Impact of bubble nucleation on the functioning of the pulsating heat pipe: numerical simulation study

Abstract

In this communication, we discuss results obtained with the numerical in-house PHP simulation code CASCO (French abbreviation for Advanced PHP simulation code). The aim is to study the impact of bubble generation (boiling) on the established oscillation of a PHP with a high turn number (10-turn water-copper tubular PHP with independently heated turns in the evaporator region). We vary the nucleation barrier value, i.e. the local superheating $Δ$Tnucl at which the nucleation occurs and the heat load Pe; other simulation parameters are kept constant. The PHP heat transfer performance is evaluated with the PHP thermal resistance Rth for both horizontal and vertical favorable PHP orientation. Since the bubble generation plays a positive role for the PHP functioning, one expects that the function Rth($Δ$Tnucl) monotonously increases. This is true for high $Δ$Tnucl. For small $Δ$Tnucl, the Rth($Δ$Tnucl) function is decreasing, thus a minimum occurs. It appears because of a transition between the regimes of stable PHP functioning. The regimes strongly differ by the average penetration of liquid plugs into the evaporator. For horizontal PHP, these regimes correspond to the intermittent and continuous oscillations. The regimes are discussed and the regime map in the coordinates Pe -$Δ$Tnucl is obtained.