A closed two-phase thermosyphon operating with Refrigerant-11 and with imposed convection boundary conditions at the heated and cooled surfaces is experimentally investigated and analytically modeled with a lumped parameter model for varying working fluid temperatures. The thermosyphon exhibits different operational modes depending on the heating and cooling fluids' temperature difference. An increase of this temperature difference produces at first a maximum heat transfer rate identified with the flooding heat transfer limit. Beyond this limit the thermosyphon operation reverts to a different steady state through a transient non-equilibrium process. The new steady state, identified as the thermal blocking condition, produces a lower heat transfer capacity and is attributed to the simultaneous existence of: (1) a new flooding state near or at the exit of the adiabatic section, and (2) the dryout in the evaporator resulting from the transfer of liquid in the evaporator pool to the condenser during the transient process which leads to the thermal blocking condition. The limiting operational modes of the thermosyphon are modeled by a lumped parameter model that accounts for different geometrical configurations and liquid entrainment in the vapor. A comparison between the predicted and experimental heat transfer rates, prior and during the thermal blocking condition, demonstrates the model's utility to predict complex thermohydrodynamic processes in a thermosyphon.
EXPERIMENTAL INVESTIGATION AND ANALYTICAL MODELING OF A CLOSED TWO-PHASE THERMOSYPHON WITH IMPOSED CONVECTION BOUNDARY CONDITIONS
CASAROSA, CLAUDIO;
1988-01-01
Abstract
A closed two-phase thermosyphon operating with Refrigerant-11 and with imposed convection boundary conditions at the heated and cooled surfaces is experimentally investigated and analytically modeled with a lumped parameter model for varying working fluid temperatures. The thermosyphon exhibits different operational modes depending on the heating and cooling fluids' temperature difference. An increase of this temperature difference produces at first a maximum heat transfer rate identified with the flooding heat transfer limit. Beyond this limit the thermosyphon operation reverts to a different steady state through a transient non-equilibrium process. The new steady state, identified as the thermal blocking condition, produces a lower heat transfer capacity and is attributed to the simultaneous existence of: (1) a new flooding state near or at the exit of the adiabatic section, and (2) the dryout in the evaporator resulting from the transfer of liquid in the evaporator pool to the condenser during the transient process which leads to the thermal blocking condition. The limiting operational modes of the thermosyphon are modeled by a lumped parameter model that accounts for different geometrical configurations and liquid entrainment in the vapor. A comparison between the predicted and experimental heat transfer rates, prior and during the thermal blocking condition, demonstrates the model's utility to predict complex thermohydrodynamic processes in a thermosyphon.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
