Tank stratification

The influence of airflows from ventilating systems must also be considered. Processes using mediums of different physical qualities when mixed will have separation into different layers. Transmission of energy between molecules in flowing mediums takes place in the direction of the velocity. This strengthens the separation into parallel layers. The level of fluid in containers and tanks is due to stratification of horizontal temperature layers, while airflow after batteries, heat-recovery systems, and humidifiers or dehumidifiers will separate into parallel layers. 

Note that the recommended value for p is not always conservative. In some cases, heat input may be so high that the safety valve cannot vent all the generated vapor. In such cases, the internal pressure will rise until the bursting overpressure is reached, which may be much higher than the vessel s design pressure. For example, Droste and Schoen (1988) describe an experiment in which an LPG tank failed at 39 bar, or 2.5 times the opening pressure of its safety valve. Note also that this method assumes that the fluid is in thermodynamic equilibrium yet, in practice, stratification of liquid and vapor will occur (Moodie et al. 1988). 

The solution to stratification problems is to avoid mixing fuel grades, keep tank temperatures lower rather than higher, provide mechanical agitation where practical, and supplement operational actions with the use of a polymeric antisettling dispersant. 

Mixing status in the tank has large affection on outlet response for the ice storage tank with out agitation. If the ice packing factor is small, thermal characteristics of the tank resembles to a stratified water tank. Since the ratio of sensible heat to latent heat is relatively large, conditions should be set to maintain stratification as much as possible. Therefore, large temperature difference in the inlet is preferable. 

The temperature stratification is used to avoid mixing in a water storage tank. These tanks are not only deep ones but also shallow ones as shown in Figure 184. The degree of stratification depends on momentum of water and density or temperature difference at inlet. The appropriate condition at inlet can stratify water in a tank whatever the depth of a tank is. As the deep tank has difficulties of construction, the shallow tanks in basement are often applied. 

Lack of any mixing arrangements caused stratification of strong sulfuric acid and (probably) sodium carbonate solutions in the same tank. When gas evolution caused intermixing of the layers, a violent eruption of the tank contents occurred. 

To prevent stratification in an initially homogeneous tank which is known to be already in jet induced circulation, assume 0.5F of the values computed from the above expressions. 

If the jet nozzle velocity is too low, and the liquid coming from it is much different in density from the liquid in the tank, it is possible to get stratification instead of good mixing. The minimum velocity can be estimated from fluid properties and vessel geometry, by the relation... 

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