Effect of heating condition on double-diffusive rollover

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20030489

Munakata, Tetsuo; Tanasawa, Ichiro

The spontaneous destabilization of stably-stratified fluids due to the reversal of the density gradient, caused by heat and/or mass transfer, sometimes in conjunction with evaporation, is known as rollover. This phenomenon occurs in nature and in industrial processes, best known in the storage of liquefied natural gas (LNG). This study models the process of numerically solving the transient momentum, energy, and mass transfer equations for a binary solution in a cylindrical enclosure. The main purpose of the study is to clarify the effect of heating condition on the rollover phenomenon. Initially the fluid is stably stratified, with the upper layer having a higher concentration of the lighter component. Heating through the walls is then applied with three different heating conditions, i.e., (1) side wall heating, (2) bottom wall heating, and (3) side and bottom wall heating, resulting in buoyancy-driven convection accompanied by heat and mass transfer, and often finally in rollover. Computations are performed for a Prandtl number of 30, Schmidt number of 5500 and for the range of modified thermal Rayleigh numbers of 6.56 x 10{sup 8} {le} Ra*{sub T} {le} 1.394 x 10{sup 10} and solutal Rayleigh numbers of 4.415 x 10{sup 9} {le} Ra{sub S} {le} 1.766 x 10{sup 10} which correspond to the range of modified thermal Marangoni numbers of 1.368 x 10{sup 6} {le} Ma*{sub T} {le} 2.907 x 10{sup 7} and solutal Marangoni numbers of 5.42 x 10{sup 6} {le} Ma{sub S} {le} 2.16 x 10{sup 7}, respectively. As expected, the tendency to rollover increases with increasing Ra*{sub T} (Ma*{sub T}) and decreases with increasing Ra{sub S} (Ma{sub S}). The most important mechanism which triggers rollover for the side wall heating is the buoyancy-driven penetration of the lower fluid into the upper layer along the heated side wall. On the contrary, for the bottom wall heating, the interface of the upper and lower fluids becomes gradually unstable and the interface is suddenly collapsed. Both characteristics are observed under the side and bottom wall heating case. The rollover onset time becomes also different due to the different rollover onset mechanisms.

• Research Organization: Mechanical Engineering Lab., Tsukuba, Ibaraki (JP)
• OSTI ID: 20030489
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
HEATING
LIQUEFIED NATURAL GAS
NATURAL CONVECTION
NUMERICAL ANALYSIS
STORAGE
TANKS