recommended velocity applies only to rich DEA flowing through the tubeside of a lean/rich exchanger. Dailey (1970) and Smith and Younger (1972) rqport Aat severe corrosion occurred in the tubes of a lean/rich exchanger when the tubeside velocity exceeded 5.25 ft/sec. 

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