Possible Use of Internal Mixing Devices to Destabilise Stratification

Adding and mixing fresh liquid to the existing heel, to prevent stratification. If cold is added to hotter liquid, the vapour flash volume may be greater than if hot is added to cold liquid. This applies to any pair of cryogenic liquids being mixed, whether LNG or LPG. 

When removing stratification by mixing the two layers. Bottom to top mixing may generate more vapour flash than top to bottom mixing. 

When a rollover occurs, the mixing is irreversible and therefore path-dependent. The spontaneous penetrative mixing is from bottom to top, and the vapour flash volume can therefore be expected to be larger than that predicted from the heat of mixing and thermal overfill of the two layers. 

Since the heat of mixing contains a thermal equilibration between two layers together with an irreversible increase in entropy due to compositional equilibration, computer modelling of rollover BORs can never be very accurate. Every rollover produced at Southampton was different and could only be correlated between Mode 1 events (slow rise by about 5-10 fold increase of BOR) and Mode 2 events (fast rise by between 10 and IOOh- fold increase in BOR). 

13 Possible Use of Internal Mixing Devices to Destabilise Stratification 

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