TRANSIENT HEAT AND MASS-TRANSFER IN A NATURAL CIRCULATION LOOP

Comprehensive work has been performed by theoretical and numerical met hods in order to study the steady state, transient and stability chara cteristics of a double diffusive natural circulation loop. It was foun d that the behavior of the flow in the system depends on the initial c onditions and on the location of the state in the seven-parameter spac e of the thermal and saline Rayleigh numbers, Ra(T), Ra(S), the modifi ed Prandtl and Schmidt numbers, Pr, Sc, the dimensionless heat and mas s transfer coefficients, H(T), H(S), and the ''aspect ratio'' (between the height and width) of the loop, gamma. Numerical results are prese nted here, showing the flow in each of the five regions formed in the stability chart. The steady state solutions include convection (consta nt velocity flow), conduction (no-flow) and periodic with constant amp litude and frequency. Two main new results were obtained: long term pe riodic oscillations where the amplitude is not symmetric around the co nduction solution, and an overshoot of the velocity in transients befo re reaching the stable convection solutions. In the monotonic instabil ity region of the conduction solution, convection solutions (constant velocity flow) develop, and in the global stability region the flow de cays to the conduction solution (no flow), regardless of the initial c onditions.